Polysiloxane Graft Copolymers, Flexible Coating Compositions Comprising Same and Branched Polysiloxane Macromers for Preparing Same II

This invention relates to resins and flexible coating compositions comprising same which have excellent adherence to metal and plastic and possess superior weathering properties. More particularly, the invention relates to hydroxy functional polysiloxane graft copolymers and to coating compositions comprising same.

Recently, there has been interest in the use of resilient coating materials for areas which are subject to mechanical shock, such as automobile bumpers, moldings and front ends. To maintain the desired appearance for a protective coating on a motor vehicle body panel or like application, any such coating must have certain properties, such as a high degree of extensibility, impact resistance, and resistance to cracking and degradation under severe environmental conditions such as low temperature and high humidity. Conventional coatings, including those heretofore employed on rubber and similar extensible objects, do not have the required combination of properties. Generally, compositions that are flexible enough to be applied over both metal and plastic substrates have rather poor weatherability, appearance and/or overall durability.

U.S. Pat. No. 3,882,189 and U.S. Pat. No. 3,962,522 are exemplary of numerous patents which describe flexible coating compositions, wherein the resin comprises polyurethane modified polyesters formed by reacting polyisocyanate with polyester polyols. These resins are cured with amine-aldehyde crosslinkers. It is taught therein, that the presence of the urethane groups in the polymer significantly contributes to the flexibility as well as improved weathering properties, gloss, and abrasion resistance of the coating. Such coatings, however, are not of an overall quality to meet certain applications, particularly automotive applications. Accordingly, it is an object of the present invention to provide novel polysiloxane graft copolymers and solvent based, thermosetting coating compositions comprising same, suitable to produce flexible cured coatings with good adhesion over diverse substrates including metal an plastic. In this regard, it is a particular object of the invention to provide such flexible coating compositions at sufficiently low Volatile Organic Content (VOC) to aid in meeting governmental emissions guidelines and yet which can be applied to a substrate by spraying or other known methods. It is another object of the invention to provide a composition which will form a coating on a substrate, which coating has advantageous physical properties including, for example, humidity and solvent resistance, flexibility and corrosion protection for the underlying substrate.

Additional aspects and advantages of the invention will be apparent from the following description thereof.

According to the present invention, a novel, non-gelled, hydroxy functional polysiloxane graft copolymer is provided. The copolymer is crosslinkable by hydroxy-reactive crosslinking agent and, in particular, is suitable for use in thermosetting coating compositions adapted to form a flexible cured coating over a variety of substrates, such as metal and plastic. The copolymer of the invention has a number average molecular weight between about 1300 and about 15,000, has a hydroxyl number between about 30 and about 300, and is the reaction product of carbon-carbon double bond-reactive monoethylenically unsaturated monomer with hydroxy functional carbon-carbon double bond-bearing branched polysiloxane macromer. This reaction is performed under free radical polymerization reaction conditions and the monomer bears substantially no functionality which would be substantially reactive with the hydroxy functionality of the macromer under such reaction conditions. The macromer is the reaction product of (i) hydroxy functional polysiloxane reactant containing 0-10 urethane linkages per molecule, with (ii) silane compound having the general chemical formula: ##STR2## wherein R is H or an alkyl group with one to three carbon atoms and R' is a phenylene or substituted phenylene group (including amino functionality) or a carboxylate group. The integer n is 0, 1, 2 or 3. The X moiety is halogen, substituted glycol monoether, alkoxy or acyloxy.

According to the coating composition aspect of the invention, the aforesaid copolymer is employed with polyfunctional, hydroxy-reactive crosslinking agent selected, preferably, from aminoplast crosslinking agent, polyisocyanate crosslinking agent, blocked polyisocyanate crosslinking agent comprising at least two isocyanate groups blocked by reaction with active hydrogen bearing blocking agent, and any compatible mixture thereof. The coating compositions of the invention can be formulated as either one component coating compositions or two component coating compositions. Typically, unblocked polyisocyanate crosslinking agent is employed in two component compositions in view of its reactivity. A composition of the invention can be formulated, for example, as a one component primer, typically employing blocked polyisocyanate or aminoplast crosslinking agent, as a one component topcoat, preferably employing aminoplast crosslinking agent, or as a two component coating, typically employing polyisocyanate crosslinking agent. Also, the graft copolymer of the invention can be formulated as a pigmented base coat, typically a one component composition, for a base coat/clear coat system such as are known for use as automotive finishes. It also can be formulated as the clear coat thereof, either as a one component or a two component composition.

Advantageously, the flexible coatings of the invention possess superior weathering properties as well as excellent adhesion to metal and plastic, thus making them well suited for use as coatings, on, for example, various motor vehicle components. It is believed that the use of the silicon compound in forming the polysiloxane macromer is, in part, responsible for the excellent weatherability and durability of the coating composition of this invention. Additionally, the use of such silicone compounds also allows for the coating compositions of this invention to be formulated as high solids compositions. The ability to use the same coating composition on metal and plastic components in motor vehicle production offers distinct commercial advantages, particular in terms of production efficiency. Still further, because these coatings can be employed on metal as well as plastic components, the problem of color matching, which must be resolved when using different coatings on metal and plastic parts which are to be in proximity to one another, is eliminated. The siloxane moieties incorporated into the graft copolymer advantageously provide enhanced flexibility, durability and weatherability and provide lower viscosity for high solids coatings. These and additional features and advantages of the invention will be better understood in view of the following detailed disclosure.

The resin of the invention is a novel, hydroxy functional polysiloxane graft copolymer of number average molecular weight (M.sub.n) between about 1,300 and about 4,000, and having a hydroxyl number between about 30 and about 300, preferably between about 50 and about 150. The resin is optionally urethane-modified, more specifically, containing about 0.10 urethane linkages per molecule. Preferably, the resin contains about 0-5 urethane linkages per molecule. As disclosed above, the resin is the reaction product of carbon-carbon double bond-reactive monoethylenically unsaturated monomer with certain hydroxy functional carbon-carbon double bond-bearing branched polysiloxane macromer. Each of these reactants is discussed below in greater detail.

Numerous carbon-carbon double bond-reactive monoethylenically unsaturated monomers suitable for making the graft copolymer are known to the skilled of the art. Included are many which are commercially available and many which will be readily apparent in view of the present disclosure. The choice of monomer reactant employed in making the graft copolymer will depend to a large extent upon the particular application intended for the resin or for the coating composition in which the resin is to be used. Examples of suitable monoethylenically unsaturated monomers include, for example, vinyl aromatic hydrocarbons such as styrene, alpha methyl styrene, and vinyl toluene, vinyl acetate, vinyl chloride, and the like.

Preferred monomers are acrylate monomers Numerous suitable acrylate monomers are known to the skilled of the art and include many which are commercially available and which will be readily apparent in view of the present disclosure. As noted above, the choice of monomer reactant employed in preparing the resin of the invention will depend to a large extent upon the particular application intended for the resin or for the composition in which the resin is used. Suitable hydroxy-substituted alky(meth)acrylates (where "alkyl(meth)acrylates" means, in the alternative, alkylacrylates and alkylmethacrylates) which can be employed comprise members selected from the group consisting of the following esters of acrylic or methacrylic acid and C.sub.2 -C.sub.12 aliphatic glycols:

2-hydroxy ethyl acrylate; 3-chloro-2-hydroxypropyl acrylate; 2-hydroxy-1-methylethyl acrylate;

2-hydroxypropyl acrylate; 3-hydroxypropyl acrylate;

2,3-dihydroxypropyl acrylate; 2-hydroxybutyl acrylate;

4-hydroxybutyl acrylate; diethyleneglycol acrylate;

5-hydroxypentyl acrylate; 6-hydroxyhexyl acrylate;

triethyleneglycol acrylate; 7-hydroxyheptyl acrylate;

2-hydroxy-1-methylethyl methacrylate; 2-hydroxypropyl methacrylate; 3-hydroxypropyl methacrylate;

2,3-dihydroxypropyl methacrylate; 2-hydroxybutyl methacrylate; 4-hydroxybutyl methacrylate;

3,4-dihydroxybutyl methacrylate; 5-hydroxypentyl methacrylate; 6-hydroxyhexyl methacrylate;

1,3-dimethyl-3-hydroxybutyl methacrylate;

5,6-dihydroxyhexyl methacrylate; and 7-hydroxyheptyl methacrylate. Although one of ordinary skill in the art will recognize that many different hydroxy-substituted alkyl(meth)acrylates including those listed above could be employed, the preferred hydroxy functional monomers for use in the resin of this invention are hydroxy-substituted alkyl acrylates and methacrylates having a total of 5 to 7 carbon atoms, i.e., esters of C2-C3 dihydric alcohols and acrylic or methacrylic acids, such as hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate and hydroxypropyl acrylate.

Most preferably, the hydroxy-substituted alkyl(meth)acrylate monomer comprises a compound of the formula: ##STR3## where R.sup.1 is hydrogen or methyl and R.sup.2 and R.sup.3 are independently selected from the group consisting of hydrogen and alkyl of from 1 to 6 carbon atoms. Illustrative of these particularly suitable hydroxy-substituted alkyl(meth)acrylate monomers are 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate and 2-hydroxy-1-methylhexyl acrylate.

suitable non-hydroxy substituted alkyl(meth)acrylate monomers which may be employed are (meth)acrylates (as before, meaning esters of either acrylic or methacrylic acids) as well as mixtures of acrylates and vinyl hydrocarbons. Preferred non-hydroxy substituted monomers are esters of C.sub.1 -C.sub.12 monohydric alcohols and acrylic or methacrylic acids, e.g., methylmethacrylate, ethylacrylate, butylacrylate, butyl-methacrylate, hexylacrylate, 2-ethylhexylacrylate, lauryl-methacrylate, glycidyl methacrylate, and the like.

Particularly preferred non-hydroxy substituted monomers are compounds selected from the group consisting of monomers of formula: ##STR4## wherein R.sup.4 is alkyl of from 1 to 6 carbon atoms and R.sup.5 is hydrogen or methyl. Particularly preferred are butyl acrylate, butyl methacrylate and methyl methacrylate.

The aforesaid monovinyl aromatic hydrocarbons, preferably containing from 8 to 12 carbon atoms, including styrene, alpha-methyl styrene, vinyl toluene, t-butyl styrene, chlorostyrene and the like, when employed, will generally be present in an amount of from about 5 to 95 weight percent, preferably from about 5 to 25 weight percent of the total monoethylenically unsaturated monomer.

In addition, other suitable monethylenically unsaturated monomers such as vinyl chloride, acrylonitrile, methacrylonitrile, vinyl acetate, acrylic acid and methacrylic acid also may be employed. In the case of acrylic acid, when employed, this monomer will generally be present in an amount from about 2 to 5 weight percent of the total monomer mixture. The remaining above-mentioned monomers will generally be used in an amount of from 3 to 10 weight percent of the monomer mixture, when employed.

The hydroxy functional polysiloxane macromer is reacted with the above described monoethylenically unsaturated monomer according to any of various methods well known to the skilled of the art, which methods will be apparent in view of the present disclosure. Specifically, the macromer and the monomer are employed in a weight ratio of from about 90:10 to about 40:60, more preferably from about 75:25 to about 50:50, respectively. Preferably, all double bonds of the macromer are reacted with monomer double bonds. It will be apparent that the resulting resin will be hydroxy functional by virtue of the macromer hydroxyl groups and the monomer hydroxyl groups (if any). Suitable reaction conditions will be apparent to the skilled of the art and, generally, will include a solvent system and reaction temperature favoring free radical polymerization reaction.

The hydroxy functional polysiloxane macromer is the reaction product of any of certain hydroxy functional polysiloxane reactants with any of certain silane compounds. Each of these reactants is discussed below in greater detail.

The hydroxy functional polysiloxane reactant has a number average molecular weight (M.sub.n) preferably between about 1,000 and about 12,000, more preferably between about 1,000 and about 3,000, and has a hydroxyl number preferably between about 30 and about 300, more preferably between about 50 and about 150. As discussed further below, this polysiloxane reactant preferably, but not necessarily, is urethane modified, that is, bears urethane linkages in the polysiloxane backbone. Suitable hydroxy functional polysiloxane reactants, both urethane modified and unmodified, will be apparent in view of the present disclosure and can be prepared according to known methods which also will be apparent in view of the present disclosure. The choice of polysiloxane reactant will depend to a large extent upon the particular application intended for the final resin or composition in which such resin is used.

One suitable class of polysiloxane reactants comprises the reaction products of first reactant comprising polyol with second reactant comprising certain alkoxy silicone and, optionally, dicarboxylic acid or an anhydride thereof. where the graft copolymer is to be employed in a high solids coating for motor vehicle exterior body panels, for example, such second reactant preferably comprises about 5%-35% by weight alkoxy silicone and the remainder dicarboxylic acid or anhydride; more preferably the second reactant comprises about 5%-15% alkoxy silicone. Obviously, where the second reactant comprises dicarboxylic acid or anhydride, the reaction product of the second reactant with polyol will contain polyester linkages as well as polysiloxane linkages. Herein, such reaction product will be referred to simply as polysiloxane regardless whether it has such polyester linkages. The alkoxy silicone can be reacted with polyol either simultaneously with the dicarboxylic acid or sequentially (in either order) and the alkoxy silicone and diacid also can be reacted with separate portions of the polyol. Most preferably the polysiloxane is an oligomeric polysiloxane.

Preferably, the diacid is selected from the group consisting of saturated and unsaturated, cyclic and acyclic aliphatic dicarboxylic acids, aromatic dicarboxylic acids, and suitable anhydrides thereof. Preferred dicarboxylic acids are the C.sub.6 -C.sub.36 acids, which include, for example, adipic, azelaic, sebasic, dodecane dicarboxylic acid, cyclohexanedicarboxylic acid and dimer acids. More preferably, the dicarboxylic acids employed are aliphatic dicarboxylic acids, most preferably additionally being linear, for example, adipic, azelaic, dimer, and dodecanoic. Also suitable for use are blocked dicarboxylic acids such as dimethyl-1,4-cyclohexanedicarboxylate. Mixtures of suitable diacids and/or their anhydrides may also be used as the dicarboxylic acid component in this invention.

Numerous suitable alkoxy silicones for use in making the hydroxy functional polysiloxane reactant are known to the skilled of the art and will be readily apparent in view of the present disclosure. Included are many commercially available alkoxy silicones and others which can be readily prepared according to known methods. Preferred alkoxy silicones have number average molecular weight between about 350 and about 10,000, more preferably between about 350 and about 1000. Preferred are those of the general formula: ##STR5## wherein each Q is independently selected from hydrogen, alkyl, alkoxy, aryl, aryloxy and the like, each alkyl moiety preferably being C.sub.1 to C.sub.7 and each aryl moiety preferably being C.sub.6 -C.sub.8 ; each Q' is independently selected from alkyl, preferably C.sub.1 to C.sub.7 alkyl; and n is 1 to about 75, preferably about 1 to about 25. Preferred alkoxy silicones include certain commercially available products such as, for example, alkoxy silicone SR 191 (Trademark; General Electric Company, Waterford, N.Y.) which is a 100% silicone resin having siloxane content of 88.9%, methoxy content of 15%, and number average molecular weight of 600. Another suitable alkoxy silicone is SR-193 (trademark; General Electric Company), which is similar to SR-191, but contains certain silicone modifying agents and produces a somewhat more brittle product. Also suitable is Silikophen P50/300 (trademark; available from Goldschmidt Chemical Corp., Hopewell, Virginia) a phenyl methyl polysiloxane resin in a xylene/2-methoxypropanol-1 solvent. Also suitable is Wacker Silicone-Intermediate SY-231 (trademark; Wacker-Chemie GmbH, Munich, Germany) which is taught for use in preparing polyesters and coating compositions and has an average polyesters and coating compositions and has an average molecular weight of 800, methoxy content of 14 weight percent, total silicone content of 89 weight percent (all methoxy groups replaced by Si--O--Si bonds) and SiO.sub.2 content of 44 weight percent gravimetric. Mixtures of alkoxy silicones also may be used in reaction with the polyol reactant to prepare the hydroxy functional polysiloxane reactant.

Numerous suitable polyols for making the hydroxy functional polysiloxane reactant are known to the skilled of the art and will be readily apparent in view of the present disclosure. Included are many commercially available polyols and other which are readily prepared according to known methods. Preferably, the polyol comprises diol and triol in hydroxyl equivalent ratio of from about 4:1 to about 1:4, more preferably from about 3:1 to about 3:2.5, respectively. Suitable diols include, but are not limited to, alkylene glycols, such as butylene glycol, neopentyl glycol, 1,5-pentene glycol, 3-cyclohexene-1,1-dimethylol, and other glycols such as hydrogenated bisphenol A, caprolactone diol (e.g., the reaction product of caprolactone and ethylene glycol), hydroxy alkylated bisphenol, polyether glycols, e.g., poly(oxytetramethylene) glycol, polyester diols, e.g., 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, and the like. Preferred diols are neopentyl glycol and 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate, the latter material being commercially available as Esterdiol 204 (trademark; Union Carbide Corp., Danbury, Conn.)

The polyol generally should comprise at least about 5 weight percent triol and may consist substantially entirely of triol. The polyol component also may comprise tetrols and higher functionality polyols, but these generally are less preferred. By employing diols in the polyol component in addition to the triols, the flexibility of the coating composition is generally increased. Thus, selection of the polyol component to be used in forming the polysiloxane will be dependent on the particular desired properties and application of the coating composition. When diols are employed in the polyol component, the polyol preferably comprises from about 10 to about 80 weight percent triols and from about 90 to about 20 weight percent diols. Preferred triols are conventional low molecular triols such as 1,2,6-hexanetriol, 1,1,1-trimethylolpropane, 3-(2-hydroxypropoxy)-1,2-propanediol and polycaprolactone triols, which are commercially available as, for example, Tone-301 (trademark; Union Carbide Corp., Danbury, Conn.). Additional preferred polycaprolatone triols are described in U.S. Pat. No. 4,165,345, incorporated herein by reference. Suitable tetrols will be apparent also and include, for example, pentaerythritol and the like.

While a number of types of polyols have been mentioned above as suitable for use in making the hydroxy functional polysiloxane reactant, their disclosure is not meant to be limiting. A great many additional suitable diols, triols, etc. are known in the art and selection of other polyols which would be suitable for use would be well within the skill of those in the art in view of this disclosure.

The polyol reactant (i.e., diols, triols and optionally tetrols, etc.) and the second reactant (i.e., alkoxy silicone and, optionally, dicarboxylic acid or anhydride thereof) are combined and reacted, generally in the presence of a catalyst and at elevated temperatures, to produce the aforesaid hydroxy functional polysiloxane. Suitable catalysts for the carboxy/hydroxy condensation reaction include such catalysts as tetraisopropyl titanate, strong acids such as p-toluene phosphonic acid, phosphoric acid, sulfuric acid and materials such as zinc oxide, antimony oxide (Sb.sub.2 O.sub.3), dibutyl tin oxide, hydrated monobutyl tin oxide, and sodium acetate. Other catalysts will be apparent to those skilled in the art in view of this disclosure. The polyol and second reactant are reacted preferably in such proportions as to provide a molar equivalent ratio of polyol OH to combined alkoxy silicone --OQ' (as defined above) and diacide COOH from about 6:2 to about 6:5, respectively. Sufficient polyol must be used to provide a hydroxy functional product.

As noted above, the hydroxy functional polysiloxane is optionally urethane modified and typically may contain about 1-10 urethane groups per molecule. According to one embodiment of the invention, urethane groups are introduced by reaction of the above-described hydroxy functional polysiloxane with organic diisocyanate. Such reaction is carried out according to known methods, generally in the presence of solvents commonly employed for coating formulations such as toluene, xylene, methyl amyl ketone, and the like. Numerous suitable organic diisocyanates are readily commercially available and will be apparent to the skilled of the art in view of the present disclosure. Suitable diisocyanates include hydrocarbon diisocyanate or substituted hydrocarbon diisocyanate, such as 1,6-hexamethylene diisocyanate, isophorone diisocyanate, p-phenylene diisocyanate, biphenyl diisocyanate, toluene diisocyanate, and 3,3-dimethyl-4,4-biphenylene diisocyanate. While the diisocyanate may be any of a number of aliphatic, cycloaliphatic, and aromatic diisocyanates, it is preferred that the diisocyanate be an aliphatic diisocyanate. As would be apparent to those skilled in the art, mixtures of various diisocyanates may also be employed as the diisocyanate component used in forming urethane-modified polysiloxane. Typically, the hydroxy functional polysiloxane and diisocyanate are reacted in such proportions as to provide about 4-10 hydroxyl groups per isocyanate group.

While urethane modification may be introduced in the manner discussed above, according to an alternative embodiment of the invention the polyol reactant employed in reaction with the second reactant comprises urethane modified polyol. In this case, there is no need to react with diisocyanate the hydroxy functional polysiloxane. Employing urethane modified polyol is found to provide a final resin, i.e., graft copolymer, which is somewhat more flexible than when the urethane groups are introduced by reaction of the hydroxy functional polysiloxane with diisocyanate. Suitable urethane modified polyols are commercially available or readily prepared according to known methods. Exemplary urethane modified diols are made by reaction of diol and diisocyanate in a molar ratio of from about 4:1 to about 4:3, preferably from about 2:0.8 to about 2:1.2, more preferably about 2:1. Suitable diols and diisocyanates include those mentioned above. Such ratio of diol to diisocyanate (i.e., a molar excess of diol) causes the reaction product to be substantially free of unreacted isocyanate groups. This urethane modified diol is then combined with other portions of the polyol reactant (e.g., additional diol, triol, tetrol, etc.) for reaction with the second reactant, generally at elevated temperature and in the presence of a catalyst (as discussed above) to produce the hydroxy functional polysiloxane, specifically, a hydroxy functional urethane modified polysiloxane. It will be apparent to those skilled in the art, that urethane modified triol, urethane modified tetrols, etc. can be used in addition to or in lieu of urethane modified diol, according to the methods and guidelines discussed above, to provide hydroxy functional urethane modified polysiloxane.

Silane compound reactants suitable for reaction with hydroxy functional polysiloxane reactant in making the polysiloxane macromer of the invention are those according to the general chemical formula: ##STR6## wherein R is H or an alkyl group with one to three carbon atoms and R' is a phenylene or substituted phenylene group (including amino functionality) or a carboxylate group. Typical substitution of the hydrogen on the phenylene is by methylene, hexamethylenediamine, tetramethylenediamine and so forth. Many such organic groups are known and selection of suitable organic groups useful in this invention would be apparent to one skilled in the art in view of the present disclosure. The integer n is 0, 1, 2 or 3. The X moiety is halogen, substituted glycol monoether, alkoxy or acyloxy. The X moiety is chosen to impart hydroxy-reactive functionality to the silane compound.

Commercially available silane compounds useful in this invention include vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriacetoxysilane, vinyl-tris-(2-methoxyethyoxysilane), gamma-methacryloxypropyltrimethoxysilane, gamma-methacryloxypropyl-tris-(2-methoxyethoxy)silane, all available from Union Carbide, New York, N.Y., and N-2-(vinylbenzylamino)-ethyl-3-aminopropyltrimethoxysilanemonohydrogen chloride (available from Dow Corning, Midland, MI.) and the like. The silane compound reactant employed to make the polyester macromers of this invention has a molecular weight of about 200 to about 100. The choice of silane compound employed in preparing the polyester macromer will depend largely upon the particular application intended for the final resin or composition comprising resin. As will be apparent to one skilled in the art in view of the present disclosure, a compatible mixture of silane compounds may also be employed as the silane compound reactant.

The silane compound and hydroxy functional polysiloxane reactant are reacted together according to known methods and reaction conditions. Typically, these two reactants are employed in molar ratio of about 2:1 to about 1:2 respectively, more preferably about 1:1. More generally, the silane compound is used in an amount insufficient to yield a gelled reaction product. Also, the silane compound reactant is used in an amount insufficient to react with all of the hydroxy functionality of the hydroxy functional polysiloxane reactant, since the reaction product, the polysiloxane macromer, must have hydroxy functionality to react with the crosslinking agent during cure. In preparing the macromer a catalyst is generally employed for the reaction between the hydroxy-reactive functionality of the silane compound and the hydroxy functionality of the hydroxy functional polysiloxane reactant. The particular catalyst employed for the reaction of the hydroxyl group/hydroxy-reactive functionality would, of course be dependent on the particular hydroxy-reactive functionality of the silane. For example, if the hydroxy-reactive functionality if alkoxy, an acid base catalyst, such as tetraisopropyltitanate may be employed. To catalyst hydroxyl/epoxide reactions, sulfonic acid catalysts are often employed. Suitable catalysts will be apparent in view of the present disclosure. It is also preferred to employ an agent to inhibit polymerization reaction of the carbon-carbon double bonds of the silane compound reactant. Suitable inhibiting agents are well known and include, for example, hydroquinone and others which will be apparent in view of this disclosure.

According to another aspect of the invention, the above-described hydroxy functional polysiloxane graft copolymer is employed in an organic solvent based thermosetting coating composition together with suitable polyfunctional hydroxy-reactive crosslinking agent. such crosslinking agent is selected, preferably, from aminoplast crosslinking agents and polyisocyanate crosslinking agents, either blocked or unblocked depending upon the intended application. Coating compositions of the invention can be formulated so as to be suitable for numerous different applications including, particularly, as motor vehicle body panel coatings. Thus, for example, a coating composition of the invention can be formulated as a primer or as a topcoat, such as a basecoat for a basecoat/clearcoat system, a clearcoat for a basecoat/clearcoat system, or as a one-coating topcoat. Moreover, any of these coatings can be formulated as either a one-component (i.e., resin and crosslinker combined) or a two-component (i.e., resin and crosslinker segregated) coating composition, except that the basecoat of a base/clear system generally would be formulated only as a one-component coating in view of the high pigment content thereof and the mixing and dispersion problems which would result in attempting to add the crosslinking agent at the time of application to a substrate. It is, of course, well known to the skilled of the art to employ unblocked polyisocyanate crosslinking agents generally only in two-component formulations to prevent premature reaction thereof with the hydroxy functional copolymer. Blocked polyisocyanate crosslinkers are employed in one-component coatings, but typically these are employed in primers since the two-component unblocked polyisocyanate coatings of the invention are found generally to provide better surface appearance. The amino resin crosslinking agents also are employed, typically, in one component formulations.

In a coating composition intended for use as a high solids base coat or clear coat of a base/clear automotive coating formulation, typically it is preferred that the graft copolymer have a number average molecular weight (M.sub.n) between about 1,500 and about 3,000, more preferably between about 1,500 and about 2,500. Also, for such use the resin preferably has a hydroxy number between about 50 and about 150.

The crosslinking agent is generally included in compositions of the invention in an amount sufficient to cure the composition. Preferably, the polyisocyanate or block polyisocyanate crosslinking agent is included in compositions of the invention in amounts such that, at the cure temperature of the composition, they provide between about 0.5 and about 1.6, more preferably between about 0.5 and about 1.0 reactive isocyanate groups per hydroxyl group present in the hydroxy functional polyester graft copolymer. When melamine based crosslinking agent is employed, it preferably is employed in amounts between about 5% and about 60% by weight of the total weight of resin solids, i.e., the total weight of crosslinkable resins and crosslinker. More preferably, the aminoplast crosslinking agent is employed in an amount between about 20% and about 40% by weight of the total weight of resin solids. Selection of the optimal amount of crosslinking agent to be employed in the coating composition is dependent upon the desired properties (e.g., flexibility) of the coating as well as its intended use (which determines, in part, its desired cure response and desired shelf stability), and selection of such amount would be within the skill of one in the art.

Polyisocyanate crosslinking agents, i.e., isocyanate compounds containing two or more isocyanate groups per molecule, are well known in the art and numerous suitable organic polyisocyanates will be apparent to those skilled in the art. Among the many suitable polyisocyanates are aliphatic, cycloaliphatic and aromatic isocyanate compounds. Representative of the numerous isocyanates which can be employed are (1) aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, ethylidene diisocyanate, butylidene diisocyanate, 4,4'-bis(isocyanate hexyl) methane, bis(2-isocyanate-ethyl)fumarate, 2,6-diisocyanate methyl caproate, 2,2,4-(2,4,4)-trimethylhexamethylene diisocyanate, and dimer acid diisocyanates;

(2) cycloaliphatic diisocyanates such as 1,3-cyclopentane diisocyanate, 1,4-cyclopentane diisocyanate, 1,2-cyclopentane diisocyanate, and methylcyclohexylene diisocyanate;

(3) aromatic diisocyanates such as m=phenylene diisocyanate, p-phenylenediisocyanate, 4,4'-diphenyl diisocyanate;

(4) aliphatic/aromatic diisocyanates such as 4,4'-diphenylene methane diisocyanates, 2,4- or 2,6-tolylene diisocyanate, 4,4'-toluidene diisocyanate, 1,4-xylylene diisocyanate;

(5) nuclear substituted aromatic compounds such as dianisidine diisocyanate, 4,4'-diphenylether diisocyanate, chlorodiphenylene diisocyanate;

(6) triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanate benzene, 2,4,6-triisocyanate toluene;

(7) tetraisocyanates such as 4,4'-diphenyl dimethylmethane 2,2',5,5'-tetraisocyanate;

(8) polymerized isocyanates such as tolylene diisocyanate dimers and timers and the like;

and (9) polyisocyanates such as prepolymers derived from a polyol, including polyether polyols or polyester polyols (including polyethers which are reacted with excess polyisocyanates to form isocyanate terminated prepolymers), simple polyols such as glycols (e.g., ethylene glycol, propylene glycol), other polyols such as glycerol, trimethylol propane, hexane triols, pentaerythritol and the like, as well as monoethers, e.g., diethylene glycol, tripropylene glycol and the like, and polyethers, i.e., alkylene oxide condensates of the above. While the polyisocyanate crosslinking agent may be any organic polyisocyanate as has been noted above, such crosslinking agents for coating composition to be employed as clear (top) coats are preferably aliphatic and cycloaliphatic polyisocyanates, due to their superior weatherability.

Especially preferred for us in clearcoat compositions of the invention are trimerized products of aliphatic diisocyanates such as 1,6-hexamethylene diisocyanate. Still another particularly preferred type of crosslinking agent is a polyisocyanate having a biuret structure. This type of polyisocyanate is well known, as are methods for making the same. Suitable such polyisocyanate crosslinking agents are high molecular weight biurets of 1,6-hexamethylene diisocyanate sold by Mobay Chemical Company under the trademarks Desmodur N and Desmodure L 2291. Exemplary of other biuret type polysiocyanates are those prepared in accordance with U.S. Pat. No. 3,976,622 to Wagner et al.

Blocked polyisocyanate crosslinking agents are well known to the skilled of the art and many suitable for use in compositions of the invention are commercially available or readily prepared and will be apparent from the present disclosure. More specifically, blocked polyisocyanate crosslinking agents comprise the reaction product of a polyisocyanate, such as those mentioned above, with a blocking agent, that is, an active hydrogen-bearing reactant. Exemplary blocked polyisocyanates are described, for example, in United States patent 4,497,938, which description is incorporated herein by reference.

Melamine based crosslinking agents suitable for crosslinking hydroxy functional bearing materials are well known in the art. Typically, these crosslinking materials are products of reactions of melamine, or urea with formaldehyde and various alcohols containing up to and including 4 carbon atoms. Preferably, the melamine based crosslinking agents are amine-aldehyde resins such as condensation products of formaldehyde with melamine, substituted melamine, urea, benzoquinamine or substituted benzoguanamine. Preferred members of this class are methylated melamine-formaldehyde resins such as hexamethoxymethylmelamine. Particularly preferred crosslinkers are the high solids melamine resins which have substantially 95+percent nonvolatile content. For so-called "high solids" compositions of this invention, it should be recognized that it is important not to introduce extraneous diluents that lower the final solids content of the coating. Other suitable melamine based crosslinking agents will be apparent to one skilled in the art. Melamine based crosslinking agents are preferred for basecoat compositions of the invention. The melamine based crosslinking agent is generally included in a basecoat composition in an amount of between about 5 and about 60, preferably between about 20 and about 40 weight percent. However, selection of the particular amount of melamine based crosslinking agent to be employed in any such composition is dependent on the desired properties of the composition as well as its intended use and would be apparent to one skilled in the art.

Particularly preferred melamine based crosslinking agents are the amino-aldehyde crosslinking agents sold by American Cyanamid under the trademark "Cymel". In particular, Cymel 301, 303, 1130, 1133, 1156, 1161 and 1168 (trademarks) are alkylated melamine aldehyde resins useful in the compositions of this invention. The crosslinking reactions are catalytically accelerated by acids. One such catalyst, for example, which may be so employed is p-toluene sulfonic acid, which when employed is generally added to the composition in about 0.5% by weight based on the total weight of the polyester graft copolymer and crosslinking agent.

Additional materials which may be employed in the coating compositions of this invention include a high molecular weight linear polyurethane which has a number average molecular weight of between about 15,000 and about 40,000, preferably between about 20,000 and about 30,000. It may be made by reacting one of the above mentioned dissocyanates and diols, such as oligoester diol, polycaprolactone diol, polyoxypropylene diol, polyether diols, etc. Suitable high molecular weight linear polyurethane materials are commercially available, for example, as Spenlite L06-30S, (trademark, Spencer-Kellogg, Buffalo, N.Y.). It has been found that these high molecular weight polyurethanes may be employed in metallic flake pigment-bearing topcoat compositions in small amounts, typically up to about 15 weight percent based on the total weight of the polyester graft copolymer and crosslinking agent, to improve the orientation of the metallic flake pigment in the cured coating. It has been found that by including such linear polyurethane, for example, in a basecoat of a basecoat/clearcoat system, the depth of color and metallic glamour of the system may be improved.

Other materials which may be included in the coating compositions of this invention include, for example, catalysts, antioxidants, U.V. absorbers (for topcoats), solvents, surface modifiers and whitening agents. Solvents used in the coating composition of this invention are those which are commonly used, e.g., to facilitate spray application and high solids content and include toluene, xylene, methylethyl ketone, acetone, 2-ethoxy-1-ethanol, diacetone alcohol, tetrahydrofuran, ethyl acetate, dimethylsuccinate, dimethylglutarate, dimethyladipate and mixtures thereof. The solvent in which the polysiloxane graft copolymer is prepared may be employed as a solvent for the composition, thus eliminating the need for drying the resin after preparation, if such is desired.

Typical ultraviolet light stabilizers that are useful in topcoat compositions of this invention are benzophenones such as dodecyl oxibenzophenone, 2,4-dihydroxybenzophenone, hydroxybenzophenones containing sulfonic groups, 2,4-dihydroxy-3',5'-ditertiarybutylbenzophenone, 2,2',4'-trihydroxybenzophenone esters of dicarboxylic acids, 2-hydroxy-4-acryloxyethoxybenzophenone, aliphatic monoesters of 2,2',4-trihydroxy-4'-alkoxybenzophenone, 2-hydroxy-4-methoxy-2-carboxybenzophenone, triazoles such as 2-phenyl-4-(2'4'-dihydroxybenzolyl)-triazoles, substituted benzotriazoles such as hydroxyphenyltriazoles such as 2-(2'-hydroxy-5'-methyphenyl)benzotriazole, 2-(2'-hydroxyphenyl)benzotriazole, and 2-(2'-hydroxy-5'-octylphenyl)naphthiotriazole.

Another type of ultraviolet light stabilizer and one that is particularly preferred for use in the coatings of this invention is that taught in U.S. patent 4,480,094 entitled "Polymeric Light Stabilizers" to Kordomenos et al. These stabilizers contain the sterically hindered polyalkylpiperidine radical and at least two primary hydroxyl groups available for reacting with the crosslinking agent, e.g., amine-aldehyde or polyisocyanate, of the coating composition.

Typical antioxidants which may be employed in the coating composition include tetrakis alkylene (di-alkyl hydroxy aryl) alkyl ester alkanes such as tetrakis methylene 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)proprionate methane (available under the trademark Irganox 1010 from Ciba-Geigy Corp.). Also suitable are the reaction product of p-amino diphenylamine and glycidyl methacrylate, the reaction product of n-hexyl-N'-phenyl-p-phenylene diamine and glycidyl methacrylate, pentaerythritol tetrakis(thioglycolate), trimethylol propane tris(thioglycolate), trimethylol ethane tris(thioglycoate), N-(4-anilinophenyl)maleimide, alkylhydroxyphenyl groups bonded through carboalkoxy linkages to nitrogen atom of a heterocyclic nucleus containing an imidodicarbonyl group or an imidodithiocarbonyl group, 3,3-diterbutyl-4-hydroxy-cinnamonitrile, ethyl-3,5-diterthexyl-4-hydroxy-cinnamate, substituted benzyl esters of beta-substituted (hydroxyphenyl)-propionic acids, bis-(hydroxyphenylalkylene)alkyl isocyanurate compounds, tetrakis hydroxy benzyl phosphonium halides alone or in combination with a dialkylthiodialkanoate, thiodimethylidyne tetrakisphenols alone or in combination with a dialkyl thiodialkanoate or phosphite or phosphonate, dihydrocarbyl-hydroxyphenyl aryl or alkyl phosphonites or phosphonates or phosphates or phosphinites or phosphinates or phosphionites or phosphorothionates or phosphinothionates, diphenyl-bis(3,5-ditertbutyl-4-hydroxyphenoxy)silane, hydrocarbylhydroxyphenyl-dihydrocarbyldithio-carbamates such as 3,5-diterbutyl-4-hydroxyphenyl dimethyldithiocarbamate and amino benzyl thioether.

In one preferred embodiment a base/clear topcoat system is provided, wherein both the basecoat and the clearcoat comprise a resin and crosslinker composition according to the invention. The basecoat would preferably contain only a benzotriazole U.V. stabilizer such as Tinuvin 328 (trademark, Ciba-Geigy, Ardsley, N.Y.), and the clearcoat would contain a benzotriazole U.V. stabilizer, e.g., Tinuvin 328, the polymeric hindered amine light stabilizer of the aforementioned U.S. patent 4,480,084 to Kordomenos et al and an antioxidant, e.g., Irganox-1010 (trademark; Ciba-Geigy). While preferred combinations of stabilizers and antioxidants have been described, these teachings are not meant to be limiting. Selection of suitable stabilizers and antioxidants is within the skill of one in the art.

Surface modifiers or wetting agents are common additives for liquid paint compositions. The exact mode of operation of these surface modifiers is not known, but it is thought that their presence contributes to better adhesion of coating compositions to the surface being coated and helps formation of thin coatings, particularly on metal surfaces. The choice of surface modifiers or wetting agents is dependent upon the type(s) of surface to be coated. Selection of appropriate surface modifiers is well within the skill of the art. Typical of these surface modifeers are polybutyl acrylate and a wide variety of silicon wetting agents which are commercially available.

For many applications of the coating compositions of the invention, particularly high solids compositions, it may be desirable to employ flow control additives to provide sag free coatings. Among the many such materials which are known are non-aqueous dispersions (NAD's) such as described by Porter (S. Porter, Jr., and B. N. McBane, U.S. Pat. No. 4,025,474, May 24, 1977). These particle dispersions may be included generally in an amount up to 15% by weight of the total composition. Other types of NAD's such as described by D. L. Maker and S. C. Peng (U.S. Pat. No. 3,814,721, June 4, 1974) or by S. K. Horvath (U.S. application Ser. No. 292,853, filed Aug. 14, 1981) also may be included in the coating compositions.

Coating compositions according to certain embodiments of the invention may contain pigments. Thus, for example, primer compositions and the basecoat of a base/clear system may comprise any of the wide variety of suitable pigments which are known to the art and readily commercially available. Selection of suitable pigments and the amounts of same will depend largely on the intended use and desired properties of the coating, for example, desired color, hiding properties, etc., and is within the skill of those in the art.

The coating composition can be applied by conventional methods known to those in the art. These methods include roll coating, spray coating, dipping or brushing. The particular application technique chosen will depend upon the particular substrate to be coated and the environment in which the coating operation takes place. Preferred techniques for applying these coating compositions, particularly when applying the same to automobiles, is spray coating through the nozzle of the spray gun. A basecoat, for example, can be applied as a single component by means of a single component spray gun. On the other hand, in spray applying a two component clearcoat composition, the polysiloxane graft copolymer, and additives such as pigments, U.V. absorbers, antioxidants and other nonreactive materials are admixed with a solvent. These materials are fed as one component of a two component system into a spray gun which combines the materials as they are sprayed into the automotive substrate The other material is the polyisocyanate crosslinking agent, which may or may not be cut with a suitable nonreactive solvent.

The invention will be further understood by referring to the following detailed examples. It should be understood that the specific examples are presented by way of illustration and not by way of limitation. Unless otherwise specified, all references to "parts" are intended to mean parts by weight.

Hydroxy functional oligomeric polysiloxane reactant was prepared according to this example. Into a suitable reactor were charged 255 parts phthalic anhydride, 720 parts Esterdiol-204 (trademark, Union Carbide, Danbury, Conn.; 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate), 440 parts trimethylolpropane, 80 parts adipic acid, and 172 parts SR-191 (trademark; General Electric Co.; Waterford, N.Y.; phenyl-methyl silicone resin). The above mixture was heated to 300.degree. F.-350.degree. F. and water and methanol distilled off until the acid number dropped below 10. The mixture was cooled to 200.degree. F. at which time the batch was thinned with 333 parts xylene. To this solution was added dropwise 167 parts Desmodur W (Trademark, Mobay chemical Co., Pittsburgh, Pa.; diisocyanate) over a period of two hours. The batch was post-cooked at 210.degree. F. until no NCO peak was observed in an IR spectrum.

Hydroxy functional carbon-carbon double bond-bearing branched polysiloxane macromer was prepared according to this example. Into a suitable reactor were charged 840 parts of the resin from Example I, 0.7 parts hydroquinone, and 0.1 parts tetraisopropyltitanate. This mixture was heated to 200.degree. F. at which time 62.6 parts gamma-methacryloxypropyltrimethoxysilane was added over a period of 15 minutes. The mixture was post cooked at 200.degree. F. until no further methanol was evolved.

Hydroxy functional polysiloxane graft copolymer was prepared according to this example. Into a suitable reactor was placed 217 parts Exxate 600 (Trademark, Exxon Chemical Co., Houston, Texas). This solvent was heated to 300.degree.-10.degree. F. at which time a mixture of 671 parts of the resin from Example II, 197 parts iso-butylmethacrylate, 54 parts styrene, 24 parts hydroxyethylacrylate, 18.2 parts acrylic acid, and 35 parts Lupersol 533-M75 (Trademark, Pennwalt Chemical Co., Buffalo, N.Y., ethyl 3,3-di(t-amylperoxy)-butyrate) was added dropwise over a period of 4 hours. The reaction mixture was post-cooked at 300.degree. F. for an additional 30 minutes and 4 parts Luersol 533-M75 (Trademark, Pennwalt Chemical Co.) was added. The reaction mixture was held at 300.degree. F. for an additional 2 hours then cooled. The final resin had a viscosity of Y at 63.5% solilds

Hydroxy functional urethane modified oligomeric polysiloxane reactant was prepared according to this example. Into a suitable reactor were charged 720 parts Esterdiol 204 (trademark; Union Carbide Corp.; diol), 490 parts Tone 301 (Trademark, Union Carbide, New York, N.Y.;polycaprolactone triol), 255 parts phthalic anhydride, 287 parts ZV33/400 (silicon resin available from Tego Chemie Service) and 8 parts Fascat 4100 (Trademark; M&b T Chemical, Rahway, New Jersey;catalyst). The mixture was heated to 400.degree. F. and water and methanol were distilled off until the acid number dropped to 9.0. The mixture was cooled and thinned with 611 parts xylene. The mixture was then heated to 200.degree. F. and 122 parts Desmodur W (Trademark, Mobay Chemical Co.,) was added dropwise over a period of two hours. The reaction mixture was post-cooked at 200.degree. F. until no NCO peak appeared in the IR spectrum.

Hydroxy functional carbon-carbon double bond-bearing branched polysiloxane macromer was prepared according to this example. Into a suitable reactor were charged 650 parts of the resin from Example IV, 0.7 parts hydroquinone and 0.07 parts tetraisopropyltitanate. The mixture was heated to 220.degree. F. at which time 40 parts .alpha.-methacryloxy-propyltrimethoxysilane was added over a period of 20 minutes. The reaction mixture was heated at 225.degree. F. until no further methanol was evolved.

Hydroxy functional polysiloxane graft copolymer was prepared according to this example. Into a suitable reactor were charged 110 parts Exxate 600 (Trademark; Exxon Chemical Co.) and 19.4 parts cumene hydroperoxide. The solution was heated to 300.degree. F. at which time a mixture of 539 parts of the resin from Example V, 145 parts iso-butylmethacryalte, 18 parts hydroxyethylacrylate, 40 parts styrene, 13 parts acrylic acid, and 23 parts t-butylperbenzoate was added dropwise over a period of three hours. The reaction mixture was post-cooked at 300.degree. F. for three hours to afford a resin with a Z.sub.4 viscosity at 72.3% solids.

Flexible primer compositions according to this invention are formulated according to the following examples. The coating compositions are applied over Bonderite steel panels and baked at 380.degree. F. for 20 minutes to afford flexible, durable coatings which exhibited excellent adhesion and hardness.

The following materials charged into a ball mill and ground to form a millbase.

Flexible enamel compositions according to the present invention were formulated according to the following examples and applied over both metal and plastic substrates and baked at 250.degree. F. for 30 minutes to afford coatings which were flexible and durable.

WHITE MILLBASE FORMULATION

The following materials were charged into a ball mill and ground to form a millbase.

Universal basecoats were formulated according to the following examples:

One component universal clearcoats according to the present invention were formulated according to the following examples.

One component basecoat/clearcoat combinations according to the present invention were prepared according to these examples. Specifically, the one component basecoat and clearcoat were applied, by spraying, wet on wet over both metal and plastic substrates. The coatings were cured at 250.degree. F. for 30 minutes. Film thicknesses ranged from 0.6-0.8 mils for basecoats and from 1.8-2.0 mils for clearcoat upon cure. The cured coatings were tested for flexibility, resistance to methyl ethyl ketone (MEK), and resistance to ultraviolet light degradation. The test results are shown in Table A.

Two component universal clearcoats are formulated according to the following examples.

One component basecoat/two component clearcoat coating systems according to the present invention are prepared according to these examples. Specifically, the one component basecoats and the two component clearcoats identified in Table B are applied, by spraying, wet on wet over both metal and plastic substrates. The coatings are cured at 250.degree. F. for 30 minutes. Film thicknesses range from 0.6-0.8 mils for basecoats and from 1.8-2.0 mils for clearcoats upon cure. The cured coatings are tested for flexibility, resistance to methyl ethyl ketone (MEK), and resistance to ultraviolet light degradation. The test results are shown in Table B.

In view of the disclosure, many modifications of this invention will be apparent to those skilled in the art. It is intended that all such modifications which fall within the true scope of this invention be included within the terms of the appended claims.