Patent GB-1091647-A (GB)
Title: Coating compositions
IPC: C08G18/10
Filed: 1966-05-11
Abstract: A coating composition which is a solution or suspension in an organic liquid comprises (a) from 10 to 90 parts by weight of a polyurethane which has a molecular weight of 1000 to 5000 and consists of a polyester or polyether backbone capped with organic diisocyanate units; (b) from 90 to 10 parts by weight of a cellulose ester so that (a) + (b) equals 100 parts by weight; (c) an isocyanate blocking agent in a molar concentration at least equal to that of the unreacted isocyanate units; and (d) an isocyanate curing agent in a molar concentration of at least 10% of the molar concentration of unreacted isocyanate units, the composition having a viscosity of 100 to 5000 c.p.s. and a total solids content of 5 to 65% by weight.  On application to a substrate, the compositions spontaneously form an interior cellular structure without the use of foaming agents in the compositions themselves.  Upon curing the films develop a thin skin over the cellular structures. The polyurethane (a) suitably has a polyester backbone prepared from adipic acid, propylene glycol and ethylene glycol units, which backbone is preferably capped with toluene diisocyanate units.  Cellulose acetate butyrate having a hydroxyl content of 1% to 3% and a butyryl content of 38% to 50% is the preferred cellulose ester but cellulose acetate and cellulose acetate propionate may also be used.  The isocyanate blocking agent may be a ketoxime, phenol, lactam, imide, aryl mercaptan, diethyl malonate or acetyl acetone. Suitable isocyanate curing agents are polyols or polyamines.  The coating composition may also contain a polyurethane plasticizer such as sucrose diacetate hexaisobutyrate, butyl benzyl phthalate or tricresyl phosphate or pigments such as aluminium flake, titanium dioxide, carbon black, toluidine red and other organic pigments.  The organic liquid in which the composition is dissolved or dispersed may be any organic liquid which will not interfere with cell formation within the film when the composition is applied to a substrate.  Such organic liquids are petroleum ether, methyl ethyl ketone, dioxane, tetrahydrofuran, acetone and toluene, especially acetone and acetone/ toluene mixtures.ALSO:Bonderised and solvent-treated steel may be coated with a composition which forms a spontaneous interior cellular structure upon coating without the use of a foaming agent, the composition comprising a solution or suspension in an organic liquid of (a) from 10 to 90 parts by weight of a polyurethane having a M.W. of 1000 to 5000 and consisting of a polyester or polyether backbone capped with organic diisocyanate units, (b) from 90 to 10 parts of a cellulose ester so that (a) + (b) equals 100 parts by weight, (c) an isocyanate blocking agent in a molar concentration at least equal to that of the unreacted isocyanate units and (d) an isocyanate curing agent in a molar concentration of at least 10% of the molar concentration of unreacted isocyanate units, the composition having a viscosity of 100 to 5000 cps and a total solids content of 5 to 65% by weight.  Upon curing the films develop a thin skin over the cellular structure.  Examples describe the spraying onto bonderised steel of compositions comprising (1) a toluene diisocyanate capped polyester, cellulose acetate butyrate, methyl ethyl ketoxime as blocking agent and a polyol as curing agent in a toluene/acetone organic solvent and (2) a composition as in (1) above and containing in addition butylbenzyl phthalate, sucrose diacetate hexa-isobutyrate, titanium dioxide, peptised carbon black, the monoethyl ether of ethylene glycol acetate and ethyl alcohol.  The bonderised steel panel having the composition coated thereon is then cured to provide a coating which comprises a cellular interior overlaid with a thin, smooth exterior surface.