PROCESS FOR PREPARING POLYAMIDE POWDERS BY PRECIPITATION

Abstract

Process for producing polyamide powders by precipitation The present invention relates to a process for producing polyamide powders and to the polyamide powders obtainable by this process. The present invention additionally relates to the use of the polyamide powder as sintering powder in selective laser sintering.

Claims

1.-12. (canceled)

13. A process for producing polyamide powder comprising the process steps of a) heating a mixture comprising a polyamide and a lactam to a temperature greater than a cloud temperature (T.sub.Cl) above which the polyamide is fully dissolved in the lactam to obtain a melt which comprises the polyamide fully dissolved in the lactam, b) cooling the melt obtained in process step a) to a temperature lower than or equal to the cloud temperature (T.sub.Cl) and subsequently adding water to obtain a suspension comprising the polyamide powder suspended in a solution comprising water and the lactam, and c) removing the polyamide powder from the suspension obtained in process step b), wherein the lactam has a melting temperature (T.sub.M) and the melt obtained in process step a) is cooled in process step b) to a temperature in the range from equal to the cloud temperature (T.sub.Cl) to greater than the melting temperature (T.sub.M) of the lactam and water is subsequently added, wherein the amount of the water added in process step b) is 1 to 100 parts by weight of water based on one part by weight of the polyamide present in the melt, wherein the polyamide powder obtained according to process step c) has a D10 value in the range from 5 to 50 μm, a D50 value in the range from 20 to 80 μm and a D90 value in the range from 40 to 150 μm.

14. The process according to claim 13, wherein in process step a) the mixture is heated to a temperature in the range from 170° C. to 250° C. to obtain the melt.

15. The process according to claim 13, wherein the addition of water in process step b) is effected at a temperature in the range from 20 to <170° C. and after reaching or going below the cloud temperature (T.sub.Cl).

16. The process according to claim 13, wherein the polyamide has a crystallization temperature (T.sub.Cr) and the melt obtained in process step a) is cooled in process step b) to a temperature in the range from equal to the cloud temperature (T.sub.Cl) to not more than 20° C. below the crystallization temperature (T.sub.Cr) of the polyamide and water is subsequently added.

17. The process according to claim 13, wherein the melt obtained in process step a) comprises the polyamide in amounts in the range from 5 to 60 wt % based on the total weight of the melt obtained in process step a).

18. The process according to claim 13, wherein the water content of the melt obtained in process step a) is in the range from 0 to less than 5 wt % based on the total weight of the melt obtained in process step a).

19. The process according to claim 13, wherein the lactam is selected from the group consisting of 3-aminopropanolactam, 4-aminobutanolactam, 5-aminopentanolactam, 6-aminohexanolactam, 7-aminoheptanolactam, 8-aminooctanolactam, 9-nonanolactam, 10-decanolactam, 11-undecanolactam, and 12-dodecanolactam.

20. The process according to claim 13, wherein the polyamide is selected from the group consisting of PA 4, PA 6, PA 7, PA 8, PA 9, PA 11, PA 12, PA 46, PA 66, PA 69, PA 610, PA 612, PA 613, PA 1212, PA1313, PA 6T, PA MXD6, PA 6l, PA 6-3-T, PA 6/6T, PA 6/66, PA 6/12, PA 66/6/610, PA 6l/6T, PA PACM 12, PA 6l/6 T/PACM, PA 12/MACMI, PA 12/MACMT, PA PDA-T and copolyamides formed from two or more of the abovementioned polyamides.

21. The process according to claim 13, wherein the melt present in process step a) comprises at least one anti-nucleation agent selected from the group consisting of lithium chloride, nigrosine, methylene blue and neutral red.

22. The process according to claim 13, wherein the anti-nucleation agent is added in process step a) in amounts such that the polyamide powder obtained according to process step c) comprises the anti-nucleation agent in amounts in the range from 0.1 to 3 wt % based on the total weight of the polyamide obtained according to process step c).

23. A polyamide powder obtainable by a process according to claim 13, wherein the polyamide powder comprises less than 5% by weight of fines, based on the total weight of the polyamide powder, wherein fines are understood to be polyamide particles having a particle size smaller than 10 μm.

24. A method comprising producing a molded article by selective laser sintering utilizing the polyamide powder obtained by the process according to claim 13 as sintering powder.

Description

EXAMPLE 1

[0164] 40 g of polyamide 6 having a viscosity number of 144 ml/g and 160 g of ε-caprolactam were initially charged into a 1 L four-necked flask fitted with an internal thermometer. The mixture was then inertized with nitrogen and heated to 190° C. (internal temperature) with stirring. After four hours, a melt which comprised the polyamide 6 fully dissolved in the ε-caprolactam was obtained. The melt was subsequently cooled to a temperature lower than the cloud temperature (T.sub.Cl). The flask contents solidified at an internal temperature of 125° C. 300 mL of deionized water (DI water) were then added to dissolve the ε-caprolactam. The flask contents were stirred here at 100 rpm. A suspension comprising the polyamide powder suspended in a solution comprising water and the ε-caprolactam was obtained. The polyamide powder was subsequently removed by means of a pressure filter (Seitz-Filter T1500) and washed with water and subsequently dried for 16 hours at 80° C. under a nitrogen atmosphere in a vacuum drying cabinet.

[0165] The polyamide powder had a D10 value of 24.0 μm, a D50 value of 62.7 μm and a D90 value of 129 μm.

[0166] The particle size distribution was determined by laser diffraction with a Malvern Mastersizer 3000. Evaluation was by means of Fraunhofer diffraction.

EXAMPLE 2

[0167] 18.5 g of polyamide 6 having a viscosity number of 144 ml/g and 166.5 g of ε-caprolactam were initially charged into a pressure reactor and inertized with nitrogen. This mixture was subsequently heated with stirring to 190° C. (internal temperature) to obtain a melt which comprised the polyamide 6 fully dissolved in the ε-caprolactam. In a second pressure cylinder 185 ml of DI water were heated to 140° C. After 4.5 hours the melt was slowly cooled to a temperature below the cloud temperature (T.sub.Cl). The external temperature of the pressure reactor was 145° C. The internal temperature was determined via a temperature sensor and was 140.8° C. The internal temperature of the pressure reactor subsequently increased slightly. This is attributable to the onset of crystallization of the polyamide 6. Directly after detection of the temperature increase the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The thus obtained suspension was stirred for 30 minutes. The mixture was subsequently cooled to room temperature (20° C.) and the obtained polyamide powder removed, worked up and analyzed as described hereinabove in connection with example 1.

[0168] The thus obtained polyamide powder had a D10 value of 22 μm, a D50 value of 38 μm and a D90 value of 60 μm.

[0169] The particle size distribution was determined by laser diffraction with a Malvern Mastersizer 3000. Evaluation was by means of Fraunhofer diffraction.

EXAMPLE 3

[0170] 166.5 g of ε-caprolactam was initially charged into a pressure reactor having an internal thermometer and inertized with nitrogen. The ε-caprolactam was then melted by heating to 120° C. 18.5 g of polyamide 6 having a viscosity number of 120 ml/g and 0.69 g of Ultrabatch (40% nigrosine, 60% polyamide 6) were added with stirring to the ε-caprolactam melt and the mixture was subsequently heated to 190° C. (internal temperature) over 5 hours to obtain a melt which comprised the polyamide 6 fully dissolved in the ε-caprolactam.

[0171] In a second pressure cylinder 185 ml of DI water were heated to 170° C. The melt was slowly cooled to a temperature below the cloud temperature (T.sub.Cl). The external temperature of the pressure reactor was 132° C. The internal temperature was 132.8° C. The mixture was held at this temperature for 10 minutes. 30 seconds after an increase in the internal temperature of the pressure reactor was detected the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The thus obtained suspension was subsequently reheated to 170° C. (internal temperature). After 10 minutes the mixture was cooled to room temperature (20° C.) with stirring and the obtained polyamide powder removed, worked up and analyzed as described hereinabove in connection with example 1.

[0172] The thus obtained polyamide powder had a D10 value of 37.2 μm, a D50 value of 63.2 μm and a D90 value of 104.5 μm.

[0173] The particle size distribution was determined by laser diffraction with a Malvern Mastersizer 3000. Evaluation was performed by means of Fraunhofer diffraction.

EXAMPLE 4

[0174] 166.5 g of ε-caprolactam was initially charged into a pressure reactor having an internal thermometer and inertized with nitrogen. The ε-caprolactam was then melted by heating to 120° C. 18.5 g of polyamide 6 having a viscosity number of 120 ml/g and 0.69 g of Ultrabatch (40% nigrosine, 60% polyamide 6) were added to the ε-caprolactam melt with stirring and the mixture was subsequently heated to 190° C. (internal temperature) with stirring over 5 hours to obtain a melt which comprised the polyamide 6 fully dissolved in the ε-caprolactam.

[0175] In a second pressure cylinder 185 ml of DI water were heated to 20° C. The melt was slowly cooled to a temperature below the cloud temperature (T.sub.Cl). The external temperature of the pressure reactor was 130° C. The internal temperature was 130.3° C. 2 minutes after an increase in the internal temperature of the pressure reactor was detected the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The thus obtained suspension was subsequently cooled to room temperature (20° C.) with stirring and the obtained polyamide powder removed, worked up and analyzed as described hereinabove in connection with example 1.

[0176] The thus obtained polyamide powder had a D10 value of 19.4 μm, a D50 value of 33.2 μm and a D90 value of 49.2 μm.

[0177] The particle size distribution was determined by laser diffraction with a Malvern Mastersizer 3000. Evaluation was by means of Fraunhofer diffraction.

EXAMPLE 5

[0178] 166.5 g of ε-caprolactam was initially charged into a pressure reactor having an internal thermometer and inertized with nitrogen. The ε-caprolactam was then melted by heating to 120° C. 18.5 g of polyamide 6 having a viscosity number of 120 ml/g and 0.69 g of Ultrabatch (40% nigrosine, 60% polyamide 6) were added to the ε-caprolactam melt with stirring and the mixture was subsequently heated to 190° C. (internal temperature) over 5 hours to obtain a melt which comprised the polyamide 6 fully dissolved in the ε-caprolactam.

[0179] In a second pressure cylinder 185 ml of DI water were heated to 150° C. The melt was slowly cooled to a temperature below the cloud temperature (T.sub.Cl). The internal temperature was 150° C. Before an increase in the internal temperature of the pressure reactor was detected the water preheated in the second pressure cylinder was supplied to the pressure reactor with stirring. The thus obtained suspension was subsequently cooled to room temperature (20° C.) with stirring and the obtained polyamide powder 0.30 removed, worked up and analyzed as described hereinabove in connection with example 1.

[0180] The thus obtained polyamide powder had a D10 value of 30.2 μm, a D50 value of 57.6 μm and a D90 value of 100.4 μm.

[0181] The particle size distribution was determined by laser diffraction with a Malvern Mastersizer 3000. Evaluation was performed by means of Fraunhofer diffraction.