DESCRIPTION

SOLVENT-BASED RELEASE COATING-FORMING ORGANOPOLYSILOXANE COMPOSITION AND RELEASE FILM OR SHEET

Technical Field

[0001] The present invention relates to a release coating-forming organopolysiloxane composition and more particularly relates to a solvent-based release coating-forming organopolysiloxane composition that forms a cured coating layer that exhibits an extremely good release performance versus tacky or adhesive materials without causing a decline in the adhesiveness thereof, that exhibits excellent curing properties and a light release force, and that exhibits little silicone migration to the reverse surface from the coating layer. The present invention further relates to a release film or sheet.

Background Art [0002] As an well-known method for obtaining material that exhibits releasability from tacky or adhesive materials, a cured release coating-forming silicone composition is coated on the surface of a film or sheet substrate (e.g., paper, laminated paper, synthetic resin film, metal foil, and so forth) and a cured coating layer is then formed by the, application of heat. The cured release coating-forming silicone composition used in this method can, as is known, take the form of a silicone composition that has alkenyl-functional organopolysiloxane and organohydrogenpolysiloxane as its base components and that cures by an addition reaction in the presence of a platinum-type catalyst. In order to improve the performance of such a silicone composition, cured release coating-forming silicone compositions have been introduced that contain, in addition to the aforementioned components, alkenyl-free organopolysiloxane, for example, a dimethylsiloxane gum or a dimethylsiloxane- methylphenylsiloxane copolymer (for example, Patent References 1 to 3).

[0003] With the goal, on the other hand, of improving the silicone migration to the reverse surface from the release surface, Patent Reference 4 provides a solvent-based cured release coating-forming silicone composition comprising hexenyl-functional organopolysiloxane having a high degree of polymerization, organohydrogenpolysiloxane, platinum-type catalyst, and organic solvent.

[0004] In addition, with the goal of providing a release coating for which the post-cure release resistance value exhibits a large dependence on the speed in the case of high-speed peeling, Patent Reference 5 provides a solventless cured release coating-forming silicone composition afforded by incorporating organopolysiloxane having silicon-bonded hydrogen at both molecular chain terminals in a solventless cured release coating-forming silicone composition that is based on a relatively low viscosity alkenyl-functional organopolysiloxane.

[0005] These compositions, however, have exhibited some drawbacks such as an impairment in the adhesiveness of the tacky or adhesive material and/or an impaired suitability for printing by the reverse surface from the coating due to silicone migration, and are not always satisfactory depending on the particular application. In addition, the cured release coating layers yielded by the cure of these compositions exhibit a large release force, and a particular problem has been their inadequate capacity for light release when peeling is carried out at low speeds (speed — 0.3 m/minute).

[0006] Moreover, the preceding references describe only cured release coating-forming silicone compositions that cure by the application of heat, and they do not teach the ability to realize a reduction in the release force, which is a release property different from the silicone migration behavior and different from the speed dependence of the release resistance value.

[0007] Patent References:

[Patent Reference 1] JP 50-025644 A (JP 53-028943 B) [Patent Reference 2] JP 02-145650 A (JP 07-091471 B) [Patent Reference 3] JP 60-133051 A (JP 03-052498 B) [Patent Reference 4] JP 09-125004 A [Patent Reference 5] JP 2001-335747 A

Disclosure of Invention

[0008] Problems to Be Solved by the Invention:

The present invention was pursued in order to solve the problems cited above. Thus, an object of the present invention is to provide a solvent-based cured release coating-forming silicone composition that forms a cured coating layer that exhibits excellent release properties without lowering the adhesiveness of the tacky or adhesive material and that exhibits little silicone migration to the reverse surface from the coating layer. A further object of the present invention is to provide a solvent-based cured release coating-forming silicone composition that forms a cured coating layer that in particular exhibits an excellent light releasability when peeled at low speed (speed = 0.3 m/minute).

[0009] Means Solving the Problems:

The objects cited above are achieved by

"[1] A solvent-based release coating-forming organopolysiloxane composition comprising (A) 100 weight parts of organopolysiloxane that has at least two alkenyl groups per molecule,

(B) 0.5 to 100 weight parts of organohydrogenpolysiloxane that has a viscosity at 25°C of 1 to 1,000 mPa • s and that has in each molecule at least three silicon-bonded hydrogen atoms bonded in side-chain position on the molecular chain, (C) 1 to 120 weight parts of straight-chain organohydrogenpolysiloxane that has a viscosity at 25°C of 2.5 to 2,000 mPa • s and that has silicon-bonded hydrogen at both molecular chain terminals,

(D) a platinum-type catalyst in a catalyst quantity, and

(E) 10 to 2,000 weight parts of organic solvent.

[2] The solvent-based release coating-forming organopolysiloxane composition according to [1], which further comprises

(F) 0.01 to 2.5 weight parts of photopolymerization initiator.

[3] The solvent-based release coating-forming organopolysiloxane composition according to [1], wherein component (C) is the straight-chain organohydrogenpolysiloxane represented by the following structural formula (1):

(in the formula, R ¹ is Cl-IO monovalent hydrocarbyl group or monovalent halohydrocarbyl group that lacks an aliphatically unsaturated bond and n is a number that provides a viscosity at 25°C of 2.5 to 500 mPa • s).

[4] The solvent-based release coating-forming organopolysiloxane composition according to [1], characterized in that the 30 weight% toluene solution of component (A) has a viscosity at 25°C of 1,000 to 100,000 mPa • s.

[5] The solvent-based release coating-forming organopolysiloxane composition according to [1] or [4], characterized in that component (A) is organopolysiloxane that contains at least two alkenyl groups in each molecule and that is represented by the following structural formula (2):

.2 .

(in the formula, each R is independently selected from the group consisting of the hydroxyl group, alkenyl group, unsubstituted alkyl group, and substituted alkyl group,

2 wherein at least two of the total R population are alkenyl groups; m and p are positive integers that satisfy 0.90 < m/(m + p) < 1.0 and 0.0 < p/(m + p) < 0.10; and (m + p) has a value such that the 30 weight% toluene solution of component (A) has a viscosity at 25°C of 1,000 to 100,000 mPa • s).

[6] The solvent-based release coating-forming organopolysiloxane composition according to any of [1], [4], and[5], characterized in that component (A) is organopolysiloxane that has at least two hexenyl groups in each molecule.

[7] A release film or sheet comprising a film substrate or a sheet substrate having a release coating layer formed thereon, wherein the release coating layer is a cured material from a solvent-based release coating-forming organopolysiloxane composition according to any of [1] to [6].

[8] A release film or sheet comprising a film substrate or sheet substrate having a release coating layer formed thereon, wherein the release coating layer is provided by curing a solvent-based release coating-forming organopolysiloxane composition according to [2] by heat and exposure to ultraviolet radiation.."

[0010] Effects of the Invention:

The present invention can provide a solvent-based cured release coating-forming silicone composition that forms a cured coating layer that exhibits excellent release properties without lowering the adhesiveness of the tacky or adhesive material and that exhibits little silicone migration to the reverse surface from the coating layer. The present invention can also provide a solvent-based cured release coating-forming silicone composition that forms a cured coating layer that in particular provides an excellent light release property when peeled at low speed (speed = 0.3 m/minute).

[0011] Best Mode for Carrying Out the Invention: The solvent-based cured release coating-forming silicone composition of the present invention characteristically comprises the following components (A) to (E).

[0012] (A) 100 weight parts of organopolysiloxane that has at least two alkenyl groups per molecule, (B) 0.5 to 100 weight parts of organohydrogenpolysiloxane that has a viscosity at 25°C of 1 to 1,000 mPa- s and that has in each molecule at least three silicon-bonded hydrogen atoms bonded in side-chain position on the molecular chain,

(C) 1 to 120 weight parts of straight-chain organohydrogenpolysiloxane that has a viscosity at 25°C of 2.5 to 2,000 mPa- s and that has silicon-bonded hydrogen at both molecular chain terminals,

(D) a platinum-type catalyst in a catalyst quantity, and (E) 10 to 2,000 weight parts of organic solvent.

[0013] The solvent-based cured release coating-forming silicone composition of the present invention may optionally also contain, in addition to the above-cited components (A) to (E), the component (F) and/or component (G) described below. Thus, a photopolymerization initiator (F) may optionally be incorporated in an amount that provides 0.01 to 2.5 weight parts per 100 weight parts component (A) and an addition reaction inhibitor (G) may be incorporated in an amount that provides 0.001 to 5 weight parts per 100 weight parts component (A).

[0014] Components (A) to (G) will be discussed in detail at first, while providing preferred embodiments thereof.

[0015] Component (A) is the base component of the composition of the present invention and must be an organopolysiloxane that contains at least two alkenyl groups in each molecule. Through the hydrosilylation reaction of the alkenyl groups in component (A) with the silicon-bonded hydrogen radicals in components (B) and (C), the composition of the present invention forms a cured coating layer that exhibits excellent release properties and little silicone migration to the reverse side from the coating layer, and does so without reducing the adhesiveness of the tacky or adhesive material.

[0016] The alkenyl group in component (A) may be bonded in molecular chain terminal position or side-chain position. In addition, component (A) may be organopolysiloxane that has a straight-chain polysiloxane structure or may be organopolysiloxane that has a partially branched chain polysiloxane structure. An alkenyl-functional organopolysiloxane resin may also be incorporated in order to reduce the cured coating layer's release force versus the tacky or adhesive material. An organopolysiloxane having the straight-chain polysiloxane structure

shown by the following structural formula (2) can be preferably used for component (A) in the present invention.

[0017] structural formula (2):

[0018] Each R ² in the formula is independently selected from the group consisting of the hydroxyl group, alkenyl groups, unsubstituted alkyl groups, and substituted alkyl groups, wherein at least two of the total R ² population is alkenyl groups, m and p are preferably positive integers that satisfy 0.90 ≤ m/(m + p) ≤ 1.0 and 0.0 ≤ p/(m + p) ≤ 0.10.

[0019] An organopolysiloxane having at least two alkenyl groups with a desired degree of polymerization (viscosity) may be selected for component (A), but component (A) is preferably organopolysiloxane that has a high degree of polymerization and in specific terms the 30 weight% toluene solution of component (A) preferably has a viscosity at 25°C in the range from 1,000 to 100,000 mPa • s. More specifically, component (A) is particularly preferably an alkenyl-functional organopolysiloxane having structural formula (2) wherein (m + p) has a value such that the 30 weight% toluene solution of component (A) has a viscosity at 25°C in the range from 1 ,000 to 100,000 mPa • s. When the 30 weight% toluene solution of component (A) has a viscosity at 25°C in the range from 1,000 to 100,000 mPa • s, the cured coating layer afforded by the cure of the composition of the present invention exhibits its optimal light releasability during low-speed peeling (speed = 0.3 m/minute) and also exhibits an even greater improvement in silicone migration to the reverse surface from the release surface of the coating layer.

[0020] The alkenyl group in component (A) is preferably C2-10 alkenyl group and can be specifically exemplified by vinyl, allyl, butenyl, pentenyl, hexenyl, heptenyl, octenyl, nonenyl, and decenyl groups. Viewed from the perspective of the curing properties, the alkenyl group in component (A) is preferably hexenyl group and most preferably all of the alkenyl group in component (A) is hexenyl gorup. The non-alkenyl silicon-bonded organic groups can be exemplified by alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, nonyl, decyl, and so forth; halogenated alkyl groups such as chloromethyl, 3- chloropropyl, 3,3,3-trichloropropyl, and so forth; aryl groups such as phenyl, tolyl, xylyl, and so forth; aralkyl groups such as benzyl, phenethyl, and so forth; the same or different monovalent hydrocarbyl groups in which all or a part of the carbon-bonded hydrogen in the preceding groups is replaced by, for example, a halogen atom, the cyano group, and so forth; and the hydroxyl group (-OH). The non-alkenyl silicon-bonded organic group is preferably the hydroxyl group, substituted alkyl, or unsubstituted alkyl, and methyl groups is particularly preferred. Viewed from a practical standpoint, methyl group preferably makes up at least 50 mole% of all the silicon-bonded organic groups present in component (A).

[0021] Components (B) and (C) are components that contain the silicon-bonded hydrogen atom in the molecule and are crosslinking agents in the composition of the present invention. The composition of the present invention is characterized by the co-use of two species of crosslinking agent: component (B), which has silicon-bonded hydrogen atom bonded in side-chain position on the molecular chain, and component (C), which has silicon- bonded hydrogen atom bonded in molecular chain terminal position. Through their hydrosilylation reaction with the alkenyl groups in component (A), the composition of the present invention forms a cured coating layer that exhibits excellent release properties and little silicone migration to the reverse side from the release surface, and does so without reducing the adhesiveness of the tacky or adhesive material.

[0022] It is particularly preferred that the co-use of components (B) and (C), the two species of crosslinking agent, be carried out with a component (A) having a high degree of polymerization for a solvent-based formulation. More specifically, an optimal light releasability in low-speed peeling (speed = 0.3 m/minute) and even greater improvements in the silicone migration to the reverse side from the release coating are obtained by the co-use

in the solvent-based cured release coating-forming organopolysiloxane composition of components (B) and (C), described below, with a component (A) whose 30 weight% toluene solution has a viscosity at 25°C of 1,000 to 100,000 mPa • s.

[0023] Component (B) has a viscosity at 25 ⁰ C of 1 to 1 ,000 mPa • s and is organohydrogenpolysiloxane that has in each molecule at least three silicon-bonded hydrogens in side-chain position on the molecular chain. The molecular structure of this component (B) can be exemplified by straight chain and partially branched straight chain wherein straight chain is preferred. The molecular chain terminal groups for the case of a straight chain molecular structure for component (B) can be specifically exemplified by trimethylsiloxy group, dimethylphenylsiloxy group, dimethylhydrogensiloxy group, and dimethylhydroxysiloxy group. The viscosity of component (B) at 25°C is 1 to 1,000 mPa • s and more preferably is 2 to 500 mPa s. When the viscosity of component (B) at 25°C exceeds the cited upper limit, it is then not easy to produce component (B) and the cured release coating afforded by the cure of the solvent-based cured release coating-forming organopolysiloxane composition may in particular exhibit an impairment of its light releasability during low-speed peeling (speed = 0.3 m/minute).

[0024] The content of the silicon-bonded hydrogen atoms in component (B) is preferably 0.1 to 1.6 weight% and most preferably is 0.5 to 1.6 weight%.

[0025] Component (B) is more preferably organohydrogenpolysiloxane that is given by structural formula (3) below and has at least three silicon-bonded hydrogens in side-chain position on the molecular chain. structural formula (3):

[0026] Each R in the formula is independently the hydrogen atom, the hydroxyl group, or monovalent hydrocarbyl excluding alkenyl. R can be specifically exemplified by alkyl such as methyl, ethyl, propyl, butyl, and so forth; aryl such as phenyl, tolyl, xylyl, and so forth; aralkyl such as benzyl, phenethyl, and so forth; halogenated alkyl such as 3- chloropropyl, 3,3,3-trichloropropyl, and so forth; the hydroxyl group; and hydrogen; and methyl or hydrogen is preferred. In the formula, r is a number with a value of at least 0; s is a number with a value of at least 3; and (r + s) is a number such that the viscosity of component (B) at 25°C is in the range of 1 to 1,000 mPa • s.

[0027] The component (B) content is in the range of 0.5 to 100 weight parts per 100 weight parts of component (A) and is more preferably in the range of 1 to 10 weight parts per 100 weight parts of component (A). An inadequate cure may be obtained when the component (B) content is below the cited lower limit. When, on the other hand, the component (B) content exceeds the cited upper limit, the cured coating layer may then give a large value for the low-speed release resistance and the release resistance value of the cured coating layer may change over time.

[0028] Component (C) is straight-chain organohydrogenpolysiloxane that has a viscosity at 25°C in the range of 2.5 to 2,000 mPa • s and that contains silicon-bonded hydrogen at both of its molecular chain terminals. The co-use of this component (C) with component (B) is one of the features of the present invention.

[0029] Component (C) has a straight-chain molecular structure, or may have a partially branched straight-chain structure as long as silicon-bonded hydrogens are present at both of its molecular chain terminals. An example of an optimal component (C) is straight-chain organohydrogenpolysiloxane endblocked at both molecular chain terminals by the dimethylhydrogensiloxy group. The viscosity of component (C) at 25°C is in the range of 2.5 to 2,000 mPa • s and more preferably is in the range of 2.5 to 500 mPa • s; the range of 50 to 500 mPa • s is most preferred for a light releasability of cured coating layer when peeled at low speed (speed = 0.3 m/minute). When the viscosity of component (C) at 25°C exceeds the cited upper limit, it is then not easy to produce component (C) and the cured release coating

layer afforded by curing of the solvent-based cured release coating-forming organopolysiloxane composition may in particular exhibit an impairment of its light releasability during low-speed peeling (speed = 0.3 m/minute).

[0030] The silicon-bonded hydrogen content in component (C) is preferably 0.001 to 0.5 weight% and most preferably is 0.005 to 0.01 weight%.

[0031] As an even more preferred embodiment, component (C) is straight-chain organohydrogenpolysiloxane that is given by the following structural formula (1) and that is endblocked at both molecular chain terminals by the dimethylhydrogensiloxy group, structural formula (1):

. 1 .

[0032] R in the formula is C]. io monovalent hydrocarbyl or monovalent

, 1 . halohydrocarbyl gropus, in each case lacking an aliphatically unsaturated bond. R' is specifically exemplified by alkyl groups such as methyl, ethyl, propyl, butyl, and so forth; aryl groups such as phenyl, tolyl, xylyl, and so forth; aralkyl groups such as benzyl, phenethyl, and so forth; and halogenated alkyl groups such as 3-chloropropyl, 3,3,3- trichloropropyl, and so forth; and is preferably all methyl group, n in the formula is a positive number at which the viscosity of component (C) at 25°C is in the range of 2.5 to 500 mPa • s; a positive number for which the range is 50 to 500 mPa • s is particularly preferred from the standpoint of having the cured coating layer exhibit a light releasability when peeled at low speed (speed = 0.3 m/minute).

[0033] The component (C) content is 1 to 120 weight parts per 100 weight parts component (A) and more preferably is 5 to 50 weight parts per 100 weight parts component (A). An inadequate cure may be obtained when the component (C) content is below the cited

lower limit. When, on the other hand, the component (C) content exceeds the cited upper limit, the cured coating layer may then give a large value for the low-speed release resistance and the release resistance value of the cured coating layer may change over time.

[0034] Component (D) is a platinum-type catalyst and is a catalyst that promotes cure by the hydrosilylation reaction between the alkenyl in component (A) and the silicon-bonded hydrogen in components (B) and (C). Specific examples of preferred platinum-type catalysts are chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, chloroplatinic acid/ketone complexes, chloroplatinic acid/vinylsiloxane complexes, platinum tetrachloride, finely divided platinum powder, solid platinum supported on a carrier of alumina or silica, solid platinum supported on an active carbon carrier, platinum black, platinum/olefin complexes, platinum/alkenylsiloxane complexes, platinum/carbonyl complexes, and thermoplastic organic resin powder (e.g., methyl methacrylate resin, polycarbonate resin, polystyrene resin, silicone resin, and so forth) that contains a previously cited platinum-type catalyst. Particularly preferred among the preceding are platinum / alkenylsiloxane complexes such as chloroplatinic acid / divinyltetramethyldisiloxane complexes, chloroplatinic acid / tetramethyltetravinylcyclotetrasiloxane complexes, platinum / divinyltetramethyldisiloxane complexes, platinum / tetramethyltetravinylcyclotetrasiloxane complexes, and so forth.

[0035] Component (D) is present in a so-called catalytic quantity. In specific terms, this is 1 to 1 ,000 ppm and preferably 5 to 200 ppm, in each case as platinum group metal with reference to the total weight of components (A), (B), and (C). The cure rate for the resulting release coating-forming organopolysiloxane composition slows down substantially at less than 1 ppm as the quantity of platinum group metal. More than 1000 ppm as the quantity of platinum group metal not only produces such problems as discoloration of the resulting release coating-forming organopolysiloxane and the cured coating layer yielded by the cure of this composition, but in many cases is also uneconomical since no further promotion of the required reaction can be expected.

[0036] The organic solvent (E) is a component that reduces the viscosity of the release coating-forming organopolysiloxane composition comprising components (A) to (D) and

thereby enables the application of a thin coating of this composition on the substrate. This organic solvent can be exemplified by alcohol solvents such as isopropyl alcohol and so forth; aromatic hydrocarbon solvents such as toluene, xylene, and so forth; ether solvents such as dioxane, tetrahydrofuran (THF), and so forth; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and so forth; aliphatic hydrocarbon solvents such as hexane, heptane, and so forth; ester solvents; chlorinated hydrocarbon solvents; and mixtures of the preceding. Component (E) in the present invention is preferably toluene, xylene, hexane, or heptane.

[0037] The component (E) content is in the range of 10 to 2,000 weight parts and more preferably in the range of 50 to 1,500 weight parts, in each case per 100 weight parts of component (A). Given that component (E) reduces the viscosity of the inventive composition to enable the application of a thin coating of this composition on the substrate, component (E) is preferably incorporated at 100 to 1,500 weight parts per 100 weight parts of component (A) and more preferably at 150 to 1,000 weight parts per 100 weight parts of component (A) when a high viscosity component (A) is employed and specifically when the 30 weight% toluene solution of component (A) has a viscosity at 25°C in the range from 1,000 to 100,000 mPa • s. The incorporation of component (E) at less than the cited lower limit may make it impossible to apply a thin coating of the composition on the substrate. The incorporation of component (E) in excess of the cited upper limit can reduce the composition's ability to form a cured coating layer. The incorporation of component (E) in excess of the cited upper limit is also undesirable because this imposes a large environmental burden since large quantities of organic solvent must then be evaporated during curing process.

[0038] The release coating-forming organopolysiloxane composition of the present invention comprises the components (A) to (E) described hereinabove and through an addition reaction at room temperature or 50-200°C as described below forms a cured coating layer that exhibits excellent release properties. However, additional curing with ultraviolet radiation is preferred from the standpoint of the physical properties and releasability of the resulting cured coating layer.

[0039] A photopolymerization initiator (F) is therefore preferably incorporated in order to impart ultraviolet curability to the release coating-forming organopolysiloxane composition of the present invention. An addition reaction inhibitor (G) is also preferably incorporated in addition to the previously cited components. These components are described in the following.

[0040] The photopolymerization initiator (F) is a component that imparts ultraviolet curability to the solvent-based release coating-forming organopolysiloxane composition of the present invention. The co-use of the addition reaction-mediated cure and an ultraviolet- mediated cure offers the advantage of enabling further improvement in the silicone migration behavior of the composition of the present invention. Compounds heretofore known to produce radicals by exposure to ultraviolet radiation can be used as this component (F), for example, a suitable selection from among organoperoxides, carbonyl compounds, organosulfur compounds, azo compounds, and so forth, can be used. Specific examples are acetophenone, propiophenone, benzophenone, xanthol, fluorein, 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-nonylxanthone, benzoin, benzoin methyl ether, benzoin butyl ether, bis(4-dimethylaminophenyl) ketone, benzyl methoxy ketal, 2-chlorothioxanthone, diethylacetophenone, 1 -hydroxycyclohexyl phenyl ketone, 2-methyl[4-(methylthio)phenyl]- 2-morpholino- 1 -propanone, 2,2-dimethoxy-2-phenylacetophenone, diethoxyacetophenone, and so forth. Benzophenone, 4-methoxyacetophenone, 4-methylbenzophenone, diethoxyacetophenone, and 1 -hydroxycyclohexyl phenyl ketone are preferred as component (F) for imparting ultraviolet curability to the composition of the present invention, while diethoxyacetophenone and 1 -hydroxycyclohexyl phenyl ketone are more preferred.

[0041] A single photopolymerization initiator (F) may be used or two or more may be used in combination. The content of component (F) is not particularly limited and is the range from 0.01 to 10 weight parts per 100 weight parts component (A) and suitably is 0.01 to 2.5 weight parts per 100 weight parts component (A) and more suitably is 0.05 to 2.5 weight

parts per 100 weight parts component (A). When the component (F) content is in the cited range, the release coating afforded by the cure of the composition of the present invention exhibits an improved silicone migration behavior and excellent physical properties, e.g., strength and so forth.

[0042] The addition reaction inhibitor (G), also known as a cure retarder, is a component that inhibits the occurrence at ambient temperature of addition reaction-mediated gelation and curing in the release coating-forming organopolysiloxane composition of the present invention. The use of this component can retard curing in the inventive composition after the intermixing of components (A) to (E) and the optional component (F) and particularly after the admixture of the component (C) curing catalyst. Since this component is therefore intended to support retention of the working life, from the start of coating of the inventive composition on a substrate up to and including the completion of the coating process, while also enabling heat curability, it is preferably incorporated when the inventive composition is put to practical use. Component (G) is exemplified by acetylenic compounds, ene-yne compounds, organonitrogen compounds, organophosphorus compounds, and oxime compounds. Specific examples are alkynyl alcohols such as 3 -methyl- l-butyn-3-ol, 3,5- dimethyl-l-hexyn-3-ol, 3-methyl-l-pentyn-3-ol, phenylbutynol, and so forth; methylalkenylcyclosiloxanes such as l,3,5,7-tetramethyl-l,3,5,7-tetravinylcyclotetrasiloxane, l,3,5,7-tetramethyl-l,3,5,7-tetrahexenylcyclotetrasiloxane, and so forth; benzotriazole; 3- methyl-3-penten-l-yne; 3,5-dimethyl-l-hexyn-3-ene; benzotriazole; 1-ethynyl-l- cyclohexanol; methyltris(3-methyl-l-butyn-3-oxy)silane; dimethylbis(3 -methyl- 1 -butyn-3- oxy)silane; and methylvinylbis(3-methyl-l-butyn-3-oxy)silane.

[0043] The component (G) content is in the range generally of 0.001 to 20 weight parts per 100 weight parts of component (A), preferably 0.005 to 10 weight parts per 100 weight parts of component (A), and more preferably 0.01 to 5 weight parts per 100 weight parts of component (A). However, the quantity of component (G) is to be selected as appropriate as a function of the anticipated storage period, the type of component (G), the properties and content of the platinum-type catalyst (D), the alkenyl content of component (A), and the silicon-bonded hydrogen content in components (B) and (C).

[0044] The composition according to the present invention comprises components (A) to (E), and can further incorporate component (F) in order to impart ultraviolet curability. The composition of the present invention may additionally contain component (G) on an optional basis. It may also incorporate an inorganic filler (e.g., finely divided silica and so forth), pigment, or thickener in order to adjust the viscosity of the coating fluid. Various additives other than those previously cited may also be incorporated insofar as the objects and effects of the present invention are not impaired; these additives can be exemplified by the known polymerization inhibitors, oxidation inhibitors, defoamers and antifoams, heat stabilizers, leveling agents, ultraviolet absorbers, dyes, organic resin powders, and so forth. Considering the coatability by this composition on filmic substrates, the viscosity of the composition as a whole at 25°C is preferably in the range of 50 to 2,000 mPa • s.

[0045] The composition of the present invention can be prepared by mixing components (A) to (E) and optionally components (F) and (G) — or these components and any other optional components — to homogeneity using a known mixing means. The order of incorporation of the individual components is not particularly limited; however, when the composition will not be used immediately after mixing, in a preferred embodiment the mixture of components (A), (B), (C), and (E) is stored separately from component (D) and the two are mixed immediately before use. In the case of the composition comprising components (A) to (G), through selection of the type of component (G) and adjustment of its quantity of incorporation a composition is preferably obtained that does not undergo crosslinking reaction at ambient temperature but which crosslinks and cures under the application of heat.

[0046] A cured coating layer that exhibits an excellent slipperiness, that has an appropriate release resistance versus tacky or adhesive substances, and that exhibits little silicone migration to the reverse surface from the release surface is formed on the surface of any of various film-form or sheet-form substrates when the solvent-based cured release coating-forming organopolysiloxane composition of the present invention as described above is uniformly coated on the surface of any of various sheet-form substrates (e.g., glassine paper, cardboard, clay-coated paper, polyolefin-laminated paper and particularly polyethylene-laminated paper, thermoplastic resin films (for example, polyester film,

polyethylene film, polypropylene film, polyamide film), natural fiber fabrics and textiles, synthetic fiber fabrics and textiles, metal foils (for example, aluminum foil), and so forth) and is heated or exposed to ultraviolet radiation under conditions sufficient to bring about crosslinking through the hydrosilylation reaction between component (A) and components (B) and (C).

[0047] Temperatures of 50 to 200°C are ordinarily suitable for the curing temperature for the solvent-based cured release coating-forming organopolysiloxane composition of the present invention elaborated on the sheet-form or film-form substrate, but temperatures in excess of 200°C may be used when the substrate has a good heat resistance. In order to achieve rapid formation of the cured coating layer, component (D) is preferably a platinum/alkenylsiloxane complex catalyst and the curing temperature is preferably 80 to 150°C for an amount of incorporation of this catalyst of 50 to 500 ppm as the quantity of platinum metal with reference to the total quantity of the composition. The curing time can be selected as appropriate in view of the amount of catalyst, the thickness of the film coating, and the heating temperature, and is generally in the range of 1 to 120 seconds and preferably is 20 to 60 seconds. The heating method is not particularly limited and can be exemplified by heating in a forced convection oven, passage through a longitudinal oven, and thermal irradiation using an infrared lamp or halogen lamp.

[0048] The solvent-based cured release coating-forming organopolysiloxane composition of the present invention preferably comprises the components (A) to (E) described above as well as component (F) in order to provide ultraviolet curability. In particular, the execution of curing using a combination of heat curing as described above and exposure to ultraviolet radiation is particularly preferred because this can provide additional improvements in the silicone migration behavior of the release coating.

[0049] Ultraviolet radiation usable for curing the composition of the present invention can be ultraviolet radiation in the wavelength range of 200 to 400 run emitted from, for example, a mercury arc, medium-pressure mercury lamp, high-pressure mercury lamp, and so forth. The amount of radiation should be an amount that can cure the above-described film coating layer; for example, taking the use of a 1 to 2 kW high-pressure mercury lamp as an

example, exposure is preferably carried out for 0.1 to 10 seconds from a distance of approximately 8 cm. Prior to the execution of the ultraviolet cure, the composition of the present invention is preferably subjected to a preliminary addition curing by air drying or the application of heat, and in particular the solvent is preferably evaporated off to a certain degree prior to the ultraviolet cure.

[0050] The exposure dose during the ultraviolet cure can be selected as appropriate and preferably is a value in the range from 10 to 10,000 mJ/cm ² and more preferably is a value from 100 to 5,000 mJ/cm ² . The improvement in the physical strength of the release coating that can be expected from the ultraviolet cure will in some cases be inadequate when the exposure dose is below the cited lower limit. An exposure dose above the cited upper limit results in an overly long exposure time and can reduce the productivity.

[0051] There are no particular limitations on the coater used to coat the cured release coating-forming organopolysiloxane composition of the present invention on the surface of the sheet-form or film-form substrate, and the coater can be exemplified by roll coaters, gravure coaters, air coaters, curtain flow coaters, and offset transfer roll coaters. The tacky or adhesive material applied to the release sheet or film may be any of various pressure-sensitive adhesives, any of various adhesives, and so forth, and such tacky or adhesive material can be exemplified by acrylic resin-based pressure-sensitive adhesives, rubber-based pressure- sensitive adhesives, and silicone-based pressure-sensitive adhesives, and by acrylic resin- based adhesives, synthetic rubber-based adhesives, silicone-based adhesives, epoxy resin- based adhesives, and polyurethane-based adhesives. Additional examples are asphalt, sticky food products such as rice-cakes, glue paste, and birdlime.

[0052] The composition of the present invention is useful for forming a cured coating layer that exhibits excellent surface slipperiness and that exhibits an excellent release performance to tacky or adhesive materials, and is particularly well adapted as a cured release coating-forming agent for process paper, asphalt packaging paper, and various plastic films. Furthermore, sheet-form and film-form substrates bearing a release coating layer afforded by curing the inventive composition are well adapted in particular for use as process paper and

paper for packaging or wrapping tacky substances and for use with pressure-sensitive tape, pressure-sensitive labels, and so forth.

Examples [0053] Examples and comparative examples are provided as below in order to specifically describe the invention, but the present invention is not limited to the following examples. In the examples and comparative examples that follow, parts and ppm refer, respectively, to weight parts and weight-ppm.

[0054] The viscosity was measured in the examples at 25°C by the method described as below. The cured coating layers was obtained from the solvent-based cured release coating- forming organopolysiloxane compositions on the surface of polyethylene terephthalate film by the method described as below. And, the properties of the cured coating layers are evaluated by determining, in each case at 25°C, the release force value, its residual adhesiveness (%) to adhesive materials, and its silicone migration.

[0055] [Viscosity]

The viscosity of the organopolysiloxane and the viscosity of the solvent-based cured release coating-forming organopolysiloxane composition were measured at 25 ⁰ C using a digital display viscometer (Vismetron model VDA2 from Shibaura Systems Co., Ltd.).

[0056] [Formation of the cured coating layer]

Using a printability tester (RI-2 from Meiseisakusho Kabushiki Kaisha), the solvent-based cured release coating-forming organopolysiloxane composition was coated, in an amount that provided 0.2 g/m ² as siloxane quantity, on the surface of polyethylene terephthalate film. A cured coating layer was formed by heating the coated film for 30 seconds at 110°C in a forced convection oven followed by exposure to ultraviolet radiation by a single pass at a velocity of 10 m/minute through a conveyor-type ultraviolet irradiator (EYE GRANDAGE, trade name, from Eye Graphics Co., Ltd.) using a 120 W/cm high-pressure mercury lamp light source.

[0057] [Release force evaluation!

An acrylic-type solvent-based pressure-sensitive adhesive (trade name: Oribain BPS-5127, from Toyo Ink Mfg. Co., Ltd.) was uniformly coated using an applicator at 30 g/m ² as solids on the surface of the cured coating layer produced by the method described above and heating was carried out for 2 minutes at 70°C. High-quality paper (areal weight = 64 g/m ² ) was then pasted on the surface of this acrylic-type pressure-sensitive adhesive and the resulting adhered paper was cut to a width of 5 cm to fabricate the test specimen. A load of 20 g/cm ² was placed on this test specimen followed by standing for 24 hours in the air at a temperature of 25°C and a humidity of 60%. Using a tensile tester (Tensilon universal testing instrument, from A & D Co., Ltd.), the adhered paper was then peeled off at an angle of 180° and a peel rate of 0.3 m/minute and the force (N) required for peeling was measured.

[0058] [Residual adhesiveness]

Pressure-sensitive adhesive tape (width = 38 mm, Nitto 3 IB (trade name) pressure-sensitive adhesive tape, from Nitto Denko Corporation) was pasted on the surface of the cured coating layer and a load of 20 g/cm ² was applied followed by standing for 1 day at 7O ⁰ C. The tape was then peeled off and applied to a stainless steel plate (JIS C2107), after which it was pressed with a 2-kg roller and aged for 30 minutes at 25°C and a humidity of 60%. The tape was subsequently peeled from the stainless steel plate at 180° and a rate of 0.3 m/minute, at which time the release force f (mN) was measured. For the blank specimen, the Nitto 3 IB pressure-sensitive adhesive tape was pasted on polytetrafiuoroethylene film in place of the silicone-treated paper and the same procedure as above was followed in order to measure the release force fo (mN); this value was designated the blank value. The residual adhesiveness

(%) was calculated with the following formula using the values measured for the release force.

Residual adhesiveness (%) = f X 100/f ₀

[0059] [Silicone migration]

A clean synthetic resin film (polyethylene terephthalate film) was pasted on the surface of the cured coating layer and a load of 100 kg/cm ² was applied with a press followed by standing for 30 minutes at 25°C. The synthetic resin film was then peeled off and a line was drawn with Magic Ink (registered trademark) on the side that had been in contact with the coated

film. The degree of repellency to the oil-based ink was evaluated by visual inspection based on the following criteria.

none: silicone migration was presumed to be absent when there was no repellency to the oil-based ink, and an evaluation of "none" was rendered. slight: a slight silicone migration was presumed to be present when repellency to the oil-based ink was not entirely absent, but was also not present to a clearly observable degree, and an evaluation of "slight" was rendered present: silicone migration was presumed to be present when the repellency to the oil- based ink could be clearly observed, and an evaluation of "present" was rendered

[0060] Example 1

100 weight parts of dimethylsiloxane • methylhexenylsiloxane copolymer endblocked at both molecular chain terminals by trimethylsiloxy-groups (viscosity of the 30 weight% toluene solution of this copolymer = 5,000 mPa • s) (Al) was dissolved in 275.44 weight parts of toluene (El). The following were then added to and dissolved to homogeneity in the resulting solution: 2.4 weight parts of methylhydrogenpolysiloxane endblocked at both terminals by trimethylsiloxy-groups (silicon-bonded hydrogen content = 1.6 weight%, viscosity = 20 mPa • s) (Bl), 20 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy-groups (silicon-bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa • s) (Cl), 2 weight parts of 3-methyl-l-butyn-3- ol (Gl), and 0.16 weight part of diethoxyacetophenone (Fl). A chloroplatinic acid/1,3- divinyltetramethyldisiloxane complex (Dl) was additionally admixed in an amount that provided 200 ppm of platinum metal, thereby producing a solvent-based cured release coating-forming silicone composition [I]. A cured coating layer was prepared from this composition by the previously described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1.

[0061] Example 2

A solvent-based cured release coating-forming silicone composition [2] was prepared as described in Example 1, but in this case using 10 weight parts of the straight-chain polysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy- groups (silicon-bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa • s) (Cl) rather than the 20 weight parts of this component (Cl) that was used in Example 1. A cured coating layer was prepared from this composition by the previously described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1.

[0062] Example 3

A solvent-based cured release coating-forming silicone composition [3] was prepared as described in Example 1, but in this case using 20 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy-groups (silicon-bonded hydrogen content = 0.02 weight%, viscosity = 135 mPa • s) (C2) in place of the 20 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy-groups (silicon- bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa • s) (Cl) that was used in Example 1. A cured coating layer was prepared from this composition by the previously described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1.

[0063] Example 4

A solvent-based cured release coating-forming silicone composition [4] was prepared as described in Example 1, but in this case using 10 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy-groups (silicon-bonded hydrogen content = 0.02 weight%, viscosity = 135 mPa ^■ s) (C2) in place of the 20 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy-groups (silicon- bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa • s) (Cl) that was used in Example 1. A cured coating layer was prepared from this composition by the previously

described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1.

[0064] Example 5 A solvent-based cured release coating-forming silicone composition [5] was prepared as described in Example 1, but in this case using 20 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy (silicon-bonded hydrogen content = 0.06 weight%, viscosity = 5 mPa • s) (C3) in place of the 20 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy (silicon-bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa ■ s) (Cl) that was used in Example 1. A cured coating layer was prepared from this composition by the previously described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1.

[0065] Comparative Example 1

A solvent-based cured release coating-forming silicone composition [7] was prepared as described in Example 1, but in this example without incorporating the 20 weight parts of straight-chain polysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy (silicon-bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa • s) (Cl) that was used in Example 1. A cured coating layer was prepared from this composition by the previously described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1. The cured release coating provided by composition [7] gave a high release force and did not exhibit a light releasability.

[0066] Comparative Example 2

A solvent-based cured release coating-forming silicone composition [8] was prepared as described in Example 1, but in this example using 20 weight parts of straight-chain dimethylpolysiloxane endblocked at both molecular chain terminals by dimethylhydroxysiloxy (-Si(CH ₃ ) ₂ OH) groups (viscosity of the 30 weight% toluene solution of this polysiloxane = 15,000 mPa • s) in place of the 20 weight parts of straight-chain

polysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy groups (silicon-bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa • s) (Cl) that was used in Example 1. A cured coating layer was prepared from this composition by the previously described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1. The cured release coating provided by composition [8] gave a reduced residual adhesiveness and exhibited a slight silicone migration.

[0067] Comparative Example 3 A solvent-based cured release coating-forming silicone composition [9] was prepared as described in Example 1, but in this case using 4 weight parts of dimethylpolysiloxane • methylphenylpolysiloxane copolymer endblocked at both molecular chain terminals by trimethylsiloxy (-Si(CH3)3) groups (viscosity of this polysiloxane copolymer = 10,000 mPa • s) in place of the 20 weight parts of straight-chain polysiloxane endblocked at both molecular chain terminals by dimethylhydrogensiloxy groups (silicon-bonded hydrogen content = 0.01 weight%, viscosity = 400 mPa • s) (Cl) that was used in Example 1. A cured coating layer was prepared from this composition by the previously described method and the obtained cured coating layer was evaluated for its release force, residual adhesiveness (%), and silicone migration; the results are shown in Table 1. The cured release coating provided by composition [9] gave a substantially reduced residual adhesiveness and exhibited silicone migration.

[0068] Table 1

Industrial Applicability

[0069] The solvent-based cured release coating-forming organopolysiloxane composition according to the present invention is useful for the formation, on the surface of a film-form or sheet-form substrate, of a cured coating layer that exhibits excellent release properties versus tacky or adhesive materials, that does not lower the tack or adhesiveness of tacky or adhesive materials, and that exhibits little silicone migration to the reverse surface from the coating layer of release surface. Film-form and sheet-form substrates bearing a cured coating layer obtained from the composition according to the present invention are useful as release film and release sheet, as process paper, as paper for wrapping or packaging tacky substances, for pressure-sensitive tapes, for pressure-sensitive labels, and so forth.