Silicone-organic coating compositions

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BACKGROUND OF THE INVENTION

The present invention relates to coating compositions which provide films, such as adhesive release films and protective films, having improved water resistance, to a method for coating a substrate therewith and to a method for preparing stable emulsion forms thereof.

More particularly the present invention relates to coating compositions comprising a silicon-free, film-forming organic polymer and a liquid silicone resin which provide a film having the strength of the organic polymer and the water resistance of the silicone resin.

The liquid silicone resin which is used in the compositions and methods of this invention has been disclosed by J. D. Blizzard and T. J. Swihart in U.S. Pat. No. 4,310,678.

The liquid silicone resin component has further been mixed with certain vinyl- and/or hydroxyl-containing polydiorganosiloxane fluids to provide curable silicone compositions, as disclosed by J. D. Blizzard in U.S. Pat. No. 4,322,518. The curable silicone compositions of Blizzard are useful for coating a substrate. For example, a paper substrate is coated to provide a selectable-force adhesive release coating thereon.

While the compositions of Blizzard are useful for providing a selectable-force adhesive release coating, said force is in the premium to moderate force range, i.e., in the range of 20 to 50 N/m. Although a premium to moderate release force is highly desirable, higher release forces are also desired.

The compositions of Blizzard have the disadvantage that they are relatively expensive, compared to organic polymer-based coating compositions.

Film-forming organic polymers, such as poly(vinyl alcohol) and poly(styrene-co-butadiene), are relatively inexpensive compared to silicone polymers; however, they often lack the water resistance of silicone films.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide coating compositions which provide a coating on a substrate that possesses the water resistance of a silicone coating and the strength of an organic coating. It is a further object of this invention to provide silicone-containing coating compositions which are less expensive than all-silicone coating compositions. It is another object of this invention to provide coating compositions which provide an adhesive release coating having intermediate-force release. It is also an object of this invention to provide a method for preparing water-based, silicone resin-containing coating compositions. It is yet another object of the present invention to provide a method for coating a substrate.

Briefly stated, these objects, and others which will be obvious upon consideration of the following disclosure and appended claims, are obtained by mixing the liquid silicone resins disclosed by Blizzard and Swihart in U.S. Pat. No., 4,310,678, with a silicon-free film-forming organic polymer, in the presence of compatibilizing liquid to provide a homogeneous composition and, thereafter, coating a substrate therewith and evaporating the compatibilizing liquid. In a highly preferred embodiment of this invention the compatibilizing liquid is water and the resulting homogeneous composition is an aqueous emulsion. The coating compositions of this invention can further contain a curing catalyst, if desired.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises three aspects. In a first aspect this invention relates to compositions. In a second aspect this invention relates to a method for preparing compositions of this invention in aqueous emulsion form. In a third aspect this invention relates to a method for coating a substrate, using the compositions of this invention.

In said first aspect the present invention relates to a composition consisting essentially of a homogeneous mixture of (I) a liquid silicone resin prepared by (A) forming a homogeneous mixture having an acid number greater than zero and consisting essentially of (a) an organic solvent solution of a resinous copolymeric siloxane consisting silicon-bonded hydroxyl radicals and consisting essentially of R.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units wherein the ratio of the number of said R.sub.3 SiO.sub.1/2 siloxane units to the number of said SiO.sub.4/2 siloxane units has a value of from 0.6/1 to 0.9/1 and each R denotes, independently, a monovalent hydrocarbon radical and (b) a liquid organohydrogenpolysiloxane wherein each organic radical is, independently, a monovalent hydrocarbon radical, there being an average of at least one silicon-bonded hydrogen radical per molecule of said organohydrogenpolysiloxane, and (B) heating the homogeneous mixture of (A) to remove substantially all of said organic solvent therefrom, (II) one or more silicon-free, film-forming organic polymers and (III) a compatibilizing liquid in at least a sufficient amount to render the composition homogeneous; the weight ratio of the amount of component (I) to the amount of component (II) having a value of from 1/99 to 99/1.

Component (I) of the compositions of this invention is designated herein as a liquid silicone resin and is disclosed in U.S. Pat. No. 4,310,678, the disclosure of which is hereby incorporated herein by reference to teach its preparation. It is prepared by reacting a first reactant (a), designated herein as a resinous copolymeric siloxane, with a second reactant (b), desiganted herein as a liquid organohydrogenpolysiloxane.

Component (a) that is used to prepared the liquid silicone resin (I) is an organic solvent solution of a resinous copolymeric siloxane which consists essentially of R.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units. The resinous copolymeric siloxane has a complex, as-yet-undetermined structure; however, for the purposes of this disclosure it is fully characterized by the ratio of said siloxane units therein, by its silanol, i.e. silicon-bonded hydroxyl, content and by its solubility in organic solvents, such as benzene.

The resinous copolymeric siloxane portion of component (a) consists of from 0.6 to 0.9 R.sub.3 SiO.sub.1/2 units for every SiO.sub.4/2 unit. Each R denotes a monovalent hydrocarbon radical; such as an alkyl radical, such as methyl, ethyl, isopropyl, butyl and hexyl; an alkenyl radical, such as vinyl and allyl; an aryl radical, such as phenyl, tolyl and xylyl; an arylalkyl radical, such as beta-phenylethyl and beta-phenylpropyl; and a cycloaliphatic radical, such as cyclopentyl, cyclohexyl and cyclohexenyl. Preferably all R radicals in component (a) are lower alkyl radicals although a minor portion of them can be replaced with other monovalent hydrocarbon radicals, such as the vinyl radical and/or the phenyl radical, to provide additional properties for the resinous copolymer, such as the reactivity attendant therewith. The resinous copolymeric siloxane portion further comprises from 0.1 to 5 percent by weight of silicon-bonded hydroxyl radicals and frequently comprises trace amounts of silicon-bonded alkoxy radicals such as methoxy, ethoxy or isopropoxy radicals which arise from the particular method that is used to prepare said resinous copolymeric siloxane.

In a preferred component (I) of the composition of this invention the resinous copolymeric siloxane portion of component (a) consists essentially of (CH.sub.3).sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units, in the number ratio stated above, and has a silicon-bonded hydroxyl content of from 1 to 5 percent by weight.

Resinous copolymeric siloxanes consisting of R.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units are well known in the art and are described by Daudt et al., U.S. Pat. No. 2,676,182, and by Goodwin, U.S. Pat. No. 2,857,356, the disclosures of which are hereby incorporated herein by reference to teach how to prepare resinous copolymeric siloxanes which are suitable for preparing component (I) of the compositions of this invention. Briefly, an aqueous solution of sodium silicate (e.g. No. 9 sodium silicate sold by DuPont) is acidified to the proper pH by adding it to a mixture of hydrochloric acid and isopropanol and the resulting acidic silica hydrosol is then treated with a source of R.sub.3 SiO.sub.1/2 siloxane units such as R.sub.3 SiOCH.sub.3, R.sub.3 SiCl or R.sub.3 SiOSiR.sub.3 dissolved in a mixture of isopropanol and xylene. After being heated the reaction mixture is cooled and is separated into an aqueous phase, which is discarded, and a non-aqueous phase comprising the resinous copolymeric siloxane, which is further washed with water to reduce its acid number and to remove water-soluble components, such as isopropyl alcohol. Preferably the acidic resinous copolymeric siloxanes which are prepared by these methods are washed with water to remove most, but not all, of the acid therein. For example, resinous copolymeric siloxanes which have been prepared by the method of Daudt et al. typically have sufficient acid remaining therein to provide an acid number of from 0.2 to 2.0, as measured by the method hereinafter disclosed, based on the amount of solvent-free resinous copolymeric siloxane. These materials are preferred for the purposes of this invention.

Resinous copolymeric siloxanes are typically prepared in an organic solvent which can conveniently serve as the organic solvent portion of component (a). Alternatively, the resinous copolymeric siloxane can be prepared in one organic solvent and subsequently can be transferred to a second organic solvent, if desired, to form component (a). If the resinous copolymeric siloxane does not contain any organic solvent, one or more organic solvents should be mixed therewith before or during the preparation of the homogeneous mixture of (a) and (b).

The particular organic solvent portion of component (a) is not critical and can be, for example, an aliphatic hydrocarbon, an aromatic hydrocarbon or halogenated derivatives of either or mixtures thereof. Preferably the organic solvent is one that forms an azeotrope with water so that any water that is formed during the subsequent heating step, detailed below, can be conveniently removed by azeotropic distillation. Particularly useful organic solvents include benzene, toluene, xylene, trichloroethylene and mineral spirits.

The amount of resinous copolymeric siloxane contained in component (a) is not critical and can range from 10 to 90 percent by weight. It is preferred that only as much organic solvent as is needed to prepare a homogeneous mixture of resinous copolymeric siloxane and liquid organohydrogenpolysiloxane be used in order to minimize the amount of time and/or energy needed to subsequently remove it from the mixture as described hereinafter. A preferred component (a) contains approximately 60 to 70 percent by weight resinous copolymeric siloxane and the balance solvent.

Component (b) that is used to prepare the liquid silicone resin component (I) is any liquid organohydrogenpolysiloxane containing an average of at least one silicon-bonded hydrogen radical per molecule, and can have a linear, cyclic or branched structure or combinations thereof. Thus, component (b) has the unit formula R'.sub.m H.sub.n SiO.sub.(4-m-n)/2 wherein m and n denote positive numbers whose sum is less than 4, preferably from 1.9 to 2.1. The organic radicals (R') in component (b) can be any of the R radicals denoted above. Preferably, although not necessarily, the organic radicals (R') in component (b) are the same as the organic radicals (R) in component (a).

Examples of organohydrogenpolysiloxanes that are suitable for use as component (b) include cyclic organohydrogenpolysiloxanes of the unit formula R'.sub.m H.sub.2-m SiO, such as {(CH.sub.3)(H)SiO}.sub.x wherein x is 3, 4, 5, 6 and higher and {(CH.sub.3)(H)SiO}.sub.y {(CH.sub.3).sub.2 SiO}.sub.z wherein the sum of y plux z is 3, 4, 5, 6 and higher; and linear organohydrogenpolysiloxanes of the formula R"R'.sub.2 SiO(R'.sub.2 SiO).sub.a (R'HSiO).sub.b SiR'.sub.2 R", such as R"(CH.sub.3).sub.2 SiO{(CH.sub.3).sub.2 SiO}.sub.a {(CH.sub.3)(H)SiO}.sub.b Si(CH.sub.3).sub.2 R" wherein R" denotes H or methyl and a and b each denote zero or a number greater than zero, provided there is at least one silicon-bonded hydrogen radical per molecule. Examples of linear organohydrogenpolysiloxanes having the above formula include H(CH.sub.3).sub.2 SiO{(CH.sub.3).sub.2 SiO}.sub.a Si(CH.sub.3).sub.2 H, (CH.sub.3).sub.3 SiO{(CH.sub.3)(H)SiO}.sub.b Si(CH.sub. 3).sub.3, (CH.sub.3).sub.3 SiO{(CH.sub.3)(H)SiO}.sub.b {(CH.sub.3).sub.2 SiO}.sub.a Si(CH.sub.3).sub.3 and H(CH.sub.3).sub.2 SiO{(CH.sub.3).sub.2 SiO}.sub.a {(CH.sub.3)(H)SiO}.sub.b Si(CH.sub.3).sub.2 H.

An organohydrogenpolysiloxane having the formula (CH.sub.3).sub.3 SiO{(CH.sub.3)(H)SiO}.sub.b Si(CH.sub.3).sub.3 wherein b has an average value of from 30 to 70 is a highly preferred component (b) for the purposes of this invention, particularly when it is desired that the liquid silicone resin prepared therefrom contain relatively large amounts of silicon-bonded hydrogen radicals.

Liquid organohydrogenpolysiloxane (b) can have aany viscosity; however, it preferably has a viscosity of less than 1 pascal-second at 25.degree. C. when used in amounts of less than 60 parts by weight for every 40 parts by weight of resinous copolymeric siloxane.

Organohydrogenpolysiloxanes and their preparation are well known in the organosilicon polymer art; some are commercially available. Briefly the preparation of organohydrogenpolysiloxanes can be accomplished, for example, by hydrolyzing a suitable mixture of hydrolyzable silanes, such as chlorosilanes, and equilibrating the resulting hydrolyzate under acid catalysis. Alternatively, a mixture of suitable siloxanes, such as cyclic siloxanes and linear siloxanes, can be copolymerized and equilibrated under acid catalysis.

In the preparation of component (I) the amounts of resinous copolymeric siloxane and liquid organohydrogenpolysiloxane that are mixed may vary widely. Generally, the viscosity of the liquid silicone resin that is produced varies directly with the viscosity of the organohydrogenpolysiloxane and inversely with its relative amount in the homogeneous mixture of components (a) and (b). Liquid silicone resins can be obtained when as little as about 10 percent by weight of organohydrogenpolysiloxane is used, based on the weight of resinous copolymeric siloxane plus organohydrogenpolysiloxane.

For the purposes of this invention a highly preferred liquid silicone resin component is obtained when the homogeneous mixture that is heated comprises from 40 to 60 parts by weight of resinous copolymeric siloxane consisting of (CH.sub.3).sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units and containing from 1 to 5 percent by weight of silicon-bonded hydroxyl radicals and from 40 to 60 parts by weight of organohydrogenpolysiloxane having the formula (CH.sub.3).sub.3 SiO{(CH.sub.3)(H)SiO}.sub.30 to 70Si(CH.sub.3).sub.3.

In the preparation of component (I) a homogeneous mixture is formed by thoroughly mixing the desired amounts of component (a) and component (b) and, if necessary, an acid, preferably a strong acid such as hydrochloric acid, to provide an acid number greater than zero therefor. Preferably the acid number of the homogeneous mixture, extrapolated to zero solvent content, has a value of from 0.1 to 1. Preferably component (a) is sufficiently acidic, as prepared, to provide this acidity for the homogeneous mixture.

The resulting homogeneous mixture of (a) plus (b) is immediately or subsequently heated to volatilize the organic solvent therefrom. Said heating is preferably initially done at atmospheric pressure and is then continued at reduced pressure to accelerate the removal of said solvent.

In a preferred embodiment of this invention the homogeneous mixture of (a) plus (b) is heated to about 150.degree. C. at atmospheric pressure and is then subjected to a gradually decreasing pressure, without an increase in temperature, to remove substantially all of the organic solvent therefrom. By substantially it is meant herein that the liquid silicone resin contains less than about 5 percent, and preferably less than about 1 percent, by weight organic solvent.

Alternatively the homogeneous mixture of (a) plus (b) can be partially devolatilized at room temperature, such as by evaporation, and the partially devolatilized mixture then heated to remove substantially all of the organic solvent therefrom.

The liquid silicone resin (I) contains silicon-bonded hydroxyl radicals and/or silicon-bonded hydrogen radicals which provide chemical reactivity therefor in the compositions of this invention. The amount of silicon-bonded hydrogen radicals and/or silicon-bonded hydroxyl radicals therein depends upon the ratio of said radicals in, and the acid number of, the homogeneous mixture of (a) plus (b) that is used for its preparation.

To assure that the liquid silicone resin contains silicon-bonded hydrogen radicals, for subsequent reaction with e.g. silicon-bonded hydroxyl radicals, it is believed that the homogeneous mixture of (a) and (b) that is prepared should have at least 2, and preferably at least 3, silicon-bonded hydrogen radicals in (b) for every silicon-bonded hydroxyl radical in (a). An upper limit of 2580 for the ratio of silicon-bonded hydrogen radicals to silicon-bonded hydroxyl radicals in the homogeneous mixture occurs in a mixture of 10 parts by weight of resinous copolymeric siloxane having a silanol content of 0.1 percent by weight and 90 parts by weight of the highly preferred organohydrogenpolysiloxane having a silicon-bonded hydrogen content of 1.7 percent by weight.

To assure that the liquid silicone resin contains silicon-bonded hydroxyl radicals, for subsequent reaction with e.g. silicon-bonded hydroxyl or hydrogen radicals, it is believed that the acid number of the homogeneous mixture that is heated should have a value of less than about 2.

Component (II) of the composition of this invention is any silicon-free, film-forming organic polymer. By silicon-free it is meant that the molecular structure of the organic polymer does not contain silicon atoms. By film-forming it is meant that the organic polymer can be formed into a coherent film using any of the conventional film-forming methods known in the art, such as solvent casting, extruding, melt casting, spraying, roller coating, calendering and blowing. Component (II) is alternatively designated herein as the organic polymer.

The organic polymers that are used in the present invention are well known in the organic polymer art; many are commercially available.

One class of organic polymers that is particularly useful in the present invention comprises the water-soluble organic polymers, such as poly(vinyl alcohol) and poly(acrylic acid). Water-soluble organic polymers are particularly benefitted by the present invention because films prepared from the resulting compositions of this invention have greatly increased water resistance, compared to the unmodified organic polymer films.

Another class of organic polymers that is useful in the present invention comprises the water-dispersed organic polymers that are prepared by aqueous emulsion polymerization of suitable monomers. Examples of water-dispersed organic polymers include poly(styrene-co-butadiene), poly(vinyl chloride), poly(vinyl chloride-co-ethylene), poly(methyl methacrylate) and poly(vinyl acetate). The compositions of this invention that are prepared from water-dispersed organic polymers also provide films that have improved water resistance, even though a film prepared from the organic polymer alone has appreciable water resistance.

A highly preferred organic polymer to be used in the compositions of this invention is poly(vinyl alcohol). One reason, noted above, for this preference is the greatly increased water resistance conferred upon a poly(vinyl alcohol) film by this invention. Another reason for this preference is that the emulsion stability that is provided for aqueous compositions of this invention by even small amounts of poly(vinyl alcohol) is significant and useful. In a preferred embodiment of this invention aqueous emulsion compositions having as little as one part of poly(vinyl alcohol) for every 25 parts of liquid silicone resin are provided. Advantageously, the resulting aqueous emulsion can be readily mixed with aqueous emulsions of organic polymers, such as poly(styrene-co-butadiene) latex, or additional poly(vinyl alcohol), to prepare other compositions of this invention.

Component (III) of the compositions of this invention can be any liquid which, when used in a sufficient amount, will compatibilize the normally incompatible mixture of liquid silicone resin and silicon-free, film-forming organic polymer and provide a homogeneous composition thereof.

For example, the compatibilizing liquid can be an organic solvent, or a mixture of two or more organic solvents, which is unreactive with the other components of the composition, thereby providing a homogeneous composition which is a solution or non-aqueous emulsion. Because the organic polymers that are useful in the compositions of this invention are quite varied the organic solvent that is used to prepare said compositions will vary considerably. Thus, when the organic polymer is a polar polymer, such as poly(vinyl alcohol), the organic solvent should comprise a polar solvent; such as a ketone, such as acetone or methyl isobutyl ketone or an ester, such as ethyl acetate or other polar solvent, such as dimethylsulfoxide butanol, tetrahydrofuran or dimethylformamide. When the organic polymer is a non-polar polymer, such as poly(styrene-co-butadiene), the organic solvent should comprise a non-polar solvent such as toluene, xylene, cyclohexane, hexane or mineral spirits.

Component (III) is preferably water, optionally comprising one or more surfactants, thereby providing a homogeneous composition which is an aqueous emulsion. This preference for water as the compatibilizing liquid is based on environmental, economic and efficacious considerations. That is to say, water is preferred as a compatibilizing liquid for the compositions of this invention because it it non-hazardous and non-polluting when the composition is prepared and used, as hereinafter disclosed; because it is inexpensive and because the organic polymers used herein are typically available as aqueous solutions or as aqueous emulsions.

The amount of compatibilizing liquid that is used in the compositions of this invention is merely that amount that will provide a homogeneous mixture of liquid silicone resin component and organic polymer component. Within this restriction the amount of compatibilizing liquid is not critical and can be selected to establish the solids content, i.e. concentration of non-volatile components, as desired.

When one or more surfactants are used to prepare the aqueous emulsion compositions of this invention their identity and amount can be selected by following well-known principles that are used in the emulsification of water-insoluble components, as a dispersed phase, in water, as a continuous phase.

The amounts of liquid silicone resin and silicon-free, film-forming organic polymer that are present in the compositions of this invention may vary widely, depending upon the exact nature of the components and the desired properties of the composition obtained therefrom. A range of amounts of from 1 part by weight of component (I) or (II) for every 99 parts by weight of component (II) or (I), respectively, is contemplated by this invention.

In a preferred embodiment of this invention, noted above, wherein the organic polymer is poly(vinyl alcohol) and the compatibilizing liquid is water, the ratio of the weight of liquid silicone resin to organic polymer has a value of about 25. Such a composition has its principal, but not sole, utility as an intermediate emulsion from which additional compositions of this invention can be prepared.

In a highly preferred embodiment of this invention the liquid silicone resin and the organic polymer are used in substantially equal amounts so that their weight ratio has a value of about 1 in the resulting composition of this invention.

In such "equal-weight" compositions a maximum influence of the liquid silicone resin and the organic polymer on the water resistance and the strength, respectively, of a film prepared from the composition is obtained.

Without limiting the present invention by theory it can be said that it is believed that when such "equal-weight" compositions of this invention are used to coat a substrate by a method of this invention, hereinafter delineated, a film comprising an interpenetrating network of liquid silicone resin and organic polymer is obtained whose properties are not merely fractionally additive, based on weight, of the properties of the individual components but are substantially undiminished from the properties of the neat component. That is, while the film that is formed from such a composition is only 50% liquid silicone resin and 50% organic polymer, it typically possesses the water resistance of the 100% liquid silicone resin and the strength of the 100% organic polymer.

The compositions of the present invention can further contain non-essential components which are commonly used in silicone resin compositions or in organic polymer compositions. Exemplary of non-essential components are extending and reinforcing fillers, such as silica, carbon black, ground quartz, sand, starch, calcium carbonate, clay and alumina; fibers, such as asbestos and glass fibers; pigments, such as titania and red iron oxide; thickening agents, such as bentonite clays; and stabilizing agents, such as antioxidants, buffers and biocides such as bactericides and mildewcides.

The solution compositions of the present invention can be prepared by merely mixing the components thereof in the desired amounts until a homogeneous composition is obtained.

The emulsion compositions of this invention can be prepared by well-known emulsion techniques. For example, the liquid silicone resin component can be emulsified in water using a suitable surfactant and the resulting emulsion mixed with an aqueous emulsion of silicon-free, film-forming organic polymer.

In a second aspect the present invention relates to a method for preparing a composition consisting essentially of a homogeneous mixture of (I) a liquid silicone resin prepared by (A) forming a homogeneous mixture having an acid number greater than zero and consisting essentially of (a) an organic solvent solution of a resinous copolymeric siloxane containing silicon-bonded hydroxyl radicals and consisting essentially of R.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units wherein the ratio of the number of said R.sub.3 SiO.sub.1/2 siloxane units to the number of said SiO.sub.4/2 siloxane units has a value of from 0.6/1 to 0.9/1 and each R denotes, independently, a monovalent hydrocarbon radical and (b) a liquid organohydrogenpolysiloxane wherein each organic radical is, independently, a monovalent hydrocarbon radical, there being an average of at least one silicon-bonded hydrogen radical per molecule of said organohydrogenpolysiloxane, and (B) heating the homogeneous mixture of (A) to remove substantially all of said organic solvent therefrom, (II) poly(vinyl alcohol) and, optionally, one or more other silicon-free, film-forming organic polymers and (III) water, optionally containing one or more surfactants, in at least a sufficient amount to render the composition homogeneous, the weight ratio of the amount of component (I) to the amount of component (II) having a value of from 1/99 to 99/1; said method comprising (i) emulsifying the (I) liquid silicone resin with an aqueous phase comprising poly(vinyl alcohol) and (ii) mixing with the emulsion of step (i) an aqueous phase comprising any remaining portion of the (II) poly(vinyl alcohol) and any other silicon-free, film-forming organic polymer.

In the method of this invention for preparing aqueous emulsion compositions of this invention the liquid silicone resin and organic polymer components, and relative amounts thereof, used therein including preferred embodiments thereof, are as delineated above for the compositions of this invention.

In this method the liquid silicone resin is first emulsified, in step (i), with an aqueous phase which comprises poly(vinyl alcohol). Therefore, the compositions of this invention which are prepared by the method of this invention comprise poly(vinyl alcohol) as at least a portion of the silicon-free, film-forming organic polymer component thereof. The resulting emulsion is then further mixed with additional organic polymer, if desired, in step (ii).

In a preferred embodiment of the method of this invention the highly preferred liquid silicone resin, delineated above, is emulsified, in step (i), with an aqueous phase consisting essentially of water, poly(vinyl alcohol) and one or more surfactants, the weight ratio of the liquid silicone resin to the poly(vinyl alcohol) having a value of about 25. The resulting emulsion composition of this invention has sufficient stability to permit its storage and/or shipment, as desired, until subsequently being used to prepare other emulsion compositions of this invention.

For example, an aqueous emulsion composition prepared in step (i) of the preferred embodiment method of this invention can be conveniently mixed with additional aqueous poly(vinyl alcohol) or other organic polymer in aqueous emulsion form, such as a styrene-butadiene copolymer latex, to prepare aqueous emulsion compositions of this invention having a liquid silicone resin to organic polymer weight ratio of less than about 25, preferably about 1.

When the method of this invention is used to prepare aqueous emulsion compositions wherein the organic polymer is solely poly(vinyl alcohol) an alternative preferred embodiment thereof consists of omitting step (ii), the entire amount of poly(vinyl alcohol) being used in step (i).

In step (i) of the method of this invention the liquid silicone resin is preferably mixed with an aqueous solution of poly(vinyl alcohol), optionally containing one or more surfactants and the resulting mixture is then subjected to shear to reduce the size of the liquid silicone resin particles to less than 10 .mu.m, preferably less than 1 .mu.m. Any shear means capable of producing said particle sizes can be used to prepare the emulsion of step (i). A particularly useful shear means is a colloid mill.

In step (ii) of the method of this invention the emulsion of step (i) is mixed with an aqueous phase comprising additional organic polymer. This aqueous phase is preferably a stable solution, emulsion or dispersion of organic polymer in water which requires only simple low shear mixing with the emulsion of step (i) to prepare the aqueous emulsion compositions of this invention.

The homogeneous compositions of this invention are useful as coating compositions to provide a substrate, coated therewith, with a water-resistant film. The resulting film can serve as a protective coating or as an intermediate-force adhesive release coating.

Thus, the present invention has, as a third aspect, a method for coating a substrate.

In said third aspect the present invention relates to a method for coating a substrate, said method comprising (1) aplying to said substrate a composition consisting essentially of a homogeneous mixture of (I) a liquid silicone resin prepared by (A) forming a homogeneous mixture having an acid number greater than zero and consisting essentially of (a) an organic solvent solution of a resinous copolymeric siloxane containing silicon-bonded hydroxyl radicals and consisting essentially of R.sub.3 SiO.sub.1/2 siloxane units and SiO.sub.4/2 siloxane units wherein the ratio of the number of said R.sub.3 SiO.sub.1/2 siloxane units to the number of said SiO.sub.4/2 siloxane units has a value of from 0.6/1 to 0.9/1 and each R denotes, independently, a monovalent hydrocarbon radical and (b) a liquid organohydrogenpolysiloxane wherein each organic radical is, independently, a monovalent hydrocarbon radical, there being an average of at least one silicon-bonded hydrogen radical per molecule of said organohydrogenpolysiloxane, and (B) heating the homogeneous mixture of (A) to remove substantially all of said organic solvent therefrom, (II) one or more silicon-free, film-forming organic polymer, (III) a compatibilizing liquid in at least a sufficient amount to render the composition homogeneous; the weight ratio of the amount of component (I) to the amount of component (II) having a value of from 1/99 to 99/1, and, optionally, (IV) a curing catalyst in sufficient amount to improve the curing rate of the coating and (2) evaporating the compatibilizing liquid from the applied composition.

In this method for coating a substrate with a coating composition, the coating composition used therein, including the preferred coating compositions used therein, are as delineated above for the compositions of this invention and for the method of this invention for preparing aqueous emulsion forms thereof.

The coating compositions that are used in the coating method of this invention, preferably, although not necessarily, further comprise a curing catalyst for the liquid silicone resin and/or the organic polymer.

One class of suitable curing catalysts is the silanol-condensing catalysts which are well known in the silicone coatings art. Examples of silanol-condensing catalysts include the organic acid salts of lead, tin and iron, such as iron octoate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, lead octoate and stannous octoate.

Another class of suitable curing catalysts is the hydrosilylation catalysts such as compounds of platinum or rhodium which are well known in the silicone coating art.

The amount of curing catalyst to be used is merely that amount that will improve the curing rate of the cured coating composition. Typically the amount of silanol-condensing curing catalyst that is used to cure the compositions of this invention ranges from 5 to 25, preferably 10 to 20, percent by weight, based on the weight of liquid silicone resin in the composition. Hydrosilation catalysts are typically used in much lower concentrations, such as 1 to 100 parts per million parts of liquid silicone resin.

The coating compositions of this invention are typically applied to a substrate as a thin film, using any suitable application method, such as spraying, dipping, brushing, offset coating or rolling. The thickness of the applied film is not critical, it being limited only by the requirement that the compatibilizing liquid component thereof be removable therefrom. Typically the coating composition is applied as a film having a thickness of from 20 to 2000, preferably from 50 to 250, micrometers.

After the coating composition has been applied the compatibilizing liquid is allowed, or forced, to volatilize, thereby providing a water-resistant solid coating on the substrate. If desired, the resulting coating can be heated to further improve the water resistance and/or the strength of the solid coating. For example, after the compatibilizing liquid has been allowed to substantially completely evaporate therefrom the coating can be heated to a temperature short of the degradation temperature of the coating and its substrate for a sufficient length of time to improve the water resistance of the coating.

The compositions of this invention can be applied to any substrate such as a metal substrate such as aluminum, iron and steel; a siliceous substrate, such as glass, concrete, brick, mortar, clay or ceramic; a polymeric substrate,