Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1998-07-22
1999-12-28
Yao, Sam Chuan
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156296, 1563334, 264109, C08G 1818
Patent
active
060076496
DESCRIPTION:
BRIEF SUMMARY
A process is claimed for producing pressed materials, preferably particle boards, by the hot compaction of raw materials containing lignocellulose which are mixed and/or impregnated with polyisocyanates as binders, with the use in conjunction of new types of latent, thermally activatable catalysts based on ammonium salts, such as those produced by the reaction of primary, secondary and/or tertiary amines with malonic acid.
Pressed materials, such as particle boards, composite boards or other moulded bodies for example, are usually produced by the hot compaction, as a so-called mixed bonding system, of an inorganic or organic raw material, e.g. a composition comprising wood chips, wood fibres and/or other material containing lignocellulose, with polyisocyanates and water, optionally with polyols or other binders such as urea/formaldehyde or phenol/formaldehyde resins. The use of polyisocyanates as binders improves the stability of the products and their behaviour under humid conditions, and enhances their mechanical properties. In addition, polyisocyanates as binders possess extensive process technology advantages, as disclosed in DE-OS 2 109 686 for example.
In principle, catalysts of the type which are known in the art from polyurethane chemistry, e.g. those which are cited in DE-OS 2 854 384 on pages 26 to 29 and 31 to 33, can also be used in conjunction in prior art processes (see DE-AS 2 711 958 for example) to reduce the pressing times. This is particularly important in what are termed single daylight presses. However, this usage generally results in unwanted foam formation and premature bonding, even during the mixing of the components and the storage of the wood chips bonded with isocyanates before compaction; this is due to the action of the catalyst on the reactive NCO groups, which occurs immediately. For this reason, the conjoint use of catalysts mostly has to be avoided and longer pressing times have to be accepted.
A process is known from EP 133 680 for producing pressed materials using urethanes as binders, in which tertiary or quaternary ammonium phosphonates or quaternary ammonium phosphates are used as thermally activatable catalysts. Even when these catalysts are used, the reduction in pressing time which is observed is always not always quite sufficient for the process to be carried out economically. Moreover, pressing times which are sufficiently short cannot be achieved using the processes described in DE 4 229 396 and DE 3 438 735 for producing particle boards or fibre boards using polyisocyanates as binders.
The object of the present invention is therefore to provide a latent catalyst system for the production of pressed materials containing polyisocyanate binders, which is capable of activating the reactions of polyisocyanates at elevated temperatures but which does not exhibit catalytic behaviour at temperatures up to 80.degree. C.
This catalyst system can even be admixed with the polyisocyanate used, or with the formulation which is used for the production of pressed bodies and which comprises polyisocyanates, water, materials containing lignocellulose such as fibres, wood chips or straw-like fibres, and other polyhydroxyl compounds which are optionally to be used in conjunction, without unwanted reactions occurring at room temperature and on mixing and storage at temperatures up to 80.degree. C. However, the pressing times can be considerably reduced due to the more rapid bonding during pressing which takes place as a result of the catalysis which becomes effective at higher temperatures. Surprisingly, it has now been found that the catalysts described in detail below, which are based on amine salts of malonic acid, are very suitable for the object described, since up to 80.degree. C. they constitute latent catalysts in the polyisocyanate formulation but at pressing temperatures they catalyse isocyanate reactions and thus fulfil the conditions specified above.
The present invention relates to a process for producing pressed materials, preferably wood particle boards, by the hot c
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Haas Peter
Kasperek Peter
Vehlewald Peter
Bayer Aktiengesellschaft
Gil Joseph C.
Whalen Lyndanne M.
Yao Sam Chuan
LandOfFree
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