CORRUGATED COEXTRUDED FOAMED POLYCARBONATE SHEET AND A METHOD FOR PRODUCTION THEREOF

Abstract: A rigid polycarbonate sheet for use as an outdoor building material is formed of a layer of foamed polycarbonate (12) and a co-extruded skin layer of UV protective polycarbonate (14). A system for the production of such a polycarbonate sheet includes an extruder, a co-extruder, an extrusion die, and a thermoformer.

Description: CORRUGATED COEXTRUDED FOAMED POLYCARBONATE SHEET AND A METHOD FOR PRODUCTION THEREOF FIELD OF THE INVENTION The present invention relates to outdoor building materials in general and to polycarbonate sheet material for roofing and cladding in particular. BACKGROUND OF THE INVENTION In the industrial world there is a strong need for outdoor building materials that will perform for many years in harsh environments. In general, the existing materials do not perform as well as needed by current standards, and therefore substitute materials are in great demand. The main requirements for outdoor building materials can be summarized, as follows: 1) service temperature of up to 80 - 90°C and down to -30°C (service temperature is the temperature range in which the material is stable); 2) UV resistance for 20 - 50 years in extreme radiation conditions (the ozone hole problem is making this issue more important); 3) corrosion resistance; 4) impact resistance to wind, hail and flying debris; 5) water resistance and water impermeability; 6) chemical resistance to airborne chemicals such as acid precipitation; smoke, dust and soot; resistance to biodegradation; 7) flexibility and resilience: the ability to perform even after suffering deformations; 8) fire resistance and fire performance that will not compromise safety and if possible will improve safety; 9) good heat and sound insulation; and 10) environmentally friendly. Existing roofing, siding and cladding materials such as wood, steel sheets, fiberglass, asbestos cement and PVC sheets, suffer from several disadvantages. For example, wood board is corrosive, water-sensitive, and has bad fire performance. In addition, wood is not considered environmentally friendly and commonly, toxic materials are used to treat prime grade wood against biodegradation and to improve fire resistance. Steel sheets are very corrosive and react strongly to humid air and polluted environments. Anti-corrosive coatings used on steel are impact- and weather-sensitive. Furthermore, steel is not resilient, is not flexible, suffers from permanent deformation after strong forces are applied and has a high heat transfer coefficient and a low insulating coefficient. Fiberglass sheets are brittle, and have low impact resistance, bad UV and fire resistance. Also, the use of glass fibers in their production and disposal is not environmentally sound. Glass fibers are suspected of causing diseases, such as fibrosis. Asbestos cement sheets are brittle, corrosive and biodegradable (i.e. fungus growth in the pores causes color change and embrittlement), have low heat insulation, can cause asbestosis to human beings chronically exposed to the asbestos cement and are dangerous in fires, tending to explode and shatter in extensive heat. PVC sheets are generally only suitable for use in light colors and in medium temperature climates. Clear PVC sheets suffer from low impact resistance and low UV resistance unless special modifiers are used. Japanese Patent 8,183,054 assigned to JSP Corp. of Japan describes a flat, foamed polycarbonate sheet. Furthermore, commercially available sheets of PC laminated with acrylic are produced by Tsutsunaka Plastic of Tokyo, Japan. SUMMARY OF THE INVENTION It is an object of the present invention to provide a polycarbonate (PC) sheet material which can be used as an outdoor building material which overcomes the limitations and disadvantages of existing materials. A system for the production of the PC sheet is also provided. There is provided in accordance with a preferred embodiment of the present invention a rigid polycarbonate (PC) sheet includinf a foamed PC layer, and a second PC layer co-extruded with the foamed PC layer. Moreover, in accordance with a preferred embodiment of the present invention, the second PC layer includes UV-resistant material. Furthermore, in accordance with a preferred embodiment of the present invention, the sheet is one of a group including: a flat sheet, a corrugated sheet and a multi-wall sheet. Additionally, in accordance with a preferred embodiment of the present invention, the rigid PC sheet further includes a third PC layer co-extruded with the foamed PC layer on the side opposite to the second PC layer. Moreover, in accordance with a preferred embodiment of the present invention, the third PC layer includes UV-resistant material. Furthermore, in accordance with a preferred embodiment of the present invention, the rigid PC sheet further includes a third PC layer co-extruded with the second PC layer on the side opposite to the foamed PC layer. Additionally, in accordance with a preferred embodiment of the present invention, the third PC layer includes UV-resistant material. There is provided in accordance with a preferred embodiment of the present invention a method for production of a rigid polycarbonate (PC) sheet, the method comprising the steps of feeding a first PC material into a first extrusion line, foaming the first PC material, feeding a second PC material into a second extrusion line, co-extruding the first PC material and the second PC material into a melt, extruding the melt through an extrusion die, and solidifying the melt into a rigid sheet. The second PC material forms a layer on the first PC material. Moreover, in accordance with a preferred embodiment of the present invention, the step of foaming includes adding a chemical blowing agent to the first PC material. Furthermore, in accordance with a preferred embodiment of the present invention, the step of foaming includes adding a liquid blowing agent to the first PC material. Additionally, in accordance with a preferred embodiment of the present invention, the step of foaming includes injecting liquefied gases at sufficiently high pressure into the first PC material. Moreover, in accordance with a preferred embodiment of the present invention, the step of foaming includes adding a chemical blowing agent to the first PC material prior to the first PC material being fed into the first extrusion line. Furthermore, in accordance with a preferred embodiment of the present invention, the method includes at least one additional step of thermoforming the rigid sheet. The at least one additional step of thermoforming is performed on-line or off-line. There is provided in accordance with a preferred embodiment of the present invention, a sheet material for outdoor building use comprising a foamed PC layer, and a second PC layer co-extruded with the foamed PC layer. Moreover, in accordance with a preferred embodiment of the present invention, the second PC layer includes UV-resistant material. Furthermore, in accordance with a preferred embodiment of the present invention, the sheet is one of a group including: a flat sheet, a corrugated sheet and a multi-wall sheet. Additionally, in accordance with a preferred embodiment of the present invention, the thickness of the foamed PC layer is 1 - 10 millimeters, and the thickness of the second PC layer is 25 - 100 microns. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which: Fig. 1 A is a schematic cross-section illustration of a flat polycarbonate (PC) sheet, according to a preferred embodiment of the present invention; Fig. 1 B is a schematic cross-section illustration of a corrugated polycarbonate (PC) sheet, according to a further preferred embodiment of the present invention; Fig. 2 is a block diagram illustration of a system for the production of a polycarbonate (PC) sheet, according to a preferred embodiment of the present invention; Fig. 3 is a schematic flowchart of the operation of the system of Fig. 2; Figs. 4 and 5 are graphs of results of an accelerated weathering test on a PC sheet, according to a preferred embodiment of the present invention; and Fig. 6 is a table of results of a heat insulation test on a PC sheet, according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION Reference is now made to Fig. 1A, which is a schematic illustration of a cross-section of a flat polycarbonate (PC) sheet 10, according to a preferred embodiment of the present invention. The polycarbonate (PC) sheet 10 comprises a rigid bulk foamed PC sheet 12 and a rigid skin layer 14 of UV protective PC. The skin layer 14 is applied via co-extrusion, but it will be apparent to those skilled in the art that any other suitable method for applying the skin layer may be utilized. In a non-limiting example, the skin layer 14 of UV protective PC has a thickness of 30 microns. In a preferred embodiment, a PC sheet for outdoor building is preferably composed of a 30-micron layer of UV protective PC and a 2-mm layer of foamed PC. The PC sheet 10 is shown as being flat, having been extruded through a flat sheet die. It will be appreciated that any shape of sheet may be produced, depending on the die used. Reference is now made to Fig. 1 B, which is a schematic illustration of a cross-section of a corrugated polycarbonate sheet. The flat polycarbonate sheet 10 of Fig. 1 has been thermoformed into a corrugated sheet. The foamed PC sheet 12 and the skin layer 14 are thermoformed together into a corrugated sheet. In alternative embodiments, thermoforming may be used to transform the flat PC sheet 10 of Fig. 1 into complex or small size articles, such as, but not limited to, multi-wall sheets, roof ridges, roof tiles, flashings and accessories. Fig. 2 is a block diagram illustration of a system for the production of a polycarbonate (PC) sheet, according to a preferred embodiment of the present invention. The system comprises an extruder 20, a co-extruder 22, a flat sheet extrusion die 24, a thermoformer 26, an edge trimmer 28, a cross cutter 30 and a stacker 32. Reference is now made additionally to Fig. 3, which is a schematic flowchart of the operation of the system of Fig. 2. In operation, a polycarbonate (PC) material 34 is fed (step 100) into the extruder 20. In a preferred embodiment of the present invention, a foaming agent 36, such as a chemical blowing agent, is fed (step 102) with the PC material 34 into the extruder 20. Other foaming agents can be used, for example, but not limited to, liquid blowing agents, which are chemicals that decompose at the extrusion temperatures and release a gas that causes foaming. In another embodiment, the foaming could be achieved by using "physical blowing", which is the injection of water or liquefied gases, such as, but not limited to, C0 2 and N 2 . In this embodiment, no chemical reaction is used to cause the foaming. In a further alternative embodiment, the PC material already contains the chemical blowing agent, and the addition of a blowing agent on-line can be omitted. A special PC compound 38 with increased UV resistance properties is fed (step 104) into the co-extruder 22. Proximate the exit of extruder 20, the UV protective PC compound 38 is combined (step 106) with the PC material 34 into a melt. This process, known as skin layer UV co-extrusion, is well known in the art. The melt consisting of the PC material 34 and the UV protective PC compound 38 is forced (step 108) through the flat sheet extrusion die 24. At the exit of the melt from the extrusion die 24, the PC material 34 foams due to the expansion of the gas released by the foaming agent 36. The UV protective PC compound 38 does not foam. The melt is then solidified (step 110) into a flat sheet. The flat sheet can be used as is or can be further thermoformed either on-line or off-line. On-line thermoforming into corrugated sheets and multi-wall sheets is the preferred method for sheets for building. Off-line thermoforming of more complex or small size articles is the preferred method for producing roof ridges, roof tiles, flashings and accessories. If thermoforming is used, the flat sheet is passed (step 112) through the thermoformer 26. The corrugated (or flat) sheet is trimmed (step 114) by the edge trimmer 28, cut (step 116) to its final size by the cross cutter 30 on-line and stacked (step 118) by the stacker 32 on pallets for shipment. The properties of a PC sheet comprising foamed PC and a skin layer of UV protective PC make it suitable for use as an outdoor building material. It is well known in the art that PC is resistant to fungus, microorganisms, humic acids and termite attack. It is also known that PC is water-resistant and impermeable. PC can be colored internally, with no need to paint or coat. PC is suitable for contact with food. Furthermore, since no hazardous materials are used in the production or disposal of PC, and since it is fully recyclable, PC is an environmentally friendly material. Another advantage of PC is that its service temperature is above 100°C. This is very important for dark colored building materials that are subject to strong solar radiation and may heat up to temperatures of 80 - 90°C. The properties mentioned hereinabove are described in L. Bottenbruch, Engineering Thermoplastics: Polycarbonates, Polyacetals, Polyesters. Cellulose Esters, Carl Hanser Verlag (1996) pp. 177 - 181 , 194, 198, 200, 254 and 259. It is known in the art that PC has good sound insulation properties. The skin layer of UV protective PC provides UV and weathering resistance. An accelerated weathering test using the QUV Accelerated Weathering Tester produced by Q-Panel Lab Products of Cleveland, Ohio, USA was conducted on a PC sheet according to a preferred embodiment of the present invention. The test exposes materials to alternating cycles of light and moisture at controlled elevated temperatures, thereby reproducing the damage caused by sunlight, rain and dew. The test involved exposing the PC sheet to UV exposure (UVB, 20h radiation, 4h condensation, 45°C), and then testing tensile strength at yield (ASTM D-638 - 10 mm/min) and elongation at break (ASTM D-638 - 10 mm/min). The results are shown in Figs. 4 and 5, to which reference are now made, which are graphs of tensile strength (in MPa) and elongation (in %), respectively, per hours of QUV exposure. The conclusion of the test was that the PC sheet retains its mechanical properties after 1500 hours of QUV exposure. It is well known that PC, being a plastic, is non-corrosive. Furthermore, as described in Chemical Resistance - Thermoplastics, 2 nd edition, Plastics Design Library USA, (1994) vol. 1 , p. 404, PC is resistant to acid rain and air pollution. According to the Applicant's internal impact tests, the PC sheet of the present invention is ductile and resilient, as well as resistant to hail and wind. A falling bag test according to the Australian/New Zealand standard, AS/NZS 4040.4:1996 "Design and installation of sheet roof and cladding / part 3: plastics", was conducted on a PC sheet according to a preferred embodiment of the present invention. The sandbag did not penetrate the PC sheet, and no holes nor splinters were formed, leaving the PC sheet intact. Reference is now made to Fig. 6, which is a table of results of a heat insulation test conducted by the Standards Institution of Israel on a PC sheet according to a preferred embodiment of the present invention. The standard test (ASTM-C 177-85) was conducted on two PC sheets of approximately 30x30x3 cm, and it was found that the PC sheet has good heat insulation due to its foam structure. Standard burn tests (ASTM-D 635 - 91) were conducted by Warnock Hersey Inc. on PC sheets according to a preferred embodiment of the present invention. The results, that foamed polycarbonate had an average extent of burn of 14.8 mm, show that the PC sheet is fire resistant. Self-venting properties allow it to melt and disappear in extreme heat, thereby allowing smoke to escape from a burning building, and reducing the likelihood of injuries due to smoke inhalation. It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow:

Claims: CLAIMS 1. A rigid polycarbonate (PC) sheet comprising: a foamed PC layer; and a second PC layer co-extruded with said foamed PC layer. 2. A rigid PC sheet according to claim 1 , wherein said second PC layer comprises UV-resistant material. 3. A rigid PC sheet according to claim 1 , wherein said sheet is one of a group including: a flat sheet, a corrugated sheet and a multi-wall sheet. 4. A rigid PC sheet according to claim 1 , further comprising a third PC layer co-extruded with said foamed PC layer on the side opposite to said second PC layer. 5. A rigid PC sheet according to claim 4, wherein said third PC layer comprises UV-resistant material. 6. A rigid PC sheet according to claim 1 , further comprising a third PC layer co-extruded with said second PC layer on the side opposite to said foamed PC layer. 7. A rigid PC sheet according to claim 6, wherein said third PC layer comprises UV-resistant material. 8. A method for production of a rigid polycarbonate (PC) sheet, the method comprising the steps of feeding a first PC material into a first extrusion line; foaming said first PC material; feeding a second PC material into a second extrusion line; co-extruding said first PC material and said second PC material into a melt, whereby said second PC material forms a layer on said first PC material; extruding said melt through an extrusion die; and solidifying said melt into a rigid sheet. 9. The method according to claim 8, wherein said step of foaming comprises adding a chemical blowing agent to said first PC material. 10. The method according to claim 8, wherein said step of foaming comprises adding a liquid blowing agent to said first PC material. 11. The method according to claim 8, wherein said step of foaming comprises injecting liquefied gases at sufficiently high pressure into said first PC material. 12. The method according to claim 8, wherein said step of foaming comprises adding a chemical blowing agent to said first PC material prior to said first PC material being fed into said first extrusion line. 13. The method according to claim 8 wherein said method of production comprises at least one additional step of thermoforming said rigid sheet. 14. The method according to claim 13 wherein said at least one additional step of thermoforming is performed on-line. 15. The method according to claim 13 wherein said at least one additional step of thermoforming is performed off-line. 16. A sheet material for outdoor building use comprising a foamed PC layer; and . a second PC layer co-extruded with said foamed PC layer. 17. A sheet material according to claim 16, wherein said second PC layer comprises UV-resistant material. 18. A sheet material according to claim 16, wherein said sheet is one of a group including: a flat sheet, a corrugated sheet and a multi-wail sheet. 19. A sheet material according to claim 17, wherein the thickness of said foamed PC layer is 1 - 10 millimeters, and the thickness of said second PC layer is 25 - 100 microns.

Inventors: BEN ZVI GUY, RIOS PABLO FABIAN, BEN ZVI, GUY, RIOS, PABLO, FABIAN
Applicants: BEN ZVI GUY, PALTOUGH IND 1998 LTD, RIOS PABLO FABIAN, BEN ZVI, GUY, PALTOUGH INDUSTRIES (1998) LTD., RIOS, PABLO, FABIAN
Application year: 1999
Main classification: B32B3
IPC codes: B29D7, B32B3