GB594075A - Coated flexible sheet material - Google Patents

Abstract

Flexible sheet material is coated with a film of N-alkoxymethyl polyamide prepared according to the process of Specification 573,482 from a synthetic linear polyamide having a relative viscosity above 40, said alkoxymethyl polyamide having at least 28 per cent of the amide nitrogen atoms substituted by methylol or alkoxymethyl groups and less than 4 per cent of them by methylol groups. The proportions of methylol and alkoxymethyl groups may be adjusted by hydrolysis or methylation of the N-alkoxymethyl polyamide as first formed. The modified polyamides form adequately stable solutions in ethanol containing a little water. N-alkoxymethylpolyamide may be made by dissolving the high viscosity polyamide in formic acid and treating at at 25 DEG -150 DEG C. with alcohol and formaldehyde. The reaction mixture is then dissolved in acetone-water (1 : 1) and isolated by addition of ammonia or caustic soda. Increase in the amount of formaldehyde present and decrease in the amount of water increases the degree of methylol substitution which is also decreased by greater ether formation if methanol is added near the end of the reaction; or if the product is subsequently reacted with methanol in presence of acid. Removal of methylol groups by hydrolysis can be effected by treatment with caustic soda or with sodium sulphite either in aqueous alcoholic solution or by mechanically working the N-methoxymethyl polyamide with sodium sulphite. The polyamides of high viscosity used as starting materials are obtained by forming them in the absence of a stabiliser and with a final short heating period under vacuum. Coatings according to the invention have particularly high flex durability. The coatings may be applied from solutions which also contain plasticisers, dyes, pigments, e.g. carbon black or mica and fillers or by calendering or milling (see Group VIII). Vegetable or fatty oil or wax alcohol may be added to the composition to assist stripping from the calendar rolls. Water may also be added. The coated products may be baked at 90-125 DEG C. and may be hot calendered or embossed. These treatments may last for a few seconds or for days and improve the properties of the coatings especially if the coating includes a small amount of oxygen-containing acid catalyst, e.g. phosphoric acid. Top coats may be applied of other materials or of N-alkoxymethyl polyamide containing finely divided silica to improve surface dryness or a dulling agent to reduce gloss. The surface of the coated products may also be modified by superficial hydrolysis, e.g. by warming in contact with dilute mineral acid. A list of alcohols suitable for the production of the N-alkoxymethyl polyamide is given in the Specification. Plasticisers may be included in the compositions, e.g. the ester type, aromatic sulphonamides, diphenyloloctadecane, octyl phenol, methyl 10-phenylolstearate, or salicylamides. Suitable solvents are phenols, organic acids, inorganic acids, or alcohols, alone or blended with other materials, e.g. water or halogenated hydrocarbons such as chloroform or trichlorethylene. Aqueous or alcoholic solutions of salts such as alkali earth halides or alkali thiocyanates can also be used. The products are useful as upper material for footwear, handbags, upholstery, garments, containers for food or oil, &c. A number of specific examples are given. Specifications 461,236, 461,237 and 576,363 also are referred to.