Electron beam-curable composition for release material and process for preparation of release material

Abstract: A release material of a good release property is prepared by shaping a resin composition comprising a thermoplastic polyolefin resin, a dimethylpolysiloxane and a functional compound, irradiating the shaped composition with electron beams, and if desired, heat-treating the shaped composition.

Description: BACKGROUND OF THE INVENTION (1) Field of the Invention The present invention relates to a process for preparing a release material comprising a substrate and a film laminated on the substrate of an electron beam curable composition The release material obtained according to the process of the present invention gives a release property, for example, to a base surface of a sticker or seal or to a back surface of a wound packaging tape. (2) Description of the Related Art In order to impart a release property to the surface of a release paper used as the base of an adhesive tape of a sticker or seal or to the back surface of a wound packaging adhesive tape, a method has been adopted in which an expensive reactive silicone is coated on the polyolefin-laminated base surface and a thermosetting treatment is carried out. However, an apparatus having a length of scores of meters is necessary for the steps of coating the silicone and carrying out the heat treatment. Furthermore, since a solvent such as toluene is used in the step of coating the reactive silicone, large equipment cost and energy are necessary for recovering the solvent. As means for eliminating this disadvantage, a method may be considered in which the silicone is incorporated into a thermoplastic resin, whereby the large-scale step can be omitted. This method, however, has problems in that the release property required for the release paper is not manifested, and the silicone bleeding to the surface migrates to the adhesive layer of a sticker or seal to reduce the adhesive force of the adhesive layer. As means for solving the above-mentioned problem, a method has been proposed in which a radiation-curable reactive organopolysiloxane is incorporated into a resin, the resulting composition is shaped by the lamination or inflation method and the shaped composition is irradiated with radioactive rays (see Japanese Unexamined Patent Publication No. 57-187221 and Japanese Unexamined Patent Publication No. 62-85930). According to this method, however, an expensive organosiloxane containing a mercapto group, a vinyl group and the like must be used, and if shaping is carried out at a high temperature, during the shaping step, the organopolysiloxane is reacted with a polyolefin type thermoplastic resin as the matrix or molecules of the organopolysiloxane are reacted with each other, with the result that the organopolysiloxane is hardly caused to bleed to the surface of the shaped body and no substantial release property is manifested. The DE-A-3 347 861 relates to a release material comprising a β-olefin polymer having at least two CH₃ groups per monomer unit, further comprising as an optional component at least one of comonomers having reactive carbon carbon double- or triple bonds, compounds having active hydrogen, compounds having hydroxy groups being capable to polycondensate and/or organic silicon compounds. According to this reference the release material disclosed therein may be formed into a film or foil by extrusion or other conventional methods. A radiation curable composition on the basis of a triorganosiloxane-end blocked diorganosiloxane fluid, further comprising a methylvinyl polysiloxane and a vinyl monomer is disclosed in FR-A-2 352 032. Also this composition is used as a release coating, preferably on paper. This coating is applied by commonly known coating methods. We previously developed a process for preparing a release material by incorporating a dimethylpolysiloxane in a polyolefin type thermoplastic resin, shaping the composition and irradiating the shaped composition with electron beams (see Japanese unexamined Patent Publication No. 63-248834 and Japanese unexamined Patent Publication No. 63-249627). However, this process has a problem in that the control of the release property is difficult and the long-period stability of the release property is not satisfactory. SUMMARY OF THE INVENTION Under this background, we made research with a view to developing a cheap release material without any complicated steps while solving the problems of the conventional techniques. As the result, it was found that if a composition comprising a chemically stable dimethylpolysiloxane which is difficult to cure when singly heated or irradiated with electron beams, an olefin polymer type thermoplastic resin and a polyfunctional compound is extrusion-laminated into a film and the laminated film is irradiated with electron beams, a stable release property can be manifested. It is therefore a primary object of the present invention to provide a process for advantageously preparing a release material comprising a substrate and a film laminated on the substrate, which has an excellent release property and does not degrade the adhesiveness of an adhesive, without using a large-scale apparatus. More specifically, in accordance with one aspect of the present invention, there is provided a process for the preparation of a release material comprising a substrate and a film laminated on the substrate, which comprises the steps of : melt-extruding a resin composition onto the substrate to form the film laminated on the substrate, said resin composition comprising: (a) a thermoplastic olefin polymer selected from polyethylene, polypropylene, copolymers mainly composed of ethylene or propylene, and mixtures thereof, and having a melt flow rate (MFR) of 0.01 to 200 g/10 min., (b) 0.1 to 30% by weight, based on the resin composition, of a dimethylpolysiloxane having a termial group represented by the formula: -SiR₁R₂R₃ wherein R₁, R₂ and R₃ independently represents methyl, hydroxyl or alkoxy with 1-3 carbon atoms, and having a viscosity of 50 x 10⁻⁶ to 8 m²/s (=50 to 8 x 10⁶ cs) as measured at 25°c, and (c) 0.01 to 30% by weight, based on the resin composition, of a polyfunctional compound having at least two vinyl groups or at least two thiol groups; and irradiating the laminated film with electron beams. As the substrate on which the resin composition is laminated, paper or other materials may be used. DESCRIPTION OF THE PREFERRED EMBODIMENTS As the thermoplastic olefin polymer used as the starting material of the composition of the present invention, there can be mentioned high-density polyethylene, medium-density polyethylene, low-density polyethylene, polypropylene, copolymers mainly composed of ethylene or propylene, ethylene/vinyl ester copolymers, ethylene/α,β-unsaturated carboxylic acid ester copolymers, and blends thereof. Among them, low-density polyethylene, an ethylene copolymer, an ethylene/butene copolymer and polybutene are preferred. The most preferred thermoplastic olefin polymer is a blend of low-density polyethylene and a mono-olefin copolymer rubber. The melt index (MI) or melt flow rate (MFR) of the thermoplastic polyolefin resin is 0.01 to 200 g/10 min, preferably 1 to 100 g/10 min, especially preferably 1 to 20 g/10 min. In the blend of low-density polyethylene and the mono-olefin copolymer rubber, which is most preferably used in the present invention, as the low-density polyethylene, there can be used high-pressure low-density polyethylene or linear low-density polyethylene, which has a density of 0.850 to 0,935 g/cm³, linear low-density polyethylene or a blend thereof, which has a MI of 0.01 to 200 g/10 min, preferably 0.1 to 100 g/10 min, more preferably 1 to 20 g/10 min. As the mono-olefin copolymer rubber, there can be mentioned a rubber of a copolymer of at least two mono-olefins having 2 to 15 carbon atoms and a rubber of a copolymer of at least two mono-olefins having 2 to 15 carbon atoms and a polyene. For example, there can be mentioned an ethylene/propylene copolymer rubber and an ethylene/propylene/non-conjugated diene rubber. As the non-conjugated diene, there can be mentioned dicyclopentediene, 1,4-hexadiene, dicyclooctadiene and ethylidene-norbornene. These mono-olefin copolymer rubbers can be used alone or in the form of a mixture of two or more thereof. The Mooney viscosity ML₁+₄ of the mono-olefin copolymer rubber at 100°C is 5 to 300, preferably 20 to 250. If the Mooney viscosity at 100°C is lower than 5, mixing is difficult, and if the Mooney viscosity at 100°C is higher than 300, the flowability of the composition is poor. The mixing ratio between the low-density polyethylene and the mono-olefin copolymer rubber is such that the content of the low-density polyethylene is 20 to 90% by weight, preferably 40 to 80% by weight, more preferably 50 to 70% by weight, and the content of the mono-olefin copolymer rubber is 80 to 10% by weight, preferably 60 to 20% by weight, more preferably 50 to 30% by weight. If the content of the low-density polyethylene is lower than 20% by weight and the content of the mono-olefin copolymer rubber is higher than 80% by weight, the shapeability is degraded although a good release property is obtained. If the content of the low-density polyethylene is higher than 90% by weight and the content of the mono-olefin copolymer rubber is lower than 10% by weight, the stability of the release property is degraded. The dimethylpolysiloxane to be incorporated in the thermoplastic olefin polymer is a dimethylpolysiloxane having a terminal group -SiR¹R²R³ (R¹, R² and R³ independently stand for a member selected from a methyl group, a hydroxyl group and an alkoxy group having 1 to 3 carbon atoms. Dimethylpolysiloxanes having both terminals blocked with a trimethylsilyl or hydroxydimethylsilyl group are especially preferred. The kinetic viscosity (hereinafter referred to as "viscosity") at 25°C of the dimethylpolysiloxane is 50 x 10⁻⁶ m²/s to 8 m²/s (50 to 8 x 10⁶ CS), preferably 500 to 60,000 CS. If the viscosity at 25°C is lower than 50x10⁻⁶ m²/s (50 CS) mixing with the thermoplastic olefin polymer is difficult and also the shaping is difficult, and a large irradiation dose is necessary for manifesting a satisfactory release property. Moreover, the mechanical strength of the thermoplastic olefin polymer as the matrix is reduced and the cost increases. If the viscosity at 25°C exceeds 8 m²/s (8 x 10⁶ CS), it is difficult to manifest a satisfactory release property. The incorporated amount of the dimethylpolysiloxane is 0.1 to 30% by weight, preferably 1 to 15% by weight, more preferably 2 to 6% by weight, based on the resin composition. If the amount of the dimethylpolysiloxane is smaller than 0.1% by weight, no satisfactory release property can be obtained. If the amount of the dimethylpolysiloxane exceeds 30% by weight, the shaping becomes difficult and the cost increases. A compound having a plurality of functional groups which readily cause reaction under irradiation with electron beams, such as vinyl groups (inclusive of allyl groups, acryloyl groups and methacryloyl groups) and thiol groups (inclusive of mercapto groups) is used as the polyfunctional compound to be incorporated into the thermoplastic olefin polymer together with the dimethylpolysiloxane. As the compound having a plurality of vinyl groups, there can be mentioned divinylbenzene, and as the compound having a plurality of acryloyl groups, there can be mentioned polyethylene glycol diacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, neopentyl glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol (monohydroxy)pentaacrylate and dipentaerythritol hexaacrylate. As the compound having a plurality of methacryloyl groups, there can be mentioned polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane tetramethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,4-butanediol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol (monohydroxy)pentamethacrylate and dipentaerythritol hexamethacrylate. As the compound having a plurality of allyl groups, there can be mentioned diallyl terephthalate, diallyl adipate, triallyl cyanurate, triallyl isocyanurate, pentaerythritol triallyl ether, glycerol diallyl ether, trimethylolpropane diallyl ether, diglycerol diallyl ether, diglycerol triallyl ether, allyl methacrylate, diallyl phthalate, diallyl maleate, diallyl isophthalate, triallyl trimellitate, tetraallyl pyromellitate, allyl glycol acrylate and allyl glycol methacrylate. As the compound having a plurality of thiol groups (mercapto groups), there can be mentioned trimethylolpropane tris-3-mercaptopropionate, 1,11-undecanedithiol, 4-ethylbenzene-1,3-dithiol, 1,8-octanedithiol, 1,18-octadecane dithiol, 4,8-dithioundecane-1,11-dithiol, dithiopentaerythritol, 1,2-dimercapto-1,3-butanediol, 2,6-dimethyloctane-2,6-dithiol, 2,4-dimethylbenzene-1,3-dithiol, 4,5-dimethylbenzene-1,3-dithiol, 1,10-decanedithiol, 1,12-dodecanedithiol, 2,5-toluenedithiol, 3,4-toluenedithiol, 1,6-hexanedithiol, 1,7-heptanedithiol, 1,4-benzenedithiol, 1,2-benzenedithiol, ethylene glycol dithioglycolate, 1,2,3-propanetrithiol, 1,2,4-butanetrithiol, trimethylolpropane trithioglycolate, pentaerythritol trithioglycolate, 1,3,5-benzenetrithiol, 2,4,6-mesitylenetrithiol, neopentane tetrathiol and pentaerythritol tetrakis(3-mercaptopropionate). Trimethylolpropane trimethacrylate, tetramethylolmethane tetramethacrylate, triallyl cyanurate and triallyl isocyanurate are preferred, and triallyl isocyanurate and trimethylolpropane triacrylate are especially preferred. These polyfunctional compounds may be used either alone or in combination. The amount of the polyfunctional compound is 0.01 to 30% by weight, preferably 0.5 to 15% by weight, more preferably 1 to 5% by weight, based on the resin composition. If the amount of the polyfunctional compound is smaller than 0,01% by weight, a sufficient stability of the release property cannot be obtained. If the amount of the polyfunctional compound exceeds 30% by weight, the shaping is difficult and the cost increases. An apparatus customarily used for mixing and kneading synthetic resins can be used for mixing the thermoplastic olefin polymer with the dimethylpolysiloxane and the polyfunctional compound. For example, melt mixing can be accomplished by a Banbury mixer, a kneader, a twin-screw extruder, a single-screw extruder or a roll mill. Especially, where a dimethylpolysiloxane having a low viscosity is used, mixing is difficult by an ordinary method. In this case, a method is adopted in which mixing is carried out by feeding the dimethylpolysiloxane under pressure into an intermediate position of a cylinder of an extruder, or a method in which the dimethylpolysiloxane is added little by little by using a Banbury mixer. The above-mentioned resin composition is subjected to extrusion lamination to form a film laminated on a paper layer or a layer of another material. The resin composition surface of the laminated film is irradiated with electron beams, whereby a release surface is formed. As the laminated film, a three-layer structure comprising a paper sheet, a polyolefin and the resin composition obtained according to the process of the present invention is often used because this structure is suitable for use as a release sheet. As another examples of the laminated film, there can be mentioned a structure of polyamide, polycarbonate, polyolefin or polyvinyl chloride/polyolefin/resin composition of the present invention, and a structure of polyester/polyolefin/resin composition of the present invention. A known adhesive or adhesive resin can be used for lamination of these material according to need. For the electron beam treatment, a method can be adopted in which electron beams are emitted from an electron beam irradiation apparatus of the Cockcroft type, Cockcroft-Walton type, Van de Graaff type, insulated core transformer type, linear type, dynamitron type, high frequency type or electron curtain type. The irradiation dose can be changed within a broad range according to the properties of the material to be irradiated. The irradiation dose is generally 1 to 30 Mrad, and preferably the irradiation dose is 1 to 15 Mrad, especially 3 to 10 Mrad. If the irradiation dose is smaller than 1 Mrad, no desired effect is obtained, and if the irradiation dose exceeds 30 Mrad, the mechanical properties of the matrix polymer are drastically degraded and the practical utility is lost. The acceleration voltage is not particularly critical, but from the practical viewpoint, preferably the acceleration voltage is 100 to 300 KV. An inert gas is preferred as the irradiation atmosphere. As the inert gas, there can be mentioned, for example, nitrogen, carbon dioxide gas and helium. The reason why irradiation with electron beams results in manifestation of a good release property has not been completely elucidated. However, it is believed that, when the thermoplastic olefin polymer which is readily crosslinked or decomposed under irradiation with electron beams is exposed to electron beams in the presence of the dimethylpolysiloxane and polyfunctional compound, radicals formed in the thermoplastic olefin polymer, radicals formed in the dimethylpolysiloxane and radicals formed in the polyfunctional compounds are delicately influenced by one another, and grafting reaction through the polyfunctional compound and crosslinking of molecules of the dimethylpolysiloxane are promoted, whereby a special performance is manifested. If the resin composition which has been irradiated with electron beams is further heat-treated, the release property is further improved. The reason is considered to be that the reaction which has not been completed by irradiation with electron beams is further advanced by the heat treatment. As the heat treatment method, there can be mentioned a method in which the irradiated laminated film is kept in the form of a roll in a circulation type or stationary oven, a method in which the irradiated laminated film is passed through such an oven, and a method in which the irradiated laminated film is passed through a hot roll. It is especially preferred that the irradiated laminated film be kept in a circulation type or stationary oven. The heat treatment temperature is lower than the melting point of the thermoplastic olefin polymer constituting the resin composition, and the heat treatment temperature is changed according to the kind of the resin, but especially preferably the heat treatment temperature is lower by at least 10°C than the melting point of the thermoplastic olefin polymer. The heat treatment time is changed according to the incorporated amount of the silicone, the composition of the resin and the irradiation dose in the preceding step of irradiation with electron beams, but the heat treatment time is mainly decided in view of the heat treatment temperature. Even if the heat treatment time is too long, no trouble is caused in connection with manifestation of the release property but in some resin the mechanical characteristics are degraded. It is generally preferred that the heat treatment time be several seconds to 1 week, especially 10 seconds to 3 days. Ordinary additives such as an antioxidant, a light stabilizer, a lubricant, an antiblocking agent, a pigment and a filler can be added to the resin composition of the present invention. An antioxidant that prevents deterioration of the polyfunctional compound at the step of extruding the composition at a high temperature and does not hinder irradiation with electron beams should be selected. As specific examples, there can be mentioned 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 4,4'-thiobis(3-methyl-6-t-butylphenol), 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)S-triazine, 2,4,6-(1H,3H,5H)trione, 1,3,5-trimethyl-2,4,6-tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzene, pentaerythritol tetrakis)β-laurylthiopropionate), tetrakis(2,4-di-t-butylphenyl)-4,4-biphenylene-diphosphite, calcium (3,5-di-t-butyl-4-hydroxybenzylmonoethylphosphonate), distearyl thiodipropionate and bis(2,4-di-t-butylphenyl)pentaerythritol. Among them, 2,6-di-t-butyl-p-cresol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and pentaerythrityltetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] are preferred, and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate is especially preferred. The release material obtained according to the process of the present invention has an excellent release property, and the release performance can be freely controlled by appropriately selecting the kinds and amounts of the resin component of the composition, the electron beam irradiation treatment conditions and the heat treatment conditions. Furthermore, the process of the present invention is advantageous over the conventional techniques in that a large-scale apparatus for the heat treatment or the recovery of the solvent need not be used. The present invention will now be described in detail with reference to the following examples and comparative examples. In the examples and comparative examples, with respect to each of samples prepared under various conditions, the peel strength and the residual adhesion ratio, and the stabilities of these properties, were determined. The release strength and residual adhesiveness ratio were measured in the following manner. More specifically, a Pyron craft tape (supplied by Kyowa) was used as the standard tape and this tape was bonded to the composition-laminated surface of a release paper, and the 180° peel test was carried out according to JIS-Z-0237. Furthermore, the residual adhesion ratio was measured according to JIS-Z-1523. To examine the stabilities of the peel strength and residual adhesion ratio, the standard tape bonded to the composition-laminated surface was allowed to stand in this state for a certain period, and the peel strength and residual adhesion ratio were measured. Note, a higher residual adhesion ratio is preferred, and a smaller change of the peel strength or residual adhesion ratio with the lapse of time is preferred. Example 1 A resin composition comprising high-pressure low-density polyethylene (Sholex supplied by Showa Denko; hereinafter referred to as "LD-A") having a MI of 20 g/10 min and a density of 0.916 g/cm³, 5% by weight (all of "%" given hereinafter are by weight) of a dimethylpolysiloxane (supplied by Shin-Etsu Chemical) having a viscosity of 6 x 10⁻² m²/s (60,000 cs) at 25°C and having both of the terminals blocked with a trimethylsilyl group and 2% of triallyl isocyanurate (hereinafter referred to as "TAIC") was melt-extruded and laminated at a resin temperature of 270°C and a lamination thickness of 20 µm on the polyethylene surface of a polyethylene-laminated kraft paper, and the laminated composition was then subjected to an electron beam irradiation treatment in an atmosphere having an oxygen concentration lower than 10 ppm at a line speed of 30 m/min and an irradiation dose of 6 Mrad. The release material characteristics of the sample were measured. Example 2 A sample was prepared in the same manner as described in Example 1 except that a resin composition comprising a mixture formed by melt-mixing high-density polyethylene (Sholex supplied by Showa Denko; hereinafter referred to as "HD") having a MI of 22 g/10 min and a density of 0.960 g/cm³ and high-pressure low-density polyethylene (LD-A) having a MI of 20g/10min and a density of 0.916 g/cm³ at an HD/LD-A weight ratio of 70/30, 2% of a dimethylpolysiloxane (supplied by Toray Silicone) having a viscosity of 5 x 10⁻⁴ m²/s (500 cs) at 25°C and having both of the terminal groups blocked with a trimethylsilyl group, and 2% of TAIC was used, and the irradiation dose was changed to 10 Mrad. The release material characteristics of the sample were measured. Example 3 A sample was prepared in the same manner as described in Example 1 except that an ethylene/vinyl acetate copolymer (Sholex supplied by Showa Denko; hereinafter referred to as "EVA") having a MI of 8 g/10 min and a vinyl acetate content of 9% was used as the thermoplastic olefin polymer and the extrusion lamination was carried out at a resin temperature of 250°C. The release material characteristics of the sample were measured. Example 4 A three-layer laminate of paper/polyolefin mixture/resin composition was shaped by co-extrusion lamination. Namely, a resin composition comprising polypropylene (Shoallomer supplied by Showa Denko; hereinafter referred to "PP") having a MFR of 30 g/10 min, 4% of a dimethylpolysiloxane (supplied by Shin-Etsu Chemical) having a viscosity of 5 x 10⁻³ m²/s (5,000 cs) at 25°C and having both of the terminals blocked with a trimethylsilyl group and 1% of trimethylolpropane triacrylate (hereinafter referred to as "TMPTA"), and a polyolefin mixture formed by melt-mixing PP having a MFR of 30 g/10 min and high-pressure low-density polyethylene (LD-B) having a MI of 2 g/10 min and a density of 0.925 g/cm³ at a PP/LD-B weight ratio of 80/20, were co-extruded on a kraft paper at a olefin polymer mixture temperature of 290°C and a release composition temperature of 270°C, so that the lamination thickness of each of the polyolefin mixture and the release composition was 15 µm. The laminate was irradiated with electron beams at a line speed of 30 m/min and an irradiation dose of 3 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. The release material characteristics of the obtained samples were measured. Example 5 A sample was prepared in the same manner as described in Example 2 except that diallyl terephthalate (hereinafter referred to as "DATP") was used instead of TAIC, and the release material characteristics of the sample were measured. Example 6 A sample was prepared in the same manner as described in Example 1 except that 4% of a dimethylpolysiloxane having a viscosity of 5x10⁻³ m²/s (5,000 cs) at 25°C was used instead of 5% of the dimethylpolysiloxane having a viscosity of 6x10⁻² m²/s (60,000 cs) at 25°C and 1% of TMPTA was used instead of 2% of TAIC, and the release material characteristics of the sample were measured. Comparative Example 1 A sample was prepared in the same manner as described in Example 1 except that TAIC was not added, and the release material characteristics of the sample were measured. Comparative Example 2 A sample was prepared in the same manner as described in Example 2 except that TAIC was not added, and the release material characteristics of the sample were measured. Comparative Example 3 A sample was prepared in the same manner as described in Example 3 except that TAIC was not added, and the release material characteristics of the sample were measured. Comparative Example 4 A sample was prepared in the same manner as described in Example 4 except that TMPTA was not added, and the release material characteristics of the sample were measured. Comparative Example 5 A sample was prepared in the same manner as described in Example 6 except that TMPTA was not added, and the release material characteristics of the sample were measured. Comparative Example 6 A sample was prepared in the same manner as described in Example 1 except that the irradiation with electron beams was not effected, and the release material characteristics of the sample were measured. The measurement results obtained in Examples 1 through 6 and Comparative Examples 1 through 6 are collectively shown in Table 1. No. Initial stage After 1 week After 1 month Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Examples 1 32 82 105 78 96 78 2 47 79 173 70 182 69 3 28 82 122 75 113 74 4 95 74 204 65 211 64 5 55 79 142 68 147 68 6 36 81 201 70 195 69 Comparative Examples 1 39 80 295 51 482 41 2 56 78 358 45 461 40 3 37 81 311 50 412 42 4 89 73 484 40 553 38 5 53 79 313 51 467 40 6 306 52 515 40 712 31 Example 7 A resin composition comprising high-pressure low-density polyethylene (LD-A) having a MI of 20 g/10 min and a density of 0.916 g/cm³, 5% of the same dimethylpolysiloxane as used in Example 1, which had a viscosity of 6x10⁻² m²/s (60,000 cs) at 25°C, and 2% of TAIC was extrusion-laminated on a polyethylene-laminated kraft paper at a resin temperature of 270°C and a lamination thickness of 20 µm, and the laminate was subjected to an electron beam irradiation treatment at a line speed of 30 m/min and an irradiation dose of 4 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. Then, the irradiated laminate was heat-treated in the form of a roll in a gear oven maintained at 80°C for 3 days. The release material characteristics of the obtained sample were measured. Example 8 A sample was prepared in the same manner as described in Example 7 except that a resin composition comprising a mixture formed by melt-mixing high-density polyethylene (HD) having a MI of 22 g/10 min and a density of 0.960 g/cm³ and high-pressure low-density polyethylene (LD-A) having a MI of 20 g/10 min and a density of 0.916 g/cm³ at a weight ratio of 70/30, 2% of the same dimethylpolysiloxane as used in Example 2, which had a viscosity of 5x10⁻⁴ m²/s (500 cs) at 25°C, and 2% of TAIC, was used and the electron beam irradiation was carried at an irradiation does of 6 Mrad, The release material characteristics of the sample were measured. Example 9 A sample was prepared in the same manner as described in Example 7 except that EVA having a MI of 8 g/10 min and a vinyl acetate content of 9% was used as the thermoplastic olefin polymer and the extrusion lamination was carried out at a resin temperature of 250°C. The release material characteristics of the sample were measured. Example 10 A resin composition comprising polypropylene having MFR of 30 g/10 min, 4% of the same dimethylpolysiloxane as used in Example 4, which had a viscosity of 5x10⁻³ m²/s (5,000 cs) at 25°C, and 1% of TMPTA, and a polyolefin mixture comprising polypropylene having a MFR of 30 g/10 min and high-pressure low-density polyethylene having a MI of 2 g/10 min and a density of 0.918 g/cm³ at a weight ratio of 80/20, were co-extruded and laminated on a kraft paper at an olefin polymer mixture temperature of 290°C and a resin composition temperature of 270°C so that the lamination thickness of each of the mixture and composition was 10 µm, whereby a three-layer laminate of a paper olefin polymer mixture resin composition was shaped. Then, the laminate was irradiated with electron beams at a line speed of 30 m/min and an irradiation dose of 3 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. Then, the irradiated laminate was heat-treated in the form of a roll for 3 days in a gear oven maintained at 50°C. The release material characteristics of the obtained sample were measured. Example 11 A sample was prepared in the same manner as described in Example 8 except that DATP was used instead of TAIC, and the release material characteristics of the sample were measured. Example 12 A sample was prepared in the same manner as described in Example 7, except that 4% of a dimethylpolysiloxane having a viscosity of 5x10⁻³ m²/s (5,000 cs) at 25°C was used and 1.0% of TMPTA was used instead of TAIC, and the release material characteristics of the sample were measured. Comparative Example 7 A sample was prepared in the same manner as described in Example 7 except that TAIC was not added, and the release material characteristics of the sample were measured. Comparative Example 8 A sample was prepared in the same manner as described in Example 7 except that the electron beam irradiation treatment was not carried out, and the release material characteristics of the sample were measured. The results obtained in Examples 7 through 12 and Comparative Examples 7 and 8 are collectively shown in Table 2. No. Initial stage After 1 week After 1 month Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Examples 7 24 84 85 79 80 79 8 42 80 152 72 156 72 9 25 83 103 78 98 77 10 52 78 195 66 182 66 11 45 80 107 77 110 77 12 28 83 142 72 147 72 Comparative Examples 7 40 80 303 49 405 45 8 315 52 523 40 702 31 Example 13 A resin composition comprising a mixture formed by melt-mixing an ethylene/propylene/non-conjugated diene copolymer (hereinafter referred to as "EFDM-1") having an ethylene/propylene/ethylidene-norbornene weight ratio of 60/35/5 and a Mooney viscosity ML₁+₄ of 100 and high-pressure low-density polyethylene (LD-C) having a MI of 20 g/10 min and a density of 0.918 g/cm³ at an EPDM-1/LD-C weight ratio of 40/60, 4% of the same dimethylpolysiloxane as used in Example 4, which had a viscosity of 5x10⁻³ m²/s (5,000 cs) at 25°C, and 2% of TAIC, was extrusion-laminated on the polyethylene surface of a polyethylene-laminated kraft paper at a resin temperature of 270°C and a lamination thickness of 20 µm. The laminate was irradiated with electron beams at a line speed of 30 m/min and an irradiation dose of 6 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. The release material characteristics of the obtained sample were measured. Example 14 A sample was prepared in the same manner as described in Example 13 except that DATP was used instead of TAIC, and the release material characteristics of the sample were measured. Example 15 A resin composition comprising a mixture formed by melt-mixing an ethylene/propylene copolymer rubber (EP) having a propylene content of 35% and a MFR of 5 g/10 min and LD-C and EPDM-1 used in Example 13 at an LD-C/EP/EFDM-1 weight ratio of 60/30/10, 4% of the same dimethylpolysiloxane as used in Example 2, which had a viscosity of 5x10⁻⁴ m²/s (500 cs) at 25°C, and 2% of TAIC, was extrusion-laminated on the polyethylene surface of a polethylene-laminated kraft paper at a resin temperature of 270°C and a lamination thickness of 20 µm. The laminate was irradiated with electron beams at a line speed of 30 m/min and an irradiation dose of 6 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. The release material characteristics of the obtained sample were measured. Comparative Example 9 A sample was prepared in the same manner as described in Example 13 except that TAIC was not added. The release material characteristics of the sample were measured. Comparative Example 10 A sample was prepared in the same manner as described in Example 13 except that the electron beam irradiation treatment was not carried out. The release material characteristics of the obtained sample were measured. The measurement results obtained in Examples 13 through 15 and Comparative Examples 9 and 10 are collectively shown in Table 3. No. Initial stage After 1 week After 1 month Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Examples 13 50 80 56 80 59 80 14 80 77 85 76 86 76 15 55 80 60 79 60 79 Comparative Examples 9 62 78 123 74 203 56 10 235 65 351 51 402 44 Example 16 A resin composition comprising a mixture formed by melt-mixing an ethylene/propylene/non-conjugated diene copolymer rubber (EPDM-1) having an ethylene/propylene/ethylidene-norbornene weight ratio of 60/35/5 and a Mooney viscosity ML₁+₄ of 100 and high-pressure low-density polyethylene (LD-C) having a MI of 20 g/10 min and a density of 0.918 g/cm³ at an EPDM-1/LD-C weight ratio of 40/60, 4% of the same dimethylpolysiloxane as used in Example 4, which had a viscosity 5x10⁻³ m²/s of (5,000 cs) at 25°C, and 2% of TAIC was extrusion laminated on the polyethylene surface of a polyethylene-laminated kraft paper at a resin temperature of 270°C and a lamination thickness of 20 µm. The laminate was irradiated with electron beams at a line speed of 30 m/min and an irradiation dose of 4 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. The irradiated laminate was heat-treated in the form of a roll for 3 days in a gear oven maintained at 50°C. The release material characteristics of the obtained sample were measured. Example 17 A sample was prepared in the same manner as described in Example 16 except that DATP was used instead of TAIC, and the release material characteristics of the sample were measured. Example 18 A resin composstion comprising a mixture formed by melt-mixing an ethylene/propylene copolymer rubber (EP) having a propylene content of 35% an a MFR of 5 g/10 min and the same LD-C and EPDM-1 as used in Example 16 at an LD-C/EP/EPDM-1 weight ratio of 60/35/10, 4% of the same dimethylpolysiloxane (supplied by Toray Silicone) as used in Example 2, which had a viscosity of 5x10⁻⁴ m²/s (500 cs) at 25°C, and 2% of TAIC was extruded and laminated on the polyethylene surface of a polyethylene-laminated kraft paper at a resin temperature of 270°C and a lamination thickness of 20 µm. The laminate was irradiated with electron beams at a line speed of 30 m/min and an irradiation dose of 4 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. The irradiated laminate was heat-treated in the form of a roll for 3 days in a gear oven maintained at a temperature of 50°C. The release material characteristics of the obtained sample were measured. Comparative Example 11 A sample was prepared in the same manner as described in Example 16 except that TAIC was not added. The release material characteristics of the sample were measured. Comparative Example 12 A sample was prepared in the same manner as described in Example 16 except that the electron beam treatment was not carried out, and the release material characteristics of the sample were measured. The measurement results obtained in Examples 16 through 18 and Comparative Examples 11 and 12 are collectively shown in Table 4. Initial stage After 1 week After 1 month No. Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ration (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Examples 16 31 83 30 83 32 83 17 82 77 85 76 86 76 18 20 86 21 86 20 86 Comparative Examples 11 65 75 125 74 235 54 12 235 65 351 51 402 44 Example 19 A resin composition comprising high-pressure low-density polyethylene (Sholex supplied by Showa Denko) having a MI of 12 g/10 min and a density of 0.916 g/cm³, 4% of a dimethylpolysiloxane having a viscosity of 5x10⁻⁴ m²/s (500 cs) at 25°C and having both of the terminals blocked with a trimethylsilyl group, 2% of TAIC and 0.1% of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, which was maintained at 270°C, and high-pressure low-density polyethylene having a MI of 11 g/10 min and a density of 0.917 g/cm³, which was maintained at 290°C, were co-extruded and laminated on a kraft paper so that the lamination thickness of each of the composition and low-density polyethylene was 15 µm, whereby a three-layer laminate of paper/low-density polyethylene release composition was obtained. Then, the laminate was irradiated with electron beams at a line speed of 30 m/min and an irradiation dose of 10 Mrad in an atmosphere having an oxygen concentration lower than 10 ppm. The irradiated laminate was heat-treated at 180°C for three days. The release material characteristics of the obtained sample were measured. Example 20 A sample was prepared in the same manner as described in Example 1 except that a composition comprising a mixture formed by melt-mixing linear low-density polyethylene (Sholex supplied by Showa Denko; hereinafter referred to as "LLD-A") having a MI of 6 g/10 min and a density of 0.916 g/cm³ and containing butene as a comonomer and high-pressure low-density polyethylene (Sholex supplied by Showa Denko; hereinafter referred to as "LD-C") having a MI of 12 g/10 min and a density of 0.916 g/cm³ at an LLD-A/LD-C weight ratio of 70/30, 5% of a dimethylpolysiloxane having a viscosity of 5x10⁻³ cm²/s (5,000 cs) at 25°C and having both of the terminal groups blocked with a trimethylsilyl group and 2% of TAIC, was used, and the irradiation dose was changed to 10 Mrad. The release material characteristics of the sample were measured. Example 21 A sample was prepared in the same manner as described in Example 1, except that 1% of a dimethylpolysiloxane having a viscosity of 5x10⁻⁴ m²/s (500 cs) at 25°C and having both of the terminals blocked with a trimethylsilyl group was used. The release material characteristics of the sample were measured. Example 22 A sample was prepared in the same manner as described in Example 1 except that 8% of a dimethylpolysiloxane having a viscosity of 5x10⁻⁴ m²/s (500 cs) at 25°C and having both of the terminals blocked with a trimethylsilyl group was used, and the release material characteristics of the sample were measured. Example 23 A sample was prepared in the same manner as described in Example 1 except that the amount of TAIC used was changed to 0.5%, and the release material characteristics of the sample were measured. Example 24 A sample was prepared in the same manner as described in Example 1 except that the amount of TAIC used was changed to 6%, and the release material characteristics of the sample were measured. Example 25 A sample was prepared in the same manner as described in Example 1 except that the irradiation dose was changed to 0.5 Mrad, and the release material characteristics of the sample were measured. Example 26 A sample was prepared in the same manner as described in Example 1 except that 4% of a dimethylpolysiloxane having a viscosity of 2x10⁻⁵ m²/s (20 cs) at 25°C and having both of the terminals blocked with a trimethylsilyl group was used. Since the mixing and shaping were very difficult, a good portion of the sample was selected and subjected to the measurement of the release material characteristics. Example 27 A sample was prepared in the same manner as described in Example 26 except that the irradiation dose was changed to 20 Mrad, and the release material characteristics of the sample were measured. Example 28 A sample was prepared in the same manner as described in Example 1 except that 4% of a dimethylpolysiloxane having a viscosity of 12 m²/s (12 x 10⁻⁶ cs) at 25°C and having both of the terminals blocked with a trimethylsilyl group was used, and the release material characteristics of the sample were measured. Comparative Example 13 A sample was prepared in the same manner as described in Example 1 except that 4% of pentaphenyltrimethyltrisiloxane having a viscosity of 1,75x10⁻⁴ m²/s (175 cs) at 25°C was used as the siloxane, and the release material characteristics of the sample were measured. The measurement results obtained in Examples 19 through 28 and Comparative Example 13 are collectively shown in Table 5. Initial stage After 1 week After 1 month No. Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Peel strength (g/20 mm) Residual adhesion ratio (%) Examples 19 5 92 7 90 10 90 20 40 80 125 75 122 75 21 55 78 200 65 230 63 22 25 60 55 51 55 52 23 32 81 293 51 353 50 24 85 75 252 52 450 40 25 255 52 503 41 653 35 26 105 73 255 58 359 50 Comparative Examples 13 325 35 538 30 652 28

Claims: A process for the preparation of a release material comprising a substrate and a film laminated on the substrate, which comprises the steps of: melt-extruding a resin composition onto the substrate to form the film laminated on the substrate, said resin composition comprising: (a) a thermoplastic olefin polymer selected from polyethylene, polypropylene, copolymers mainly composed of ethylene or propylene, and mixtures thereof, and having a melt flow rate (MFR) of 0.01 to 200 g/10 min., (b) 0.1 to 30% by weight, based on the resin composition, of a dimethylpolysiloxane having a termial group represented by the formula: -SiR₁R₂R₃ wherein R₁, R₂ and R₃ independently represents methyl, hydroxyl or alkoxy with 1-3 carbon atoms, and having a viscosity of 50 x 10⁻⁶ to 8 m²/s (=50 to 8 x 10⁶ cs) as measured at 25°C, and (c) 0.01 to 30% by weight, based on the resin composition, of a polyfunctional compound having at least two vinyl groups or at least two thiol groups; and irradiating the laminated film with electron beams. The process as claimed in claim 1 which further comprises the step of heat-treating the irradiated laminated film at a temperature lower than the melting point of the thermoplastic olefin polymer. The process as claimed in claim 1 or 2 wherein the thermoplastic olefin polymer is a mixture of low-density polyethylene and a rubber of a mono-olefin copolymer. The process as claimed in any of claims 1 to 3 wherein the irradiation dose of electron beams is 1 to 30 Mrad. The process as claimed in any of claims 1 to 4 wherein the polyfunctional compound having at least two vinyl groups is divinylbenzene. The process as claimed in any of claims 1 to 4 wherein the vinyl groups are acryloyl groups. The process as claimed in claim 6 wherein the polyfunctional compound having at least two acryloyl groups is selected from polyethylene glycol diacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, neopentyl glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol(monohydroxy)pentaacrylate and dipentaerythcitol hexaacrylate. The process as claimed in any of claims 1 to 4 wherein the vinyl groups are allyl groups. The process as claimed in claim 8 wherein the polyfunctional compound having at least two allyl groups is selected from diallyl terephthalate, diallyl adipate, triallyl cyanurate, triallyl isocyanurate, pentaerythritol triallyl ether, glycerol diallyl ether, trimethylolpropane diallyl ether, diglycerol diallyl ether, diglycerol triallyl ether, allyl methacrylate, diallyl phthalate, diallyl maleate, diallyl isophthalate, triallyl trimellitate, tetraallyl pyromellitate, allyl glycol acrylate and allyl glycol methacrylate. The process as claimed in any of claims 1 to 4 wherein the vinyl groups are methacryloyl groups. The process as claimed in claim 10 wherein the polyfunctional compound having at least two methacryloyl groups is selected from polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane tetramethacrylate, ethylene glybol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,4-butanediol dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, dipentaerythritol(monohydroxy)pentamethacrylate and dipentaerythritol hexamethacrylate. The process as claimed in any of claims 1 to 4 wherein the polyfunctional compound having at least two thiol groups is selected from trimethylolpropane tris-3-mercaptopropionate, 1,11-undecanedithiol, 4-ethylbenzene-1,3-dithiol, 1,8-dioctanedithiol, 1,18-octadecanedithiol, 4,8-dithioundecane-1,11-dithiol, dithiopentaerythritol, 1,2-dimercapto-1,3-butanediol, 2,6-dimethyloctane-2,6-dithiol, 2,4-dimethylbenzene-1,3-dithiol, 4,5-dimethylbenzene-1,3-dithiol, 1,10-decanedithiol, 1,12-dodecanedithiol, 2,5-toluenedithiol, 3,4-toluenedithiol, 1,6-hexanedithiol, 1,7-heptanedithiol, 1,4-benzenedithiol, 1,2-benzenedithiol, ethylene glycol dithioglycolate, 1,2,3-propanetrithiol, 1,2,4-butanetrithiol, trimethylolpropane trithioglycolate, pentaerythritol trithioglycolate, 1,3,5-benzenetrithiol, 2,4,6-mesitylenetrithiol, neopentane tetrathiol and pentaerythritol tetrakis(3-mercaptopropionate). The process as claimed in any of claims 1 to 4 wherein the polyfunctional compound is selected from trimethylolpropane trimethacrylate, tetramethylolmethane tetramethacrylate, triallyl cyanurate and triallyl isocyanurate.

Inventors: ARAKI TAKUMI, KUROSAWA SHIGERU, NAGAISHI HIROYUKI, ARAKI, TAKUMI, KUROSAWA, SHIGERU, NAGAISHI, HIROYUKI, ARAKI, TAKUMI C/O SHOWA DENKO K.K. OITA WORKS, KUROSAWA, SHIGERU C/O SHOWA DENKO K.K.,OITA WORKS, NAGAISHI, HIROYUKI C/O SHOWA DENKO K.K. OITA WORKS
Applicants: SHOWA DENKO KK, SHOWA DENKO KABUSHIKI KAISHA
Application year: 1989
Main classification: C08L23
IPC codes: B32B7, B32B27, C08K5, C09J7, C08J7, C08L23