Injection molding process and product produced using the same
View Patent ↗A method of molding a solid article such as a syringe with zero draft or very low draft is disclosed. The method includes heating a low draft mold to expand it, then injection molding the part, followed by cooling at least part of the low draft mold element to thermally contract at least a portion of the low draft element away from the solid low draft formed surface sufficiently to release the low draft element from the low draft formed surface. Syringes and other articles formed by this method are also disclosed having and interior draft angle of 0 to 0.5 degrees, optionally at least substantially zero degrees. The syringe plunger can be selectively coated with lubricity coatings and other functional coatings to improve performance of the syringe.
1. A method of molding a solid article, comprising:
providing multiple-use injection molding equipment including a substantially rigid surface defining a cavity and a substantially rigid core, the cavity and core defining a molding space between them, at least one of the cavity and the core being movable with respect to the other along a parting axis to open the molding space for removing molded articles, at least one portion of the core being a low draft element having a draft angle of from greater than 0° to 0.5 degree with respect to the parting axis;
heating at least part of the low draft element to a first selected temperature to expand it;
before, during or after heating, injecting a fluid molding material into the molding space;
forming at least a surface of the fluid molding material against the low draft element to define a low draft formed surface;
solidifying at least the low draft formed surface to provide a solid low draft formed surface;
cooling at least part of the low draft element to a second selected average temperature less than the first selected temperature to thermally contract at least a portion of the low draft element away from the solid low draft formed surface to create a clearance between the low draft element and the low draft formed surface sufficiently to release the low draft element from the low draft formed surface;
parting the cavity and core along the parting axis; and
removing the solid article from the molding space without causing defects on the solid article.
2. The method of claim 1 , in which the temperature of the fluid molding material when injected into the molding space is above its glass transition temperature.
3. The method according to claim 1 , in which the solidifying step is carried out by cooling at least the formed surface of the injected molding material below its glass transition temperature.
4. The method according to claim 1 , in which the low draft element has a draft angle of up to 0.25°.
5. The method according to claim 1 , in which the low draft element has a draft angle of up to 0.16°.
6. The method according to claim 1 , in which the low draft element has a draft angle of up to 0.03°.
7. The method according to claim 1 , in which the low draft element has a draft angle of up to 0.014°.
8. The method according to claim 1 , in which the molding material comprises polyethylene terephthalate, cyclic olefin copolymer, cyclic olefin polymer, polypropylene, or a combination thereof.
9. The method according to claim 1 , in which the low draft element comprises steel.
10. The method according to claim 1 , wherein the molding space is configured to form a syringe barrel, wherein a bore of the barrel has a draft angle of from greater than 0° to 0.16° relative to a central axis of the barrel.
11. The method according to claim 1 , in which the low draft element comprises H13 tool grade steel.
12. The method according to claim 1 , in which the low draft element has a draft angle of up to 0.06°.
13. The method according to claim 12 , in which the solid article is a syringe barrel, the method further comprising the step of applying, after molding, a SiOx barrier layer on the solid low draft formed surface, wherein x is from 1.5 to 2.9 and the barrier layer is from 5 to 200 nm thick.
14. The method according to claim 10 , wherein the bore of the barrel has a draft angle of from greater than 0° to 0.06° relative to the central axis of the barrel.