Patent GB-983325-A (GB)
Title: Improvements in producing regenerated cellulose film
IPC: B29C48/10
Filed: 1962-07-16
Abstract: 983,325. Producing regenerated cellulose films. E. I. DU PONT DE NEMOURS & CO. July 16, 1962 [July 17, 1961], No. 27290/62. Heading B5B. Regenerated cellulose film is produced by extruding an aqueous solution, such as viscose, from which cellulose can be regenerated in the form of a tubular film into a coagulating bath in such a manner as to provide at least one longitudinal " lane " in the film where the wall is thinner than over the remainder of the film, advancing the tubular film through the bath to form a gel tubular film, inflating the tubular film, and subsequently regenerating the cellulose. The inflated tubular film may be slit along the centre of each longitudinal lane and the resulting flat film treated to regenerate the cellulose. The term " lane " is defined as a strip or narrow path running along the film in the longitudinal or machine direction. The width of each longitudinal lane may be about 10% of the circumference of the tubular film. As shown in Fig. 1, viscose is extruded through a die having an annular extrusion orifice into tank 13 containing coagulating liquid 14 to form a tubular film 11. The coagulating liquid is fed into the tank through inlets 15 and 16 and an additional inlet 74 shown in Fig. 3, which is a side elevation in section of a preferred form of extrusion die and its feed channel. The coagulating liquid overflows from tank 13 through outlets 17 and 18 and in Fig. 3 through the hollow interior of shaft 59. The circular die 12 consists of an inner die lip 51 and an outer die lip 52, the annular space between the lips providing the annular extrusion orifice 53. Inner die lip 51 is mounted by means of ball-bearings 54 and 55 on the upper die body 56, which in turn is mounted by means of roller bearing 57 on the mandrel support 58, which is welded to the hollow cylindrical motor-driven drive-shaft 58. Also welded to the drive-shaft 59 is a drive-plate 60 connected by a drive-lug 61 to the inner die lip 51 for rotation therewith. The outer die lip 52 is also rotatably mounted around shaft 59 but is not driven by this shaft. It is mounted by means of bearings 62 and 63 on the lower die body 64, which in turn is mounted by means of bearing 65 on a mandrel support 66 welded to the shaft 59. The outer die lip 52 is driven by a drive-shaft 69 through a gearwheel 68 which is mounted on the driveshaft 68 and engages a gear ring 67 bolted to the base of the lip 52. To provide longitudinal lanes 25 (Fig. 1) in the tubular viscose film extruded through the orifice 53 (Fig. 3), at least one throttling plate 70 is disposed in the viscose supply channel 71 upstream of the orifice 53. The throttling effect of the plate 70 is adjustable by means of the bolt 72. The viscose is supplied to the channel 71 through the entry port 73. An alternative form of extrusion die in which only the inner lip is rotatable is shown and described. The rotation of one die lip or of both die lips relatively to each other helps to produce tubular film which is of uniform thickness except for the thin lanes purposely provided. After being extruded the coagulated tubular gel film is then passed over guide roll 19 (Fig. 1), through the nip of rolls 20 and 21 and then through the nip of positivelydriven rolls 22 and 23. Between the two sets of nip rolls the tubular film is inflated to stretch it transversely by the introduction of slightly pressurized air through the tube 24. The formation of the thinner lanes 25 is ensured or augmented by the provision of travelling belts 26 and 27 which resist inflation of the tubular film 11 beyond a predetermined extent by contacting its circumference except over the longitudinal lane or lanes and are moved at the same rate as the advancing tubular film by the driven rolls 28 to 31. After the inflated film is collapsed by passing through the nip of rolls 22, 23, it is slit by a knife 32 along the median line of each of the (in this case two) lanes and the resulting two flat sheets of gel film 50A and 50B are then led as superimposed sheets by rolls 33- 43 through a regenerating bath 44, a purification bath 45 and a softening bath 46 in the usual manner. The film sheets are thereafter passed through the drying chamber 47 and the dried sheets are separated and wound on rolls 48 and 49.