Binder compositions for laser sintering processes

• US 6,048,954 A
• Filed: 06/24/1997
• Issued: 04/11/2000
• Est. Priority Date: 07/22/1994
• Status: Expired due to Fees

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Vail, Neal K., Barlow, Joel W.
• Primary Examiner(s): Lipman, Bernard
• Application Number:
  US08/879,688
• Time in Patent Office: 1,022 Days
• Field of Search: 526/329.7, 526/328.5
• US Class Current: 526/328.5
• CPC Class Codes: B22F 10/28 Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• CPC Class Codes: B29C 41/003 characterised by the choice of material
• CPC Class Codes: B29C 64/165 using a combination of solid and fluid materials, e.g. a powder selectively bound by a liquid binder, catalyst, inhibitor or energy absorber
• CPC Class Codes: B29K 2503/04 Inorganic materials
• CPC Class Codes: B33Y 70/00 Materials specially adapted for additive manufacturing
• CPC Class Codes: B33Y 70/10 Composites of different types of material, e.g. mixtures of ceramics and polymers or mixtures of metals and biomaterials
• CPC Class Codes: C04B 35/634 Polymers C04B35/636 takes precedence
• CPC Class Codes: C04B 35/63424 Polyacrylates; Polymethacrylates
• CPC Class Codes: C04B 35/63444 Nitrogen-containing polymers, e.g. polyacrylamides, polyacrylonitriles, polyvinylpyrrolidone [PVP], polyethylenimine [PEI]
• CPC Class Codes: C08F 220/12 of monohydric alcohols or phenols
• CPC Class Codes: Y02P 10/25 Process efficiency

Abstract

The development of polymer binder compositions that provide novel binders for high temperature inorganic particulates, especially metal and ceramic particulates is described. These materials are especially useful in a laser beam sintering process known as SLS™ that forms accurately shaped high strength green objects. The new binders may be thermally removed in post-shaping operations without significant residual ash. The resulting structures contain only metal, ceramic, or metal ceramic materials. The inventive methods developed for producing the new polymeric binder materials are based in part on using emulsion forms of selected polymers at controlled low molecular weights and high melt flow. An important aspect of the process is the semi-batch addition of selected chain transfer agents to the reacting emulsion. This optimizes coating characteristics of the polymer binder and results in high part strengths of the prototype parts produced in the SLS™ process.

Claims

1. An amorphous polymeric binder composition comprising an 80/20 molar ratio p(MMA-co-nBMA) methacrylate copolymer that has at least 95% mer units containing quaternary carbon atoms on the mer backbone wherein said copolymer has a T_g of between about 40°

C. and about 100°

C., a melt flow index of 20-50 g/10 min and a particle size between about 50-250 nm.

12. The amorphous polymeric binder composition of claim 1, wherein said binder is thermally depolymerizable to gaseous products in a reducing atmosphere at temperatures between about 275°

C. and about 400°

C.

13. The amorphous polymeric binder composition of claim 1, wherein said binder decomposes to less than about 0.5 wt. % residue in a non-oxidizing environment at temperatures between about 275°

C. and about 400°

C.

2. An amorphous polymeric binder composition comprising a methacrylate copolymer that has at least 95% mer units containing quaternary carbon atoms on the mer backbone wherein said copolymer has a T_g of between about 40°

C. and about 100°

C., a melt flow index of 20-50 g/10 min and a particle size between about 50-250 nm and further including about 2-5 mol % of a termonomer adhesion promoter.

3. The amorphous polymeric binder composition of claim 2 wherein the adhesion promoter is methacrylamide, N,N-dimethyl-aminoethyl methacrylate or methacrylic acid.

4. The amorphous polymeric binder composition of claim 2 wherein the adhesion promoter is N,N-dimethyl aminoethyl methacrylate.

14. The amorphous polymeric binder composition of claim 2, wherein said binder is thermally depolymerizable to gaseous products in a reducing atmosphere at temperatures between about 275°

C. and about 400°

C.

15. The amorphous polymeric binder composition of claim 2, wherein said binder decomposes to less than about 0.5 wt. % residue in a non-oxidizing environment at temperatures between about 275°

C. and about 400°

C.

5. An amorphous polymeric binder composition comprising a copolymer of methyl methacrylate and n-butylmethacrylate with a T_g of about 80 to about 89°

C. and a melt index of about 25 g/10 min at 200°

C. and 75 psi extrusion pressure.

16. The amorphous polymeric binder composition of claim 5, wherein said binder is thermally depolymerizable to gaseous products in a reducing atmosphere at temperatures between about 275°

C. and about 400°

C.

17. The amorphous polymeric binder composition of claim 5, wherein said binder decomposes to less than about 0.5 wt. % residue in a non-oxidizing environment at temperatures between about 275°

C. and about 400°

C.

6. A polymer binder prepared by continuous addition of a water soluble monomer of metbacrylic acid ester and n-butylmethacrylic acid ester to an aqueous emulsion of an ionic initiator and a chain transfer agent wherein said continuous addition promotes formation of a copolymer product having a particle size of about 100 nm and a melt flow index of between 1-50 g/10 min at 200°

C. and 75 psi extrusion pressure.

18. The amorphous polymeric binder composition of claim 6, wherein said binder is thermally depolymerizable to gaseous products in a reducing atmosphere at temperatures between about 275°

C. and about 400°

C.

19. The amorphous polymeric binder composition of claim 6, wherein said binder decomposes to less than about 0.5 wt. % residue in a non-oxidizing environment at temperatures between about 275°

C. and about 400°

C.

7. An amorphous polymeric binder composition comprising dimethyl amino ethyl methacrylate and methacrylamide or methyl methacrylate and butyl methacrylate copolymer that has at least 95% mer units containing quaternary carbon atoms on the mer backbone wherein said copolymer has a T_g of between about 40°

C. and about 100°

C., a melt flow index of 20-50 g/10 min and a particle size between about 50-250 nm.

20. The amorphous polymeric binder composition of claim 7, wherein said binder is thermally depolymerizable to gaseous products in a reducing atmosphere at temperatures between about 275°

C. and about 400°

C.

21. The amorphous polymeric binder composition of claim 7, wherein said binder decomposes to less than about 0.5 wt. % residue in a non-oxidizing environment at temperatures between about 275°

C. and about 400°

C.

8. A copolymeric methacrylate amorphous binder composition having the following properties:

(a) A T_g of between about 40°

C. and about 100°

C.;

(b) A melt flow index of between about 1 and about 50 g/10 min at 200°

C. and 75 psi extrusion pressure;

(c) thermally depolymerizable to gaseous products in a reducing atmosphere;

(d) alternately placed quaternary carbons on the methacrylate copolymer backbone; and

(e) an 80/20 molar ratio p(MMA-co-nBMA) copolymer; and

wherein said binder decomposes to less than about 0.5 wt. % residue in a non-oxidizing environment at temperatures between about 275°

C. and about 400°

.

9. A copolymeric methacrylate amorphous binder composition having the following properties:

(a) A T_g of between about 40°

C. and about 100°

C.;

(b) A melt flow index of between about 1 and about 50 g/10 min at 200°

C. and 75 psi extrusion pressure;

(c) thermally depolymerizable to gaseous products in a reducing atmosphere;

(d) alternately placed quaternary carbons on the methacrylate copolymer backbone; and

(e) including about 2-5 mol % of a copolymeric termonomer adhesion promoter; and

wherein said binder decomposes to less than about 0.5 wt. % residue in a non-oxidizing environment at temperatures between about 275°

C. and about 400°

.

10. The amorphous polymeric binder composition of claim 9 wherein the adhesion promoter is methacrylamide, N,N-dimethyl-aminoethyl methacrylate or methacrylic acid.

11. The amorphous polymeric binder composition of claim 9 wherein the adhesion promoter is N,N-dimethyl aminoethyl methacrylate.