DESCRIPTION Organohydrogenpolysiloxane Mixture and Silicone Release Coating Composition [0001] This invention relates to an organohydrogenpolysiloxane mixture and a silicone release coating composition comprising the organohydrogenpolysiloxane mixture. The organohydrogenpolysiloxane mixture which is useful as a crosslinker also acts as an adhesion promoter for silicone compositions cured via addition reaction. When cured, the silicone release coatings comprising these organohydrogenpolysiloxane mixtures exhibit release properties with respect to tacky substances and also exhibit an excellent adherence for a variety of substrates.

[0002] It is known that coating compositions that exhibit excellent releasability from various tacky substances can be obtained by coating and then curing a silicone release coating composition on the surface of a substrate such as paper, corrugated cardboard, laminated paper, synthetic resin films, clothing and fabrics, synthetic fibers, and metal foils. The silicone release coating compositions used for this purpose have included a variety of addition reaction-curing silicone compositions based on alkenyl-functional organopolysiloxane, SiH-functional organohydrogenpolysiloxane, and platinum catalyst.

The organohydrogenpolysiloxane used here is typically a single cmpound with a low viscosity of approximately 5 centipoise to 70 mm2/s and a narrow molecular weight distribution (refer, for example, to EP 371404, EP 1004632 and Japanese Patent Application Publication (Kokai) Numbers Hei 7-258606 (258,606/1995), 2000-160101). However, addition reaction-curing silicone compositions containing such organohydrogenpolysiloxane have suffered from unsatisfactory post-cure adherence to substrate and in particular have been difficult to adhere to synthetic resin films and clay-coated paper.

[0003] One object of this invention is to provide an organohydrogenpolysiloxane mixture that is useful both as a crosslinker and as an adhesion promoter for addition reaction-curing silicone compositions. Another object of this invention is to provide a silicone composition that forms a release coating upon curing that is strongly adherent to a variety of substrates on which the silicone composition is coated.

[0004] The present invention relates to an organohydrogenpolysiloxane mixture comprising partially branched straight-chain organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms in each molecule, such mixture having a viscosity at 25°C of 80 to 700 mPa-s and a dispersity (weight-average molecular weight/number-average molecular weight) of 2. 0 to 10.0.

[0005] The organohydrogenpolysiloxane mixture is a mixture of partially branched straight-chain organohydrogenpolysiloxanes that have different molecular weights and at least two silicon-bonded hydrogen atoms in each molecule. This organohydrogenpolysiloxane will generally contain RSiO3/2 siloxane unit where R is an alkyl group or aryl group. Examples of the alkyl groups of R include methyl, ethyl, propyl, and butyl. An example of the aryl group of R is phenyl. Preferably, the organohydrogenpolysiloxane will contain from 1 to 20 RSi03/2 siloxane units in each molecule, with 1 to 10 being more preferable.

[0006] The viscosity at 25°C of the organohydrogenpolysiloxane mixture is 80 to 700 mPa s, preferably 100 to 500 mPa s, and more preferably 100 to 300 mPa s. This mixture should have a broad molecular weight distribution ranging from the low molecular weight region to the high molecular weight region, and its dispersity (weight-average molecular weight/number-average molecular weight) should be in the range of 2.0 to 10.0, preferably in the range of 2.0 to 6.0 and more preferably in the range of 2.5 to 5.5.

[0007] The silicon-bonded groups in the organohydrogenpolysiloxane other than hydrogen can include hydroxyl in addition to the aforementioned alkyl and aryl. The organohydrogenpolysiloxane can be specifically exemplified with the following general formula: (RHSi02/2) x (RSi03/2) y (R2Si02/2) z (R3SiOi/2) w where R is as defined above, x is a number with a value of at least 2, y is a number with a value of at least 1, z is a number with a value of at least 0, w is a number with a value of at least 3, and (x + y + z + w) is a number that provides a viscosity at 25°C of 80 to 700 mPa s.

The subscript y is preferably from 1 to 20 and more preferably from 1 to 10; (y/x) is preferably from 0.01 to 0.10 and more preferably from 0.01 to 0.06 ; and (z/x) is preferably no greater than 0.10 and more preferably is no greater than 0.08.

[0008] The present organohydrogenpolysiloxane mixture can be prepared, for example, by reacting a cyclic SiH-functional organohydrogensiloxane and a trimethylsiloxy- endblocked dimethylsiloxane oligomer for 1 to 3 hours at 30 to 50°C in the presence of an acid catalyst and then raising the temperature to 70 to 100°C and reacting for 1 to 24 hours.

The present organohydrogenpolysiloxane mixture can also be prepared by heating a straight- chain organohydrogenpolysiloxane having a low degree of polymerization for 1 to 24 hours at 70°C to 100°C in the presence of an acid catalyst. It is believed that the RS 103/2 unit is produced in these methods through conversion of some of the SiH in the RHSiO unit to silanol by the trace amounts of water present in the starting materials and then dehydration condensation between the resulting R (HO) SiO and RHSiO units. The introduction of water to the heating and reaction step enables the preparation of organohydrogenpolysiloxane mixtures with relatively higher viscosities through addition of the water.

[0009] The inventive organohydrogenpolysiloxane mixture as described above is characterized by its ability to function as a crosslinker for addition reaction-curing silicone compositions and in particular by its ability to function as a crosslinker that provides excellent adherence to substrates on which addition reaction-curing silicone compositions are coated. The inventive mixture can be used both in solvent-based and solventless addition reaction-curing silicone compositions. Also the inventive mixture can be used in emulsion- based addition reaction-curing silicone compositions. For the purposes of this invention, addition reaction-curing refers to curing by a hydrosilylation reaction between an alkenyl- functional organopolysiloxane and an organohydrogenpolysiloxane in the presence of an addition-reaction catalyst.

[0010] The present invention also relates to a release coating silicone composition comprising (A) an organopolysiloxane having at least two alkenyl groups in each molecule and a viscosity at 25°C of at least 40 mPa s, (B) an organohydrogenpolysiloxane mixture comprising partially branched straight-chain organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms in each molecule, such mixture having a viscosity at 25°C of 80 to 700 mPa-s and a dispersity (weight-average molecular weight/number-average molecular weight) of 2.0 to 10.0, and (C) an addition-reaction catalyst.

[0011] Component (A) comprises an organopolysiloxane having at least two alkenyl groups in each molecule. Component (A) may be generally represented by the average unit

formula R aSiO. , where R represents monovalent hydrocarbyl groups. Examples of R1 include alkyl groups such as methyl, ethyl, propyl, and butyl; alkenyl groups such as vinyl, allyl, butenyl, pentenyl, and hexenyl; aryl groups such as phenyl, tolyl, and xylyl ; aralkyl groups such as benzyl and phenethyl ; and halogen-substituted alkyl groups such as 3- chloropropyl and 3,3, 3-trifluoropropyl. The subscript a in the preceding formula is a number with a value of 1.95 to 2.05.

[0012] The molecular structure of component (A) is not critical and can be exemplified by straight-chain, cyclic, network, and partially branched straight-chain molecular structures.

The straight-chain molecular structure is preferred. In the case of the straight-chain molecular structure, groups residing in molecular chain terminal position can be, for example, trimethylsiloxy, dimethylvinylsiloxy, dimethylphenylsiloxy, or dimethylhydroxysiloxy.

[0013] The viscosity of component (A) at 25°C should be at least 40 mua s with an upper limit up to and including the viscosity of gums. Viscosities below 40 mua-s may result in an overly large permeation of the silicone release coating composition into the substrate. When the release coating composition is employed in solventless form, component (A) preferably has a viscosity in the range of 40 to 10,000 mPa s and more preferably in the range of 100 to 5,000 mPa s. With a solvent-based release coating, component (A) preferably has a viscosity from 100,000 mPa-s up to and including the viscosity of gums and more preferably has a viscosity from 500,000 mPa-s up to and including the viscosity of gums.

[0014] Examples of component (A) include dimethylvinylsiloxy-endblocked dimethylpolysiloxanes, <BR> <BR> <BR> <BR> <BR> dimethylvinylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxane copolymers,<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> dimethylvinylsiloxy-endblocked dimethylsiloxane-methylphenylsiloxane copolymers,<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> trimethylsiloxy-endblocked methylvinylpolysiloxanes,<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> trimethylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxane copolymers, trimethylsiloxy-endblocked dimethylsiloxane-methyl (5-hexenyl) siloxane copolymers, <BR> <BR> <BR> <BR> dimethylhexenylsiloxy-endblocked dimethylsiloxane-methyl (5-hexenyl) siloxane copolymers, dimethylvinylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxane- methylphenylsiloxane copolymers, dimethylhydroxysiloxy-endblocked methylvinylpolysiloxanes, and dimethylhydroxysiloxy-endblocked dimethylsiloxane-methylvinylsiloxane copolymers.

[0015] Component (B) comprises an organohydrogenpolysiloxane mixture comprising partially branched straight-chain organohydrogenpolysiloxanes having at least two silicon- bonded hydrogen atoms in each molecule, such mixture having a viscosity at 25°C of 80 to 700 mPa-s and a dispersity (weight-average molecular weight/number-average molecular weight) of 2. 0 to 10.0. The organohydrogenpolysiloxane mixture of component (B) is as described above. Component (B) is admixed preferably at from 0.5 to 20 weight parts per 100 weight parts component (A) and more preferably at from 1 to 10 weight parts per 100 weight parts component (A). The cure of the present inventive composition becomes unsatisfactory when component (B) is admixed at less than 0.5 weight part, while the release characteristics of the cured coating deteriorate when component (B) is admixed at more than 20 weight parts.

[0016] The addition-reaction catalyst (C) is a catalyst that induces cure of the inventive composition by promoting the addition reaction between the alkenyl groups in component (A) and the silicon-bonded hydrogen atoms in component (B). This addition-reaction catalyst is preferably a platinum catalyst and can be exemplified by chloroplatinic acid, alcohol solutions of chloroplatinic acid, chloroplatinic acid/olefin complexes, chloroplatinic acid/vinylsiloxane complexes, chloroplatinic acid/diketone complexes, platinum supported on finely divided alumina, platinum supported on finely divided silica, and platinum black.

Component (C) should be blended in a catalytic quantity, but its blending proportion is not otherwise critical. Preferably, component (C) is employed in a quantity that provides from 1 to 1,000 ppm platinum metal per component (A).

[0017] In preferred embodiments, the present composition may also comprise an addition-reaction inhibitor for the purpose of improving the room-temperature storage stability. Examples of this addition-reaction inhibitor include alkynyl alcohols such as 3- methyl-l-butyn-3-ol, 3, 5-dimethyl-1-hexyn-3-ol, 3-methyl-1-pentyn-3-ol, and phenylbutynol, and by 3-methyl-3-penten-1-yne, 3, 5-dimethyl-1-hexyn-3-ene, benzotriazole, 1-ethynyl-l- cyclohexanol, and methylvinylsiloxane cyclics. This addition-reaction inhibitor will generally be admixed in the range of 0.001 to 5 weight parts per 100 weight parts component (A).

[0018] The present composition may also contain one or more other ingedients, as necessary or desired, including controlled-release additives, heat stabilizers, organic resin powder, photosensitizers, dyes, pigments, and a thickener such as finely divided silica.

Further, the inventive composition may contain low-viscosity organohydrogenpolysiloxanes

having a viscosity at 25°C of less than 80 mPa s. The organic solvent used to prepare solvent-based formulations of the present inventive composition should be capable of homogeneously dissolving the present inventive composition, but is not otherwise critical.

Examples of useful organic solvents include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as pentane, hexane, and heptane; halogenated hydrocarbons such as trichloroethylene, perchloroethylene, trifluoromethylbenzene, 1,3- bis (trifluoromethyl) benzene, and methylpentafluorobenzene; and also by ethyl acetate, methyl ethyl ketone, and methyl isobutyl ketone. In case the present composition is a solventless formulation, the viscosity of the present inventive composition at 25°C is preferably from 50 to 5,000 mua-s and more preferably is from 100 to 2,000 mPa s.

[0019] The curing conditions for the present composition are not critical, but curing by heating in the range from 50 to 200°C is generally preferred. Curing may also be effected through the combined use of heating and exposure to ultraviolet radiation.

[0020] A characteristic feature of the present silicone release coating composition as described hereinabove is its ability to form, on a variety of substrate surfaces, cured release coatings that exhibit both an appropriate peel resistance versus tacky substances as well as an excellent residual adherence. Applicable substrates in this regard include paper, corrugated cardboard, clay-coated paper, laminated paper, synthetic resin films, clothing and fabrics, synthetic fibers, and metal foils. More particularly, the inventive composition has the advantage of being strongly adherent to synthetic resin films (e. g. , polyethylene terephthalate) and clay-coated paper, which have been troublesome for prior-art silicone release agents. Substrates bearing a cured release coating generated by the present inventive composition can be used for process paper, asphalt paper, tapes, and labels.

[0021] The present invention is explained below in greater detail through working examples, disclosed to further teach, but not limit, the invention, which is properly delineated by the appended claims. In the examples"parts"denotes weight parts and the values reported for viscosity were measured at 25°C using a rotary viscometer.

Test Methods [0022] Cured adherence

The silicone release coating composition was coated at 0.5 g/m2 on polyethylene terephthalate film. A cured coating was then produced by heating for 30 seconds at 140°C in a forced convection oven. After this coating had been held for 48 hours at 40°C and a humidity of 90%, it was forcefully rubbed with a finger and the presence/absence of coating debonding was determined. A score of + was assigned when the coating did not debond from the film and thus was strongly adhered thereto. A score of x was assigned when debonding of the coating was observed.

[0023] Cured coating peel resistance The silicone release coating composition was coated at 1.0 g/m2 on the surface of polyethylene-laminated paper and a cured coating was then produced by heating for 30 seconds at 160°C in a forced convection oven. The resulting cured coating was coated with an acrylic pressure-sensitive adhesive (Oribain BPS5127 from Toyo Ink Mfg. Co. , Ltd.) followed by drying by heating for 2 minutes at 70°C in a forced convection oven. Backing paper was subsequently applied and the resulting assembly was held under a load of 20 g/cm for 24 hours at 25°C and 60% humidity. After the 24-hour period, the backing paper was peeled off at an angle of 180° using a Tensilon and the force (mN) required for peeling was measured. The test width was 5 cm in all cases.

[0024] Residual adherence of tacky material The silicone release coating composition was coated at 1.0 g/m2 on the surface of polyethylene-laminated paper and a cured coating was prepared. Pressure-sensitive adhesive tape (Nitto Polyester Adhesive Tape 31B from Nitto Denko Corporation) was applied onto the coated surface followed by aging for 20 hours at 70°C under a load of 20 g/cm. The pressure-sensitive adhesive tape was then peeled off and the peeled tape was itself pasted on a stainless steel plate. After holding for 30 minutes at 25°C under a load of 20 g/cm2, this pressure-sensitive adhesive tape was pulled off at an angle of 180° at a rate of 0.3 m/minute and the force (gf) required for peeling was measured. In the blank test, the pressure-sensitive adhesive tape (Nitto Polyester Adhesive Tape 31B from Nitto Denko Corporation) was applied under the same conditions as described above on a polyfluoroethylene sheet and the force (gf) required to peel this pressure-sensitive adhesive tape from a stainless steel plate was then also measured under the same conditions as

described above. The residual adherence (%) was calculated using the following equation from the obtained measurement values. force (gf) required to peel the pressure-sensitive adhesive tape that had been applied to the cured coating generated from the silicone composition residual adherence (%) = x 100 force (gf) required to peel the pressure-sensitive adhesive tape that had been applied to polyfluoroethylene [0025] Example 1: 4.35 parts hexamethyldisiloxane and 4.05 parts active clay were mixed into 145.65 parts tetramethyltetrahydrogentetracyclosiloxane followed by reaction for 2 hours at 40°C and then reaction for another 10 hours with the temperature raised to 80°C.

Filtration after cooling yielded a methylhydrogenpolysiloxane mixture with a viscosity of 150 mPa s. Analysis of this methylhydrogenpolysiloxane mixture by nuclear magnetic resonance spectroscopy (NMR analysis) confirmed it to be a mixture of straight-chain methylhydrogenpolysiloxanes with partial branching in the molecule where molecular chain terminals were endblocked with trimethylsiloxy groups and the main chains were composed of siloxane units with the following formulas and y/x was 0.03.

The dispersity (weight-average molecular weight/number-average molecular weight) according to gel permeation chromatographic analysis (GPC analysis) was 2.87.

[0026] Example 2: 4.35 parts hexamethyldisiloxane and 4.05 parts active clay were mixed into 145.65 parts tetramethyltetrahydrogentetracyclosiloxane followed by reaction for 2 hours at 40°C and then reaction for another 10 hours with the temperature raised to 90°C.

Filtration after cooling yielded a methylhydrogenpolysiloxane mixture with a viscosity of 250 mPa s. NMR analysis of this methylhydrogenpolysiloxane mixture confirmed it to be a mixture of straight-chain methylhydrogenpolysiloxanes with partial branching in the molecule where molecular chain terminals were endblocked with trimethylsiloxy groups and

the main chains were composed of siloxane units with the following formulas and y/x was 0.04.

The dispersity (weight-average molecular weight/number-average molecular weight) according to GPC analysis was 5.38.

[0027] Example 3: A solvent-based silicone release coating composition was prepared by intermixing: 100 parts trimethylsiloxy-endblocked dimethylsiloxane- methylvinylsiloxane copolymer gum (vinyl content = 0.9 wt%), 2 parts of the methylhydrogenpolysiloxane mixture with a viscosity of 150 mPa-s that was prepared in Example 1, chloroplatinic acid/1, 3-divinyltetramethyldisiloxane complex in an amount sufficient to provide 200 ppm platinum metal, 1 part 3-methyl-1-butyn-3-ol, and 1957 parts toluene. The resulting silicone composition was tested for its cured adherence to substrate, cured coating peel resistance, and residual adherence of tacky material. The results are reported in Table 1.

[0028] Example 4: A solvent-based silicone release coating composition was prepared by intermixing: 100 parts trimethylsiloxy-endblocked dimethylsiloxane- methylvinylsiloxane copolymer gum (vinyl content = 0.9 wt%), 2 parts of the methylhydrogenpolysiloxane mixture with a viscosity of 250 mua-s that was prepared in Example 2, chloroplatinic acid/1, 3-divinyltetramethyldisiloxane complex in an amount sufficient to provide 200 ppm platinum metal, 1 part 3-methyl-1-butyn-3-ol, and 1957 parts toluene. The resulting silicone composition was tested for its cured adherence to substrate, cured coating peel resistance, and residual adherence of tacky material. The results are reported in Table 1.

[0029] Comparative Example 1: A solvent-based silicone release coating composition was prepared as in Example 3, but in this case replacing the methylhydrogenpolysiloxane mixture (viscosity = 150 mPa s) used in Example 3 with

trimethylsiloxy-endblocked methylhydrogenpolysiloxane (SP7297 from Dow Corning Toray Silicone Co. , Ltd. ) having a viscosity of 25 mua-s and a dispersity of 1.41. The resulting silicone composition was tested for its cured adherence to substrate, cured coating peel resistance, and residual adherence of tacky material. The results are reported in Table 1.

[0030] Example 5: A solvent-based silicone release coating composition was prepared by intermixing: 100 parts trimethylsiloxy-endblocked dimethylsiloxane- methylhexenylsiloxane copolymer gum (hexenyl content = 0. 5 wt%), 2 parts of the methylhydrogenpolysiloxane mixture with a viscosity of 150 mPa-s that was prepared in Example 1, chloroplatinic acid/1, 3-divinyltetramethyldisiloxane complex in an amount sufficient to provide 200 ppm platinum metal, 1 part 3-methyl-1-butyn-3-ol, and 1957 parts toluene. The resulting silicone composition was tested for its cured adherence to substrate, cured coating peel resistance, and residual adherence of tacky material. The results are reported in Table 1.

[0031] Comparative Example 2: A solvent-based silicone release coating composition was prepared as in Example 5, but in this case replacing the methylhydrogenpolysiloxane mixture (viscosity= 150 mPa s) used in Example 5 with trimethylsiloxy-endblocked methylhydrogenpolysiloxane (SP7297 from Dow Corning Toray Silicone Co. , Ltd. ) having a viscosity of 25 mPa-s and a dispersity of 1.41. The resulting silicone composition was tested for its cured adherence to substrate, cured coating peel resistance, and residual adherence of tacky material. The results are reported in Table 1.

[0032] Example 6: A solventless silicone release coating composition with a viscosity of 390 mPa-s was prepared by intermixing : 100 parts dimethylhexenylsiloxy- endblocked dimethylsiloxane-methylhexenylsiloxane copolymer with a viscosity of 400 mPa s (hexenyl content = 1. 0 wt%), 3 parts of the methylhydrogenpolysiloxane mixture with a viscosity of 250 mua-s that was prepared in Example 2, chloroplatinic acid/1, 3- divinyltetramethyldisiloxane complex in an amount sufficient to provide 200 ppm platinum metal, and 1 part 1-ethynyl-l-cyclohexanol. The resulting silicone composition was tested for its cured adherence to substrate, cured coating peel resistance, and residual adherence of tacky material. The results are reported in Table 1.

[0033] Comparative Example 3: A solventless silicone release coating composition was prepared as in Example 6, but in this case replacing the methylhydrogenpolysiloxane mixture (viscosity = 250 mPa s) used in Example 6 with trimethylsiloxy-endblocked methylhydrogenpolysiloxane (SP7297 from Dow Coming Toray Silicone Co. , Ltd. ) having a viscosity of 25 mua-s and a dispersity of 1.41. The resulting silicone composition was tested for its cured adherence to substrate, cured coating peel resistance, and residual adherence of tacky material. The results are reported in Table 1.

Table 1. cured adherence peel resistance residual adherence (PET) (mN/5 cm) (%) Example 3 + 412 96 Example 4 + 412 95 Example 5 + 333 94 Example 6 + 353 95 Comp. Ex. 1 x 392 94 Comp. Ex. 2 x 323 95 Comp. Ex. 3 x 343 95