Method for producing multi-layered lignocellulose materials having a core with special properties and at least one upper and one lower cover layer

A process for the batchwise or continuous production of multilayer lignocellulose materials with a core and with at least one upper and one lower outer layer, comprising the following steps:

• a) mixing of the components of the individual layers separately from one another,
• b) layer-by-layer scattering of the mixtures (for the core layer and for the outer layers) to give a mat,
• c) precompaction after the scattering of the individual layers,
• d) application of a high-frequency electrical field before, during and/or after the precompaction, and then
• e) hot pressing,
• where, in step a),
• for the core, the lignocellulose particles A) [component A)] are mixed with
• B) from 0 to 25% by weight of expanded plastics particles with bulk density in the range from 10 to 150 kg/m3 [component B)],
• C) from 1 to 15% by weight of one or more binders selected from the group consisting of aminoplastic resin and organic isocyanate having at least two isocyanate groups [component C)],
• D) from 0 to 3% by weight of ammonium salts [component D)],
• E) from 0 to 5% by weight of additives [component E)] and
• F) from 0.1 to 3% by weight of alkali metal salts or alkaline earth metal salts from the group of the sulfates, nitrates, halides and mixtures of these [component F)],
• and for the outer layers, the lignocellulose particles G) [component G)] are mixed with
• H) from 1 to 15% by weight of one or more binders selected from the group consisting of aminoplastic resin and organic isocyanate having at least two isocyanate groups [component H)],
• I) from 0 to 2% by weight of ammonium salts [component I)],
• J) from 0 to 5% by weight of additives [component J)] and
• K) from 0 to 2% by weight of alkali metal salts or alkaline earth metal salts from the group of the sulfates, nitrates, halides and mixtures of these [component K)],
• wherein, after step a), the mixture for the core comprises, based on the total dry weight of the mixture of components A) to F) from 3 to 15% by weight of water, the mixture(s) for the outer layers comprise(s), based on the total dry weight of the mixture(s) of components G) to K), from 5 to 20% by weight of water, and the following conditions are met:
• component F)≧1.1•component K) and
• [component F)+component D)]≧1.1•[component K)+component I)].

A multilayer lignocellulose material with a core and with at least one upper and one lower outer layer, where the core comprises, based on the lignocellulose particles A) [component A)], the following components:

• B) from 0 to 25% by weight of expanded plastics particles with bulk density in the range from 10 to 150 kg/m3 [component B)],
• C) from 1 to 15% by weight of one or more binders selected from the group consisting of aminoplastic resin and organic isocyanate having at least two isocyanate groups [component C)],
• D) from 0 to 3% by weight of ammonium salts [component D)],
• E) from 0 to 5% by weight of additives [component E)] and
• F) from 0.1 to 3% by weight of alkali metal salts or alkaline earth metal salts from the group of the sulfates, nitrates, halides and mixtures of these [component F)],
• and where the outer layers comprise, based on the lignocellulose particles G) [component G)], the following components:
• H) from 1 to 15% by weight of one or more binders selected from the group consisting of aminoplastic resin and organic isocyanate having at least two isocyanate groups [component H)],
• I) from 0 to 2% by weight of ammonium salts [component I)],
• J) from 0 to 5% by weight of additives [component J)] and
• K) from 0 to 2% by weight of alkali metal salts or alkaline earth metal salts from the group of the sulfates, nitrates, halides and mixtures of these [component K)],
• and the following conditions are met:
• component F)≧1.1•component K) and
• [component F)+component D)]≧1.1•[component K)+component I)].