RF active compositions for use in adhesion, bonding and coating

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of application Ser. No. 09/404,200, filed Sep. 23, 1999, which is a continuation-in-part of application Ser. No. 09/270,505, filed Mar. 17, 1999, which claims the benefit of U.S. provisional application No. 60/078,282, filed Mar. 17, 1998 the contents of each of which are fully incorporated by reference herein.

This patent application is related to the following co-pending U.S. utility patent application: “Radio Frequency Heating System,” application Ser. No. 09/270,507, filed Mar. 17, 1999, the contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the use of media containing ionic compounds and/or nonionic compounds with high dipole moments as a radio frequency (RF) susceptors in RF activated systems.

2. Related Art

Radio frequency (RF) heating is a well established non-contact precision heating method that is used to generate heat directly within RF susceptors, and indirectly within materials that are in thermally conductive contact with RF susceptors. RF susceptors are materials that have the ability to couple and convert RF energy into heat energy within the material.

Conventional adhesives are not suitable RF susceptors that can be directly heated and activated by RF heating. Rather, these conventional adhesives are typically heated indirectly through thermally conductive contact with an RF susceptor material.

FIG. 1

illustrates two conventional methods that are currently used in industry for indirect RF heating of conventional adhesives: The first method is illustrated in

FIG. 1A

, where susceptor material

102

exists as a bulk macroscopic layer. RF susceptor material

102

is directly heated by RF energy, and adhesive layer

104

is indirectly heated through thermally conductive contact with RF susceptor material

102

. For example, adhesive layer

104

may be applied to a continuous surface of susceptor material

102

, such as steel or aluminum. The second method is illustrated in

FIG. 1B

, where susceptor material

112

consists of discrete macroscopic particles. Adhesive layer

114

is loaded with macroscopic particles of a RF susceptor material

112

, such as macroscopic particles or flakes of metal oxides, metallic alloys, or aluminum. With this conventional method, each RF susceptor particle

112

acts as a discrete RF susceptor, generating heat throughout adhesive layer

114

.

An example of a conventional RF energy activated composition, such as that shown in

FIG. 1B

, is described in U.S. Pat. No. 5,378,879, issued to Monovoukas (“Monovoukas”). Monovoukas utilizes macroscopic “loading particles” as discrete RF susceptors. The particles are heated by RF energy and in turn conduct heat to the surroundings. These macroscopic loading particles are thin flakes (i.e. in thin disk-like configuration) that are designed to be admixed to relatively thick extruded materials. However, these flakes are not well suited for use as susceptors in thin film bonding applications in which physical distortions, discolorations in the surface, or opacity of the bonded films would result from the flakes.

Another example of a conventional inductively activated adhesive is described in U.S. Pat. No. 3,574,031, issued to Heller et al. (“Heller”). Heller describes a method of heat welding thermoplastic bodies using an adhesive layer that contains uniformly dispersed macroscopic RF susceptors, typically iron oxide particles. These discrete RF susceptor particles are ferromagnetic in nature. A disadvantage of this type of method is that a tradeoff must be made between the size of the particle employed versus the power level and duration of the inductive heating process. For example, if susceptor particles are kept small in size, the mechanical strength of the bond tends to increase. However, as the size of these discrete susceptors is reduced, the power levels and dwell times required to heat the RF susceptor material and achieve acceptable bonds tend to increase. Another disadvantage of this type of method is the high levels of loading of the medium with RF susceptor particles that is required for efficient activation. Such high loading levels detract from the physical properties and rheology of the adhesive composition. Still another disadvantage is the dark color and opacity of the composition, which renders the composition undesirable for many applications.

An example of adhesive activated by a dielectric process is described in U.S. Pat. No. 5,661,201, issued to Degrand (“Degrand”). Degrand describes a thermoplastic film including at least one ethylene copolymer and a sufficient quantity of N,N-ethylene-bisstearamide that is capable of being sealed utilizing a current at a frequency of about 27.12 megahertz (MHz). A disadvantage of this type of film and sealing process is the inherent tendency to also heat the adherand.

U.S. Pat. No. 5,182,134, issued to Sato, discloses methods of curing a thermoset composition by applying an RF signal having a frequency of about 1 to 100 MHz to a composition comprising a major portion of a thermoset and a receptor. The receptor is described as being one of the alkali or alkaline earth metal sulfate salts (e.g. calcium sulfate), aluminum trihydrate, quaternary ammonium salts, phosphonate compounds, phosphate compounds, polystyrene sulfonate sodium salts or mixtures thereof. According to this patent, all of the exemplified compositions took longer than one second to heat.

U.S. Pat. No. 5,328,539, issued to Sato, discloses methods of heating thermoplastic susceptor compositions by applying an RF signal having a frequency of about 1 to 100 MHz. The susceptors are described as being one of the alkali or alkaline earth metal sulfate salts (e.g. calcium sulfate), aluminum trihydrate, quaternary ammonium salts, phosphonate compounds, phosphate compounds, polystyrene sulfonate sodium salts or mixtures thereof. According to this patent, all of the exemplified compositions took longer than one second to heat.

U.S. Pat. No. 4,360,607, issued to Thorsrud, discloses a composition suitable for sensitizing thermoplastic compositions to the heating effects of microwave energy comprising (1) an alcohol amine or derivative thereof, (2) a simple or polymeric alkylene glycol or derivative thereof, (3) silica and, optionally, (4) a plasticizer.

U.S. Pat. No. 5,098,962, issued to Bozich, discloses a water dispersible hot melt adhesive composition comprising:

(a) from about 40% to 95% by weight of a water dispersible ionically substituted polyester resin having a molecular weight from about 10,000 to about 20,000 daltons;

(b) from about 60% to about 5% by weight of one or more compatible plasticizers; and

(c) from about 0.1% to about 1.5% of one or more compatible stabilizers of the anti-oxidant type.

Examples of plasticizers that may be used according to this patent include one or more low molecular weight polyethylene glycols, one or more low molecular weight glycol ethers, glycerin, butyl benzyl phthalate and mixtures thereof.

U.S. Pat. No. 5,750,605, issued to Blumenthal et al., discloses a hot melt adhesive composition comprising:

(i) 10 to 90% by weight of a sulfonated polyester condensation polymer;

(ii) 0 to 80% by weight of a compatible tackifier;

(iii) 0 to 40% by weight of a compatible plasticizer;

(iv) 5 to 40% by weight of a compatible wax diluent with a molecular weight below 500 g/mole containing at least one polar functional group, said group being present at a concentration greater than 3×10

−3

equivalents per gram;

(v) 0 to 60% by weight of a compatible crystalline thermoplastic polymer; and

(vi) 0 to 3% by weight of a stabilizer.

What is needed is a composition (e.g. adhesive composition or coating) containing either dissolved or finely dispersed susceptor constituents that are preferably colorless or of low color. Further, the composition should be transparent or translucent throughout an adhesive matrix or plastic layer. This type of RF susceptor will result in more direct and uniform heating throughout an adhesive matrix or plastic layer. Further, it is desirable that such a composition will allow bonding with no physical distortion or discoloration in the bonded region of thin films. Still another desirable feature is activation of the RF susceptors at frequencies, e.g. of about 15 MHz or below, most preferably about 13.5 MHz, which are more economical to generate than higher frequencies and do not substantially heat dielectric substrates. A further desirable feature is that the composition can be activated or melted in less than one second and that it exhibit acceptable shear strength. It is also desirable to have a formulation which may be optimized for a particular application, such as cutting, coating, or bonding substrates.

SUMMARY OF THE INVENTION

The present invention generally relates to the creation and use of a composition (also referred to as a “susceptor composition”) that can bond two or more layers or substrates to one another and that can be used to coat or cut a substrate. The susceptor composition is activated in the presence of radio frequency (RF) energy.

In one embodiment, the susceptor composition of the present invention comprises a susceptor and a carrier. The carrier and susceptor are blended with one another and form a mixture, preferably a substantially uniform mixture. The susceptor is present in an amount effective to allow the susceptor composition to be heated by RF energy. In a preferred embodiment, the susceptor also functions as an adhesive or coating.

In another embodiment of the present invention, the susceptor composition further comprises an adhesive compound. The adhesive compound, susceptor, and carrier are blended with one another to form a mixture that is activated in the presence of RF energy. Preferably, the mixture is substantially uniform.

In another embodiment of the present invention, the susceptor composition further comprises at least one of a thermoplastic polymer, thermoset resin, elastomer, plasticizer, filler or other material. The additive, susceptor, and carrier are blended with one another to form a mixture that is activated in the presence of RF energy.

In yet another embodiment of the present invention, the composition can further comprise a second carrier that is an insoluble porous carrier that is saturated with the composition.

The susceptor is an ionic or polar compound and acts as either a charge-carrying or an oscillating/vibrating component of the susceptor composition. The susceptor generates thermal energy in the presence of an RF electromagnetic or electrical field (hereafter RF field). According to the present invention, the susceptor can be an inorganic salt (or its respective hydrate), such as stannous chloride (SnCl

2

), zinc chloride (ZnCl

2

) or other zinc salt, or lithium perchlorate (LiClO

4

), or an organic salt, such as lithium acetate (LiC

2

H

3

O

2

). The susceptor can be a non-ferromagnetic ionic salt. The susceptor can also be a polymeric ionic compound (“ionomer”) which preferably also functions as an adhesive or coating. Under RF power levels of about 0.05 kilowatt (kW) to 1 kW, and frequencies of about 1 to 100 MHz, the susceptor composition of the present invention facilitates (a) the bonding of single layers of polymeric materials such as polyolefins, non-polyolefins, and non-polymeric materials, as well as multilayer stacks of these materials, and (b) coating on a substrate such as a printed pattern on plastic films, metallic foils, etc.

Surprisingly, it has been discovered that when an ionomer is combined with a polar carrier, much more heating occurs when exposed to RF energy than when the ionomer or carrier is exposed separately to RF energy. Also surprisingly, it has been discovered that when the polar carrier is present at about 13-30% weight percent, more preferably, about 15-25 weight percent, most preferably, about 20-23 weight percent, very short heating times are possible while retaining acceptable shear strength of the bond.

According to another embodiment of the present invention, a method of bonding a first material or substrate to a second material or substrate comprises interposing a composition according to the invention between the first and second materials and applying RF energy to the composition to heat the composition, thereby causing the first and second materials to become bonded. In one embodiment, the composition comprises a susceptor and a carrier that are distributed in one another to form a mixture, preferably, a substantially uniform mixture. Optionally, the composition may further comprise other compounds and additives as described herein. The susceptor is present in the composition in an amount effective to allow the composition to be heated by RF energy.

According to another embodiment of the present invention, a method of bonding or adhering a first substrate to a second substrate includes: applying a first composition onto the first substrate; applying a second composition onto the second substrate; contacting the first composition with the second composition; applying RF energy to the first and second compositions to heat the compositions, thereby causing the first and second substrates to become adhered or bonded; wherein one of the compositions comprises a susceptor and the other of the susceptors is a polar carrier, and the susceptor and/or the carrier are present in amounts effective to allow the first and second compositions to be heated by RF energy.

According to yet another embodiment of the present invention, a method of bonding or adhering a first substrate to a second substrate includes: applying a first composition onto the first substrate; applying a second composition onto the first composition; contacting the second substrate with the second composition; and applying RF energy to the first and second compositions to heat the compositions, thereby causing the first and second substrates to become adhered or bonded, wherein one of the compositions comprises a susceptor and the other of the compositions is a polar carrier, and the susceptor and/or the carrier are present in amounts effective to allow the first and second compositions to be heated by RF energy.

According to another embodiment of the present invention, a method of making a susceptor composition comprises admixing a susceptor and a carrier, wherein, preferably, the carrier and susceptor are substantially uniformly dispersed in one another and form a uniform mixture. The susceptor and/or carrier are present in the composition in an amount effective to allow the susceptor composition to be heated by RF energy.

According to a further embodiment of the present invention, an adhered or a bonded composition can be obtained according to the disclosed methods.

According to a further embodiment of the present invention, a kit for bonding a first material to a second material comprises one or more containers, wherein a first container contains a composition comprising a susceptor and a carrier that are dispersed in one another and form a mixture. The kit may also contain an adhesive or elastomeric compound or other additives as disclosed herein. The susceptor and/or carrier are present in an amount effective to allow the composition to be heated by radio frequency energy.

According to a further embodiment of the present invention, a kit for adhering or bonding a first substrate to a second substrate, comprises at least two containers, wherein one of the containers comprises a susceptor and another of the containers comprises a polar carrier, wherein when the susceptor and the carrier are applied to substrates and the susceptor and carrier are interfaced, a composition is formed that is heatable by RF energy.

The invention also relates to a composition comprising an ionomeric polymer and a polar carrier.

The invention also relates to a method of curing a thermoset resin, comprising combining the thermoset resin with a polar carrier to give a mixture and exposing the mixture to RF energy.

The invention relates to an apparatus, having: a first portion having a first mating surface; a second portion, having a second mating surface; a composition disposed between the first mating surface and the second mating surface, wherein the composition comprises a susceptor and a polar carrier wherein the susceptor and/or the polar carrier are present in amounts effective to allow the composition to be heated by RF energy, and wherein the composition adheres the first mating surface to the second mating surface such that application of a force to separate the first mating surface and the second mating surface results in breakage of the apparatus unless the composition is in a melted state.

The invention also relates to a method of applying a protective film or printed image/ink on a substrate.

The invention also relates to a method for dynamically bonding a first adherand to a second adherand. The method includes: (1) creating an article of manufacture comprising the first adherand, the second adherand, and a composition, the composition being between the first adherand and the second adherand, wherein the composition can be activated in the presence of an RF field; (2) moving the article of manufacture along a predetermined path; (3) generating along a portion of the predetermined path an RF field having sufficient energy to activate the composition, wherein the composition is activated by its less than one second exposure to the RF field.

The invention also relates to a method for applying a susceptor composition to a substrate. In one embodiment, the method includes: (1) formulating the susceptor composition as a liquid dispersion; (2) applying the liquid dispersion of the susceptor composition to the substrate; (3) drying the susceptor composition, wherein the drying step includes the step of applying RF energy across the composition, thereby generating heat within the liquid dispersion. In a preferred embodiment, one may roll up the substrate after the susceptor composition has dried.

The invention also relates to a method for cutting a substrate. The method includes: (1) applying a composition to a portion of the substrate, wherein the composition comprises a susceptor and polar carrier wherein the susceptor and/or said polar carrier are present in amounts effective to allow the composition to be heated by RF energy, and wherein the portion of the substrate defines a first section of the substrate and a second section of the substrate; (2) melting the portion of the substrate by heating the composition via RF energy; and (3) after the portion of the substrate has begun to melt, applying a force to the substrate to separate the first section from the second section.

The method also relates to a method of dynamically bonding a first substrate to a second substrate. The method including: applying a composition onto the first substrate; after applying the composition onto the first substrate, forming a roll of the first substrate; storing the roll; unrolling the roll; and while unrolling the roll: joining an unrolled portion of the first substrate with a portion of the second substrate such that the portion of the second substrate is in contact with a portion of the composition applied onto the first substrate; and applying RF energy to the portion of the composition, wherein the portion of the composition heats and melts as a result of the RF energy being applied thereto.

Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.

FIGS. 1A and 1B

illustrate conventional schemes for inductively heating adhesives.

FIG. 2

shows an RF active composition according to the present invention.

FIG. 3

shows a susceptor composition placed between two polyolefin layers to be attached according to the present invention.

FIG. 4

illustrates a block diagram of an RF heating system according to a first embodiment.

FIG. 5

illustrates a block diagram of a heating system according to a second embodiment.

FIG. 6

illustrates a two probe heating system.

FIGS. 7A and 7B

further illustrate the two probe heating system.

FIG. 7C

illustrates a probe having a curled end to reduce corona effects.

FIG. 8

illustrates one embodiment of an alternating voltage supply.

FIG. 9

is a flow chart illustrating a process for heating a composition according to the present invention.

FIG. 10A

further illustrates one embodiment of an impedance matching circuit.

FIG. 10B

further illustrates another embodiment of an impedance matching circuit.

FIG. 11

shows a method of bonding adherents using a composition that is activated in the presence of RF energy.

FIGS. 12

to

17

illustrate additional embodiments of probes

602

and

604

.

FIG. 18

illustrates one embodiment of an application system for applying a composition according to the present invention to a substrate.

FIG. 19

illustrates one embodiment of a system for bonding or adhering various adherents.

FIGS. 20A and 20B

illustrates a static bonding system for bonding adherents.

FIG. 20C

illustrates an electrically insulating block for housing probes.

FIG. 21

illustrates an in-line bonding system.

FIG. 22

further illustrates one embodiment of the in-line bonding system illustrated in FIG.

21

.

FIGS. 23-27

illustrate alternative designs of the in-line bonding system illustrated in FIG.

21

.

FIGS. 28A and 28B

illustrate one embodiment of a system for the manufacture of flexible packaging material.

FIG. 29

further illustrates film

2815

.

FIG. 30

illustrates one embodiment of film

2870

.

FIG. 31

illustrates an alternative system for manufacturing an RF activated adhesive film for use in the flexible packaging industry.

FIG. 32

illustrates a conventional aseptic package material construction.

FIG. 33

illustrates an aseptic package material according to one embodiment that does not include metallic foil.

FIG. 34

illustrates another embodiment of an aseptic packaging material construction that does not use metallic foils.

FIG. 35

illustrates a conventional cap sealing construction.

FIG. 36

illustrates a seal, according to one embodiment, for sealing a bottle.

FIG. 37

illustrates a design for adhering a flexible bag to an outer box.

FIG. 38

illustrates a step and repeat manufacturing system.

FIG. 39

illustrates an index table bonding system.

FIG. 40

shows an example experimental set-up utilized to test compositions according to the present invention.

FIG. 41

illustrates another experimental set-up for testing compositions according to the present invention.

FIG. 42

illustrates test probes.

FIG. 43

illustrates a process for assembling a book, magazine, or periodical, or the like.

FIG. 44

illustrates a paper substrate coated with a susceptor composition.

FIG. 45

illustrates a stack of coated paper substrates.

FIGS. 46 and 47

illustrates one embodiment of an envelope or mailer according to the present invention.

FIG. 48

illustrates a cross-section of a container sealed with a susceptor composition of the present invention.

FIG. 49

illustrates another example of a device sealed or otherwise joined together with a composition of the present invention.

FIG. 50

shows another example of a device sealed or otherwise joined together with a composition of the present invention.

FIG. 51

illustrates still another example of a cross-section of a container

5100

that has been sealed with the adhesive of the present invention.

FIG. 52

illustrates a system for bonding two substrates.

FIG. 53

illustrates another embodiment of a system for bonding two substrates.

FIG. 54

depicts a graph showing RF activation time vs. % Glycerin for a composition comprising AQ55S.

FIG. 55

depicts a graph showing shear holding time vs. % glycerin for a composition comprising AQ55S.

FIG. 56

depicts a graph showing RF activation time vs. % glycerin for a composition comprising AQ35S.

FIG. 57

depicts a graph showing shear holding time vs. % glycerin for a composition comprising AQ35S.

FIG. 58

depicts a family of curves showing RF activation time vs. % various polar carriers.

FIG. 59

depicts a graph showing RF activation time vs. % PARICIN 220 in a composition comprising 80% AQ55S/20% glycerin.

FIG. 60

depicts a graph showing brookfield viscosity vs. % PARICIN 220 in a composition comprising 80% AQ55S/20% glycerin.

FIG. 61

depicts a graph showing RF activation time vs. % glycerin in a composition comprising the sodium salt of an ethylene acrylic acid copolymer (MICHEM Prime 48525R).

FIG. 62

illustrates a seam sealing system according to one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Overview and Discussion of the Invention

II. Terminology

A. Sulfonated Polymers

B. Acrylic Acid and Maleic Anhydride Polymers and Copolymers

C. Starch/Polysaccharide Derivatives

D. Proteins

E. Others

III. The Polar Carrier

IV. Further Additives to the Susceptor Compositions

A. Adhesive/Thermoplastic Additives

B. Adhesive/Coating Thermoset Additives

C. Surfactant Additives

D. Plasticizer Additives

E. Tackifiers

F. Fillers

G. Stabilizers and Antioxidants

H. Other Additives

V. Applying the Susceptor Compositions to Substrates

VI. Apparatus For Activating the Various Compositions of the Present Invention

VII. Method of Bonding Substrates

VIII. Additional Probe Embodiments

IX. Applicator System for Applying a Composition of the Present Invention to a Substrate/Adherand

X Systems for Adhering or Bonding two Adherands.

XI. Exemplary Specific Applications of the Present Invention

A. Manufacture of Flexible Packaging

B. Food Packaging and Cap Sealing

C. Printing Applications

D. Bookbinding and Mailers

E. Security Devices

F. Thermal Destruction

G. Seam Sealing

XII. Kits

XIII. Experimental Set-up

XIV. Examples

I. Overview and Discussion of the Invention

The present invention is directed towards an RF susceptor composition and methods and systems of bonding, cutting, and/or coating substrates and surfaces using the susceptor composition. The susceptor composition is a mixture of RF susceptors and/or adhesive/coating compounds and/or other additives dissolved or finely dispersed in a matrix. Preferably, the RF susceptors and/or adhesive compounds and/or other additives are uniformly dissolved or finely dispersed in the matrix. The susceptor composition is capable of coupling efficiently in an RF field having a frequency of about 15 MHz or below. In order to be useful in industry and commercial products, a susceptor composition preferably has the following characteristics: (1) an activation time in the presence of a low power RF field on the order of 1 second or less, (2) adequate bond or adhesive strength for the intended use, (3) transparency or translucency and only slight coloration (if any), (4) minimal distortion of the substrates being attached, and (5) on demand bonding of preapplied adhesive. Further, it is desirable that the susceptor composition have coupling ability in the absence of volatile solvents, although the presence of nonvolatile liquids (such as plasticizers) may be desirable. These characteristics are important in providing sufficient heat transfer to the substrates or layers to be bonded to one another, or for adhesion to take place at the interface. Additionally, the susceptor composition should not interfere with the thermal bonding or inherent adhesive properties of the substrates or layers to be bonded or adhered to one another.

According to the present invention, a susceptor composition used to bond or adhere substrates or layers can be directly heated by exposure to an RF field having frequencies ranging from 1-100 MHz. The susceptor composition comprises a susceptor, and a carrier blended with one another to form a mixture. In addition, the susceptor composition can further comprise one or more adhesive compounds blended with the susceptor and carrier to form the mixture.

Susceptors are either ionic or polar compounds introduced as a component of a composition, such that RF heating of the resulting susceptor composition occurs. An ionic susceptor is an ionic compound introduced as a sufficiently charge-carrying or oscillating component of the composition. A polar susceptor is a polar compound which has sufficiently high dipole moment that molecular oscillations or vibrations of the compound occur when exposed to an RF field. As shown in

FIG. 2

, a susceptor composition

202

comprises a continuous mixture of susceptors such as microscopic, ionic salts or polymeric ionic compounds or dipoles

204

, which generate thermal energy in the presence of the RF field. It has been discovered that acceptable bonding results occur with inorganic salts such as stannous chloride (SnCl

2

); zinc salts such as chloride (ZnCl

2

), bromide (ZnBr

2

) and the like; and lithium perchlorate (LiClO

4

), and organic salts such as lithium acetate (LiC

2

H

3

O

2

). These salts or combination of salts, when distributed in the mixture, create an ionic and/or polar medium capable of being heated by RF energy.

II. Terminology

“RF Energy” means an alternating electromagnetic field having a frequency within the radio frequency spectrum.

A “susceptor composition” comprises a susceptor and a carrier interfaced with one another and/or mixed or blended together. Preferably, the susceptor and carrier are mixed together. More preferably, the susceptor and carrier are substantially uniformly mixed together. In another embodiment, the susceptor and carrier are interfaced together by disposing a layer of the susceptor onto a layer of the carrier or visa versa. In this embodiment, the susceptor may be coated onto a first substrate and the carrier, with or without added ingredients such as a wax or other additives that prevent the carrier from evaporating substantially, may be coated onto a second substrate. The first and second substrates containing the susceptor and carrier layers, respectively, may then be brought into contact or interfaced and activated then or at a later time.

The susceptor compositions of the invention may further comprise one or more adhesive compounds or other additives mixed, preferably substantially uniformly mixed, together with the susceptor and the carrier. The susceptor composition is activated in the presence of radio frequency (RF) energy. The susceptor composition can be used to bond two or more layers or substrates to one another, can be used as a coating, and can be used to thermally cut substrates.

A “carrier” provides the mobile medium in which the susceptors are dissolved, distributed, or dispersed. Preferably, the carrier is a polar carrier as defined below which enhances the activation of the compositions. Carriers (also referred to as mobile media) can be liquids, such as solvents and plastisizers, or polymers that are utilized for their polar functionality and for their ability to be heated by RF energy.

An “adhesive compound” refers to polymers, copolymers and/or ionomers as described herein that are blended into the susceptor composition to enhance its adhesive properties.

“Bonding” is defined as the joining of one substrate to another substrate to cause a physical joining process to occur.

“Adhesion” is an interaction between two adherands at their interface such that they become attached or joined.

A “substantially transparent” mixture refers to a mixture that transmits greater than about 50% of incident visible light.

“Thermal bonding” or “welding” is defined as the reflowing of one substrate into another substrate to cause a physical joining process to occur.

“Mechanical bonding” occurs between adherands when a susceptor composition holds the adherands together by a mechanical interlocking action.

An RF “susceptor” converts coupled RF energy into heat energy in the susceptor composition. According to the present invention, the susceptor, as described above, is either the charge carrying or oscillating ionic compound or the oscillating polar compound having a sufficiently high dipole moment comprising a composition to generate thermal energy in the presence of an RF field. Generally, the susceptor can be a salt. For example, the susceptor can be an inorganic salt or its respective hydrate(s), such as stannous chloride (SnCl

2

), stannous chloride dihydrate (SnCl

2

x2H

2

O), lithium perchlorate (LiClO

4

), lithium perchlorate trihydrate (LiClO

4

x3H

2

O) or an organic salt, such as an alkali metal salt of a C

1-4

alkanoic acid such as lithium acetate (LiC

2

H

3

O

2

), lithium acetate dihydrate (LiC

2

H

3

O

2

x2H

2

O), or sodium acetate and the like; alkali metal salts of arylcarboxylic acids such as lithium benzoate, sodium benzoate, and the like; alkali metal salts of alkyl and aryl sulfonates such as sodium methylsulfonate and sodium p-toluenesulfonate and the like. Other types of salts and their respective hydrates include, but are not limited to, magnesium acetate, magnesium nitrate, sodium-based salts (such as sodium chloride, sodium bromide and the like), lithium-based salts (such as lithium bromide, lithium carbonate, lithium chloride, etc.) and potassium-based salts. Many of these salts are commercially available from Aldrich Chemical Company, Milwaukee, Wis. See the Aldrich Catalog Handbook of Fine Chemicals 1996-1997. It is not intended that this list of salts is an exclusive or comprehensive list. These salts are disclosed as typical examples. The present invention is not restricted to the listed salts, as would be apparent to those of skill in the art.

The susceptor can also be an ionomer. Preferably, the ionomer also functions as an adhesive and/or coating. Examples of such ionomers include without limitation styrenated ethylene-acrylic acid copolymer or its salts, sulfonated polyesters and their salts, sulfonated polystyrene and its salts and copolymers, polyacrylic acid and its salts and copolymers, hydroxy/carboxylated vinylacetate-ethylene terpolymers, functionalized acrylics, polyesters, urethanes, epoxies, alkyds, latex, gelatin, soy protein, casein and other proteins, alginate, carrageenan, starch derivatives, ionic polysacharides, and the like. An example of an ionomer that does not function as an adhesive is sodium polystyrenesulfonate.

Examples of ionomer adhesives are described in more detail below.

A. Sulfonated Polymers

Sulfonated polyesters and copolymers thereof are described in U.S. Pat. Nos. 5,750,605, 5,552,495, 5,543,488, 5,527,655, 5,523,344, 5,281,630, 4,598,142, 4,037,777, 3,033,827, 3,033,826, 3,033,822, 3,075,952, 2,901,466, 2,465,319, 5,098,962, 4,990,593, 4,973,656, 4,910,292, 4,525,524, 4,408,532, 4,304,901, 4,257,928, 4,233,196, 4,110,284, 4,052,368, 3,879,450, and 3,018,272. The invention relates to compositions comprising sulfonated polyesters and copolymers thereof, e.g. as described in these patents, together with a polar carrier as described herein as well as the adhesive compositions described in these patents (comprising the sulfonated polyesters and copolymers thereof) together with the polar carrier. Such sulfonated polyesters and copolymers thereof are one preferred embodiment of the present invention, as such materials function both as an ionomeric susceptor and as an adhesive.

In a preferred embodiment, the sulfonated polyester is a higher Tg (about 48° C. to about 55° C. or higher) linear polyester which shows improved heat resistance compared to lower Tg (about 35° C.) linear or branched sulfonated polyesters. Once blended with the polar carrier, the Tg of the resulting composition should be higher than the temperature at the intended use, e.g. higher than body temperature for diaper adhesives. For example, a linear sulfonated polyester with a Tg of 55° C. (e.g. AQ55S) blended with a sufficient amount (greater than 10%) of polar carrier (e.g. glycerin) to achieve RF activity will result in a Tg higher than body temperature if the polar carrier is no more than about 35% of the composition.

In another embodiment, a salt comprising a sulfonated polyester and a cationic dye as described in U.S. Pat. No. 5,240,780, are employed. Such salts provide a colored susceptor composition that may be used, e.g. in printing.

Sulfonated polyesters may be prepared by the polycondensation of the following reactants:

(a) at least one dicarboxylic acid;

(b) at least one glycol;

(c) at least one difunctional sulfomonomer containing at least one metal sulfonate group attached to an aromatic nucleus wherein the functional groups may be hydroxy, carboxyl, or amino groups.

The dicarboxylic acid component of the sulfonated polyesters comprises aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, aromatic dicarboxylic acids, or mixtures of two or more of these acids. Examples of such dicarboxylic acids include oxalic; malonic; dimethylmalonic; succinic; glutaric; adipic; trimethyladipic; pimelic; 2,2-dimethylglutaric; azelaic; sebacic; fumaric; maleic; itaconic; 1,3-cyclopentanedicarboxlyic; 1,2-cyclohexanedicarboxylic; 1,3-cyclohexanedicarboxylic; 1,4-cyclohexanedicarboxylic; phthalic; terephthalic; isophthalic; 2,5-norbornanedicarboxylic; 1,4-naphthalic; diphenic; 4,4′-oxydibenzoic; diglycolic; thiodpropionic; 4,4′-sulfonyldibenzoic; and 2,5-naphthalenedicarboxylic acids. If terephthalic acid is used as the dicarboxylic acid component of the polyester, at least 5 mole percent of one of the other acids listed above may also be used.

It should be understood that use of the corresponding acid anhydrides, esters, and acid chlorides of these acids is included in the term “dicarboxylic acid.” Examples of these esters include dimethyl 1,4-cyclohexanedicarboxylate; dimethyl 2,5-naphthalenedicarboxylate; dibutyl, 4,4′-sulfonyldibenzoate; dimethyl isophthalate; dimethyl terephathalate; and diphenyl terephthalate. Copolyesters may be prepared from two or more of the above dicarboxylic acids or derivatives thereof.

Examples of suitable glycols include poly(ethylene glycols) such as diethylene glycol, triethylene glycol, tetraethylene glycol, and pentaethylene, hexaethylene, heptaethylene, octaethylene, nonaethylene, and decaethylene glycols, and mixtures thereof. Preferably the poly(ethylene glycol) employed in the present invention is diethylene glycol or triethylene glycol or mixtures thereof. The remaining portion of the glycol component may consist of aliphatic, alicyclic, and aralkyl glycols. Examples of these glycols include ethylene glycol; propylene glycol; 1,3-propanediol; 2,4-dimethyl-2-ethylhexane-1,3,diol; 2,2-dimethyl-1,3-propanediol; 2-ethyl-2-butyl-1,3-propanediol; 2-ethyl-2-isobutyl-1,3-propanediol; 1,3-butanediol; 1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol; 2,2-4-trimethyl-1,6-hexanediol; thiodiethanol; 1,2-cyclohexanedimethanol; 1,3-cyclohexanedimethanol; 1,4-cyclohexanedimethanol; 2,2,4,4-tetramethyl-1,3-cyclobutanediol; p-xylylenediol. Copolymers may be prepared from two or more of the above glycols.

The difunctional sulfo-monomer component of the sulfonated polyester may advantageously be a dicarboxylic acid or an ester thereof containing a metal sulfonate group or a glycol containing a metal sulfonate group or a hydroxy acid containing metal sulfonate group.

Advantageous difunctional sulfo-monomer components are those wherein the sulfonate salt group is attached to an aromatic acid nucleus such as benzene, naphthalene, diphenyl, oxydiphenyl, sulfonyldiphenyl, or methylenediphenyl nucleus. Particular examples include sulfophthalic acid, sulfoterephthalic acid, sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, and their esters; metalosulfoaryl sulfonate having the general formula.

wherein X is a trivalent aromatic radical derived from a substituted or unsubstituted aromatic hydrocarbon, Y is a divalent aromatic radical derived from a substituted or unsubstituted aromatic hydrocarbon, A and B are carboalkoxy groups containing 1 to 4 carbon atoms in the alkyl portion or a carboxy group, the metal ion M is Li

+

, Na

+

, K

+

, Mg

++

, Ca

++

, Ba

++

, Cu

++

, Fe

++

, Fe

+++

, and n is 1 for monovalent M or 2 for divalent M or 3 for trivalent M. When a monovalent alkali metal ion is used, the resulting sulfonated polyesters are less readily dissipated by cold water and more rapidly dissipated by hot water. When a divalent or a trivalent metal ion is used, the resulting sulfonated polyesters are not ordinarily easily dissipated by cold water, but are more readily dissipated in hot water. Depending on the end use of the polymer, either of the different sets of properties may be desirable. It is possible to prepare the sulfonated polyester using, for example, a sodium sulfonate salt and later by ion-exchange replace this ion with a different ion, for example, calcium, and thus alter the characteristics of the polymer. In general, this procedure is superior to preparing the polymer with divalent metal salt inasmuch as the sodium salts may be more soluble in the polymer manufacturing components than are the divalent metal salts. Polymers containing divalent or trivalent metal ions are less elastic and rubber-like than polymers containing monovalent ions. One such metallosulfoaryl sulfonate component may be prepared as shown by the following general reactions:

and other chlorinating agents (e.g., thionyl chloride, phosphorus trichloride, phosphorous oxychloride) may be used. In addition, the reaction between the sulfonyl chloride and the sulfophenol may be carried out in water or an inert organic solvent, and the base used may be an alkali metal hydroxide or a tertiary amine. Such suitable compounds are disclosed in U.S. Pat. No. 3,734,874.

Optionally, the polycondensation reaction may be carried out in the presence of one or more of the following:

(d) an unsaturated mono- or dicarboxylic acid; and,

(e) a difunctional hydroxycarboxylic acid having one —CH

2

—OH group, an aminocarboxylic acid having one —NRH group, an amino alcohol having one —CR

2

—CH and one —NRH group, a diamine having two —NRH groups, or a mixture thereof, wherein each R is hydrogen or a C

1-4

alkyl group.

The &agr;,&bgr;-unsaturated acids (d) are described by the following structure:

R—CH═CH—R

1

wherein R is H, alkylcarboxy, or arylcarboxy and R

1

is carboxy or arylcarboxy. Polymers derived from the above components can be used in combination with polymers derived from other components and/or in combination with other ethylenically unsaturated comonomers (e.g., acrylic acid, acrylamide, butyl acrylate, diacetone acrylamide). The comonomers can be from 1-75 parts by weight, preferably 5-25 parts by weight &agr;,&bgr;-unsaturated acids.

Advantageous difunctional components which are aminoalchohols include aromatic, aliphatic, heterocyclic and other types as in regard to component (e). Specific examples include 5-aminopentanol-1,4-aminomethylcyclo-hexanemethanol, 5-amino-2-ethyl-pentanol-1,2-(4-&bgr;-hydroxyethoxyphenyl)-1-aminoethane, 3-amino-2,2-dimethylpropanol, hydroxyethylamine, etc. Generally these aminoalcohols contain from 2 to 20 carbon atoms, one —NRH group and one —CR

2

—OH group.

Such difunctional monomer components which are aminocarboxylic acids include aromatic, aliphatic, heterocylic, and other types as in regard to component (c) and include lactams. Specific examples include 6-aminocaproic acid, its lactam known as caprolactam, omegaaminoundecanoic acid, 3-amino-2-dimethylpropionic acid, 4-(&bgr;-aminoethyl)benzoic acid, 2-(&bgr;-aminopropoxy)benzoic acid, 4-aminomethylcyclohexanecarboxylic acid, 2-(&bgr;-aminopropoxy)cyclohexanecarboxylic acid, etc. Generally these compounds contain from 2 to 20 carbon atoms.

Examples of such difunctional monomer component (e) which are diamines include ethylenediamine; hexamethylenediamine; 2,2,4-trimethylhexamethylenediamine; 4-oxaheptane-1,7-diamine; 4,7-dioxadecane-1,10-diamine; 1,4-cyclohexanebismethylamine; 1,3-cycloheptamethylene-diamine; dodecamethylenediamine, etc.

Greater dissipatability is achieved when the difunctional sulfo-monomer constitutes from about 6 mole percent to about 25 mole percent out of a total of 200 mole percent of (a), (b), (c), (d), and any (e) components of the polyester or polyesteramide. The total of 200 mole percent can also be referred to as 200 mole parts.

Any of the above-identified difunctional monomers generally contain hydrocarbon moieties having from 1 to about 40 carbon atoms in addition to their two functional groups, but they may in general also contain up to six non-functional groups such as —O—, —S—, —SO

2

—, —SO

2

—O—, etc. For example, the poly(ethylene glycol) monomer used may contain from 1 to about 19 oxy groups, such as —O— groups.

In a preferred embodiment, the ionomer is one of the sulfonated polyesters sold by Eastman Chemical Company, Kingsport, Tenn. (hereafter “Eastman”). which are water dispersible, linear or branched polyesters formed by the polycondensation of glycols with dicarboxylic acids, some of which contain sodiosulfo groups. Sulfopolyester hybrids may also be employed which are formed by the in situ polymerization of vinyl and/or acrylic monomers in water dispersions of SULFOPOLYESTER. Such Eastman sulfonated polyesters may be purchased from Eastman under nos. AQ1045, AQ1350, AQ1950, AQ14000, AQ35S, AQ38S, AQ55S and EASTEK 1300.

The sulfonated polyesters and copolymers thereof may range from about 10 to about 90 weight percent, more preferably, about 60 to 80 weight percent, most preferably about 70 weight percent of the total composition. The polar carrier may range from about 10 to about 90 weight percent, more preferably, about 20 to about 40 weight percent, most preferably, about 30 weight percent of the total composition. The remainder of the composition may comprise one or more of the other additives described herein.

Compositions comprising branched sulfonated polyesters tend to give clear, tacky and flexible films. Compositions comprising linear polyesters tend to give clear or white, tack-free, flexible films.

Other sulfonated polymers that can be used in the practice of the invention include polystyrene sulfonate, acrylaminopropane sulfonate (AMPS) based polymers (e.g. 2-acrylamido-2-methylpropanesulfonic acid and its sodium salt available from Lubrizol Process Chemicals). In addition, urethane ionomers can be prepared by reacting a diisocyanate with a diol that has sulfonate functionality (e.g. butane diol sulfonate).

B. Acrylic Acid and Maleic Anhydride Polymers and Copolymers

Other ionomers include acrylic acid polymers and copolymers and salts thereof. Such polymers and copolymers are described in U.S. Pat. Nos. 5,821,294, 5,717,015, 5,719,244, 5,670,566, 5,618,876, 5,532,300, 5,530,056, 5,519,072, 5,371,133, 5,319,020, 5,037,700, 4,713,263, 4,696,951, 4,692,366, 4,617,343, 4,948,822, and 4,278,578.

The invention relates to compositions comprising the acrylic acid polymers and copolymers thereof described in these patents together with a polar carrier as described herein as well as the adhesive compositions described in these patents (comprising the acrylic acid polymers and copolymers thereof) together with the polar carrier.

Specific examples of such acrylic acid copolymers include ethylene acrylic acid copolymer and the ammonium (MICHEM 4983P) and sodium (MICHEM 48525R) salts thereof available from Michelman Incorporated, Cincinnati, Ohio. A further example is vinyl acetate acrylic copolymers (e.g. ROVACE HP3442) available from Rohm and Hass, Philadelphia, Pa.

The acrylic acid polymers and copolymers may range from about 10 to about 90 weight percent, more preferably, about 40 to 80 weight percent, most preferably about 50-70 weight percent of the total composition. The polar carrier may range from about 10 to about 90 weight percent, more preferably, about 10 to about 40 weight percent, most preferably, about 30 weight percent of the total composition. The remainder of the composition may comprise one or more of the other additives described herein.

Compositions comprising ethylene acrylic acid copolymers and a polar carrier tend to give clear, colorless, tack-free films with very good adhesion that heat in well under one second when exposed to RF. Vinyl acetate acrylic copolymer compositions tend to give clear, colorless, flexible but very tacky films with very good adhesion that heat in well under one second when exposed to RF.

In a preferred embodiment, compositions comprising acrylic acid polymers or coplymers are applied as liquid dispersions and dried into an RF susceptive coating.

Alternatively, maleic anhydride based copolymers such styrene maleic anhydride, ethylene maleic anhydride, and popylene maleic anhydride (availbe from Eastman Chemicals) may be employed as an ionomer. Such compositions are preferably applied as an aqueous dispersion at room temperature and dried into an RF susceptive coating.

C. Starch/Polysaccharide Derivatives

Other ionomers include starch and polysaccharide derivatives such as polysulfonated or polysulfated derivatives, including dextran sulfate, pentosan polysulfate, heparin, heparan sulfate, dermatan sulfate, chondroitin sulfate, a proteoglycan and the like. Dextran sulfate is available from Sigma Chemical Corporation, St. Louis, Mo., with molecular weights of 10,000, 8,000 and 5,000. Examples of other ionic polysaccharides include carrageenan, chitosan, xanthan gum, etc.

Phosphorylated starch as disclosed in U.S. Pat. No. 5,329,004 may be employed as a susceptor.

The starch/polysaccharide derivatives may range from about 10 to about 90 weight percent, more preferably, about 60 to 80 weight percent, most preferably about 70 weight percent of the total composition. The polar carrier may range from about 10 to about 90 weight percent, more preferably, about 20 to about 40 weight percent, most preferably, about 30 weight percent of the total composition. The remainder of the composition may comprise one or more of the other additives described herein.

D. Proteins

Other ionomers include proteins such as gelatin, soy protein, casein, etc. Gelatin is the purified protein derived from the selective hydrolysis if collagen. Collagen is the principal organic component of the bones and skin of mammals. Common raw materials include bones, cattle hides and pigskins. Gelatins are classified as either acid type (A type) or limed (B type) according to the process by which they are made. Particular examples of gelatins include KNOX gelatin as well as types P, D, D-I, LB, LM and K, available from PB Gelatins. See also the gelatin described in U.S. Pat. No. 5,877,287. In a preferred embodiment, the gelatin is 45Y56-853-3V0-6CS, available from Eastman Gelatin, Peabody, Mass. Alternatively, a gelatin-modified polyurethane as disclosed in U.S. Pat. No. 5,948,857 may be used.

In a preferred embodiment, the pH of the gelatin is raised or lowered in order to enhance the ionomeric character of the gelatin. The pH may be raised by the addition of aqueous base to an aqueous solution or suspension of the gelatin. Examples of suitable bases include alkali metal hydroxides, alkali metal carbonates and bicarbonates, alkali metal acetates, ammonia, amino compounds such as methylamine, dimethylamine, trimethylamine, triethylamine, and the like. Alternatively, a basic buffer solution may be added, e.g. a solution comprising 2-amino-2-methyl-1-propanol; or a glycine buffer at pH 9.4 and 10.4; each of which is available from Sigma Chemical Corporation, St. Louis, Mo. Other buffers include 0.01 borax (pH 9.2), TRIS (pH 7-9.1 depending on concentration), 0.05 M carbonate (pH 9.93), and 0.05 M trisodium phosphate (pH 12). See “The Chemist's Companion,” A. J. Gordon and R. A. Ford, John Wiley & Sons, New York, N.Y., 1972. The pH may be lowered by the addition of an acid such as HCl, HBr, H

2

SO

4

, H

3

PO

4

, or an organic acid such as C

1-4

alkanoic acid (e.g. acetic acid, propionic acid or butyric acid), an arylcarboxylic acid (e.g. benzoic acid), or arylsulfonic acid (e.g.p-toluenesulfonic acid). Alternatively, an acidic buffer may be added, e.g. acetate buffer at pH 4.5, 4.9 and 5.0; citrate buffer at pH 4.8; or a phosphate-citrate buffer at pH 5.0; each of which is available from Sigma Chemical Corporation. Other buffers include 0.005 M potassium tetraoxalate (pH 1.7), saturated potassium tartrate (pH 3.6), 0.05 M potassium phthalate (pH 4.0), and 0.05 M sodium succinate (pH 5.3). See “The Chemist's Companion,” A. J. Gordon and R. A. Ford, John Wiley & Sons, New York, N.Y., 1972. As discussed in the Examples, it has been discovered unexpectedly that when the pH of the gelatin composition is shifted into the acidic or basic range, the composition exhibits enhanced heating in an RF field compared to the untreated gelatin. The best heating occurs when the pH is low. Such gelatin compositions give flexible films that attach well to substrates and heat in under one second.

In a preferred embodiment, the pH of the gelatin may range from about 8 to about 12. In a most preferred embodiment, the pH of the gelatin is about 10. In another preferred embodiment, the pH of the gelatin may range from about 1 to about 6. In a most preferred embodiment, the pH of the gelatin is about 2.

The gelatin may range from about 10 to about 90 weight percent, more preferably, about 60 to 80 weight percent, most preferably about 70 weight percent of the total composition. The polar carrier may range from about 10 to about 90 weight percent, more preferably, about 20 to about 40 weight percent, most preferably, about 30 weight percent of the total composition. The remainder of the composition may comprise one or more of the other additives described herein.

E. Others

Other ionomers that may be used in the practice of the invention include sulfonated novolak resins obtained by a process comprising reacting an aromatic compound with a sulfonated agent to form a sulfonated aromatic compound, condensing the sulfonated aromatic compound with a non-sulfonated phenolic compound and an aldehyde or aldehyde precursor to form a sulfonated condensate, and reacting the condensate with a monovalent or divalent metal oxide, hydroxide, carbonic acid, boronic acid or carboxylic acid. See U.S. Pat. No. 5,098,774. Other ionomers that can be used are lignosulfonates and their sodium salts which are available with different molecular weights and levels of sulfonation from Westvaco, North Charleson, S.C.

In addition, urethane ionomers can be prepared by reacting a diisocyanate with a diol that has carboxy functionality (e.g. dimethylol).

III. The Polar Carrier

In a preferred embodiment, the ionomer is combined with a carrier that is a flowable polar compound, such as a polar solvent, having a high dielectric constant, e.g. &egr;(20° C.)≧about 10, more preferably, ≧about 20. A preferred dielectric constant range is about 13-63 (25° C.), more preferably, about 17-43 (25° C.). It has been unexpectedly discovered that compositions comprising an ionomer and such a carrier heat much more rapidly when exposed to RF energy, even at low levels, compared to when the ionomer or carrier are exposed separately. Without being bound by any particular theory, it is believed that upon exposure to RF energy, the polar carrier allows for the migration and/or vibration of protons or metal ions from the ionomer, resulting in the generation of heat.

Such polar carriers include, but are not limited to, water, dimethylformamide (DMF), dimethylacetamide (DMAC), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), polypropylene carbonates, ketones (such as acetone, acetyl acetone, cyclohexanone, diacetone alcohol, and isophorone), alcohols (such as ethanol, propanol, 2-methyl-1-propanol, and the like) amino alcohols (such as ethanolamine), oxazolidines, polyols, organic acids (such as formic, acetic, propionic, butyric and dimethylol butyric acid and the like), anhydrides (such as acetic anhydride and maleic anhydride), amides (such as formamide, acetamide and propionaminde), nitriles (such as acetonitrile and propionitrile), and nitro compounds (such as nitrobenzene, nitroaniline, nitrotoluene, nitroglycerine and any of the nitroparaffins). Any polar carrier that can weaken, to some degree, the ionic interaction between the anion and cation of the ionic susceptor, even if the susceptor component is a non-ionic compound, may be utilized in the present invention. Preferred polar carriers are humectants (e.g., glycerin, 1,2-propanediol and polyethyleneglycol), i.e., they retain at least a low level of moisture after application. It is believed that the low level of residual moisture enhances the RF activation of the compositions.

Examples of polyols that may be used as a polar carrier include glycols such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, thioethylene glycol, and pentaethylene, hexaethylene, heptaethylene, octaethylene, nonaethylene, and decaethylene glycols, and mixtures thereof, as well as aliphatic, alicyclic, and aralkyl glycols. Particular examples of these glycols include ethylene glycol; 1,2-propylene glycol; 1,3-propanediol; 2,4-dimethyl-2-ethylhexane-1,3,diol; 2,2-dimethyl-1,3-propanediol; 2-ethyl-2-butyl-1,3-propanediol; 2-ethyl-2-isobutyl-1,3-propanediol; 1,3-butanediol; 1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol; 2,2-4-trimethyl-1,6-hexanediol; thiodiethanol; 1,2-cyclohexanedimethanol; 1,3-cyclohexanedimethanol; 1,4-cyclohexanedimethanol; 2,2,4,4-tetramethyl-1,3-cyclobutanediol; p-xylylenediol. Also included are polyethylene glycols, e.g. having weight average molecular weights ranging from about 400 to about 2,000; mixed poly(ethylene)-poly(propylene) glycols having weight average molecular weights ranging up to about 6,000 and containing from about 30 to about 90 weight percent ethylene oxide; the monomethyl, monoethyl and monobutyl ethers of ethylene glycol, propylene glycol and diethylene glycol, the monomethyl and monoethyl ethers of triethylene glycol; the dimethyl and diethyl ethers of diethylene glycol, dipropylene glycol and trimethylene glycol. Examples of polyols containing three or more hydroxy groups include glycerin and derivatives of glycerin such as glycerol mono-, di-, and triacetate, or monomethacrylate. Also included is polyvinylalcohol, which also functions as an adhesive compound. Polyvinylalcohols of molecular weights 89,000-98,000, 85,000-146,000, 124,000-186,000, 31,000-50,000, 85,000-146,000, 124,000-186,000, 13,000-23,000, 50,000-85,000, with various levels of hydrolysis, are available from Aldrich Chemical Company.

The polar carrier may also be an alkanolamine and substituted alkanolamine based on ethanol and isopropanol such as mono-, di- and triethanolamine, mono-, di- and triisopropanolamine, methylethanolamine, dibutylethanolamine, phenyldiethanolamine, di-(2-ethylhexyl)ethanolamine, dimethylisopropanolamine, dibutylisopropanolarnine, and the like as well as mixtures thereof.

N-Alkyl sulfonamides are also useful carriers.

The present invention is not restricted to the listed carriers, and mixtures of carriers may be utilized, as would be apparent to those of skill in the art. Such polar carriers may comprise about 10 to 90 weight percent of the composition. In a preferred embodiment, the polar carrier comprises about 30 weight percent of the total composition. In a more preferred embodiment, the polar carrier comprises about 13-30% weight percent, more preferably, about 15-25 weight percent, most preferably, about 20-23 weight percent. At these percentages, very short heating times are possible while retaining acceptable shear strength of the bond.

Preferable high dielectric constant carriers are those that can generate heat without being highly volatile, in order to preserve RF susceptor mobility in the composition. Preferred carriers are glycols such as glycerine and N-methyl pyrrolidone (NMP). NMP has a high dipole moment of 4.09 Debye, which produces a dielectric constant, K, of 32.2 at 25° C. NMP is noncorrosive, biodegradable, and almost odorless. NMP has a low order of oral toxicity and is neither a skin irritant nor a sensitizer. NMP is also an excellent solvent both for a wide range of organic compounds and polymers, as well as for some inorganic salts. In short, it is a very useful medium for dissolving or dispersing susceptors and film formers that are employed in the bonding or adhering of substrates or layers according to the present invention.

A further preferred high dielectric constant carrier is glycerine. Glycerine has a dielectric constant of 42.5 at 25° C., is noncorrosive, biodegradable, and odorless. Glycerine is nontoxic and is neither a skin irritant nor a sensitizer. Thus, glycerine is a preferred carrier for consumer products containing adhesives and coatings. Glycerine is also an excellent solvent both for a wide range of organic compounds and polymers, as well as for some inorganic salts.

A suitable susceptor composition according to the present invention comprises a susceptor present in a concentration of from about 10% to about 50% and a carrier present in a concentration of from about 1% to about 75%. Additionally, another suitable susceptor composition further comprises an adhesive compound or other additive as described herein present in a concentration of from about 10% to about 35%. The susceptor composition can be used to bond or adhere substrates or layers to one another. The substrates can include single layers of polyolefins and non-polyolefins, as well as multilayer stacks. Such stacks may comprise 2, 3, 4, 5 or more layers. One or more susceptor compositions, which may be the same or different, may be between 2 or more layers of the multilayer stacks. All composition concentrations described herein correspond to weight-weight percentages, unless indicated otherwise.

IV. Further Additives to the Susceptor Compositions

A number of different additives may be added to the susceptor compositions of the present invention including the carrier or mobile medium. In order to provide uniform heating of a susceptor composition, the susceptors are dissolved, distributed, or dispersed, preferably substantially uniformly, in a carrier containing either various polymers and/or solvents or plastisizers. Some carriers, such as solvents, plastisizers, or polymers, are utilized for their polar functionality and for their ability to enhance the heating process.

A. Adhesive/Thermoplastic Additives

The adhesive properties of the susceptor composition of the present invention are enhanced by the presence of one or more thermoplastic or adhesive compounds, such as polymers or copolymers, that are blended in the susceptor composition. Some of the thermoplastic or adhesive compounds utilized in the present invention include, but are not limited to, polyesters such as a thermoplastic methylol polyester prepared from the reaction of at least one dicarboxylic acid with a diglycidyl ether, a diglycidyl ester or combination thereof (see U.S. Pat. No. 5,583,187) or a cyanoacrylate/polyester adhesive composition (see U.S. Pat. No. 5,340,873); polyamides; polyurethanes (see U.S. Pat. No. 5,391,602); polysiloxanes; elastomers; polyvinylpyrrolidone; ethylene vinyl acetate copolymers (see U.S. Pat. No. 4,460,728), vinylpyrrolidone vinyl acetate copolymers; vinyl ether copolymers (e.g. polyvinyl methyl ether); polyvinyl alcohol; partially hydrolyzed polyvinyl acetate; copolymers comprising a starch ester (see U.S. Pat. No. 5,498,224) and starch hydrolysates (see U.S. Pat. No. 5,827,553); graft copolymer prepared from a vinyl monomer and a polyalkylene oxide polymer, and a hydroxy-containing ester or acid wax (see U.S. Pat. No. 5,852,080); copolymers comprising a graft copolymer prepared from a vinyl monomer, at least one polyalkylene oxide polymer, a polar wax and other optional ingredients (see U.S. Pat. No. 5,453,144); thermoplastic block copolymers comprising an aromatic vinyl copolymer block, a diene polymer or hydrogenated derivative thereof and other additives (see U.S. Pat. No. 5,723,222); vinyl chloride copolymers; vinylidene chloride copolymers; vinylidene fluoride copolymers; vinyl pyrrolidone homo- and copolymers; vinyl pyridine homo- and copolymers; hydrolyzed polyvinyl alcohol and compositions thereof (see U.S. Pat. No. 5,434,216); cellulose esters (e.g. cellulose acetate and starch acetate, see U.S. Pat. No. 5,360,845) and ethers (e.g. hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, propyl cellulose and the like; see U.S. Pat. No. 5,575,840, 5,456,936 and 5,356,963); modified starch ester containing adhesives (see U.S. Pat. No. 5,360,845); high amylose starch containing adhesive (see U.S. Pat. No. 5,405,437); poly-alpha olefins; propylenehomo- and copolymers; ethylene homo- and copolymers (especially those of vinyl acetate, vinyl alcohol, ethyl- and butyl-acrylate, carbon monoxide, acrylic and methacrylic acid, crotonic acid, and maleic anhydride), an alkyl acrylate hot melt adhesive (see U.S. Pat. No. 4,588,767), a hot melt adhesive comprising an alkyl acrylate and an alpha-olefin (see U.S. Pat. No. 4,535,140), a hot melt adhesive comprising an ethylene n-butyl acrylate copolymer (see U.S. Pat. No. 5,331,033), a hot melt adhesive comprising a graft copolymer comprising at least one vinyl monomer and at least one polyalkylene oxide polymer (see U.S. Pat. No. 5,217,798), a vinyl acetate copolymer copolymerized with a cyclic ureido compound (see U.S. Pat. No. 5,208,285), a hydrophilic polycarbodiimide (see U.S. Pat. No. 5,100,994), a photopolymerized, pressure sensitive adhesive comprising an alkyl acrylate, a monethylenically unsaturated polar copolymerizable monomer, ethylene vinylacetate copolymer and a photo initiator (see U.S. Pat. No. 5,079,047), a hot melt adhesive comprising tackifying resins, oil diluent, and a substantially radial styrene-butadiene block copolymer (U.S. Pat. No. 4,944,993), an adhesive prepared from the vinyl ester of an alkanoic acid, ethylene, a dialkyl maleate, an N-methylol comonomer, and an ethylenically unsaturated mono- or dicarboxylic acid (see U.S. Pat. No. 4,911,960), an adhesive prepared from the vinyl ester of an alkenoic acid, ethylene, a dialkyl maleate, and a monocarboxylic acid (see U.S. Pat. No. 4,892,917), a hot melt adhesive consisting essentially of an ethylene n-butyl acrylate copolymer (U.S. Pat. No. 4,874,804), hot melt adhesive compositions prepared from styrene-ethylene-butylene-styrene tri-block and/or styrene-ethylene-butylene di-block copolymers that are tackified (U.S. Pat. No. 4,822,653), a hot melt packaging adhesive comprising a ethylene n-butyl acrylate copolymer with n-butyl acrylate (U.S. Pat. No. 4,816,306), polysaccharide esters containing acetal and aldehyde groups (U.S. Pat. No. 4,801,699), polysaccharide aldehyde derivatives (U.S. Pat. No. 4,788,280), an alkaline adhesive comprising a latex polymer or a halohydrin quaternary ammnonium monomer and starch (U.S. Pat. No. 4,775,706), polymeric fatty acid polyamides (U.S. Pat. No. 4,419,494), hot melt adhesives comprising resins containing 2-methylstyrene, styrene and a phenol (U.S. Pat. No. 4,412,030). The present invention is not restricted to the listed adhesive compounds and compositions, as would be apparent to those of skill in the art.

Such adhesive additives may comprise about 1 to 50 weight percent of the composition, more preferably, about 25 weight percent.

B. Adhesive/Coating Thermoset Additives

It is also possible to add a thermoset resin to the susceptor compositions of the present invention. Such thermosets are capable of being cross-linked or cured through heat and/or catalysts and include those described in U.S. Pat. No. 5,182,134, e.g. epoxies, polyurethanes, curable polyesters, hybrid thermosets, and curable acrylics. Others include bismaleimides, silicons, phenolics, polyamids and polysulfides among others. Further examples include maleate resins formed by the reaction of various polyols with maleic anhydride. Orthophthalic resins may be used which are formed by the reaction of phthalic anhydride and maleic anhydride or fumaric anhydride as the dibasic acid. Isophthalic resins may also be used which may be formed by reacting isophthalic acid and maleic anhydride. Others include the bis-phenol fuimarides, chlorendic polyester resins, vinyl esters, dicyclopentadiene resins, orthotolyl biguanine, the diglycidyl ether formed from bis-phenol A and epichlorohydrin, triglycidyl isocyanurate thermosetting compositions, bis-phenol A-epichlorohydrin diglycidyl ether cured with phenolic cross-linking agents, aliphatic urethane thermosetting compositions such as an unblocked isofuron diisocyanate-E-caprolactam, BTDA thermosetting compositions which are generally the reaction product of 3,3,4,4-benzophenone tetracarboxylic dianhydride and a bis-phenol A-epichlorohydrin diglycidyl ether, hybrid thermosetting compositions which are the reaction product of a carboxylated saturated polyester curing agents and bis-phenol A-epichlorohydrin diglycidyl ether, standard bis-phenol A-epichlorohydrin diglycidyl thermosets such as those which are cured from 2-methylimidazole, and standard bis-phenol A-epichlorohydrin diglycidyl ether thermosets which are cured with 2-methylimidazole and dicyandiamide thermosetting compositions. See U.S. Pat. Nos. 5,182,134, 5,387,623.

Other thermosets and adhesives/coatings that may be added to the susceptor compositions of the invention include a reactive polyurethane prepolymer and 2,2′-dimorpholinoethyl ether or di(2,6-dimethylmorpholinylethyl) ether catalyst (see U.S. Pat. No. 5,550,191), a free radical polymerizable acrylic monomer, diazonium salt/activator composition (see U.S. Pat. No. 4,602,073), a diphenylmethane diisocyanate, a caprolactone triol, a neopentyl adipate ester diol, and, optionally, at least one polypropylene diol together with a catalyst (U.S. Pat. No. 5,057,568), an aqueous polyurethane dispersion comprising an isocyanate-terminated polyurethane prepolymer containing carboxylic acid salt groups, and an active hydrogen containing chain extender (U.S. Pat. No. 4,801,644).

The susceptor compositions of the present invention may also be combined with a shelf stable thermosetting resin as described in U.S. Pat. No. 5,739,184, which is then activated by RF energy to give coatings, e.g. for wood or paper products. This thermosetting resin comprises an epoxy resin, a rosin and an organometallic compound in an amount effective to provide improved adhesion to wood or paper substrates.

Curing agents may also be combined together with the susceptor/thermoset compositions of the invention, including melamines such as dialkyl melamines, amides such as dicyandiamide, adipamide, isophthalyl diamide, ureas such as ethylene thiourea or guanylurea, azides such as thiosemicarbazide, azoles such as guanazole or 3-amino-1,2,4-triazole, and anilines such as dialkylanilines such as dimethyl aniline and diethyl aniline.

Such thermoset additives may comprise about 1 to 50 weight percent of the composition, more preferably, about 25 weight percent.

It has also been discovered that thermoset compositions may be activated with only the polar carrier and without a susceptor. Thus, the invention also relates to compositions comprising a thermoset and a polar carrier. The thermoset may comprise about 60 to 95 weight percent of such a composition. The polar carrier may comprise about 5 to 40 weight percent. The invention relates as well to methods of bonding, adhering or coating substrates with such thermoset/polar carrier compositions.

C. Surfactant Additives

According to another embodiment of the present invention, surfactant additives can be added to the susceptor composition to enhance the ability to draw down the susceptor composition of the present invention onto the layers or substrates to be bonded, adhered or coated. Depending on the types of materials that are to be joined or coated, surfactant additives, such as SURFYNOL 104PA (available from Air Products Corporation) and SURFADONE LP 300 (N-dodecyl-2-pyrrolidone, available from International Specialty Products), can be used to wet a variety of substrates such as Mylar and polyethylene (PE). A further plasticizer is p-toluenesulfonamide, a good plasticizer that also dissolves stannous chloride. The present invention is not restricted to the listed surfactant additives, as would be apparent to those of skill in the art. Such surfactants may comprise about 0.1 to 5 weight percent of the composition.

D. Plasticizer Additives

The susceptor compositions of the present invention may further comprise a plasticizer to modify the flexibility of the adhesive or coating. Examples of such plasticizers include, but are not limited to acetyl tributyl citrate, butyl benzyl phthalate, butyl phthalyl butyl glycolate, dibutyl phthalate, dibutyl sebacate, diethyl phthalate, diethylene glycol dibenzoate, dipropylene glycol, dipropylene glycol dibenzoate, ethyl phthalyl ethyl glycolate, ethyl-p-toluene sulfonamide, hexylene glycol, methyl phthalyl ethyl glycolate, polyoxyethylene aryl ester, tributoxyethyl phthalate, triethylene glycol polyester of benzoic acid and phthalic acid, glycerin, or mixtures thereof. Other plasticizers that may be used include N-methyl-2-pyrrolidone (NMP), and substituted toluene sulfonamides (e.g. p-toluenesulfonamide, RIT-CIZER #8™ and RIT-O-LITE MHP™ from Rit-Chem Co., Inc., Pleasantville, N.Y.). Such plasticizers may comprise about 1 to 40 weight percent of the composition.

E. Tackifiers

The tackiness of the compositions of the invention may be increased by the addition of a suitable tackifier, e.g. one or more of hydrogenated aromatic petroleum resins, hydrogenated aliphatic petroleum resins, and hydrogenated terpene resins (see U.S. Pat. No. 5,418,052), coumarone-indene, ester gum, gum rosin, hydrogenated rosin, phenolic modified hydrocarbon resins, rosin esters, tall oil rosins, terpene phenolic, terpene resins, toluene sulfonamide-formaldehyde resin, wood rosin (see U.S. Pat. No. 5,442,001), distilled rosin, dimerized rosin, maleated rosin, polymerized rosin (see U.S. Pat. No. 5,532,306). Other tackifiers and modifiers, include (but are not limited to) styrene and alpha methyl styrene resins, glycerol and pentaerithritol esters, etc. Particular tackifiers include WINGTACK 95 from Goodyear, Herculin D and PICCOLYTE C from Hercules, EASTOTACK H100 from Eastman, and ECR 149B or ECR 179A from Exxon Chemical (see U.S. Pat. No. 5,559,165). Other tackifiers include rosin and its derivatives available from Reichold Chemicals, Manila Copal (softening point 81-90° C. acid No. 110-141), Pontianac (softening point 99-135° C. acid No. 1120129) and Sanarec (softening point 100-130° C., acid no. 117-155). Such tackifiers may comprise about 1 to 25 weight percent of the composition.

F. Fillers

A number of different fillers may be added to the susceptor compositions of the invention, including, but not limited to cellulose, bentonite, calcium carbonate, calcium silicate, clay, mica silica, talc, alumina, glass beads, fibers and the like. Such fillers may comprise about 0 to 40 weight percent of the composition.

G. Stabilizers and Antioxidants

Stabilizers and antioxidants may be added to the susceptor compositions of the invention in amounts effective to achieve the intended result. Included amoung such stabilizers include high molecular weight hindered phenols and multifunctional phenols such as sulfur and phosphorous-containing phenols. Representative hindered phenols include 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, pentaerythritol tetrakis-3-(3,5-di-tert-butyl-4-hydroxypropionate, n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 4,4′-methylenebis(2,6-di-tert-butylphenol), 4,4′-thiobis(6-tert-butyl-o-cresol), 2,6-di-tert-butylphenol, 6-(4-hydroxyphenoxy)-2,4-bis(n-octylthio)-1,3,5-triazine, di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, 2-(n-octylthio)ethyl-3,5-di-tert-butyl-4-hydroxybenzoate, and sorbitol hexa[3-(3,5-di-tert-butyl-4-hydroxylphenyl)propionate (see U.S. Pat. No. 5,574,076). Such stabilizers and antioxidants may comprise about 0.01 to 5 weight percent of the composition.

H. Other Additives

According to another embodiment of the present invention, other types of additives to the susceptor composition may include flow aids, heat and UV stabilizers, coupling agents, waxes, pigments and other organic compounds. For example, in some instances, waxes can facilitate lower melt temperatures. Waxes that can be utilized include, but are not limited to, Bees wax (SYNCHROWAX BB4), Candelilla wax, CARBOWAX 3350 (available from Union Carbide Corporation), Carnauba wax, and CASTORWAXNF. Other waxes include N-(2-hydroxyethyl)-2,2′-ethylene-bis-stearamide, stearamide, 12-hydroxystearamide wax, hydrogenated castor oil, oxidized synthetic waxes, poly(ethylene oxide) having a molar average molecular weight of above about 1000, and functionalized synthetic waxes such as carbonyl containing ESCOMER H101 from Exxon (see U.S. Pat. No. 5,532,306). Preferably, the wax polar as described in U.S. Pat. 5,750,605. A preferred polar wax is Peracin 200. Also preferably, the polar wax is present at no more than about 25%, more preferably, no more than 17% of the composition, most preferably, no more than 10% of the composition.

Other additives include elastomers such as those described in U.S. Pat. Nos. 5,506,298, 5,739,184, 5,169,890, 5,039,744, 4,761,198 may be used, including styrene butadiene rubber, polybutadiene rubber, rubber, nitrile rubbers, butyl rubber and halogenated butyl rubber.

When the compositions are applied and activated as coatings, they may further comprise one or more additives to impart color to the composition. Such additive include, without limitation, titanium dioxide, iron oxide pigments, carbon black and organic pigments such as isoindoline yellow.

The present invention is not restricted to the listed additives, as would be apparent to those of skill in the art. Such other additives may comprise about 1 to 25 weight percent of the composition.

V. Applying the Susceptor Compositions to Substrates

The compositions of the invention may be formulated to be applied as a liquid at room temperature, hot melt, or powder. Liquid compositions may be solvent borne or water-borne. The liquid applied compositions may be applied as a liquid at room temperature and dried down to give the desired coating. The liquid applied coating may be applied to a substrate by any conventional method including spraying, ink-jet, brushing, rolling, gravure printing, dripping and the like. Methods of actively drying down liquid compositions include but are not limited to conventional oven drying, forced air, heat lamps, microwave heating, RF heating or various combinations of these or other methods. When a liquid composition is dried down, it loses some or all of its volatiles. RF drying of a liquid applied composition may be accomplished by applying RF energy across the composition in order to generate sufficient heat within the liquid to facilitate or enhance the evaporative loss of water or solvent(s). The RF energy can be applied across the liquid at constant, intermittent, or gradient intensities to achieve the desired rate and degree of drying. Similarly, other methods of drying may be applied at constant, intermittent or gradient intensities to achieve the desired drying result.

Hot melt applied systems are applied in their molten state at an elevated temperature and then cooled to yield the desired solid coating. The hot melt compositions can be heated to a molten state by various methods including but not limited to conventional melt tanks, microwave heating and RF heating. Once the hot melt composition is melted, it may be applied in a variety of different types of hot melt coatings, including but not limited to spirals and beads, hot blown, slot coat, and co-extrusion. After application, the molten hot melt composition can be passively or actively cooled to return to its solid form. Active cooling may be accomplished by blowing cool air across the applied material, or by allowing the substrate to make contact with a heat-sink surface.

Powdered applied systems are applied in their “fine” particle state (1-20 &mgr;m) by electrostatic spray or gun. The applied layer is activated by RF energy as in liquid or hot-melt systems.

Once dried and/or cooled, the substrate may be stored until activation of the composition is desired. Many of the applied compositions of the invention are substantially non-tacky and may be applied to a substrate which is then rolled up. Upon unrolling and activating, the substrate may be adhered to one or more other substrates. Those compositions that are tacky may be activated immediately after being applied and dried if necessary. Alternatively, they may be covered with a removable strip or dusted with talc or similar material.

One aspect of the invention also relates to a method for applying a susceptor composition to a substrate, comprising:

(1) formulating the susceptor composition as a liquid dispersion;

(2) applying the liquid dispersion of the susceptor composition to the substrate;

(3) drying the susceptor composition, wherein the drying step includes the step of applying RF energy across the composition, thereby generating heat within the liquid dispersion. In a preferred embodiment, one may roll up the substrate after the susceptor composition has dried.

The susceptor compositions may be applied to any conventional substrates including, without limitation, woven and nonwoven substrates such as polyolefins, such as PP and PE webs, non-wovens, films and the like, cellulose substrates prepared from, for example, wood pulp (such as paper, cardboard and the like), cotton fibers (e.g. textiles such as cloth, sheeting and industrial fabrics), glass, ceramic surfaces, rubber and synthetic polymeric substrates such as polyester or polyolefin substrates prepared from, for example, polypropylene and polyethylene, polyvinyl alcohol, polyhydroxyvalerate butyrate, polylactides, cellulosics, polyamides, polyvinyl chloride, polystyrene, acrylics, synthetic textile products, etc. and any combination of the aforementioned. Other substrates include metal (e.g. aluminum foil and other metal foils), wood, composites, etc.

VI. Apparatus For Activating the Various Compositions of the Present Invention

Generally, the compositions of the present invention may be heated (i.e., activated) by any system capable of generating an electromagnetic field of sufficient strength and frequency.

FIG. 4

illustrates a high level block diagram of an RF heating system

400

that is capable of generating an electromagnetic field for activating the compositions of the present invention. Heating system

400

includes an RF power supply

402

that provides about a 1 kW, 1 to 15 MHz, RF signal

404

to a heat station

406

. Heating system

400

also includes an inductor

408

that is coupled to RF power supply

402

through heat station

406

. Generally, heat station

406

includes a capacitor connected either in series with or parallel to inductor

408

.

RF signal

404

provided to heat station

406

by RF power supply

402

creates an alternating current flowing through inductor

408

, which creates an electromagnetic field. Heating of a sample

410

, which is or includes a composition of the present invention, occurs when sample

410

is placed in proximity to inductor

408

. The best heating takes place when sample

410

is placed near the proximal (or “terminal”) end

411

of inductor

408

, and little or no heating occurs when sample

410

is placed at the distal (or “turn”) end

412

of inductor

408

. Further, there is a heating gradient from terminal end

411

to turn end

412

. In theory and without limitation, the best heating occurs at the terminal end

411

because it is believed that the intensity of the electric field component of the electromagnetic field at terminal end

411

is greater than at the distal end

412

.

FIG. 5

illustrates a high level block diagram of another embodiment of a heating system

500

that is capable of generating an electromagnetic field for activating the compositions of the present invention. Heating system

500

includes an alternating voltage generator

502

and a probe

504

, which is connected to an output terminal

501

of voltage generator

502

. Voltage generator

502

alternately positively charges and negatively charges probe

504

, thereby creating an electromagnetic field

506

centered at probe

504

. Heating can occur when sample

410

is placed in proximity to probe

504

. How quickly and how much heating occurs depends on the sample itself, the strength of the electromagnetic field at the sample, and the frequency of the alternating voltage

509

produced by voltage generator

502

.

Generally, probe

504

is a conductive material, such as, but not limited to copper, aluminum, or stainless steel. Generally, probe

504

can have a variety of shapes, including cylindrical, square, rectangular, triangular, etc. Preferably, probe

504

is square or rectangular. Probe

504

can be hollow or solid, preferably hollow.

Generally, probe

504

can be straight or non-straight, such as curved. The preferred characteristics of probe

504

ultimately depends on the application that it is being used for.

In yet another embodiment, which is illustrated in

FIG. 6

, heating system

500

includes at least two probes

602

and

604

for activating the compositions of the present invention. Probe

602

is connected to output terminal

610

, and probe

604

is connected to output terminal

612

. Like probe

504

, probes

602

and

604

are made from conductive materials as discussed above. Probes

602

and

604

can have a variety of shapes. For example, they can be either straight or curved. Preferably, at least a portion of probe

602

is parallel to a portion of probe

604

, although not a required.

In the system shown in

FIG. 6

, probe

602

has a net positive charge when probe

604

has a net negative charge, and probe

602

has a net negative charge when probe

604

has a net positive charge. When probes

602

and

604

are oppositely charged, a strong electromagnetic field

606

is present between the probes. Thus, sample

410

is preferably heated by placing it in a region above (or equivalently below) the region between probe

602

and probe

604

, as illustrated in

FIGS. 7A and 7B

. This region is referred to as an activation region. Preferably, an insulating layer

702

(see

FIG. 7A

) is placed between sample

410

and probes

602

and

604

, although this is not a requirement.

Generally, the vertical distance between sample

410

and probes

602

and

604

ranges from about 0.01 to 2 inches, more preferably from about 0.02 to 1 inch, and most preferably from about 0.025 to 0.185 inches. Sample

410

can also be heated by placing it between probes

602

and

604

. Generally, The center to center distance between probes

602

and

604

ranges from about 0.1 to 3 inches, more preferably from about 0.2 to 2 inches, and most preferably from about 0.25 to 0.75 inches. Additionally, in general, the height and width of a rectangular probe, or the diameter for a cylindrical probe, ranges between about 0.02 and 0.5 inches, and the length generally ranges from about 0.25 inches to 20 feet.

In one embodiment, the distal end

750

of probe

602

is curled to reduce corona effect (see FIG.

7

C). For the same reason, the distal end of probe

604

is also curled.

An advantage that the two probe system shown in

FIG. 6

has over the system shown in

FIG. 4

, is that sample

410

heats equally as well at the proximal end of probes

602

,

604

as it does at the distal end. Consequently, the system of

FIG. 6

does not experience the heating gradient problem that is encountered with the system of FIG.

4

.

Generally, the compositions of the present invention may be activated by a frequency of the alternating voltage

509

ranging from about 1 KHz to 5 GHz, more preferably from about 1 MHz to 80 MHz, and most preferably from about 10 to 15 MHz. The peak to peak voltage between probes

602

and

604

generally ranges from 1 to 15 kilo volts (kV). Generally, the duration of RF energy application to the sample

410

(also referred to as dwell time), for most applications, ranges from about 100 milliseconds to 30 seconds. However, there are some applications where the dwell time greatly exceeds 30 seconds. In the case of a composition comprising a thermoset resin, the dwell time ranges from about 1 second to 20 minutes, preferably from about 1 to 10 minutes, and most preferably from about 2.5 to 5.0 minutes to initiate cross linking reactions(s) leading to a high degree of thermoset character.

FIG. 8

illustrates one embodiment of alternating voltage supply

502

. The invention, however, is not limited to this or any particular voltage supply, since any system capable of generating a strong enough electromagnetic field could be utilized to activate the compositions of the present invention. In one embodiment, voltage supply

502

includes direct current (DC) voltage source

802

that is connected to a broadband amplifier

806

through DC power rail

804

. The function of DC voltage source

802

is to provide a DC voltage to broadband amplifier

806

. The DC voltage produced by DC voltage source

802

can range from 0 volts to 200 volts. The magnitude of the voltage provided to broadband amplifier

806

is dependent upon an output signal

815

from a main controller

814

. Output signal

815

of main controller

814

can be controlled manually by a user

821

through user interface

820

, or automatically by a production line control system

822

.

Broadband amplifier

806

amplifies a low level RF signal

817

generated by frequency controller

816

, and thus generates a high level RF power signal

808

. Preferably, the frequency of RF signal

817

ranges between 10 MHz and 15 MHz. RF signal

808

is passed through a power sensor

810

and provided to an impedance matching circuit

812

(also referred to herein as “heat station”) through an RG393 50 ohm cable

811

. Upon RF signal

808

being inputted into impedance matching circuit

812

, an electromagnetic field

606

is generated at the probes

602

and

604

. This electromagnetic field is used to heat the compositions of the present invention.

While RF signal

808

is applied to impedance matching circuit

812

, power sensor

810

continuously feeds a reflected power signal

832

to frequency controller

816

and main controller

814

. Power sensor

810

also continuously feeds a forward power signal to main controller

814

. Reflected power signal

832

represents the amount of reflected power and forward power signal

830

represents the amount of forward power.

Frequency controller

816

uses reflected power signal

832

to continually adjust the frequency of RF signal

817

so as to minimize the amount of reflected power. Main controller

814

uses forward power signal

830

and reflected power signal

832

to maintain the power level set by user

821

through user interface

820

or set by production line control system

822

. Main controller maintains the correct power level by adjusting the level of DC voltage supplied by DC voltage source

802

and by adjusting the output level of RF signal

817

generated by frequency controller

816

.

As sample

410

changes during a heating process, the impedance on the probes

602

and

604

change, which causes a change in the forward and reflected power. Frequency controller

816

will detect this change in reflected power because it is receiving reflected power signal

832

from power sensor

810

. Frequency controller

816

changes the frequency of RF signal

817

so as to minimize reflected power, thereby achieving an optimum impedance match and insuring a repetitive power transfer from heating system

800

to sample

410

.

DC voltage source

802

, sensor

810

, frequency controller

416

, and main controller

814

are further described in U.S. patent application Ser. No. 09/113,518, entitled, “RF Power Supply,” which is incorporated herein by reference in its entirety. A broadband amplifier suitable for use in heating system

800

is described in U.S. patent application Ser. No. 09/270,506, filed Mar. 17, 1999, entitled, “High Frequency Power Amplifier,” which is incorporated in its entirety herein by reference.

FIG. 9

is a flow chart illustrating a process for heating a composition according to the present invention using heating system

800

. The process begins with step

902

when user

821

or production line control system

822

sends a “heat-on” signal to the main controller

814

. Upon receiving the “heat-on” signal, main controller

814

begins an initial tunning process for determining the frequency of RF signal

817

that produces the minimum amount of reflected power. The initial tuning process encompasses steps

904

-

908

. In step

904

, main controller

814

directs DC voltage source

802

to output a “tune” voltage. The “tune” voltage is the lowest voltage level that can provide a sufficient signal to measure the reflected power over a range of frequencies. The objective is to consume the least amount of energy during the initial tunning process. Typically, the “tune” voltage level is 10% of the full scale voltage, where the full scale voltage is the voltage at which the composition is intended to be heated.

After step

904

, control passes to step

906

. In step

906

, heating system

800

performs course tunning. That is, heating system

800

determines a course estimate (i.e., rough estimate) of the frequency that produces the minimum reflected power. Hereafter this frequency shall be referred to as the resonant frequency. The course estimate of the resonant frequency can be determined by sampling reflected power over a first predetermined frequency range. After step

906

, control passes to step

908

. In step

908

, the heating system

800

performs fine tunning. That is, the heating system

800

determines a fine estimate (i.e., more precise estimate) of the resonant frequency. The fine estimate can be determined by sampling the reflected power over a second frequency range, which includes the course estimate of the resonant frequency. After step

908

, control passes to steps

910

and

912

in parallel. In step

910

, main controller

814

ramps (i.e., rapidly increases) the voltage output by the DC voltage source

802

such that within approximately 30 milliseconds the voltage increases from the “tuning” voltage level to approximately the full scale voltage level. In step

912

, the heating system

800

continuously tracks the resonant frequency until a power off indication is received. The methods for course tuning, fine tuning, and tracking resonant frequency are described in U.S. patent application Ser. No. 09/113,518.

FIG. 10A

further illustrates one embodiment of impedance matching circuit

812

. Impedance matching circuit

812

is used to match the impedance of 50 ohms on the input to the variable impedance of the probes

602

and

604

and sample

410

. The impedance of the probes

602

and

604

and sample

410

is typically in the order of 200 to 500 ohms. The impedance of the sample has an equivalent circuit of a resistance between 500 Ohms and 50 Kilo Ohms in parallel with a 0.1 picofarad capacitor.

Circuit

812

includes a connector

1001

, two capacitors

1002

and

1004

, and an inductor

1006

. Capacitor

1002

is a variable capacitor, which is adjustable from 10 to 50 picofarades (pf) to achieve impedance match to the varying impedance of probes

602

and

604

and sample

410

. The capacitance of capacitor

1004

is preferably 100 pf, and the inductance of inductor

1006

is preferably 1.0 micro henries (&mgr;H). Capacitor

1004

and inductor

1006

form a parallel resonance circuit that will resonate typically at a frequency between 12.5 and 14.5 MHz. Capacitor

1004

and inductor

1006

are water cooled with a flow rate of approximately half a gallon per minute. Probe

602

is connected to a node

1020

of circuit

812

, and probe

604

is connected to a node

1022

of circuit

812

. The high power RF input

411

(typically less than 1 kilowatt) from a 50 ohm source generator is connected to connector

1001

.

A process for setting the capacitance of variable capacitor

1002

will now be described. The process begins by applying a low level RF signal (typically 10 watts) to input

1001

of circuit

812

. The frequency of the applied RF signal is adjusted until the amount of reflected power is minimized. The capacitance of capacitor

1002

is then adjusted to optimize the reflected power minima. To achieve the least amount of reflected power that is practical to achieve, which is about two percent reflected power (or 1.25 voltage standing wave ratio (VSWR)), the frequency of the applied RF signal and the capacitance of capacitor

1002

are adjusted in an iterative process. Once the process is completed, sample

410

is placed in proximity to probes

602

and

604

. At this point it may be necessary to adjust the frequency of operation and capacitor

1002

in order to achieve an optimum reflected power. Once optimum reflected power is achieved, the power level of the input RF signal is increased. As the input RF power level is increased the resonant frequency of the matching circuit and probes

602

and

604

and sample

410

will change requiring a change of operating frequency to continue to minimize the reflected power.

FIG. 10B

illustrates another embodiment of impedance matching circuit

812

. In this embodiment, impedance matching circuit

812

includes a connector

1051

, a 1:1 balun transformer

1052

, two variable capacitors

1054

and

1056

, and one inductor

1060

. Capacitors

1054

and

1056

are adjustable from about 3 to 25 picofarades (pf) to achieve impedance match to the varying impedance of probes

1082

and

1084

and sample

410

. The inductance of inductor