CORRUGATED SHEET, METHOD FOR ITS PRODUCTION AND PRESS INSTALLATION USED IN THIS METHOD

Abstract: A corrugated sheet, for example for use as a roof covering or outside wall cladding, consists of 50-80% separate cellulose fibres and 20-50% polyurethane. The thickness of the sheet is between 2 and 5 mm, preferably about 3 mm. To produce this sheet, a nonwoven mat comprising cellulose fibres is sprayed on two sides with polyurethane, the sprayed mat is guided between two corrugated conveyor belts which are situated in a chamber in which the temperature is kept between 70 and 90 DEG C, and the corrugated sheet thus formed is conveyed out of the said chamber and is sawn into pieces of desired length.

Description: Title: Corrugated sheet, method for its production and press installation used in this method The invention relates firstly to a corrugated sheet which comprises fibres and binder. Corrugated sheets are frequently used as a roof covering and also as outside wall cladding. Corrugated sheets are in widespread use, in particular in the agricultural sector. A conventional material for corrugated sheets is eternite (fibre-reinforced cement) which is 6 to 7 mm thick. These known corrugated sheets have a number of drawbacks. They absorb 25-40% moisture. They are not inherently strong enough on a roof to be walked on between the purlins, and they are difficult to fit owing to their considerable weight. A solution has been found to avoiding the problem of a quadruple overlap on a roof with fibre-reinforced, cement-bonded corrugated sheets, namely bevelling at a corner, which represents a time- consuming job. Owing to the considerable thickness and rigidity of eternite sheets, overlaps do not fit together, resulting in a gap being formed. Finally, eternite corrugated sheets have the drawback of producing hazardous dust when they are sawn to size, and during this operation people in the area have to wear a dust mask. The object of the invention is to avoid the abovementioned drawbacks and to provide a corrugated sheet consisting of fibres and binder which is considerably more lightweight and stronger than cement-bonded corrugated sheets, which is flexible and which absorbs a negligible percentage of moisture, and over which it is possible to walk between the purlins (when used on a roof). According to the invention, to this end the corrugated sheet is characterized in that it consists of 50-80% separate cellulose fibres and 20-50% polyurethane, and in that the thickness of the sheet is between 2 and 5 mm. Cellulose fibres may be derived from flax, elephant grass, jute, hemp, sisal and the like. In our area, flax will be particularly suitable. The corrugated sheet preferably consists of 65-75% cellulose fibres and 25-35% polyurethane. The corrugated sheets according to the invention can be processed using standard woodworking machines. It can be screwed without predrilling (with cement-bonded corrugated sheets, holes must first be predrilled). Due to their flexibility, the relatively thin corrugated sheets can fit together without a gap when screwed through. Bevelling is not required for a quadruple overlap. The weight is only 2 to 2.5 kg/m 2 , while the strength is 3 to 4 times greater than that of cement-bonded corrugated sheets. Owing to the low weight and the high strength, it is possible to use a continuous production operation to produce a product which is in principle endless. No special accessories are required to raise corrugated sheets onto the roof, in view of the low weight (less than 25 kg). The invention also relates to a method for producing a corrugated sheet according to the invention. The intention is for it to be possible to carry out this process very quickly and efficiently using inexpensive means. According to the invention, to this end the method is characterized in that a nonwoven material comprising carded and needled cellulose fibres is sprayed on two sides with polyurethane, the sprayed mat is guided between two corrugated conveyor belts which are situated in a chamber in which a temperature of between 70 and 90°C is maintained, and in that the corrugated sheet thus formed is conveyed out of the said chamber and is sawn into pieces of desired length. The method is suitable in particular for a continuous process, in which case the corrugated sheet formed is sawn into pieces using a saw which moves with the corrugated sheet. Finally, the invention relates to a press installation for forming a corrugated sheet with the aid of the method described above. According to the invention, this press installation comprises a chamber with a temperature-control system, two belt conveyors, which are arranged one above the other in the said chamber, the outwardly directed surface of which is corrugated and in which the distance between the parts facing one another is between 2 and 5 mm, and a feed device for guiding a mat into the chamber between the said parts, means for spraying the mat on two sides with a binder, such as polyurethane, before the mat enters the gap between the said parts. In a technically advantageous embodiment of the belt conveyors, the latter are composed of metal links which are connected to one another by flexible rubber or plastic pieces. Preferably, a pressure-exerting conveyor is arranged inside each of the belt conveyors, which pressure-exerting conveyor can move synchronously with the belt conveyor and is composed of chain links, to the outer surface of which blocks are attached, bearing against a said part. The invention will now be explained in more detail with reference to the figures, in which: Figure 1 shows a diagrammatic view of the device. Figure 2 shows a longitudinal section through part of the press. In Figure 1 , a continuous nonwoven mat of carded and needled cellulose fibres is denoted by 1. Carding and needling methods for orienting the fibres and making the mat cohesive are generally known per se. The mat 1 is guided into a chamber 5, which is indicated by dot-dashed lines and in which a temperature of approximately 80°C (70-90°C) is maintained, by means of a diverting roller 2 and a roller 4 which is driven by a motor 3 with transmission. Inside the chamber 5, polyurethane is sprayed onto two surfaces of the nonwoven mat 1 by means of two spraying devices 6 and 7. Obviously, this may also take place outside the chamber 5. In the chamber 5, there is a corrugated-sheet press comprising two belt conveyors 8 and 9 which are arranged one above the other and two pressure-exerting conveyors 10 and 1 1, each arranged inside a belt conveyor 8 and 9, respectively. Each of the belt conveyors 8, 9 comprises a belt which is guided around diverting wheels 12, 13 and comprises metal corrugated parts 14 and connecting parts 15 which are formed from flexible material (rubber or plastic) with a corrugated shape over part of the surface. The metal corrugated parts 14 are connected to the flexible connecting parts 15 in such a manner that the outwardly facing surface of the belt conveyors is corrugated, with a corrugation peak of one conveyor 8 always fitting into a corrugation valley of the other conveyor 9. A distance of, for example, 3 mm, into which the nonwoven mat which has been sprayed with polyurethane is introduced, is left free between the mutually facing parts of the belt conveyors 8, 9. On two sides, the flexible connecting parts 15 have L-shaped parts 16 which fit into recesses in metal corrugated parts 14 and are blocked by L-shaped strips 17 which are attached to the parts 14 by bolts 18. The nonwoven mat 1 - which has now been sprayed with polyurethane - is located in the said gap between the mutually facing parts of the conveyor belts 8 and 9, which are guided around diverting rollers 12, 13, one of which is driven. The diverting rollers 12, 13 rotate in opposite directions, in such a manner that the nonwoven mat - as seen in the figure - is conveyed towards the right. The pressure-exerting conveyors 10, 1 1 comprise endless chains which are guided around sprocket wheels 20, 21, one of which is driven in such a manner that the endless chains move in the same direction as the belt conveyors 8, 9 inside which the pressure- exerting conveyor in question is situated. Pressure-exerting blocks 22 are attached to the chains of the pressure-exerting conveyors, which blocks, during operation, prevent mutually facing parts of the conveyor belt 8. 9 from moving away from one another. While the nonwoven mat is being conveyed inside the chamber 5, which lasts for 3 to 5 minutes, the polyurethane, which is applied in liquid form, will cure. The result is a lightweight, continuous corrugated strip which is about 3 mm thick and comprises cellulose fibres which are dispersed separately in the cured polyurethane. The edges of the cured corrugated sheet are cut off by a saw 23, while a computer- controlled saw 24, which moves with the mat. saws the corrugated sheet into pieces of desired length. The product obtained is: 1. lightweight (2 to 2.5 kg/m") and thin (approx. 3 mm), 2. strong (3 to 4 times as strong as a fibre-containing, cement-bonded corrugated sheet with a thickness of 6 to 7 mm and a weight of approx. 12 kg/m 2 ), 3. scarcely absorbs any moisture (approx. 2% instead of 25-40%) in the case of a cement-bonded, fibre-containing corrugated sheet). 4. can be walked on between the purlins on a roof. 5. can be produced in endless form due to the low weight, the high strength and the production technology employed, 6. in view of its low weight, can be fitted to a roof without special accessories, 7. will produce little dust during mechanical processing, and furthermore this dust is not hazardous, so that there is no need to wear dust masks, 8. can be processed using standard woodworking machines (wood saw) and can be provided with screws without holes having to be predrilled, 9. is so flexible that overlapping parts can be pressed together without a gap (when screwed through), 10. can be used without problems with four locally overlapping pieces, 1 1. has a uniform appearance and identical colour all the way through and does not have to be provided with a coating. Significant advantages of polyurethane are that it does not contain a solvent, that there is no evaporation of hazardous substances and that it can be obtained from potato starch. In the end product, the cellulose fibres are substantially separate from one another, in contrast to the nonwoven starting mat. As a result of the production process with special press described above, the corrugations on the die and mating die sides are identical, so that both surfaces of the product are identical to one another. The product cures inside the press in 3 to 5 minutes, representing a huge advantage over the approximately 28 days required for a cement- bonded corrugated sheet. It is possible to use short fibres. In the case of the possible starting plant flax, the long fibres are suitable for producing linen, while the waste - the short fibres - can be used for the production of the corrugated sheets according to the invention.

Claims: Claims 1. Corrugated sheet produced from fibres and binder, characterized in that it consists of 50-80%) separate cellulose fibres and 20-50%) polyurethane, and in that the thickness of the sheet is between 2 and 5 mm. 2. Corrugated sheet according to Claim 1 , characterized in that it consists of 65-75% cellulose fibres and 25-35%o polyurethane. 3. Corrugated sheet according to Claim 1 or 2, characterized in that the polyurethane is formed by chemical reaction of the isocyanate and a polyol which is derived from potato starch. 4. Corrugated sheet according to one of the preceding claims, characterized in that the thickness of the sheet is between 2.8 and 3.2 mm. 5. Corrugated sheet according to one of the preceding claims, characterized in that the cellulose fibres consist of flax fibres. 6. Method for producing a corrugated sheet according to one of the preceding claims, characterized in that a nonwoven mat comprising carded and needled cellulose fibres is sprayed on two sides with polyurethane, the sprayed mat is guided between two corrugated conveyor belts which are situated in a chamber in which a temperature of between 70 and 90°C is maintained, and in that the corrugated sheet thus formed is conveyed out of the said chamber and is sawn into pieces of desired length. 7. Method according to Claim 6, characterized in that the process takes place continuously and the corrugated sheet formed is sawn into pieces using a saw which moves with the corrugated sheet. 8. Method according to Claim 6 or 7, characterized in that the waste from the method is comminuted and is returned to the fibre stock and processed into the nonwoven mat. 9. Press installation for forming a corrugated sheet with the aid of the method according to Claim 6, 7 or 8, characterized by a chamber (5) with a temperature-control system, two belt conveyors (8, 9), which are arranged one above the other in the said chamber, the outwardly directed surface of which is corrugated and in which the distance between the parts facing one another is between 2 and 5 mm, and a feed device (2, 3, 4) for guiding a mat into the chamber between the said parts, means (6, 7) for spraying the mat on two sides with a binder, such as polyurethane, before the mat enters the gap between the said parts. 10. Press installation according to Claim 9, characterized in that the said belt conveyors are composed of metal links (14) which are connected to one another by flexible rubber or plastic pieces (15). 11. Press installation according to Claim 9 or 10. characterized in that a pressure- exerting conveyor (10; 11) is arranged inside each of the belt conveyors (8, 9), which pressure-exerting conveyor can be driven synchronously with a belt conveyor and is composed of chain links, to the outer surface of which blocks (22) are attached, bearing against a said part of a belt conveyor.

Inventors: TINGA JIPPE, TINGA, JIPPE
Applicants: TINGA JIPPE, TINGA RESEARCH & DEV B V, TINGA RESEARCH & DEVELOPMENT B.V., TINGA, JIPPE
Application year: 2000
Main classification: E04C2
IPC codes: E04C2, E04D3