Patent GB-1352747-A (GB)
Title: Multi-ply thermoplastic boards
IPC: B29C48/09
Filed: 1971-04-19
Abstract: 1352747 Laminates; extrusion GUNZE KOBUNSHI KOGYO KK 19 April 1971 [21 Feb 1970 8 May 1970 11 Sept 1970 26 Nov 1970 2 Feb 1971 12 Feb 1971 15 Feb 1971] 22290/71 Headings B5N and B5A A method of making a multi-ply thermoplastic board, comprises the steps of forming at least two strips of fused thermoplastic material, each of the strips having a plurality of continuous ribs on at least one surface thereof, the ribs being spaced with respect to each other across the width of each strip, arranging the strips so that the ribbed surfaces face each other, the ribs on one strip being arranged to cross the ribs on an adjacent strip, and pressing the strips together with at least the tops of the ribs in a fused condition so that the tops of the ribs of the mutually facing strips are united. The strips having the ribbed surfaces may be produced from one or more tubes formed by extruding fused thermoplastic material from an extrusion die, the or each tube being fed from an extrusion die, longitudinally split into at least one section and then spread out to form one or more strips. The strips which may be united immediately after extrusion or after storage, may be produced by extruding a single tube from a single die and slitting the tube into at least two sections; alternatively, the strips may be made by extruding at least two continuous tubes from separate extrusion dies and slitting each tube longitudinally to form a single strip. The thermoplastic material may be high density polyethylene, polypropylene, polystyrene, a homo- or copolymer of vinyl chloride, an acrylonitrile - butadiene - styrene terpolymer, polymethyl methacrylate, nylon or a mixture thereof. The ribs on a strip may be parallel with the edges of the strip; alternatively, the ribs may meander with respect to the edges of the strip, examples of boards formed with strips having varying rib configurations being shown in Fig. 4. In a preferred embodiment, a strip having ribs on each surface is sandwiched between two strips each having ribs only on the inward facing surface. An apparatus for effecting the method of the invention comprises at least one extrusion die 11, 11<SP>1</SP> for extruding at least one tube 17, 17<SP>1</SP> of fused thermoplastic material, the or each extrusion die including means providing a plurality of spaced continuous ribs on at least one surface of the tube(s), means 23, 23<SP>1</SP> for cutting the tube(s) to form strips 24, 24<SP>1</SP>, guide means 26, 26<SP>1</SP>, 27, 271 for conveying the strips with the ribbed surfaces facing each other and the ribs on one strip arranged to cross the ribs on another strip and means for uniting the strips. When the apparatus comprises more than one extrusion die, each extrusion die may be positioned on a separate extruder; alternatively, each extrusion die may be connected to a common extruder. In the embodiment shown in Fig. 2, the extruder 10 comprises an extruder screw 12 through which a thermoplastic material is fed in a fused condition to the die 11 through crosshead 14, a conical passage 15 formed within the die leading to an annular slot 16 through which the material is extruded in tubular form 17. The annular slot is defined by inner and outer concentric peripheral walls forming part of the die, a plurality of spaced linear serrations 18 being formed on one of the walls, the serrations being spaced equidistantly or unequidistantly and extending substantially parallel to the longitudinal axis of the tube. In operation of the extruder, the die 11 may be held stationary, rotated or reciprocated through a limited angle about its axis by combination rack and worm gear arrangement 19, rotation or reciprocation of the die resulting in the formation of a tube with ribs at an angle to the longitudinal axis of the tube. In preferred embodiments, the serrations are of generally rectangular section and are arranged in groups, or are of uniform or non- uniform trapezoidal section. In the embodiment shown in Fig. 5, and used in conjunction with the extruders shown in Fig. 1, a thermoplastic material, preferably of the foamable type, is fed in fused condition to a third extrusion die 43 having an elongated slot 43a to form an extruded strip 44 which is pressed by rollers 42 and 42<SP>1</SP> into the gaps between the ribbed surfaces 25 and 25<SP>1</SP> of the strips 24 and 24<SP>1</SP>. When the die is rotated or reciprocated, means 50 (Fig. 8) may be provided intermediate the extrusion die 11 and the cutting means 23 for use with a tube having an inner ribbed surface for controlling the angle of the ribs with respect to the longitudinal axis of the tube. The means 50 comprise a hollow drum 51 having an inner peripheral wall 51a of diameter substantially equal to the outside diameter of the tube 17, the drum being supported on movable table 53 and being in communication with suction means, control of the density of the rib pattern and of the angle of the ribs being effected by regulating the subatmospheric pressure in the drum and the distance of the drum from the extrusion die. A similar (Fig. 9, not shown) is described for use with a tube having an outer ribbed surface.