FIELD OF THE INVENTION

The invention relates to a method for injecting a coating material onto a surface of a material article as defined in the preamble of claim 1 and a method for manufacturing a layered product as defined in the preamble of claim 16 and a layered product as defined in the preamble of claim 20.

BACKGROUND OF THE INVENTION

Known from prior art are various plywoods, ve- neer boards or the like. Known from prior art is the gluing of veneers by various glues, e.g. polyurethane or phenolic glue, for providing a plywood or the like. Further, known from prior art is different types of methods for manufacturing plywoods.

From the previous applications

PCT/FI2009/050132 and PCT/FI2009/050663 are known different films for using as glues or coatings.

US 6645336 discloses the utilisation of extrusion coating.

The publication of International Journal of adhesion and adhesives, 1999, discloses the utilisation of coupling agents such as maleic acid and anhydride to bond damp wood having 6 - 30 % moisture. The coupling agents alter the surface energies of the polymer so that there is improved compatibility between the wood and polymer. However, the overall adhesive properties are still only physical. There is no mention or indication of a chemical bond i.e. ester bond. The coupling agent is simply a polymer modifier to render the poly- mer more hydrophilic. EP1733804 discloses the utilisation of extrusion to form a bond between the molten polymer and epoxy or some other adhesive applied to wood prior to extrusion. The aim is to solve the problem of improving the adhesion. The patent refers to maleic acid and anhydride as polymer modifiers but they also state that this modification is not enough and the overall adhesi ^¬ on is not good enough. Instead the modification is utilised to get better adhesion between the epoxy and molten polymer.

The publication of Silva Fennica Research Articles, 2001, investigates the development of an industrially suitable extrusion method to laminate plywood and veneers. The invention incorporates utilising paper lamination technology (extrusion coating and chill roll) to coat a veneer but there is no reference made to the chemicals or adhesives that can be employed to form a strong adhesive bond between the wood and po ^¬ lymer. Also, no indication of maximum moisture content of the plywood and veneers is indicated. The aim and focus of the design is to lower the bubbling of the coating .

OBJECTIVE OF THE INVENTION

The objective of the invention is to disclose a new type of method for injecting a coating material onto a surface of a material article. Further, the objective of the invention is to disclose a new type of method for manufacturing a layered product. Further, the objective of the invention is to disclose a new type of a layered product.

SUMMARY OF THE INVENTION Methods and a layered product according to the invention are characterized by what is presented in the claims .

The invention is based on a method for inject- ing a coating material onto a surface of a material article. In accordance with the invention the coating material is injected onto the surface of the material article, the coating material contains at least one polymer and a coupling agent, the moisture content of the material article is kept below 10 %, and the coupling agent is activated to its active state in connection with the injection to form chemical bonds, e.g. cova- lent bonds, between the material article and the coupling agent, in preferable embodiment in the molten state. The coupling agent has reactive groups which are reactive with the material article and specially are reactive with the reactive groups, e.g. -OH or -H groups or the like groups, of the material article. In order to avoid de-activated the coupling agent the moisture content of the material article is kept below 10 %.

Further, the invention is based on a method for manufacturing a layered product, e.g. a layered board, wood board, plywood or the like, wherein the layered product comprising multiple veneer layers is formed from a number of veneers in such manner that the veneers are laid one above the other and joined together to form the layered product. In accordance with the invention, the coating material containing at least one polymer and a coupling agent which has reactive groups being reactive with the veneer is injected onto the surfaces of the veneers, the moisture content of the veneers are kept below 10 %, and the coupling agent is activated to its active state in connection with the injection to form chemical bonds between the veneers and the coupling agent in order to gluing the veneers together. Further, the invention is based on a layered product, for example layered board, plywood, wood board or the like, which comprises a number of veneers which are laid one above the other and combined together to form the layered product. In accordance with the invention, the coating material is injected onto the surfaces of the veneers, the coating material contains at least one polymer and a coupling agent which has reactive groups being reactive with the veneer, and the chemical bonds are formed between the coupling agent and the veneers, e.g. -OH groups of the veneers, so that the moisture content of the veneers has been kept below 10 % during the manufacturing of the layered product .

In this context, a material article can be any article, product, pre product or intermediate product. In one embodiment the material article can be selected from the group: a veneer, a board, a layered board, e.g. plywood, a wood article, a part of the wood board, timber, beam, a composite article, a formable product, a fiber product, and their combinations or the like. In one embodiment the material of the material article is selected from the group: natural based material, wood, wood based material, cellulose based material, metal, plastic, plastic based material, composite material and their combinations.

In this context, a layered product can be any layered wood article, layered board, plywood, wood board, panel product, layered composite product or the like. Preferably the layered product is formed of a number of layers, preferably veneer layers, in which the layers are laid one upon the other and glued together .

In this context, a veneer refers to any ve- neer or any layers of a layered product. The veneer can be formed of any material, e.g. natural based material, wood-based material, e.g. birch, spruce, pine, Eucalyptus, bamboo or any wood species, cellulose based material, fiber material, composite material, metal, metal based material, plastic, plastic based ma ^¬ terial or their combinations or the like. In this con ^¬ text, the veneer refers to any layer of the layered product. The thicknesses of the veneer layers can vary. Typically the veneer is a thin layer.

In this context, an injection means any injection, extrusion or the like.

The invention is specifically based on the extrusion/inj ection coating or lamination of the material article, e.g. veneers, or a layered product, e.g. a wood board, or parts of the layered product with molten chemically activated polymer composition so that the overall adhesion is excellent and consists of a combination of physical and chemical bonding, e.g. covalent bonding. The extrusion/injection makes it possible to coat a material article, a veneer, a layered product or a part of the layered product with polymer composition without having to first make a se ^¬ parate adhesive film. The invention is different to the prior art in that the coupling agent injected/extruded in the polymer melt is activated during injection/extrusion or activated before injection/extrusion by utilizing heat, e.g. more than 190 °C, and/or with or without a catalyst and then chemically bonded, e.g. covalent or ester bond, with the material article when in the molten state. To attain this aim, the method according to the invention requires that the moisture content of the material article is kept below 10 %, preferably below 5 %, so that the injected or extruded molten polymer of the coating material can intimately contact the material article and the coupling agent is not deactivated.

In one embodiment the coating material is in the form melt, liquid, suspension, solid or the like. In one embodiment the coating material is in the form of a film. Preferably, the coating material containing polymer and coupling agent can be injected or extruded directly onto the surface of the material article.

In one embodiment the coupling agent is reactive with -OH groups of the material of the material article, e.g. wood or cellulose. In one embodiment the coupling agent is reactive with -H groups of the material of the material article.

Wood is a porous material and it relies on both interlocking and charge interactions to create a proper adhesive bond. In order for the wood bond to be durable for exterior applications the adhesive needs to be wetting and of low enough viscosity to penetrate the wood and also to form a covalent bond with wood. With exiting adhesives there is no proof of chemical bonding and therefore bonding is only a combination of interlocking and weak forces, which explains why guite many of them fail for exterior applications. In the case of phenol formaldehyde resins covalent bonding with the wood is not important as the adhesive penetrates the wood cell wall. However, in the case of thermoplastics penetration in to the cell wall is not possible and therefore to create a bond that will be durable requires also a durable chemical bond, e.g. covalent bond. The bonding mechanisms are not self- excluding and several may be occurring at the same time in a given adhesive bond depending on the circumstances. Therefore the strength of the thermoplastic adhesive bond will depend on both interlocking and charge interactions but the more covalent bonds the higher the overall adhesive strength will be. Without a coupling agent polyethylene only forms physical bonds and no chemical bonds and for the physical bonds to even function at all there would need to be deep penetration, i.e. need for very thick and low viscosity films, which would result overall in weak mechanical properties of the glue-line. Even with ext- rusion coating this depth of penetration is probably not possible.

In one embodiment polymer of the coating material is selected from the group: polyethylene, e.g. LLDPE, LDPE, MDPE, HDPE, polypropylene, bio-plastics, petrochemical based plastics, other suitable polymer or their combinations and copolymers. In one embodiment a melt index of the polymer is in the range 0.2 - 30 g/ 10 min being measured by the method ASTM D 1238 (condition E) . The properties of the polymer laminati ^¬ on /coating will be considerably affected by the melt index and density. Generally in extrusion coating / lamination polyethylene having a melt index 4 - 7.5 g/ 10 min measured at ASTM D 1238 (condition E) are em- ployed. While these melt index properties indicate low viscosity and therefore good penetration into the substrate the mechanical properties of the polymer are not so good. With regards to the extrusion only being utilised as a coating or in flat plywood this is not so much a problem and therefore melt index 4 - 7.5 g/ 10 min are desirable. However, for applications of formable plywood polymers melt index 4 - 7.5 g/ 10 min on reheating and shaping could tear in the plywood. Therefore, for formable plywood melt index 0.3 - 4 g/ 10 min, measured by the method ASTM D 1238 (condition E) , are preferred. In one embodiment the melt index can be 0.3 - 7.5 g/10 min measured at ASTM D 1238 (condition E) . In one embodiment blends and polypropylene are suitable where the melt index is preferably in the range 7 - 15 g/10 min measured by the method ASTM D 1238 (condition L) .

In one embodiment polymer of the coating material is selected from the group: bio-plastics and especially bio-plastics with properties similar to polyethylene and polypropylene. In one embodiment the polymer of the coating material is selected from the group: hot-melts, thermoplastic hot-melts, their com- binations with polyolefins, e.g. with polyethylene, polypropylene and their copolymers, and reactive hot- melts including polyurethane .

In one embodiment the coating material with the coupling agent is a self-adhesive material which adheres on the surface of the material article and which glues the material articles together.

In one embodiment the coupling agent includes organic coupling agents, e.g. isocyanates, amides, imides, acrylates, ^' epoxides, anhydrides, organic acids, monomers and polymer, inorganic coupling agents, e.g. silicates, organic-inorganic coupling agents, e.g. silanes and. titanates, and/or their combinations. The invention is not limited to these only. One preferred coupling agent for the invention is anhydride grafted polyolefin.

In one embodiment of the invention the coating material contains maleic anhydride as the coupling agent. In one embodiment the coating material contains maleic anhydride grafted polyolefin, e.g. MAPP (maleic anhydride polypropylene) or MAPE (maleic anhydride polyethylene) . In one embodiment, maleic acid is converted to maleic anhydride during the activation in the injection or during the manufacturing of the coating material. In one embodiment the amount of the maleic anhydride-polyolefin added in the process of making the coating material can vary between 1-10 %, typically 1-5 % and preferably 2-3 % is sufficient.

In one embodiment the coupling agent is se- lected from the group: grafted silanes, grafted isocyanates, grafted epoxy groups, maleic anhydride grafted polyolefin, maleic anhydride grafted copolymer and their combinations. The invention is not limited to these coupling agents only, they are only examples. Preferably the coupling agent forms covalent bonds, ester bonds and/or covalent bonds via esterification with the material of the material article, e.g. celluloses -OH groups.

In one embodiment of the invention the moisture content of the material article is kept below 5 %, so that the extruded or injected molten polymer of the coating material can intimately contact the material article and the coupling agent is not deactivated .

In one embodiment of the invention the coating material is extruded onto the surface of the material article. In this context, extrusion refers to any extrusion or co-extrusion or the like. In the injection according to the invention there can be used any extrusion method.

In one embodiment of the invention the coating material is injected onto the surface of the material article by the injection device.

In one embodiment of the invention the coupling agent is activated to its active state by means of the heat, catalyst or their combinations. In one embodiment the coupling agent is converted to its active state by means of the heat, catalyst or their combinations. In one embodiment the coupling agent is activated to its active state by means of the heat. In one embodiment the coupling agent is activated to its active state by means of the catalyst. In one embodiment the coupling agent is activated to its active state by means of the heat and catalyst.

In one embodiment of the invention the coupling agent is activated during the injection. In one embodiment the coupling agent is activated during the extrusion .

In one embodiment of the invention the coupling agent is activated before the injection. In one embodiment the coupling agent is activated before the extrusion. In one embodiment the coating material is heated during or before the injection. In one embodiment the material article is heated before the injection of the coating material. In one embodiment the surface of the material article is heated just before the coating material is injected onto the surface in order to remove moisture from the surface. Then the coating material adheres better onto the surface of the material article.

In one embodiment the coupling agent is activated at temperatures of more than 190 °C. In one embodiment of the invention the coupling agent is activated at temperature between 190 to 240 °C. In one embodiment the coupling agent activated is reactive with -OH groups of the material article, e.g. wood.

In one embodiment of the invention the activation of the coupling agent is prepared by a catalyst so that the coupling agent is activated by means of a catalyst. The activation can be made with or without a catalyst. In one embodiment the catalyst is selected from the group: zinc anhydride, hydrated zinc acetate, zinc acetate dehydrate and their derivatives, sodium hypophosphite monohydrate (SHP) , sodium hypophosphite (NaH ₂ P0 ₂ ) , sodium phosphate (NaH ₂ P0 ₄ ) , sodium phosphinate monohydrate (NaH ₂ P0 ₂ H ₂ 0) , potassium phosphate, ammonium phosphate, titanium dioxide and their combinations. The invention is not limited to these catalysts only, they are only examples.

In one embodiment of the invention the coupling agent is activated by means of heat and a catalyst during the extrusion or injection. In one embodiment extrusion temperatures 160 to 240 °C are commonly employed.

In one embodiment the coating material contains at least one additive selected from the group: compatibilizing agent, colour dyes, biocides, fire re- tardants, water repellents, dimensional stabilisers, pigments, nanoparticles , bio-resistant agents, flores- cent particles, fatty acids, modified fatty acids, oils, densification resins, emulsions, hardeners, UV protectors, reinforcement fibers, other wood modification agent and their combinations.

In one embodiment the coating formed of the coating material comprises at least one layer. The coating can consist of one or more layers. In one embodiment the extruded coating material is at least 2- layer co-extruded material which is provided on the surface of the material article, e.g. the veneer or wood board, and where at least one layer contains coupling agent. In one embodiment the coating material can be 3-layer material where at least one outer layer contains coupling agent. The compositions of the different layers can be varied. In a preferable embodiment all the layers of the coating can be prepared by extrusion. For example, the middle layer in the coating can be any suitable material and it can be printed on or even function as a decorative layer. RFID, sensors or barcode indicators can also be incorporated into the extruded coating. There can also be a reinforced layer that comprises of organic fibers different plants or chemically modified organic fibers or polymer fibers having melting point greater than melting point of polypropylene and polyethylene, glass fibers or carbon fibers. The fiber material can be woven or non-woven or separately orientated or non- orientated .

In one embodiment it is provided on the surface of the material article at least one material layer before the coating with the coating material. The material layer can contain any material, e.g. textile (woven and nonwoven) , paper, metal, porous material or their combinations or the like. Creating a composite layered coating of varying properties is advantageous . When co-extrusion is utilised it is possible to restrict the functional group grafted polymer, preferably maleic anhydride grafted polymers, in the desired layers of the coating. Co-extrusion also allows for different polymer grades and additives to be utilised in different layers in order to create polymer coatings/adhesives of optimised mechanical properties. The aim of co-extrusion is to incorporate different materials in each of the layers. The coupling agent can be de-activated if other additives are included in the same layer. Therefore it is desirable to only extrude the bulk polymer and maleated polymer in the layer to be adhered to the material article, e.g. the wood. For example, the middle layer of the coating can contain fire retardants and other materials.

In one embodiment the coating formed of the coating material is cross-linked. In one embodiment the cross-linking is carried out in connection with the coating by injecting. In one embodiment the cross- linking is carried out after the coating, such as the injection. It is also possible to add silane grafted polyethylene and radiation sensitive grade polyethylene in order to cross-link the polymer. These materials are commercially available. In the case of silane versions a catalyst master batch is also required. The aim is to cross-link the polymer, for example between the veneers or on the surface of the veneer, in the layered products, e.g. wood board, and the coatings of the material article. In the other words, in the case of radiation treatment of the coating material on the material article the cross-linking can be performed by microwave, electron-beam, Gamma and UV treatment. However, in the case of cross-linking the polymers between each of the layered product layers much deeper penetration is required. The depth of penetration of E-beam, Gamma and X-ray also mean that any material article that are impregnated with any material modifi- cation treatments can. be cured also by these treatments at the same time as cross-linking the polymers in the material article or its coating material or coating the material article or surrounding the material article with the polymer. For layered product that is not more than, for example, 20 mm thick an E- beam is sufficient. However, in the case of thicker materials X-ray treatment can be applied. Both E-beam and X-ray treatment don't require the polymer to be heated during treatment. Both Gamma and E-beam treatment can damage the wood strength properties; however, this is not the case with X-ray treatment. For example, with X-ray treatment it is possible to cure to depths of 240 mm, depending on the density, at energies of only 3 MeV and low dose rate 2 kGy/min.

Also the material article, e.g. wood board, can be impregnated with chemicals that can then be cured, e.g. cross-linked or polymerized, while cross- linking the other materials in the material article, e.g. wood board. The impregnated materials can be dyes, fire retardants, biocides, dimensional stabilizing chemicals and wood densifying chemicals or the like. Also, wood plasticisers , e.g. monomers and polyethylene glycol, can be impregnated to give the wood a more plastic nature.

While the coupling agent chemically bonds with the wood it is important for the polymer to sufficiently wet the wood so it can intimately be in contact to increase the frequency of the chemical bond. However, modification of the polymer by corona treatment or flame, plasma or ozone treatment can further increase the surface energies of the polymer. This treatment is possible during the extrusion process. In addition to these treatments another on-line modification is ozone treatment.

In this context, a coating refers to any coating layer or lamination layer or the like on the surface of the material article, e.g. the veneer or the layered product.

In one embodiment the method in accordance with the invention is used in the gluing the veneers together for forming layered products and sandwich products .

In one embodiment the method in accordance with the invention is used in the coating of the material article for forming a coating on the surface of the material article.

In one embodiment of the invention the coating material containing coupling agent is provided on the surface of the veneer. In one embodiment the material article is coated with extruded or injected coating material. In one embodiment the parts of the material article is coated with extruded or injected coating material. In one embodiment the layered board is formed of the veneers which are coated by extrusion or by injection as defined above. In one embodiment the veneers are coated by extrusion or by injection directly after the veneer dryer. In another embodiment the veneers are coated on one side only by extrusion or injection, preferably the smooth side to ensure good penetration, or both sides.

In one embodiment the veneers are coated at high temperature (> 240 °C) and high shear, e.g. extruder, twin extruder or co-extruder, followed by vacuum suction or pressure, e.g. hot press, contact press, continuous press with and without a shear zone, to impregnate the polymer into the veneer. In another embodiment the molten polymer is extruded into a high shear mixer, where the veneers are dipped followed by vacuum suction or pressure, e.g. hot press, contact press, continuous press with and without a shear zone. In another embodiment the molten polymer is applied in the form of a spray at high shear followed by vacuum suction or pressure, e.g. hot press, contact press, continuous press with and without a shear zone.

A layered product, e.g. wood board or plywood, according to the invention can comprise veneer layers of different thickness. The thicknesses of the veneer layers can vary. The veneer layers can be arranged in the desired position, i.e. crosswise or lengthwise in the desired order. The veneers can be bonded together using the usual methods, e.g. the cold press (hot coated veneers), hot pressing technique, hot-cold pressing technique, high frequency-cold pressing technique or their combinations, in connection with layered product manufacturing.

In one embodiment to aid high frequency (10- 50 MHz) the polymer dielectric properties can be increased by addition of the following materials ceramic fillers, glass fibres, EVA, MAPE, MAPP, zinc oxide, carbon black and talc. The invention is not limited to these materials only they are only examples.

In one embodiment the coated veneers can be first cooled or the veneers can be utilised hot layed- up to make layered board. The extruded or injected polymer acts as an adhesive to make thermoplastic chemically bonded layered board. The layered board formed is formable on reheating and can be cross- linked to render the glue-line with viscoelastic like properties. The coated veneers can be layed-up while still hot to take advantage of the hot-polymer and its ability to penetrate the veneer layed-up either side. If this technique is carried out rapidly enough then there is no need for hot-pressing or high frequency pressing (10-50 MHz). In one embodiment a cold press, cold rollers or stacking and cooling under pressure is required. The still very hot polymer (over 120 - 140 °C) will penetrate the opposite veneer in the lay-up construction . In one embodiment the material article, e.g. the veneer or layered product, is dried before the injection, the coating and/or before the layered product manufacturing .

The moisture content affects greatly on penetration of the polymer into the material owing to blow-out during layered product, e.g. wood board, manufacturing, intimate contact between the material, e.g. wood, and polymer, chemical bonding between them. Blow-out during layered board manufacture is a major problem even when phenol formaldehyde adhesives are used. It is caused by the vapour pressure in the layered board being greater than the strength of the adhesive bond. In one embodiment the material article is hot-pressed above 100 °C which means that any moisture in the material is converted to steam. When the hot-press is opened if the strength of the adhesive bond is not strong enough the material article will blow. This occurrence can be minimized by keeping the moisture content of the material below 5 %. However, it should also be remembered that unlike thermosets thermoplastics do not form there strongest bond until the temperature falls below the polymer crystalline temperature. Therefore, the ideal condition to avoid blow-out is to keep the moisture content of e.g. the wood below 3 % or and keep the pressure applied until the temperature is below the polymer's crystallization temperature. This is possible by following the hot- press with a cold press or using a continuous hot-cold press. Plasma treatment of the material is possible after material article drying or before injection or extrusion coating or lamination. This process will reduce the surface energy of the material to render it more compatible with the polymer.

In one embodiment the method comprises at least one heating stage, e.g. hot-pressing, for heating and drying the material article, e.g. veneers. Various heat devices and methods can be used. In one embodiment the method for forming layered product comprises at least one cooling stage for cooling the ve ^¬ neers. Various cooling devices and methods can be used. In one embodiment the method comprises at least one heating stage and at least one cooling stage. Preferably the heating stage should be followed by the cooling stage.

In one embodiment it is possible to extrude or inject the coating material onto the surface of the material article straight after the dryer. This is extremely advantageous from the point of view the material articles are utilised hot and don't require cooling. Also, the moisture content is 2 - 5 % and the majority of the moisture has already been vaporized and will therefore not cause any problems during injection and polymer adhesion. The material article from the dryer can be continuously injected or the material articles, e.g. veneers, can be cut first before the injection. The material articles, e.g. boards or veneers, can be double sided injected and again this can be done before or after cutting to the required size. If the injection is only applied to one side of the material article then it is advantageous to extrude or inject on the non peeled side, e.g. smooth side. The smooth side is the most difficult to penetrate with a thermoplastic and therefore the penetration will be much greater e.g. with extrusion coating.

The layered product can be made using apparatuses and methods known per se. Laying the veneers one upon the other, joining them together, pressing and other typical steps in making the layered product can be performed in any manner known per se in the art.

In the embodiment of the layered product manufacturing the veneers is glued for joining together with the present coating material. In one embodiment the coating material is in the form of a film. In one embodiment the film is formed by the injection, preferably by the extrusion, on the surface of the material article, e.g. the veneer. In one embodiment the coating material is extruded in the form of the film onto the surface of the material article, e.g. the veneer. In one embodiment the film contains more than one film layer. In one embodiment the multilayer film is formed by a co-extrusion.

In one embodiment the coating material is a film is formed of polyolefin - coupling agent composition containing reactive groups which are reactive with reactive groups of the material article, e.g. with -OH groups of the wood, for forming bonds via es- terification between the material article and the film. In one embodiment the coating material is a self-adhesive polyolefin film modified maleic anhydride. In one embodiment the film can comprise more than one layer, e.g. two or three layers where the outer layers contain maleic anhydride grafted polyethylene or polypropylene. In one embodiment the film is the self-adhesive polyolefin film, as defined in patent applications PCT/FI2009/050130 and PCT/FI2009/050662. In one embodiment the film is used to create the layered product that has strength properties and fibre breakage percentage that exceeds that of phenol formaldehyde bonded layered board.

In one embodiment of the invention the layered product formed can be coated by injection coating or by extrusion coating, according to the invention as defined above. The layered product formed is coated with a coating material, the coating material contains at least one polymer and a coupling agent containing reactive groups being reactive with the veneers, the coating material is injected onto the surface of the layered product, and the coupling agent is activated to its active state in connection with the injection to form chemical bonds between the layered product and the coupling agent.

In one embodiment the layered product can be edge sealed by extrusion coating or by injection coating of the polymer and activated coupling agent.

In the case where the layered product is for- mable the layered product can be reheated in an oven or microwave or via high-frequency. Pressure is not required during the re-heating but it is desired that the layered product is formed under pressure and cooled in order not to damage the bonds formed during the initial hot-pressing. It is found that reheating and pressing actually improves on the bonding quality. In one embodiment the layered product, e.g. wood panel or plywood, is molded during manufacturing of the layered product. If a microwave is used to reheat the layered product then the polymer needs to be able to absorb microwaves. Most polymers do not absorb microwaves to a sufficient extent to be heated. Polymers have very low dielectric properties and therefore can be improved by the addition of fillers e.g. zinc oxide, carbon black, talc, glass, ceramic, EVA, MAPP and MAPE. The invention is not limited to these materials only.

In one embodiment the material article can be cross-linked before moulding into shape, in order to take advantage of the viscoelastic or elastomer prop ^¬ erties. Cross-linked polyethylene, above it's crystalline melting point, can be stretched a lot more than its uncross-linked version.

An advantage of the invention is to provide more highly water resistant layered products, veneer products, wood board products and other products.

By means of the method of the invention the molten thermoplastic coating material can applied onto the surface of the material directly e.g. from an extruder. The injection with molten coating material, e.g. thermoplastic coating material, eliminates the need to manufacture the coating film separate.

The method and layered product in accordance with the invention are suitable for various applications. The material articles of the invention can be used to form wet resistance products, dimensionally stable products, furniture, children's furniture and kitchens and the like. In addition to this the material article can be utilised in the transport and ship building industries, automotive, construction including scaffolding, in technically challenging parts, e.g. wind mills, musical instruments and sound insulated wood board for buildings and stairs, side walls and floors of vans, trailers, trains, coaches, vans lorries and horse boxes, play ground equipment, sports equipment, flight cases, sign boards, die boards, rotary die boards, DIY applications and yachts. However, the invention is not limited to these examples only.

The self-adhesive coating material in accordance with the invention is suitable for bonding with itself to create self-sealing material. It also bonds to veneers, plywood, textiles, woven and non-woven material, metals, paper, cardboard, other plastics, basically any material which posses either hydroxyl or oxide groups. In addition to this it also penetrates and bonds to porous materials.

LIST OF FIGURES

In the following, the invention is described by means of detailed embodiment example with reference to accompanying figures 1 - 5, in which

Fig. 1 shows a schedule of a method according to the invention, Fig. 2 shows a reaction of conversion of maleic acid to maleic anhydride and its reaction with wood hydroxide groups in the coating and lamination,

Fig. 3 shows a reaction of conversion of maleic acid to maleic anhydride and its reaction with wood hydroxide groups in the wood board manufacturing,

Fig. 4 shows a coating process to carry out the method of the invention, and

Fig. 5a, 5b and 5c show another extrusion processes to carry out the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1 In this example, the plywood is manufactured by the method of the invention. In figure 1 it is shown a process for manufacturing the extruded thermoplastic bonded plywood.

The first step 1 is selection of the raw materials, like wood la, e.g. veneer, plywood or other boards, polymer lb, e.g. thermoplastics, hot- melt or curable hot-melt, and coupling agent lc, e.g. maleated polymer, and possible additives lc. The ma- leated material of the polymer is conversed from rtia- leic acid to maleic anhydride, in the extruder 2 or prior to extrusion utilising heat with or without a catalyst. The examples of conversion reactions and bonding reactions between maleic anhydride and the wood hydroxide groups are shown in figures 2 and 3 and their combinations. The extruded polymer containing maleic anhydride is extruded onto the veneers in connection with the extrusion 2 where the active maleic anhydride groups react with the hydroxide groups of the wood to form an ester bond. Alternatively, the film 3 can be manufactured, e.g. by blowing or by cast, from polymer raw material lb. The film can be used as glue material.

The next step is laying up of the veneers for forming a plywood. The veneers can be cooled 4a before the laying up 4b. The veneers can be treated e.g. by chill roller and/or under pressure. Alternatively, the veneers can be utilized hot layed-up 5 to make plywood. Alternatively, the veneers can be layed-up also by another method 6. The veneers can be bonded toget- her using e.g. hot-pressing and/or high frequency technique 7a and/or cold pressing 7b.

The plywood 8 formed can be reheated and moulded into shape 9 and/or cross-linked or cured 10. The plywood 8 formed can be supplied to the injection moulding 11. The plywood formed can be coated with the extruded polymer containing maleic anhydride or a separate coating material during the plywood manufacture process, or it can be coated after the plywood manufacture. In addition to this the plywood can also be completely encapsulated in polymer creating a water resistant product that is formable.

Example 2

Some possible extrusion coating pro- cesses are shown in Figures 4 and 5a, 5b and 5c. The invention is not limited to these techniques only.

Figure 4 shows the basic extrusion coating 20 of plywood and veneers 21; however, if the moisture content is high there will be no possibility for the vapour pressure to escape and therefore there will be bubbling of the coating. However cooling 22 under pressure 23, e.g. cold press or chill roll, should prevent this and also keeping moisture content below 10 %, preferably below 5 %.

Figure 5a shows a chill roll extrusion coating technology. A veneer 31 is provided to move round the chill roll 34 by a conveyor 35. This allows for the veneer 31 to be coated by an extrusion die 32 with molten polymer and coupling agent 33 before the chill roll 34 to avoid ^' the steam bursting through the plastic, more intimate contact between the wood and polymer. Then a thermoplastic coated veneer 36 is formed.

Figure 5b shows a chill roll extrusion coating technology. A veneer is conveyed by a conveyer belt 37 in the direction 38 of a movement. A coating material containing molten polymer and coupling agent is extruded by an extruder 32. The veneer is treated by the chill roll 34 after the extrusion 32.

Figure 5c shows an extrusion lamination of a veneer. The veneer 31 from a veneer dryer 39 is laminated by three-layer film. The film is co-extruded in the form of the three-layer film by a co-extrusion device 40 directly onto the surface of the veneer 31.

Example 3

In this example, the layered board is manufactured from the veneers by the method of the invention .

Extrusion coating on veneers were done using 240 mm width extrusion coating line. In the trial the polymer mass was mixed and melted in extrusion unit and run through a slit nozzle onto a veneer surface after which the coated veneers were run through a nip and cooled down with a chill roll. In the trials extrusion coating was done onto top side of the veneers. Extrusion coating line used in this trial is a typical laboratory extrusion coating line used commonly in pa- per/paperboard extrusion coating.

The veneers were extrusion coated with the coating material according to the invention. The coa- ting material included polyethylene as a polymer and 3 % by weight MAPE (maleic anhydride polyethylene) as a coupling agent.

After the extrusion coating of veneers laboratory scale plywood samples were manufactured in hot-press and then cooled down under pressure using cold press. Adhesion and gluing quality was tes ^¬ ted from extrusion coated veneers and from plywood samples .

Extrusion coating line parameters were: line width was 240 mm; melt polymer setup temperature in extruder was 300°C; running speed was 10-15 m/min; air gap (distance between nozzle and veneer) was 100 mm; as polymer feeding pressure is used very moderate and free flow from nozzle; and nip pressure was very moderate .

Extrusion materials were: polymer was LDPE (MI5; Density 909kg/m ³ DSC melting point 105 °C Vi- cat) ; coupling agent was MAPE (Fusabond DE MB- 226DE/Dupont ) ; and color was blue.

As veneers were used birch and spruce veneers. Veneer thicknesses were 1.5 mm, 1 mm and 0.6 mm. Veneer moisture contents were < 2%, 5% and 8%. Ve ^¬ neer size was 240mm x 600mm.

Three different extrusion coating trial points were run: 1) PE 90g/m ² (about 0,1mm) + some blue colouring, birch veneers; 2) PE + 3%MAPE 90g/m ² (about 0,1mm) + some blue colouring, birch veneers; and PE + 3%MAPE 150g/m ² (about 0,16 mm), birch and spruce veneers .

Adhesion of extrusion coating on veneers was evaluated by peeling tests. Peeling was made by hand by pulling the coating in 90° angle from the veneer. Peeling was done to dry and to boiling pre-treated samples. Boiling was done according to BFU 100 (4 hour boiling, 20 hours drying, 4 hour boiling) . 1

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A part of the extrusion coated veneers were also hot pressed before peeling test in order to simulate the plywood manufacturing process. Hot pressing parameters used were for birch 1,7 N/mm ² , 140°C, 5 min and for spruce 1,2 N/mm ² , 140°C, 5 min.

Hand peeling from not hot pressed veneers: Extruded coating can be peeled of by hands from dry and boiled veneer samples. Adhesion is regarded to be sufficient for further processing steps in plywood ma- nufacturing.

Hand peeling from hot pressed veneers: Adhesion is excellent in both dry and boiled samples.

The extrusion coated veneers (about 200mm x 200mm) were placed on top of each other every other veneer in cross direction (normal plywood structure) and hot pressed (inner temperature 130 °C) . After the hot pressing the panels were cooled under pressure (cold pressing, inner temperature < 70 °C ) . Panel structure was 7 ply, cross lay-up. Hot pressing pa- rameters were for birch 1,7 N/mm ² , 140°C, 5 min and for spruce 1,2 N/mm ² , 140°C, 5 min. Cold press parameters were for birch 1,7 N/mm ² , 5 min and for spruce 1,2 N/mm ² , 5 min.

Testing of plywood samples were done accor- ding to EN 314 Glue line shearing strength. Glue line shearing strength was measured after soaking and in one case after boiling pre treatments.

BFU 100 pre-treatment: All extruded coatings passed the boiling pre-treatment, in other words, ext- ruded coating stayed on the veneer surface after boiling.

From the test results it was discovered that the adhesion and gluing quality in the veneers and plywood samples was very good when the coating mate- rial with the coupling agent was used.

From the tests it was discovered that a method of the invention is suitable to be used for coating veneers, plywood and layered products easily and cost effectively.

A method for injecting the coating material and a layered product according to the invention are suitable in its different embodiments for different types of applications.

The embodiments of the invention are not limited to the examples presented rather many variations are possible within the scope of the accompanying claims .