Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1994-10-06
2002-04-09
Gallagher, John J. (Department: 1733)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C156S331400, C528S077000, C528S078000
Reexamination Certificate
active
06368714
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to moisture-activated adhesive compositions and methods for their production and use. More specifically, the present invention is directed to moisture-activated adhesive compositions which are cold curable.
BACKGROUND OF THE INVENTION
Adhesives suitable for use in wood products which demonstrate a prolonged pot life and a fast cure rate have long been desirable. Such adhesives would be useful in the manufacture of plywood, chip board, fiberboard, etc. However, these characteristics have proven to be difficult to obtain in simple formulations.
The plywood industry also has a need for adhesives which can effectively bond lignocellulosic solutions having a relatively high moisture content to effectively produce laminated veneers. For example, it would be desirable for adhesives used in these industries to be able to bond substrates having a moisture content of, e.g., 10% to 20%. Most conventional adhesives, such as those of the phenol-formaldehyde type, require a moisture content below 7%.
Examples of such phenol-formaldehyde type resins are disclosed, e.g., in
Plywood and Adhesive Technology
, Sellers, Jr., Marcel Dekker, Inc. (1985). These resins provide excellent adhesion, but are disadvantageous in that they require heat activation and a considerable amount of time to cure. Moreover, as noted above, such resins cannot be used effectively with substrates having high moisture levels. Thus, the substrates must be dried to a relatively low moisture content (generally about 5% by weight) resulting in a loss of wood volume and an increase in the cost and time of production.
Isocyanate-based adhesives are also known and have been employed in the preparation of laminated wood and paper structures. Polyisocyanates have been used as adhesives in the formation of waferboard, fiberboard and paper laminates from cellulose and lignocellulosic materials. An example of an isocyanate based adhesive is set forth in U.S. Pat. No. 4,414,361 which discloses polyisocyanate-cyclic alkaline carbonate binder compositions and their use in the preparation of lignocellulosic composite molded products. This patent discloses the addition of the adhesive to lignocellulosic material and molding this mixture at temperatures of from about 140° C. to 220° C. These polyisocyanates require temperatures of up to 200° C. or more for curing in order to develop acceptable physical bonding strengths. The use of such extreme temperatures reduces wood volume and is often not desirable from a cost or processing standpoint.
Accordingly, it can be seen that there is a need for one component adhesive compositions useful in the preparation of lumber replacements, such as laminated veneer lumber, which fully cure at relatively low temperatures, e.g., room temperature. There is also a need for such adhesives which have a prolonged pot life suitable for use in commercial production methods. Moreover, there is a need for processes for preparing composite products with cellulosic and lignocellulosic materials using such adhesives.
SUMMARY OF THE INVENTION
These objectives are obtained by the present adhesive compositions which demonstrate excellent adhesive properties with a prolonged pot life and fast cure, particularly at room temperature. The present compositions are activated by the moisture present in the substrate with which they are being used and thus, they may be most effectively used with substrates having a relatively high moisture content, such as 7% or more. Accordingly, the present compositions are effectively used with various types of lignocellulosic materials and are particularly useful in the preparation of lumber replacements as discussed above. The present adhesive compositions have a further advantage over prior art systems in that they are cold curable, i.e., may be cured at room temperature, or by the application of heat.
The present invention is directed to moisture-activated adhesive compositions comprising the reaction product of (a) a polyisocyanate and (b) an isocyanate-reactive component comprising at least one aliphatic tertiary amine-initiated polyol having an ethylene oxide content of at least 1%. The present invention is further directed to a process for bonding multiple substrates comprising: (1) applying to a surface of at least one substrate a moisture-activated adhesive composition comprising the reaction product of (a) a polyisocyanate and (b) an isocyanate-reactive component comprising at least one aliphatic tertiary amine-initiated polyol having an ethylene oxide content of at least 1%; (2) contacting this surface of the substrate with a surface of a second substrate; (3) applying pressure to the contacted surfaces; and (4) curing the adhesive composition.
DETAILED DESCRIPTION OF THE INVENTION
The present adhesive compositions comprise about 99 to about 70%, preferably about 93 to about 80% and most preferably about 90 to about 80% by weight of the polyisocyanate component.
Polyisocyanates useful in the present invention are those having a number-average isocyanate functionality greater than 2.0, preferably greater than 2.1, more preferably greater than 2.3 and most preferably greater than 2.5. Useful polyisocyanates should have a number average molecular weight of from about 100 to about 5000 and preferably about 120 to about 1800. Preferably, at least 50 mole percent and preferably at least 90 mole percent of the isocyanate groups are bonded directly to aromatic groups.
Suitable aromatic polyisocyanates include, e.g., p-phenylene diisocyanate; m-phenylene diisocyanate; 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; naphthalene diisocyanate; dianisidine diisocyanate; polymethylene polyphenyl polyisocyanate; 2,4′-diphenyl methane diisocyanate (2,4′-MDI) ; 4,4′-diphenylmethane diisocyanate (4,4′-MDI); 3,3′-dimethyl-4,4′-biphenylene diisocyanate; polydiphenylmethane polyisocyanate having a functionality of greater than 2; and mixtures thereof. The polyisocyanates should have a 2,4′-MDI content of less than 18.0%, preferably less than 10% and most preferably less than 5%. The MDI isomers, mixtures of these isomers with polydiphenylmethane polyisocyanates, polydiphenylmethane itself and derivatives thereof are preferred.
The polyisocyanate may include minor amounts of aliphatic polyisocyanates. Suitable aliphatic polyisocyanates include isophorone diisocyanate; 1,6-hexamethylene diisocyanate; 1,4-cyclohexyl diisocyanate; saturated analogues of the above-mentioned aromatic polyisocyanates and mixtures thereof.
The polyisocyanate component of the present composition is preferably a polymeric polyisocyanate, and more preferably a polymeric diphenylmethane diisocyanate. Commercially available polymeric polyisocyanates include Rubiflex® 26A available from ICI Americas Inc., Wilmington, Del.
Isocyanate-terminated prepolymers may also be employed in the present invention. As used herein, the term “isocyanate-terminated prepolymer” includes the prepolymer as well as the pseudoprepolymer, i.e., a mixture of the prepolymer and the polyisocyanate from which the prepolymer is prepared. The isocyanate-terminated prepolymer useful in the present compositions should have a free isocyanate (NCO) content of from about 10 to about 26%, preferably about 16 to about 26%. In general, the polymeric polyisocyanate may be prepared by the reaction of an excess of a polyisocyanate and a polyol, including aminated polyols or imino/enamines thereof.
Suitable polyols for preparing the isocyanate-terminated prepolymers include:
(a) polyether polyols, thioether polyols and/or hydrocarbon-based polyols having a molecular weight of from about 1000 to 3000 and an average hydroxyl functionality of from about 1.9 to 4;
(b) polyester polyols having a molecular weight of 1000 or more and an average hydroxyl functionality of from about 1.9 to 4.
A particularly preferred isocyanate-terminated prepolymer useful in the present invention are MDI prepolymers which are the reaction product of an excess of polymeric MDI and polyether
Robertson John Russell
Yavorsky James Anthony
Boland Kevin J.
Gallagher John J.
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