US4237089A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of reducing internal stresses and improving the mechanical properties of injection molded thermoplastic resins
Assignee: Valmet AB
•
Filing: 1978-07-19
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Granted: 1980-12-02
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Expires: 1998-07-19
Abstract
Abstract A method of reducing internal stresses in and improving the mechanical properties of injection molded articles made of thermoplastic resins is disclosed wherein under in other respects normal injection molding conditions thermoplastic resins are injection molded at high injection and holding pressures within the range 250-800 MPa.
Inventors
- 👤 Josef Kubat
- 👤 Jan K. Djurner
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 20:09
CPC Classifications
B; B29; B29C; B29C45/00; B29C45/17; B29C45/46; B29C45/57; B29C45/0001; B29C45/572; B29C2045/575; B29C45/0025
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
69 words
In a method of injection molding a thermoplastic resin under conditions of melt temperature, mold temperature, injection time, holding time, and cooling time appropriate for said thermoplastic resin, the improvement comprising carrying out the injection molding at injection and holding pressures from 250-800 MPa, whereby the molded thermoplastic resin has reduced internal stresses and an essentially reduced tendency to mold shrinkage, warping, crazing and cracking, post-shrinkage and time-dependent deformation.
Claim 2
Dependent Claim
69 words
In a method of injection molding a thermoplastic resin under conditions of melt temperature, mold temperature, injection time, holding time, and cooling time appropriate for said thermoplastic resin, the improvement comprising carrying out the injection molding at injection and holding pressures from 250-800 MPa, whereby the molded thermoplastic resin has reduced internal stresses and an essentially reduced tendency to mold shrinkage, warping, crazing and cracking, post-shrinkage and time-dependent deformation.
Claim 3
Dependent Claim
34 words
The method according to claim 1 wherein polyethylene having a molecular weight of 200,000 to 1,500,000 is used as the thermoplastic resin, whereby highly improved mechanical properties of the injection molded articles are obtained.
Claim 4
Dependent Claim
29 words
The method according to claim 1, characterized in that by adjusting the injection and holding pressures properly the mold shrinkage of the molded part can be reduced to zero.
Claim 5
Dependent Claim
26 words
The method according to claim 1, wherein the crystallinity of difficultly crystallizing thermoplastics is enhanced by using the high injection and holding pressures within said range.
Claim 6
Dependent Claim
13 words
The method according to claim 1 wherein the pressures are from 300-500 MPa.
Claim 7
Dependent Claim
35 words
The method according to claim 1 wherein the thermoplastic resin is selected from the group consisting of olefin plastics, styrene plastics, acrylic plastics, amide plastics, acetal plastics, carbonate plastics, polyesters, cellulose plastics and vinyl plastics.
Claim 8
Dependent Claim
42 words
The method according to claim 6 wherein the thermoplastic resin contains at least one crystalline phase and the crystallinity is changed in volume or structure by the injection and holding pressures resulting in improved mechanical strength properties of the injected molded resin.
Claim 9
Dependent Claim
27 words
The method according to claim 7 wherein the resin is selected from the group consisting of olefin plastics, amide plastics, acetal plastics, polycarbonate plastics and polyalkylene terephthalates.
References Cited (Backward Citations)
US2033735A
Cited
US3243851A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1983-12-02 | 1984-06-02 | 1984-12-02 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-12-02 | 1988-06-02 | 1988-12-02 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-12-02 | 1992-06-02 | 1992-12-02 | $7700.00 | Window Closed / Lapsed |