Process of manufacturing a three-dimensional article
This invention involves a new and better solution to the problems associated with the premature softening of PLA filaments in the additive manufacturing of three dimensional articles. It is based upon the finding that poly(lactic acid) filaments with high crystallinity offer much better resistance to heat-induced softening. The crystalline poly(lactic acid) filament of this invention can accordingly be used in the additive manufacturing of three dimensional articles without encountering the problems associated with premature softening, such as poor quality and printer jamming. The crystalline poly(lactic acid) filaments of this invention can also be used in additive manufacturing of three dimensional articles without compromising the quality of the ultimate product, reducing printing speed, increasing cost, or leading to increased printer complexity. This invention more specifically discloses a filament for use in three-dimensional printing which is comprised of crystallized poly(lactic acid), wherein said filament has a diameter which is within the range of 1.65 mm to 1.85 mm.
1. A method for manufacturing crystalline poly(lactic acid) filaments which are particularly useful in the additive manufacturing of three dimensional articles, said method including the steps of: (1) extruding molten poly(lactic acid) into the form of an amorphous filament, (2) collecting the amorphous filament on a spool to make a spool of amorphous poly(lactic acid) filament, and (3) heating the spool of amorphous poly(lactic acid) filament to a temperature of at least the glass transition temperature of the poly(lactic acid) for a period of time which is sufficient to substantially crystallize the poly(lactic acid), and (4) allowing the spool of crystallized poly(lactic acid) filament to cool to ambient temperature.
2. The method as specified in claim 1 , wherein the spool of amorphous poly(lactic acid) is heated to a temperature which is within the range of 55° C. to about 145° C. in step (3).
3. The method as specified in claim 1 , wherein amorphous filament is drawn to a draw ratio which is within the range of 1 to 3.5.
4. The method as specified in claim 1 , wherein amorphous filament is drawn to a draw ratio which is within the range of 1.1 to 1.75.
5. The method as specified in claim 1 , wherein the spool of amorphous poly(lactic acid) filament is crystallized in step (3) to a degree of crystallinity which is within the range of 5 percent to 40 percent, and wherein said crystalized poly(lactic acid) has a melting point which is within the range of about 145° C. to about 185° C.
6. The method as specified in claim 1 , wherein said crystalized poly(lactic acid) has a degree of crystallinity which is within the range of 10 percent to 40 percent.
7. The method as specified in claim 1 wherein said crystallized poly(lactic acid) filament has a diameter which is within the range of 1.65 mm to 1.85 mm.
8. The method as specified in claim 1 , wherein said crystallized poly(lactic acid) filament has a diameter which is within the range of 1.70 mm to 1.80 mm.
9. The method as specified in claim 1 wherein said crystallized poly(lactic acid) filament has a diameter which is within the range of 2.75 mm to 3.15 mm.
10. The method as specified in claim 1 wherein said crystallized poly(lactic acid) filament has a diameter which is within the range of 2.80 mm to 3.05 mm.