Patent GB-831042-A (GB)
Title: Improvements in or relating to coating compositions
IPC: C09D133/12
Filed: 1958-01-31
Abstract: Steel vehicle body panels treated with "Bonderite" (Registered Trade Mark) are prime coated with a conventional primer containing about 52% by wt. of soya oil modified glycerol phthalate resin as the film-former and baked for 15 minutes at 400 DEG  F. to give a dry coating about 0.5 mil. thick.  A sealer coat of the type described in Specification 807,913 and containing as the film-forming material in lacquer solvents 34% by wt. of lacquer-grade nitrocellulose, 49% by wt. of shellac, and 17% by wt. of polyvinyl butyraldehyde resin, and 28.5% pigment (based on total organic filmforming material) is applied over the prime coat.  A methyl methacrylate lacquer thinned to about 18% by wt. solids with a "Cellosolve" (Registered Trade Mark) acetate, acetone, isopropyl alcohol, xylene and butyl alcohol mixture in a 3:6:4:6:1 weight ratio and sprayed on to the previously prepared panels.  Finally, the coated panels are baked at 93 DEG  C. for about 30 minutes giving a methyl methacrylate lacquer top coat of about 2 mils. thick.  The methacrylate lacquer used had the composition (in parts by weight): homopolymer of methyl methacrylate of "relative viscosity" 1.15-60.5 parts, benzyl butyl phthalate plasticizer 11.0, lacquer-grade nitrocellulose 7.5, polyester 21.0, pigment 5.0, toluene-acetone solvent ( 70/30 weight ratio) 201.0 in conformity with the following specified ranges of composition: 40-75 parts by weight of a polymer of methyl methacrylate having a "relative viscosity" of 1.117-1.196, 0-25 parts of plasticizer for the polymer, 5-20 parts of lacquer grade nitrocellulose, 20-50 parts of a polyester obtainable by reacting with heating 1 molar proportion of at least one aliphatic dicarboxylic acid having 4-10 carbon atoms or an acid chloride or anhydride thereof with at least 1.5 molar proportions of at least one bisphenol or bisphenol acetate, the whole being dissolved in a solvent (see Group IV (a)).  The polyester used in the example given is prepared by reacting adipyl chloride with bis-(4-hydroxyphenyl)-2,2-propane.  The evaluation of the methyl methacrylate top coat on the panel for absence of crazing when a lacquer is sprayed on the top coat is described.  Specifications 763,158, 807,895 and 831,041 are referred to.ALSO:A coating composition comprises solvent, 40-75, preferably 50-70, parts by weight of a polymer of methyl methacrylate having a relative viscosity of 1.117-1.196, 0-25, preferably 10-20, parts of plasticizer for the polymer, 5-20, preferably 5-10, parts of lacquer grade nitro-cellulose and 20-50, preferably 20-30, parts of a polyester obtainable by reacting under the influence of heat 1 molar proportion of at least one aliphatic dicarboxylic acid having 4-10 carbon atoms or an acid chloride or anhydride thereof with at least 1.5, and preferably 1.5 to 2.0, molar proportions of at least one bisphenol or bisphenol acetate. The methyl methacrylate polymers may be either homopolymers or copolymers of methyl methacrylate with minor proportions, e.g. 2-25% by weight of another copolymerizable material, e.g. acrylic acid, methacrylic acid, the methyl to butyl esters of acrylic acid, the ethyl to butyl esters of methacrylic acid, vinyl acetate, acrylonitrile or styrene.  A preferred copolymer contains about 98% by weight methyl methacrylate and 2% by weight of methacrylic acid.  Copolymers of 80-98% by weight methyl methacrylate and 20-2% by weight glycidyl methacrylate can also be used.  The relative viscosity of the methyl methacrylate polymer is defined as the efflux time of a solution of 0.25 gram of the polymer in 50 ml. of ethylene dichloride divided by the efflux time of the solvent, both efflux times being determined at 25 DEG  C. in a modified Ostwald viscometer, Series 50 according to the prodecure of A.S.T.M.-D-445-46T, method B.  The plasticizer for the polymer may be benzyl butyl phthalate, dibutyl phthalate, triphenyl phosphate, 2-ethyl hexyl benzyl phthalate, and dicyclohexyl phthalate.  The nitrocellulose may be a grade in the 1/4 -5 second viscosity range. The acid, acid chloride and anhydride used to prepare the polyester may be succinic acid, adipic acid, suberic acid, sebacic acid, a ,b -dimethylsuccinic acid, maleic acid, glutaconic acid, adipyl-, suberyl-, sebacyl-, or a ,b -dimethyl succinyl chloride, or maleic anhydride.  The preferred class of bisphenols which are reacted with the acidic component have the general formula <FORM:0831042/IV (a)/1> wherein R1 is a hydrogen atom or an alkyl radical containing 1 to 4 carbon atoms, R2 is a hydrogen atom, or an alkyl radical containing 1 to 4 carbon atoms or a cyclohexyl radical and R3 and R4 is a hydroxyphenyl radical or a monoalkylated hydroxyphenyl radical, the alkyl group of which contains 1 to 3 carbon atoms.  The preferred bisphenol is bis-(4-hydroxyphenyl) - 2,2 - propane.  Monoacetates or diacetates of the bisphenols may be used.  In an example, a methyl methacrylate lacquer is prepared by mixing 450 parts of a mill base (prepared by grinding 100 parts of carbon black with 15 parts of 1/2 second lacquer-grade nitrocellulose and 200 parts of benzyl butyl phthalate and then diluted to 20% solids content with ethyl acetate) with 637 parts of a polyester solution (prepared by reacting 366 parts by weight of adipyl chloride with 912 parts of bis - (4-hydroxy - phenyl) - 2,2 - propane partially dissolved in 600 parts of toluene at 70 DEG  C.), 3030 parts of a 40% solution of a methyl methacrylate homopolymer (relative viscosity 1.15) in toluene-acetone mixture ( 70/30 weight ratio) and 20 parts of benzyl butyl phthalate.  Coatings of the composition of the invention on substrates such as steel sheets do not, like conventional methyl methacrylate lacquer baked coatings, craze when a further coating containing solvents is applied over them. The polyesters are preferably prepared by heating one of the bisphenols, preferably with a small proportion of a solvent, such as xylene, toluene, benzene, hexane or decane, then slowly adding one of the aforementioned acid chlorides, and maintaining the mixture at 50-120 DEG  C., preferably 80-100 DEG  C. until all the HCl byproduct is driven off, usually in 1-5 hours.  An amine such as pyridine may be added to the reaction mixture to combine with the hydrochloric acid, and the resulting hydrochloride then washed out of the reaction mixture with water.  Another preferred method of making the polyester is to add the aliphatic dicarboxylic acid to the monoacetate of the bisphenol (prepared by heating the bisphenol with acetic anhydride in 1:1 mol. ratio at 100-200 DEG  C., preferably 140-160 DEG  C., until acetic acid is no longer evolved) and the resulting mixture maintained at 150-220 DEG  C. until acetic acid is no longer evolved. The polyester may also be prepared by heating a mixture of the dicarboxylic acid and the bisphenol to 250 DEG  C. in the presence of an esterification catalyst such as litharge, lime or toluene sulphonic acid.  Specifications 763,158, 807,895, 807,913 and 831,041 are referred to.