Adhesive system and wood based panels with low subsequent formaldehyde emission and suitable production procedure

A multilayer low formaldehyde emission board comprising:

• A) a core layer comprising a first adhesive composition, and
• B) a face layer comprising a second adhesive composition;
• wherein
• 1) each of said first and second adhesive compositions comprises an aminoplastic resin that has a dry base composition comprising between 0 and 15% melamine, and
• 2) the aminoplastic resin of said first adhesive composition:
• i) has a formaldehyde:NH2 molar ratio (F/(NH2)2) of:
• a) between 0.70 and 1.05 when said resin comprises melamine, or
• b) greater than 0.85 when said resin is essentially free of melamine and when said resin comprises urea as well as other NH2 containing components, and
• iii) has a formaldehyde:urea molar ratio (F/U) of more than 0.85 when said resin is essentially free of melamine and comprises urea as the only NH2 component, and
• 3) the aminoplastic resin of said second adhesive composition has:
• iii) a formaldehyde:NH2 molar ratio (F/(NH2)2) of:
• a) between 0.6 and 0.9, when said resin comprises up to 15% melamine, or
• b) greater than 0.65 when said resin is essentially free of melamine and when said resin comprises urea as well as other NH2 containing components, and
• iv) a formaldehyde:urea molar ratio (F/U) of more than 0.60 when said resin is essentially free of melamine and comprises urea as the only NH2 component, and
• 4) said board emits:
• a) 0.5 mg/ml or less formaldehyde as measured in a Desiccator Test JIS A 1460, or
• b) 0.04 ppm or less formaldehyde as measured in an EN 717-1 climate chamber, and
• 5) said first and second adhesive compositions are not the same.

A method for modifying first production process to a second production process of forming a particle or MDF board satisfying at least one of

• (i) the EN standards EN 312 or EN 622-5, respectively,
• (ii) the physical properties of JIS A 5905 and 5908, respectively,
• wherein the boards made according the first production process further satisfy at least one of
• (1) the formaldehyde emission specification according to JIS A 5905 and 5908, respectively exceeding the limit of 0.3 mg/l when tested according to the Desiccator Test JIS A 1460, or
• (2) a maximum formaldehyde emission of more 0.03 ppm when tested in the climate chamber test according to EN 717-1,
• and wherein the boards as produced by said second production process satisfy
• (a) the F**** specification according to JIS A 5905 and 5908, respectively, by satisfying the limit of 0.3 mg/l or less when tested according to the Desiccator Test JIS A 1460, or
• (b) a maximum formaldehyde emission of 0.03 ppm or less in the climate chamber test according to EN 717-1,
• and wherein said first and said second production processes are essentially identical and comprise the use of an aminoplastic resin,
• said method of modifying the process comprises the step of
• (a) adjusting the melamine level of said aminoplastic resin to more than 0% and less than 15%, wherein
• (a1) the molar ratio of F/(NH2)2 is more than 0.70, preferably more than 0.80, and still more preferably more than 0.85, and less than 1.05 and preferably less than 1.00, if said resin comprises more than 0% of melamine;
• or
• (b) formulating said aminoplastic resin essentially free of melamine, wherein
• (b1) the molar ratio of F/U is more than 0.85, preferably more than 0.90, and still more preferably more than 0.95, when urea is the only NH2-group containing raw material for said aminoplastic resin, or wherein
• (b2) the molar ratio of F/(NH2)2 is more than 0.85, preferably more than 0.90, and still more preferably more than 0.95, when urea as well as other NH2-group containing raw materials like ammonia are used as raw materials for said aminoplastic resin;
• wherein the solids content of said aminoplastic resin is more than 66% but not more than 74% on a dry basis when said aminoplastic resin is applied in a core layer.