ANTI-NUCLEATING AGENT FOR LASER SINTERING POWDER

Abstract

The present invention relates to a process for producing shaped bodies by selective laser sintering of a sinter powder (SP) comprising a polyamide (P) and 0.1% to 5% by weight of at least one additive (A). The present invention also relates to shaped bodies comprising polyamide (P) and 0.1% to 5% by weight of at least one additive (A). The present invention further relates to the production of sinter powders (SP) comprising polyamide (P) and 0.1% to 5% by weight of at least one additive (A).

Claims

1.-13. (canceled)

14. A process for producing shaped bodies by selective laser sintering of a sinter powder (SP) comprising a polyamide (P) and 0.1% to 5% by weight of at least one additive (A), based on the total weight of the sinter powder (SP), wherein the at least one additive (A) is selected from the group consisting of compounds of the formula (I) ##STR00016## in which R and R.sup.2 are independently selected from the group consisting of H, C.sub.1-to C.sub.4-alkyl and NR.sup.5R.sup.6, where R.sup.5 and R.sup.6 are independently selected from the group consisting of H and C.sub.1-to C.sub.4-alkyl, R.sup.3 and R.sup.4 are independently selected from the group consisting of H, C.sub.1-to C.sub.4-alkyl and NR.sup.9R.sup.10, where R.sup.9 and R.sup.10 are independently selected from the group consisting of H and C.sub.1-to C.sub.4-alkyl, X is N, S.sup.+ or N.sup.+R.sup.13, where R.sup.13 is selected from the group consisting of H and C.sub.1-to C.sub.4-alkyl, where the compounds of the formula (I) have a positive charge when X is S.sup.+ or N.sup.+R.sup.13 and the compounds of the formula (I) then comprise an anion Y.sup., where Y.sup.+ is selected from the group consisting of hydroxide, chloride, bromide, iodide, sulfate, sulfite, phosphate and phosphite.

15. The process according to claim 14, wherein X in compounds of the formula (I) is N, S.sup.+ or N.sup.+R.sup.13, where the compounds of the formula (I) have a positive charge when X is S.sup.+ or N.sup.+R.sup.13 and the compounds of the formula (I) then comprise an anion Y.sup.31 , where Y.sup. is selected from the group consisting of hydroxide and chloride.

16. The process according to claim 14, wherein the at least one additive (A) is selected from the group consisting of methylene blue and neutral red.

17. The process according to claim 14, wherein the polyamide (P) is at least one polyamide 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, PA 1313, PA 6T, PA MXD6, PA 61, PA 6-3-T, PA 6/6T, PA 6/66, PA 66/6, PA 6/12, PA 66/6/610, PA 6I/6T, PA PACM 12, PA 6I/6T/PACM, PA 12/MACMI, PA 12/MACMT, PA PDA-T and copolyamides formed from two or more of the abovementioned polyamides.

18. The process according to claim 14, wherein the polyamide (P) is at least one polyamide selected from the group consisting of nylon-6 (PA 6), nylon-6,6 (PA 66), nylon-6/6,6 (PA 6/66), nylon-6,6/6 (PA 66/6), nylon-6,10 (PA 610), nylon-6/6T (PA 6/6T), nylon-12 (PA 12) and nylon-12,12 (PA 1212).

19. The process according to claim 14, wherein the sinter powder (SP) has a sintering window (W.sub.SP) and the polyamide (P) present in the sinter powder (SP) has a sintering window (W.sub.P), where the sintering window (W.sub.SP; W.sub.P) in each case is the difference between the onset temperature of the melting (T.sub.M.sup.onset) and the onset temperature of the crystallization (T.sub.C.sup.onset), and where the sintering window (W.sub.SP) of the sinter powder (SP) is at least 5% larger than the sintering window (W.sub.P) of the polyamide (P) present in the sinter powder (SP).

20. The process according to claim 14, wherein the particle size of the sinter powder (SP) is in the range from 10 to 250 m.

21. A process for producing a sinter powder (SP), comprising the following steps: a) dissolving a polyamide (P) in a solvent (S), with addition of the at least one additive (A) before, during and/or after the dissolution, to obtain a polyamide solution (PS) comprising the at least one additive (A), b) adding a precipitant (PR) to the polyamide solution (PS) comprising the at least one additive (A) from process step a) to obtain a suspension comprising the sinter powder (SP) suspended in a solution comprising the solvent (S) and the precipitant (PR), c) separating the sinter powder (SP) from the suspension obtained in process step b).

22. A process for producing a sinter powder (SP), comprising the following steps: a) heating a mixture comprising a polyamide (P) and a solvent (S) to a temperature greater than the cloud temperature (T.sub.C) above which the polyamide (P) dissolves completely in the solvent (S), with addition of the at least one additive (A) before, during and/or after the heating, to obtain a polyamide solution (PS) comprising the at least one additive (A), b) cooling the polyamide solution (PS) which comprises the at least one additive (A) and has been obtained in process step a) to a temperature of not more than the cloud temperature (Tc) and subsequently adding a precipitant (PR) to obtain a suspension comprising the sinter powder (SP) suspended in a solution comprising the solvent (S) and the precipitant (PR), c) separating the sinter powder (SP) from the suspension obtained in process step b).

23. The process according to claim 21, wherein the solvent (S) is selected from the group consisting of alcohol, lactam and ketone.

24. The process according to claim 21, wherein the precipitant (PR) comprises at least 50% water, based on the total weight of the precipitant (PR).

25. The process for producing shaped bodies by selective laser sintering according to claim 14, wherein the sinter powder (SP) is produced by a process according to claim 21.

26. A shaped body obtained by the process according to claim 14.

Description

EXAMPLES

[0346] The following components were used:

[0347] Polyamide (P):

TABLE-US-00003 (P1) nylon-12 (PA2200, EOS) (P2) nylon-6 (Ultramid B27, BASF SE) (P3) nylon-6,10 (Ultramid S3k Balance, BASF SE) (P4) nylon-6,6 (Ultramid A27, BASF SE)

[0348] Additive (A):

TABLE-US-00004 (A1) nigrosin (Orient Chemical) (A2) neutral red (3-amino-7-dimethylamino-2-methylphenazine hydrochloride; Carl Roth) (A3) lithium chloride

[0349] Production of the Sinter Powder

[0350] Table 1 indicates whether the sinter powder has been produced by precipitation or by grinding.

[0351] For the sinter powders produced by grinding, the components reported in table 1 were compounded in the ratio specified in table 1 in a twin-screw extruder (ZSK 40) at a speed of 200 rpm, a barrel temperature of 240 C. and a throughput of 50 kg/h with subsequent extrudate pelletization. The thus obtained pelletized material was subjected to cryogenic grinding to obtain the sinter powder (SP).

[0352] To produce the sinter powder by precipitation, the polyamide (P) was dissolved in the amounts specified in table 1 in a solvent consisting of 40% by weight of caprolactam and 60% by weight of water, based in each case on the total weight of the solvent, using a temperature ramp of 2 hours at 120 C., 2 hours at 160 C. and 0.5 hours at 175 C., and subsequently precipitated by cooling. After washing with water and drying, the polyamide (P) was obtained as a powder. The thus obtained powder of the polyamide (P) was subsequently contacted with a solution of the additive (A), using the polyamide (P) and the additive (A) in the ratio specified in table 1. The solvent used in the solution of the additive (A) was ethanol for nigrosin as additive (A); water was used for neutral red or lithium chloride as additive (A). After drying, the sinter powder (SP) was obtained.

TABLE-US-00005 TABLE 1 (P1) (P2) (P3) (P4) (A1) (A2) (A3) [% by [% by [% by [% by [% by [% by [% by Example wt.] wt.] wt.] wt.] wt.] wt.] wt.] Production C1 100 C2 100 grinding I3 99.24 0.76 grinding I4 97.5 2.5 grinding C5 100 precipitation C6 100 precipitation I7 99.25 0.75 precipitation I8 99.5 0.5 precipitation I9 99.75 0.25 precipitation I10 99.875 0.125 precipitation C11 99.75 0.25 precipitation C12 100 I13 99.24 0.76 grinding C14 100 I15 99.24 0.76 grinding

[0353] The onset temperature of melting (T.sub.M.sup.onset) and the onset temperature of crystallization (T.sub.C.sup.onset) of the sinter powder were determined as described for FIG. 1. This was used to determine the sintering window (W).

[0354] Tensile bars were also produced to determine warpage.

[0355] Production of Tensile Bars

[0356] The sinter powders were introduced with a layer thickness of 0.1 mm into the cavity at the temperature specified in table 2. The sinter powder was subsequently exposed to a laser with the laser power output specified in table 2 and the point spacing specified, with the speed of the laser over the sample during exposure as specified in table 2. The point spacing is also known as laser track spacing or lane spacing. Selective laser sintering typically involves scanning in stripes. The point spacing gives the distance between the centers of the stripes, i.e. between the two centers of the laser beam for two stripes.

TABLE-US-00006 TABLE 2 Laser power Laser Point Temperature output speed spacing Example [ C.] [W] [m/s] [mm] C1 171 11 5 0.15 C2 I3 200 20 5 0.25 I4 194 25 5 0.15 C5 201 23 5 0.2 C6 202 25 5 0.2 I7 I8 208 15 5 0.15 I9 208 15 5 0.15 I10 C11 C12 I13 202 20 5 0.15 C14 I15

[0357] Determination of Warpage

[0358] To determine the warpage of the sintered bars obtained, the sintered bar was placed concave side down on a planar surface. The distance (am) between the planar surface and the upper edge of the middle of the sintered bar was determined. In addition, the thickness (dm) in the middle of the sintered bar was determined. Warpage in % is then determined by the following formula:

W=100.Math.(a.sub.m-d.sub.m)/d.sub.m

[0359] The dimensions of the sintered bars were typically length 80 mm, width 10 mm and thickness 4 mm.

[0360] The results for the measurement of the sintering window (W) and of warpage are reported in table 3.

TABLE-US-00007 TABLE 3 Sintering T.sub.m.sup.onset T.sub.c.sup.onset window W Warpage Example [ C.] [ C.] [K] [%] C1 178.7 152.5 26.2 C2 207.4 190.7 16.7 50 I3 206.6 185.3 21.3 27 I4 206.7 173.5 33.2 13 C5 214.1 188.8 25.3 C6 214.6 189.3 25.3 I7 213.6 170.4 43.2 I8 211.5 175.6 35.9 I9 212.4 178.4 34.0 C12 213.5 195.2 18.3 I13 212.6 187.9 24.7

[0361] It is clearly apparent from table 3 that the use of at least one additive (A) in the sinter powder (SP) results in a markedly widened sintering window. In addition, warpage is markedly reduced.