Patent Description:
In the prior art approach for preventing adhesion or bonding between sheet-like substrates such as paper and plastic sheets and pressure-sensitive adhesives, a cured film of an organopolysiloxane composition is disposed on the substrate surface to impart release properties. The following methods are known for forming a cured organopolysiloxane film on the substrate surface.

Among the above methods (<NUM>), (<NUM>) and (<NUM>), method (<NUM>) for forming a releasable film through addition reaction is widely utilized because it can accommodate a variety of requisite release properties covering from low-speed release to high-speed release.

Method (<NUM>) for forming a releasable film through addition reaction includes a solvent type in which an organopolysiloxane composition is dissolved in an organic solvent, an emulsion type in which an organopolysiloxane composition is dispersed in water using an emulsifier, and a solventless type using just organopolysiloxane. Since the solvent type is harmful to the human body and environment, a switchover from the solvent type to the solventless type is in progress in view of safety. The emulsion type needs enormous energy for removal of water and it is difficult to reduce the release force because a noticeable amount of emulsifier is left behind.

For this reason, the solventless type is most often used. As a basic formulation, a solventless type composition is composed of a base oil (vinyl-containing siloxane), a crosslinker (SiH-containing siloxane), an inhibitor (acetylene compound), and a platinum catalyst.

When products (i.e. release papers or release films) are obtained by coating and curing a solventless type organopolysiloxane release paper composition, the smoothness of the cured organopolysiloxane composition layer on their surface significantly affects the release force. If the surface has asperities or variations of coating weight, a pressure-sensitive adhesive (PSA) is caught in asperities which serve as anchors, indicating an increase of release force. Fine asperities on the surface are formed during high-speed coating as a result of waving of the organopolysiloxane composition on the roll surface or mist generation from the roll surface. Although the cause of mist generation is not well understood, the mist consists of scattered particles of the organopolysiloxane composition. Mist generation is observable even with the naked eye as coating speed is increased to <NUM>/min or higher. As the coating speed increases, the amount of mist generated increases. The organopolysiloxane composition flies off from the roll surface as a mist. As the amount of generated mist increases, more asperities are formed on the surface, leading to a higher release force.

Recently efforts have been made to accelerate the coating speed of organopolysiloxane compositions for the purposes of increasing the productivity and reducing the fabrication cost of release papers or release films. Specifically, although the prior art sets the peripheral velocity of a coating roll in the range of <NUM> to <NUM>/min, there are found many attempts to conduct the step of coating an organopolysiloxane composition at a higher speed by increasing the peripheral velocity to <NUM>/min or higher. However, when the coating speed exceeds <NUM>/min, the organopolysiloxane composition generates a large volume of mist, which is never encountered at a low coating speed. With the mist generation, the organopolysiloxane composition coating becomes roughened on its surface and the adhesive is caught or anchored in asperities on the surface of the cured composition layer. As a result, release forces at low and high speeds are increased.

In order to mitigate surface asperities, the amount of mist generation must be reduced.

Heretofore, a relationship between the amount of generated mist and the surface properties or release force of the completed release sheet (release paper or release film) has not been reported.

An object of the invention, which has been made under the above-mentioned circumstances, is to provide a solventless silicone release composition, a release sheet comprising a cured film of the composition, and a method for preparing the release sheet, the composition being effective, when a release sheet such as release paper or release film is produced by coating the composition at a high speed of at least <NUM>/min, for eliminating surface roughness formed by high-speed rotation of a roll and preventing formation of surface asperities by mist generation, and being able to form a release sheet which exhibits a low release force inherent to cured silicone after PSA is attached to the sheet.

Making extensive investigations to attain the above object, the inventors have found that a solventless silicone release composition comprising specific amounts of the following components is effective for eliminating any surface roughness formed due to high-speed rotation of a roll and preventing formation of surface asperities by mist generation during high-speed coating to a sheet-like substrate, and useful in preparing a release sheet which includes a cured silicone film having satisfactory smoothness on its surface and which exhibits a reduced high-speed release force relative to a PSA-coated substrate,.

As used herein, the term "high-speed release force" means a release force required for peeling a PSA tape at a speed of at least <NUM>/min, preferably at least <NUM>/min from a release sheet such as release paper or release film.

Accordingly, the invention provides a solventless silicone release composition, release sheet, and release sheet preparation method, as defined in the claims.

The solventless silicone release composition is effective, when coated onto a sheet-like substrate at a high speed and cured, for eliminating any surface roughness brought by high-speed rotation of a roll, because of its low viscosity. Also, formation of fine asperities on the surface is minimized because component (E) mitigates mist generation. The composition is thus useful in preparing release sheets such as release paper or release film which includes the cured silicone film having satisfactory smoothness on its surface and which is low in high-speed release force relative to a PSA-coated substrate.

Component (A) is an alkenyl-containing organopolysiloxane containing at least two, preferably <NUM> to <NUM> alkenyl groups per molecule and having a vinyl value of <NUM> mol/<NUM> to <NUM> mol/<NUM> and a kinematic viscosity at <NUM> of <NUM><NUM>/s to <NUM><NUM>/s, represented by the general formula (<NUM>).

Herein M is R<NUM>SiO<NUM>/<NUM>, Mvi is R<NUM>PSiO<NUM>/<NUM>, D is R<NUM>SiO<NUM>/<NUM>, Dvi is RPSiO<NUM>/<NUM>, T is RSiO<NUM>/<NUM>, Tvi is PSiO<NUM>/<NUM>, Q is SiO<NUM>/<NUM>, R is each independently a C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, P is an alkenyl group of the formula: -(CH<NUM>)a-CH=CH<NUM> wherein "a" is an integer of <NUM> to <NUM>, α, β, δ and ζ are each independently an integer of at least <NUM>, not all β, δ and ζ are <NUM> at the same time, <NUM> ≤ β+δ+ζ ≤ <NUM>, γ is an integer of <NUM> to <NUM>, ε is an integer of <NUM> to <NUM>, and η is an integer of <NUM> to <NUM>.

In formula (<NUM>), R is each independently a substituted or unsubstituted monovalent hydrocarbon group of <NUM> to <NUM> carbon atoms, preferably <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, free of aliphatic unsaturation. Examples include alkyl groups such as methyl, ethyl, propyl, butyl and octyl, cycloalkyl groups such as cyclohexyl, aryl groups such as phenyl and tolyl, aralkyl groups such as benzyl and phenethyl, and substituted forms of the foregoing in which some or all hydrogen atoms are substituted by halogen atoms, typically halogenated alkyl groups such as chloropropyl and trifluoropropyl. Preferably methyl accounts for at least <NUM> mol% of R in view of curability of the composition and a low release force of the cured product.

P is an alkenyl group of the formula: -(CH<NUM>)a-CH=CH<NUM> wherein "a" is an integer of <NUM> to <NUM>, examples of which include vinyl, allyl, butenyl, propenyl, <NUM>-hexenyl, octenyl, and decenyl, with vinyl being preferred.

In formula (<NUM>), α, β, δ and ζ are each independently an integer of at least <NUM>, not all β, δ and ζ are equal to <NUM> at the same time, β+δ+ζ is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, α is preferably an integer of <NUM> to <NUM>, β is preferably an integer of <NUM> to <NUM>, δ is preferably an integer of <NUM> to <NUM>, and ζ is preferably an integer of <NUM> to <NUM>.

In formula (<NUM>), γ indicative of the number of D units (R<NUM>SiO structure) is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, more preferably an integer of <NUM> to <NUM>, and most preferably an integer of <NUM> to <NUM>. If γ is less than <NUM>, a more amount of mist is generated so that the surface of the silicone release composition coating is roughened. If γ exceeds <NUM>, the organopolysiloxane and hence, the solventless silicone release composition has too high a kinematic viscosity and becomes inefficient to coat so that the coating is aggravated in smoothness and largely varies in coating weight locally.

In formula (<NUM>), ε is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, and η is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>.

Component (A) should have a vinyl value of <NUM> mol/<NUM> to <NUM> mol/<NUM>, preferably <NUM> mol/<NUM> to <NUM> mol/<NUM>, and more preferably <NUM> mol/<NUM> to <NUM> mol/<NUM>. A vinyl value of less than <NUM> mol/<NUM> means that in formula (<NUM>), the degree of polymerization (DOP) of D, T, and Q units free of vinyl is greater than the DOP of vinyl-containing units. Since ε indicative of the DOP of T units is <NUM> to <NUM> and η indicative of the DOP of Q units is <NUM> to <NUM>, the structure of formula (<NUM>) having a low vinyl value becomes a structure with less vinyl groups and more D units. Extremely stated, the structure having a vinyl value of less than <NUM> mol/<NUM> is a structure of formula (<NUM>) wherein the number of vinyl groups is <NUM> and all α, δ, ε, ζ and η are <NUM>, that is, Mvi<NUM>Dγ wherein the value of γ is at least <NUM>, which empirically has a kinematic viscosity of at least <NUM><NUM>/s. Therefore, if the vinyl value is less than <NUM> mol/<NUM>, component (A) becomes least wettable and spreadable over the substrate to be coated and varies in coating weight on the substrate, like the situation (described below) wherein component (A) has a kinematic viscosity at <NUM> in excess of <NUM><NUM>/s. Also, if the vinyl value is in excess of <NUM> mol/<NUM>, the crosslinking density becomes too high and the low-speed release force (i.e. release force required for peeling at <NUM>/min) becomes high.

Component (A) should have a kinematic viscosity at <NUM> of <NUM><NUM>/s to <NUM><NUM>/s, preferably <NUM><NUM>/s to <NUM><NUM>/s. If the kinematic viscosity is less than <NUM><NUM>/s, component (A) becomes excessively wettable and spreadable, resulting in a shortage of coating weight on the substrate. If the kinematic viscosity is more than <NUM><NUM>/s, inversely component (A) becomes less wettable and spreadable and varies in coating weight on the substrate. It is noted that the kinematic viscosity can be measured by an Ostwald viscometer (the same holds true, hereinafter).

Illustrative examples of the organopolysiloxane as component (A) include both end alkenyl-containing siloxanes, side chain alkenyl-containing siloxanes, one end and side chain alkenyl-containing siloxanes, both end and side chain alkenyl-containing siloxanes, and branched end alkenyl-containing siloxanes.

Examples as expressed by structural formula include Mvi<NUM>Dγ, M<NUM>DγDviδ, Mvi<NUM>DγT<NUM>, Mvi<NUM>DγT<NUM>, Mvi<NUM>DγDviδ, Mvi<NUM>DγQ<NUM>, and MαDγDviδTviζ wherein M, Mvi, D, Dvi, T, Tvi, Q, γ, δ, and ζ are as defined above (the same hereinafter). Illustrative structures include Mvi<NUM>D<NUM>, M<NUM>D<NUM>Dvi<NUM>, M<NUM>D<NUM>Dvi<NUM>, M<NUM>D<NUM>Dvi<NUM>, M<NUM>D<NUM>Dvi<NUM>, Mvi<NUM>D<NUM>T<NUM>, Mvi<NUM>D<NUM>T<NUM>, Mvi<NUM>D<NUM>Dvi<NUM>, Mvi<NUM>D<NUM>Dvi<NUM>, and M<NUM>D<NUM>Dvi<NUM>Tvi<NUM>.

Component (B) is an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule and having a kinematic viscosity at <NUM> of <NUM><NUM>/s to <NUM><NUM>/s.

The organohydrogenpolysiloxane as component (B) should have at least two, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM> silicon-bonded hydrogen atoms (SiH groups). An addition reaction takes place between SiH groups in the organohydrogenpolysiloxane and vinyl groups in the organopolysiloxane having formula (<NUM>) to form a crosslinked organopolysiloxane.

The content of SiH groups in component (B) is preferably <NUM> to <NUM> mol/<NUM>, more preferably <NUM> to <NUM> mol/<NUM>, and even more preferably <NUM> to <NUM> mol/<NUM>. A too low content of SiH groups may adversely affect curability and adhesion whereas a too high content may cause a tightening of release force.

Component (B) should have a kinematic viscosity at <NUM> of <NUM><NUM>/s to <NUM><NUM>/s, preferably <NUM><NUM>/s to <NUM><NUM>/s, more preferably <NUM><NUM>/s to <NUM><NUM>/s. If the kinematic viscosity is lower than <NUM><NUM>/s, the substrate adhesion is noticeably aggravated although the reactivity is high because of the low molecular weight. If the viscosity is higher than <NUM><NUM>/s, the reactivity is aggravated or the curability is lost, from which a drop of residual adhesion rate and an increase of release force due to short cure are observable.

The organohydrogenpolysiloxane as component (B) preferably has a structure of the general formula (<NUM>).

Herein M is R<NUM>SiO<NUM>/<NUM>, MH is R<NUM>HSiO<NUM>/<NUM>, D is R<NUM>SiO<NUM>/<NUM>, DH is RHSiO<NUM>/<NUM>, T is RSiO<NUM>/<NUM>, TH is HSiO<NUM>/<NUM>, Q is SiO<NUM>/<NUM>, R is each independently a C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, o', π', ρ' and τ' are each independently an integer of at least <NUM>, σ' is an integer of <NUM> to <NUM>, ϕ' is an integer of <NUM> to <NUM>, χ' is an integer of <NUM> to <NUM>, not all π', σ' and ϕ' are <NUM> at the same time, and <NUM> ≤ π'+σ'+ϕ' ≤ <NUM>.

In formula (<NUM>), examples of R are as exemplified above for R in formula (<NUM>), with C<NUM>-C<NUM> alkyl groups being preferred.

In formula (<NUM>), o', π', ρ' and τ' are each independently an integer of at least <NUM>, o' is preferably an integer of <NUM> to <NUM>, π' is preferably an integer of <NUM> to <NUM>, ρ' is preferably an integer of <NUM> to <NUM>, τ' is preferably an integer of <NUM> to <NUM>. Also, σ' is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, and more preferably an integer of <NUM> to <NUM>, ϕ' is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, χ' is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, not all π', σ' and ϕ' are equal to <NUM> at the same time, π'+σ'+ϕ' is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, and σ': ρ' is preferably from <NUM>:<NUM> to <NUM>:<NUM>.

The organohydrogenpolysiloxane preferably has a weight average molecular weight of <NUM> to <NUM>,<NUM>, more preferably <NUM> to <NUM>,<NUM>. If Mw is too low, the substrate adhesion may be largely aggravated. If Mw is too high, the reactivity is aggravated or the curability is lost, from which a drop of residual adhesion rate and an increase of release force due to short cure are observable. As used herein, the weight average molecular weight (Mw) is measured by gel permeation chromatography (GPC) versus polystyrene standards (the same holds true, hereinafter).

Illustrative examples of the organohydrogenpolysiloxane as component (B) include both end hydrogensilyl-containing siloxanes, side chain hydrogensilyl-containing siloxanes, one end and side chain hydrogensilyl-containing siloxanes, and both end and side chain hydrogensilyl-containing siloxanes.

Examples expressed by structural formula include MH<NUM>Dρ', M<NUM>DHσ', M<NUM>Dρ'DHσ', MH<NUM>Dρ'DHσ', MH<NUM>Dρ'T<NUM>, MH<NUM>Dρ'T<NUM>, and Mo'Dρ'DHσ'THϕ' wherein M, MH, D, DH, T, TH, o', ρ', σ', and ϕ' are as defined above (the same hereinafter). Illustrative structures include MH<NUM>D<NUM>, MH<NUM>D<NUM>, MH<NUM>D<NUM>T<NUM>, MH<NUM>D<NUM>T<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, and M<NUM>D<NUM>DH<NUM>T<NUM>.

Component (B) may be used alone or in admixture of two or more.

Component (B) is used in an amount to give <NUM> to <NUM> moles, preferably <NUM> to <NUM> moles of silicon-bonded hydrogen atoms (SiH groups) per mole of alkenyl groups in component (A). The amount corresponds to a SiH functionality content of <NUM> to <NUM> mol/<NUM>. A less amount of component (B) is insufficient for cure and adhesion. If the amount of component (B) is too large, the amount of residual SiH increases to tighten the release force, but the release force declines with time as the SiH amount decreases with time.

Component (C) is a platinum group metal base catalyst which may be selected from well-known addition reaction catalysts. Suitable platinum group metal base catalysts include, for example, platinum, palladium, rhodium and ruthenium base catalysts, with the platinum base catalysts being preferred. Examples of the platinum base catalyst include chloroplatinic acid, alcohol or aldehyde solutions of chloroplatinic acid, and complexes of chloroplatinic acid with various olefins or vinylsiloxanes.

The platinum group metal based catalyst is added in a catalytic or effective amount, preferably in such an amount as to give <NUM> to <NUM>,<NUM> ppm, more preferably <NUM> to <NUM> ppm of platinum group metal based on the total weight of components (A), (B), (D) and (E).

Component (D) is an addition reaction inhibitor, which is optional and serves to control the catalytic activity of the platinum group metal base catalyst. Included are organonitrogen compounds, organophosphorus compounds, acetylene compounds, oxime compounds, and organic chlorine compounds. Examples include acetylene alcohols such as <NUM>-ethynyl-<NUM>-cyclohexanol, <NUM>-methyl-<NUM>-butyn-<NUM>-ol, <NUM>,<NUM>-dimethyl-<NUM>-hexyn-<NUM>-ol, <NUM>-methyl-<NUM>-pentyn-<NUM>-ol, and phenylbutynol, acetylene compounds such as <NUM>-methyl-<NUM>-penten-<NUM>-yne and <NUM>,<NUM>-dimethyl-<NUM>-hexene-<NUM>-yne, the reaction products of acetylene compounds with alkoxysilanes, siloxanes or hydrogensilanes, e.g. <NUM>,<NUM>-dimethylpropynyloxytrimethylsilane, vinylsiloxanes such as cyclic tetramethylvinylsiloxane, organonitrogen compounds such as benzotriazole, organophosphorus compounds, oxime compounds, maleic acid compounds, and organic chlorine compounds.

When used, the addition reaction inhibitor (D) is blended in an amount sufficient to provide satisfactory stability to a processing bath and typically <NUM> to <NUM> parts by weight, preferably <NUM> to <NUM> parts by weight per <NUM> parts by weight of component (A).

Component (E) is an organopolysiloxane containing a crosslinked structure and having fluidity. It is effective as a mist suppressant when added.

The crosslinked structure indicates the addition reaction product of a vinyl-containing organopolysiloxane and an organohydrogenpolysiloxane or the condensation reaction product of a hydroxyl-containing organopolysiloxane and an alkoxy-containing organopolysiloxane, but also encompasses organopolysiloxanes containing R<NUM>SiO<NUM>/<NUM> units (M units), R<NUM>SiO<NUM>/<NUM> units (D units), RSiO<NUM>/<NUM> units (T units), and optionally SiO<NUM>/<NUM> units (Q units) in the molecule wherein R is as defined above. Since organopolysiloxanes containing too much T or D units become gel or resinous, oily organopolysiloxanes are preferred because of release paper and release film applications.

The organopolysiloxane as component (E) has fluidity. The organopolysiloxane after solvent removal preferably has an absolute viscosity at <NUM> of <NUM>,<NUM> to <NUM>,<NUM>,<NUM> mPa·s, more preferably <NUM>,<NUM> to <NUM>,<NUM> mPa·s. If the absolute viscosity is too low, the release force may be increased. If the absolute viscosity is too high, the organopolysiloxane may be difficult to disperse in the silicone release composition. As used herein, the absolute viscosity may be measured by a rotational viscometer.

Examples of the organopolysiloxane (E) containing a crosslinked structure and having fluidity include organopolysiloxanes obtained from addition reaction of an organopolysiloxane having a structure of the following average compositional formula (<NUM>) and an organohydrogenpolysiloxane having a structure of the following average compositional formula (<NUM>) in the presence of a platinum base catalyst. These organopolysiloxanes contain a crosslinked structure and flow well.

Herein M is R<NUM>SiO<NUM>/<NUM>, Mvi is R<NUM>PSiO<NUM>/<NUM>, MH is R<NUM>HSiO<NUM>/<NUM>, D is R<NUM>SiO<NUM>/<NUM>, Dvi is RPSiO<NUM>/<NUM>, DH is RHSiO<NUM>/<NUM>, T is RSiO<NUM>/<NUM>, Tvi is PSiO<NUM>/<NUM>, TH is HSiO<NUM>/<NUM>, Q is SiO<NUM>/<NUM>, R is each independently a C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, P is an alkenyl group of the formula: -(CH<NUM>)a-CH=CH<NUM> wherein a is an integer of <NUM> to <NUM>, θ, <IMG>, κ, λ, µ, o, π, ·ρ, σ, and τ are each independently <NUM> or a positive number, ν is <NUM> or a positive number of up to <NUM>, ϕ is <NUM> or a positive number of up to <NUM>, ξ is <NUM> or a positive number of up to <NUM>, χ is <NUM> or a positive number of up to <NUM>, not all <IMG>, λ and v are <NUM> at the same time, not all π, σ and ϕ are <NUM> at the same time, <NUM> ≤ <IMG>+λ+v ≤ <NUM>, <NUM> ≤ π+σ+ϕ ≤ <NUM>, and not both <IMG>+λ+ν and π+σ+ϕ are <NUM> at the same time.

The structural formulae (<NUM>) and (<NUM>) also imply average compositional formulae.

In formulae (<NUM>) and (<NUM>), examples of R and P are as exemplified above for R and P in formula (<NUM>), respectively. Among others, R is preferably selected from hydrocarbon groups of <NUM> to <NUM> carbon atoms, more preferably <NUM> to <NUM> carbon atoms, specifically alkyl groups such as methyl, ethyl, and propyl and aryl groups such as phenyl and tolyl. P is preferably selected from vinyl, allyl, butenyl, and propenyl.

In formulae (<NUM>) and (<NUM>), θ, <IMG>, κ, λ, µ, o, π, ρ, σ, and τ are each independently <NUM> or a positive number, θ is preferably <NUM> or a positive number of <NUM> to <NUM>, <IMG> is preferably <NUM> or a positive number of <NUM> to <NUM>, κ is preferably a positive number of <NUM> to <NUM>, λ is preferably <NUM> or a positive number of <NUM> to <NUM>, µ is preferably <NUM> or a positive number of <NUM> to <NUM>, o is preferably <NUM> or a positive number of <NUM> to <NUM>, π is preferably <NUM> or a positive number of <NUM> to <NUM>, ρ is preferably <NUM> or a positive number of <NUM> to <NUM>, σ is preferably <NUM> or a positive number of <NUM> to <NUM>, τ is preferably <NUM> or a positive number of <NUM> to <NUM>, v is <NUM> or a positive number of <NUM> to <NUM>, preferably <NUM> or a positive number of <NUM> to <NUM>, ϕ is <NUM> or a positive number of <NUM> to <NUM>, preferably <NUM> or a positive number of <NUM> to <NUM>, ξ is <NUM> or a positive number of <NUM> to <NUM>, preferably <NUM> or a positive number of <NUM> to <NUM>, χ is <NUM> or a positive number of <NUM> to <NUM>, preferably <NUM> or a positive number of <NUM> to <NUM>, not all <IMG>, λ and v are equal to <NUM> at the same time, not all π, σ and ϕ are equal to <NUM> at the same time, <IMG>+λ+ν is a positive number of <NUM> to <NUM>, preferably a positive number of <NUM> to <NUM>, π+σ+ϕ is a positive number of <NUM> to <NUM>, preferably a positive number of <NUM> to <NUM>, and not both <IMG>+λ+ν and π+σ+ϕ are equal to <NUM> at the same time.

The organopolysiloxane of formula (<NUM>) preferably has a vinyl content in the range of <NUM> to <NUM> mol/<NUM>, more preferably <NUM> to <NUM> mol/<NUM>.

Also the organopolysiloxane of formula (<NUM>) preferably has a Mw in the range of <NUM> to <NUM>,<NUM>, more preferably <NUM>,<NUM> to <NUM>,<NUM>.

Illustrative examples of the organopolysiloxane of formula (<NUM>) include both-end alkenyl-containing siloxanes, side chain alkenyl-containing siloxanes, one-end and side chain alkenyl-containing siloxanes, both-end and side chain alkenyl-containing siloxanes, and branch-end alkenyl-containing siloxanes.

Examples as expressed by structural formula include Mvi<NUM>Dκ, M<NUM>DκDviλ, Mvi<NUM>DκT<NUM>, Mvi<NUM>DκT<NUM>, Mvi<NUM>DκDviλ, Mvi<NUM>DκQ<NUM>, and MθDκDviλTviv wherein M, Mvi, D, Dvi, T, Tvi, Q, θ, κ, λ, and v are as defined above (same hereinafter). Illustrative structures include Mvi<NUM>D<NUM>, M<NUM>D<NUM>Dvi<NUM>, M<NUM>D<NUM>Dvi<NUM>, M<NUM>D<NUM>Dvi<NUM>, M<NUM>D<NUM>Dvi<NUM>, Mvi<NUM>D<NUM>T<NUM>, Mvi<NUM>D<NUM>T<NUM>, Mvi<NUM>D<NUM>Dvi<NUM>, Mvi<NUM>D<NUM>Dvi<NUM>, and M<NUM>D<NUM>Dvi<NUM>Tvi<NUM>.

The organohydrogenpolysiloxane of formula (<NUM>) preferably has a SiH content in the range of <NUM> to <NUM> mol/<NUM>, more preferably <NUM> to <NUM> mol/<NUM>.

Also the organohydrogenpolysiloxane of formula (<NUM>) preferably has a Mw in the range of <NUM> to <NUM>,<NUM>.

Illustrative examples of the organohydrogenpolysiloxane of formula (<NUM>) include both end hydrogensilyl-containing siloxanes, side chain hydrogensilyl-containing siloxanes, one end and side chain hydrogensilyl-containing siloxanes, and both end and side chain hydrogensilyl-containing siloxanes.

Examples as expressed by structural formula include MH<NUM>Dρ, M<NUM>DHσ, M<NUM>DρDHσ, MH<NUM>DρDHσ, MH<NUM>DρT<NUM>, MH<NUM>DρT<NUM>, and MoDρDHσTHϕ wherein M, MH, D, DH, T, TH, o, ρ, σ, and ϕ are as defined above (same hereinafter). Illustrative structures include MH<NUM>D<NUM>, MH<NUM>D<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, M<NUM>D<NUM>DH<NUM>, MH<NUM>D<NUM>T<NUM>, MH<NUM>D<NUM>T<NUM>, MH<NUM>D<NUM>DH<NUM>, MH<NUM>D<NUM>DH<NUM>, and M<NUM>D<NUM>DH<NUM>TH<NUM>.

For reaction, the organopolysiloxane of formula (<NUM>) and the organohydrogenpolysiloxane of formula (<NUM>) are preferably used in such a proportion as to give <NUM> to <NUM> moles, more preferably <NUM> to <NUM> moles of alkenyl groups in the organopolysiloxane of formula (<NUM>) per mole of SiH groups in the organohydrogenpolysiloxane of formula (<NUM>).

Suitable platinum base catalysts used in the addition reaction between the organopolysiloxane of formula (<NUM>) and the organohydrogenpolysiloxane of formula (<NUM>) include chloroplatinic acid, alcohol or aldehyde solutions of chloroplatinic acid, and complexes of chloroplatinic acid with various olefins or vinylsiloxanes.

The platinum base catalyst is added in a catalytic or effective amount. Specifically, it is preferably used in an amount to give <NUM> to <NUM>,<NUM> ppm, more preferably <NUM> to <NUM> ppm of platinum group metal based on the total weight of the organopolysiloxane of formula (<NUM>) and the organohydrogenpolysiloxane of formula (<NUM>).

A solvent may be used in the addition reaction. Suitable solvents used herein include organic solvents compatible with organopolysiloxanes (exclusive of siloxane solvents) such as toluene, hexane, xylene, and methyl ethyl ketone, and organopolysiloxanes (i.e. siloxane solvents), for example, low viscosity cyclic siloxanes such as octamethyltetrasiloxane and decamethylpentasiloxane, linear siloxanes such as M<NUM>Dn wherein M and D are as defined above and n is an integer of <NUM> to <NUM>, preferably <NUM> to <NUM>, and branched siloxanes such as M<NUM>+mDnTm wherein M, D, and T are as defined above, n is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>, and m is an integer of <NUM> to <NUM>, preferably an integer of <NUM> to <NUM>.

The amount of the solvent used is preferably <NUM> to <NUM> times, more preferably <NUM> to <NUM> times the total weight of the organopolysiloxane of formula (<NUM>) and the organohydrogenpolysiloxane of formula (<NUM>).

For the addition reaction between the organopolysiloxane of formula (<NUM>) and the organohydrogenpolysiloxane of formula (<NUM>), preferred reaction conditions include a temperature of <NUM> to <NUM>, especially <NUM> to <NUM> and a time of <NUM> to <NUM> hours, especially <NUM> to <NUM> hours.

The thus obtained organopolysiloxane of crosslinked structure preferably contains <NUM> to <NUM> moles, more preferably <NUM> to <NUM> moles of crosslinked structure (silalkylene bonds such as silethylene bonds) per <NUM>,<NUM> moles of siloxane units, as computed from <NUM>H-NMR analysis.

When the synthesis is carried out in an organic solvent such as toluene, the preferred procedure includes adding a low-viscosity organopolysiloxane as a solvent to the reaction mixture and heating the reaction mixture under reduced pressure to distill off the organic solvent, yielding an organopolysiloxane mixture devoid of the organic solvent.

The reduced pressure is preferably <NUM> to <NUM> mmHg, more preferably <NUM> to <NUM> mmHg. The heating conditions are preferably at <NUM> to <NUM> for <NUM> minutes to <NUM> hours, more preferably at <NUM> to <NUM> for <NUM> minutes to <NUM> hours.

The low-viscosity organopolysiloxane is preferably used as a solvent in such an amount that it may account for <NUM> to <NUM>% by weight, more preferably <NUM> to <NUM>% by weight of the organopolysiloxane mixture.

Illustrative structures of component (E) are given below, but not limited thereto.

A crosslinked product formed by mixing MVi<NUM>D<NUM> and M<NUM>D<NUM>DH<NUM> in a Vi/H ratio of <NUM> and heating for reaction in the presence of an addition reaction catalyst such as a platinum base catalyst.

A crosslinked product formed by mixing MVi<NUM>D<NUM>T<NUM> and MH<NUM>D<NUM> in a Vi/H ratio of <NUM> and heating for reaction in the presence of an addition reaction catalyst such as a platinum base catalyst.

A crosslinked product formed by mixing MVi<NUM>D<NUM>DVi<NUM> and MH<NUM>M<NUM>D<NUM>Q<NUM> in a Vi/H ratio of <NUM> and heating for reaction in the presence of an addition reaction catalyst such as a platinum base catalyst.

A crosslinked product formed by mixing MVi<NUM>M<NUM>D<NUM>Q<NUM> and MH<NUM>D<NUM> in a Vi/H ratio of <NUM> and heating for reaction in the presence of an addition reaction catalyst such as a platinum base catalyst.

Also useful as the organopolysiloxane containing a crosslinked structure and having fluidity are the condensation reaction products of a hydroxyl-containing organopolysiloxane with an alkoxysilane, alkoxy-containing organopolysiloxane or methylhydrogenorganopolysiloxane. The condensation reaction products preferably contain T units or RSiO<NUM>/<NUM> units wherein R is as defined above.

Illustrative structures are given below. Notably, MOH is (HO)RSiO<NUM>/<NUM>, MOCH3 is (CH<NUM>O)R<NUM>SiO<NUM>/<NUM>, and R is as defined above.

A crosslinked product formed by mixing MOH<NUM>D<NUM> and CH<NUM>Si(OCH<NUM>)<NUM> or a partial hydrolytic condensate thereof in a OH/OCH<NUM> ratio of <NUM> and heating for condensation in the presence of a condensation reaction catalyst such as an organotin catalyst.

A crosslinked product formed by mixing MOH<NUM>D<NUM> and MOCH3<NUM>D<NUM>T<NUM> in a OH/OCH<NUM> ratio of <NUM> and heating for reaction in the presence of an organotin catalyst.

The organopolysiloxane containing a crosslinked structure and having fluidity as component (E) is added in an amount of <NUM> to <NUM> parts by weight, preferably <NUM> to <NUM> parts by weight, and more preferably <NUM> to <NUM> parts by weight per <NUM> parts by weight of component (A). If the amount of component (E) is too small, the release force may be tight. If the amount is too large, the silicone release composition may become less curable.

Component (F) is a high-molecular-weight linear organopolysiloxane for the purpose of imparting slippage, which has the general formula (<NUM>).

Herein M<NUM> is R<NUM><NUM>SiO<NUM>/<NUM>, D is R<NUM>SiO<NUM>/<NUM>, R is as defined above, R<NUM> is a C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation or a hydroxyl group, and Ψ is a positive number of <NUM> to <NUM>,<NUM>. Component (F) enables to form a surface having a low coefficient of friction despite a low content of migration component because component (F) is kept entangled in a coating having a moderate crosslinking density.

In formula (<NUM>), examples of R are as exemplified above for R in formula (<NUM>), with C<NUM>-C<NUM> alkyl groups being preferred. R<NUM> is a C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation or a hydroxyl group. Examples of the C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation are as exemplified above for R in formula (<NUM>). R<NUM> is preferably a C<NUM>-C<NUM> alkyl group or hydroxyl group.

In formula (<NUM>), Ψ is a positive number of <NUM> to <NUM>,<NUM>, preferably <NUM> to <NUM>,<NUM>. A compound of formula (<NUM>) wherein Ψ is less than <NUM> tends to be a migration component because of a low molecular weight, so that the residual adhesion rate is aggravated or reduced, and a label peeled from the release sheet (release paper or release film) may be reduced in adhesive force. Inversely, a compound of formula (<NUM>) wherein Ψ exceeds <NUM>,<NUM> has so high a viscosity that it takes a time until the compound is dissolved in components (A), (B), (D) and (E), and the final composition obtained by mixing them has so high a viscosity that the coating weight may vary locally and high-speed coating may be accompanied by a large volume of mist.

Illustrative structures of component (F) include M<NUM><NUM>D<NUM>, M<NUM><NUM>D<NUM>, M<NUM><NUM>D<NUM>, M<NUM><NUM>D<NUM>, and M<NUM><NUM>D<NUM>.

Component (F) is blended in an amount of <NUM> to <NUM> parts by weight, preferably <NUM> to <NUM> parts by weight per <NUM> parts by weight of component (A).

While the solventless silicone release composition of the invention is obtained by mixing the predetermined amounts of the foregoing components (A), (B), (C), (E) and (F), any optional components may be added thereto if necessary as long as the objects and benefits of the invention are not impaired. Any well-known additives which are commonly used in silicone release compositions may be added in standard amounts. Although the solventless silicone release composition of the invention is designed as a solventless system in consideration of safety to the environment, its characteristics are not degraded even when it is diluted with an organic solvent.

As the optional component, the foregoing component (D), aryl-containing silicone resins, silicone resins, silica, and low-molecular-weight organopolysiloxanes having neither silicon-bonded hydrogen nor alkenyl for the purpose of adjusting release force, and the like may be added if necessary. The amounts of optional components may be standard amounts not to interfere with the benefits of the invention.

The solventless silicone release composition of the invention is prepared, preferably by premixing the foregoing components (A), (B), (F), (E) and optional components until uniform, and adding component (C) to the premix. Each component may be used alone or in admixture of two or more species.

The resulting solventless silicone release composition preferably has a kinematic viscosity at <NUM> of up to <NUM><NUM>/s, more preferably <NUM> to <NUM><NUM>/s, and even more preferably <NUM> to <NUM><NUM>/s. If the kinematic viscosity is too low, the coating weight may be reduced. If the kinematic viscosity is too high, the coating weight may vary or a large volume of mist may be generated.

The solventless silicone release composition thus prepared is coated onto a sheet-like substrate such as paper or plastic film by means of a coating roll or the like, and heat cured in a standard way. The sheet-like substrate having a cured silicone film of the solventless silicone release composition disposed on one side is advantageously used as a release sheet. Exemplary plastic films include polyethylene, polypropylene, and polyethylene terephthalate.

When applied by a coating roll, the solventless silicone release composition is effective for reducing the amount of mist generated even at a peripheral velocity of at least <NUM>/min, specifically <NUM> to <NUM>/min.

The solventless silicone release composition is uniformly coated onto the surface of a sheet-like substrate and heat cured. The coating weight of the solventless silicone release composition may be sufficient to form a cured silicone film on the substrate surface and is, for example, about <NUM> to <NUM>/m<NUM>. A too much coating weight may rather invite a decline of release properties. The heat curing conditions may be selected from the range of about <NUM> and about <NUM> seconds to about <NUM> and about <NUM> seconds although the temperature varies with the type of substrate and coating weight.

In a preferred embodiment of the release paper prepared as above, after the release paper having the cured silicone film is let float on a <NUM>% by weight aqueous solution of brilliant green dye such that one surface of the cured silicone film is immersed in the solution for <NUM> minute, and the one surface of the cured silicone film is washed with water, the cured silicone film shows no penetration of the dye from the one surface immersed in the dye solution to the opposite surface.

In the release paper prepared as above, the difference between maximum and minimum values of coating weight (cured silicone film weight) is preferably up to <NUM>/m<NUM>, more preferably <NUM> to <NUM>/m<NUM> as measured by X-ray fluorescence analysis.

Synthesis Examples, Examples, Reference Examples and Comparative Examples are given below for further illustrating the invention. It is noted that the kinematic viscosity is measured at <NUM> by an Ostwald viscometer and the absolute viscosity is measured by a rotational viscometer.

The silicone release compositions were evaluated for release force, residual adhesion rate, amount of generated mist, coating, and coating weight variation by the following methods. All silicone release compositions were cured without raising any problems.

The silicone release composition was coated onto the top rubber roller of three rollers of a Misting Tester (Toyo Seiki Seisaku-sho, Ltd). The rollers were rotated at a peripheral velocity of <NUM>/min for <NUM> seconds to perform high-speed coating, then stopped, and after a glassine paper was immediately inserted between the top rubber roller and the middle metal roller, rotated again at a low speed to transfer the silicone release composition from the rubber roller to the glassine paper. The coating weight of the silicone release composition on the glassine paper was <NUM>/m<NUM>. The glassine paper having the silicone release composition transferred thereon was heated in a hot-air dryer at <NUM> for <NUM> seconds, completing a release paper having a cured silicone film with a coating weight of <NUM>/m<NUM>. The release paper in this state was aged at <NUM> for one day, after which an emulsion type acrylic adhesive (BPW-6111A by Toyo Ink Co. ) as a pressure-sensitive adhesive was coated onto the cured silicone film surface (i.e. surface of the silicone transferred from the rubber roller) of the release paper and dried at <NUM> for <NUM> seconds. Next, a woodfree paper sheet was attached to the PSA surface, which was cut to a size of <NUM> × <NUM> and press bonded by rolling back and forth a roller of <NUM>, obtaining a sample. The sample was aged at <NUM> for <NUM>-<NUM> hours. Thereafter, an end portion of the sample was detached, and the end of the PSA-coated woodfree paper sheet was pulled back at an angle of <NUM>° relative to the glassine paper as the substrate and a peeling speed of <NUM>/min, during which a force (N/<NUM>) required for peeling was measured by a tensile tester (model AGS-<NUM> by Shimadzu Corp. ) and reported as a release force.

As in the release force test, a release or parting paper was prepared by forming a cured silicone film in a coating weight of <NUM>/m<NUM> on a glassine paper. The release paper was aged at <NUM> for one day. A polyester pressure-sensitive adhesive (PSA) tape No. 31B (by Nitto Denko Corp. , referred to as 31B tape, hereinafter) was attached to the cured silicone film surface of the release paper and press bonded under a pressure of <NUM>/cm<NUM> for <NUM> hours in a dryer at <NUM>. Then the 31B tape was peeled, and attached to a stainless steel (SUS304) plate. The assembly was pressed by rolling back and forth a roller of <NUM>, and allowed to stand for <NUM> minutes. Thereafter, an end portion of the 31B tape was detached and the end of the tape was pulled back at an angle of <NUM>° relative to the SUS304 plate and a peeling speed of <NUM>/min, during which a force (N/<NUM>) required for peeling was measured and reported as release force A.

As a blank, a 31B tape was attached to a Teflon® plate and press bonded under a pressure of <NUM>/cm<NUM> for <NUM> hours in a dryer at <NUM> as described above. Then the 31B tape was peeled, and attached to a SUS304 plate. The assembly was pressed by rolling back and forth a roller of <NUM>, and allowed to stand for <NUM> minutes. An end portion of the 31B tape was detached and the end of the tape was pulled back at an angle of <NUM>° relative to the SUS304 plate and a peeling speed of <NUM>/min, during which a force (N/<NUM>) required for peeling was measured and reported as release force B.

A residual adhesion rate (%) was determined by computing (A/B)× <NUM>.

An amount of generated mist was determined by coating <NUM> of the silicone release composition onto the top roller of a Misting Tester (Toyo Seiki Seisaku-sho, Ltd), rotating three rollers at <NUM>,<NUM> rpm (<NUM>/min), and measuring the amount of generated mist by a Dust Trak Aerosol Monitor Model <NUM> (TSI Inc. One opening of a vinyl tube having an inner diameter of <NUM> was placed <NUM> straight above the top roller while the other opening was connected to the suction port of the Dust Trak. While mist amount measurement was continued for <NUM> seconds, the maximum value was recorded.

For inspection of asperities on surface, a release paper was prepared by forming a cured silicone film in a coating weight of <NUM>/m<NUM> on the surface of a glassine paper as in the release force test. The release paper was let float on the surface of a <NUM>% by weight aqueous solution of brilliant green (C<NUM>H<NUM>O<NUM>S) dye such that only the surface of the silicone transferred to the glassine paper from the rubber roller (i.e. surface of the cured silicone film) was immersed in the solution for <NUM> minutes. The surface of the cured silicone film which had been immersed in the dye solution was washed with water. Coating was rated according to the following criteria by the degree of penetration of the dye to the back surface of the film. Thin areas of the cured silicone film are susceptible to chipping, which evidences the penetration of the dye.

Using a X-ray fluorescence spectrometer ZSX Primus II (Rigaku Corp. ), a sample having the silicone release composition coated thereon was quantitatively determined for elemental silicon content. Measurement was made at <NUM> points on the coating surface, from which the difference between maximum and minimum values was computed.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol and <NUM> part by weight of <NUM>,<NUM>-dimethylpropynyloxytrimethylsilane as addition reaction inhibitor component (D), and <NUM> parts by weight of mist suppressant <NUM> or organopolysiloxane containing a crosslinked structure and having fluidity in Synthesis Example <NUM> below as component (E) and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), (D), and (E), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and a H/Vi ratio (i.e. ratio of SiH groups to alkenyl groups in the composition) of <NUM>.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol as addition reaction inhibitor component (D), <NUM> parts by weight of mist suppressant <NUM> or organopolysiloxane containing a crosslinked structure and having fluidity in Synthesis Example <NUM> below as component (E), and <NUM> parts by weight of high-molecular-weight linear organopolysiloxane (<NUM>) as component (F) and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), (D), (E), and (F), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and H/Vi=<NUM>.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) and <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol and <NUM> part by weight of <NUM>,<NUM>-dimethylpropynyloxytrimethylsilane as addition reaction inhibitor component (D), <NUM> parts by weight of mist suppressant <NUM> or organopolysiloxane containing a crosslinked structure and having fluidity in Synthesis Example <NUM> below as component (E), and <NUM> parts by weight of high-molecular-weight linear organopolysiloxane (<NUM>) as component (F), and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), (D), (E), and (F), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and H/Vi=<NUM>.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol and <NUM> part by weight of <NUM>,<NUM>-dimethylpropynyloxytrimethylsilane as addition reaction inhibitor component (D), and <NUM> parts by weight of mist suppressant <NUM> or organopolysiloxane containing a crosslinked structure and having fluidity in Synthesis Example <NUM> below as component (E), and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), (D), and (E), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and H/Vi=<NUM>.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), and <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol and <NUM> part by weight of <NUM>,<NUM>-dimethylpropynyloxytrimethylsilane as addition reaction inhibitor component (D), and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), and (D), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and H/Vi=<NUM>.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol as addition reaction inhibitor component (D), and <NUM> parts by weight of high-molecular-weight linear organopolysiloxane (<NUM>) as component (F), and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), (D) and (F), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and H/Vi=<NUM>.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) and <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol and <NUM> part by weight of <NUM>,<NUM>-dimethylpropynyloxytrimethylsilane as addition reaction inhibitor component (D), and <NUM> parts by weight of high-molecular-weight linear organopolysiloxane (<NUM>) as component (F), and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), (D), and (F), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and H/Vi=<NUM>.

A silicone release composition was prepared by combining <NUM> parts by weight of methylvinylpolysiloxane (<NUM>) as component (A), <NUM> parts by weight of methylhydrogenpolysiloxane (<NUM>) as component (B), <NUM> part by weight of <NUM>-ethynyl-<NUM>-cyclohexanol as addition reaction inhibitor component (D), <NUM> parts by weight of mist suppressant <NUM> or organopolysiloxane containing a crosslinked structure and having fluidity in Synthesis Example <NUM> below as component (E), and <NUM> parts by weight of high-molecular-weight linear organopolysiloxane (<NUM>) as component (F), and stirring them until uniform. A platinum-vinylsiloxane complex as addition reaction catalyst (C) was added to the mixture in such an amount as to give <NUM> ppm of platinum atom based on the total weight of components (A), (B), (D), (E), and (F), which were stirred until uniform. The resulting silicone release composition had a kinematic viscosity of <NUM><NUM>/s and H/Vi=<NUM>.

A polysiloxane blocked with dimethylvinylsiloxy at both molecular ends, consisting of (CH<NUM>)<NUM>SiO units except both ends, having vinyl value <NUM> mol/<NUM> and kinematic viscosity <NUM><NUM>/s.

{(CH<NUM>=CH)(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>.

A polysiloxane blocked with trimethylsiloxy at the molecular ends, based on a siloxane chain consisting of (CH<NUM>)(CH<NUM>=CH)SiO units and (CH<NUM>)<NUM>SiO units, and having vinyl value <NUM> mol/<NUM> and kinematic viscosity <NUM><NUM>/s.

{(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>{(CH<NUM>=CH)(CH<NUM>)SiO}<NUM>.

A branched polysiloxane blocked with dimethylvinylsiloxy at three ends of the molecular chain, having vinyl value <NUM> mol/<NUM> and kinematic viscosity <NUM><NUM>/s.

{(CH<NUM>=CH)(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>{(CH<NUM>)SiO<NUM>/<NUM>}<NUM>.

A polysiloxane blocked with dimethylvinylsiloxy at molecular ends, having vinyl value <NUM> mol/<NUM> and kinematic viscosity <NUM><NUM>/s.

A methylhydrogenpolysiloxane blocked with trimethylsiloxy at both molecular ends, consisting of (CH<NUM>)HSiO units except both ends, having SiH content <NUM> mol/<NUM> and kinematic viscosity <NUM><NUM>/s.

{(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)(H)SiO}<NUM>.

A methylhydrogenpolysiloxane blocked with trimethylsiloxy at both molecular ends, based on a siloxane chain consisting of (CH<NUM>)HSiO units and (CH<NUM>)<NUM>SiO units in a ratio ((CH<NUM>)HSiO units/(CH<NUM>)<NUM>SiO units) of <NUM>/<NUM>, having SiH content <NUM> mol/<NUM> and kinematic viscosity <NUM><NUM>/s.

{(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>{(CH<NUM>)(H)SiO}<NUM>.

<NUM> of a side chain methylhydrogenpolysiloxane of the formula: {(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>{(CH<NUM>)HSiO}<NUM> and <NUM> of a branched vinylmethylpolysiloxane of the formula: {(CH<NUM>=CH)(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>{(CH<NUM>)SiO<NUM>/<NUM>}<NUM> were mixed (SiH : vinyl = <NUM> mol : <NUM> mol) in <NUM> of toluene (corresponding to <NUM> times the total weight of the side chain methylhydrogenpolysiloxane and the branched vinylmethylpolysiloxane). A vinylmethylpolysiloxane-coordinated platinum base catalyst was added in an amount to give <NUM> ppm of platinum based on the total weight of the reaction system. The system was heated and reaction was performed at a temperature of <NUM> for <NUM> hours. The reaction product took the form of a toluene solution having an absolute viscosity of <NUM> mPa·s and had an absolute viscosity of <NUM>,<NUM> mPa·s after removal of toluene. It had <NUM> mol of silethylene bonds per <NUM>,<NUM> mol of siloxane units as computed from <NUM>H-NMR data. To the reaction product was added <NUM> of a dimethylpolysiloxane of the formula: {(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>. Under nitrogen bubbling, this was subjected to vacuum distillation under <NUM> mmHg or below at <NUM> for <NUM> hours, yielding a siloxane mixture, which (<NUM> wt%) consisted of <NUM> wt% of dimethylpolysiloxane and <NUM> wt% of the reaction product (i.e. organopolysiloxane containing crosslinked structure and having fluidity) and had a kinematic viscosity of <NUM><NUM>/s.

<NUM> of a both end hydroxyl-containing dimethylpolysiloxane of the formula: {(HO)(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM> and <NUM> of a branched methoxymethylpolysiloxane of the formula: {(CH<NUM>O)(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>{(CH<NUM>)SiO<NUM>/<NUM>}<NUM> were mixed (SiOH : SiOCH<NUM> = <NUM> mol : <NUM> mol) in <NUM> of toluene (corresponding to <NUM> times the total weight of the both end hydroxyl-containing polysiloxane and the branched methoxymethylpolysiloxane). A dioctyltin dicarboxylate (i.e. dioctyltin dineodecanoate) was added in an amount to give <NUM> wt% of tin based on the total weight of the siloxanes. The system was heated and reaction was performed at a temperature of <NUM> for <NUM> hours. The reaction product took the form of a toluene solution having an absolute viscosity of <NUM> mPa·s and had an absolute viscosity of <NUM>,<NUM> mPa·s after removal of toluene. To the reaction product was added <NUM> of a dimethylpolysiloxane of the formula: {(CH<NUM>)<NUM>SiO<NUM>/<NUM>}<NUM>{(CH<NUM>)<NUM>SiO}<NUM>. Under nitrogen bubbling, this was subjected to vacuum distillation under <NUM> mmHg or below at <NUM> for <NUM> hours, yielding a siloxane mixture, which (<NUM> wt%) consisted of <NUM> wt% of dimethylpolysiloxane and <NUM> wt% of the reaction product (i.e. organopolysiloxane containing crosslinked structure and having fluidity) and had a kinematic viscosity of <NUM><NUM>/s.

The silicone release compositions of Examples, Reference Examples and Comparative Examples were evaluated for the aforementioned properties, with the results shown in Tables <NUM> and <NUM>.

The silicone release compositions of Examples <NUM> and <NUM> and Reference Examples <NUM>, <NUM> and <NUM>, in which organopolysiloxane (E) containing a crosslinked structure and having fluidity (mist suppressant) is added, have a kinematic viscosity of up to <NUM><NUM>/s and a maximum amount of generated mist as low as <NUM> to <NUM>/m<NUM>. By virtue of these properties, in Examples <NUM> and <NUM> and Reference Examples <NUM>, <NUM> and <NUM>, no penetration of the dye solution to the back surface is observed in the coating test and the coating weight variation is as small as <NUM>/m<NUM> or less.

On the contrary, the silicone release compositions of Comparative Examples <NUM> to <NUM> in which a mist suppressant is not added have a maximum amount of generated mist as high as <NUM> to <NUM>/m<NUM>. In the release papers using the silicone release compositions of Comparative Examples <NUM> to <NUM>, the penetration of the dye solution from the front surface to the back surface is observed and the coating weight variation is <NUM>/m<NUM> or greater, indicating a rough surface.

Claim 1:
A solventless silicone release composition comprising the following components (A), (B), (C), (E) and (F):
(A) alkenyl-containing organopolysiloxane containing at least two alkenyl groups per molecule and having a vinyl value of <NUM> mol/<NUM> to <NUM> mol/<NUM> and a kinematic viscosity at <NUM> of <NUM><NUM>/s to <NUM><NUM>/s, when measured by an Ostwald viscometer, represented by the general formula (<NUM>)

        MαMviβDγDviδTεTviζQη     (<NUM>)

wherein M is R<NUM>SiO<NUM>/<NUM>, Mvi is R<NUM>PSiO<NUM>/<NUM>, D is R<NUM>SiO<NUM>/<NUM>, Dvi is RPSiO<NUM>/<NUM>, T is RSiO<NUM>/<NUM>, Tvi is PSiO<NUM>/<NUM>, Q is SiO<NUM>/<NUM>, each R independently is a C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation, P is an alkenyl group of the formula -(CH<NUM>)a-CH=CH<NUM> wherein a is an integer of <NUM> to <NUM>, α, β, δ and ζ are each independently an integer of at least <NUM>, not all of β, δ and ζ being <NUM> at the same time, <NUM> ≤ β+δ+ζ ≤ <NUM>, γ is an integer of <NUM> to <NUM>, ε is an integer of <NUM> to <NUM>, and η is an integer of <NUM> to <NUM>,
(B) organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule and having a kinematic viscosity at <NUM> of <NUM><NUM>/s to <NUM><NUM>/s, when measured by an Ostwald viscometer, in an amount to give <NUM> to <NUM> moles of silicon-bonded hydrogen atoms per mole of alkenyl groups in component (A),
(C) an effective amount of platinum group metal base catalyst,
(E) <NUM> to <NUM> parts by weight, per <NUM> parts by weight of component (A), of organopolysiloxane containing a crosslinked structure and having fluidity, and
(F) <NUM> to <NUM> parts by weight per <NUM> parts by weight of component (A) of a high-molecular-weight linear organopolysiloxane having the general formula (<NUM>):

        M<NUM><NUM>DΨ     (<NUM>)

wherein M<NUM> is R<NUM><NUM>SiO<NUM>/<NUM>, D is as defined above, R<NUM> is a C<NUM>-C<NUM> substituted or unsubstituted monovalent hydrocarbon group free of aliphatic unsaturation or a hydroxyl group, and Ψ is a positive number of <NUM> to <NUM>,<NUM>.