Patent GB-673879-A (GB)
Title: Method of treating polyethylene fabrics
IPC: D06M11/05
Filed: 1949-10-12
Abstract: Polyethylene fabrics comprising oriented "annealed" monofilaments or yarns are pre-shrunk and stabilized against subsequent shrinkage at temperatures up to a predetermined temperature by heating all portions of the fabric uniformly to a temperature between the initial shrinkage temperature of the filaments or yarns and the melting-point of the polyethylene, while the fabric is held at full open width, in flat condition, in the absence of external forces tending to compress the fabric, and under conditions of relaxation permitting shrinkage of the fabric in all directions to any predetermined extent under the influence of the heat.  The fabric may be heated by means of hot air, steam, hot water, radiant energy, or a heated organic liquid which is not a solvent for the polyethylene.  By "annealed" filaments or yarns are meant filaments or yarns which have been oriented by stretching and then stabilized by heat while held at constant length.  In an example an automobile seating fabric 9 (Fig. 4) woven from monofilaments of polyethylene and having a residual shrinkage capacity of 6-8 per cent at 75 DEG  C., is fed into a bath of water 2 at 82 DEG  C. between feed rolls 3 and 3a and between two stationary adjustable guide plates 5 and 6 submerged in the hot water and disposed one above the other to provide a passageway between them for the fabric.  The width of the guide-plates is at least as great as the width of the fabric 9.  The ends of plates 5 and 6 are flared upwardly and downwardly respectively to facilitate the feeding of the fabric.  The fabric passes between the plates, and is held in substantially flat condition between them, without sagging or buckling, and p  <PICT:0673879/IV (a)/1> <PICT:0673879/IV (a)/2> <PICT:0673879/IV (a)/3> <PICT:0673879/IV (a)/4> is free to shrink to the predetermined extent determined by the temperature of the bath, the length of the bath, and the rate of feed in correlation with the rate of draw-off, the rate of feed being greater than the rate at which the fabric is removed from the bath.  In the example the time of immersion of the fabric in the water is 7.2 seconds.  The preshrunk fabric is withdrawn from vessel 2 over guide roll 48 and is treated batchwise on the decatizer 45 shown in Fig. 5.  The decatizer consists of a perforated drum adapted to project steam outwardly through numerous and uniformly spaced perforations located in the periphery of the drum and includes a blanket 50.  The fabric 9 is wrapped up on the perforated surface of the decatizer with the blanket 50 by passing the fabric 9 and blanket 50 through spreading and guiding rolls 51 and 52 and over guide roll 53 so that the blanket is disposed against the surface of the drum and between the layers of polyethylene fabric.  After the complete assembly comprising the blanket and preshrunk polyethylene fabric has been wound on the decatizer, it is steamed on the decatizer for 10 seconds at 100 DEG  C.  The comparatively light pressure exerted by the blanket on the fabric is sufficient to maintain it in a flattened condition while permitting the filaments or yarns to contract and thus eliminate puckers.  The residual shrinkage capacity of the final treated fabric is 1.5 per cent in the warp and 0.7 per cent in the filling at 75 DEG  C. in the relaxed condition.  The fabric may be in fully relaxed or semi-relaxed condition during its travel through the bath.  Generally the fabric is preshrunk to such an extent that the residual shrinkage capacity in both the warp and the filling directions, when the fabric is composed of polyethylene having a melting point of 110 DEG  C., is not over 2 per cent between 65 DEG and 100 DEG  C.  The heating medium may be hot water at 65 DEG  C. and the contact time about 5 minutes, if fabric is required to be shrinkage-stable at 65 DEG  C., but preferably the water temperature is 5-25 DEG  C. above the temperature at which the fabric is to be stabilized, but not higher than about 10 DEG  C. below the melting-point of the polyethylene.  The contact time may then be of the order of 5 seconds to one minute, being shorter, the higher the bath temperature.  In two other embodiments of the invention the fabric 10 (Figs. 2 and 3) is fed into the vessel 11 containing hot water maintained at the preshrinking temperature over the rolls 12-14 on to the guide-plate 15, under the over-feed roll 16, over the supporting roll 60 and then to two positively driven endless tracks which run side-by-side, in spaced relation and comprise a form of tenter, one such track 17, supported in toothed wheels 18-24 (of which the wheel 18 is driven through pulleys 30 and 31 and belt 29a) being shown.  The distance between the tracks is adjustable and the tracks carry selvage-engaging members such as the upstanding pins 25. The peripheral speed of roll 16 is greater than the speed of the tracks, as a result of which ripples are produced in the fabric, which is laid down in the rippled condition.  A brush roll 26 to push the selvages of the fabric down on to the pins 25 is provided adjacent to each track 17.  In the preferred embodiment, the fabric is fed to the tracks in full width and the tracks are arranged to converge to a predetermined distance as the fabric is carried through the bath to permit shrinkage in the filling direction to the pre-determined extent. The ripples are removed from the fabric as it passes through the bath due to warpwise shrinkage of the fabric.  As shown in Fig. 2, the flat preshrunk fabric emerging from the hot water bath is passed directly to the electrically-heated press rolls 27, 28, and hot-pressed while it is maintained at approximately the same temperature as that at which it was pre-shrunk.  The fabric then passes directly to the nip of the rolls 32, 33 which are cooled in any suitable manner, to set the fabric in the preshrunk, hot-pressed condition.  The press rolls 27 and 28 may be omitted and/or the water bath substituted by a steam-box over which the tenter runs so that the fabric is exposed to the steam and thereby preshrunk.  As shown in Fig. 3, the fabric is withdrawn from the bath and passes under guide roll 38 and over guide roll 39 to the steaming and pressing zone comprising the bank of heated cylinders 40.  The polyethylene fabric is carried between the endless blankets 41 and 42 which may be formed of any suitable textile fabric which is not thermoplastic at the temperatures of the cylinders.  The cylinders are heated to a temperature such that the water in and on the polyethylene fabric is vaporized as the blanketed fabric passes between the cylinders.  The pressure exerted in the fabric is sufficient to maintain it in a flat condition but light enough to permit creep in the fabric with removal of wrinkles or puckers present thereon.  The fabric is pressed and heated at a temperature at least as high as the initial shrinkage temperature for the filaments or yarns and emerges as a dry fabric. The pressure exerted on the fabric during its steaming is preferably 1-50 p.s.i. and its temperature 100-108 DEG  C. for a time interval (usually inversely related to the temperature) between about 15 seconds and 2 seconds.  The preshrunk fabric may be calendered before or after the steaming and pressing operation.  The preshrunk, steamed or otherwise heated and pressed fabric may be dried by running through an oven or exposed to compressed air jets, but generally such extraneous drying processes are not required.