Method of manufacturing a multilayer material

Abstract

A multilayer material is disclosed which consists of polyethylene foam sandwiched between two external layers of high-density polyethylene. A two-step manufacturing process for forming such a multilayer material is disclosed, which consists of (1) thermal bonding of a roll stock of PE foam with a roll stock of HDPE/LDPE laminate, followed by cutting into composites, and (2) thermal bonding of two composites to form a multilayer material.

Claims

1. A method of forming a multilayer material comprising forming three-layer composites, comprising: a. providing a first pre-formed roll comprised of an outer material layer in communication with an intermediate material layer; b. providing a second pre-formed roll comprised of an inner material layer; c. feeding said first and second pre-formed rolls through rollers; d. joining said intermediate material layer of said first pre-formed roll to said inner material layer of said second pre-formed roll so as to form a three-layer material; e. cutting said three-layer material into three-layer composites of a pre-determined length; f. providing a first and a second composite from step e., both composites having the same orientation; g. reversing the orientation of said second composite, so that the bowing of said second composite is opposite to the bowing of said first composite; and h. joining the inner material layers of said first and second composites.

2. The method of claim 1, wherein said composites include sheets.

3. The method of claim 1, wherein said joining includes thermal bonding.

4. The method of claim 1, wherein said outer material layer is laminated to said intermediate material layer, in said first pre-formed roll.

5. The method of claim 1, wherein said inner material layer of said second pre-formed roll has a thickness of 5 to 100 millimeters.

6. The method of claim 1, wherein said outer material layer is comprised of high density polyethylene (HDPE).

7. The method of claim 1, wherein said intermediate material layer is comprised of low density polyethylene (LDPE).

8. The method of claim 1, wherein said inner material layer is comprised of polyethylene foam.

9. The method of claim 8, wherein said polyethylene foam is closed-cell, cross-linked polyethylene foam.

10. The method of claim 8, wherein said polyethylene foam has a density of 10 to 100 kilograms per cubic meter.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

(2) FIG. 1A is a perspective view of an exemplary embodiment of a multilayer material according to the present invention, including a partial cross-sectional view cut from a corner.

(3) FIG. 1B is an enlarged cross-sectional view of the cross-section of FIG. 1A.

(4) FIG. 2 is a diagram showing the first step of an exemplary two-step manufacturing process for forming the multilayer material of FIGS. 1A and 1B.

(5) FIG. 3 is a diagram showing the second step of an exemplary two-step manufacturing process for forming the multilayer material of FIGS. 1A and 1B.

(6) FIGS. 4 and 5 are exemplary applications of a multilayer material according to an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) The present invention is a multilayer material and a method for its manufacture. The principles of the present invention may be better understood with reference to the drawings and the accompanying description.

(8) FIG. 1A shows article 100, which is an exemplary multilayer material, for example in a sheet form, according to an embodiment of the invention. Article 100 is formed from at least two composites 101, for example, in the form of sheets, each composite 101 including an outer layer 104, an intermediate layer 106 and an inner layer 108. The inner layers 108 of each composite 101 are joined to each other, to form article 100.

(9) Layers 104, 106, and 108 are preferably made of high density polyethylene (hereafter HDPE), low density polyethylene (hereafter LDPE), and closed-cell, cross-linked polyethylene foam (hereafter PE foam). In addition to polyethylene, each of layers 104, 106, and 108 may also include various additives to enhance such properties as flame resistance, resistance to chemicals, ultraviolet resistance, resistance to static charging, scratch resistance, impact resistance, and the like.

(10) One advantage of polyethylene is that it presents fewer health and environmental problems than other thermoplastics such as polyvinyl chloride and polycarbonate. Other advantages include its low weight-to-strength ratio, thermal conductivity, and water absorption.

(11) Exemplary properties of layers 104, 106, and 108 are as follows. The thicknesses of the HDPE and LDPE layers are preferably in the range of 0.1 to 2 mm., and their densities are preferably in the range of 900 to 970 kg/m.sup.3. The thickness of the PE foam layer is preferably in the range of 5 to 100 mm., and its density is preferably in the range of 10 to 100 kg/m.sup.3.

(12) FIG. 1B shows an enlarged cross-sectional view of the cross-section of FIG. 1A. Exterior surfaces 112 may be made highly parallel, typically to within a mechanical tolerance of 1 degree. Furthermore, the highly parallel feature is maintained, even after temporary compression of the PE foam layers by external impact forces.

(13) FIG. 2 is a diagram of the first step of a two-step manufacturing process for forming the exemplary multilayer material of FIGS. 1A and 1B. Arrow 120 indicates the direction of the process.

(14) Roll stock 108 is a pre-formed cylindrical roll of PE foam 108. Roll stock 108 is available from many manufacturers; for example, Palziv Group Ltd., located at Kibbutz Ein Hanatziv, Israel. Many different varieties are available, in accordance with customer specifications of roll width, color, and PE foam density and cell size.

(15) Roll stock 110 is a pre-formed cylindrical roll of a two-layer laminate, having HDPE layer 104 on one side and LDPE layer 106 on the other. The laminate is bonded together by any of several means, such as co-extrusion, adhesive bonding, thermal lamination, and the like. Roll stock 110 is available from many manufacturers; for example, Polyraz Ltd. located at Kibbutz Maoz Haim, Israel. Many different varieties are available, in accordance with customer specifications of roll width, color, and HDPE/LDPE density and finish.

(16) Roll stocks 110 and 108 are rotated in opposite directions, as indicated by arrows 130 and 140, respectively. The directions of rotation are reversed so that the natural curvatures of the roll stock are opposite to each other, as they enter flame roll laminator 180.

(17) Rotation of roll stocks 110 and 108 is preferably by means of electric motors (not shown). As the radii of the roll stocks decrease, it is necessary to adjust continually the rate of rotation of the electric motors, so as to equalize the linear velocities of the feed stocks entering laminator 180.

(18) Roll stock 110 is mounted as shown in FIG. 2, so that (a) LDPE layer 106 is in closer proximity to heat source 150 than HDPE layer 104, and (b) LDPE layer 106 is brought in proximity to PE foam layer 108.

(19) Tension rollers 135 and 145 feed the roll stocks into laminator 180. During lamination, heat and pressure are applied simultaneously, by means of heat source 150, upper pressure rollers 160, and lower pressure rollers 170. The linear velocity of the feed stock passing through laminator 180 is typically in the range of 1 to 10 meters per minute, and is maintained constant to an accuracy of within 0.01 meters per second.

(20) The temperature of heat source 150 is preferably in the range of 900 to 1100 C., in order to bring the lamination surfaces to a desired softening point for thermal bonding. The softening point of LDPE, as measured for example by the Vicat softening temperature, is at a substantially lower temperature than that of HDPE (e.g. by as much as 30 C.). One of the key reasons for thermally bonding the PE foam layer to LDPE, and not directly to HDPE, is to achieve lamination at lower temperature, and thus to avoid melting the PE foam layer or damaging its closed-cell structure. Another reason for thermally bonding the PE foam layer to LDPE, and not directly to HDPE, is that the bond between PE foam and LDPE appears to be far stronger and more stable than the bond between PE foam and HDPE. This may be a consequence of the chemical structure of LDPE, which has weaker intermolecular forces than HDPE.

(21) Pressure rollers 160 and 170 apply pressure to the feed stock in a direction perpendicular to the plane of translation. The amount of pressure applied is that which is necessary to compress the PE foam layer by about 10%. Applying too low a pressure results in non-uniform lamination; applying too high a pressure may damage the closed-cell structure of the PE foam.

(22) Cutting table 190 is used to cut the output stock into composites 101 of equal length. Typical lengths are in the range of 0.5 to 10 meters. Composites 101 are generally not planar; rather, there is a slight bowing in the direction indicated by curved lines 212. The amount of bowing is slight because the roll stocks have been placed so that the natural curvature of roll stock 110 opposes the natural curvature of roll stock 108.

(23) FIG. 3 is a diagram of the second step of a two-step manufacturing process for forming the exemplary multilayer material of FIGS. 1A and 1B. Arrow 220 indicates the direction of the process. Arrows 202 indicate the initial orientation of composites 101. Mechanism 210 reverses the orientation of one composite so that it faces in direction 204, which is opposite to direction 202. In this way, after thermal bonding in flame sheet laminator 280, the bowing of one composite cancels out the bowing of the other. It is this cancellation which provides the high degree of parallelism between surfaces 112 of article 100.

(24) The two composites 101 are fed into laminator 280 by means of a conveyor mechanism and input rollers (both not shown). The input rollers are tensioned to keep the feed stock flat and well-aligned. The linear velocity of the feed stock passing into laminator 280 is typically in the range of 0.5 to 5 meters per minute.

(25) Heat and pressure are applied simultaneously inside laminator 280 so as to thermally bond together the PE foam layers of the two composites. The temperature of heat source 250 is preferably in the range of 300 to 350 C., in order to bring the PE foam surfaces to a desired softening point for thermal bonding. Pressure rollers 260 and 270 apply pressure to the composites 101 in a direction perpendicular to their plane of translation. The amount of pressure applied is approximately the same as that used in the first step of the manufacturing process.

(26) After thermal bonding, article 100 is allowed to cool at room temperature (about 25 C.) and is then off-loaded to a storage facility. This completes the second step of the two-step manufacturing process for forming article 100.

(27) FIGS. 4 and 5 are exemplary applications of a multilayer material according to an embodiment of the invention. In FIG. 4, sheets of article 100 are used to construct the sides of a building. In FIG. 5, sheets of article 100 have been cut into interlocking male and female shapes.

EXAMPLE

(28) TABLE-US-00001 Article 100 Layer number of layers thickness (mm) density (kg/m.sup.3) HDPE 2 1.2 950 LDPE 2 0.1 920 PE foam 2 10 70

(29) HDPE Layer 104 Thickness: 1.2 mm Density: 950 kg/m.sup.3 Shore hardness: 68 D Vicat softening temperature: 123 C.

(30) LDPE Layer 106 Thickness: 0.1 mm Density: 920 kg/m.sup.3

(31) TABLE-US-00002 PE Foam Layer 108 Measured Property Standard Result unit Thickness 10 mm Density ISO 845 70 Kg/m.sup.3 Tensile strength - MD* ISO 1798 692 kPa Tensile strength - TD** ISO 1798 575 kPa Elongation - MD* ISO 1798 141 % Elongation - TD** ISO 1798 148 % Compression 10% ISO 844 80 kPa Compression 25% ISO 844 105 kPa Compression 50% ISO 844 191 kPa Compression Set 25% 0.5 H ISO 1856 6 % Compression Set 25% 24 H ISO 1856 3 % Compression Set 50% 0.5 H ISO 1856 17.5 % Compression Set 50% 24 H ISO 1856 10 % Working Temperature Range Internal 60 \ 90 C. Water Absolution % Vol (max) Internal 1 % Thermal Conductivity at 10 C. ASTM C177 0.0430 W/mK Thermal Conductivity at 40 C. ASTM C177 0.0470 W/mK Shore hardness ASTM D2240 29 A *MDmachine direction - along extruder axis **TDtransverse direction - perpendicular to extruder axis
The above parameters are by way of example only, and many variations are possible within the scope of this disclosure.

(32) Formation of article 100 follows the two-step manufacturing process outlined above, to wit: In the first step, a pre-prepared roll of HDPE/LDPE laminate is thermally bonded to a pre-prepared roll of PE foam by means of flame roll laminator 180, and then cut into composites 101. In the second step, a pair of composites 101 is thermally bonded together by means of flame sheet laminator 280, so that the two PE foam layers form an inner core, and the HDPE layers form the outer surfaces.

(33) To those skilled in the art of thermoplastic materials and production processes, it is readily apparent that the principles of this invention may be extended to forming more complex multilayer materials. For example, any number of additional layers of LDPE and PE foam may be inserted between HDPE layers 104 of article 100, using the same thermal bonding techniques and parameters as those outlined above.

(34) Thus, it will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.