Patent GB-1287286-A (GB)
Title: Preparation of fibrous reinforced sausage casings from polyvinyl alcohol resins
IPC: B29C48/08
Filed: 1969-10-02
Abstract: 1287286 Coated sausage casing TEE-PAK Inc 2 Oct 1969 [18 Oct 1968 21 Oct 1968 26 May 1969 (2)] 48537/69 Heading B2E [Also in Division F2] A synthetic sausage casing comprises a tube of a long fibre saturating tissue longitudinally seamed and impregnated and coated with a continuous polyvinyl alcohol resin film, the film resulting from depositing on the tissue a film-forming polyvinyl alcohol resin having a degree of substitution with regard to hydroxyl groups of at least 20%. The polyvinyl alcohol resin may be deposited on the tissue by roller, doctor blade, knife, reverse roll, direct roll, contra-coating, as an organic solvent solution or an aqueous or aqueous alkaline solution, or by melt-extrusion. A polyvinyl alcohol resin may be depositedby contact with a coagulating agent or by evaporating the solvent from the resin solution-impregnated tissue. Further insolubilization of the deposited resin may be carried out by reaction with a cross-linking agent which is either incorporated in the impregnating and coating resin solution or melt or brought into contact with the impregnated and coated tissue in a separate step, e.g. by spraying. Examples of cross-linking agents are given. The tissue may be formed into a tube at the time of the deposition and insolubilization; or the tissue is impregnated and coated in the form of a flat sheet and subsequently formed into a tube. The polyvinyl alcohol resin may be prepared by hydrolysis of polyvinyl ester homopolymers, or carboxylated polyvinyl ester polymers, e.g. vinyl esterethylenically unsaturated carboxylic acid copolymers. The resin may be plasticized for application by extrusion. Examples of plasticizers are given. The casings may be treated: inside and/or outside with surface-applied lubricants and release agents, e.g. silicon oils, polymethyl hydrogen siloxane, acetylated monoglycerides, 1-18C fatty ketene dimers, cetyl alcohol, aluminium sulphate, lactic acid, inositol, methyl- and carboxymethyl cellulose; inside surface-applied shrinkage and adhesive coating agents, e.g. gelatin-acetylated monoglyceride mixtures, gelatin cured with dialdehydes; outside surface-applied water- and vapour-permeability reducing coating materials, e.g. vinylidene chloride homopolymers and copolymers, polymeric mixtures of a paraffin wax and a dimerized ester of an epichlorohydrinbis-phenol reaction product. As shown in Fig. 2, a ribbon of long fibre hemp saturating tissue 11 is formed into tubular form by formers 15 and 16, and proceeds downwardly over a mandrel 17, through forming ring 19 and through coating die 20 which applies an aqueous or organic solvent solution of polyvinyl alcohol resin to the outer surface of the tube. The mandrel 17 extends through drying chamber 23. From the lower end of the drier 23, the dried coated casing is collapsed before passing to another drier 29 in an inflated condition. In another embodiment (Fig. 3 not shown), mandrel 17 extends into a coagulating bath through which a coated and impregnated casing is guided and subsequently passes through further coagulating bath, and finally a bath containing plasticizer and crosslinking agent, e.g. formaldehyde before being collapsed and inflated for drying. In another embodiment (Fig. 10 not shown) the coating die is replaced by a melt extruding die through which the casing centrally passes, and the mandrel is surrounded by cooling chamber to cool the web after extrusion of the polyvinyl alcohol resin film thereon. The mandrel also extends into a container containing a crosslinking agent. In a further embodiment, as shown in Fig. 11, a web of saturating tissue 341 and extruded resin film 342 in face-to-face surface contact are passed through the nip of cooled rollers 343 and 344, the resulting sheet 345 is slit by knife means 346, guided through a bath of a cross-linking agent and formed into a tube by passage over former 355. Adhesive applicator 357 cooperates with former 355 and applies adhesive 356 to the sheet as the edges are overlapped in the forming operation. Insolubilization of the resin is completed in drier 359.