Method of making moisture-resistant polyurethane-based pressure-sensitive adhesives
AssigneeAnchor Continental, Inc.
InventorRalph L. Anderson
Life of this patent
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Abstract
In U.S. Pat. Nos. 3,437,622 and 3,761,307 and U.S. Pat. application Ser. No. 323,944, filed January 15, 1973 and now abandoned, are disclosed pressure-sensitive adhesives, the required cohesive strength of which is provided by a polyurethane polymer in place of the natural or synthetic rubber of the prior art. However, some of such polyurethane-based adhesives are not highly resistant to moisture unless special procedures are used. For example, they may lose 20 to 75% of their adhesiveness after exposure for 3 days or less to 90% relative humidity at 150.degree.F. This invention discloses means of overcoming this problem by combinations of excluding moisture, adding minor proportions of the reaction-products of hydroxylated elastomers or of hexamethylene tetramine.
Claims25
A method of making a moisture-resistant, polyurethane-based, pressure-sensitive adhesive which comprises carrying out the following steps with substantial exclusion of moisture in steps (1) through (5):
- (1) reacting an aromatic polyisocyanate with polyols of average molecularweight between 1500 and 5000 and hydroxyl number between 30 and 100 containing dissolved, compatible, tackifying resins in amount between 40 and 150 per cent of the combined weight of the polyol of step (1) and the elastomer of the following step (2), in the proportion of from 1.1 to 1.7 equivalents of isocyanate per equivalent of hydroxyl;
- (2) reacting a liquid hydroxylated elastomer of hydroxyl number between 20 and 60 with an aromatic polyisocyanate in the proportion of between 1.7 and 1.1 equivalents of isocyanate per equivalent of hydroxyl;
- (3) adding to the product of step (1) an amount of the product of step (2) to make a mixture containing between 6 and 25% of the product of step (2);
- (4) adding active polyurethane catalyst to the product of step (3) in amount between 0.3 and 5 per cent of the weight of polyurethane polymers therein;
- (5) coating the product of step (4) upon a stable, flexible, inert backing material in amount to leave a final weight of solids of between 3 and 11 grams per square foot;
- (6) heating the product of step (5) at a temperature of between 180.degree. and 360.degree.F. for a time sufficient to substantially complete the reaction of isocyanate and leave a dry coating, but not substantially longer.
Dependencies are inferred from the claim text.