| 摘要 |
<p>1428003 Acrylic powder coating compositions E I DU PONT DE NEMOURS & CO 31 Oct 1973 [1 Nov 1972] 50577/73 Heading C3P Thermoplastic acrylic polymer powder coating compositions comprise finely divided particles having a particle size of 1-75 microns, which particles are composed of an intimately mixed blend of film-forming constituents comprising (A) 50-74À5% by weight of polymethyl methacrylate and/or a copolymer of methyl methacrylate containing 2-10% by weight of units of a C 2 -C 12 -alkyl methacrylate, the polymer or copolymer having a number average molecular weight of 65,000 to 100,000; (B) 10-20% by weight of a copolymer of (1) 50- 85% by weight of methyl methacrylate, (2) 9À5-40% by weight of a C 2 -C 12 -alkyl methacrylate or a C 1 -C 12 -alkyl acrylate, (3) 0À5-15% by weight of a C 2 -C 4 -hydroxy alkyl acrylate or methacrylate and (4) 0À1-5% by weight of anα,#-ethylenically unsaturated carboxylic acid, the copolymer having a number average molecular weight of 20,000 to 40,000; (c) 15-30% by weight of an organic plasticizer having a free hydroxyl content of up to 2À0% by weight; and (D) 0À5-3À0% by weight of a cross-linking agent which is an alkylated melamine resin or a blocked polyisocyanate, the combined film-forming constituents having a melt viscosity below 75,000 poise at 160‹ C. and the powder particles having a Tg (i.e. the temperature at which the viscosity is 10<SP>13</SP> poise) of 30-60‹ C. The powder particles may also contain 0À2-50% by weight of a pigment, and other components such as silicone resins (to enhance flow and reduce cratering). The acid component of copolymer (B) may be, for example, acrylic, methacrylic, ethacrylic or itaconic acid. Suitable plasticizer components include phthalates, adipates and polyesters. The powder particles can be used for coating metal, glass, plastics or fibre-reinforced plastics substrates by such techniques as electrostatic spraying, fluidized beds or electrostatic fluidized beds.</p> |
