Patent GB-1124467-A (GB)
Title: Patterned sheet material and method of making same
IPC: B44F1/04
Filed: 1965-11-09
Abstract: 1,124,467. Laminates. ROWLAND PRODUCTS Inc. 9 Nov., 1965 [31 Dec., 1964], No. 47419/65. Heading B5N. [Also in Divisions B6 and G2] Sheet material providing a visual moire pattern comprises a multiplicity of closely spaced curvilinear lens-like formations arranged in a first pattern on the front surface thereof and a multiplicity of closely spaced light reflective formations arranged in a second pattern in a parallel plane spaced from said front surface, the sheet material being such that when placed so that its front surface is horizontal the formations diminish in horizontal cross-section along the vertical and horizontal axes of the sheet material from a major portion to provide tapering side walls along the horizontal axes of the sheet material. The lens-like formations are curvilinear along both horizontal and vertical axes of said sheet material, and the reflective formations phase in and out of axial registry with said lens-like formations along at least one horizontal axis of the sheet material. Each of the patterns has a plurality of axes along which the formations are arranged, and the lens-like and reflective formations are in substantially the same degree of axial alignment over a multiplicity of formations along one axis of one pattern in some areas of the sheet material and the period for the formations to phase into and out of axial registry is greater along this axis in at least some areas of the sheet material than the period for such phasing along another axis of the sheet material. The variations in period and extended areas of alignment produce bands of brightly reflective areas and poorly reflective areas which form the visual moire pattern, and is provided by effecting variations in alignment of the pattern of formations of the front surface with respect to that of the parallel plane. The desired variation relies upon three types of distortion in one or both patterns either alone or in combination, and these three types are (1) where one of the axes of a pattern is curvilinear and crosses an axis of the other pattern, the latter axis being rectilinear, or of equal curvature and extending oppositely, or of dissimilar curvature; (2) where an asymmetric pattern is superposed with another asymmetric pattern, or a curvilinear pattern so that axes of each extend parallel and at least one other axis of each diverge; (3) where the spacing between centres of the formations of the pattern becomes greater and smaller cyclically within not more than 10% of the average spacing along at least one axis, and such a pattern is superposed upon a similar pattern out-of-phase or upon a uniformly spaced pattern wherein the spacing approaches the average of the varying pattern. The several types of distortion of pattern may be produced by stretching sheet material carrying regularly spaced formations arranged in a pattern having symmetrical axes. The lens-like formations are preferably embossments having a curvilinear convex periphery and horizontal cross-section e.g. parabolic configurations, major segments of spheres. The reflective formations may be embossments on the rear surface of prismatic or conical or preferably convex lens-like configurations. The preferred pattern employs a hexagonal array of embossments. A reflective colouring agent may be applied to the rear surface. Multicoloured optical effects may be produced by providing a first colouring agent on a first portion of the embossments and a different colouring agent on a second or third portion. Portions of the embossments may be free from colouring agent. The colouring agents may be lacquers, paints, dyes, metallic films applied by printing, coating with vaporizable solvents solutions, vacuum metallizing, spraying, rolling, brushing, wiping, chemical deposition. The first colouring agent may be applied to the tops of the reflective embossments, and the different colouring agent applied over the entire rear surface of the sheet, or the entire surface may be coated with the first colouring agent, the tops of the embossments lightly abraded to remove the first colouring agent and then the different colouring agent is applied. The sheet material may be of synthetic plastics such as polyacrylic acid esters e.g. methyl methacrylate, cellulose acetate, nitrate, acetate-butyrate, or proprionate, vinyl chloride polymers copolymers, polystyrene, polycarbonates, polypropylene, polyethylene, and laminates e.g. with thin surface films of polyethylene terephthalate. The sheets may be formed by laminating back-to-back two strips of sheet material each embossed on one surface under conditions which produce the desired patterns of embossments, the lamination being effected by the use of solvent or a layer of adhesive and applying pressure. The desired phasing and variations in period and alignment of the embossments can be assured by the use of two different embossing rolls having different patterns of embossments or the same embossing roll may be used for both strips and the strips stretched or shrunk non-uniformly. Differential cooling, localized stress relieving following uniform stretching and localized heating may also be utilized. In Figs. 4 and 5 (not shown) an embossing roll 2 employing a hexagonal pattern of embossments co-operates with a rubber-faced back-up roll 4 to define a nip through which sheet material 6 issuing from extruder 9 passes. Sheet material 6 then passes over steel idler roll 10 and is drawn over rubbersurfaced stretching roll 12 which rotates at a tangential speed greater than that of rolls 2, 10. The distortion that takes place in the sheet material is illustrated in Figs. 2, 3, 9, 10 (not shown). Stretching roll 12 may provide a cyclic increase or decrease in the degree of stretch by using phased eccentric cams on both ends of the drive shaft assembly to give the distortion illustrated in Fig. 21 (not shown), and may be arranged to stretch the sheet material eccentrically and cyclically first to one side of the centre line of the sheet and then to the other side by cams on both ends of the drive shaft assembly which are out-of-phase by 180 degrees, giving the distortion illustrated in Fig. 20 (not shown). By stretching the material over a relatively short distance and frictionally constraining the material between a pair of rubbersurfaced stretching rolls, the material may be elongated without contraction transversely to increase the spacing between the centres of the embossments in the direction of stretch altering the rectilinearity of the axes, and the stretching may be cyclic and/or eccentric. Various visual patterns obtained by the combination of two sheet materials at least one of which carries a distorted embossment patten are illustrated e.g. "knothole" and "ribbon" visual patterns.