Method for making aqueous polyimide electrocoating mixtures
AssigneeGeneral Electric Company
InventorsJohn H. Lupinski, Edith M. Boldebuck, Wilson J. Barnes
Life of this patent
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Abstract
A method is provided for making stable electrocoatable polyimide mixtures having a high water content. A solution of polyimide in a dipolar aprotic solvent is heated in the presence of base resulting in a transitory viscosity decrease. Major amounts of water can thereafter be added to the mixture during its reduced viscosity state to produce a stable aqueous mixture.
Claims7
A method for making an electrocoatable polyamide acid salt mixture having a high water content which comprises,
- 1. heating a polyimide solution of a dipolar aprotic organic solvent having at least 15% by weight of polyimide, to a temperature in the range of between about 50.degree. C to 150.degree. C in the presence of a base whose ionization constant in water at 25.degree. C has a value greater than 10.sup.-2, until the viscosity of the resulting mixture is less than 4,000 centistokes at 25.degree. C.
- 2. adding sufficient water to the resulting mixture of (1) while its viscosity is less than 4,000 centipoises at 25.degree. C, to produce a mixture having from 5% to 40% by weight of dipolar aprotic organic solvent, 40% to 95% by weight of water and 1 to 15% by weight of solids, where the total weight of solids, water and dipolar aprotic solvent is equal to 100%, and the base is utilized in the solution of (1) at a concentration which is sufficient to neutralize any carboxy radicals of the polyimide, while providing from 0.01 to about 1 meq of base/g of polyimide having a MW sufficient to produce a viscosity of at least 1,000 centristokes at 25.degree. C in N-methylpyrrolidone when present at 25% by weight solids.
A method for making an electrocoatable polyamide acid salt mixture having a high water content which comprises
- 1. heating a solution of a polyimide which is the reaction product of a bis(n-4-carboxyphthalimide) and an organic diisocyanate in N-methylpyrrolidone having at least 15% by weight of such polyimide, to a temperature in the range of between 50.degree. C to 150.degree. C in the presence of sodium hydroxide until the viscosity of the resulting mixture is less than 4,000 centistokes at 25.degree. C,
- 2. adding sufficient water to the resulting mixture of (1) while its viscosity is less than 4,000 centistokes at 25.degree. C to produce a mixture having from 5-15% by weight solids, 15-40% by weight of N-methylpyrrolidone and 45-80% by weight of water where the sodium hydroxide is used to a concentration which is sufficient to neutralize any carboxy radicals of the polyimide while providing from 0.01 to about 1 meq of sodium hydroxide per gram of polyimide.
Dependencies are inferred from the claim text.