GB734414A - Improvements in or relating to preparation and use of finely-divided cellulose esters, ethers and mixed ether-esters - Google Patents

Abstract

A film-forming cellulose ether, ester or ester-ether, alone or with a plasticizer, is powdered by forming a lacquer-in-water emulsion containing, in addition to water, the cellulose derivative and a water-immiscible volatile solvent for the cellulose derivative or mixture of derivative and plasticizer, or a major proportion of such solvent with a minor proportion of a water-miscible solvent, and spraying the emulsion thus formed into a heated gaseous medium to vaporize liquid from the emulsion and to provide a powder containing solid and hollow spheroids of the cellulose derivative or derivative-plasticizer mixture. The bulk density of this powder may be 0.3-0.45 g./ml. and its mean particle diameter may be below 15 microns. The gaseous medium may be air or a flue gas, e.g. obtained by burning a manufactured domestic gas, and its inlet and outlet temperature ranges at the drier may be 300-500 DEG and 175-225 DEG F. respectively. When ethyl cellulose or cellulose acetate is used it is preferable to use a solvent containing 80-95 parts by weight of methylene chloride and 20-5 parts of a lower aliphatic alcohol such as methanol, ethanol, propanol or butanol. The cellulose derivative may be the acetate, propionate, butyrate, benzoate, stearate, crotonate, acetate propionate, acetate butyrate, acetate benzoate, acetate phthalate, or acetate crotonate; ethyl cellulose, ethyl hydroxyethyl cellulose or benzyl cellulose; hydroxyethyl cellulose acetate, ethyl cellulose acetate, ethyl cellulose crotonate or benzyl cellulose acetate. In an example a solution of 20 lb. of ethyl cellulose (ethoxy content 47.5-49 per cent) in 72 lb. of methylene chloride and 8 lb. of ethanol, 50 lb. of water and 0.25 lb. of sodium dioctyl sulphosuccinate are emulsified by one pass through a colloid mill, and spray-dried in air at a blow-case pressure of 25 p.s.i., an atomizer pressure of 60 p.s.i., an air inlet temperature of 380-400 DEG F. and an air outlet temperature of 175-190 DEG F. In other examples ethyl cellulose plasticized with dibutyl phthalate and octyl phenol, cellulose acetate plasticized with methyl phthalyl ethyl glycolate and cellulose acetate alone respectively are powdered by similar methods. In an example of the use of ethyl cellulose (powdered according to the invention) for coating paper, 75 parts by weight of the ethyl cellulose are mixed first with 100 parts of water and then with 25 parts of octyldecylphthalate and 2.25 parts of octylphenol, and the mixture is ground overnight in a pebble mill. Films of the mixture are cast on clay-coated paper stock, water is allowed to be absorbed into the paper (10-20 seconds), and the coating is fused for 30 seconds in a forced-draught oven at 200 DEG C. to give a continuous glossy coating. In another example the coating dispersion is prepared by adding with stirring to 60 parts of spray-dried cellulose acetate first a mixture of 15 parts of diacetone alcohol and 85 parts of a petroleum naphtha, and then 40 parts of methyl phthalyl ethyl glycolate, and grinding the mixture in a ball mill overnight. The dispersion is applied on a polished stainless steel panel and fused for 1.5-5 minutes at 235 DEG C. Plastisols may be formed with the cellulose derivative powders by mixing the powder with a plasticizer which dissolves the derivative at elevated but not at ordinary temperatures, e.g. chlorinated diphenyl may be dissolved in mineral oil, and the solution mixed with ethyl cellulose powder to form a thick paste, which is fused for 30 seconds at 180 DEG C. on a metal plate to form a tough plastic film. The plastisol dispersion preferably contains 10-50 per cent of plasticizers.