Patent GB-540765-A (GB)
Title: Improvements relating to the coating of surfaces with cellulose esters
IPC: C09D101/10
Filed: 1940-04-19
Abstract: 540,765. Cellulose ester coating compositions; coated fabrics ; compound sheets. KODAK, Ltd. (Eastman Kodak Co.). April 19, 1940, No. 7084. [Class 2 (ii)] [Also in Group VIII] Surfaces are coated by applying thereto a molten composition containing a cellulose ester of one or more organic carboxylic acids containing from 4 to 8 carbon atoms and a quantity of plasticizer which is up to 50 per cent of the weight of the cellulose ester, the cellulose ester being one having a melting point of not more than 210‹C. a charring point of at least 260‹C. and a fundamental cuprammonium viscosity of less than 10 centipoises. The layer of molten composition is set by cooling. The fundamental cuprammonium viscosity is the viscosity at 25‹C. of a cuprammonium solution of the cellulose ester in which the concentration of cellulose is 2.5 per cent, the quantity of cellulose ester required to form such a solution being calculated from the acyl content of the ester. Preferably the charring point is at least 70‹C. above the melting point. The cellulose ester may have a viscosity of 2-50 centipoises when measured as to the viscosity of a 10 per cent solution in acetone at 25‹C. The cellulose ester may contain a proportion of ester groups of one or more other organic acids in addition to those specified above. The total acyl content is preferably at least 45 per cent of the ester. The composition may be applied to paper, fabric, metal foil, leather, wire, and other flexible materials, and to rigid objects of metal, wood, glass, and other material. The molten composition may be applied from a hopper through a slit and spread by means of a blade or air-brush. The coated material if flexible may be wound up in a roll shortly after application of the coating. The composition may be applied by a heated roller dipping into the molten composition or supplied with a thin film of the composition by use of a doctor-blade. The composition may be applied by spraying. The coated material may be passed through heated smoothing rollers or in contact with a blade or air-brush, or it may be passed under a heated embossing roller. The cellulose ester may be a butyrate or acetobutyrate containing at least 20 per cent of butyryl. The melting points of various stable cellulose butyrates and aceto-butyrates are shown in the accompanying graph. The preferred esters are those which are completely esterified or nearly so and which contain less than 21 per cent of acetyl. The esters falling within the area ABC are specially preferred. A small part of the butyryl groups and any or all of the acetate groups may be replaced by propionyl groups. To ensure that the cellulose esters used have a high charring point they should be substantially free from sulphur. Cellulose butyrate may be prepared with sulphuric acid as catalyst and the re-action mixture may be treated with sufficient water to convert the residual anhydride to acid, the addition being made at such a rate that the resulting temperature is between 38‹C. and 49‹C. The sulphuric acid is neutralized and the ester is precipitated, washed, and boiled in pure water to obtain a stable product. If desired, the ester may be stabilized bv boiling it in water having a pH value of from 7.2 to 8.5. The composition may contain pigments, dyestuffs, waxes, resins, or anti-oxidants. The plasticizer may be an ester such as dibutyl phthalate, dibutyl sebacate, methyl or methoxy-ethyl stearate, cetyl acetate, cetyl lactate, tricresyl phosphate, or sucrose octa-acetate. Coated materials suitable for wrapping materials or artificial leather may be obtained. Coated sheets of glass may be united by an intermediate cellulose ester layer in the production of safety glass. In an example, a molten mixture of a stable cellulose tributyrate and triphenyl phosphate is applied to a sheet of paper by means of a roller. While the coating is still soft, the coated paper is pressed with a heated embossing roller. A flexible artificial leather is produced.