DISTILLATIVE SEPARATION OF KETAZINE FROM POLYURETHANE DISPERSIONS

Abstract

The present invention relates to a process for removing ketazine from polyurethane dispersions by means of distillation below the boiling point of ketazine.

Claims

1. Process for removing ketazine from a polyurethane dispersion comprising the step of the distillation of the polyurethane dispersion, wherein the vapour temperature exceeds the temperature at which removal of acetone is achieved by at maximum 10%.

2. Process according to claim 1, wherein the distillation is carried out at a pressure of at least 120 mbar and a vapour temperature of at most 53 C.

3. Process according to claim 2, wherein the temperature at the bottom is at most 53 C.

4. Process according to claim 2, wherein the distillation is commenced at a temperature at the bottom of at most 45 C. and is continued until the temperature at the bottom is at maximum 53 C.

5. Process according to claim 1, wherein the distillation is continued for at least two hours after reaching a temperature at the bottom of 48 C.

6. Process according to claim 2, wherein the pressure does not exceed 140 mbar.

7. Process according to claim 1, wherein the polyurethane dispersion comprises acetone and water.

8. Process according to claim 1, wherein the polyurethane was constructed by chain extension of a prepolymer with hydrazine.

9. Process according to claim 1, wherein the ketazine content of the polyurethane dispersion after the end of the distillation is below 1000 ppm.

Description

EXAMPLE 1: PREPARATION OF A CRUDE DISPERSION

[0052] The crude dispersion was prepared as follows: a polyester polyol and further polyols having a molar mass <400 g/mol were initially charged in a polymerization reactor and heated to 70 C. A polyisocyanate mixture was then metered in and the internal reactor temperature Increased to 100C. The reaction mixture was stirred at 100C until the theoretical NCO value of 4.47% by weight had been reached. The resulting isocyanate-functional prepolymer was then cooled to 60 C. and dissolved in acetone. After complete dissolution in acetone, the prepolymer solution was transferred to the distillation reactor and, at 40C, the aqueous solution of a mixture of the sodium salt of aminoethylaminoethanesulphonic acid with hydrazine for the chain extension was added with stirring and the mixture then stirred for a further 15 min. Finally, the dispersion with water was carried out. The slightly milky polyurethane crude dispersion had a pH of 6.9 and a solids content of 23.8% by weight.

EXAMPLE 2 (COMPARATIVE): CONVENTIONAL DISTILLATION OF THE CRUDE DISPERSION

[0053] The crude dispersion was heated to 40 C. in the distillation reactor. A vacuum was then applied which was lowered stepwise to 120 mbar. After reaching 120 mbar, the bottom temperature and also the vapour temperature increased continuously. On reaching a vapour temperature of 48.5 C., the acetone content of the dispersion was below 1% by weight and the distillation was terminated.

[0054] The ketazine content at the end of the distillation was 1100 ppm.

EXAMPLE 3: INVENTIVE DISTILLATION PROCESS

[0055] The crude dispersion was heated to 40 C. in the distillation reactor. A vacuum was then applied which was lowered stepwise to 120 mbar. After reaching 120 mbar, the bottom temperature and also the vapour temperature increased continuously.

[0056] After reaching a vapour temperature of 48.5 C., the bottom temperature was increased to 51 C. over a time period of two hours at an unchanged pressure of 120 mbar.

[0057] At the end of the distillation process according to the invention, the ketazine content was 65 ppm.