Silicone composition for forming a peelable cured film and a release sheet

Abstract

The present invention relates to a silicone composition for forming a peelable cured film, which comprises: (A) a chain polyorganosiloxane having a viscosity at 25°C exceeding 100,000 mPa·s and having at least two alkenyl groups with 2 to 12 carbon atoms only in the side chains of the molecular chain; (B) a chain polyorganosiloxane having a viscosity at 25°C of 1,000 to 100,000 mPa·s and having at least two alkenyl groups with 2 to 12 carbon atoms only in the side chains of the molecular chain, and the content of the alkenyl group being 0.0018 to 0.0148 mol / 100 g; (C) a polyorganosiloxane having at least two silicon-bonded hydrogen atoms in one molecule; and (D) a catalyst in a catalytic amount for a hydrosilylation reaction. This composition can form a peelable cured film, and the peelable cured film exhibits a relatively low peel resistance to an adhesive substance, has a small change over time, and further inhibits a decrease in the residual adhesion rate of the 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 Art

[0002] The silicone composition for forming a peelable cured film is used to form a cured film that exhibits appropriate peeling performance against an adhesive substance. As such a silicone composition for forming a peelable cured film, for example, Patent Document 1 discloses a composition containing a polyorganosiloxane having a viscosity at 25°C of 500,000 cSt or more, containing at least 0.1 mol% of methylvinylsiloxane units and having a hydroxyl group or a vinyl group at the molecular chain end, a polyorganosiloxane having a viscosity at 25°C of 10 to 100,000 cSt and having a vinyl group at the molecular chain end, a polyorganosiloxane having at least three silicon atoms bonded to hydrogen atoms in one molecule, and a catalyst for hydrosilylation reaction. Patent Document 2 discloses a composition containing a polyorganosiloxane having a viscosity at 25°C of 50 to 10,000 cps, having at least two vinyl groups in one molecule, at least one of which is located on the side chain of the molecular chain and the content of the vinyl group is 0.5 to 10 mol%, a polyorganosiloxane having a viscosity at 25°C of 100,000 cps or more and a lower vinyl group content than the above polyorganosiloxane, a polyorganosiloxane having at least two silicon atoms bonded to hydrogen atoms in one molecule, and a catalyst for hydrosilylation reaction. Patent Document 3 discloses a composition containing a polyorganosiloxane having two or more alkenyl groups having 2 to 8 carbon atoms in one molecule, a polyorganosiloxane having at least two silicon atoms bonded to hydrogen atoms in one molecule, a polyorganosiloxane having no alkenyl group and no silicon atom bonded to a hydrogen atom in one molecule, a hydrosilylation reaction inhibitor, and a catalyst for hydrosilylation reaction.

[0003] However, the composition of Patent Document 1 uses a polyorganosiloxane having a viscosity at 25°C of 10 to 100,000 cSt and having a vinyl group at the molecular chain end, and the composition of Patent Document 2 uses a polyorganosiloxane having a viscosity at 25°C of 50 to 10,000 cps and a large vinyl group content, but both have the following technical problems: it is difficult to form a peelable cured film with a low peel resistance, and the peel resistance changes over time. On the other hand, for the composition of Patent Document 3, since a polyorganosiloxane having no alkenyl group and no silicon atom bonded to a hydrogen atom in one molecule is used, although a peelable cured film with a low peel resistance can be formed, there is a technical problem of significantly reducing the residual adhesion rate of the adhesive substance.

[0004] On the other hand, Patent Document 4 discloses a composition comprising a dimeric organosiloxane having a viscosity of 500 cSt or more at 25°C in a 30 wt% toluene solution, having an alkenyl group with 4 to 8 carbon atoms in the side chain of the molecular chain, and having a hydroxyl group, an alkenyl group, or an alkyl group at the molecular chain end; a dimeric organosiloxane having a viscosity of 500 cSt or more at 25°C in a 30 wt% toluene solution, having a hydroxyl group, an alkenyl group, or an alkyl group at the molecular chain end, and having at least one alkenyl group in one molecule; a polyorganosiloxane having a viscosity of 1 to 1000 cSt at 25°C and having at least three silicon atoms bonded to hydrogen atoms; a catalyst for hydrosilylation reaction; a hydrosilylation reaction inhibitor; and an organic solvent. However, for the composition of Patent Document 4, since two high-molecular-weight polyorganosiloxanes are incorporated, there are technical problems such as high viscosity of the composition, lack of coatability, and poor handling workability (operability).

[0005] Moreover, Patent Document 5 discloses a composition comprising a polyorganosiloxane having a viscosity of 1.5 to 70 Pa·s at 25°C in a 30 wt% toluene solution and having an alkenyl group at the molecular chain end; a polyorganosiloxane having a viscosity of 0.1 to 500 Pa·s at 25°C, having an alkenyl group in the side chain of the molecular chain, and having an alkenyl group content that is 0.2 to 5 times the alkenyl group content of the polyorganosiloxane; a polyorganosiloxane having at least three silicon atoms bonded to hydrogen atoms in one molecule; a catalyst for hydrosilylation reaction; and an organic solvent. However, in the composition of Patent Document 5, although the coatability and handling workability (operability) are improved, there is a problem that the technical problem of forming a cured film with low peel resistance cannot be sufficiently solved.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 50-025644

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 61-159480

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 02-145650

[0011] Patent Document 4: Japanese Patent Application Laid-Open No. 09-125004

[0012] Patent Document 5: Japanese Patent Application Laid-Open No. 2004-190202 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] An object of the present invention is to provide a silicone composition for forming a peelable cured film, which can form a peelable cured film that exhibits a relatively low peel resistance to an adhesive substance, 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 a relatively low peel resistance to an adhesive substance, has little change over time, and further suppresses a decrease in the residual adhesion rate of the adhesive substance.

[0015] Means for solving the problems

[0016] The silicone composition for forming a peelable cured film of the present invention comprises:

[0017] (A) A linear polyorganosiloxane having a viscosity at 25 °C of more than 100,000 mPa·s and having at least two alkenyl groups having 2 to 12 carbon atoms only in the side chains of the molecular chain;

[0018] (B) A linear polyorganosiloxane having a viscosity at 25 °C of 1,000 to 100,000 mPa·s and having at least two alkenyl groups having 2 to 12 carbon atoms only in the side chains of the molecular chain, the content of the alkenyl groups being 0.0018 to 0.0148 mol / 100 g [in an amount such that the mass ratio of component (A) to component (B) {(A) / (B)} is 10 / 90 to 90 / 10];

[0019] (C) A polyorganosiloxane having at least two silicon-bonded hydrogen atoms in one molecule {in an amount such that the number of silicon-bonded hydrogen atoms in component (C) is 0.5 to 5 moles relative to 1 mole of the total alkenyl groups in components (A) and (B)}; and

[0020] (D) A catalytic amount of a catalyst for hydrosilylation reaction.

[0021] Preferably, in the present composition, the alkenyl group in component (A) is a hexenyl group.

[0022] Preferably, in the present composition, the mass ratio of component (A) to component (B) {(A) / (B)} is 40 / 60 to 80 / 20.

[0023] Preferably, the present composition further contains (E) a hydrosilylation reaction inhibitor.

[0024] Preferably, the present composition further contains (F) an organic solvent.

[0025] The release sheet of the present invention is characterized in that it has a peelable cured film formed by curing the above-described silicone composition for forming a peelable cured film.

[0026] Advantages of the invention

[0027] The silicone composition for forming a peelable cured film of the present invention has the following characteristics: it can form a peelable cured film, which exhibits a relatively low peel resistance to an adhesive substance, has a small change over time, and further suppresses a decrease in the residual adhesion rate of the adhesive substance. In addition, the release sheet of the present invention has the following characteristics: it exhibits a relatively low peel resistance to an adhesive substance, has a small change over time, and further suppresses a decrease in the residual adhesion rate of the adhesive substance. Detailed Description

[0028] <Definition of Terms>

[0029] The term "viscosity" used in this specification refers to the value at 25°C (unit: mPa·s or Pa·s) measured using a B-type rotational viscometer in accordance with the method specified in JIS K 7117-1:1999 "Plastics - Liquid, Emulsion or Dispersed Resins - Method for Measuring Apparent Viscosity Using a Brookfield-Type Rotational Viscometer".

[0030] The term "plasticity" used in this specification refers to the value (unit: mm) when a load of 1 kgf is applied to a 4.2 g spherical specimen for 3 minutes according to the method specified in JIS K 6249:2003 "Test Methods for Uncured and Cured Silicone Rubbers".

[0031] <Silicone Composition for Forming a Peelable Cured Film>

[0032] The silicone composition for forming a peelable cured film of the present invention will be described in detail.

[0033] Component (A) is a linear polyorganosiloxane having at least two alkenyl groups with 2 to 12 carbon atoms only in the side chains of the molecular chain. Examples of the alkenyl group in component (A) include vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, and preferably hexenyl. Such an alkenyl group needs to exist only in the side chain of the molecular chain and not at the end of the molecular chain. Examples of the group bonded to the silicon atom other than the alkenyl group in component (A) include alkyl groups having 1 to 12 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl; aryl groups having 6 to 12 carbon atoms such as phenyl, tolyl, and xylyl; aralkyl groups having 7 to 12 carbon atoms such as benzyl and phenethyl; fluoroalkyl groups having 3 to 12 carbon atoms 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, and preferably methyl. In addition, in component (A), within the range not impairing the object of the present invention, alkoxy groups having 1 to 3 carbon atoms such as hydroxy, methoxy, and ethoxy may be bonded to the silicon atom in a small amount.

[0034] The content of the alkenyl group in component (A) is not limited, and is preferably in the range of 0.0185 to 0.1110 mol / 100 g, or in the range of 0.0185 to 0.0739 mol / 100 g. This is because if the content of the alkenyl group in component (A) is above the lower limit of the above range, the present composition is sufficiently cured, the migration of the organosilicon component to the adhesive substance of the obtained peelable cured film is suppressed, and the decrease in the residual adhesion rate of the adhesive substance can be suppressed. On the other hand, if the content of the alkenyl group in component (A) is below the upper limit of the above range, the obtained peelable cured film has an appropriate light peeling resistance.

[0035] Component (A) is a polyorganosiloxane with a high degree of polymerization having a viscosity exceeding 100,000 mPa·s at 25°C. If the degree of polymerization increases, it becomes a raw rubber-like state where its viscosity can no longer be measured by a rotational viscometer. In the case where component (A) is in a raw rubber-like state, its plasticity is preferably 3.0 mm or less, or 0.5 to 3.0 mm.

[0036] The molecular structure of component (A) is substantially linear, but a part of its molecular chain may be branched. Examples of such component (A) include a dimethylsiloxane-methylhexenylsiloxane copolymer capped at both ends of the molecular chain with trimethylsiloxy groups, and a dimethylsiloxane-methylhexenylsiloxane copolymer capped at the end of the molecular chain substantially with trimethylsiloxy groups and capped at the end of a part of the molecular chain with dimethylhydroxysiloxy groups.

[0037] (Component (B) is a linear polyorganosiloxane having at least two alkenyl groups with 2 to 12 carbon atoms only in the side chain of the molecular chain. As the alkenyl group in component (B), the same alkenyl groups as those in component (A) can be exemplified, and vinyl is preferred. Such alkenyl groups need to exist only in the side chain of the molecular chain and not at the end of the molecular chain. As the groups bonded to the silicon atom other than the alkenyl group in component (B), the same groups as those in component (A) can be exemplified, and methyl is preferred. In addition, in component (B), within the range not impairing the object of the present invention, alkoxy groups having 1 to 3 carbon atoms such as hydroxyl group, methoxy group, and ethoxy group can also be bonded to the silicon atom in a small amount.)

[0038] (The viscosity of component (B) at 25 °C is in the range of 1000 to 100000 mPa·s, preferably in the range of 1000 to 70000 mPa·s, 2000 to 50000 mPa·s, or 3000 to 50000 mPa·s. This is because if the viscosity of component (B) is above the lower limit of the above range, the curability of the present composition can be improved. On the other hand, if the viscosity of component (B) is below the upper limit of the above range, a cured film with a light peel resistance and a small change over time can be formed.)

[0039] (The content of the alkenyl group in component (B) is in the range of 0.0018 to 0.0148 mol / 100 g. Preferably, when the viscosity is 1000 mPa·s or more and 10000 mPa·s or less, the content of the alkenyl group in component (B) is in the range of 0.0026 to 0.0148 mol / 100 g. When the viscosity exceeds 10000 mPa·s and is 100000 mPa·s or less, the content of the alkenyl group in component (B) is in the range of 0.0018 to 0.0111 mol / 100 g, or when the viscosity is 1000 mPa·s or more and 10000 mPa·s or less, the content of the alkenyl group in component (B) is in the range of 0.0037 to 0.0148 mol / 100 g. When the viscosity exceeds 10000 mPa·s and is 100000 mPa·s or less, the content of the alkenyl group in component (B) is in the range of 0.0018 to 0.0074 mol / 100 g. This is because if the content of the alkenyl group in component (B) is above the lower limit of the above range, the present composition is sufficiently cured, the migration of the organosilicon component to the adhesive substance of the obtained peelable cured film is inhibited, and the reduction of the residual adhesion rate of the adhesive substance can be inhibited. On the other hand, if the content of the alkenyl group in component (B) is below the upper limit of the above range, the obtained peelable cured film can have an appropriate light peel resistance and a small change over time.)

[0040] It should be noted that the reason why the preferred content of the alkenyl group varies depending on the viscosity of the component (B) is as follows. When the viscosity of the component (B) is low, the molecular weight becomes low. Therefore, even with the same content of the alkenyl group, the number of alkenyl groups in one molecule becomes small. The reactivity of such a component (B) is low, so the migration of the silicone component to the adhesive substance of the peelable cured film is likely to occur. For this reason, in order to suppress this situation, it is preferable to increase the content of the alkenyl group in the component (B). On the other hand, when the viscosity of the component (B) is high, the molecular weight becomes high. Therefore, even with the same content of the alkenyl group, the number of alkenyl groups in one molecule becomes large. The reactivity of such a component (B) is high, so it rarely exists locally on the surface of the peelable cured film. Usually, unreacted silicon-bonded hydrogen atoms may remain on the surface of the peelable cured film, or they react with moisture to form silicon-bonded hydroxyl groups, which is considered to be the reason for the increase in the interaction between the peelable cured film and the adhesive substance over time. For this reason, in order to suppress the remaining of the silicon atom-bonded hydrogen atoms on the surface of the peelable cured film, it is necessary to promote the local existence of the component (B) on the cured film surface and create a difference in the relative reactivity with the component (A). Therefore, when the viscosity of the component (B) is high, it is preferable to reduce the content of the alkenyl group in the component (B).

[0041] In this composition, the content of the component (B) is an amount such that the mass ratio of the component (A) to the 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 the component (A) to the component (B) {(A) component / (B) component} is above the lower limit of the above range, the curability of this composition can be improved, especially the curability at a low temperature of about 100 °C, and the strength of the obtained cured film can be improved. On the other hand, if the mass ratio of the component (A) to the component (B) {(A) component / (B) component} is below the upper limit of the above range, a peelable cured film with a lower peel resistance can be formed. In this composition, since the component (B) is blended with the component (A) at a specific ratio, a peelable cured film with a reduced peel resistance and a suppressed residual adhesion rate of the adhesive substance can be formed.

[0042] (C) component is a polyorganosiloxane having at least two silicon-bonded hydrogen atoms in one molecule and is a crosslinking agent for this composition. The bonding position of the silicon-bonded hydrogen atom in the (C) component is not limited, and examples thereof include the molecular chain end and / or the molecular chain side chain. Examples of the group bonded to the silicon atom other than the hydrogen atom in the (C) component include: alkyl groups having 1 to 12 carbon atoms such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl; aryl groups having 6 to 12 carbon atoms such as phenyl, tolyl, and xylyl; aralkyl groups having 7 to 12 carbon atoms such as benzyl and phenethyl; and fluoroalkyl groups having 3 to 12 carbon atoms 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 being preferred. In addition, in the (C) component, within the range not impairing the object of the present invention, alkoxy groups having 1 to 3 carbon atoms such as hydroxyl group, methoxy group, and ethoxy group may be bonded to the silicon atom in a small amount.

[0043] (C) The viscosity of the component at 25 °C is not limited, and it is preferably in the range of 1 to 1000 mPa·s, or in the range of 5 to 500 mPa·s. This is because if the viscosity of the (C) component is above the lower limit of the above range, the volatilization of this component from this composition is suppressed and the composition is stable. On the other hand, if the viscosity of the (C) component is below the upper limit of the above range, the curability of this composition is promoted.

[0044] The molecular structure of such a (C) component is not limited, and examples thereof include: linear, linearly branched with partial branches, branched, cyclic, or resinous. Examples of such a (C) component include: dimethylsiloxane-methylhydrogensiloxane copolymer capped with trimethylsilanoxy groups at both ends of the molecular chain, dimethylsiloxane-methylhydrogensiloxane copolymer capped with dimethylhydrogensilanoxy groups at both ends of the molecular chain, dimethylpolysiloxane capped with dimethylhydrogensilanoxy groups at both ends of the molecular chain, methylhydrogenpolysiloxane capped with trimethylsilanoxy groups at both ends of the molecular chain, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane-dimethylsiloxane copolymer, and copolymers composed of siloxane units represented by the formula: H(CH3)2SiO 1 / 2 and siloxane units represented by the formula: SiO 4 / 2 and copolymers composed of siloxane units represented by the formula: (CH3)3SiO 1 / 2 and siloxane units represented by the formula: H(CH3)2SiO 1 / 2 and siloxane units represented by the formula: SiO 4 / 2

[0045] ​In this composition, the content of component (C) is an amount such that, relative to 1 mole of the total of the alkenyl groups in components (A) and (B), the silicon atom-bonded hydrogen atoms in component (C) are in the range of 0.5 to 5 moles, preferably in the range of 0.6 to 3.0, or in the range of 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 cures sufficiently. On the other hand, if the content of component (C) is below the upper limit of the above range, the resulting peelable cured film has a moderate light peel resistance and its change over time is also small.

[0046] Component (D) is a hydrosilylation reaction catalyst for promoting the hydrosilylation reaction of this composition. Examples of such component (D) include: platinum-based catalysts, palladium-based catalysts, rhodium-based catalysts, with platinum-based catalysts being preferred. Examples of this platinum-based catalyst include: chloroplatinic acid, chloroplatinic acid hexahydrate, platinum dichloride, alcohol-modified chloroplatinic acid, platinum olefin complexes, platinum carbonyl complexes, platinum alkenylsiloxane complexes, platinum diketone complexes. In addition, in the platinum alkenylsiloxane complex, examples of the alkenylsiloxane include: 1,3-divinyltetramethyldisiloxane, 1,1,3,3-tetravinyldimethyldisiloxane, dimethylvinylsilanyloxy-terminated methyl(3,3,3-trifluoropropyl)siloxane oligomer.

[0047] The content of component (D) is the amount of catalyst for promoting the hydrosilylation reaction of this composition. Specifically, relative to the total amount of components (A) to (C), the catalyst metal in this component is in the range of 0.1 to 1000 ppm, in the range of 0.1 to 500 ppm, in the range of 5 to 500 ppm, in the range of 0.1 to 300 ppm, or in the range of 5 to 300 ppm in terms of mass unit. This is because, if the content of component (D) is above the lower limit of the above range, the curing of the composition is promoted. On the other hand, if the content of component (D) is below the upper limit of the above range, problems such as coloring are less likely to occur in the resulting peelable cured film.

[0048] In addition, in this composition, an (E) hydrosilylation reaction inhibitor for adjusting the curing rate may also be contained. Examples of such (E) components include: alkynols such as 2-methyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol, 3-methyl-1-pentyn-3-ol, 2-phenyl-3-butyn-2-ol, 1-ethynyl-1-cyclohexanol, 2-ethynyl isopropyl alcohol, 2-ethynyl butane-2-ol; silylated acetylene alcohols such as trimethyl(3,5-dimethyl-1-hexyn-3-oxy)silane, dimethyl bis(3-methyl-1-butyn-oxy)silane, methyl vinyl bis(3-methyl-1-butyn-3-oxy)silane, and [(1,1-dimethyl-2-propynyl)oxy]trimethylsilane; enyne compounds such as 2-isobutyl-1-butene-3-yne, 3,5-dimethyl-3-hexene-1-yne, 3-methyl-3-pentene-1-yne, 3-methyl-3-hexene-1-yne, 1-ethynylcyclohexene, 3-ethyl-3-butene-1-yne, and 3-phenyl-3-butene-1-yne; 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; vinyl group-containing siloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane; and benzotriazole.

[0049] The content of the (E) component in this composition is not limited, and is preferably 5 parts by mass or less, or 3 parts by mass or less, relative to 100 parts by mass in total of the (A) component and the (B) component. On the other hand, the lower limit of the content of the (E) component is 0.001 parts by mass or more, 0.01 parts by mass or more, or 0.1 parts by mass or more.

[0050] In addition, in this composition, an (F) organic solvent for improving coatability and handling workability (operability) may also be contained. 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 having 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 the (F) component is arbitrary and can be appropriately determined in order to adjust the film thickness when applying this composition to a substrate.

[0051] Moreover, the obtained peelable cured film has excellent physical properties and peelability. Therefore, it is preferable to cure this composition by irradiating energy rays, such as ultraviolet rays and electron beams, particularly ultraviolet rays. In this case, curing with ultraviolet rays can be carried out only by ultraviolet curing or by combining 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 photoinitiator into this composition. This photoinitiator is a component that imparts ultraviolet curability to this composition and has the following advantages: by combining heat curing based on hydrosilylation reaction and ultraviolet curing, heat-induced damage to a plastic film substrate with low heat resistance can be reduced, and the adhesion of the obtained peelable cured film to the plastic film is improved. Moreover, it also has the advantage of being able to further reduce the migration of silicone.

[0052] As this photoinitiator, known compounds that generate free radicals by irradiation with ultraviolet rays can be used. For example, they can be appropriately selected and used from organic peroxides, carbonyl compounds, organic sulfur compounds, azo compounds, etc. Specifically, examples include: acetophenone, propiophenone, benzophenone, xanthol, fluorene, 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-chloroxanthone, 3,9-dichloroxanthone, 3-chloro-8-nonyloxanthone, benzoin, benzoin methyl ether, benzoin butyl ether, bis(4-dimethylaminophenyl) ketone, benzyl methyl ketal, 2-chlorothioxanthone, diethylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl [4-(methylthio)phenyl] 2-morpholin-1-one, 2,2-dimethoxy-2-phenylacetophenone, and diethoxyacetophenone. When curing this composition with ultraviolet rays, benzophenone, 4-methoxyacetophenone, 4-methylbenzophenone, diethoxyacetophenone, and 1-hydroxycyclohexyl phenyl ketone are preferable, and diethoxyacetophenone and 1-hydroxycyclohexyl phenyl ketone are particularly preferable.

[0053] Such a photoinitiator can be used alone or in combination of two or more. Its content is not particularly limited, and it is preferably in the range of 0.01 to 10 parts by mass, or in the range of 0.01 to 2.5 parts by mass, relative to 100 parts by mass of the component (A). This is because when the content of the photoinitiator is within the above range, the migration of silicone in the peelable cured film obtained by curing this composition is improved, and a peelable cured film having excellent physical properties such as strength is obtained.

[0054] Moreover, in this composition, as other optional components, it may also contain: adhesion promoters such as 3-glycidoxypropyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane; antioxidants such as phenolic, quinone-based, amine-based, phosphorus-based, phosphate-based, sulfur-based, and thioether-based antioxidants; light stabilizers such as triazole-based and benzophenone-based light stabilizers; flame retardants such as phosphate-based, halogen-based, phosphorus-based, and antimony-based flame retardants; surfactants such as cationic surfactants, anionic surfactants, and nonionic surfactants; and known additives such as antistatic agents, heat-resistant agents, dyes, and pigments.

[0055] This composition can be prepared by uniformly mixing component (A) to component (D), further component (E), component (F), and other optional components. The addition order of each component is not limited. When this composition is not used immediately after preparation, it is preferable to store the mixture formed by mixing component (A), component (B), and component (C) and component (D) separately, and mix the two immediately before use. In addition, in a composition containing component (A) to component (D), any component (F), and other components, it is also possible to achieve non-crosslinking at room temperature and crosslinking by heating by adjusting the type and content of component (E).

[0056] <Release sheet>

[0057] Next, the release sheet of the present invention will be described in detail.

[0058] The release sheet of the present invention is characterized in that it has a release cured film formed by curing the above-mentioned silicone composition for forming a release cured film. Specifically, this release sheet is for the following purposes: having a release cured film on the surface of a substrate, an adhesive substance adheres to this release cured film, and then the adhesive substance is peeled off with a light peeling resistance.

[0059] The base material of this release sheet is not limited. For example, it can include: films formed of plastics such as polyethylene terephthalate, polyethylene naphthalate, etc.; polyolefins such as polypropylene, poly-4-methyl-1-pentene; polycarbonate; polyimide; and polyvinyl acetate; as well as papers such as Japanese paper, paperboard, corrugated paper, cellophane, clay-coated paper, polyolefin-laminated paper, polyethylene-laminated paper, synthetic paper; cloths such as natural fiber cloth, synthetic fiber cloth, artificial leather cloth; and glass wool, metal foil. The film can be single-layered or composed of two or more layers containing the same or different plastics. As this base material, a plastic film is preferred, a polyester film is particularly preferred, polyethylene terephthalate film is further preferred, and biaxially oriented polyethylene terephthalate film is particularly preferred. Polyethylene terephthalate film is not likely to generate dust, etc. during processing or use. Therefore, it can effectively prevent poor coating of the adhesive substance due to dust, etc. In addition, by subjecting the polyethylene terephthalate film to an antistatic treatment and using it as the base material, the occurrence of poor coating of the adhesive substance, etc. can be prevented.

[0060] The thickness of the base material of this release sheet is not limited, usually 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.

[0061] The method for producing this release sheet is not limited. For example, the following methods can be cited: using well-known coating methods such as gravure coating, rod coating, spraying, spin coating, knife coating, roll coating, die coating, etc. to coat this composition on the base material, and then curing the composition. The thickness of the release-curing film on the base material is not limited, preferably in the range of 0.01 to 3 μm, or in the range of 0.03 to 1 μm. This is because if the thickness of the release-curing film is above the lower limit of the above range, the adhesive substance will be easily peeled off. On the other hand, if the thickness of the release-curing film is below the upper limit of the above range, the occurrence of adhesion can be suppressed when the obtained release sheet is wound into a roll.

[0062] Examples

[0063] The silicone composition for forming a peelable cured film and the release sheet of the present invention will be further described in detail by way of examples, but the present invention is not limited to these examples. In addition, the viscosity and plasticity in the examples are the values at 25 °C. The viscosity is measured using a digital display B-type rotational viscometer (VISMETRON VDA2 type manufactured by Shibaura Systems Co., Ltd.) in accordance with the method specified in JIS K 7117-1:1999 "Plastics - Liquid, Emulsion or Dispersed Resins - Method for Measuring Apparent Viscosity Using a Brookfield-Type Rotational Viscometer". The plasticity is the value (unit: mm) when a load of 1 kgf is applied to a 4.2 g spherical specimen for 3 minutes in accordance with the method specified in JIS K 6249:2003 "Test Methods for Uncured and Cured Silicone Rubbers".

[0064] In addition, the production and evaluation of the release sheet are carried out as follows.

[0065] <Method for Producing Release Sheet>

[0066] The silicone composition for forming a peelable cured film was applied to the surface of a 38 μm thick polyester film (biaxially stretched polyester film manufactured by Mitsubishi Chemical Corporation) in an amount of 0.6 g / m² in terms of the solid content after removing the solvent using a Mayer bar. After coating, the composition on the polyester film was cured by heating in a hot air circulation oven at 120 °C for 30 seconds. Then, it was left standing in air at 23 °C and 60% humidity for 72 hours to produce a release sheet. 2 After coating, the composition on the polyester film was cured by heating in a hot air circulation oven at 120 °C for 30 seconds. Then, it was left standing in air at 23 °C and 60% humidity for 72 hours to produce a release sheet.

[0067] <Peel Resistance>

[0068] A tape (TESA7475 tape) manufactured by TESA was adhered to the surface of the release sheet produced as described above, and a load of 20 gf / cm² 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 tape was stretched under the conditions of an angle of 180 degrees and a peeling speed of 0.3 m / minute, and the peel resistance (mN / 25 mm) was measured. 2 A tape (TESA7475 tape) manufactured by TESA was adhered to the surface of the release sheet produced as described above, and a load of 20 gf / cm² 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 tape was stretched under the conditions of an angle of 180 degrees and a peeling speed of 0.3 m / minute, and the peel resistance (mN / 25 mm) was measured.

[0069] In addition, a tape (TESA7475 tape) manufactured by TESA was adhered to the surface of the release sheet produced as described above, and a load of 20 gf / cm² was applied 2The load is left standing in a hot air circulation oven at 70°C for 24 hours. Then, it is cooled to 23°C, and using a tensile testing machine [TENSILON universal testing machine manufactured by A&D Company, Limited], the tape is stretched under the conditions of an angle of 180 degrees and a peeling speed of 0.3 m / minute to measure the peeling resistance (mN / 25 mm). It should be noted that in Tables 1 and 2, the peeling resistance values when left standing in air at 23°C and a humidity of 60% for 24 hours, the peeling resistance values when left standing at 70°C for 24 hours, and the differences between them are shown.

[0070] <Residual adhesion rate>

[0071] The tape No. 31B manufactured by Nitto Denko Corporation is adhered to the surface of the peeling sheet produced as described above, and a load of 20 gf / cm 2 is applied, and it is left standing in a hot air circulation oven at 70°C for 20 hours. Then, the tape is peeled off, and the peeled tape is adhered to a stainless steel plate, a load of 20 g / cm 2 is applied, and it is left standing in air at 23°C and a humidity of 60% for 30 minutes. Then, using a tensile testing machine [TENSILON universal testing machine manufactured by A&D Company, Limited], the tape is stretched under the conditions of an angle of 180 degrees and a peeling speed of 0.3 m / minute to measure the force required for peeling (gf1). In addition, as a blank test, the above tape is adhered to a TEFLON (registered trademark) sheet in the same manner as above, and the force required for peeling of this tape is measured in the same manner as above (gf2). Based on these values, the residual adhesion rate (%) is calculated according to the following formula.

[0072] Residual adhesion rate (%) = (gf1 / gf2) × 100

[0073] <Examples 1 to 4, Comparative Examples 1 to 5>

[0074] The following components are uniformly mixed so as to have the compositions shown in Tables 1 and 2 to prepare a silicone composition for forming a peelable cured film. It should be noted that in Tables 1 and 2, the content of component (D) is such that the platinum in component (D) is 200 ppm in terms of mass unit relative to the total amount of components (A) to (C). In addition, "SiH / vinyl" in Tables 1 and 2 represents the number of moles of silicon atom-bonded hydrogen atoms in component (C) relative to 1 mole of the total of vinyl groups in components (A) and (B). The characteristics of the peeling sheet produced using the silicone composition for forming a peelable cured film prepared in this way are measured, and these results are shown in Table 1 and Table 2.

[0075] As component (A), the following components are used.

[0076] (a-1): A dimethylsiloxane-methylhexenylsiloxane copolymer with a viscosity exceeding 100,000 mPa·s, a plasticity of 1.15, and the two ends of the molecular chain capped with trimethylsilyloxy groups (hexenyl content = 0.0296 mol / 100 g).

[0077] (a-2): A dimethylsiloxane-methylhexenylsiloxane copolymer with a viscosity exceeding 100,000 mPa·s, a plasticity of 1.15, and the two ends of the molecular chain capped with trimethylsilyloxy groups (hexenyl content = 0.0185 mol / 100 g).

[0078] As component (B), the following components are used.

[0079] (b-1): A dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 5000 mPa·s and the two ends of the molecular chain capped with trimethylsilyloxy groups (vinyl content = 0.0055 mol / 100 g).

[0080] (b-2): A dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 40,000 mPa·s and the two ends of the molecular chain capped with trimethylsilyloxy groups (vinyl content = 0.0055 mol / 100 g).

[0081] In addition, for comparison of component (B), the following components are used.

[0082] (b-3): A dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 35,000 mPa·s and the two ends of the molecular chain capped with trimethylsilyloxy groups (vinyl content = 0.0185 mol / 100 g).

[0083] (b-4): A dimethylpolysiloxane with a viscosity of 2000 mPa·s and the two ends of the molecular chain capped with dimethylethenylsiloxy groups (vinyl content = 0.0085 mol / 100 g).

[0084] (b-5): A dimethylsiloxane-methylvinylsiloxane copolymer with a viscosity of 350 mPa·s and the two ends of the molecular chain capped with trimethylsilyloxy groups (vinyl content = 0.0462 mol / 100 g).

[0085] (b-6): A dimethylpolysiloxane with a viscosity of 5000 mPa·s and the two ends of the molecular chain capped with trimethylsilyloxy groups.

[0086] As component (C), the following components are used.

[0087] (c-1): Methylhydrogenpolysiloxane with a viscosity of 20 mPa·s, capped at both ends of the molecular chain with trimethylsiloxy groups (content of silicon atoms bonded to hydrogen atoms = 1.56 moles / 100 g).

[0088] (c-2): Dimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 55 mPa·s, capped at both ends of the molecular chain with trimethylsiloxy groups (content of silicon atoms bonded to hydrogen atoms = 0.99 moles / 100 g).

[0089] As component (D), the following components are used.

[0090] (d-1): 1,3-Divinyltetramethyldisiloxane solution of platinum's 1,3-divinyltetramethyldisiloxane complex (platinum content 4000 ppm).

[0091] As component (E), the following components are used.

[0092] (e-1): 2-Methyl-3-butyn-2-ol.

[0093] As component (F), the following components are used.

[0094] (f-1): Toluene.

[0095] [Table 1]

[0096]

[0097] [Table 2]

[0098]

[0099] As can be seen from the results shown in Tables 1 and 2, as the component (B), in the case of using a polyorganosiloxane having an alkenyl content in terms of vinyl exceeding 0.0148 mol / 100 g (Comparative Example 1) or in the case of using a polyorganosiloxane having an alkenyl group at the molecular chain end (Comparative Example 2), the peel resistance is large, and the difference in peel resistance between the case of standing at 23°C and the case of standing at 70°C is large. Therefore, there is a possibility of time-dependent change in peel resistance. Further, it can be seen that as the component (B), in the case of using a polyorganosiloxane having a viscosity of less than 1000 mPa·s (Comparative Example 3), the peel resistance at 23°C can be reduced, but the difference in peel resistance between the case of standing at 23°C and the case of standing at 70°C is large. Therefore, there is a possibility of time-dependent change in peel resistance. Further, it can be seen that as the component (B), in the case of using a polyorganosiloxane having no alkenyl group (Comparative Example 5), the peel resistance can be reduced, but the residual adhesion rate is significantly decreased. In contrast, it can be seen that in the present invention (Examples 1 to 4), the peel resistance is small, the change in peel resistance over time is small, and the residual adhesion rate is not decreased.

[0100] Industrial applicability

[0101] The silicone composition for forming a peelable cured film of the present invention has a low peel resistance, a small change in peel resistance over time, and does not reduce the residual adhesion rate of the adhesive substance. Therefore, it is suitable as a material for forming a peelable cured film, which is used for manufacturing process release paper in the manufacturing processes of optical components such as liquid crystal panels, plasma displays, polarizing plates, and retardation plates that require a relatively low peel resistance, or electrical / electronic parts such as printed circuit boards, ICs, transistors, and capacitors.

Claims

1. A silicone composition for forming a peelable cured film, comprising: A: A linear polyorganosiloxane having a viscosity at 25 °C exceeding 100,000 mPa·s and having at least two alkenyl groups with 2 to 12 carbon atoms only in the side chains of the molecular chain in one molecule; B: A linear polyorganosiloxane having a viscosity at 25 °C of 1,000 to 100,000 mPa·s and having at least two alkenyl groups with 2 to 12 carbon atoms only in the side chains of the molecular chain, the content of the alkenyl groups being 0.0018 to 0.0148 mol / 100 g, and the mass ratio of component A to component B, i.e., A component / B component, being in an amount of 10 / 90 to 90 / 10; C: A polyorganosiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and the amount of silicon-bonded hydrogen atoms in component C being 0.5 to 5 moles relative to 1 mole of the total alkenyl groups in components A and B; and D: A catalytic amount of a catalyst for hydrosilylation reaction.

2. The silicone composition for forming a peelable cured film according to claim 1, wherein the alkenyl group in component A is a hexenyl group.

3. The silicone composition for forming a peelable cured film according to claim 1, wherein the mass ratio of component A to component B, i.e., A component / B component, is 40 / 60 to 80 / 20.

4. The silicone composition for forming a peelable cured film according to claim 1, wherein the silicone composition for forming a peelable cured film further contains E, a hydrosilylation reaction inhibitor.

5. The silicone composition for forming a peelable cured film according to claim 1, wherein the silicone composition for forming a peelable cured film further contains F, an organic solvent.

6. A release sheet having a peelable cured film formed by curing the silicone composition for forming a peelable cured film according to any one of claims 1 to 5.

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