GB1124690A - Coating composition - Google Patents

Abstract

A liquid coating composition comprises (A) at least one of (1) polymethyl methacrylate, (2) polyethyl methacrylate, (3) polypropyl methacrylate, (4) polyisopropyl methacrylate, (5) a copolymer of methyl methacrylate with a C1 to C20-alkyl acrylate, a C2 to C18-alkyl methacrylate or styrene, (6) a copolymer consisting predominantly of the monomer units of the polymer defined in any of (1) to (5) above and containing up to 5% by weight of one or more other monomer units, or (7) any mixture of polymers (1) to (6); (B) at least one of (1) a copolymer of methyl methacrylate with a C1 to C10-alkyl acrylate or a C4 to C18-alkyl methacrylate, said copolymer optionally containing up to 5% of one or more other monomer units, or (2) any mixture of said polymers, dissolved in (C) a liquid carrier, each of (A) and (B) being present in a concentration of at least 5% of the total weight of (A) and (B) and the difference between the glass transition temperatures of (A) and (B) being at least 30 DEG C. In preferred embodiments, (i) (A) is polymethyl methacrylate and (B) is a copolymer of methyl methacrylate with methyl, ethyl butyl or 2-ethylhexyl acrylate or with octyl or lauryl methacrylate and (ii) (A) and (B) are both copolymers of methyl methacrylate with butyl methacrylate or one of the said acrylates or methacrylates, the copolymers containing the same monomers in different proportions. The other monomers which may be present in polymers (A) and (B) include acrylic and methacrylic acid, acrylonitrile, glycidyl methacrylate and 2-dimethyl-aminoethyl methacrylate. The compositions exemplified contain in Examples 1 and 2 polymethyl methacrylate, a methyl methacrylate/n-butyl acrylate copolymer, an alkyd resin derived from coconut oil, ethylene glycol and phthalic anhydride, cellulose acetate butyrate, carbon black and aluminium flake, the composition of Example 1 also containing 2-hydroxy - 4 - dodecyloxy benzophenone, a silicone and green pigments and that of Example 2 also containing blue pigments; in Example 3, the composition contains polymethyl methacrylate, a methyl methacrylate/ethyl acrylate copolymer, butyl benzyl phthalate, a methyl methacrylate/ethyl acrylate/methacrylic acid copolymer and TiO2; in Example 4 the composition contains 2 different methyl methacrylate/n-butyl acrylate copolymers, polymethyl methacrylate, the said alkyd resin, green pigments, carbon black and aluminium flake and in Example 5 the composition contains polymethyl methacrylate, a methyl methacrylate/2-ethylhexyl acrylate copolymer, and bis-(benzyl)-triethylene glycol phthalate. The solvents in the lacquers comprise at least 3 of the following: 2-ethoxyethyl acetate, toluene, xylene, acetone, methyl ethyl ketone and isopropanol.ALSO:Metal panels, in particular auto body panels, are coated by spraying, dipping or brushing with a lacquer comprising a solution in organic solvents of two acrylic polymers, the difference between the glass transition temperatures of the polymers being at least 30 DEG C. The polymers used in Examples 1 and 2 are polymethyl methacrylate and a methyl methacrylate/n-butyl acrylate copolymer, in Example 3 they are polymethyl methacrylate and a methyl methacrylate/ethyl acrylate copolymer, in Example 4 they are 2 different methyl methacrylate/n-butyl acrylate copolymers and in Example 5 they are polymethyl methacrylate and a methyl methacrylate/2-ethylhexyl acrylate copolymer. Other components of the lacquers are selected from alkyd resins, silicones, cellulose acetate butyrate, organic pigments, carbon black, aluminium flake and plasticisers.