Source: http://www.google.com/patents/US5330796?ie=ISO-8859-1
Timestamp: 2014-03-12 10:33:07
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Matched Legal Cases: ['arts98', 'arts60', 'arts60', 'arts60', 'arts2', 'arts2', 'arts1']

Patent US5330796 - Method of forming coating films - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsThe invention provides a method of forming a coating film by forming in sequence a pigmented base coat and a clear top coat on a substrate followed by finishing by the two-coat one-bake technique, the method being characterized by using, as a coating composition for pigmented base coat formation, a composition...http://www.google.com/patents/US5330796?utm_source=gb-gplus-sharePatent US5330796 - Method of forming coating filmsAdvanced Patent SearchPublication numberUS5330796 APublication typeGrantApplication numberUS 07/878,461Publication dateJul 19, 1994Filing dateMay 5, 1992Priority dateMay 15, 1991Fee statusLapsedAlso published asDE69204538D1, DE69204538T2, EP0513814A1, EP0513814B1Publication number07878461, 878461, US 5330796 A, US 5330796A, US-A-5330796, US5330796 A, US5330796AInventorsSatoru Ito, Akira Kasari, Shigeru NakamuraOriginal AssigneeKansai Paint Company, Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (1), Referenced by (13), Classifications (24), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetMethod of forming coating filmsUS 5330796 AAbstract The invention provides a method of forming a coating film by forming in sequence a pigmented base coat and a clear top coat on a substrate followed by finishing by the two-coat one-bake technique, the method being characterized by using, as a coating composition for pigmented base coat formation, a composition comprising, as essential components thereof,
(3) a polyorganosiloxane
( 5 ) an organic solvent,
(1) an OH-containing base resin which further contains at least one group selected from the class consisting of a silanol group and a hydrolyzable group bound directly to a silicon atom,
( 2 ) an amino resin, and
( 3 ) an organic solvent.
We claim: 1. A method of forming a coating film by forming in sequence a pigmented base coat and a clear top coat on a substrate followed by finishing by the two-coat one-bake technique, the method being characterized by using, as a coating composition for pigmented base coat formation, a composition comprising, as essential components thereof,(1) at least one OH-containing resin selected from the group consisting of an OH-containing polyester resin and an OH-containing vinyl resin, each having a hydroxyl value of about 20 to 200, (2) a methylol amino resin etherified with an alcohol, (3) a polyorganosiloxane which has, on an average, at least two groups, per molecule, each selected from the class consisting of a silanol group and an alkoxysilane group and has a number average molecular weight of at least 1,000 the polyorganosiloxane optionally having, on an average, at least one epoxy group per molecule, the polyorganosiloxane being prepared by subjecting to hydrolysis condensation a silane compound of the general formula R.sup.1.sub.x Si(OR.sup.2).sub.4-x                         (I) wherein R.sup.1 and R.sup.2 may be the same or different and each is a hydrocarbon group containing 1 to 13 carbon atoms and x is 1, the epoxy-containing polyorganosiloxane being prepared by subjecting to hydrolysis cocondensation a silane compound of the general formula (I) wherein x is 1, 2 or 3 and an epoxy-containing silane of the general formula ##STR3## wherein R.sup.3 and R.sup.4 may be the same or different and each is a hydrocarbon group consisting 1 to 13 carbon atoms, Y is 1, 2 or 3, G is a group of the formula ##STR4## wherein R.sup.5 is a bivalent hydrocarbon group containing 1 to 13 carbon atoms and the R.sup.6 groups may be the same or different and each is a hydrogen atom or a methyl group, (4) a flaky metal powder and/or a mica powder, and (5) an organic solvent,and using, as a coating composition for clear top coat formation, a composition comprising, as essential components thereof, (1) a base resin which is (i) an OH-containing resin further containing at least one group selected from the class consisting of a silanol group and a hydrolyzable group bound directly to a silicon atom within the same molecule or (ii) a mixed resin composed of a resin containing at least one group selected from the class consisting of a silanol group and a hydrolyzable group bound directly to a silicon atom and an OH-containing resin, (2) a methylol amino resin etherified with an alcohol, and (3) an organic solvent. 2. A method of forming coating films as claimed in claim 1, wherein, in the pigmented base coat composition, the proportions of the OH-containing resin, methylol amino resin and polyorganosiloxane are 5 to 90% by weight, 5 to 50% by weight and 1 to 40% by weight, respectively, based on the total amount (resin solids) of the OH-containing resin, methylol amino resin and polyorganosiloxane.
3. A method of forming coating films as claimed in claim 1, wherein, in the clear top coat composition, the proportion of the methylol amino resin is 2 to 100 parts by weight per 100 parts by weight of the base resin.
Coating compositions based on thermosetting acrylic resin/melamine resin, those based on thermosetting polyester resin/melamine resin and the like are now mainly used as coating compositions for top coat in the automobile industry. In terms of the degree of levelness and smoothness, these compositions have almost reached their limit, while there is still much room for improvement in these and other film performance characteristics. Another problem is that their low-temperature curability is not fully satisfactory. Furthermore, such problems as ebullition of coating films due to condensation byproducts (formalin etc.) generated in the curing step and environmental pollution remain to be solved.
The invention provides a method of forming coating films by forming in sequence a pigmented base coat and a clear top coat on a substrate followed by finishing by the two-coat one-bake technique, the method being characterized by, as a coating composition for pigmented base coat formation, a composition comprising, as essential components thereof,
(4) a flaky metal powder and/or a mica powder and
(2) an amino resin, and
The invention is now described in more detail in the following.
Pigmented base coat In the coating method of this invention, the pigmented base coat is formed from a base coat composition which comprises, as essential components thereof, (1) an OH-containing resin (hereinafter sometimes referred to as "OH-containing base coat resin"), (2) an amino resin, (3) a polyorganosiloxane having, on an average, at least two groups each selected from the group consisting of a silanol group and an alkoxysilane group and having a number average molecular weight of at least 1,000 (hereinafter sometimes referred to as "polyorganosiloxane") for short), (4) a flaky metal powder and/or a mica powder (hereinafter sometimes referred to as "metal flake" for short) and (5) an organic solvent.
The OH-containing polyester resins preferably have a hydroxyl value of about 20 to 200, more preferably about 50 to 150. When the hydroxyl value is smaller than 20, the rate of curing of the base coat film becomes slower than that of the top coat film, so that the curing of the top coat film goes ahead of that of the base coat film. As a result, the top coat film tends to develop defects such as shrinkage, leading to impairment of the appearance of the finished film. Furthermore, the curing can hardly be complete, so that the performance characteristics (e.g. water resistance, impact resistance) of the coating film will unfavorably be deteriorated. On the other hand, hydroxyl values exceeding about 200 are undesirable since, in that case, a large number of unreacted hydroxyl groups remain within the coating film, leading to deteriorated performance characteristics (e.g. water resistance, weather resistance ) of the coating film.
Said OH-containing polyester resins may contain one or more carboxyl groups within the molecule. In particular, the carboxyl group can increase the rate of reaction between the hydroxyl group and the amino group, between the hydroxyl group and the silanol or alkoxysilane group, or between one silanol or alkoxysilane group and another silanol or alkoxysilane group, to thereby effectively improve the finish of the coating film. Recommendably, the carboxyl group content should correspond to about 0 to 50, preferably about 5 to 20 in an acid value of resin.
As the polybasic acid, there may be mentioned, for example, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydroterephthalic acid, hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, chlorendic acid, trimellitic acid, hexahydrotrimellitic acid, pyromellitic acid, cyclohexanetetracarboxylic acid, methyltetrahydrophthalic acid, methylhexahydrophthalic acid, endomethylenehexahydrophthalic acid, methylendomethylenetetrahydrophthalic acid, maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, suberic acid, pimelic acid, dimer acids (dimers of tall oil fatty acid), tetrachlorophthalic acid, naphthalenedicarboxylic acid, 4,4 '-diphenylmethanedicarboxylic acid and 4,4 '-dicarboxybiphenyl, acid anhydrides of these, and dialkyl esters of these, in particular dimethyl esters.
The (oil-free) alkyd resins mentioned above can be produced by any of the conventional methods, for example by subjecting a mixture of the above-mentioned polybasic acid and polyhydric alcohol and, if necessary, monobasic acid to esterification or transesterification in the presence of an esterification catalyst (e.g. dibutyltin dilaurate). Said polybasic acid and polyhydric alcohol are desirably used in proportions such that the number of moles of the polybasic acid component(s) is within the range of about 0.7 to 0.99, preferably about 0.8 to 0.98, per mole of the polyhydric alcohol component(s). The esterification catalyst is desirably used in an amount of about 0.1 to 1.0 part by weight, preferably about 0.2 to 0.5 part by weight, per 100 parts by weight of the sum total of the polyhydric alcohol and polybasic acid components. As for the reaction conditions, the reaction temperature is generally about 160 280 reaction period is generally about 5 to 12 hours, preferably about 6 to 8 hours.
As the OH-containing polyester resin, vinyl-modified alkyd resins, for instance, may also be used. Usable as said vinyl-modified alkyd resins are, for example, reaction products from an OH-containing (oil-free) alkyd resin and a COOH-- or NCO-containing vinyl resin, reaction products from an OH-- and COOH-containing (oil-free) alkyd resin and an epoxy-containing vinyl resin, products of radical polymerization of a vinyl monomer [e.g. a polymerizable unsaturated monomer (b) mentioned below] in the presence of an (oil-free) alkyd resin having a radical-polymerizable unsaturated group [e.g. an alkyd resin containing a drying oil as an essential component, an alkyd resin derived from an OH-- and COOH-containing (oil-free) alkyd resin by reaction with glycidyl (meth)acrylate], and products of polymerization of a vinyl monomer [e.g. a polymerizable unsaturated monomer (b) mentioned below] in the presence of an (oil-free) alkyd resin or vinyl-modified alkyd resin such as mentioned above, for instance, as a suspension stabilizer, in an organic solvent in which said monomer and suspension stabilizer can be dissolved but the polymer particles obtained from said monomer will not be dissolved.
Usable as the OH-containing vinyl resins are, for example, (co)polymers obtained by radical polymerization of at least one of the OH-containing vinyl monomers (a) mentioned below, optionally together with at least one of other polymerizable unsaturated monomers (b) mentioned below.
As said OH-containing vinyl monomers (a), there may be mentioned, for example, the following (a-1) to (a-5).
(a-5) Adducts of (a-1) to (a-4) with a lactone (e.g. ε-caprolactone, γ-valerolactone).
As other polymerizable unsaturated monomers (b), there may be mentioned, for example, C.sub.1-24 alkyl or cycloalkyl esters of (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate and cyclohexyl (meth)acrylate; COOH-- containing compounds such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid (anhydride), fumaric acid and 2-carboxyethyl (meth)acrylate; aromatic vinyl compounds such as styrene and vinyltoluene; perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate, perfluoroisononylethyl (meth)-acrylate and perfluorooctylethyl (meth)acrylate; (meth)acrylonitrile; olefins; fluoroolefins; vinyl esters; cyclohexyl or alkyl vinyl ethers; and allyl ethers.
Said OH-containing vinyl resins can be produced in the conventional manner, for example by subjecting the above monomer or monomers (a), optionally together with one or more other monomers (b), to polymerization in a substantially inert organic solvent in the presence of a radical polymerization initiator at about 80 to 18 hours.
Radical polymerization initiators which can be used include, among others, azo type initiators such as 2,2'-azobisisobutyronitrile and 2,2'-azobis ( 2,4-dimethylvaleronitrile), and peroxide type initiators such as benzoyl peroxide, lauryl peroxide and tert-butyl peroctoate. The OH-containing vinyl resins may have a number average molecular weight of about 2,000 to 80,000, preferably about 4,000 to 20,000. When the molecular weight is smaller than about 2,000, the melt viscosity of the base coat decreases excessively during baking, allowing the orientation of metal flakes to change. As a result, coating films with a metallic tone can hardly be obtained. Molecular weights higher than about 80,000 are also undesirable since the workability in coating decreases.
R.sup.1.sub.x Si(OR.sup.2).sub.4-x                         (I)
wherein R.sup.1 and R.sup.2 may be the same or different and each is a hydrocarbon group containing 1 to 13 carbon atoms and x is 1, to hydrolysis condensation.
As the R.sup.1 and R.sup.2 groups mentioned above, there may be mentioned, for example, methyl, ethyl, propyl, butyl and phenyl.
The epoxy-containing polyorganosiloxane can be prepared by subjecting to hydrolysis cocondensation a silane representable by the general formula (I) wherein x is 1, 2 or 3 and an epoxy-containing silane of the general formula ##STR1## wherein R.sup.3 and R.sup.4 may be the same or different and each is a hydrocarbon group containing 1 to 13 carbon atoms, y is 1, 2 or 3, G is a group of the formula (III ) or (IV) given below. ##STR2## In the above formulas (III)and (IV), R.sup.5 is a bivalent hydrocarbon group containing 1 to 13 carbon atoms and the R.sup.6 groups may be the same or different and each is a hydrogen atom or a methyl group.
As the R.sup.3 and R.sup.4 groups mentioned above, there may be mentioned, for example, methyl, ethyl, propyl, butyl and phenyl. As the R.sup.5 group mentioned above, there may be mentioned, for example, methylene, ethylene, propylene, butylene and hexamethylene.
The hydrolysis condensation or cocondensation of the silane compounds mentioned above is carried out by mixing the silane compound(s) with a water-soluble solvent (e.g. alcohol type or cellosolve type solvent) as necessary and allowing the hydrolysis and condensation reactions to proceed in the presence of an inorganic acid such as hydrochloric acid, sulfuric acid or phosphoric acid or an organic acid such as formic acid or acetic acid and in the presence of water, preferably at a pH of not more than 6, at a temperature of about 20 stirring for about 30 minutes to 20 hours.
The molecular weight of the polyorganosiloxane can suitably be controlled by adjusting or selecting the amount o f water, the kind and amount of catalyst, the reaction temperature and the reaction time, among others.
When, in the above-mentioned polyorganosiloxane, the average number of silanol and/or alkoxysilane groups per molecule is below 2, the rate of curing of the base coat film becomes slower than that of the top coat film and the curing of the top coat film begins before curing of the base coat film, so that the top coat film develops defects such as shrinkage and the finished coating film presents an unsatisfactory appearance.
As examples of the organic solvent, there may be mentioned aromatic hydrocarbons such as xylene and toluene, esters such as ethyl acetate, propyl acetate and butyl acetate, ketones such as acetone and methyl ethyl ketone, and ethers such as ethylene glycol, cellosolve, butylcellosolve and cellosolve acetate. Such organic solvents may be used either singly or in the form of a mixture of two or more of them. From the standpoint of finishing performance, the boiling point should preferably be not higher than about 150
Other additives for coating composition than those mentioned above which can be incorporated in the base coat composition as necessary include organic pigments, inorganic pigments, pigment dispersing agents, finely divided polymers, ultraviolet absorbers, coated surface modifiers, curing catalysts, cellulose acetate (and derivatives thereof), etc.
Clear top coat The top coat is formed from a clear coating composition (top coat composition) comprising, as essential components thereof, an OH-containing base resin (hereinafter referred to as "top coat base resin") which further contains one or more groups each selected from the group consisting of a silanol group and a hydrolyzable group bound directly to a silicon atom (hereinafter referred to as "hydrolyzable silyl group"), an amino resin and an organic solvent.
The hydrolyzable group in the above top coat base resin is a group capable of undergoing hydrolysis in the presence of water to form a silanol group. Said group includes, among others, C.sub.1-5 alkoxy groups; aryloxy groups such as phenoxy, tolyloxy, p-methoxyphenoxy, p-nitrophenoxy and benzyloxy; acyloxy groups such as acetoxy, propionyloxy, butanoyloxy, benzoyloxy, phenylacetoxy and formyloxy; and residues of the formula --N(R.sup.7).sub.2, --ON(R.sup.7).sub.2, --ON═C(R.sup.7).sub.2 or --NR.sup.8 COR.sup.7 (in which the R.sup.7 groups are the same or different and each is C.sub.1-8 alkyl, aryl or aralkyl and R.sup.8 is H or C.sub.1-8 alkyl).
The top coat base resin to be used in the practice of the invention may be an OH-containing resin which further contains at least one group selected from the class consisting of a silanol group and a hydrolyzable silyl group as an additional essential functional group component within the same molecule (hereinafter said resin being sometimes referred to as "single resin") or a mixed resin composed of a resin having at least one group selected from the class consisting of a silanol group and a hydrolyzable silyl group [hereinafter said resin being sometimes referred to as "resin (or polymer) A"] and an OH-containing resin [hereinafter sometimes referred to as "resin (or polymer) B"]. In kind, said resins include vinyl polymers, polyester resins and polyether polyester resins, among others. These resins should desirably have a number average molecular weight of about 2,000 to 100,000 preferably about 4,000 to 80,000, in the case of vinyl polymers, about 500 to 20,000, preferably about 1,000 to 5,000, in the case of polyester and polyether polyester resins. When the number average molecular weight is below the lower limit mentioned above, the paint film surface tends to develop such defects as shrinkage. When the number average molecular weight is above the upper limit, the workability in painting will be inferior and the paint film surface tends to develop such defects as orange peel.
Among the resins mentioned above, vinyl polymers, which are excellent in performance characteristics such as weather resistance, acid resistance and mar resistance, are preferred as the top coat base resin to be used in the practice of the invention. Such vinyl polymers are mentioned below in further detail.
As examples of the single resin of the vinyl polymer type, there may be mentioned vinyl copolymers produced by copoymerizing a silanol- and/or hydrolyzable silyl-containing vinyl monomer (c) and an OH-containing vinyl monomer (a), optionally together with some other polymerizable unsaturated monomer (b), and polymers produced by first preparing a functional group-containing vinyl polymer and then reacting said vinyl polymer with a silanol- and/or hydrolyzable silyl-containing silane compound which further has a group complementarily reacting with the functional group of said vinyl polymer (the silanol and/or hydrolyzable silyl group may be the complementarily reacting group), for example polymers produced by reacting a copolymer of glycidyl (meth)acrylate and an OH-containing vinyl monomer (a) and some other vinyl monomer (b) with γ-aminopropyltrimethoxysilane and polymers produced by reacting a copolymer of (meth)acrylic acid, an OH-containing vinyl monomer (a) and some other polymerizable unsaturated monomer (b) with γ-glycidoxypropyltrimethoxysilane.
Said vinyl polymers should desirably have, on an average, at least one silanol and/or hydrolyzable silyl group per molecule. When the average number of silanol and/or hydrolyzable silyl groups is less than one per molecule, the curability will be unsatisfactorily low and coating films excellent in weather resistance, acid resistance, mar resistance and other characteristics can hardly be formed. Furthermore, said vinyl polymers should desirably have hydroxyl groups in a content such that the hydroxyl value amounts to about 30 to 300, preferably about 50 to 200. When the hydroxyl value is below about 30, the curability will be low and coating films excellent in weather resistance, acid resistance, mar resistance and other characteristics will not be obtained. Conversely, when the hydroxyl value exceeds 300, a large number of unreacted hydroxyl groups will remain in the coating film, unfavorably leading to decreased water resistance, for instance.
As examples of the mixed resin of the vinyl polymer type, there may be mentioned, as polymer A, vinyl polymers produced by (co)polymerizing a silanol- and/or hydrolyzable silyl-containing vinyl monomer (c), optionally with another polymerizable unsaturated monomer (b) and polymers produced by first preparing a functional group-containing vinyl polymer and then reacting said vinyl polymer with a silanol- and/or hydrolyzable silylcontaining silane compound which further has a group complementarily reacting with the functional group of said vinyl polymer (the silanol and/or hydrolyzable silyl group may be the complementarily reacting group), for example polymers produced by reacting a copolymer of glycidyl (meth)acrylate and some other polymerizable unsaturated monomer (b) with γ-aminopropyltrimethoxysilane and polymers produced by reacting a copolymer of (meth)acrylic acid and some other polymerizable unsaturated monomer (b) with γ-glycidoxypropyltrimethoxysilane, and, as polymer B, polymers produced by polymerizing an OH-containing vinyl monomer (a) and copolymers of said vinyl monomer (a) and some other polymerizable unsaturated monomer (b).
Said polymer A should desirably have, on an average, at least one silanol and/or hydrolyzable silyl group per molecule. When the average number of silanol and/or hydrolyzable silyl groups is less than one per molecule, the curability will be low and it will be impossible to form coating films excellent in weather resistance, acid resistance, mar resistance, etc.
Said polymer B should preferably have a hydroxyl value of not less than about 30. When the hydroxyl value is less than about 30, the curability will be low and paint films excellent in weather resistance, acid resistance, mar resistance and other characteristics can hardly be formed. When the hydroxyl value is excessively high, a large number of unreacted hydroxyl groups will remain in the coating film, causing the water resistance and other properties of the coating film to decrease. Hence, the hydroxyl value should preferably be not more than about 300.
Said polymer A and polymer B are admixed in a polymer A/polymer B weight ratio of 90:10 to 10:90, preferably 80:20 to 20:80.
Among the single and mixed resins mentioned above, single resins, which can readily form coating films excellent in appearance and performance characteristics with uniform curing, are preferred.
As the monomers (a) and (b), there may be mentioned those already mentioned hereinbefore.
As the vinyl monomer (c) mentioned above, there may be mentioned, for example, acrylic silane compounds such as γ-(meth )acryloxyethyltrimethoxysilane, γ-(meth)-acryloxypropyltrimethoxysilane, γ-(meth )acryloxypropyltriethoxysilane, γ-(meth)acryloxypropyltripropoxysilane, γ-(meth )acryloxypropylmethyldimethoxysilane, γ-(meth)-acryloxypropylmethyldiethoxysilane, γ-(meth)acryloxypropylmethyldipropoxysilane, δ-(meth)acryloxybutylphenyldimethoxysilane, δ-(meth)acryloxybutylphenyldiethoxysilane, δ-(meth)acryloxybutylphenyldipropoxysilane, γ-(meth)acryloxypropyldimethylmethoxysilane, γ-(meth)acryloxypropyldimethylethoxysilane, γ-(meth)acryloxypropylphenylmethylmethoxysilane, γ-(meth)acryloxypropylphenylmethylethoxysilane and γ-(meth)acryloxypropyltriacetoxysilane; vinylsilane compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; allylsilane compounds such as allyltriethoxysilane; and styrylsilane compounds such as 2-styrylethyltrimethoxysilane.
The top coat base resin to be used in the practice of the invention may be a COOH-containing one. A method of introducing the carboxyl group into said resin comprises, for instance, using a COOH-containing vinyl monomer as the other vinyl monomer (b) component in the vinyl polymer production. Such monomer, when employed, is used generally in an amount such that the COOH-containing vinyl monomer amounts to about 5 to 50% by weight, preferably about 10 to 40% by weight, on the vinyl polymer basis.
The amino resin to be used in combination with the above-mentioned top coat base resin includes, among others, those methylol amino resins and etherified amino resins (derived from methylol amino resins by etherification with an alcohol) mentioned above for the pigmented base coat paint composition.
Said amino resin is used suitably in an amount of about 2 to 100 parts by weight per 100 parts by weight of the base resin. When its amount is less than 2 parts by weight, the water resistance and other characteristics will be unsatisfactory, while, when its amount is above 100 parts by weight, the weather resistance will be adversely affected.
Useful as the organic solvent are, for example, hydrocarbon solvents such as heptane, toluene, xylene, octane and mineral spirit; ester solvents such as ethyl acetate, n-butyl acetate, isobutyl acetate, methylcellosolve acetate and butylcarbitol acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone; alcohol solvents such as ethanol, isopropanol, n-butanol, sec-butanol and isobutanol; and ether solvents such as n-butyl ether, dioxane, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether.
The clear coating composition to be used in clear top coat formation in accordance with the invention can be prepared by dissolving or dispersing the above-mentioned top coat base resin and amino resin in an organic solvent. Said composition may be in the form of a nonaqueous dispersion coating composition.
Said clear coating composition may contain, when necessary, a curing catalyst for the silanol and/or hydrolyzable silyl group, in addition to the above-mentioned base resins and organic solvent.
As the curing catalyst, there may be mentioned, for example, acidic compounds such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, trichloroacetic acid, phosphoric acid, mono-n-propyl phosphate, monoisopropyl phosphate, mono-n-butyl phosphate, monoisobutyl phosphate, mono-tert-butyl phosphate, monooctyl phosphate, monodecyl phosphate, other monoalkyl phosphates, di-n-propyl phosphate, diisopropyl phosphate, di-n-butyl phosphate, diisobutyl phosphate, di-tert-butyl phosphate, dioctyl phosphate, didecyl phosphate, other dialkyl phosphates, β-hydroxyethyl (meth)acrylate phosphate, mono-n-propyl phosphite, monoisopropyl phosphite, mono-n-butyl phosphite, monoisobutyl phosphite, mono-tert-butyl phosphite, monooctyl phosphite, monodecyl phosphite, other monoalkyl phosphites, di-n-propyl phosphite, diisopropyl phosphite, di-n-butyl phosphite, diisobutyl phosphite, di-tert-butyl phosphite, dioctyl phosphite, didecyl phosphite, other dialkyl phosphites; tetraisopropyl titanate, tetrabutyl titanate, other titanium-containing compounds; tin octanoate, dibutyltin diacetate, dibutyltin dioctanoate, dibutyltin dilaurate, dibutyltin dimaleate, other tincontaining compounds; and basic compounds such as butylamine, tert-butylamine, dibutylamine, hexylamine, ethylenediamine, triethylamine, isophoronediamine, imidazole, lithium hydroxide, sodium hydroxide, potassium hydroxide and sodium methylate. At least one of these is used.
These curing catalysts may be used in an amount of about 0.05 to 20 parts by weight, preferably about 0.1 to 10 parts by weight, per 100 parts by weight of the top coat base resin.
When hexamethoxymethylmelamine or an etherified melamine resin derived therefrom by partial or complete substitution of the methoxy groups with a C.sub.3 or higher alcohol is used as the amino resin, a strongly acidic catalyst, such as p-toluenesulfonic acid or dodecylbenzenesulfonic acid, is generally used as the curing catalyst for the reaction of such resin with the hydroxyl group. Said strongly acidic catalyst is neutralized (blocked) with an amine compound such as triethylamine, diethanolamine or 2-amino-2-methylpropanol for providing storage stability and enabling the use of the coating composition as a one-pack type paint. This neutralized (blocked) strongly acidic catalyst can serve as a curing catalyst for alkoxysilane groups as well. Thus, at a baking temperature of 100 C. or above, the neutralized (blocked) strongly acidic catalyst serves as a common catalyst for the reaction of resins and the reaction of alkoxysilanes.
The clear coating composition may contain, as necessary, ultraviolet absorbers, antioxidants, light stabilizers, fine polymer particles and various other additives for coating composition.
The clear coating composition to be used in the practice of the invention should generally have a resin solids content of about 35 to 70% by weight.
The method of this invention can be practiced by applying the pigmented base coat composition to a substrate such as a coated surface prepared by electrodeposition coating of a steel sheet (after chemical conversion treatment) followed by or without a subsequent intercoating, or a coated surface prepared by applying a primer to any of various plastic materials with or without subsequent intercoating, and then applying the top clear coat composition. The electrodeposition coating composition and the intercoating composition are baked generally at 140 C. for 30 to 90 minutes, although the baking conditions may vary depending on the composition types. The pigmented base coat composition and top clear coat composition can be applied in the conventional manner, for example using an electrostatic or non-electrostatic coating machine or equipment. The thickness of the pigmented base coat film is preferably about 10 to 50 μm (after curing). After application of base coat composition, the coating film is dried by allowing to stand at room temperature for several minutes or by forced drying at about 50 80 applied. The clear coat film preferably has a thickness of 20 to 100 μm (after curing). The coated material is heated at about 120 180
In the method of this invention, the pigmented base coat composition to be finished by the two-coat one-bake technique contains, as a binder component, a polyorganosiloxane having a number average molecular weight of at least 1,000 and having at least two groups, per molecule, which are each selected from the class consisting of silanol group and an alkoxysilane group, so that, upon heating, the reaction between silanol groups (inclusive of silanol groups resulting from hydrolysis of alkoxysilane groups) and the reaction of a silanol group, an amino group in the amino resin and a hydroxyl group in the OH-containing resin occur rapidly. Said reactions proceed faster than the curing reaction of the clear coating composition, so that, in the early stage of baking, the viscosity of the base coat composition increases more rapidly than that of the clear coat composition. It is presumable that, for this reason, a base coat film durable to the shrinking force of the clear coat film as resulting from curing of the clear coating composition and volume change thereof due to solvent evaporation is formed and, as a result, the coating film acquires an improved finish appearance. Furthermore, the coating film formed shows excellent coating film performance characteristics (solvent resistance, weather resistance, mar resistance etc.). In addition, even when said pigmented base coat composition is applied again to the cured clear coat film for recoating, an improved adhesion between both the coating films can be observed.
PRODUCTION EXAMPLE 1 A reaction vessel was charged with 0.29 mole of isophthalic acid, 0.23 moleof phthalic acid, 0.43 mole of hexahydrophthalic acid, 0.4 mole of trimethylolpropane, 0.6 mole of neopentyl glycol and 0.1 mole of coconut oil fatty acid and the condensation polymerization was carried out at 200 with an acid value of 8 and a hydroxyl value of 72. A 60% resin solution (a-1) was prepared by adding 43 parts of xylene to 100 parts of said polyester resin. Its viscosity was Y (25 viscosity).
PRODUCTION EXAMPLE 2 An OH-containing acrylic resin solution (a-2) was prepared by reacting 30 parts of methyl methacrylate, 53 parts of n-butyl methacrylate, 15 parts of 2-hydroxyethyl acrylate and 2 parts of acrylic acid in an organic solvent composed of 85 parts of xylene and 15 parts of n-butanol. The number average molecular weight of the resin was 6,600, the resin solids content 50%, and the Gardner bubble viscosity V.
PRODUCTION EXAMPLE 3 An OH-containing acrylic resin solution (a-3) was prepared by reacting 30 parts of methyl methacrylate, 45 parts of n-butyl methacrylate and 25 parts of 2-hydroxyethyl acrylate in an organic solvent composed of 85 parts of xylene and 15 parts of n-butanol. The number average molecular weight was 5,000, the resin solids content 50%, and the Gardner bubble viscosity T.
______________________________________Production Example 4______________________________________Phenyltrimethoxysilane 198    partsDeionized water        54     parts98% Sulfuric acid      0.002  part______________________________________
The above materials were mixed up and subjected to reaction at 60 C. for 5 hours, the byproduct methanol was then distilled off under reduced pressure, and xylene was added to the remaining mixture to give a polyorganosiloxane solution (b-1) with a solids content of 50% and a Gardner viscosity of AB. The polyorganosiloxane obtained had a number average molecular weight of about 5,000 and had, on an average, 6 silanol groups per molecule.
______________________________________Production Example 5______________________________________Methyltrimethoxysilane  136 partsDiphenyldimethoxysilane 182 partsDeionized water          90 parts60% Phosphoric acid      1 part______________________________________
The above materials were mixed up and subjected to reaction at 60 C. for 10 hours, the byproduct methanol was distilled off under reduced pressure, and butyl acetate was added to the remaining mixture to give a polyorganosiloxane solution (b-2) with a solids content of 50% and a Gardner viscosity of D. The polyorganosiloxane obtained had a number average molecular weight of about 15,000 and had, on an average, 10 silanol groups per molecule.
______________________________________Production Example 6______________________________________Diphenyldimethoxysilane 182 parts&#946;-(3,4-Epoxycyclohexyl)-                   186 partsethyltrimethoxysilaneDeionized water         108 parts60% Phosphoric acid      1 part______________________________________
The above materials were mixed up and subjected to reaction at 60 C. for 15 hours, the byproduct methanol was then distilled off under reduced pressure, and butyl acetate was added to the remaining mixture to give a polyorganosiloxane solution (b-3) with a solids content of 50% and a Gardner viscosity of G. The polyorganosiloxane obtained had a number average molecular weight of about 2,000 and had, on an average, 10 silanolgroups and 7 epoxy groups per molecule.
______________________________________Production Example 7______________________________________Phenyltrimethoxysilane   198    parts&#947;-Glycidoxypropyltrimethoxysilane                    236    partsDeionized water          108    parts60% Sulfuric acid        0.1    part______________________________________
The above materials were mixed up and subjected to reaction at 60 C. for 10 hours, the byproduct methanol was distilled off under reduced pressure, and xylene was added to the remaining mixture to give a polyorganosiloxane solution (b-4) with a solids content of 50% and a Gardner viscosity of DE. The polyorganosiloxane obtained had a number average molecular weight of about 8,000 and had, on an average, 6 silanol groups and 20 epoxy groups per molecule.
PIGMENTED BASE COAT COMPOSITION Base coat composition 1 A mixture of 100 parts of the resin solution (a-1) obtained in Production Example 1 (60 parts as solids), 33.3 parts of U-Van 20SE (Note 1) (20 parts as solids), 40 parts of the polyorganosiloxane solution (b-1) obtained in Production Example 4 (20 parts as solids), 20 parts of an aluminum paste and 1 part of Reibo #3 (Note 2) was stirred and then a mixed solvent composed of Swazol #1000 (Note 3 ) and ethyl acetate (20/80 by weight ) was added to adjust the viscosity of the coating composition to 15 seconds (Ford cup #4/20 prepared was subjected to testing.
Base coat composition 2 Base coat composition 2 was prepared according to the same formulation as mentioned above for base coat composition 1 except that the polyorganosiloxane solution (b-2) was used in lieu of the polyorganosiloxane solution (b-1).
Base coat composition 3 Base coat composition 3 was prepared according to the same formulation as mentioned above for base coat composition 1 except that the polyorganosiloxane solution (b-3) was used in lieu of the polyorganosiloxane solution (b-1).
Base coat composition 4 Base coat composition 4 was prepared according to the same formulation as mentioned above for base coat composition 1 except that the polyorganosiloxane solution (b-4) was used in lieu of the polyorganosiloxane solution (b-1).
Base coat composition 5 A mixture of 112 parts of the resin solution (a-2) obtained in Production Example 2 (56 parts as solids), 40 parts of U-Van 20SE (24 parts as solids), 40 parts of the polyorganosiloxane solution (b-1) obtained in Production Example 4 (20 parts as solids), 20 parts of an aluminum paste and 1 part of Reibo #3 was stirred and then a 30:70 (by weight) mixture ofSwazol #1000 and ethyl acetate was added to adjust the viscosity of the coating composition to 15 seconds (Ford cup #4/20 resultant composition was subjected to testing.
Base coat composition 6 Base coat composition 6 was prepared according to the same formulation as mentioned above for base coat composition 5 except that the resin solution(a-3) was used in lieu of the resin solution (a-2).
Base coat composition 7 Base coat composition 7 was prepared according to the same formulation as mentioned above for base coat composition 5 except that the polyorganosiloxane solution (b-2) was used in lieu of the polyorganosiloxane solution (b-1).
Base coat composition 8 Base coat composition 8 was prepared according to the same formulation as mentioned above for base coat composition 5 except that the polyorganosiloxane solution (b-3) was used in lieu of the polyorganosiloxane solution (b-1).
Base coat composition 9 Base coat composition 9 was prepared according to the same formulation as mentioned above for base coat composition 5 except that the resin solution(a-3) was used in lieu of the resin solution (a-2) and that the polyorganosiloxane solution (b-3) was used in lieu of the polyorganosiloxane solution (b-1).
Base coat composition 10 Base coat composition 10 was prepared according to the same formulation as mentioned above for base coat composition 5 except that the polyorganosiloxane solution (b-4) was used in lieu of the polyorganosiloxane solution (b-1).
Base coat composition 11 Base coat composition 11 was prepared according to the same formulation as mentioned above for base coat composition 1 except that the polyorganosiloxane solution (b- 1) was not used.
Base coat composition 12 Base coat composition 12 was prepared according to the same formulation as mentioned above for base coat composition 5 except that the polyorganosiloxane solution (b-1) was not used.
______________________________________Production Example 8______________________________________Styrene                   100 partsn-Butyl acrylate          450 parts2-Ethylhexyl methacrylate 200 parts2-Hydroxyethyl methacrylate                     150 parts&#947;-Methacryloxypropyltrimethoxysilane                     100 partsAzobisisobutyronitirle     40 parts______________________________________
A mixture composed of the above-materials was added dropwise to the same quantity (as said mixture) of xylene at 110 maturation was effected at the same temperature for 2 hours to give a polymer solution. The clear polymer obtained had a number average molecular weight of 6,000.
______________________________________Production Example 9______________________________________Styrene                   150 partsn-Butyl methacrylate      500 parts1,4-Butanediol monoacrylate                     200 parts&#947;-Methacryloxypropyltrimethoxysilane                     150 partsAzobisisobutyronitrile     40 parts______________________________________
A mixture composed of the above materials was added dropwise to a mixed solvent composed of 500 parts of xylene and 500 parts of n-butanol at 120temperature, to give a polymer solution. The clear polymer obtained had a number average molecular weight of 6,000.
CLEAR TOP COAT COMPOSITION ______________________________________Clear top coat composition 1______________________________________Solution of Production Example 8                    140    parts(solids content 50%)Cymel 303 (note 4)       30     partsNacure 5225 (note 5)     1.5    partsSurface modifier (BYK Chemie's                    0.1    partBYK-300 solution; hereinafterthe same shall apply)Ultraviolet absorber     1.0    part(Ciba-Geigy's Tinuvin 900;hereinafter the same shall apply)______________________________________
A mixture composed of the above materials was diluted with Swazol #1000 to thereby adjust the viscosity (Ford cup #4, 20
(Note 4) Cymel 303: fully methoxylated melamine resin, available from Mitsui Cyanamid Ltd.
(Note 5) Nacure 5225: dimethyloxazolidineneutralized dodecylbenzenesulfonicacid, available from King Industries.
______________________________________Clear top coat composition 2______________________________________Solution of Production Example 9                    160    parts(solids content 50%)Cymel 303                20     partsNacure 5225              2      partsSurface modifier         0.1    partUltraviolet absorber     1.0    part______________________________________
The procedure for clear top coat composition 1 was followed using the abovematerials.
______________________________________Clear top coat composition 3______________________________________Solution of Production Example 9                    140    parts(solids content 50%)60% U-Van 20SE           50     partsDibutyltin dilaurate     0.5    partSurface modifier         0.1    partUltraviolet absorber     1.0    part______________________________________
EXAMPLES 1 TO 30 AND COMPARATIVE EXAMPLES 1 TO 6 Preparation of coated sheets An epoxy resin-based cationic electrodeposition coating film (25 μm) wasformed on dull steel sheets (after chemical conversion treatment) and, after curing thereof by heating at 170 Bake AM (trademark of Kansai Paint, an automotive coating composition of the polyester rein/melamine resin type) was applied to a film thickness of30 μm (after drying) for intercoating, which was followed by 30 minutes of baking at 140to wet sanding using a #400 sand paper and, after draining and drying, wiped using petroleum benzine, and used as a substrate.
Using the air spray coating technique, the pigmented base coat composition was applied and, three minutes thereafter, the clear top coat composition was immediately applied. The film thicknesses were 15 to 20 μm and 35 to 45 μm, respectively, after drying. Then, after 10 minutes of standing at room temperature, baking was carried out at 14030 minutes. In recoatability testing, the baking was carried out at 160 120appearance of each coating film thus obtained are shown in Table 1.
TABLE 1__________________________________________________________________________           Example           1  2  3   4  5  6  7  8  9  10 11 12 13 14 15__________________________________________________________________________Pigmented base coat composition           1  1  1   2  2  2  3  3  3  4  4  4  5  5  5Clear top coat composition           1  2  3   1  2  3  1  2  3  1  2  3  1  2  3Appearance (*1) A  A  A   A  A  A  A  A  A  A  A  A  A  A  AImage clarity (*2)           81 81 79  81 81 79 86 86 85 86 86 85 78 78 76Metallic tone (*3)           A  A  A   A  A  A  A  A  A  A  A  A  A  A  AWater resistance (*4)           A  A  A   A  A  A  A  A  A  A  A  A  A  A  ARecoatability (*5)           A  A  A   A  A  A  A  A  A  A  A  A  A  A  ASolvent resistance (*6)Coating film condition           B  B  B            A  A  A           B  B  BCoating film hardness           B/H              B/H                 2B/H         F/H                                 F/H                                    B/H         B/H                                                   B/H                                                      2B/H__________________________________________________________________________           Example           16 17 18 19 20 21 22  23 24 25 26  27 28 29 30__________________________________________________________________________Pigmented base coat composition           6  6  6  7  7  7  8   8  8  9  9   9  10 10 10Clear top coat composition           1  2  3  1  2  3  1   2  3  1  2   3  1  2  3Appearance (*1) A  A  A  A  A  A  A   A  A  A  A   A  A  A  AImage clarity (*2)           78 78 77 78 78 76 84  84 83 84 84  83 84 84 83Metallic tone (*3)           A  A  A  A  A  A  A   A  A  A  A   A  A  A  AWater resistance (*4)           A  A  A  A  A  A  A   A  A  A  A   A  A  A  ARecoatability (*5)           A  A  A  A  A  A  A   A  A  A  A   A  A  A  ASolvent resistance (*6)Coating film condition            A   A  ACoating film hardness             F/H F/H                                    B/H__________________________________________________________________________                                  Comparative Example                                  1   2   3   4   5   6__________________________________________________________________________                  Pigmented base coat composition                                  11  11  11  12  12  12                  Clear top coat composition                                  1   2   3   1   2   3                  Appearance (*1) C   C   C   C   C   C                  Image clarity (*2)                                  38  38  38  37  37  37                  Metallic tone (*3)                                  B   B   B   B   B   B                  Water resistance (*4)                                  B   B   B   B   B   B                  Recoatability (*5)                                  C   C   C   C   C   C                  Solvent resistance (*6)                  Coating film condition                                  E   E   E   E   E   E                  Coating film hardness                                  5B/H                                      6B/H                                          6B/H                                              5B/H                                                  5B/H                                                      5B/H__________________________________________________________________________Test methods(*1) Appearance: Coating films were examined for ebullition and shrinkage. A: no abnormalities; B: some abnormalities observable; C: many abnormalities observable.(*2) Image clarity: An image clarity meter (ICM; Suga Shikenki Co.) was used. The numerical values in Table 1 are ICM values which can range from 0 to 100%. A higher value indicates a higher degree of image clarity and ICM values of not less than 74 are indices of very good image clarity.(*3) Metallic tone: Coating films were looked at frontways and evaluated for metallic glitters and white reflection by the eye. A: glitters and white reflection; B: no glitters and poor white reflection; C: no glitterand no white reflection.(*4) Water resistance: Coated sheet specimens were immersed in warm water maintained at 40 by the eye. A: no abnormalities; B: some abnormalities; C: many abnormalities.(*5) Recoatability: The same base coat composition and clear coat composition as used in each example or comparative example were reapplied to the coated surface and baked at 120 coating film obtained was cut crosswise with a cutting knife, an adhesive cellophane tape was applied to the coated surface and peeled off abruptlyand the adhesion between the first coating film and second coating film (clear coating film/base coating film) was evaluated. A: no pe eling; B: slight extent of peeling; C: remarkable extent of peeling.(*6) Solvent resistance: Specimens were immersed in Nisseki Silver gasolin(trademark of Nippon Oil Co.) for 1 day and then examined for the state anhardness of coating films. State of coating film: A: no abnormalities; B: very slight extent of shrinkage; C: some extent of shrinkage; D: shrinkage; E: marked extent of shrinkage. Coating film hardness: Pencil hardness after immersion/pencil hardness before immersion.
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