Method for Injection Molding at Low, Substantially Constant Pressure
First Claim
1. A method of injecting a shot comprising a molten thermoplastic material at a low, substantially constant pressure into a mold cavity of a molding apparatus, the method comprising:
- (a) injecting the shot comprising the molten thermoplastic material into the mold cavity to cause a pressure of the shot comprising the molten thermoplastic to increase to a melt pressure upon injection; and
,(b) maintaining the melt pressure of the shot comprising the molten thermoplastic material at a substantially constant pressure of less than 6000 psi during filling of substantially the entire mold cavity,wherein;
an internal portion of the mold cavity spaced at least 2 mm from a most immediate surface of the mold cavity contacting the shot comprising the molten thermoplastic material is maintained at a temperature of less than about 100°
C., andthe molten thermoplastic material has a melt flow index of 0.1 g/10 min to about 500 g/10 min.
1 Assignment
0 Petitions
Accused Products
Abstract
Disclosed herein are methods of injection molding at low, substantially constant melt pressures. Embodiments of the disclosed method now make possible a method of injection molding that is more energy—and cost—effective than conventional high-velocity injection molding processes. Embodiments of the disclosed method surprisingly allow for the filling of a mold cavity at low melt pressure without undesirable premature hardening of the thermoplastic material in the mold cavity and without the need for maintaining a constant temperature or heated mold cavity. Heretofore, it would not have been expected that a constant pressure method could be performed at low pressure without such premature hardening of the thermoplastic material when using an unheated mold cavity or cooled mold cavity.
30 Citations
20 Claims
-
1. A method of injecting a shot comprising a molten thermoplastic material at a low, substantially constant pressure into a mold cavity of a molding apparatus, the method comprising:
-
(a) injecting the shot comprising the molten thermoplastic material into the mold cavity to cause a pressure of the shot comprising the molten thermoplastic to increase to a melt pressure upon injection; and
,(b) maintaining the melt pressure of the shot comprising the molten thermoplastic material at a substantially constant pressure of less than 6000 psi during filling of substantially the entire mold cavity, wherein; an internal portion of the mold cavity spaced at least 2 mm from a most immediate surface of the mold cavity contacting the shot comprising the molten thermoplastic material is maintained at a temperature of less than about 100°
C., andthe molten thermoplastic material has a melt flow index of 0.1 g/10 min to about 500 g/10 min. - View Dependent Claims (2, 3, 4, 5, 20)
-
-
6. A method comprising:
-
(a) filling a mold cavity of a molding apparatus by injecting a shot comprising a molten thermoplastic material into the mold cavity, the mold cavity having a mold cavity pressure, the shot comprising the molten thermoplastic material having a pre-injection pressure, prior to injection into the mold cavity, that unequal to the mold cavity pressure, and the shot comprising the molten thermoplastic material having a melt pressure that, upon injection into the mold cavity, exceeds the pre-injection pressure; and
,(b) while filling substantially the entire mold cavity with the shot comprising the molten thermoplastic material, maintaining the melt pressure substantially constant at less than 6000 psi, wherein the thermoplastic material has a melt flow index of 0.1 g/10 min to about 500 g/10 min. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
-
-
14. A method of injecting a shot comprising molten thermoplastic material at low, substantially constant pressure into a mold cavity of a molding apparatus, the method comprising:
-
(a) injecting the shot comprising the molten thermoplastic material into the mold cavity to cause a pre-injection pressure of the shot comprising the molten thermoplastic material to increase to a melt pressure upon injection; and
,(b) filling substantially the entire mold cavity with the shot comprising the molten thermoplastic material while maintaining the melt pressure of the shot comprising the molten thermoplastic material at a substantially constant pressure of less than 6000 psi, and maintaining a vacuum in the mold cavity, wherein the molten thermoplastic material has a melt flow index of 0.1 g/10 min to about 500 g/10 min. - View Dependent Claims (15, 16, 17, 18, 19)
-
Specification