| 摘要 |
<PICT:0439793/IV/1> Foils and like structures are produced by pouring a formyl cellulose reaction mass containing formic acid, dehydration medium, and formyl cellulose) on to a suitable support, evaporating wholly or partially the formic acid in the mass, and then precipitating in water. If desired, plasticizers such as ethyl acetanilide, camphor, and dibutyl phthalate may be added to the formylating mass before pouring. Foils which cannot assume an electric charge are produced when a formyl cellulose containing free hydroxyl groups is employed, e.g. formyl cellulose containing 40--45 per cent of formic acid. In an example, a formyl cellulose reaction mass obtained by treating cotton linters or pulp with formic acid in the presence of zinc chloride, is ripened and de-aerated. It is then poured from a vessel 1 into a pourer 3, and the film which forms on the runner belt 6 is led over a number of heating pipes 8. A current of air enters the chamber at 9 and leaves at 10. The belt 6 carries the partially (e.g. 75 per cent) dried film through the coagulation bath 11 consisting of water and of formic acid and zinc chloride taken up from the film, and finally the film which is detached from the belt by means of a roller 14, is passed through a series of washing and plasticizing baths 18, 19, 20, and over drying rollers 21. Formic acid and zinc chloride are recovered from the coagulating bath which preferably is caused to move in counter-current direction to the film. |
