Silicone composition and release sheet for forming peelable cured films

Abstract

The present invention relates to a silicone composition for forming a peelable cured film, said silicone composition comprising: (A) a chain organopolysiloxane that has a viscosity greater than 100,000 mPa∙s at 25°C, and has at least two C2-12 alkenyl groups per molecule, but only in a side chain of the molecule; (B) a chain organopolysiloxane that has a viscosity of 1,000-100,000 mPa∙s at 25°C, has at least two C2-12 alkenyl groups within one molecule, but only in a side chain of the molecule, and has an alkenyl group content of 0.0018-0.0148 mol / 100 g; (C) an organopolysiloxane that has at least two silicon-bonded hydrogen atoms within one molecule; and (D) a catalyst for a hydrosilylation reaction. This composition is capable of forming a peelable cured film that demonstrates a relatively light peeling resistance with regard to an adhesive substance, said peeling resistance changing little over time, and furthermore suppresses a reduction in the residual adhesion ratio of said adhesive substance.

Description

[Technical Field] 【0001】 The present invention relates to a silicone composition for forming a peelable cured film, and a release sheet having a peelable cured film obtained by curing the composition. [Background technology] 【0002】 Silicone compositions for forming peelable cured films are used to form cured films that exhibit appropriate peelability against adhesive substances. Examples of such silicone compositions for forming peelable cured films include, for example, Patent Document 1, which discloses a composition comprising an organopolysiloxane having a viscosity of 500,000 centistokes or more at 25°C, containing at least 0.1 mol% of methylvinylsiloxane units and having hydroxyl or vinyl groups at the molecular chain ends; an organopolysiloxane having a viscosity of 10 to 100,000 centistokes at 25°C and having vinyl groups at the molecular chain ends; an organopolysiloxane having at least 3 silicon-bonded hydrogen atoms in one molecule; and a catalyst for hydrosilylation reactions. Patent Document 2 discloses a composition having a viscosity of 50 to 10,000 cps at 25°C, containing at least 2 vinyl groups in one molecule, at least one of which is on the molecular chain side chain, and containing... A composition comprising an organopolysiloxane having an amount of 0.5 to 10 mol%, an organopolysiloxane having a viscosity of 100,000 cps or more at 25°C and a vinyl group content less than that of the aforementioned organopolysiloxane, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and a catalyst for hydrosilylation reactions has been disclosed. Patent Document 3 discloses a composition comprising an organopolysiloxane having two or more C2-C8 alkenyl groups in one molecule, an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, an organopolysiloxane not containing alkenyl groups or silicon-bonded hydrogen atoms in one molecule, a hydrosilylation reaction inhibitor, and a catalyst for hydrosilylation reactions. 【0003】 However, the composition in Patent Document 1 uses an organopolysiloxane with a viscosity of 10 to 100,000 centistokes at 25°C and vinyl groups at the ends of the molecular chain, and the composition in Patent Document 2 uses an organopolysiloxane with a viscosity of 50 to 10,000 cps at 25°C and a relatively high vinyl group content. However, both have the problem of being difficult to form a peelable cured film with low peel resistance, and the peel resistance changes over time. On the other hand, the composition in Patent Document 3 uses an organopolysiloxane that does not have alkenyl groups or silicon-bonded hydrogen atoms in a single molecule, so it can form a peelable cured film with low peel resistance, but it has the problem of significantly reducing the residual adhesion rate of adhesive substances. 【0004】 On the other hand, Patent Document 4 discloses a composition comprising: a diorganopolysiloxane having a viscosity of 500 centistokes or more at 25°C in a 30 wt% toluene solution, having 4 to 8 carbon atoms in the side chains of the molecular chain, and the molecular chain ends sealed with a hydroxyl group, an alkenyl group, or an alkyl group; a diorganopolysiloxane having a viscosity of 500 centistokes or more at 25°C in a 30 wt% toluene solution, with the molecular chain ends sealed with a hydroxyl group, an alkenyl group, or an alkyl group, and having at least one alkenyl group in one molecule; an organopolysiloxane having a viscosity of 1 to 1,000 centistokes at 25°C, and having at least three silicon-bonded hydrogen atoms in one molecule; a catalyst for hydrosilylation reaction; a hydrosilylation reaction inhibitor; and an organic solvent. However, the composition described in Patent Document 4 has the drawback of having high viscosity due to the inclusion of two high molecular weight organopolysiloxanes, resulting in poor coating properties and handling capabilities. 【0005】 Furthermore, Patent Document 5 discloses a composition comprising an organopolysiloxane having a viscosity of 1.5 to 70 Pa·s at 25°C in a 30 wt% toluene solution and having alkenyl groups encapsulating the molecular chain ends, an organopolysiloxane having a viscosity of 0.1 to 500 Pa·s at 25°C and having alkenyl groups in the molecular chain side chains with an alkenyl group content of 0.2 to 5 times that of the aforementioned organopolysiloxane, an organopolysiloxane having at least 3 silicon-bonded hydrogen atoms in one molecule, a catalyst for hydrosilylation reaction, and an organic solvent. However, while the composition in Patent Document 5 improves coating properties and handling ease, it does not adequately solve the problem of forming a cured film with light peel resistance. [Prior art documents] [Patent Documents] 【0006】 [Patent Document 1] Japanese Patent Application Publication No. 50-025644 [Patent Document 2] Japanese Patent Publication No. 159480 / 1983 [Patent Document 3] Japanese Patent Application Publication No. 02-145650 [Patent Document 4] Japanese Patent Application Publication No. 09-125004 [Patent Document 5] Japanese Patent Publication No. 2004-190202 [Overview of the project] [Problems that the invention aims to solve] 【0007】 An object of the present invention is to provide a silicone composition for forming a releaseable cured film that exhibits relatively low peel resistance to adhesive substances, has little change over time, and further suppresses a decrease in the residual adhesion rate of the adhesive substance. Another object of the present invention is to provide a release sheet that exhibits relatively low peel resistance to adhesive substances, has little change over time, and further suppresses a decrease in the residual adhesion rate of the adhesive substance. [Means for solving the problem] 【0008】 The silicone composition for forming a peelable curable film of the present invention is (A) A linear organopolysiloxane having a viscosity exceeding 100,000 mPa·s at 25°C and containing at least two C2-C12 alkenyl groups only in the side chains of the molecular chain in each molecule. (B) A linear organopolysiloxane having a viscosity of 1,000 to 100,000 mPa·s at 25°C, containing at least two C2-C12 alkenyl groups only in the side chains of the molecular chain, with an alkenyl group content of 0.0018 to 0.0148 mol / 100g [amount such that the mass ratio of component (A) to component (B) {component (A) / component (B)} is 10 / 90 to 90 / 10], (C) an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule {an amount such that the silicon-bonded hydrogen atoms in component (C) are 0.5 to 5 moles for every 1 mole of alkenyl groups in components (A) and (B)}, and (D) Catalytic amount of catalyst for hydrosilylation reaction It consists of. 【0009】 In this composition, the alkenyl group in component (A) is preferably a hexenyl group. 【0010】 In this composition, the mass ratio of component (A) to component (B) {component (A) / component (B)} is preferably 40 / 60 to 80 / 20. 【0011】 Preferably, this composition further contains (E) a hydrosilylation reaction inhibitor. 【0012】 Preferably, this composition further contains (F) an organic solvent. 【0013】 The release sheet of the present invention is characterized by having a release-cured film obtained by curing the above-mentioned silicone composition for forming a release-cured film. [Effects of the Invention] 【0014】 The silicone composition for forming a peelable cured film of the present invention exhibits relatively low peel resistance to an adhesive substance, has little change over time, and further has the characteristic that it can form a peelable cured film that suppresses a decrease in the residual adhesion rate of the adhesive substance. Further, the release sheet of the present invention exhibits relatively low peel resistance to an adhesive substance, has little change over time, and further has the characteristic that it suppresses a decrease in the residual adhesion rate of the adhesive substance. 【Mode for Carrying Out the Invention】 【0015】 <Definition of Terms> The term "viscosity" as used in this specification means the value (unit: mPa·s or Pa·s) at 25°C measured by a B-type rotational viscometer in accordance with the provisions of JIS K 7117-1:1999 "Plastics - Liquid, Emulsion or Dispersed Resins - Method for Measuring Apparent Viscosity by Brookfield-Type Rotational Viscometer". 【0016】 The term "plasticity" as used in this specification means the value (unit: mm) when a load of 1 kgf is applied to a 4.2 g spherical sample for 3 minutes in accordance with the method specified in JIS K 6249:2003 "Test Methods for Uncured and Cured Silicone Rubber". 【0017】 <Silicone Composition for Forming a Peelable Cured Film> The silicone composition for forming a peelable cured film of the present invention will be described in detail. 【0018】 Component (A) is a linear organopolysiloxane having at least two C2-C12 alkenyl groups only on the side chains of the molecular chain in one molecule. Examples of alkenyl groups in component (A) include vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, and octenyl groups, with hexenyl being preferred. Such alkenyl groups must be present only on the side chains of the molecular chain and not at the ends of the molecular chain. Examples of groups that bond to silicon atoms other than alkenyl groups in component (A) include C1-C12 alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups; C6-C12 aryl groups such as phenyl, tolyl, and xylyl groups; C7-C12 aralkyl groups such as benzyl and phenethyl groups; and C3-C12 fluoroalkyl groups such as 3,3,3-trifluoropropyl, 4,4,4,3,3-pentafluorobutyl, 5,5,5,4,4,3,3-heptafluoropentyl, 6,6,6,5,5,4,4,3,3-nonafluorohexyl, and 7,7,7,6,6,5,5,4,4,3,3-undecafluoroheptyl groups, with methyl groups being preferred. Furthermore, component (A) may have small amounts of hydroxyl groups, methoxy groups, ethoxy groups, or other C1-C3 alkoxy groups bonded to the silicon atoms, to the extent that it does not impair the purpose of the present invention. 【0019】 The content of alkenyl groups in component (A) is not limited, but is preferably in the range of 0.0185 to 0.1110 mol / 100g, or 0.0185 to 0.0739 mol / 100g. This is because if the content of alkenyl groups in component (A) is above the lower limit of the above range, the composition will cure sufficiently, the migration of the silicone component to the adhesive substance of the resulting peelable cured film will be suppressed, and the decrease in the residual adhesion rate of the adhesive substance will be suppressed. On the other hand, if it is below the upper limit of the above range, the resulting peelable cured film will have appropriate light peel resistance. 【0020】 Component (A) is a highly polymerized organopolysiloxane with a viscosity at 25°C exceeding 100,000 mPa·s. As the degree of polymerization increases, it becomes so rubbery that its viscosity can no longer be measured by a rotational viscometer. When component (A) is rubbery, its plasticity is preferably 3.0 mm or less, or 0.5 to 3.0 mm. 【0021】 The molecular structure of component (A) is substantially linear, but a portion of the molecular chain may be branched. Examples of such component (A) include a dimethylsiloxane-methylhexenylsiloxane copolymer in which both ends of the molecular chain are sealed with trimethylsiloxy groups, and a dimethylsiloxane-methylhexenylsiloxane copolymer in which the ends of the molecular chain are substantially sealed with trimethylsiloxy groups, and some ends of the molecular chain are sealed with dimethylhydroxysiloxy groups. 【0022】 Component (B) is a linear organopolysiloxane having at least two C2-C12 alkenyl groups only on the side chains of the molecular chain in one molecule. Examples of alkenyl groups in component (B) are the same as those in component (A), preferably vinyl groups. Such alkenyl groups must be present only on the side chains of the molecular chain and not at the ends of the molecular chain. Examples of groups that bond to silicon atoms other than alkenyl groups in component (B) are the same as those in component (A), preferably methyl groups. Furthermore, component (B) may have small amounts of C1-C3 alkoxy groups such as hydroxyl groups, methoxy groups, and ethoxy groups bonded to the silicon atoms, to the extent that it does not impair the objectives of the present invention. 【0023】 The viscosity of component (B) at 25°C is in the range of 1,000 to 100,000 mPa·s, preferably in the range of 1,000 to 70,000 mPa·s, 2,000 to 50,000 mPa·s, or 3,000 to 50,000 mPa·s. This is because if the viscosity of component (B) is above the lower limit of the above range, the curability of the composition can be improved, while if it is below the upper limit of the above range, a peelable cured film with relatively low peel resistance and little change over time can be formed. 【0024】 The content of alkenyl groups in component (B) is in the range of 0.0018 to 0.0148 moles / 100g, preferably in the range of 0.0026 to 0.0148 moles / 100g when the viscosity is 1,000 mPa·s or more and 10,000 mPa·s or less, in the range of 0.0018 to 0.0111 moles / 100g when the viscosity is greater than 10,000 mPa·s and 100,000 mPa·s or less, or in the range of 0.0037 to 0.0148 moles / 100g when the viscosity is 1,000 mPa·s or more and 10,000 mPa·s or less, and in the range of 0.0018 to 0.0074 moles / 100g when the viscosity is greater than 10,000 mPa·s and 100,000 mPa·s or less. This is because, when the content of alkenyl groups in component (B) is above the lower limit of the above range, the composition hardens sufficiently, the migration of the silicone component to the adhesive substance of the resulting peelable cured film is suppressed, and the decrease in the residual adhesion rate of the adhesive substance can be suppressed. On the other hand, when it is below the upper limit of the above range, the resulting peelable cured film has appropriate light peel resistance, and its change over time can also be kept small. 【0025】 The reason why the preferred alkenyl group content differs depending on the viscosity of component (B) is as follows: When the viscosity of component (B) is low, the molecular weight is low, so even with the same alkenyl group content, the number of alkenyl groups in one molecule is small. Since such a component (B) has low reactivity, migration of the silicone component to the adhesive substance of the release-cured film is more likely to occur. To suppress this, it is preferable to increase the alkenyl group content of component (B). On the other hand, when the viscosity of component (B) is high, the molecular weight is high, so even with the same alkenyl group content, the number of alkenyl groups in one molecule is large. Since such a component (B) has high reactivity, it is less likely to localize on the surface of the release-cured film. In general, unreacted silicon-bonded hydrogen atoms may remain on the surface of the release-cured film, or they may react with moisture to form silicon-bonded hydroxyl groups, and this is thought to be the cause of increased interaction between the release-cured film and the adhesive substance over time. In order to suppress the retention of silicon-bonded hydrogen atoms on the surface of the peelable cured film, it is necessary to promote the localization of component (B) on the surface of the cured film and to create a difference in relative reactivity with component (A). Therefore, when the viscosity of component (B) is high, it is preferable to lower the content of alkenyl groups in component (B). 【0026】 In this composition, the amount of component (B) is such that the mass ratio of component (A) to component (B) {(A) component / (B) component} is in the range of 10 / 90 to 90 / 10, preferably in the range of 30 / 70 to 90 / 10, or in the range of 40 / 60 to 80 / 20. This is because if the mass ratio of component (A) to component (B) {(A) component / (B) component} is above the lower limit of the above range, the curability of this composition, especially the curability at low temperatures of about 100°C, can be improved, and the strength of the resulting cured film can be increased. On the other hand, if it is below the upper limit of the above range, a peelable cured film with relatively low peel resistance can be formed. In this composition, since component (B) is blended with component (A) in a specific ratio, a peelable cured film with relatively low peel resistance and suppressed reduction in the residual adhesion rate of adhesive substances can be formed. 【0027】 Component (C) is an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and is a crosslinking agent for this composition. The bonding positions of the silicon-bonded hydrogen atoms in component (C) are not limited, and examples include the molecular chain ends and / or molecular chain side chains. Examples of groups that bond to silicon atoms other than hydrogen atoms in component (C) include C1-C12 alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl groups; C6-C12 aryl groups such as phenyl, tolyl, and xylyl groups; C7-C12 aralkyl groups such as benzyl and phenethyl groups; and C3-C12 fluoroalkyl groups such as 3,3,3-trifluoropropyl, 4,4,4,3,3-pentafluorobutyl, 5,5,5,4,4,3,3-heptafluoropentyl, 6,6,6,5,5,4,4,3,3-nonafluorohexyl, and 7,7,7,6,6,5,5,4,4,3,3-undecafluoroheptyl, with methyl groups being preferred. Furthermore, component (C) may have small amounts of hydroxyl groups, methoxy groups, ethoxy groups, or other carbon-1 to carbon-3 alkoxy groups bonded to the silicon atoms, to the extent that it does not impair the objectives of the present invention. 【0028】 The viscosity of component (C) at 25°C is not limited, but is preferably in the range of 1 to 1,000 mPa·s or 5 to 500 mPa·s. This is because if the viscosity of component (C) is above the lower limit of the above range, the volatilization of this component from the composition is suppressed and the composition becomes stable, while if it is below the upper limit of the above range, the curing of the composition is promoted. 【0029】 The molecular structure of such (C) component is not limited and can include, for example, linear, partially branched linear, branched, cyclic, or resinous. Examples of such (C) component include trimethylsiloxy group-sealed dimethylsiloxane / methylhydrogensiloxane copolymer, dimethylhydrogensiloxy group-sealed dimethylsiloxane / methylhydrogensiloxane copolymer, dimethylhydrogensiloxy group-sealed dimethylpolysiloxane, trimethylsiloxy group-sealed methylhydrogenpolysiloxane, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane / dimethylsiloxane copolymer, and formula: H(CH3)2SiO 1 / 2 Siloxane units and formula represented by: SiO 4 / 2 A copolymer consisting of siloxane units represented by the formula: (CH3)3SiO 1 / 2 Siloxane units and formula: H(CH3)2SiO 1 / 2 Siloxane units and formula represented by: SiO 4 / 2 A copolymer consisting of siloxane units represented by is given as an example. 【0030】 In this composition, the content of component (C) is such that the amount of silicon-bonded hydrogen atoms in component (C) is in the range of 0.5 to 5 moles per mole of total alkenyl groups in components (A) and (B), preferably in the range of 0.6 to 3.0 or 0.7 to 1.5. This is because if the content of component (C) is above the lower limit of the above range, the composition will harden sufficiently, while if it is below the upper limit of the above range, the resulting peelable hardened film will have appropriate light peel resistance and its change over time will be minimized. 【0031】 Component (D) is a hydrosilylation catalyst for promoting the hydrosilylation reaction of the composition. Examples of such component (D) include platinum-based catalysts, palladium-based catalysts, and rhodium-based catalysts, with platinum-based catalysts being preferred. Examples of platinum-based catalysts include chloroplatinic acid, chloroplatinic acid hexahydrate, platinum dichloride, alcohol-modified chloroplatinic acid, platinum olefin complexes, platinum carbonyl complexes, platinum alkenylsiloxane complexes, and platinum diketone complexes. In addition, examples of alkenylsiloxanes in platinum alkenylsiloxane complexes include 1,3-divinyltetramethyldisiloxane, 1,1,3,3-tetravinyldimethyldisiloxane, and dimethylvinylsiloxy group-blocking methyl(3,3,3-trifluoropropyl)siloxane oligomers. 【0032】 The content of component (D) is the amount of catalyst to promote the hydrosilylation reaction of this composition, and specifically, the amount of catalyst metal in this component is in the range of 0.1 to 1,000 ppm, 0.1 to 500 ppm, 5 to 500 ppm, 0.1 to 300 ppm, or 5 to 300 ppm relative to the total amount of components (A) to (C) in terms of mass units. This is because if the content of component (D) is above the lower limit of the above range, the curing of this composition is promoted, while if it is below the upper limit of the above range, problems such as discoloration are less likely to occur in the resulting peelable cured film. 【0033】 Furthermore, this composition may contain (E) a hydrosilylation reaction inhibitor to adjust the curing rate. Such (E) components include alkynes such as 2-methyl-3-butyne-2-ol, 3,5-dimethyl-1-hexyne-3-ol, 3-methyl-1-pentin-3-ol, 2-phenyl-3-butyne-2-ol, 1-ethynyl-1-cyclohexanol, 2-ethynylisopropanol, and 2-ethynylbutan-2-ol; silylated acetylene alcohols such as trimethyl(3,5-dimethyl-1-hexyne-3-oxy)silane, dimethylbis(3-methyl-1-butinoxy)silane, methylvinylbis(3-methyl-1-butyne-3-oxy)silane, and [(1,1-dimethyl-2-propynyl)oxy]trimethylsilane; 2-isobutyl-1-buten-3-in, 3,5-dimethyl-3-hexen-1-in, 3-methyl-3-penten-1-in, and 3-methyl-3- Enyne compounds such as hexen-1-yine, 1-ethynylcyclohexene, 3-ethyl-3-buten-1-yine, and 3-phenyl-3-buten-1-yine; unsaturated carboxylic acid esters such as diallyl maleate, dimethyl maleate, diethyl fumarate, diallyl fumarate, bis-2-methoxy-1-methylethyl maleate, monooctyl maleate, monoisooctyl maleate, monoallyl maleate, monomethyl maleate, monoethyl fumarate, monoallyl fumarate, and 2-methoxy-1-methylethyl maleate; alkenylsiloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane; and benzotriazoles are also examples. 【0034】 The content of component (E) in this composition is not limited, but preferably it is 5 parts by mass or less, or 3 parts by mass or less, per 100 parts by mass of the total of components (A) and (B), while the lower limit is 0.001 parts by mass or more, 0.01 parts by mass or more, or 0.1 parts by mass or more. 【0035】 Furthermore, this composition may contain an organic solvent (F) to improve coating properties and handling. Examples of such (F) components include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as hexane, octane, and isoparaffin; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and isobutyl acetate; ether solvents such as diisopropyl ether and 1,4-dioxane; cyclic siloxanes with a degree of polymerization of 3 to 6, such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane; and halogenated hydrocarbons such as trichloroethylene, perchloroethylene, trifluoromethylbenzene, 1,3-bis(trifluoromethyl)benzene, and methylpentafluorobenzene. The content of component (F) is arbitrary and can be appropriately determined to adjust the film thickness when this composition is applied to a substrate. 【0036】 Furthermore, because the resulting peelable cured film has excellent physical properties and peelability, it is preferable to cure this composition by irradiation with energy rays, such as ultraviolet light or electron beams, and especially ultraviolet light. In this case, curing with ultraviolet light can be performed by ultraviolet curing alone, or by a combination of ultraviolet curing and heat curing. The curing time of this composition can be appropriately adjusted according to the curing conditions used. In order to impart good ultraviolet curability to this composition, it is preferable to further incorporate a photopolymerization initiator into this composition. This photopolymerization initiator is a component that imparts ultraviolet curability to this composition, and by combining heat curing by hydrosilylation reaction and ultraviolet curing, thermal damage to plastic film substrates with low heat resistance is reduced, and the adhesion of the resulting peelable cured film to the plastic film is improved. Furthermore, it also has the advantage of further reducing the migration of silicone. 【0037】 As the photopolymerization initiator, known compounds that generate radicals upon irradiation with ultraviolet light can be used, and can be appropriately selected from, for example, organic peroxides, carbonyl compounds, organic sulfur compounds, and azo compounds. Specifically, acetophenone, propiophenone, benzophenone, xanthol, fluoreine, benzaldehyde, anthraquinone, triphenylamine, 4-methylacetophenone, 3-pentylacetophenone, 4-methoxyacetophenone, 3-bromoacetophenone, 4-allylacetophenone, p-diacetylbenzene, 3-methoxybenzophenone, 4-methylbenzophenone, 4-chlorobenzophenone, 4,4-dimethoxybenzophenone, 4-chloro-4-benzylbenzophenone, 3-chloroxa Examples include benzoin, 3,9-dichloroxantone, 3-chloro-8-nonylxantone, benzoin, benzoin methyl ether, benzoin butyl ether, bis(4-dimethylaminophenyl) ketone, benzyl methoxyketal, 2-chlorothioxantone, diethylacetophenone, 1-hydroxycyclohexylphenyl ketone, 2-methyl[4-(methylthio)phenyl]2-morpholino-1-propanone, 2,2-dimethoxy-2-phenylacetophenone, and diethoxyacetophenone. When curing this composition with ultraviolet light, benzophenone, 4-methoxyacetophenone, 4-methylbenzophenone, diethoxyacetophenone, and 1-hydroxycyclohexylphenyl ketone are preferred, with diethoxyacetophenone and 1-hydroxycyclohexylphenyl ketone being particularly preferred. 【0038】 Such photopolymerization initiators may be used individually or in combination of two or more. The content is not particularly limited, but it is preferably in the range of 0.01 to 10 parts by mass, or 0.01 to 2.5 parts by mass, per 100 parts by mass of component (A). This is because if the content of the photopolymerization initiator is within the above range, the silicone migration properties of the peelable cured film obtained by curing this composition are improved, resulting in superior physical properties such as strength. 【0039】 Furthermore, this composition may also contain, as other optional components, adhesion promoters such as 3-glycidoxypropyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane; antioxidants such as phenolic, quinone, amine, phosphorus, phosphite, sulfur, and thioether-based antioxidants; light stabilizers such as triazole and benzophenone-based light stabilizers; flame retardants such as phosphate esters, halogens, phosphorus, and antimony-based flame retardants; surfactants such as cationic surfactants, anionic surfactants, and nonionic surfactants; and other known additives such as antistatic agents, heat stabilizers, dyes, and pigments. 【0040】 This composition can be prepared by uniformly mixing components (A) to (D), as well as components (E), (F), and other optional components. The order of addition of each component is not limited, but if the composition is not to be used immediately after preparation, it is preferable to store the mixture of components (A), (B), and (C) separately from component (D) and mix them immediately before use. Furthermore, in a composition consisting of components (A) to (D), and optionally component (F) and other components, the type and content of component (E) may be adjusted so that it does not crosslink at room temperature but crosslinks upon heating. 【0041】 <Release sheet> Next, the release sheet of the present invention will be described in detail. 【0042】 The release sheet of the present invention is characterized by having a release-cured film obtained by curing the above-mentioned silicone composition for forming a release-cured film. Specifically, this release sheet has a release-cured film on the surface of a substrate, and is used to allow an adhesive substance to adhere to the release-cured film, and then to peel off the adhesive substance with low peeling resistance. 【0043】 The substrate of this release sheet is not limited, but examples include films made of plastics such as polyester (polyethylene terephthalate, polyethylene naphthalate, etc.), polyolefins (polypropylene, polymethylpentene, etc.), polycarbonate, polyimide, and polyvinyl acetate; as well as papers such as Japanese paper, cardboard, corrugated cardboard, glassine paper, clay-coated paper, polyolefin laminated paper, polyethylene laminated paper, and synthetic paper; fabrics such as natural fiber fabric, synthetic fiber fabric, and artificial leather fabric; and other materials such as glass wool and metal foil. This film may be a single layer or a multilayer of two or more layers made of the same or different plastics. As the substrate, a plastic film, particularly a polyester film, is preferred, and more preferably a polyethylene terephthalate film, and especially preferably a biaxially oriented polyethylene terephthalate film. Polyethylene terephthalate film is less likely to generate dust during processing and use. Therefore, it can effectively prevent poor coating of adhesive substances to the release sheet caused by dust. Furthermore, by applying an antistatic treatment to polyethylene terephthalate film and using it as a base material, it is possible to prevent defects in the coating of adhesive substances. 【0044】 The thickness of the substrate of this release sheet is not limited, but is generally in the range of 10 to 300 μm, preferably in the range of 15 to 200 μm, or in the range of 20 to 125 μm. 【0045】 The method for producing the release sheet is not limited, and for example, the composition can be applied to a substrate using a known coating method such as gravure coating, bar coating, spray coating, spin coating, knife coating, roll coating, or die coating, and then cured. The thickness of the release-cured film on the substrate is not limited, but is preferably in the range of 0.01 to 3 μm or 0.03 to 1 μm. This is because if the thickness of the release-cured film is above the lower limit of the above range, the adhesive substance will peel off easily, while if it is below the upper limit of the above range, the occurrence of blocking will be suppressed when the resulting release sheet is wound into a roll. [Examples] 【0046】 The silicone composition and release sheet for forming a peelable cured film of the present invention will be described in more detail by reference to examples, but the present invention is not limited to these examples. Furthermore, the viscosity and plasticity in the examples are values ​​at 25°C, the viscosity was measured using a digital display type B rotational viscometer (Bismetron VDA2 type manufactured by Shibaura Systems Co., Ltd.) in accordance with JIS K 7117-1:1999 "Plastics - Liquid, emulsion or dispersion resins - Method for measuring apparent viscosity using a Brookfield type rotational viscometer", and the plasticity was measured in accordance with the method specified in JIS K 6249:2003 "Test methods for uncured and cured silicone rubber", when a load of 1 kgf was applied to a 4.2 g spherical sample for 3 minutes (unit: mm). 【0047】 Furthermore, the release sheets were prepared and evaluated as follows. 【0048】 <Method for manufacturing release sheets> A silicone composition for forming a peelable curing film was applied to the surface of a 38 μm thick polyester film (biaxially oriented polyester film manufactured by Mitsubishi Chemical Corporation) using a Meyer bar, at a concentration of 0.6 g / m² (solid content excluding solvent). 2 The material was applied in the specified amount. After application, the composition on the polyester film was cured by heating in a hot air circulating oven at 120°C for 30 seconds. Subsequently, the material was left to stand in air at 23°C and 60% humidity for 72 hours to produce a release sheet. 【0049】 <Peel Resistance> On the surface of the release sheet prepared as described above, TESA adhesive tape (TESA7475 tape) was attached, and the adhesive strength was 20 gf / cm². 2A load was applied and it was left standing in air at 23°C and 60% humidity for 24 hours. Then, using a tensile testing machine [Tensilon universal testing machine manufactured by A&D Company, Limited], the adhesive tape was pulled at an angle of 180 degrees and a peeling rate of 0.3 m / min, and the peeling resistance (mN / 25 mm) was measured. 【0050】 Also, a TESA adhesive tape (TESA7475 tape) was bonded to the surface of the peeling sheet prepared as described above, and a load of 20 gf / cm 2 was applied, and it was left standing in a hot air circulation oven at 70°C for 24 hours. Then, it was cooled to 23°C, and using a tensile testing machine [Tensilon universal testing machine manufactured by A&D Company, Limited], the adhesive tape was pulled at an angle of 180 degrees and a peeling rate of 0.3 m / min, and the peeling resistance (mN / 25 mm) was measured. In Tables 1 and 2, the peeling resistance values when left standing in air at 23°C and 60% humidity for 24 hours, the peeling resistance values when left standing at 70°C for 24 hours, and the difference between them were shown. 【0051】 <Residual Adhesion Rate> A No. 31B adhesive tape manufactured by Nitto Denko Corporation was bonded to the surface of the peeling sheet prepared as described above, and a load of 20 gf / cm 2 was applied, and it was left standing in a hot air circulation oven at 70°C for 20 hours. Next, the adhesive tape was peeled off, and this peeled adhesive tape was attached to a stainless steel plate, a load of 20 gf / cm 2 was applied, and it was left standing in air at 23°C and 60% humidity for 30 minutes. Then, using a tensile testing machine [Tensilon universal testing machine manufactured by A&D Company, Limited], the adhesive tape was pulled at an angle of 180 degrees and a peeling rate of 0.3 m / min, and the force required for peeling (gf1) was measured. Also, as a blank test, the above tape was bonded to a Teflon (registered trademark) sheet in the same manner as above, and the force required for peeling this adhesive tape (gf2) was measured in the same manner as above. From these values, the residual adhesion rate (%) was calculated according to the following formula. Residual Adhesion Rate (%) = (gf1 / gf2) × 100 【0052】 <Examples 1 to 4, Comparative Examples 1 to 5> A silicone composition for forming a peelable, curable film was prepared by uniformly mixing the following components to achieve the composition shown in Tables 1 and 2. In Tables 1 and 2, the content of component (D) is such that the amount of platinum in component (D) is 200 ppm by mass relative to the total amount of components (A) to (C). Also, in Tables 1 and 2, "SiH / Alkenyl" indicates the number of moles of silicon-bonded hydrogen atoms in component (C) relative to 1 mole of the total alkenyl groups in components (A) and (B). The properties of release sheets prepared using the silicone composition for forming a peelable, curable film prepared in this manner were measured, and the results are shown in Tables 1 and 2. 【0053】 (A) The following components were used as components. (a-1): Dimethylsiloxane-methylhexenylsiloxane copolymer with a viscosity exceeding 100,000 mPa·s, a plasticity of 1.15, and with both ends of the molecular chain sealed with trimethylsiloxy groups (hexenyl group content = 0.0296 mol / 100g) (a-2): Dimethylsiloxane-methylhexenylsiloxane copolymer with a viscosity exceeding 100,000 mPa·s, a plasticity of 1.15, and with both ends of the molecular chain sealed with trimethylsiloxy groups (hexenyl group content = 0.0185 mol / 100g) 【0054】 The following components were used as component (B): (b-1): Dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 5,000 mPa·s, in which both ends of the molecular chain are sealed with trimethylsiloxy groups (vinyl group content = 0.0055 mol / 100g) (b-2): Dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 40,000 mPa·s, in which both ends of the molecular chain are sealed with trimethylsiloxy groups (vinyl group content = 0.0055 mol / 100g) 【0055】 Furthermore, the following components were used for comparison of component (B). (b-3): Dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 35,000 mPa·s, in which both ends of the molecular chain are sealed with trimethylsiloxy groups (vinyl group content = 0.0185 mol / 100g) (b-4): Dimethylpolysiloxane with a viscosity of 2,000 mPa·s, in which both ends of the molecular chain are sealed with dimethylvinylsiloxy groups (vinyl group content = 0.0085 mol / 100g) (b-5): Dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 350 mPa·s, in which both ends of the molecular chain are sealed with trimethylsiloxy groups (vinyl group content = 0.0462 mol / 100g) (b-6): Dimethylpolysiloxane with a viscosity of 5,000 mPa·s, in which both ends of the molecular chain are sealed with trimethylsiloxy groups. 【0056】 The following components were used as component (C): (c-1): Methylhydrogenpolysiloxane with a viscosity of 20 mPa·s, in which both ends of the molecular chain are sealed with trimethylsiloxy groups (silicon-bonded hydrogen atom content = 1.56 mol / 100g) (c-2): Dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 55 mPa·s, in which both ends of the molecular chain are sealed with trimethylsiloxy groups (silicon atom bonded hydrogen atom content = 0.99 mol / 100g) 【0057】 The following components were used as component (D): (d-1): Platinum 1,3-divinyltetramethyldisiloxane complex in a 1,3-divinyltetramethyldisiloxane solution (platinum content 4,000 ppm) 【0058】 The following components were used as component (E): (e-1):2-methyl-3-butyne-2-ol 【0059】 The following components were used as component (F): (f-1): Toluene 【0060】 [Table 1] 【0061】 [Table 2] 【0062】 The results shown in Tables 1 and 2 indicate that when an organopolysiloxane with an alkenyl group content (based on vinyl groups) exceeding 0.0148 moles / 100g was used as component (B) (Comparative Example 1), or when an organopolysiloxane having alkenyl groups at the end of the molecular chain was used (Comparative Example 2), the peel resistance was high, and the difference between the peel resistance when left standing at 23°C and the peel resistance when left standing at 70°C was large, suggesting that the peel resistance may change over time. Furthermore, when an organopolysiloxane with a viscosity of less than 1000 mPa·s was used as component (B) (Comparative Example 3), the peel resistance at 23°C could be reduced, but the difference between the peel resistance when left standing at 23°C and the peel resistance when left standing at 70°C was large, suggesting that the peel resistance may change over time. Furthermore, when an organopolysiloxane without an alkenyl group was used as component (B) (Comparative Example 5), it was found that the peel resistance could be reduced, but the residual adhesion rate was significantly decreased. In contrast, the present invention (Examples 1-4) was found to have low peel resistance, little change in peel resistance over time, and no decrease in residual adhesion rate. [Industrial applicability] 【0063】 The silicone composition for forming a releaseable curable film of the present invention has low peel resistance, little change in peel resistance over time, and does not reduce the residual adhesion rate of adhesive substances. Therefore, it is suitable as a material for forming a releaseable curable film for manufacturing process release paper in optical components such as liquid crystal panels, plasma displays, polarizing plates, and phase difference plates, or electrical and electronic components such as printed circuit boards, ICs, transistors, and capacitors, where relatively low peel resistance is required.

Claims

[Claim 1] (A) A linear organopolysiloxane having a viscosity at 25°C exceeding 100,000 mPa·s and containing at least two C2-C12 alkenyl groups only in the side chains of the molecular chain in one molecule. (B) A linear organopolysiloxane having a viscosity of 1,000 to 100,000 mPa·s at 25°C, containing at least two C2-C12 alkenyl groups only in the side chains of the molecular chain, with an alkenyl group content of 0.0018 to 0.0148 mol / 100g [amount such that the mass ratio of component (A) to component (B) {component (A) / component (B)} is 10 / 90 to 90 / 10], (C) an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule {an amount such that the silicon-bonded hydrogen atoms in component (C) are 0.5 to 5 moles for every 1 mole of alkenyl groups in components (A) and (B)}, and (D) Catalytic amount of catalyst for hydrosilylation reaction A silicone composition for forming a peelable curable film, comprising the following: [Claim 2] (A) The silicone composition for forming a peelable curable film according to claim 1, wherein the alkenyl group in component (A) is a hexenyl group. [Claim 3] The silicone composition for forming a peelable curable film according to claim 1, wherein the mass ratio of component (A) to component (B) {component (A) / component (B)} is 40 / 60 to 80 / 20. [Claim 4] Furthermore, the silicone composition for forming a peelable curable film according to claim 1, further comprising (E) a hydrosilylation reaction inhibitor. [Claim 5] Furthermore, the silicone composition for forming a peelable curable film according to claim 1, further comprising (F) an organic solvent. [Claim 6] A release sheet having a release-cured film obtained by curing a silicone composition for forming a release-cured film according to any one of claims 1 to 5.

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