Patent GB-724465-A (GB)
Title: Method and apparatus for solvent sealing regenerated cellulosic sheets
IPC: C08J7/12
Filed: 1953-04-13
Abstract: 724,465. Seaming non-metallic sheet material. AMERICAN VISCOSE CORPORATION. April 13, 1953 [May 14, 1952; May 14, 1952], No. 10011/53. Class 42 (1). [Also in Groups VI and XXVIII] Non-fibrous regenerated cellulose sheet is sealed as specified below at a very low temperature which increases the tensile strength of the seal 50 to 100 times. The articles made by the sealing may be sausage skins, boxes, cartons, wrappers for ice cream or frozen foods, toys, dolls or golf or tennis &c. balls or any laminated structure of such sheets. The seal or the sheet may be printed or preprinted on the opposite side to the sealing side. Tubeforming apparatus is housed in a casing 125a which may contain a refrigerating coil 126a. The seam may also be refrigerated by a refrigerant pipe (110, Fig. 3, not shown) just before the wetted seam is pressed down by endless chains of blocks, 90, 91. The sheets are sealed, e.g. at their edges, by coating the edges with an aqueous solution of an alkali metal hydroxide, e.g. sodium potassium or lithium hydroxide from 8 to 25 per cent concentration at a temperature between - 3‹ C. and -12‹ C., and then by pressing the edges together. The pressing is preferably done at a temperature between +2‹ C. and -20‹ C. After pressing and sealing the remaining alkali may be neutralized with an aqueous acid solution, e.g. acetic acid of 5-25 per cent concentration or by other weak acids such as lactic, citric or tartaric acid which may be applied by spraying, brushing or dipping. The acidneutralizing solution may also contain a plasticizer for the cellulose sheet, such as glycerol, ethylene glycol, sorbitol, ethanolamine lactate or other hygroscopic substance. A moisture-proof agent may be applied to either or both sides of the sheet which may be removed at the place to be sealed by a solvent which, with the dissolved moisture-proof material, can be removed by a wiper roll. The tube is made from a roll 7 of sheet material 10 pulled over guide rolls and a tensioning roller 15 and a V-shaped spreader 31. The spreader guides the sheet under a mandrel 5 around which it is wrapped by formers 40, 41 which overlap the edges at the closed portion 32 of the formers. A belt 43 is pressed by a curved metal shoe 48 against the overlap to seal the edges together. The shoe is hollow to receive a circulation of refrigerant. The shoe is pressed towards the belt by springs but it may be pressed by compressed air. Solvent adhesive is applied by a roller 23 in a tank 22, jacketed to receive refrigerant from a pipe 101 and to discharge it from other pipes. The solvent is supplied from a tank 26a to the tank 22. Acid to neutralize the residue of alkali solvent passes from a tank 117 and through a bore 121 inside the mandrel 5 and an opening 125 to the inside of the seam of the tube. Acid is also supplied to the outside by an endless belt 69 from a container 137. The endless belt 69 along with a complementary endless belt 70 underneath shapes and pulls the tube along the mandrel 5. The belts are pressed against the tube on the mandrel by endless chains of arcuate blocks 90, 91. In a modification (Fig. 4, not shown), cold alkali solvent for the seam is applied by a wick (232) from a refrigerated container (230), the wick lying between the overlapped edges. The tube may be made of any desired crosssection.