METHOD FOR PREPARING A POLYMER DISPERSION

Abstract

The present disclosure relates to a process and/or method for producing a polymer dispersion by free-radically initiated emulsion polymerization of radically polymerizable ethylenically unsaturated monomers within a polymerization reactor. The polymer dispersion obtained is transferred to a post-treatment reactor and is post-treated therein. The polymer dispersion within the post-treatment reactor is conveyed, simultaneously to the post-treatment, to a circuit for filtration and analysis and is then subsequently fed back into the post-treatment reactor.

Claims

1. (canceled)

2. (canceled)

3. (canceled)

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. A method for preparing a polymer dispersion, the method comprising the steps of: providing a polymerization reactor; obtaining a polymer dispersion by free-radically initiated emulsion polymerization of radically polymerizable ethylenically unsaturated monomers within the polymerization reactor; transferring the polymer dispersion obtained to a post-treatment reactor; and post-treating the polymer dispersion within the post-treatment reactor by physical and/or chemical methods and wherein the polymer dispersion in the post-treatment reactor is conveyed simultaneously to the post-treatment to a circuit for filtration and analysis and then is subsequently fed back into the post-treatment reactor.

9. The method of claim 8, wherein the polymer dispersion is an aqueous polymer dispersion.

10. The method of claim 8, wherein the circuit is configured such that the flow rate per hour corresponds to at least the liquid volume within the post-treatment reactor.

11. The method of claim 8, wherein the filtration is effected by automatic cleaning filters having mesh sizes of approximately 50 μm to approximately 1000 μm.

12. The method of claim 8, wherein the analysis comprises determining mean particle size, molar mass, solids content, viscosity, VOC content, residual monomer content, redox potential and/or pH.

13. The method of claim 12, wherein the analysis is measured using one or more analytical devices.

14. The method of claim 8, wherein the post-treatment comprises a first phase and a second phase; wherein in the first phase the polymerized polymer dispersion is depressurized to a pressure from approximately 0.1 bar to approximately 5.0 bar absolute; and wherein in the second phase a gaseous phase resulting from the depressurization during the first phase is withdrawn.

15. The method of claim 14, wherein the post-treatment further comprises a third phase and wherein in the third phase a post-polymerization occurs.

16. The method of claim 14, wherein the post-treatment further comprises a fourth phase and wherein in the fourth phase volatile components are removed by passing over or passing through inert entrainment gases.

17. The method of claim 14, wherein the post-treatment further comprises allowing the polymer dispersion to be cooled.

18. The method of claim 8, wherein the filtration and analysis is carried out in single phases of the post-treatment or in every phase of the post-treatment.

19. The method of claim 8, wherein the circuit is an external circuit.

20. The method of claim 19, wherein during the post-treatment of the polymer dispersion the polymer dispersion is conveyed continuously from the post-treatment reactor to the external circuit for filtration and analysis and is then subsequently fed back into the post-treatment reactor.

Description

[0055] The following examples and FIG. 1 serve to further elucidate the invention:

[0056] FIG. 1 shows a simplified scheme for a device for carrying out the process with a polymerization reactor 1, a post-treatment reactor 2 and a circuit 3 which is equipped with a filter device 4, a pump 5 and an analytical device 6.

COMPARATIVE EXAMPLE 1

[0057] The following components were initially charged in a ca. 600 liter volume pressure reactor:

[0058] 115 kg of water,

[0059] 105 kg of a 20% by weight polyvinyl alcohol solution of a partially saponified polyvinyl alcohol having a degree of hydrolysis of 88 mol % and a Höppler viscosity of 4 mPas (Höppler method according to DIN 53015 at 20° C. and in 4% aqueous solution), 11 kg of a 10% by weight polyvinyl alcohol solution of a partially saponified polyvinyl alcohol having a degree of hydrolysis of 88 mol % and a Höppler viscosity of 25 mPas, 70 g of an 85% aqueous solution of formic acid, 80 g of a 10% aqueous iron ammonium sulfate solution.

[0060] The reactor was evacuated, then 220 kg of vinyl acetate were added to the aqueous initial charge. The reactor was then heated to 55° C. and subjected to an ethylene pressure of 32 bar (corresponding to an amount of 28 kg of ethylene).

[0061] The polymerization was started by adding 3% by weight aqueous potassium persulfate solution at a rate of 1.5 kg/h and by adding 1.5% by weight aqueous sodium hydroxymethanesulfinate solution (Bruggolite) at a rate of 1.5 kg/h. After observing the start of the polymerization, the internal temperature was increased to 85° C. over the course of 30 minutes. From the start of the reaction, the pressure was increased to 55 bar and maintained until a further 10 kg of ethylene had been metered in. The ethylene valve was then closed and the pressure allowed to drop. After reaching the polymerization temperature of 75° C., a further 55 kg of vinyl acetate were metered in over the course of 2 hours and the initiator rates were increased to a rate of 2.0 kg/h to 2.5 kg/h. After the vinyl acetate had been metered in, the initiators ran for a further 60 minutes to polymerize the batch.

[0062] The total polymerization time was ca. 5 hours.

[0063] The polymer dispersion had a temperature of 80° C. and was subsequently depressurized from the polymerization reactor at a pressure of 55 bar abs. into a post-treatment reactor (volume ca. 2000 liters) to a pressure of 0.8 bar abs. After 30 minutes, the dispersion was degassed over a period of 30 minutes by applying a pressure of 0.5 bar abs. After completion of the degassing, 500 g of a 10% by weight aqueous solution of tertiary-butyl hydroperoxide and 145 g of a 10% by weight aqueous solution of Bruggolite were added and the dispersion post-polymerized over a period of 2 hours. After completion of the post-polymerization, the polymer dispersion was stripped by passing through steam at 60 kg/h (6 bar abs, 158° C.) for 1 hour. The mixture was then cooled for a further 1.5 hours until the temperature of the polymer dispersion was 38° C.

[0064] After completion of the post-treatment steps, a 0.5 liter sample was taken from the post-treatment reactor and the solids content, viscosity, pH, redox potential and residual monomer content analyzed in the laboratory using conventional methods. The waiting time until the analytical results were available was ca. 1.5 hours.

[0065] After checking all the analytical results, the polymer dispersion was filtered while being pumped out of the post-treatment reactor by means of a commercially available bag filter composed of nylon fabric having a mesh size of 500 μm. Due to the filtration, the hourly throughput was limited to 0.4 m.sup.3/h.

[0066] The total cycle time of the post-treatment in the post-treatment reactor in comparative example 1 adds up to 7 hours.

EXAMPLE 2

[0067] Polymerization was conducted analogously to comparative example 1 in polymerization reactor 1 having a volume of ca. 600 liters. The total polymerization time was ca. 5 hours.

[0068] The polymer dispersion had a temperature of 80° C. and was subsequently depressurized from polymerization reactor 1 at a pressure of 55 bar abs. into the post-treatment reactor 2 to a pressure of 0.8 bar abs.

[0069] As shown in FIG. 1, the post-treatment reactor 2 was equipped with an external circuit 3, a pipeline which exits at the bottom of the post-treatment reactor 2 and is fed back in the circuit to the post-treatment reactor 2. In this external circuit 3 were installed a filter 4 (bag filter composed of nylon fabric with 500 μm mesh size), a pump 5 (eccentric screw pump) and an analytical unit 6 (determination of solids content via density measurement by Coriolis with an Endress+Hauser Proline 83i, viscosity measurement via torsional vibration with a Marimex VA-300 L-LT, pH and redox potential via commercial glass probes from Knick, and residual monomer content via NIR with an IRcube FT-IR from Bruker). The analytical values were monitored online via the process control system.

[0070] 15 minutes after starting the depressurization, a liquid phase had formed at the bottom of post-treatment reactor 2 and the pump 4 was switched on and the polymer dispersion was pumped through the circuit at 1.2 m.sup.3/h.

[0071] 30 minutes after starting the depressurization, the dispersion was degassed by applying a pressure of 0.5 bar abs. over a period of 30 minutes. After completion of the degassing, 500 g of a 10% by weight aqueous solution of tertiary-butyl hydroperoxide and 145 g of a 10% by weight aqueous solution of Bruggolite were added and the dispersion post-polymerized over a period of 2 hours. After completion of the post-polymerization, the polymer dispersion was stripped by passing through steam at 60 kg/h (6 bar abs., 158° C.) for 1 hour. The mixture was then cooled for a further 1.5 hours until the temperature of the polymer dispersion was 38° C.

[0072] After cooling was complete, the pump 4 was switched on.

[0073] The polymer dispersion was free from coagulate and was mixed with 1200 g of biocide and pumped out into the storage container at an hourly throughput of 1.2 m.sup.3/h.

[0074] The total cycle time of the post-treatment in example 2 was 5.5 hours.

[0075] The comparison of example 2 (5.5 h) with comparative example 1 (7.0 h) shows that the time for the production of a polymer dispersion is significantly shortened with the process according to the invention. The hourly throughput when pumping the polymer dispersion into the storage container is significantly increased due to the continuous filtration during the post-treatment in example 2 (1.2 m.sup.3/h) compared to comparative example 1 (0.4 m.sup.3/h).

[0076] The advantages of the process according to the invention consist in that the post-processing, filtration and analysis of the polymer dispersion are no longer carried out sequentially, but instead take place in parallel or simultaneously. This causes a significant shortening of the cycle times for the production of the polymer dispersion.

[0077] When using online analytical devices, the analysis of the polymer dispersion is accelerated and the risk of exposure to VOCs for the operating personnel is drastically reduced.

[0078] Surprisingly, soft gel particles, such as those from VAE dispersions, can also be separated off by means of filtration with the method according to the invention.