WO2004048084A1

WO2004048084A1 - A coated wood-based plate, method of its production and use

Info

Publication number: WO2004048084A1
Application number: PCT/FI2003/000899
Authority: WO
Inventors: Timo Ollila; Marjaliisa Asikainen; Jouko Hannukainen; Ilkka Tarvainen; Risto Jaakkola; Merja Savola; Petri Andersen
Original assignee: Schauman Wood Oy; Bemis Valkeakoski Oy
Priority date: 2002-11-25
Filing date: 2003-11-24
Publication date: 2004-06-10
Also published as: AU2003283456A8; AU2003283456A1; FI20022095A0; FI20022095A

Abstract

A coated wood-based plate comprises a plate-like base (1) of wood material, on top of which, outermost, is attached a film (2c) containing polyolefin and polyamide. The film (2) is a polyolefin matrix into which the polyamide is blended to a discontinuous phase.

Description

A coated wood-based plate, method of its production and use

The invention relates to a coated wood-based plate, which is of the type presented in the preamble of the appended claim 1. The invention also relates to a method for coating a wood-based plate, which is of the type presented in the preamble of the appended claim 9. The invention also relates to the use of a coated wood-based plate.

It is known to coat wood-based plates, such as plywood, chipboard, fibreboard, or other boards, such as boards of sawn wood, with a plastic coating, to improve their surface properties, for example wear resistance or moisture resistance. Thus, the coating film should be durable but still firmly adherent to the surface of the wood-based material.

Coated wood-based plates are used, for example, as wall and floor material for various cargo spaces in the transportation equipment industry, as walls for concrete casting moulds, and for other purposes. Many thermoplastics are promising in the sense that a suitable coating can be selected from them, according to the properties required of the product in the use. Thermoplastics can also be moulded by means of heat and melted/softened and solidified by adjusting the temperature, by means of which they can also be made to adhere to different surfaces. Thermoplastics can also be processed in the molten state, which makes it possible to apply them to surfaces by extrusion and to form various profile shapes.

For example the international publication WO 96/32257 discloses a method for manufacturing a composite of plastic and plywood, in which the plywood surface is subjected to a special treatment (drying and crushing of the surface cells), after which a plastic film coated with a thermoplastic used as a hot-melt adhesive, such as a polyester film, can be attached to the plywood surface by means of heat and pressure.

Finnish patent application 980640, to which correspond e.g. international publication WO 99/48683 and US patent 6,451 ,444, dis- closes a plate whose coating is provided by glueing a polyamide film onto the surface of the base by means of a reactive adhesive layer. The polyamide film serves as a good base to other layers, for example polyolefin layers, whereas the reactive adhesive, which is preferably impregnated in a carrier to form a uniform adhesive film, adheres well both to the wood-based base and to the polyamide polymer. According to these publications, the outermost polyolefin layer may be a film of polypropylene.

European patent 595706 discloses a coated wood material, in whose outermost layer a mixture of polyamide and a polyolefin, particularly polypropylene, is recommended for use. The polyamide forms a matrix in which the polyolefin is dispersed. As a preferable quantity of polyamide, 50 to 70 wt-% is mentioned. Good resistance to heat, chemicals and moisture as well as mechanical strength are mentioned as advantages of the coating.

According to the patent, the outermost layer is formed in a known way by extrusion. To secure the adhesion to the wood base, a thermoplastic film is used, formed by the outermost layer in the coextru- sion and serving as an adhesive. The resulting two-layer structure can be hot pressed onto the surface of the wood material, wherein the thermoplastic film underneath it adheres the film to the wood material. In the patent, a particular commercial mixture of polyamide and polyolefin is used for the extrusion.

It is the aim of the invention to present a coated product in which the wear resistance can be achieved in a simpler and less expensive way. To achieve this purpose, the product is primarily characterized in what will be presented in the characterizing part of the appended claim 1.

In the surface film, a matrix is formed by the polyolefin, such as polyethylene or polypropylene, and the polyamide is blended with it to form a discontinuous phase. As the raw material, it is possible to use solid polyamide particles, which have not been molten in the same way as the polyolefin matrix in connection with the formation of the surface film by the melt processing, but they have maintained their solid form. Consequently, it can be stated that the polyamide particles, even when added in small amounts, clearly improve the wear resistance of the polyolefin surface film. Such particles used can be of e.g. recycled polyamide, wherein it is possible to utilize a raw material which would otherwise be treated as reject. As the raw material, it is not necessary to use any extrudable commercial polymer blend quality. The result is an inexpensive product which has improved wear resistance and which is very suitable for products intended for use under conditions under which they will come to a wearing contact with another material, particularly as so-called concreting plywood.

As to the other advantageous embodiments of the invention, reference is made to the appended dependent claims and the description hereinbelow. The surface film can be attached by means of a thin polyamide film and a reactive adhesive to the surface of the base. The polyamide film has good adhesion to the polyolefin film, and the reactive adhesive has good adhesion to both the polyamide film and the underlay wood surface.

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a coated wood-based plate according to the invention in a cross section,

Fig. 2 shows a second embodiment in a cross-section,

Fig. 3 shows a third embodiment in a cross-section,

Fig. 4 shows a surface film in a cross-section in a larger scale, and

Fig. 5 shows one principle for coating the plate by the method according to the invention. Figure 1 shows a coated wood-based plate, which is formed of a plate-like base 1 of a wood material, and a coating 2 on top. In this alternative with the simplest structure, the coating 2 has a thermoplastic surface film 2c which is glued by means of a reactive adhesive layer 2a to the surface of the base 1. There are no other films between the reactive adhesive layer 2a and the base 1. In the surface film 2c, the matrix consists of polypropylene (PP) mechanically blended with polyamide (PA). The structure of the surface film will be described in more detail below. Instead of polypropylene, it is possible to use polyethylene (PE).

The adhesive layer 2a consists of a known reactive adhesive, which is most commonly curable by heat. Examples to be mentioned include phenolic resins, polyester resins, epoxy resins, isocyanate adhesives, and polyurethane adhesives, which adhere well to polyamide. Most preferably, the reactive adhesive in an inert liquid form is impregnated in a carrier material with a large surface, such as paper or other porous thin structures, so that it can be placed as a uniform film between the base 1 and the surface film 2c before the adhesive is brought to the adhesive state by means of external factors, such as temperature. The base 1 , in turn, may be of a wood- based material, such as plywood, chipboard, fibreboard, or other boards consisting of larger of smaller wood-based elements joined together. The base may also be of sawn wood. Similarly, it is possible to consider bases made of the above-mentioned materials by lamination, as well as bases in which only the surface layer is of a wood-based material. The base 1 is, in its structure, a stiff plate whose two dimensions perpendicular to each other (width and length) are greater than its dimension in the direction perpendicular to these (thickness).

Figure 2 shows a second embodiment, in which the layer glued to the base 1 by means of a reactive adhesive layer 2a is a laminate of two layers. Underneath the surface film 2c there is another thermoplastic film, a polyamide film 2b. The polyamide film may be a film of a known polyamide quality, which can be glued as a ready solid film onto the base 1. The films may be already laminated to each other, for example formed by coextrusion, before the glueing of the coating to the base. The surface film 2c is thus the above-mentioned mixture of PP/PA or PE/PA, and the film 2b underneath it is a PA film.

Figure 3 shows an embodiment in which a coating 2 is formed on both sides of the base 1. The coating on the reverse side, which is not intended as the wear surface of the product, is indicated with the reference number 4. The coating may have a similar structure on both sides, or on one side it may be an ordinary PP/PA or PE/PA laminate, in which the polyolefin film 4c is outermost (without a blended PA phase) and the polyamide film 4b is innermost. This coating is intended as the coating of the reverse side to prevent warping of the plate. The coatings on both sides maintain the moisture equilibrium on both sides of the plate. Also the films on the reverse side may be glued to the surface of the base 1 by means of a reactive adhesive layer 4a. It is also possible to provide a printing on the surface of the polyamide film 4b on the reverse side.

Figure 4 shows the surface film 2c in a cross-section in a larger scale. Polyamide particles 3 are mechanicalle blended in the matrix polymer of the surface film 2c of polypropylene and polyethylene. The polyamide particles may remain solid when the surface film 2c is formed by a melt processing method, such as extrusion. When forming the film 2c, the polyamide particles 3 are blended with polypropylene plastic, which melts during the film formation and is solidified as a matrix. The polyamide particles 3 may consist of recycled polyamide ground to a sufficiently fine particle size of e.g. 0.1 to 1 mm. The polyamide may originate e.g. from waste pieces of laminate production. The use of recovered polyamide improves the friendliness to the environment _as_welJ as the economic efficiency. The content of the polyamide particles 3 in the surface film 2c is about 5 to 40 wt-%, preferably about 25 to 35 wt-%. The thickness of the film 2c is 100 to 2000 μm, preferably 800 to 1200 μm.

Figure 5 shows one method for coating the base 1. The base 1 , the adhesive film 2a impregnated with a reactive adhesive, and the surface film 2c, or the laminate of the surface film 2c and a polyamide film 2b, are piled on top of each other and compressed together by means of pressure and heat (arrow P). In the laminate of the polyamide film 2b and the surface film 2c, the films are directly attached to each other before the glueing.

Alternatively, the lowest polyamide film 2b and the surface film 2c coming on top of it can be directly attached to each other in the same compression step in which the polyamide film 2b is glued to the base 1 by means of the adhesive film 2a.

For the glueing of the layers to the base 1 and to each other, it is possible, in all the above-mentioned methods, to use normal hot presses, in which the base and the layers coming on top of it are compressed against each other at a given pressure between pressure contact areas, wherein the layers coming on top of the base 1 are simultaneously subjected to a given temperature. At the same time, the outer surface can be provided, by means of the pressure contact area, with a desired embossing or shaping, or it may be smooth. The layers for the reverse side can also be attached to the base 1 by hot pressing.

The adhesive film 2a between the films 2b, 2c and the base 1 may be a one-layer film, or it may be formed of several layers placed on top of each other, for example according to the desired quantity of adhesive. These layers may be provided with thin intermediate layers which do not contain any adhesive but which adhere well to the adhesive layers. Suitalbe adhesive quantities are e.g. 10 to 300 g/m², preferably 50 to 150 g/m². The thickness of the polyamide film 2b is generally less than 200 μm, e.g. 15 to 150 μm, and it is normally thinner than the surface film 2c intended to be wear_resistant,-

The plate-like base 1 with a standard thickness, shown in the figures, is straight. However, it is also possible to coat curved plate-like bases by the same principles, because the flexible films used in the coating (thermoplastic films and adhesive films) conform well to the different shapes, whether they are placed as separate films or as a prefabricated multi-layer structure onto the base. If the wood base 1 is a plywood board, its thickness is normally about 9 to 30 mm.

The above-described products, whose surface film 2c is of the described PP/PA or PE/PA composite, are preferably used as the surface defining the casting cavity, i.e. as the concrete casting plate, whose surface film 2c comes to contact with the concrete. The aim is to use the board several times for different castings. When the platelike base is a plywood board, it is called concreting plywood. The polyamide in the surface film 2c increases the wear resistance of the coating and increases the number of times that the concrete casting plates can be used by 5 to 50 % when compared with a PP or PE surface film with the same thickness.

The plate according to the invention can also be used as a floor in transportation equipment, for example as a floor in the load space of a vehicle, with the composite surface film as the wear surface.

Claims

Claims:

1. A coated wood-based plate comprising a plate-like base (1) of a wood material, onto which a film (2c) of polyolefin and polyamide has been attached outermost, characterized in that the film (2c) comprises a polyolefin matrix in which the polyamide is blended to form a discontinuous phase.

2. The plate according to claim 1 , characterized in that in the outermost film (2c), the polyamide content is 5 to 40 wt-%, preferably 25 to 35 wt-%.

3. The plate according to claim 1 or 2, characterized in that the coating (2) is glued to the surface of the base (1) by means of a reactive adhesive layer (2a).

4. The plate according to claim 3, characterized in that the coating (2) comprises an inner polyamide film (2b) which is glued to the surface of the base (1) by means of the reactive adhesive layer (2a).

5. The plate according to claim 3 or 4, characterized in that the reactive adhesive layer (2a) is based on a fenolic resin, a polyester resin, an epoxy resin, an isocyanate adhesive, or a polyurethane adhesive.

6. The plate according to claim 3, 4 or 5, characterized in that the reactive adhesive layer (2a) is an adhesive film impregnated with a reactive adhesive, such as an impregnated paper.

7. The plate according to any of the preceding claims, characterized in that the base (1) is a plywood board.

8. The plate according to any of the preceding claims, characterized in that the opposite side also comprises a coating (4) with an outermost film (4c) which contains polyolefin.

9. A method for coating a wood-based plate, in which a plate-like base (1) of a wood material, such as plywood, chipboard, fibreboard, or sawn wood, is provided with a coating (2) containing at least one thermoplastic layer, having an outermost film (2c) containing polyamide and polyolefin, characterized in that the film (2c) is a polyolefin matrix in which the polyamide is blended to form a discontinuous phase.

10. The method according to claim 9, characterized in that the coating is formed by glueing a reactive adhesive layer (2) on the base (1).

11. The method according to claim 10, characterized in that the coating is glued by attaching the lowermost polyamide film (2b) to the base (1) by means of the reactive adhesive layer (2a).

12. The method according to claim 10 or 11, characterized in that the coating is glued onto the base (1) by means of an adhesive film (2a) impregnated with a reactive adhesive, such as a paper impregnated with the reactive adhesive.

13. The method according to any of the preceding claims 9 to 12, characterized in that the film (2c) is formed by blending the polyolefin matrix with 5 to 40 wt-% of polyamide.

14. The method according to any of the preceding claims 9 to 12, characterized in that the film (2c) is formed by melt processing of the polyolefin matrix at a temperature at which the polyamide particles (3) blended in the matrix remain solid.

15. The method according to claim 14, characterized in that recycled polyamide is used as the polyamide particles.

16. The use of a plate according to any of the claims 1 to 8, or a plate made by a method according to any of the claims 9 to 15, as the surface coming into contact with concrete to be cast in a concrete casting mould.