Patent GB-1179110-A (GB)
Title: Reinforced Sheeting.
Inventor: BACON JOHN ERNEST
IPC: B29C63/02
Filed: 1966-12-28
Abstract: 1,179,110. Reinforced sheeting. IMPERIAL CHEMICAL INDUSTRIES Ltd. 23 Nov., 1967 [28 Dec., 1966], No. 57964/66. Heading B5B. [Also in Divisions B7 and E1] A process for the production of reinforced sheeting comprises the steps of placing an oriented thermoplastic sheet of thickness from 0À02 inch to 0À20 inch around a rigid support or frame, heating the sheet to a temperature at which it would shrink if unrestrained, while controlling any slipping of the sheet from around the support or frame and before, during or after said heating, rigidly and permanently anchoring said sheet to said support or frame. Preferred materials include polyvinyl chloride and polypropylene, but high density polyethylene, polyesters e.g. polyethylene terephthalate, polyamides as, e.g., that formed by the condensation of hexamethylene diamine and adipic acid, and copolymers of acrylonitrile, butadiene and styrene and polyoxymethylene polymers and copolymers may also be used. The most useful range of thickness is from 0À025 inch to 0À10 inch. Desirably, the sheet is biaxially oriented in two perpendicular directions in its plane, especially to the same degree in each of said directions. The sheet may be oriented to a greater degree in some parts of its area than in other parts. The whole of the sheet may be subjected to heating to the shrink temperature, or parts only of the sheet; alternatively, some parts may be heated to a greater temperature than other parts of the sheet. The temperature at which the sheet will shrink is normally above the temperature at which the sheet was oriented and below the crystalline softening point of the polymer. The particular temperature used within this range will depend on the amount of shrinkage and the degree of tautening which it is desired to achieve in the sheet when it is rigidly anchored to the support or frame, and on the degree of orientation of the sheet. Where a very small amount of shrinkage is required, it may be possible to use a temperature below that at which the sheet was oriented. The anchoring of the sheet to the frame may be by means of an adhesive, of a welding or heat sealing, or by means of tacks, nails or stitching. It may also be anchored to the frame by means of clamps. The sheet may be anchored over the whole length of the rigid support or frame or it may be anchored to the frame at a number of suitable positions only. Where it is desired to produce a reinforced sheet of other than a flat shape, e.g. a sheet of curved cross-section, the sheet may be in slidable contact with some parts of the frame, while rigidly anchored to other parts. In a preferred embodiment, the sheet is not rigidly anchored to the support or frame before the sheet is heated to the shrink temperature but is attached to the frame in such a way that some degree of slip occurs when the sheet is exposed to the shrink temperature and the tension in the resultant shrunk and tautened reinforced sheet is of a predetermined value. In Figure 1, a rigid frame 1 of angle irons has been covered with a sheet 2 of biaxially oriented polyvinyl chloride 0À05 inch thick provided with two projections 3 on each of its sides which, on bending over, formed overlaps on the underside which were then fastened to the angle irons by rivets 4. After the rivets had been fixed, the assembly was formed to the position shown by heating to 85‹ C. In addition to angle irons, the rigid support can be of any suitable material, e.g. of other metals, or of wood, ceramic or plastic. In Fig. 2, a uniaxially oriented sheet 5 of polypropylene 0À10 inch thick which has been drawn five times is folded over bar 6 at each end and clamped in the unshrunk condition by clamps 7. The part of the sheet between bars 6 was then heated to 140‹ C. by an infra-red heater and allowed to shrink and thereby to pull the sheet through the clamps 7 until only one inch of overlap was left. At this stage the clamps 7 were tightened so that no further shrinkage could occur and before removing the clamps rivets were passed through the foldedover sheet to secure it to bars 6. In Fig. 3 a framework 8 is shaped in the form of a car boot lid. The sheet 9 of polyvinyl chloride 0À06 inch thick which had been biaxially oriented 1À6 times in one direction and 1À3 times in the other direction was positioned over the framework in such a way that the direction of lesser orientation followed the curve of the frame and it was then welded along each of the four edges of the frame. The whole assembly was then placed in an oven at 100‹ C. in order to obtain the finished reinforced sheet. In Fig. 4 a biaxially oriented hemispherical sheet 12 of polyvinyl chloride 0À025 inch thick is reinforced by a steel ring 13. The product which may be used, e.g. as a hub cap, is produced by placing a steel ring of external diameter less than the internal diameter of the thermoplastic hemisphere within the hemisphere and locally heating that part of the hemisphere of greater internal diameter than the ring to cause radial contraction and tauten the sheet 12 about the ring 13. The reinforced sheets produced according to the process of the invention may be used as constructional panels, e.g. in building or household applications, and in the production of components for motor car panels, e.g. for boot lids, hub caps, doors or panels.