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ADHESIVE SYSTEMAND METHODOFPRODUCINGA WOOD BASED PRODUCT[0001] The present invention relates to an adhesive systemanda methodof producinga wood based product.INTRODUCTION[0002] Formaldehyde based resins suchas phenol-formal-dehyde resin, melamine-formaldehyde resin and urea-form-aldehyde resinare widely usedas bindersinthe productionofwood based products. Examplesof such wood based productsare composite products comprising layers glued togethersuchas plywood, laminated flooring products and veneeredproducts used in, e.g., Furniture. Further examples of suchwood based products are composite products such as par-ticle-, chip- and fibreboards wherein wood chips and/orfibres, together witha binder, are pressedto forma board.[0003] Upon curinga formaldehyde based resin, formalde-hyde may be released both during the manufacture of thewood based productand also later during use ofthe product.Formaldehyde emissiontoindoor air isa major concern sincemany years for health reasons.[0004] There is an increasing demand for formaldehyde-free wood adhesives which give sufficient bond strengthandoverall end-product quality making them suitable as alterna-tives to prior art adhesives containing formaldehyde basedresins.[0005] Water resistance and bond strength are generallyimportant properties reflecting quality for the wood basedproducts. Generally there exist specific quality parametersrequired for meeting an established standard fora specificend-product. For example,a particle board needs to meetcertain standards in terms of, e.g., internal bonding, thicknessswelling and water absorption, whilea laminated flooringproduct generally needsto meet certain standards in terms of,e.g., delamination and fiber tear.[0006] As an altemative to formaldehyde based resins inwood adhesive compositions starch based adhesives havebeen proposed. Lnam et al., “Wood Adhesive fromCrosslinked Poly(vinyl alcohol) and Partially GelatinizedStarch: Preparation and Properties”, Starch/Stärke 51 (1999)Nr. 6, S. 225-229, discloses an adhesive composition com-prising starchand polyvinyl alcohol, the composition furthercomprisinga melamine resin. U.S. Pat. No. 2,051,025, U.S.Pat. No. 2,102,937, U.S. Pat. No. 3,487,033, U.S. Pat. No.3,355,307 disclose starch based adhesives used for makingcorrugatedpaperboard. WO 03/069061 Al disclosesa starchbased adhesive usedin makinga paperboard product.[0007] Starch based adhesive systems havesofarnot beenusedin particle board manufacturing processes.[0008] There is stilla need for altemative starch basedadhesive systems suitable for producing wood based prod-ucts, suchas laminated products or particle boards.[0009] Accordingly, the present invention provides amethodof producinga wood based product and it also pro-vides an adhesive system.THE INVENTION[0010] The present invention relatestoa methodof produc-inga wood based product, comprising applying an adhesivesystem ontoone or more piecesofa wood-based material, andjoiningtheone or more pieces withoneor more further pieces1ofa material, preferably wood based material, the adhesivesystem comprises one component comprising starch andanother component comprising one or more polymers (P)containing an amine group oran amide group, thetwo com-ponents are applied ontothe wood based material as separatecomponents. The two components are suitably applied inasequenceof time from each other. Altematively, thetwo com-ponents are suitably applied simultaneously onto the woodbased material.[0011] By the term “adhesive system” is herein meantacombination of components which function as, and isintendedtobe used as, an adhesive when combined.[0012] In the term “adhesive” is herein also included theterm “binder”[0013] By the term “amide group” is herein included for-mamide group.[0014] By wood-based materials is herein, beside solidwood, also included wooden materials suchas fibre-, chip-,and particleboard materials. The surfacestobe joinedmay beofthe sameor different typeof wood based material.[0015] The wood based material can be any typeand formofwood based material suchas chips, fibres, sheets, laminas,veneers, pieces etc.[0016] The present invention also relates to an adhesivesystem comprising one component comprising starch andanother component comprising one or more polymers (P)containing an amine group oran amide group, thetwo com-ponents being present as unmixed separate components.[0017] The present invention also relates to the use of theadhesive system according tothe invention for producingawood based product.[0018] The invention further relates toa wood based prod-uct comprising pieces of wood based material joined withanadhesive comprising starch and one or more polymers (P)containing an amide group oran amide group.[0019] The component comprising starch may compriseastarch solutionor dispersion, or comprisethe starchasa solidmaterial. The component comprising theone or more poly-mers (P)may comprisea solution or dispersion or comprisethe polymer(P)asa solid material. Preferablytheone or morepolymers (P)are comprisedina solution or dispersion.[0020] The components ofthe adhesive systemare prefer-ably applied onto the wood based material ina sequence oftime from each other, asa first component applied and asasecond component applied ontothe wood based material.[0021] In one embodiment,a first applied component, ifbeinga solutionor dispersion, is dried after application beforethe second component is applied.[0022] Inone embodimentthe first componentofthe adhe-sive system applied onto the wood based material suitablycomprises starchand the second component applied suitablycomprisestheone or more polymers (P). The first componentapplied suitably comprisesa starch solutionor dispersionandthe second component applied suitably comprisesa solutionor dispersion ofthe one or more polymers (P).[0023] In one embodiment, the first component appliedcomprising starch is suitably dried after application andbeforethe second component applied comprising theone ormore polymers (P) is applied.[0024] In one embodiment, the first component appliedsuitably comprises solid starch and the second componentapplied suitably comprisesa solutionor dispersionoftheoneor more polymers (P).