Improvements relating to the production of reconstituted leather

Abstract

Abstract Scrap vegetable or mineral tanned leather from skivings and waste is reconstituted by grinding and binding with a natural synthetic resin to give a leather product suitable for footwear. In an example, the binder which is made up separately, consists of 20-30 per cent (based on the weight of leather present) of a natural or synthetic resin, preferably polyvinyl acetate, 5-10 per cent of resin or shellac in aqueous dispersion and 3-10 per cent of a vegetable or mineral oil such as kerosine or castor oil, to which 3-10 per cent of a plasticizer such as dibutyl phosphate, tributyl phosphate, or dibutyl phthalate is added. Scrap vegetable tanned leather is either ground dry and then suspended in water, or soaked in water preferably containing a wetting agent and then ground wet, till the fibre length is about 10 mms. and the suspension contains about 1-5 per cent of leather. An aldehyde such as formaldehyde may be added, followed by an alkali, such as caustic soda, or ammonia if an aldehyde has not previously been used, till the pH reaches 8-8.5, together with the optional addition of a colloid such as sodium alginate. The binder is then added and the mass acidified with hydrochloric acid or an acid salt such as aluminium sulphate till the pH reaches 4.2-4.5. After standing, the mass is felted by filtering on a screen, pressing and drying, and is then passed between rollers heated to 60-80 DEG C. to form sheets of the desired thickness. Increased flexibility may be obtained by bending the sheets backwards and forwards during the rolling process.ALSO:Scrap vegetable or mineral tanned leather from skivings and waste is reconstituted by grinding and binding with a natural or synthetic resin to give a leather product suitable for footwear. In an example, the binder, which is made up separately, consists of 20-30 per cent (based on the weight of leather present) of a natural or synthetic resin, preferably polyvinyl acetate, 5-10 per cent of rosin or shellac in aqueous dispersion and 3-10 per cent of a vegetable or mineral oil such as kerosine or castor oil, to which 3-10 per cent of a plasticizer such as dibutyl phosphate, tributyl phosphate, or dibutyl phthalate is added. Scrap vegetable tanned leather is either ground dry and then suspended in water, or soaked in water preferably containing a wetting agent and then ground wet, till the fibre length is about 10 mms. and the suspension contains about 1-5 per cent of leather. An aldehyde such as formaldehyde may be added, followed by an alkali, such as caustic soda, or ammonia if an aldehyde has not previously been used, till the pH reaches 8-8.5, together with the optional addition of a colloid such as sodium alginate. The binder is then added and the mass acidified with hydrochloric acid or an acid salt such as aluminium sulphate till the pH reaches 4.2-4.5. After standing, the mass is felted by filtering on a screen, pressing and drying and is then passed between rollers heated to 60-80 DEG C. to form sheets of the desired thickness. Increased flexibility may be obtained by bending the sheets backwards and forwards during the rolling process.

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