Sinterable semi-crystalline powder and near-fully dense article formed therewith

Abstract

A laser-sinterable powder product has been prepared having unique properties which allow the powder to be sintered in a selective laser sintering machine to form a sintered part which is near-fully dense. For most purposes, the sintered part is indistinguishable from another part having the same dimensions made by isotropically molding the powder. In addition to being freely flowable at a temperature near its softening temperature, a useful powder is disclosed that has a two-tier distribution in which substantially no primary particles have an average diameter greater than 180 μm, provided further that the number average ratio of particles smaller than 53 μm is greater than 80%, the remaining larger particles being in the size range from 53 μm to 180 μm. A powder with slow recrystallization rates, as evidenced by non-overlapping or slightly overlapping endothermic and exothermic peaks in their differential scanning calorimetry characteristics for scan rates of on the order of 10° C. to 20° C. per minute, will also result in sintered parts that are near-fully dense, with minimal dimensional distortion.

1. A method of producing a three-dimensional object, comprising the steps of:
 applying a layer of a powder at a target surface, the powder comprised of a semi-crystalline organic polymer, the powder having a melting peak and a recrystallization peak, as shown in differential scanning calorimetry traces, which slightly overlap when measured at a scanning rate of 10-20° C./minute.  
 
     
     
       2. The method of  claim 1 , wherein the polymer is selected from a group consisting of polyacetal, polypropylene, polyethylene, and ionomers. 
     
     
       3. The method of  claim 1 , wherein the polymer is selected from a group consisting of branched polyethylene and branched polypropylene. 
     
     
       4. The method of  claim 1 , wherein the powder has a melting point below about 200° C. 
     
     
       5. The method of  claim 1 , wherein the overlap of the melting peak and the recrystallization peak is no more than about 13° C. 
     
     
       6. The method of  claim 1 , wherein the overlap of the melting peak and the recrystallization peak is no more than about 11° C. 
     
     
       7. An article formed of a semi-crystalline organic polymer powder that is laser-sintered in layerwise fashion, the powder having a melting peak and recrystallization peak, as shown in differential scanning calorimetry traces, which slightly overlap when measured at a scanning rate of 10-20° C./minute. 
     
     
       8. The article of  claim 7 , wherein the polymer is selected from a group consisting of polyacetal, polypropylene, polyethylene, and ionomers. 
     
     
       9. The article of  claim 7 , wherein the polymer is selected from a group consisting of branched polyethylene and branched polypropylene. 
     
     
       10. The article of  claim 7 , wherein the powder has a melting point below about 200° C. 
     
     
       11. The article of  claim 7 , wherein the overlap of the melting peak and the recrystallization peak is no more than about 13° C. 
     
     
       12. The article of  claim 7 , wherein the overlap of the melting peak and the recrystallization peak is no more than about 11° C. 
     
     
       13. A method of producing a three-dimensional object, comprising the steps of:
 applying a layer of a powder at a target surface, the powder comprised of a semi-crystalline organic polyester-based polymer, the powder having a melting peak and a recrystallization peak, as shown in differential scanning calorimetry traces, which do not substantially overlap when measured at a scanning rate of 10-20° C./minute;  
 directing energy at selected locations of the layer corresponding to the cross-section of the object to be formed in the layer, to fuse the powder thereat;  
 repeating the applying and directing steps to form the object in layerwise fashion; and  
 removing unfused powder from the object.  
 
     
     
       14. An article formed of a semi-crystalline organic polyester-based polymer powder that is laser-sintered in layerwise fashion, the powder having a melting peak and a recrystallization peak, as shown in differential scanning calorimetry traces, which do not substantially overlap when measured at a scanning rate of 10-20° C./minute. 
     
     
       15. A method of producing a three-dimensional object, comprising the steps of:
 applying a layer of a powder at a target surface, the powder comprised of a semi-crystalline organic polymer having a two- tiered particle size distribution with at least  80   %  of all particles in the powder being  1 - 53  μm in size,  the powder having a caking temperature (T c ) that is greater than a softening point temperature (T s ) of the powder, as shown in differential scanning calorimetry traces;  
 directing energy at selected locations of the layer corresponding to the cross-section of the object to be formed in the layer, to fuse the powder thereat;  
 repeating the applying and directing steps to form the object in layerwise fashion; and  
 removing unfused powder from the object.  
 
     
     
       16. The method of  claim 15 , wherein the polymer is a nylon. 
     
     
       17. The method of  claim 16 , wherein the nylon is selected from a group consisting of nylon 6, nylon 11, and nylon 12. 
     
     
       18. The method of  claim 15 , wherein the polymer is a polyester-based polymer. 
     
     
       19. The method of  claim 15 , wherein the polymer is selected from a group consisting of polyacetal, polypropylene, polyethylene, and ionomers. 
     
     
       20. The method of  claim 15 , wherein the polymer is selected from a group consisting of branched polyethylene and branched polypropylene. 
     
     
       21. The method of  claim 15 , wherein the powder has a melting point below about 200° C. 
     
     
       22. A method of producing a three-dimensional object, comprising the steps of:
 applying a layer of a powder at a target surface, the powder comprised of a semi-crystalline organic polymer having a two- tiered particle size distribution with at least  80   %  of all particles in the powder being  1 - 53  μm in size,  selected from a group consisting of nylon 6, nylon 11, and nylon 12;  
 directing energy at selected locations of the layer corresponding to the cross-section of the object to be formed in the layer, to fuse the powder thereat;  
 repeating the applying and directing steps to form the object in layerwise fashion; and  
 removing unfused powder from the object.  
 
     
     
       23. An  A near- fully dense, distortion free  article formed of a semi-crystalline organic polymer powder that is laser-sintered in layerwise fashion, the powder having a caking temperature (T c ) that is greater than a softening point temperature (T s ) of the powder, as shown in differential scanning calorimetry traces and having a two- tiered particle size distribution with at least  80   %  of all particles in the powder being  1 - 53     μm in size.    
     
     
       24. The article of  claim 23 , wherein the polymer is a nylon. 
     
     
       25. The article of  claim 24 , wherein the nylon is selected from a group consisting of nylon 6, nylon 11, and nylon 12. 
     
     
       26. The article of  claim 23 , wherein the polymer is a polymer is a polyester-based polymer. 
     
     
       27. The article of  claim 23 , wherein the polymer is selected from a group consisting of polyacetal, polypropylene, polyethylene, and ionomers. 
     
     
       28. The article of  claim 23 , wherein the polymer is selected from a group consisting of branched polyethylene and branched polypropylene. 
     
     
       29. The article of  claim 23 , wherein the powder has a melting point below about 200° C. 
     
     
       30. An  A near fully- dense, distortion - free  article formed of a semi-crystalline organic polymer powder that is laser-sintered in layerwise fashion, the powder comprised of a semi-crystalline organic polymer selected from a group consisting of nylon 6, nylon 11, and nylon  12 and having a two - tiered particle size distribution with at least  80   %  of all particles in the powder being  1 - 53  μm in size.    
     
     
       31. The method according to  claim 13  further comprising applying a layer of powder wherein the powder has less than  5 %  of the particles greater than  180  μm.   
     
     
       32. The method according to  claim 31  further comprising having a major portion by weight of the particles in the powder having a sphericity of greater than  0 . 5 . 
     
     
       33. The method according to  claim 32  further comprising applying a layer of powder wherein at least  90 %  of the particles are smaller than  53  μm in size.   
     
     
       34. The method according to  claim 22  further comprising applying a layer of powder wherein the powder has less than  5 %  of the particles greater than  180  μm.    
     
     
       35. The method according to  claim 34  further comprising having a major portion by weight of the particles in the powder having a sphericity of greater than  0 . 5 . 
     
     
       36. The method according to  claim 35  further comprising applying a layer of powder wherein at least  90 %  of the particles are smaller than  53  μm in size.   
     
     
       37. The article according to  claim 23  further comprising applying a layer of powder wherein the powder has less than  5 %  of the particles greater than  180  μm.   
     
     
       38. The article according to  claim 37  further comprising having a major portion by weight of the particles in the powder having a sphericity of greater than  0 . 5 . 
     
     
       39. The article according to  claim 38  further comprising applying a layer of powder wherein at least  90 %  of the particles are smaller than  53  μm in size.   
     
     
       40. The article according to  claim 30  further comprising applying a layer of powder wherein at least  90 %  of the particles are smaller than  53  μm in size.   
     
     
       41. The article according to  claim 40  further comprising applying a layer of powder wherein the powder has less than  5 %  of the particles greater than  180  μm.   
     
     
       42. The article according to  claim 41  further comprising having a major portion by weight of the particles in the powder having a sphericity of greater than  0 . 5 .