Laminates and method of making them

A method of laminating a saran surface to another saran surface, a saran surface to a treated polyethylene surface, or a treated polyethylene surface to a treated polyethylene surface, said method comprising:

• A. applying a thin film of an adhesive composition to at least one of the surfaces to be laminated, said adhesive composition comprising an aqueous solution of a water soluble salt of a substantially linear thermoplastic polyurethane containing 0.5 to 2.5% by weight of nitrogen derived from tertiary amine groups and from 2 to 8% of nitrogen derived from isocyanate groups, said polyurethane being prepared by (a) reacting an excess of an isocyanate with a mixture of diols consisting of polyether diols having a molecular weight of from 425 to 4,000 and tertiary amine diols selected from the group consisting of N-phenyl dialkanol amine and N-lower alkyl dialkanol amines to obtain a reaction product having free isocyanate groups greater than 0.1 milliequivalents of NCO per gram of solution at 50% solids;
• (b) chain extending the reaction product with a chain extender selected from the group consisting of alkanol amines and alkylene diamines to obtain a chain extended polyurethane polymer containing from 0.07 to 0.1 milliequivalents of NCO per gram of solution at 50% solids;
• (c) reacting the free isocyanate groups with a material selected from the group consisting of water miscible alcohols, acids and water, and adding an amount of water miscible acid being added sufficient to form the acid salts with the tertiary amine groups present on the polyurethane;
• B. evaporating solvent from the film of adhesive and
• C. laminating the adhesive coated surface to the other surface to be laminated to obtain a bond strength of at least 350 grams.