Storage-stable isocyanate binders containing latent catalysts

Details Storage-stable isocyanate binders containing latent catalysts Storage-stable isocyanate binders containing latent catalysts

2001-09-21

2003-02-25

Cameron, Erma (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Solid treating member or material contacts coating

Reexamination Certificate

active

06524652

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a process for the production of derived timber products. This process comprises applying a binder to lignocellulose containing materials and heating this mixture under pressure. Suitable binders are storage-stable and comprise a polyisocyanate and an amine catalyst.
Derived timber products, for example chipboard, laminated board or other moldings are usually produced by hot pressing the inorganic or organic raw material, for example a mass of wood chips, wood fibers and/or other material containing lignocellulose, in a “mixed gluing” process with polyisocyanates and water, optionally polyols or other binders such as urea/formaldehyde or phenol/formaldehyde resins. Using polyisocyanates as the binder improves the stability and moisture performance of the products and enhances the mechanical properties thereof. As disclosed, for example, in DE-OS 21 09 686, polyisocyanates furthermore possess wide-ranging processing advantages.
Catalysts of the type known per se from polyurethane chemistry, for example those stated in DE-OS 28 54 384, pp. 26-29 and 31-33, may in principle also be used in prior art processes (c.f. for example DE-AS 27 11 958) in order to shorten pressing times. This is of particular importance in “one-daylight” presses. However, when catalysts are used, due to the immediate onset of catalyst action on the reactive NCO groups, unwanted foaming and premature setting generally occur during mixing of the components and storage of the isocyanate-glued chips. Consequently, it is generally necessary to dispense with the use of catalysts and accept longer pressing times.
EP-A 133 680 discloses a process for the production of derived timber products using polyurethanes as binders, in which tertiary or quaternary ammonium phosphonates or quaternary ammonium phosphates are used as heat-activated catalysts. However, the reduction in pressing time observable when these catalysts are used is not sufficient for economic performance of the process. Sufficiently short pressing times likewise cannot be achieved with the processes described in DE-OS 42 29 396 and DE-OS 34 38 735 for the production of chipboard or fiber board using polyisocyanates as the binder.
DE-OS 196 03 330 describes a process for the production of derived timber products using polyisocyanates as the binder which also use a latent catalyst system, in which the catalysts used are ammonium salts which are obtained by reacting amines with malonic acid. These activated binders effectively reduce pressing times and also function at elevated chip temperature. However, due to the deficient storage stability thereof in isocyanates, the catalyst must be added separately to the isocyanate directly before gluing. This separate addition entails additional plant costs and possible sources of error in the production process.
There was accordingly a need for a single component polyisocyanate binder containing catalyst which remains stable at elevated temperature over an extended period and permits pressing times to be shorted during hot pressing. Binder systems based on polyisocyanate and amine catalysts have now been discovered which are ideally suited to this purpose.
SUMMARY OF THE INVENTION
The present invention provides a process for the production of derived timber products comprising
(a) applying a storage-stable binder comprising one or more polyisocyanates and one or more amine catalysts to materials containing lignocellulose;
and
(b) heating the product of (a) under pressure, thereby forming the resultant derived timber products.
Suitable amine catalysts to be used according to the invention preferably comprise those compounds which contain dimorpholino groups. Dimorpholinodiethyl ether and dimorpholinopolyethylene glycol are particularly preferred amine catalysts for the present invention. Dimorpholino compounds have already variously been suggested as storage-stable additives to moisture-curing MDI prepolymers or PMDI/epoxy resins (see, for example, EP-A 226 287, EP-A 668 302, EP-A 732 385, U.S. Pat. No. 5,075,405, EP-A 811 645 and/or WO 94/18265, the disclosures of which are herein incorporated by reference). EP-A 668 302 is believed to correspond to U.S. Pat. No. 5,550,191 which, at column 4, lines 45-69, discloses MDI prepolymers. More specifically, this reference discloses that the polyisocyanate and polyol, polyamino or polymercapto components are combined proportions so as to yield a urethane prepolymer characterized by an isocyanate content of from about 0.25 to 15%, preferably to about 10%, and most preferably from 1.5 to 5%. EP-A 732 385 is believed to correspond to U.S. Pat. No. 5,616,625 which, at column 5, lines 25-48 describes that the polyisocyanate and polyol, polyamino or polymercapto components are combined proportions so as to yield a urethane prepolymer characterized by an isocyanate content of from about 0.25 to 15%, preferably to about 10%, and most preferably from 1.5 to 5%. EP-A 811 645 is believed to correspond to U.S. Pat. No. 6,090,307 which, at column 3, lines 36-38, discloses prepolymer components having NCO group contents of between 4 and 20%, preferably between 6 to 18% and in particular between 7 and 13% by weight. However, the use of dimorpholino compounds in unmodified isocyanates for the production of storage-stable binders which are suitable for the production of derived timber products by hot pressing was not previously known.
The binders of the present invention generally contain from 0.01 to 30% by weight of catalyst, based on 100% by weight of the isocyanate. In a preferred variant, they contain 0.02 to 2% by weight, particularly preferably 0.05 to 1% by weight, based on 100% by weight of the isocyanate.
Addition of the catalyst to the isocyanate and subsequent mixing must proceed in the absence of moisture. The mixed binder system may be stored at temperatures of up to 40° C. for at least two months, and may also briefly be exposed to temperatures of up to 60° C. without there being any impairment of the binder properties.
Suitable isocyanate components which may be considered for the performance of the process according to the invention comprise aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates, as have been described by W. Siefken in
Justus Liebigs Annalen der Chemie,
562, pp. 75-136, for example those of the formula
Q(NCO)
n
wherein:
n: represents a number from 2 to 4, preferably 2;
and
Q represents an aliphatic hydrocarbon residue having 2 to 18 carbon atoms, preferably 6 to 10 carbon atoms, a cycloaliphatic hydrocarbon residue having 4 to 23 carbon atoms, preferably 5 to 13 carbon atoms, an aromatic hydrocarbon residue having 6 to 25 carbon atoms, preferably 6 to 13 carbon atoms, or an araliphatic hydrocarbon residue having 8 to 15 carbon atoms, preferably 8 to 13 carbon atoms.
Some examples of suitable polyisocyanates for the present invention, include compounds such as, for example, 4,4′-diphenylmethane diisocyanate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate and any desired mixtures of these isomers, 2,4′- and/or 4,4′-diphenylmethane diisocyanate, and any desired mixtures of these isomers or the polymeric types from this series.
Industrially readily available polyisocyanates are generally preferred. Such polyisocyanates include, for example, 2,4- and 2,6-tolylene diisocyanate and any desired mixtures of these isomers (“TDI”), and particularly preferably polyphenylpolymethylene polyisocyanates, as are produced by aniline/formaldehyde condensation and subsequent phosgenation (“crude MDI”). The polyisocyanates used may optionally also be modified. More highly cyclic isocyanates of the diphenylmethane diisocyanate series (pMDI grades) are particularly preferably used.
The process according to the invention may also be performed using prepolymers comprising terminal isocyanate groups (i.e. NCO-terminated prepolymer) and having an average molecular weight of approx. 275 to 2000, as are obtained in a manner known per se by reacting relative

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