Low application temperature hot melt adhesive for cigarette preparation
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The present invention is directed to the use of low application temperature hot melt adhesive for cigarette filters. Specifically, the hot melt adhesives of the present invention are used to bond filter wrap seam and to anchor the filter element in place on the rod.
A standard filter tipped cigarette is produced by three different operations: (1) filter or plug manufacture, (2) rod manufacture, and (3) tipping.
The cigarette rod consists of a stream of tobacco wrapped in a paper tube, the paper tube being glued along one longitudinal edge or surface with a suitable adhesive. This operation takes place at speeds varying from 2,000 to 16,000 cigarettes per minute. The weight of the cigarette rod, diameter, and length are all closely monitored for both cost control and tax purposes.
The filter making operation is similar in many respects to the rod manufacture, but the materials and manufacturing equipment used are different. Tobacco smoke filters are most commonly manufactured from a crimped textile tow of cellulose acetate fibers. The tow Is then warmed and rolled to produce a material about 9" wide, and containing an even distribution of fibers. The tow is "bloomed" in a known manner to separate the fibers, and a high boiling point solvent, commonly called a "plasticizer", i.e., triacetin, is applied by spraying, wicking, or other suitable means. The treated tow is then pulled into a cylindrical form and wrapped with paper. During an Interval of time, which can be accelerated by heating, the plasticizer first partially dissolves the surface of the fibers causing them to become sticky and to bond together at points of contact with each other. The plasticizer then migrates into the fiber leaving the surface dry, but the fibers still remain bonded.
The bloomed tow is then formed Into a tube, and wrapped In paper or plugwrap, the paper being glued along one longitudinal edge. Before the paper meets the tow material, adhesive is applied to the center and the edge forming the anchor and the seam. During this process, heater bars are used to extend the open time of the adhesive as it meets the tow. The formed filter rod is then passed under chliler plates to set the adhesive. This is necessary as the filter is Immediately cut into smaller pieces.
In some applications, such as multi-component or charcoal type filters, a hot melt adhesive is pre-applied onto filter paper and then heat sealed by the filter making machine.
In conventional cigarette filter manufacture, a hot melt adhesive, applied at 177°C (350°C), is used for the seam and a second, aqueous adhesive, is used for the anchor. An aqueous adhesive is chosen with triacetin resistance. Because of the nature of the tow, there is a high degree of radial stress upon the glued bond, so any adhesive used must be able to stick almost instantly and hold during storage and use. This has led to the use of hot melt type adhesives, which by formulation are fast setting, and allow very high machine speeds to be used.
Currently polyethylene and ethylene vinyl acetate based hot melt adhesives are used for this filter or plugwrap application. These are preferred since they are relatively non-polar and resist the deteriorative effects of triacetin, the most commonly used plasticizer, which often migrates acting as a solvent for the adhesive causing bond deterioration.
For example
Most commercially available adhesives used in cigarette manufacture are either hot melts which require temperatures of 177°C (350°F) or are aqueous to provide triacetin resistance.
However there are problems associated with use of conventional hot melt adhesives, which are applied at elevated temperatures, usually 177°C (350°F). These high temperatures increase the operator's risks with respect both to burns and to inhalation of residual volatiles. In addition, the high temperatures require more energy, placing greater demands on the manufacturing facility. The higher temperatures can also cause premature wear and tear on the application equipment i.e., nozzles, hoses and reservoir tanks.
The present invention uses low application temperature hot melt adhesives, which can be applied at temperatures In the range 93°C to 149°C (200 to 300°F). The advantages of using such lower temperatures include reduced number of heater elements required in the adhesive reservoir, reduced volatile emissions, and reduced risk of injury and reduced wear and tear on the application equipment. The use of low temperature hot melt adhesives may also eliminate the need for use of both an aqueous and hot melt adhesive, since some of the hot melt adhesives of the present invention exhibit excellent triacetin resistance. Further, the lower temperatures reduce temperatures in the reactivation section of the machinery and eliminate the need for cooling plates. In addition, the hot melt adhesives of the present invention have a fast set speed, low bleed through, improved cuttability and are comparable or better than 177°C (350°F) hot melt adhesives In terms of triacetin resistance.
It has been found in accordance with the present invention, that low application temperature ethylene copolymer based hot melt adhesives provide unexpected advantages in cigarette filter manufacture.
The present invention is directed to the use of hot melt adhesive compositions, which can be applied at temperatures between 93°C to 149°C 200 to 300°F, in the manufacture of cigarette filters. In particular, the present invention is directed to a process of making cigarette filters, and to cigarette filters, wherein a low application temperature ethylene copolymer based hot melt adhesive Is applied to at least one longitudinal edge or surface of porous and/or non-porous plug wrap paper. The adhesives of the present invention are also applicable to multi-component filters or other filters which are prepared by preapplying the hot melt to filter paper, then heating the coated paper on the filter making machine. As used herein, low application temperatures are temperature between 93°C and 149°C (200 and 300°F), preferably, 115°C to 135°C (240°F to 275°F).
The present Invention is directed to the process, and to cigarette filters, which comprise any hot melt adhesive which can be applied at temperatures between 93°C and 149°C (200 to 300°F). Adhesives suitable for use herein include the hot melt adhesives prepared from ethylene vinyl acetate copolymers comprising 5 to 45 weight percent vinyl acetate with a melt inder of at least 400 g/min.
The ethylene vinyl acetate copolymers (EVA) useful herein are those containing at least about 15 to 45 weight percent by weight vinyl acetate and having a melt Index of at least 400 dg/min. The EVA copolymers will preferably comprise less than 40 weight percent vinyl acetate (VA), most preferably 28% VA. The preferred copolymers are available from Exxon under the designation UL 7710 and comprise approximately 28 weight percent vinyl acetate by weight and have a melt index of about 400 dg/min. The amount of the copolymer present in the adhesive varies from 5 to 45 weight percent by weight, preferably 10 to 40 weight percent by weight.
Mixtures of ethylene vinyl acetate copolymers may also be used as long as the resultant mixture falls within the described ranges of percent vinyl acetate by weight, and melt Index. It Is therefore possible to mix two ethylene vinyl acetates having different melt indices and different percentages of vinyl acetate. These copolymers are useful In the range from 20% to 50% by weight in the adhesive, preferably from 25% to 40%.
In addition to the components described above, the adhesive compositions of the present invention may optionally comprise a second EVA copolymer, specifically one containing about 28 weight percent by weight of vinyl acetate and having a melt index of 6 to 40 dg/min. The preferred copolymers are available from Exxon under the designation ESCORENE UL 7740 and contain approximately 28 weight percent vinyl acetate by weight and have a melt index of about 40 dg/min. The amount of this copolymer present In the adhesive varies from 1 to 25 weight percent by weight, preferably 5 to 20% by weight.
The present invention also contemplates the addition top the adhesive of a polymeric additive selected from the group consisting of ethylene methyl acrylate polymers containing 10 to 28 weight percent by weight methyl acrylate, ethylene acrylic acid copolymers having an acid number of 25 to 150, methyl (meth)acrylate copolymers, polyethylene, polypropylene, poly(butene-1-co-ethylene) polymers and low molecular weight and/or low melt index ethylene n-butyl acrylate copolymers. When such additive is present, it is present In amounts up to 15 weight percent by weight of composition.
The adhesives of the present invention preferably also contain a stabilizer or antioxidant. Among the applicable stabilizers or antioxidants Include those discussed above in connection with the ethylene n-butyl acrylate copolymer based adhesives.
The adhesive may optionally comprise an organic phosphoric acid ester selected from the group consisting of tricresyl phosphate, tri-isopropyl phenyl phosphate, tributyl phosphate, triethyl phosphate, trimethyl phosphate, trioctyl phosphate or diphenyl phosphate.
The ethylene vinyl acetate based adhesive also comprise tackifiers and wax. The tackifiers and wax for use herein are the same as those described above for use with ethylene n-butyl acrylate based copolymer based adhesives. Preferably the tackifier is KRYSTALEX® 3085, a low molecular weight thermoplastic hydrocarbon polymer derived largely from alpha-methylstyrene which has a Ring and Ball softening point of 85°C and is available from Hercules Inc. The preferred wax is paraffin wax with a melting point of 150°C.
Depending on the contemplated end uses of the adhesives, other additives such as plasticizers, pigments and dyestuffs conventionally added to hot melt adhesives may be Included. In addition, small amounts of additional tackifiers and/or waxes such as microcrystalline waxes, hydrogenated castor oll and vinyl acetate modified synthetic waxes may also be incorporated in minor amounts, i.e., up to 10 weight percent by weight, into the formulations of the present invention.
The present invention also contemplates that the adhesives may be a blend of poly α-olefin and EVA.
Ethylene/alpha olefin polymers useful herein are those having a composition distribution breath index greater than 50%, and Mw/Mn less than 6. In another embodiment the ethylene/alpha olefin polymers will have a melt index of 40 to 1000 dg/min, a melt point of 71 to 90°C, a density of 0.850 to 0.92, a composition distribution breath index greater than 50%, and Mw/Mn less than 6. Preferably, the ethylene/alpha olefin polymers will have a melt index of 50 to 500 dg/min and a density of 0.885 to 0.90. The ethylene/alpha olefin polymers may be copolymers of ethylene and any alpha olefin, for example butene.
As used herein, composition distribution index, or short chain branching distribution index, refers to the weight percent of polymer molecules having a comonomer content within 50% of the median total comonomer content.
The hot melt adhesive of the present application can be applied at the relatively lower temperatures below 300°F and can be used in the present invention wherein a low application temperature adhesive is applied to at least one longitudinal edge of porous and/or non porous plug wrap paper. One most preferred embodiment of an adhesive for the present invention Is an adhesive consisting of:
- a) 31 parts paraffin wax with a softening point of 150°F;
- b) 21 parts ethylene vinyl acetate copolymer with a melt index of 400 and a vinyl acetate content of 28%;
- c) 11 parts or ethylene vinyl acetate copolymer with a melt index of 43 and a vinyl acetate content of 28%;
- d) 37 parts of alpha-methyl styrene tackifying resins; and
- e) 0.5 parts of an antioxidant stabilizer.
The resultant adhesive is characterized by a viscosity of less than about 5 Pas (5000 cps) at 121°C, a Ring and Ball softening point of 80°C to 115°C, fiber tearing bonds on plugwrap paper In the range of -18°C to 51°C (0°F to 120°F).
The following examples are merely exemplary, and not Intended to limit the scope of the present invention in any manner.
In the following examples, which are provided for illustrative purposes only, all parts are by weight and all temperatures in degrees Celsius unless otherwise noted.
In the examples, all adhesive formulations were prepared In single blade mixer heated to 135°C by blending the components until homogeneous.
The adhesives were then subjected to various tests simulating the properties needed for successful commercial applications.
Melt viscosities of the hot melt adhesives were determined on a Brookfield Model RVT Thermosei viscometer using a number 27 spindle.
Test specimens for determining elevated temperature peel and shear strengths were prepared as follows: an adhesive bead was applied at 121°C to a strip of 50 pound Kraft paper 2.54 cm (1 inch) wide by 7.62 cm (3 inches) long across the width of the paper. A second piece of Kraft paper of the same dimensions was immediately placed over the first piece and 200 gram weight placed on top of the composite construction. The compressed adhesive bead width was ½ inch.
Elevated temperature peel and elevated temperature shear were determined by attaching a 100 gram weight to each specimen and placing the specimens In a forced-draft oven. The temperature was raised In 5.5°C (10°F) increments from 38°C the specimens remained at a given temperature for 15 minutes for conditioning. The healing cycle was run until the final bond failed. Each peel and shear specimen was prepared and tested in duplicate. The elevated peel and shear value shown is the average temperature of failure for the two bonds. In some cases, the sample falled as the temperature was being adjusted within the 10° increments and is noted as such.
Adhesion at various temperatures, as noted, was determined by applying a 6.35 cm (¼ inch) wide bead of adhesive widthwise to a 5.08 cm (2 inch) by 7.62 cm (3 inch) piece of non porous plug wrap paper and immediately bringing a second piece of paper into contact. The bond is aged at each temperature for 24 hours. The bonds were separated by hand and a determination of the amount of fiber tear (FT) was noted.
Bleed through was measured using porous plug wrap paper. This test Is done to measure staining of the paper by the adhesive. Six 5.08 x 2.54 cm (2x1") sheets of plug wrap paper were stacked. An adhesive bead, 6.35 mm ¼" wide was applied between the center two sheets, and aged at 43°C (110°F) for 24 hours. The bleed of the adhesive to the top and bottom sheets was noted.
Open time/set time was measured on a automated bond tester using a 1mm (0.04") uncompressed bead applied to corrugated single-walled 65 lb. Open time measures that amount of time the product can remain open, i.e., achieve 100% fiber tear, with ten seconds compression time. Set time is the amount of time necessary to compress and achieve 100% fiber tear with 1 second open time.
Triacetin resistance was measured after soaking the adhesive bond for 24 hours in triacetin.
In this example, conventional plug wrap adhesives were compared to the low application temperature adhesives of the present invention. Comparative Samples A and B are conventional plugwrap adhesives which are applied at 177°C (350°F). Samples 1-4 are In accordance with the present invention, and are applied at 121°C (250°F). The formulations of the adhesives studied are shown below:
- Sample A: is a commercially available EVA based hot melt adhesive from National Starch and Chemical Company under the designation 34-2760.
- Sample B: is a commercially available EVA based hot melt adhesive from National Starch and Chemical Company under the designation 34-2757.
The results are shown below in Table 1:
The results in Table 1 above, show that the low application temperature adhesives, Samples 1, 2, 3 and 4, have good adhesion comparable to the conventional adhesives. Samples 1 and 2 are superior In bleed through, and have good thermal stability. The large viscosity change observed with Samples A and B at 260 hours indicates that these adhesives are not stable; the EVA is degrading. Sample 2 shows excellent fiber tear even after 24 hours of exposure to triacetin.
A significant difference between the adhesives of the present invention and conventional adhesives is that the adhesives of the present invention have a long open time and a fast set time allowing for wet out and quick set prior to the cutting step of the cigarette making process.
Further embodiments of the present invention are the folowing:
- 1. A cigarette filter comprising a low application temperature ethylene copolymer based hot melt adhesive, which can be applied at temperatures between 93°C and 149°C (200 to 300°F), wherein the adhesive comprises ethylene vinyl acetate comprising 5 to 45 weight percent vinyl acetate with a melt index of at least 400 dg/min.
- 2. A cigarette filter according to embodiment additionally comprising a second ethylene vinyl acetate copolymer, wherein the second ethylene vinyl acetate copolymer comprises 28 weight percent vinyl acetate with a melt Index of 6 to 40 dg/min.
- 3. A cigarette filter according to embodiment additionally comprising a polymeric additive selected from the group consisting of ethylene methyl acrylate polymers containing 10 to 28 weight percent by weight methyl acrylate, ethylene acrylic acid copolymers having an acid number of 25 to 150, methyl (meth)acrylate copolymer, polyethylene, polypropylene, poly(butene-1-co-ethylene) polymers and low molecular weight and/or low melt Index ethylene n-butyl acrylate copolymers, and combinations thereof.
- 4. A cigarette filter according to embodiment 1 wherein the adhesive comprises a blend of poly α-olefin and EVA.
- 5. A cigarette filter according to embodiment 1 wherein the hot melt adhesive comprises:
- a) 31 parts paraffin wax with a softening point of 150°F;
- b) 21 parts ethylene vinyl acetate copolymer with a melt index of 400 and a vinyl acetate content of 28%;
- c) 11 parts or ethylene vinyl acetate copolymer with a melt index of 43 and a vinyl acetate content of 28%;
- d) 37 parts of alpha-methyl styrene lackifying resins; and
- e) 0.5 parts of an antioxidant stabilizer.
- 6. The process for preparing a cigarette filter comprising applying an ethylene copolymer based hot melt adhesive at a temperature between 93 and 149°C (200 to 300°F) to porous and/or nonporous plugwrap paper, wherein the adhesive comprises ethylene vinyl acetate comprising 5 to 45 weight percent vinyl acetate with a melt index of at least 400 dg/min.
- 7. The process according to embodiment 6 wherein the adhesive comprises a blend of poly α-olefin and
- 8. The process according to embodiment 20 wherein the adhesive comprises:
- a) 31 parts paraffin wax with a softening point of 150°F;
- b) 21 parts ethylene vinyl acetate copolymer with a melt index of 400 and a vinyl acetate content of 28%;
- c) 11 parts or ethylene vinyl acetate copolymer with a melt index of 43 and a vinyl acetate content of 28%;
- d) 37 parts of alpha-methyl styrene tackifying resins; and
- e) 0.5 parts of an antioxidant stabilizer.
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