Low formaldehyde emission adhesive system

Abstract

The invention relates to an improved two component adhesive system, a kit comprising said two adhesive components, its use and a method for production of interior wood products, in particular form-pressed products, parquet floor elements and solid wood panels with very low formaldehyde emission and to the interior wood products obtainable having improved properties. The two-component adhesive system comprises adhesive component I comprising a 50-70 wt % melamine-formaldehyde (MF) type resin in 25-40 wt % water and adhesive component II comprising 25-40 wt % of a water based dispersion adhesive, 15-40 wt % of a formaldehyde scavenger and an acidic compound in an amount such that the pH of adhesive component II is 1.5-6.5, wherein adhesive component I and II are to be applied in a weight ratio I:II of 1:0.5 to 1:1.5 and the adhesive system has a molar ratio of formaldehyde (F) to total amino group (F/NH 2 ) between 0.2 and 0.7.

What is claimed is: 
     
         1 . A two-component adhesive system comprising:
 adhesive component I comprising (in dry wt % relative to the total weight of adhesive component I):
 I.a) 50-70 wt % of a melamine-formaldehyde (MF) type resin and 
 I.b) 0-20 wt % of organic or inorganic filler, 
 I.c) 0-10 wt % of further additives, 
 I.d) 25-40 wt % water; 
   adhesive component II comprising (in dry wt % relative to the total weight of adhesive component II):
 II.a) 20-40 wt % of a water based dispersion adhesive, 
 II.b) 0-10 wt % of a thickener, 
 II.c) 15-40 wt % of a formaldehyde scavenger, 
 II.d) an acidic compound in an amount such that the pH of adhesive component II is 1.5-6.5, 
 II.e) 0-20 wt % of organic or inorganic filler, 
 II.f) 0-10 wt % of further additives, 
 II.g) 25-40 wt % water, and 
   wherein adhesive component I and II are to be applied in a weight ratio I:II of 1:0.5 to 1:1.5, and the adhesive system has a molar ratio of formaldehyde (F) to total amino group (F/NH 2 ) between 0.2 and 0.7.   
     
     
         2 . The two-component adhesive system according to  claim 1 , wherein the pH of adhesive component II is 1.5-4 and wherein the adhesive system has a molar ratio of formaldehyde (F) to total amino group (F/NH 2 ) between 0.3 and 0.7. 
     
     
         3 . The two-component adhesive system according to  claim 1 , wherein the solid weight ratio of melamine-formaldehyde (MF) type resin to formaldehyde scavenger is 1:0.11 to 1:1.20. 
     
     
         4 . The two-component adhesive system according to  claim 1 , wherein the MF type resin (I.a) in adhesive component I has a molar ratio F/NH 2  of 0.4-1.2. 
     
     
         5 . The two-component adhesive system according to  claim 1 , wherein the MF type resin (I.a) is selected from the group consisting of: MF resin, urea modified MF resin (uMF) comprising between 0.1 and 50 wt % of urea (weight of urea relative to the total of urea and melamine), modified MF and uMF resins. 
     
     
         6 . The two-component adhesive system according to  claim 1 , wherein the optional filler (I.b) in adhesive component I is an inorganic filler or an organic filler. 
     
     
         7 . The two-component adhesive system according  claim 1 , wherein the adhesive component I comprises 0.1-10 wt % of one or more further additives (I.c) is selected from the group consisting of: anti-foaming agents, thickeners, surfactants, pigments, colorants, rheology modifiers, and flexiblisers. 
     
     
         8 . The two-component adhesive system according to  claim 1 , wherein the adhesive component I has a viscosity between 1500 and 10000 mPas (viscosity measured with Brookfield RVT at 25° C., spindle 4, and at a speed of 20 rpm). 
     
     
         9 . The two-component adhesive system according to  claim 1 , wherein the adhesive component I has a pH between 7 and 12. 
     
     
         10 . The two-component adhesive system according to  claim 1 , wherein the dispersion adhesive (II.a) in adhesive component II is functionalized or un-functionalized PVAc. 
     
     
         11 . The two-component adhesive system according to  claim 1 , wherein the adhesive component II comprises 0.1-10 wt % of thickener (II.b) (different from component II.a) to adjust the viscosity. 
     
     
         12 . The two-component adhesive system according to  claim 1 , wherein the adhesive component II has a viscosity between 1500 and 10000 mPas. 
     
     
         13 . The two-component adhesive system according to  claim 1 , wherein the viscosity of the adhesive obtained after mixing of components I and II is between 1000 and 5000 mPas. 
     
     
         14 . The two-component adhesive system according to  claim 1 , wherein the formaldehyde scavenger (II.c) is an amino-compound selected from the group consisting of: urea, thiourea, amines, and ammonia. 
     
     
         15 . The two-component adhesive system according to  claim 1 , wherein the adhesive component II comprises 15 to 40 wt % of an amino-compound as formaldehyde scavenger (II.c). 
     
     
         16 . The two-component adhesive system according to  claim 1 , wherein the adhesive component II comprises an acidic compound (II.d) in an amount such that the pH of adhesive component II is between 1.5 and 6.5. 
     
     
         17 . The two-component adhesive system according to  claim 1 , wherein the acidic compound II.d is a carboxylic acid, or an acidic salt or a combination thereof. 
     
     
         18 . The two-component adhesive system according to  claim 1 , wherein the acidic compound II.d is one or more carboxylic acids selected from the group consisting of formic acid, acetic acid and lactic acid. 
     
     
         19 . The two-component adhesive system according to  claim 1 , wherein the pH of the adhesive obtained after mixing of components I and II is between 3.3 and 6.5. 
     
     
         20 . The two-component adhesive system according to  claim 1 , wherein the optional filler (II.e) in adhesive component II is chosen to be stable at pH of 1.5 to 6.5. 
     
     
         21 . The two-component adhesive system according to  claim 1 , wherein the adhesive composition II comprises at least one of: a crosslinking agent for crosslinking the dispersion adhesive II.a and thickeners present in adhesive components I or II. 
     
     
         22 . The two-component adhesive system according to  claim 1 , having a shear strength above 1100 N/inch 2  (as measured on a three layer beech plywood in cold water test according to BS 1203/1204) and an average emission below 0.5 mg/l when tested according to ISO-12460-4 (as measured on a 5 layer plywood samples glued with the glue system). 
     
     
         23 . A two-component adhesive kit comprising adhesive components I and II according to  claim 1  wherein each component is housed in a separate container. 
     
     
         24 . The two-component adhesive kit according  claim 23 , wherein the two-component adhesive kit is used in the production of interior wood products comprising form-pressed products, parquet floor elements, solid wood panels with very low formaldehyde emission. 
     
     
         25 . The two-component adhesive system according  claim 1 , wherein the two-component adhesive system is used in the production of interior wood products comprising form-pressed products, parquet floor elements, solid wood panels with very low formaldehyde emission. 
     
     
         26 . A method for the production of interior wood products with low formaldehyde emission, comprising the steps of:
 applying adhesive I and II of the two-component adhesive system comprising:   adhesive component I comprising (in dry wt % relative to the total weight of adhesive component I):
 I.a) 50-70 wt % of a melamine-formaldehyde (MF) type resin and 
 I.b) 0-20 wt % of organic or inorganic filler, 
 I.c) 0-10 wt % of further additives, 
 I.d) 25-40 wt % water; 
   adhesive component II comprising (in dry wt % relative to the total weight of adhesive component II):
 II.a) 20-40 wt % of a water based dispersion adhesive, 
 II.b) 0-10 wt % of a thickener, 
 II.c) 15-40 wt % of a formaldehyde scavenger, 
 II.d) an acidic compound in an amount such that the pH of adhesive component II is 1.5-6.5, 
 II.e) 0-20 wt % of organic or inorganic filler, 
 II.f) 0-10 wt % of further additives, 
 II.g) 25-40 wt % water; 
   wherein adhesive component I and II are to be applied in a weight ratio I:II of 1:0.5 to 1:1.5, and the adhesive system has a molar ratio of formaldehyde (F) to total amino group (F/NH 2 ) between 0.2 and 0.7;   wherein the two-component system is applied in premixed form or separate, either simultaneous or consecutively, to one surface or on both opposing surfaces of wood layers to be bonded over at least part of the surface area thereof,   assembling the wood layers provided with adhesive in a stack, and   pressing the stack at elevated temperature to shape the stack and cure the adhesive.   
     
     
         27 . The method according to  claim 26 , wherein the stack is pressed in a heated press or radio frequency press at a temperature between 60 and 120° C. at a pressure between 0.5 and 2 N/mm 2 . 
     
     
         28 . The method according to  claim 26 , wherein the interior wood products comprise at least one of: form-pressed products, parquet floor elements and solid wood panels. 
     
     
         29 . A two-component adhesive system comprising:
 adhesive component I comprising (in dry wt % relative to the total weight of adhesive component I):
 I.a) 50-70 wt % of a melamine-formaldehyde (MF) type resin and 
 I.b) 0-20 wt % of organic or inorganic filler, 
 I.c) 0-10 wt % of further additives, 
 I.d) 25-40 wt % water; 
   adhesive component II comprising (in dry wt % relative to the total weight of adhesive component II):
 II.a) 20-40 wt % of a water based dispersion adhesive, 
 II.b) 0-10 wt % of a thickener, 
 II.c) 15-40 wt % of a formaldehyde scavenger, 
 II.d) an acidic compound in an amount such that the pH of adhesive component II is 1.5-6.5, 
 II.e) 0-20 wt % of organic or inorganic filler, 
 II.f) 0-10 wt % of further additives, and 
 II.g) 25-40 wt % water 
   wherein the adhesive component II has a viscosity between 1500 and 10000 mPas.