Polyolefin resin powder suitable for selective laser sintering and its preparation method

Abstract

A method for preparing a polyolefin resin powder has the steps of a) heat dissolving a polyolefin resin in an organic solvent having a solubility parameter less than or equal to the solubility parameter of the polyolefin resin to obtain a polyolefin resin solution; b) cooling the polyolefin resin solution to precipitate a solid, thereby obtaining a solid-liquid mixture; c) optionally adding an adjuvant to the solid-liquid mixture and mixing; and d) conducting solid-liquid separation and drying to obtain a polyolefin resin powder suitable for selective laser sintering. The difference between the solubility parameters of the organic solvent and of the polyolefin resin is within 0-20% of the solubility parameter of the polyolefin resin. The polyolefin resin powder obtained according to this method has good antioxidant property, good powder flowability, moderate size, smooth surface, suitable bulk density, and suitable dispersibility and particle size distribution.

Claims

1. A method for preparing a polyolefin resin powder, comprising: a) heating and dissolving a polyolefin resin in an organic solvent having a solubility parameter less than or equal to a solubility parameter of the polyolefin resin to obtain a polyolefin resin solution; b) cooling the polyolefin resin solution to cause precipitation of a solid, thereby obtaining a solid-liquid mixture; c) optionally adding an adjuvant to the solid-liquid mixture; and d) conducting solid-liquid separation and drying the separated solid to obtain a polyolefin resin powder, wherein a difference between the solubility parameter of the organic solvent and the solubility parameter of the polyolefin resin is within 0-20% of the solubility parameter of the polyolefin resin, wherein, in the polyolefin resin solution, an amount of the organic solvent is 600-1200 parts by weight, based on an amount of 100 parts by weight of the polyolefin resin, wherein, in step b), the polyolefin resin solution is cooled to a target temperature via one or more intermediate temperatures and held for 30-90 minutes at each of said one or more intermediate temperatures, wherein the one or more intermediate temperatures are in the range of 40-100 C., and wherein the polyolefin resin powder obtained from step d) contains particles that are spherical or spheroidal particles having a particle size of 25-150 m, and a particle size distribution D10=43-69 m, D50=61-103 m, and D90=85-138 m.

2. The method according to claim 1, wherein, in step a), the polyolefin resin is at least one selected from the group consisting of polypropylene resin, polyethylene resins, homopolypropylene resin, atactic polypropylene resin, and mixtures thereof.

3. The method according to claim 2, wherein the homopolypropylene resin and the atactic polypropylene resin have a melt index of 20-100 g/10 min, measured at 210 C. and a load of 2.16 kg, and the polyethylene resin has a melt index of 20-100 g/10 min, measured at 190 C. and a load of 2.16 kg.

4. The method according to claim 1, wherein the amount of the organic solvent is 800-1000 parts by weight, based on 100 parts by weight of the polyolefin resin.

5. The method according to claim 1, wherein the organic solvent is selected from the group consisting of C.sub.5-C.sub.12 alkanes, n-pentane, isopentane, n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, cyclohexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 2,2,3-trimethylbutane, n-octane, and n-nonane.

6. The method according to claim 1, wherein, in step a), the polyolefin resin is heated to a temperature of 60-200 C. and held at said temperature for 30-90 minutes.

7. The method according to claim 1, further comprising adding a nucleating agent to the polyolefin resin, wherein the nucleating agent is selected from the group consisting of silica, calcium oxide, calcium carbonate, barium sulfate, hydrotalcite, carbon black, kaolin, mica, and mixtures thereof.

8. The method according to claim 7, wherein an amount of the nucleating agent is 0.01-2 parts by weight based on 100 parts by weight of the polyolefin resin.

9. The method according to claim 1, wherein the adjuvant in step c) is selected from the group consisting of antioxidants, powder release agents, antistatic agents, antibacterial agents, glass fiber reinforcements, and mixtures thereof.

10. The method according to claim 9, wherein the antioxidant is antioxidant 1010, antioxidant 168, or a mixture thereof, wherein an amount of the antioxidant is 0.1-0.5 parts by weight based on 100 parts by weight of the polyolefin resin.

11. The method according to claim 9, wherein the powder release agent is selected from the group consisting of an alkali metal based on alkane monocarboxylic or dimer acids, an alkaline earth metal based on alkane monocarboxylic or dimer acids, a nano-oxide, a nano-metal salt, sodium stearate, potassium stearate, zinc stearate, calcium stearate, lead stearate, silica, titanium dioxide, aluminum oxide, zinc oxide, zirconium oxide, calcium carbonate, barium sulfate, and mixtures thereof; and an amount of the powder release agent is 0.01-10 parts by weight based on 100 parts by weight of the polyolefin resin.

12. A polyolefin resin powder prepared by the method according to claim 1, wherein the powder particles are spherical and/or spheroidal, and have a particle size of 25-150 m, and a particle size distribution D10=43-69 m, D50=61-103 m, and D90=85-138 m.

13. A selective laser sintering method, comprising sintering the polyolefin resin powder prepared according to the method of claim 1 using laser radiation.

14. A method of manufacturing a three-dimensional object, comprising sintering a polyolefin resin powder prepared according to the method of claim 1.

15. The method according to claim 3, wherein the homopolypropylene resin and the atactic polypropylene resin have a melt index of 30-80 g/10 min, measured at 210 C. and a load of 2.16 kg, and the polyethylene resin has a melt index of 30-80 g/10 min, measured at 190 C. and a load of 2.16 kg.

16. The method according to claim 6, wherein, in step a), the polyolefin resin is heated to a temperature of 70-190 C. and held at said temperature for 30-90 minutes.

17. The method according to claim 16, wherein, in step a), the polyolefin resin is heated to a temperature of 80-160 C. and held at said temperature for 30-90 minutes.

18. The method according to claim 8, wherein the amount of the nucleating agent is 0.05-1 parts by weight, based on 100 parts by weight of the polyolefin resin.

19. The method according to claim 18, wherein the amount of the nucleating agent is 0.1-0.5 parts by weight, based on 100 parts by weight of the polyolefin resin.

20. The method according to claim 10, wherein the amount of the antioxidant is 0.2-0.4 parts by weight, based on 100 parts by weight of the polyolefin resin.

21. The method according to claim 11, wherein the amount of the powder release agent is 0.1-5 parts by weight, based on 100 parts by weight of the polyolefin resin.

22. The method according to claim 21, wherein the amount of the powder release agent is 0.5-1 parts by weight, based on 100 parts by weight of the polyolefin resin.

23. A method for preparing a polyolefin resin powder, comprising: a) heating and dissolving a polyolefin resin in an organic solvent having a solubility parameter less than or equal to a solubility parameter of the polyolefin resin to obtain a polyolefin resin solution; b) cooling the polyolefin resin solution to cause precipitation of a solid, thereby obtaining a solid-liquid mixture; c) optionally adding an adjuvant to the solid-liquid mixture; and d) conducting solid-liquid separation and drying the separated solid to obtain a polyolefin resin powder, wherein a difference between the solubility parameter of the organic solvent and the solubility parameter of the polyolefin resin is within 0-20% of the solubility parameter of the polyolefin resin, wherein, in the polyolefin resin solution, an amount of the organic solvent is 600-1200 parts by weight, based on an amount of 100 parts by weight of the polyolefin resin, and wherein, in step b), the polyolefin resin solution is cooled to a target temperature of 10 C.-30 C. at an average cooling rate of 0.1 C./min to 1 C./min, and is held for 30-90 minutes at the target temperature.

Description

DESCRIPTION OF FIGURES

(1) FIG. 1 is a scanning electron microscope (SEM) image of a polypropylene resin powder provided according to Example 1 of the present invention.

(2) FIG. 2 is a scanning electron microscope (SEM) image of a polyethylene resin powder provided according to Example 17 of the present invention.

(3) FIG. 3 is a scanning electron microscope image of commercially available polyamide 12 powder for selective laser sintering which is prepared by reprecipitation, for comparison with the present invention (FIGS. 1 and 2).

MODE OF CARRYING OUT THE INVENTION

(4) The present invention will be further illustrated by the following specific examples, but it should be understood that the scope of the present invention is not limited thereto. In the following examples, the particle size and particle size distribution of the obtained polyolefin resin powders were characterized using a laser particle size analyzer (Mastersizer 2000, Malvern, UK).

Example 1

(5) 100 parts by weight of homopolypropylene resin (isotacticity 95%, melt index (210 C., 2.16 kg) 30 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.2 parts by weight of calcium oxide was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 130 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 90 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 2

(6) 100 parts by weight of homopolypropylene resin (isotacticity 97%, melt index (210 C., 2.16 kg) 50 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 800 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.4 parts by weight of calcium oxide was added and mixed. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 140 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 85 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to 20 C. at a rate of 1.0 C./min, and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 1 part by weight of zinc stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 3

(7) 100 parts by weight of homopolypropylene resin (isotacticity 96%, melt index (210 C., 2.16 kg) 50 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.8 parts by weight of calcium oxide was added and mixed. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to room temperature at a rate of 0.1 C./min. In the resulting solid-liquid mixture, were added 0.1 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 as well as 0.75 parts by weight of nano-silica, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 4

(8) 100 parts by weight of homopolypropylene resin (isotacticity 96%, melt index (210 C., 2.16 kg) 80 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.3 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 85 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.1 C./min, and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.3 parts by weight of antioxidant 1010 and 0.3 parts by weight of antioxidant 168 as well as 0.9 parts by weight of nano-zinc oxide, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 5

(9) 100 parts by weight of homopolypropylene resin (isotacticity 96%, melt index (210 C., 2.16 kg) 60 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.5 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 140 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 30 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 30 minutes. In the resulting solid-liquid mixture, were added 0.2 parts by weight of antioxidant 1010 and 0.2 parts by weight of antioxidant 168 as well as 0.6 parts by weight of nano-calcium carbonate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 6

(10) 100 parts by weight of homopolypropylene resin (isotacticity 95%, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-heptane (solubility parameter 15.2 MPa.sup.1/2) were placed in an autoclave, and 0.9 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 80 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 7

(11) 100 parts by weight of homopolypropylene resin (isotacticity 95%, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of cyclohexane (solubility parameter 16.6 MPa.sup.1/2) were placed in an autoclave, and 0.2 parts by weight of silica was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 80 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 8

(12) 100 parts by weight of homopolypropylene resin (isotacticity 95%, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of 2,2,3-trimethylbutane (solubility parameter 15.7 MPa.sup.1/2) were placed in an autoclave, and 0.3 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 80 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 9

(13) 100 parts by weight of atactic polypropylene resin (isotacticity 93.9%, melt index (210 C., 2.16 kg) 35 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.2 parts by weight of silica was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 80 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 10

(14) 100 parts by weight of atactic polypropylene resin (isotacticity 94.1%, melt index (210 C., 2.16 kg) 55 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 800 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.4 parts by weight of silica was added and mixed. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 130 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 75 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to 20 C. at a rate of 1.0 C./min, and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 1 part by weight of zinc stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 11

(15) 100 parts by weight of atactic polypropylene resin (isotacticity 92.6%, melt index (210 C., 2.16 kg) 70 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.8 parts by weight of silica was added and mixed. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to room temperature at a rate of 0.1 C./min. In the resulting solid-liquid mixture, were added 0.1 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 as well as 0.75 parts by weight of nano-silica, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 12

(16) 100 parts by weight of atactic polypropylene resin (isotacticity 93.2%, melt index (210 C., 2.16 kg) 60 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.3 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 75 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.1 C./min, and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.3 parts by weight of antioxidant 1010 and 0.3 parts by weight of antioxidant 168 as well as 0.9 parts by weight of nano-zinc oxide, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 13

(17) 100 parts by weight of atactic polypropylene resin (isotacticity 94%, melt index (210 C., 2.16 kg) 65 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.5 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 30 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 30 minutes. In the resulting solid-liquid mixture, were added 0.2 parts by weight of antioxidant 1010 and 0.2 parts by weight of antioxidant 168 as well as 0.6 parts by weight of nano-calcium carbonate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 14

(18) 100 parts by weight of atactic polypropylene resin (isotacticity 93.5%, melt index (210 C., 2.16 kg) 40 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-heptane (solubility parameter 15.2 MPa.sup.1/2) were placed in an autoclave, and 0.9 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 70 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 15

(19) 100 parts by weight of atactic polypropylene resin (isotacticity 93.5%, melt index (210 C., 2.16 kg) 40 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-pentane (solubility parameter 14.4 MPa.sup.1/2) were placed in an autoclave, and 0.2 parts by weight of silica was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 70 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 16

(20) 100 parts by weight of atactic polypropylene resin (isotacticity 93.5%, melt index (210 C., 2.16 kg) 40 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-octane (solubility parameter 15.0 MPa.sup.1/2) were placed in an autoclave, and 0.3 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 70 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 17

(21) 100 parts by weight of homopolypropylene resin (isotacticity 95%, melt index (210 C., 2.16 kg) 35 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.2 parts by weight of calcium oxide was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 130 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 90 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate and 0.5 parts by weight of single walled carbon nanotubes, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 18

(22) 100 parts by weight of homopolypropylene resin (isotacticity 96%, melt index (210 C., 2.16 kg) 45 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.3 parts by weight of kaolin was added and mixed. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to room temperature at a rate of 0.1 C./min. In the resulting solid-liquid mixture, were added 0.1 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168, 0.75 parts by weight of nano-silica and 0.5 parts by weight of silver-zirconium phosphate antibacterial agent, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 19

(23) 100 parts by weight of atactic polypropylene resin (isotacticity 93.9%, melt index (210 C., 2.16 kg) 35 g/10 min, solubility parameter 16.7 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave, and 0.2 parts by weight of silica was added and mixed. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 80 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168, 0.5 parts by weight of calcium stearate and 25 parts by weight of ultra-short glass fibers with a diameter of 10 m and a length of 250 m, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain an atactic polypropylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polypropylene resin powder were listed in Table 1.

Example 20

(24) 100 parts by weight of polyethylene resin (density 0.950 g/cm.sup.3, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 70 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 21

(25) 100 parts by weight of polyethylene resin (density 0.960 g/cm.sup.3, melt index (190 C., 2.16 kg) 60 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 800 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 120 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 65 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to 20 C. at a rate of 1.0 C./min, and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 1 part by weight of zinc stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 22

(26) 100 parts by weight of polyethylene resin (density 0.970 g/cm.sup.3, melt index (190 C., 2.16 kg) 50 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to room temperature at a rate of 0.1 C./min. In the resulting solid-liquid mixture, were added 0.1 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 as well as 0.75 parts by weight of nano-silica and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 23

(27) 100 parts by weight of polyethylene resin (density 0.954 g/cm.sup.3, melt index (190 C., 2.16 kg) 70 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 65 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.1 C./min and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.3 parts by weight of antioxidant 1010 and 0.3 parts by weight of antioxidant 168 as well as 0.9 parts by weight of nano-zinc oxide, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 24

(28) 100 parts by weight of polyethylene resin (density 0.948 g/cm.sup.3, melt index (190 C., 2.16 kg) 65 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 30 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 30 minutes. In the resulting solid-liquid mixture, were added 0.2 parts by weight of antioxidant 1010 and 0.2 parts by weight of antioxidant 168 as well as 0.6 parts by weight of nano-calcium carbonate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 25

(29) 100 parts by weight of polyethylene resin (density 0.962 g/cm.sup.3, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1200 parts by weight of n-heptane (solubility parameter 15.2 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 60 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 26

(30) 100 parts by weight of polyethylene resin (density 0.950 g/cm.sup.3, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of cyclohexane (solubility parameter 16.6 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 70 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 27

(31) 100 parts by weight of polyethylene resin (density 0.950 g/cm.sup.3, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of 2,2,3-trimethylbutane (solubility parameter 15.7 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 70 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 28

(32) 100 parts by weight of polyethylene resin (density 0.930 g/cm.sup.3, melt index (190 C., 2.16 kg) 30 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 60 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 29

(33) 100 parts by weight of polyethylene resin (density 0.927 g/cm.sup.3, melt index (190 C., 2.16 kg) 70 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 800 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 55 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to 20 C. at a rate of 1.0 C./min, and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 1 part by weight of zinc stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 30

(34) 100 parts by weight of polyethylene resin (density 0.920 g/cm.sup.3, melt index (190 C., 2.16 kg) 50 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 90 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to room temperature at a rate of 0.1 C./min. In the resulting solid-liquid mixture, were added 0.1 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 as well as 0.75 parts by weight of nano-silica, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 31

(35) 100 parts by weight of polyethylene resin (density 0.915 g/cm.sup.3, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1200 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.1 MPa; then the autoclave was heated up to 90 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 55 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.1 C./min, and held at this temperature for 60 minutes. In the resulting solid-liquid mixture, were added 0.3 parts by weight of antioxidant 1010 and 0.3 parts by weight of antioxidant 168 as well as 0.9 parts by weight of nano-zinc oxide, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 32

(36) 100 parts by weight of polyethylene resin (density 0.935 g/cm.sup.3, melt index (190 C., 2.16 kg) 60 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 90 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 30 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 30 minutes. In the resulting solid-liquid mixture, were added 0.2 parts by weight of antioxidant 1010 and 0.2 parts by weight of antioxidant 168 as well as 0.6 parts by weight of nano-calcium carbonate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 33

(37) 100 parts by weight of polyethylene resin (density 0.924 g/cm.sup.3, melt index (190 C., 2.16 kg) 45 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1200 parts by weight of n-heptane (solubility parameter 15.2 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 90 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 50 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168 as well as 0.8 parts by weight of sodium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 34

(38) 100 parts by weight of polyethylene resin (density 0.930 g/cm.sup.3, melt index (190 C., 2.16 kg) 30 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-pentane (solubility parameter 14.4 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 60 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 35

(39) 100 parts by weight of polyethylene resin (density 0.930 g/cm.sup.3, melt index (190 C., 2.16 kg) 30 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-octane (solubility parameter 15.4 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 60 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168 as well as 0.5 parts by weight of calcium stearate, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 36

(40) 100 parts by weight of polyethylene resin (density 0.950 g/cm.sup.3, melt index (190 C., 2.16 kg) 35 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 110 C., and held at this temperature for 60 minutes; thereafter, the autoclave was cooled down to 70 C. at a rate of 1.0 C./min with cooling water, and held at this temperature for 60 minutes; further, the autoclave was cooled down to room temperature at a rate of 1.0 C./min. In the resulting solid-liquid mixture, were added 0.25 parts by weight of antioxidant 1010 and 0.25 parts by weight of antioxidant 168, 0.5 parts by weight of calcium stearate, 2.5 parts by weight of conductive carbon black as well as 0.1 parts by weight of carbon nanotubes, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 37

(41) 100 parts by weight of polyethylene resin (density 0.948 g/cm.sup.3, melt index (190 C., 2.16 kg) 60 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1000 parts by weight of n-hexane (solubility parameter 14.9 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.3 MPa; then the autoclave was heated up to 100 C., and held at this temperature for 30 minutes; thereafter, the autoclave was cooled down to 30 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 30 minutes. In the resulting solid-liquid mixture, were added 0.2 parts by weight of antioxidant 1010 and 0.2 parts by weight of antioxidant 168, 0.6 parts by weight of nano-calcium carbonate as well as 0.05 parts by weight of zinc pyrithione, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

Example 38

(42) 100 parts by weight of polyethylene resin (density 0.924 g/cm.sup.3, melt index (190 C., 2.16 kg) 40 g/10 min, solubility parameter 17.0 MPa.sup.1/2) and 1200 parts by weight of n-heptane (solubility parameter 15.2 MPa.sup.1/2) were placed in an autoclave. A high-purity nitrogen gas was charged to 0.2 MPa; then the autoclave was heated up to 90 C., and held at this temperature for 90 minutes; thereafter, the autoclave was cooled down to 50 C. at a rate of 0.5 C./min with cooling water, and held at this temperature for 90 minutes; further, the autoclave was cooled down to room temperature at a rate of 0.2 C./min. In the resulting solid-liquid mixture, were added 0.15 parts by weight of antioxidant 1010 and 0.15 parts by weight of antioxidant 168, 0.8 parts by weight of sodium stearate as well as 50 parts by weight of ultra-short glass fibers with a diameter of 5 m and a length of 150 m, and thereafter the material was subjected to centrifugal separation and vacuum drying to obtain a polyethylene resin powder suitable for selective laser sintering. The particle size and particle size distribution of the obtained polyethylene resin powder were listed in Table 1.

(43) TABLE-US-00001 TABLE 1 Particle size D10 D50 D90 Bulk density Example (m) (m) (m) (m) (g/cm.sup.3) Example 1 35~120 53 86 105 0.45 Example 2 40~130 55 94 118 0.41 Example 3 30~107 47 65 88 0.49 Example 4 35~130 52 78 108 0.45 Example 5 30~110 45 71 98 0.52 Example 6 43~137 55 85 113 0.42 Example 7 45~132 55 90 108 0.46 Example 8 45~130 52 81 104 0.44 Example 9 35~125 52 84 102 0.48 Example 10 40~120 58 81 97 0.45 Example 11 25~130 41 61 107 0.55 Example 12 40~135 55 86 109 0.44 Example 13 30~150 48 103 138 0.38 Example 14 45~120 58 80 95 0.42 Example 15 42~130 58 80 115 0.42 Example 16 45~127 64 85 115 0.44 Example 17 45~135 49 84 122 0.43 Example 18 42~125 56 82 105 0.44 Example 19 40~130 50 84 108 0.42 Example 20 45~135 59 90 112 0.44 Example 21 40~130 55 94 115 0.45 Example 22 30~127 48 75 101 0.57 Example 23 35~130 50 89 110 0.50 Example 24 35~120 49 71 95 0.52 Example 25 40~130 56 85 106 0.47 Example 26 42~130 58 80 115 0.44 Example 27 45~127 64 85 115 0.45 Example 28 35~115 45 71 92 0.56 Example 29 50~130 61 91 115 0.40 Example 30 30~100 46 66 85 0.54 Example 31 35~120 52 79 100 0.50 Example 32 50~150 69 97 120 0.37 Example 33 45~130 67 96 114 0.43 Example 34 45~132 55 90 108 0.43 Example 35 45~130 52 81 104 0.46 Example 36 30~110 46 74 90 0.52 Example 37 50~130 65 88 115 0.48 Example 38 45~120 58 85 110 0.41

Example 39

(44) Example 1 was repeated except that nucleating agent calcium oxide was not used. Since there was no nucleating agent in this example, molten polypropylene had less nucleating points during crystallization and thus spherulite size was larger. The finally obtained polypropylene powder particles for laser sintering had a larger particle size, ranging from 70 to 150 m, with D10=92 m, D50=113 m, and D90=132 m. Although the obtained polypropylene resin powder could satisfy the basic requirements of laser sintering process, it had a greater fraction of particles with larger size than that of Example 1.

Example 40

(45) Example 1 was repeated except that no antioxidant was used. Since there was no antioxidant in this example, the obtained polypropylene powder tended to be degraded and yellowing upon heating when used for laser sintering. Although the obtained polypropylene resin powder could satisfy the basic requirements of laser sintering process, the mechanical properties of the finished printed product were inadequate compared with Example 1.

Example 41

(46) Example 1 was repeated except that no release agent was used. Since there was no release agent in this example, the obtained polypropylene powder tended to agglomerate in a small quantity, and had a slightly poorer flowability compared with Example 1. Although the obtained polypropylene resin powder could satisfy the basic requirements of laser sintering process, the finished printed product had a slightly worse surface smoothness.

Example 42

(47) Example 20 was repeated except that no antioxidant was used. Since there was no antioxidant in this embodiment, the obtained polyethylene powder tended to be cross-linked upon heating when used for laser sintering compared with Example 20. Although the obtained polyethylene resin powder could satisfy the basic requirements of laser sintering process, the finished printed product was prone to shrink.

Example 43

(48) Example 20 was repeated except that no release agent was used. Since there was no release agent in this example, the obtained polyethylene powder tended to agglomerate in a small quantity, and had a slightly poorer flowability compared with Example 20. Although the obtained polyethylene resin powder could satisfy the basic requirements of laser sintering process, the finished printed product had a slightly worse surface smoothness.

Example 44

(49) Example 20 was repeated except that the release agent and the antioxidant were not used. Since there were neither release agent nor antioxidant in this example, the obtained polyethylene powder tended to be cross-linked upon heating when used for laser sintering, and tended to agglomerate in a small quantity, and had a slightly poorer flowability compared with Example 20. Although the obtained polyethylene resin powder could satisfy the basic requirements of laser sintering process, the finished printed product was prone to shrink and had a slightly worse surface smoothness.

Comparative Example 1

(50) Example 1 was repeated except that xylene solvent (solubility parameter 18.2 MPa.sup.1/2) was used instead of n-hexane solvent. Since the xylene solvent used in this comparative example was a good solvent for polypropylene, the polypropylene, after dissolved, had a very slow crystallization rate upon cooling. In the same experimental time as that in Example 1, the particle size of the obtained polypropylene powder particles for laser sintering was too small and the particle size distribution was worse (the particle size ranging from 10 to 55 m, D10=15 m, D50=24 m, D90=49 m). The obtained polypropylene resin powder could not satisfactorily meet the requirements of laser sintering process.

Comparative Example 2

(51) Example 1 was repeated except that toluene solvent (solubility parameter 18.4 MPa.sup.1/2) was used instead of n-hexane solvent. Since the toluene solvent used in this comparative example was a good solvent for polypropylene, the polypropylene, after dissolved, had a very slow crystallization rate upon cooling. In the same experimental time as that in Example 1, the particle size of the obtained polypropylene powder particles for laser sintering was too small and the particle size distribution was worse (the particle size ranging from 16 to 52 m, D10=25 m, D50=34 m, D90=40 m). The obtained polypropylene resin powder could not satisfactorily meet the requirements of laser sintering process.

(52) The above examples and comparative examples illustrate that the polyolefin resin powder obtained according to the method of the present invention has good oxidation resistance, good powder flowability, moderate size, suitable bulk density, well-proportioned particle shape and uniform particle size distribution, which is suitable for selective laser sintering to prepare various molded products. With the selective laser sintering method provided by the present invention, polyolefin molded products having regular shape, smooth surface and good mechanical properties can be prepared.

(53) Although the present invention has been described in detail, modifications within the spirit and scope of the present invention will be apparent to those skilled in the art. In addition, it should be understood that various aspects of the present invention described herein, various parts of different embodiments, and various features listed may be combined or totally or partially interchanged. In the respective embodiments described above, those embodiments that refer to another specific embodiment can be combined with other embodiments as appropriate, as will be understood by those skilled in the art. Moreover, those skilled in the art will understand that the foregoing description is by way of example only and is not intended to limit the present invention.