One-component hot melt polyurethane adhesive
One-component, moisture-curable polyurethane adhesives exhibit excellent handling strength before being fully cured, and excellent creep properties after curing. The adhesives include an isocyanate-terminated prepolymer made from polyols that include a crystalline polyester and hydroquinone bis (2-hydroxyethyl) ether, and a polyoxazolidine compound.
1. A one-component, moisture-curable, hot melt polyurethane adhesive composition which is a heat-softenable room temperature solid comprising:
A) 50 to 98% by weight, based on the total weight of the adhesive composition, of a polyurethane prepolymer containing free isocyanate groups, the prepolymer being a reaction product of:
1) A mixture of polyols that comprises
i) at least 35 weight percent, based on the weight of the mixture of polyols, of at least one hydroxyl-terminated polyester that is liquid at 22° C.;
ii) at least 10 weight percent, based on the weight of the mixture of polyols, of at least one hydroxyl-terminated polyester that is a solid at 22° C. and exhibits a crystalline melting temperature of 70 to 130° C.; and
iii) 5 to 20 weight percent, based on the weight of the mixture of polyols, of hydroquinone bis-(2-hydroxyethyl) ether; with
2) An excess of at least one organic polyisocyanate;
B) 1 to 10% by weight, based on the total weight of the adhesive composition, of at least one polyoxazolidine compound having a molecular weight of up to 2000; and
C) a catalytically effective amount of a catalyst for a reaction of water with an isocyanate group.
2. The one-component, moisture-curable, hot melt polyurethane adhesive composition of claim 1 wherein component ii) has a crystalline melting temperature of 75 to 100° C.
3. The one-component, moisture-curable, hot melt polyurethane adhesive composition of claim 1 wherein component ii) has a hydroxyl equivalent weight of 700 to 2500 and a hydroxyl functionality of 1.8 to 3.
4. The one-component, moisture-curable, hot melt polyurethane adhesive composition of claim 1 wherein component i) has a hydroxyl equivalent weight of 700 to 1500 and a hydroxyl functionality of 1.8 to 3.
5. The one-component, moisture-curable, hot melt polyurethane adhesive composition of claim 1 wherein the polyoxazolidine compound is represented by structure I or structure II:
wherein R is hydrogen, alkyl, aryl-substituted alkyl, phenyl or alkyl-substituted phenyl, x is from 1 to 20, and each y is independently 1 to 20.
6. The one-component, moisture-curable, hot melt polyurethane adhesive composition of claim 5 wherein the polyoxazolidine compound has the structure:
7. The one-component, moisture-curable, hot melt polyurethane adhesive composition of claim 1 wherein the mixture of polyols contains 12 to 25% by weight of component ii), based on the weight of the mixture of polyols.
8. A cured adhesive formed by curing the one-component polyurethane adhesive composition of claim 1 .
9. A cured adhesive formed by contacting the one-component polyurethane adhesive composition of claim 1 with H 2 O.
10. A method of bonding two substrates, comprising forming a layer of the one-component polyurethane adhesive of claim 1 at a bondline between two substrates, and curing the layer at the bondline to form a cured adhesive bonded to each of the substrates.
11. A method of bonding two substrates, comprising forming a layer of the one-component polyurethane adhesive of claim 1 at a bondline between two substrates, and curing the layer at the bondline by contacting the layer with H 2 O to form a cured adhesive bonded to each of the substrates.