ADHESIVE COMPOSITION AND ADHESIVE FOAM SHEET |
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| 申请号 | US14410759 | 申请日 | 2013-06-26 | 公开(公告)号 | US20150191631A1 | 公开(公告)日 | 2015-07-09 |
| 申请人 | Sika Technology AG; | 发明人 | Shunsuke Yamada; | ||||
| 摘要 | The present invention relates to an adhesive composition, including: 100 parts by weight of an unvulcanized rubber; and from 20 to 100 parts by weight of an adhesive hydrocarbon-based resin with a softening point of 40° C. or less, and also relates to an adhesive foamable sheet including: an adhesive layer including the adhesive composition mentioned above; and a foamable rubber layer including a foaming agent, a curing agent, and an unvulcanized rubber. The present invention can provide an adhesive composition having both good adhesive properties and processability, which can form an adhesive layer in which cold-flow is controlled. In addition, it can provide an adhesive foamable sheet in which cold-flow can be controlled, having an adhesive layer consisting of the adhesive composition mentioned above. | ||||||
| 权利要求 | |||||||
| 说明书全文 | Priority is claimed on Japanese Patent Application No. 2012-143909, filed on Jun. 27, 2012, the content of which is incorporated herein by reference. The present invention relates to an adhesive composition, and in addition, also relates to an adhesive foamable sheet based on the adhesive composition. Conventionally, a rubber-based foam material fills a cavity in a motor vehicle body in order to satisfy requirements for noise-reducing performance in a vehicle interior or the like. Such a rubber-based foam material is generally formed by adhering an unfoamed thermosetting foamable sheet, in which a foaming agent, a curing agent and the like are added to an unvulcanized rubber, to an interior wall of a hollowed part of steel plates for a motor vehicle body, which constitute the cavity mentioned above in a motor vehicle body, and thermosetting and foaming the sheet, for example, in a dry-heating step on an electrodeposition coating line or the like. The thermosetting foamable sheet mentioned above is usually in the form of a laminate in which adhesive layers are laminated in order to prevent the sheet from falling off the steel plate for a motor vehicle body after the sheet is adhered to the aforementioned interior wall. Such a thermosetting foamable sheet is described in, for example, JP-B-H07-119399. However, the laminate types of thermosetting foamable sheets mentioned above are produced, subsequently packed in a stacked manner and stored in a warehouse or the like until they are used. For this reason, if they are left for a long period of time, the adhesive in the adhesive layers may protrude from the side surfaces of the thermosetting foamable sheets due to loading from the upper side, resulting in the integration of the sheets with adjacent sheets or the adhesion of the sheets to the package container, whereby the handling properties may be degraded. The aforementioned tendency increases as the period of application of load increases. In particular, the tendency is remarkably observed during transportation or in the case of storing the layered products in a stacked manner in a warehouse or the like. Such a phenomenon is called cold-flow, and in order to control the cold-flow, measures such as reduction of the amount of oil in an adhesive layer, increase of the amount of a filler, and the like are taken. However, the reduction of the amount of the oil and increase of the amount of the filler cause deterioration of processability and adhesive properties of the adhesive composition forming the adhesive layer. On the other hand, if a large amount of oil is blended in order to improve the adhesive properties and processability, the cold-flow property tends to increase. Japanese Unexamined Patent Application Publication No. 2006-206454 describes control of cold-flow by adding a styrene-based thermoplastic elastomer, but fails to disclose the means for achieving both good processability and adhesive properties. Patent Document 1: Japanese Examined Patent Application Publication No. H07-119399 The present invention has been made in view of the problems mentioned above. The present invention has a first object of providing an adhesive composition which has both good adhesive properties and processability, and is capable of forming an adhesive layer in which cold-flow is controlled. The present invention has a second object of providing an adhesive foamable sheet in which cold-flow is controlled and which has an adhesive layer formed from the adhesive composition mentioned above. The first object of the present invention can be achieved by an adhesive composition, including: 100 parts by weight of an unvulcanized rubber; and from 20 to 100 parts by weight of an adhesive hydrocarbon-based resin with a softening point of 40° C. or less. The adhesive hydrocarbon-based resin preferably includes at least one selected from the group consisting of coumarone resins, aliphatic petroleum resins, aromatic petroleum resins, aliphatic/aromatic copolymer-based petroleum resins, terpene resins, rosin resins, and phenolic resins. The unvulcanized rubber is preferably selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, and modified rubbers obtained by modifying the terminals of the rubbers mentioned above. The second object of the present invention can be achieved by an adhesive foamable sheet including: an adhesive layer including the aforementioned adhesive composition; and a foamable rubber layer including a foaming agent, a curing agent, and an unvulcanized rubber. The foamable rubber layer mentioned above has a volume expansion ratio of preferably 500% or more. The foaming agent is preferably selected from the group consisting of azodicarbonamide, azobisisobutyronitrile, barium azodicarboxylate, N,N′-dinitrosopentamethylenetetramine, N,N′-dimethyl-N,N′-dinitrosoterephthalamide, 4,4′-oxybis(benzenesulfonyl hydrazide), hydrazodicarbonamide, paratoluenesulfonyl hydrazide, diphenylsulfone-3,3′-disulfonyl hydrazide, allylbis(sulfonyl hydrazide), p-toluylenesulfonyl semicarbazide, 4,4′-oxybis(benzenesulfonyl semicarbazide), sodium hydrogencarbonate, ammonium carbonate, and anhydrous sodium nitrate. The curing agent mentioned above is preferably sulfur or a sulfur-based curing agent. The unvulcanized rubber mentioned above is preferably selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, and modified rubbers obtained by modifying the terminals of the rubbers mentioned above. The adhesive foamable sheet of the present invention is preferably in the form of a hexahedron having a top surface, a bottom surface and four side surfaces. The adhesive composition of the present invention possesses both good adhesive properties and processability, and can form an adhesive layer in which cold-flow is controlled. When the adhesive hydrocarbon-based resin in the adhesive composition of the present invention includes at least one selected from the group consisting of coumarone resins, aliphatic petroleum resins, aromatic petroleum resins, aliphatic/aromatic copolymer-based petroleum resins, terpene resins, rosin resins, and phenolic resins, the adhesive properties and processability are further improved, and an adhesive layer in which cold-flow is controlled can be formed. When the unvulcanized rubber in the adhesive composition of the present invention is selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, and modified rubbers obtained by modifying the terminals of the rubbers mentioned above, the adhesive properties and processability are further improved, and an adhesive layer in which cold-flow is controlled can be formed. In the adhesive foamable sheet of the present invention, cold-flow can be controlled. Therefore, even if the adhesive foamable sheets are left in a stacked manner for a long period of time, it is possible to prevent or reduce the occurrence of a situation in which the adhesive in the adhesive layers protrude from the side surfaces of the thermosetting foamable sheets due to load from the upper side, resulting in the integration of the sheets with adjacent sheets or the adhesion of the sheets to the package container, whereby the handling properties may be degraded. The adhesive foamable sheet of the present invention has a foamable rubber layer including a foaming agent, a curing agent, and an unvulcanized rubber, and for this reason, thermosetting properties and foaming properties can be provided. Therefore, the adhesive foamable sheet of the present invention can be foamed and cured by means of heating. When the volume expansion ratio of the foamable rubber layer is 500% or more, for example, a cavity in a motor vehicle body is effectively filled, and noise-reducing performance in a vehicle interior can be improved. When the adhesive foamable sheet is in the form of a hexahedron having a top surface, a bottom surface and four side surfaces, in particular, superior handling properties can be exhibited, and the sheets can be closely laminated. The adhesive foamable sheet of the present invention has an adhesive layer with increased adhesive properties. For this reason, for example, the sheet can be prevented from falling off a steel plate for a motor vehicle body after the sheet is adhered to a hollow part of the steel plate for a motor vehicle body. An adhesive composition of the present invention includes 100 parts by weight of an unvulcanized rubber, and from 20 to 100 parts by weight of an adhesive hydrocarbon-based resin with a softening point of 40° C. or less. As a result, the adhesive composition of the present invention possesses both good adhesive properties and processability, and can constitute an adhesive layer in which cold-flow can be controlled. The adhesive foamable sheet of the present invention includes an adhesive layer including the adhesive composition of the present invention, and a foamable rubber layer including a foaming agent, a curing agent, and an unvulcanized rubber. As a result, in the adhesive foamable sheet of the present invention, cold-flow can be prevented or reduced. In addition, the manufacture of an adhesive layer is easy, and deterioration of adhesive properties of the adhesive layer can also be controlled. Hereinafter, first, an adhesive composition of the present invention is described. The adhesive composition of the present invention includes an unvulcanized rubber. The type of the unvulcanized rubber is not particularly limited, and a diene-based unvulcanized rubber is preferable. The diene-based unvulcanized rubber used can be appropriately selected from known ones. As the diene-based unvulcanized rubber, at least one selected from natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, and modified rubber obtained by modifying the terminals of the rubbers mentioned above may be used. In view of processability and foaming properties, styrene butadiene rubber is preferable. Such unvulcanized rubbers can be used alone or in combinations of a plurality thereof. The usage amount of the unvulcanized rubber is not particularly limited, and ranges, for example, from 10 to 90% by weight, preferably from 15 to 70% by weight, and more preferably from 20 to 50% by weight, based on the total weight of the adhesive composition. The adhesive composition of the present invention includes an adhesive hydrocarbon-based resin with a softening point of 40° C. or less. As the adhesive hydrocarbon-based resin with a softening point of 40° C. or less, for example, at least one selected from the group consisting of coumarone resins, aliphatic petroleum resins, aromatic petroleum resins, aliphatic/aromatic copolymer-based petroleum resins, terpene resins, rosin resins, and phenolic resins can be used. They can be used alone or in combinations of two or more types thereof. In the present invention, in view of adhesive properties and processability, one or more of coumarone resins, aliphatic petroleum resins, aromatic resins, and aliphatic/aromatic copolymer-based petroleum resins are preferable. The softening point of the adhesive hydrocarbon-based resin blended in the adhesive composition of the present invention is 40° C. or less, and preferably 35° C. or less, and more preferably ranges from 0 to 35° C., and particularly preferably from 10 to 30° C. If the softening point exceeds 40° C., the effects of the present invention cannot be exhibited. The softening point mentioned in the present invention can be measured using the ring-and-ball method of JIS K6220-1. The usage amount of the adhesive hydrocarbon-based resin with a softening point of 40° C. or less ranges from 20 to 100 parts by weight, preferably from 25 to 100 parts by weight, and more preferably from 30 to 100 parts by weight with respect to 100 parts by weight of the unvulcanized rubber. In addition, the amount of the adhesive hydrocarbon-based resin mentioned above ranges, for example, from 3 to 50% by weight, preferably from 4 to 40% by weight, and more preferably from 5 to 30% by weight, with respect to the total weight of the adhesive composition. In addition, a tackifier resin with a softening point ranging from 70° C. to 150° C. can be blended in the adhesive composition of the present invention, in addition to the components mentioned above. As the tackifier resin mentioned above, at least one hydrocarbon-based resin selected from the group consisting of coumarone resins, aliphatic petroleum resins, aromatic petroleum resins, aliphatic/aromatic copolymer-based petroleum resins, terpene resins, rosin resins, and phenolic resins, that have a softening point ranging from 70° C. to 150° C., can be used. Various conventionally-known oils, anti-ageing agents, coloring agents, inorganic fillers, processing aids, and other additives may be used together with the adhesive composition of the present invention within a range which does not impair the effects of the present invention. The adhesive composition of the present invention can be produced by mixing and kneading the components mentioned above by a conventionally known means such as a kneader, an internal mixer, a twin-roller mixer, or the like. Next, the adhesive foamable sheet of the present invention is described. The adhesive foamable sheet of the present invention includes an adhesive layer including the adhesive composition of the present invention, and a foamable rubber layer including a foaming agent, a curing agent, and an unvulcanized rubber. The adhesive foamable sheet of the present invention has an adhesive layer at a part of or over all the parts of the surface thereof in order to obtain reliable adhesion to a steel plate for a motor vehicle body or the like. The thickness of the adhesive layer is not particularly limited, and for example, ranges from 0.1 mm to 10 mm, preferably from 0.5 mm to 5 mm, and more preferably from 1 mm to 3 mm. The adhesive layer mentioned above includes the adhesive composition of the present invention. The usage amount of the adhesive composition can be appropriately determined in accordance with the degree of adhesive property to be achieved, and for example, ranges from 1 to 100% by weight, preferably from 80 to 99% by weight, and more preferably from 90 to 95% by weight, based on the total weight of the adhesive layer. The adhesive layer can be produced by, for example, using the adhesive composition of the present invention, and subjecting the adhesive composition to known molding processing such as extrusion molding, calendar rolling, press molding, or the like. Extrusion molding is preferable in view of productivity. The adhesive foamable sheet of the present invention includes a foamable rubber layer that is foamable/curable by heating. By foaming/curing the foamable rubber layer, a cavity in a steel plate for an automobile body or the like can be filled. The thickness of the foamable rubber layer is not particularly limited, and for example, ranges from 0.1 mm to 10 mm, preferably from 0.5 mm to 8 mm, and more preferably from 1 mm to 6 mm. The foaming agent included in the foamable rubber layer can be appropriately selected from publicly known ones. Examples thereof include azodicarbonamide (ADCA), azobisisobutyronitrile, barium azodicarboxylate, N,N′-dinitrosopentamethylenetetramine, N,N′-dimethyl-N,N′-dinitrosoterephthalamide, 4,4′-oxybis(benzenesulfonyl hydrazide), hydrazodicarbonamide, paratoluenesulfonyl hydrazide, diphenylsulfone-3,3′-disulfonyl hydrazide, allylbis(sulfonyl hydrazide), p-toluylenesulfonyl semicarbazide, 4,4′-oxybis(benzenesulfonyl semicarbazide), sodium hydrogencarbonate, ammonium carbonate, anhydrous sodium nitrate, and the like. They can be used alone or in combinations of two or more types thereof. In particular, in the present invention, azodicarbonamide is preferably used in view of safety and foaming performance. The usage amount of the foaming agent can be appropriately determined in accordance with the physical properties of the target foamed product, such as the expansion ratio or the like. For example, the usage amount of the foaming agent ranges from 0.5 to 20% by weight, preferably from 1 to 10% by weight, and more preferably from 2 to 5% by weight, based on the total weight of the foamable rubber layer. The volume expansion ratio of the foamable rubber layer is preferably 500% or more, more preferably 600% or more, and particularly preferably 700% or more. If the volume expansion ratio is 500% or more, when the foamable rubber layer is used for filling a cavity of an automobile body, the cavity mentioned above can be completely filled therewith. Urea may be used as a foaming aid in order to reduce the decomposition temperature of the foaming agent. The curing agent used can be appropriately selected from publicly known ones. Examples thereof include, for example, sulfur or a sulfur-based curing agent such as a thiuram, a dithiocarbamate or the like. Examples of thiurams include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetramethylthiuram monosulfide, N,N′-dimethyl-N,N′-diphenylthiuram disulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram pentasulfide, mixed alkylthiuram disulfide and the like. Examples of dithiocarbamates include zinc dimethylthiocarbamate, zinc diethylthiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dibenzyldithiocarbamate, and the like. They can be used alone or in combinations of two or more types thereof. In particular, in the present invention, tetramethylthiuram monosulfide is preferably used in view of foaming performance. The usage amount of the curing agent ranges, for example, from 0.5 to 5% by weight, and preferably from 1 to 3% by weight, based on the total weight of the foamable rubber layer. A curing accelerator can also be used together with the curing agent mentioned above within a range which does not impair the effects of the present invention. Examples of the curing accelerators include guanidines, thiazoles, sulfenamides, dithiocarbamates, xanthogens, aldehyde ammonias, aldehyde amines, thioureas, and the like. The aforementioned thiurams, dithiocarbamates or the like may be used as the curing accelerator. They can be used alone or in combinations of two or more types thereof. The unvulcanized rubber used can be appropriately selected from publicly known ones. A diene-based unvulcanized rubber is preferable. The diene-based unvulcanized rubber used can be appropriately selected from publicly known ones. As the diene-based unvulcanized rubber, at least one selected from natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, and modified rubbers obtained by modifying the terminals of the rubbers mentioned above can be used. Styrene butadiene rubber is preferable in terms of processability and foaming properties. Such unvulcanized rubbers can be used alone or in combinations of a plurality thereof. The usage amount of the unvulcanized rubber is not particularly limited, and ranges, for example, from 10 to 90% by weight, preferably from 20 to 85% by weight, and more preferably from 30 to 80% by weight, based on the total weight of the foamable rubber layer. The unvulcanized rubber contained in the foamable rubber layer may have a type and/or composition different from those of the unvulcanized rubber contained in the adhesive composition for the adhesive layer, but they preferably have the same types and/or compositions. Various oils, anti-aging agents, coloring agents, inorganic fillers, processing aids, and other additives, which are conventionally known, may be used together with the foamable rubber layer mentioned above within a range which does not impair the effects of the present invention. An adhesive may be blended in the foamable rubber layer mentioned above, but the thermosetting foamed sheet, per se, preferably does not have excessive adherence properties, and the blending amount thereof is preferably small. In order to produce the foamable rubber layer, first, the thermosetting foamable composition can be generally produced by mixing and kneading the components mentioned above by means of a conventionally known method with a kneader, an internal mixer, a twin-roller mixer, or the like. Next, the thermosetting foamable composition mentioned above is shaped into a sheet to form a foamable rubber layer. The foamable rubber layer can be produced by, for example, using the thermosetting foamable composition mentioned above, and subjecting the composition to publicly known molding processing such as extrusion molding, calendar rolling, press molding, or the like. Extrusion molding is preferable in view of productivity. The molding processing is preferably carried out at a temperature of 80° C. or less in order to control the progression of curing, decomposition of the foaming agent or the like, although the aforementioned temperature may vary depending on the formulation of the composition. The adhesive foamable sheet of the present invention can be produced by, for example, using a composition that constitutes the foamable rubber layer and a composition that constitutes the adhesive layer, and subjecting the compositions to publicly known molding processing such as coextrusion molding with a die for multilayer extrusion containing two nozzles, calendar rolling for integration by interleaving two sheets with rolls, press molding for integration by pressing two sheets, or the like. Coextrusion molding is preferable in view of productivity. The molding processing is preferably carried out at a temperature of 80° C. or less in order to control the progression of curing, or the like, although the aforementioned temperature may vary depending on the formulation of the composition. The shape of the contacting surface between the foamable rubber layer and the adhesive layer is not limited, and the cross-section thereof may be in a geometric shape formed by straight lines, curved lines, or a combination thereof. Another layer may be present on the adhesive foamable sheet, itself, or between the foamable rubber layer and the adhesive layer, if necessary. For example, the other layer mentioned above can be formed by co-extrusion molding using a die for multilayer extrusion equipped with three nozzles. In the present invention, an adhesive foamable sheet of which the surface has been cured may be produced by irradiating at least a part of the surface of the foamable rubber layer and the adhesive layer with electromagnetic waves to cure the surface mentioned above. The foamable rubber layer and the adhesive layer mentioned above include an unvulcanized rubber having an unsaturated bond. For this reason, photopolymerization is carried out by means of electromagnetic energy at the surface, or in the vicinity thereof, of the foamable rubber layer and/or the adhesive layer subjected to irradiation with electromagnetic waves. As a result, the unvulcanized rubber is thinly crosslinked and cured at the surface subjected to irradiation with electromagnetic waves, and as a result, a protective film is formed. The components of the crosslinking agent and the like in the foamable rubber layer and the adhesive layer cannot pass through the protective film. For this reason, even if the components mentioned above migrate to the surface of the sheet, bleeding out of the components mentioned above is not observed on the surface subjected to irradiation with electromagnetic waves. As the electromagnetic waves, ultraviolet rays having a wavelength of 400 nm or less are preferably used, and ultraviolet rays having a wavelength preferably ranging from 10 nm to 400 nm, and more preferably from 200 nm to 400 nm are used. As the ultraviolet rays, either UVB having a wavelength ranging from 280 nm to 315 nm or UVA having a wavelength ranging from 315 nm to 400 nm can be used. The electromagnetic wave source is not particularly limited, and any optical source can be used. As the optical source, an ultraviolet optical source is preferable. As the ultraviolet optical source, any ultraviolet optical source such as an ultraviolet laser, an ultraviolet lamp such as a xenon lamp, an ultraviolet emission LED or the like can be used. In addition, an optical source including ultraviolet rays can also be used, and a fluorescent lamp or solar light can also be utilized. As the optical source, for example, an optical source having irradiation intensity ranging from 60 to 300 kJ/m2 per hour can be used, and one having irradiation intensity ranging from 90 to 250 kJ/m2 per hour is preferably used. The irradiance level of the electromagnetic waves is not particularly limited as long as the surface of the foamable rubber layer and/or the adhesive layer which has been irradiated with electromagnetic waves is cured. Therefore, the wavelength of the electromagnetic waves, the intensity of the electromagnetic waves, and the irradiation period of the electromagnetic waves can be appropriately adjusted under the condition of curing the surface irradiated by the electromagnetic waves. In the adhesive foamable sheet of which the surface has been cured, a crosslinked and cured film is formed on the surface thereof by means of irradiation with electromagnetic waves, and preferably irradiation with ultraviolet rays, without heating the foamable sheet mentioned above. For this reason, the sheet mentioned above is not foamed. Therefore, the adhesive foamable sheet of the present invention remains unfoamed as it is. For example, the unfoamed adhesive foamable sheets of the present invention are inserted into the cavities of motor vehicle bodies as an unfoamed material, and subsequently heated and foamed for use in filling the cavities mentioned above. The shape of the adhesive foamable sheet of the present invention is not particularly limited, and is preferably a hexahedron having a top surface, a bottom surface and four side surfaces, and the electromagnetic waves irradiate the aforementioned top surface. In this case, the irradiation with the electromagnetic waves is preferably carried out at the top surface, at least one of the side surfaces, and/or the bottom surface mentioned above. In the case of carrying out irradiation with electromagnetic waves at the side surfaces, electromagnetic waves preferably irradiate as many side surfaces as possible, and preferably irradiate all four side surfaces. In the case of the adhesive foamable sheet of the present invention being in the form of a hexahedron, the sheet is preferably in the form of a general cuboid, and is more preferably in the form of a thin plate. In the case of the adhesive foamable sheet of the present invention being in the form of a thin plate, irradiation with electromagnetic waves may be omitted for the side surfaces, but electromagnetic waves preferably irradiate at least the top surface. The thickness of the sheet in the case of the adhesive foamable sheet of the present invention being in the form of a thin plate is not particularly limited. The thickness ranges, for example, from 1 mm to 20 mm, preferably from 2 mm to 10 mm, and more preferably from 3 mm to 5 mm. The adhesive composition of the present invention has both good adhesive properties and processability, and can form an adhesive layer in which cold-flow is controlled. Therefore, an adhesive layer that has increased adhesive properties and can be used in various applications can be easily produced. In addition, in the adhesive foamable sheet of the present invention, cold-flow can be controlled. Therefore, even if the adhesive foamable sheets are left in a stacked manner for a long period of time, it is possible to prevent or reduce the occurrence of a situation in which the adhesive in the adhesive layers protrude from the side surfaces of the thermosetting foamable sheets due to load from the upper side, resulting in the integration of the sheets with adjacent sheets or the adhesion of the sheets to the package container, whereby the handling properties may be degraded. In the case of carrying out irradiation with electromagnetic waves at the foamable rubber layer, operability can be improved without impairing adhesiveness to motor vehicle bodies and the like, and without impairing foaming properties which are the primary performance requirement of a thermosetting foamable sheet. The thermosetting foamable sheet of the present invention forms a foam material exhibiting an acoustic absorption effect by, for example, adhering the sheet to an interior wall of a hollow part such as a cavity inner part of steel plates of a motor vehicle body, and subsequently foaming and curing the sheet by appropriately heating it. As a result, the noise-reducing property in an interior space of a motor vehicle can be enhanced. Therefore, the thermosetting foamable sheet of the present invention can be used as a cavity filler for a motor vehicle body. Hereinafter, the present invention is described in detail on the basis of Examples and Comparative Examples. It should be understood that the present invention is not limited to these Examples. The components shown in Table 1 described below were mixed and kneaded by means of an open kneader to prepare an adhesive composition (the numerical values shown in Table 1 are based on parts by weight with respect to 100 parts by weight of rubber). The obtained adhesive composition was pressed by means of an oil hydraulic press, and an unvulcanized sheet having a thickness of 2 mm was produced. Penetration The unvulcanized sheet mentioned above of each of Examples 1 to 4 and Comparative Examples 1 to 4 was cut into pieces, each having 50 mm length by 30 mm width. 10 pieces were stacked to prepare a test sample having a thickness of 20 mm. Penetration of the obtained test sample was measured by a method in accordance with JIS K2207. A higher numerical value of penetration indicates that the test sample is softer and exhibits better processability. The results are also shown in Table 1. Shear Strength The unvulcanized sheet (adhesive material) mentioned above of each of Examples 1 to 4 and Comparative Examples 1 to 4 was cut into a test piece 25 mm square. The test piece was placed between two cold rolled steel plates of 100 mm length by 25 mm width with 0.8 mm thickness, as shown in Thickness Retention Ratio The unvulcanized sheet mentioned above of each of Examples 1 to 4 and Comparative Examples 1 to 4 was cut into pieces, each having 50 mm length by 30 cm width. 10 pieces were stacked to prepare a test sample having a thickness of 20 mm. The obtained test sample was stored for 72 hours at room temperature, and subsequently, the thickness of the sample was measured. The thickness retention ratio was calculated as a ratio of the thickness after storage for 72 hours with respect to the initial thickness. A higher thickness retention ratio indicates enhanced prevention or reduction of cold-flow. The results are also shown in Table 1. As is clear from Table 1, Comparative Examples 2 and 3 had the better thickness retention ratios as compared with Comparative Example 1, but had reduced penetration, and failed to exhibit good processability. In addition, improvement in shear strength was not observed. Comparative Example 4 had good penetration and good shear strength, but large improvement in thickness retention ratio was not observed. On the other hand, in Examples 1 to 4, both good penetration and good shear strength were exhibited, and improvement in thickness retention ratio was observed. |
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