US3940467A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of injection molding a structural foamed thermoplastic article having a uniform swirl-free and indent-free surface
Assignee: Bethlehem Steel Corp
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Filing: 1974-12-18
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Granted: 1976-02-24
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Expires: 1994-12-18
Abstract
Abstract A process for producing a swirl-free, indent-free foamed thermoplastic structural article in which water is utilized as a foaming agent. Water and a melted thermoplastic resin are mixed together in an extruder to form a pressurized foamable mixture. The foamable mixture from the extruder is collected in an accumulator and from there is delivered to a cavity in a mold in a suitable clamping device. The pressure in the cavity is lower than the pressure of the foamable mixture in the accumulator or extruder therefore when the foamable mixture enters the cavity the foaming agent is released and the thermoplastic resin is frothed and expands to completely fill the cavity. The melted foamed thermoplastic resin cools in the mold and solidifies to form a foamed thermoplastic structural article. The quantity of water introduced into the extruder is between about 0.1 weight percent to about 0.5 weight percent of the thermoplastic resin charge in the extruder. To produce a swirl-free foamed thermoplastic structural article the quantity of water introduced into the extruder is between about 0.1 weight percent and about 2.0 weight percent of the thermoplastic resin charge in the extruder.
Inventors
- 👤 Armand E. Brachman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 08:31
CPC Classifications
B; B29; B29C; B29C44/00; B29C44/34; B29C44/3442; B29C44/36; B29C44/38; B29C44/42; B29C44/421; Y; Y10; Y10S; Y10S264/00; Y10S264/05; Y10S264/14; Y10S264/83
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
146 words
In a method for producing a foamed thermoplastic structural article characterized by a smooth, uniform swirl-free surface, wherein a substantially uniform foamable mixture of water and a melted thermoplastic resin is formed in an extruder and said mixture is advanced under a predetermined pressure from the extruder to an accumulator and subsequently to a cavity in a mold, which cavity is at a lower pressure than the pressure applied to the foamable mixture in the extruder and in the accumulator, whereby the water in the form of steam causes the melted thermoplastic resin to foam and expand to completely fill the cavity in the mold, the method comprising restricting the quantity of said water introduced into said melted thermoplastic resin in said extruder within a range of between about 0.1 to about 2.0 weight percent of the charge weight of the thermoplastic resin in the extruder.
Claim 2
Dependent Claim
146 words
In a method for producing a foamed thermoplastic structural article characterized by a smooth, uniform swirl-free surface, wherein a substantially uniform foamable mixture of water and a melted thermoplastic resin is formed in an extruder and said mixture is advanced under a predetermined pressure from the extruder to an accumulator and subsequently to a cavity in a mold, which cavity is at a lower pressure than the pressure applied to the foamable mixture in the extruder and in the accumulator, whereby the water in the form of steam causes the melted thermoplastic resin to foam and expand to completely fill the cavity in the mold, the method comprising restricting the quantity of said water introduced into said melted thermoplastic resin in said extruder within a range of between about 0.1 to about 2.0 weight percent of the charge weight of the thermoplastic resin in the extruder.
Claim 3
Dependent Claim
12 words
The method according to claim 1 in which the thermoplastic is polystyrene.
Claim 4
Dependent Claim
34 words
The method according to claim 1 in which the accumulation zone melt temperature is from about 250° to about 600° F. and the accumulation zone pressure is from about 1200 to about 5000 psi.
Claim 5
Dependent Claim
18 words
The method according to claim 3 in which the mold temperature is not more than about 120° F.
Claim 6
Dependent Claim
143 words
In a method for producing a foamed thermoplastic structural article characterized by a smooth, uniform swirl-free and indent-free surface, wherein a substantially uniform foamable mixture of water and a melted thermoplastic resin is formed in an extruder and said mixture is advanced under a predetermined pressure from the extruder to an accumulator and subsequently to a cavity in a mold, which cavity is at a lower pressure than the pressure applied to the foamable mixture in the extruder and in the accumulator, whereby the water in the form of steam causes the melted thermoplastic resin to foam and expand to completely fill the cavity in the mold, the method comprising controlling the quantity of said water present in said melted thermoplastic resin in said extruder within a range of about 0.1 to about 0.5 weight percent of the charge weight in the extruder.
Claim 7
Dependent Claim
143 words
In a method for producing a foamed thermoplastic structural article characterized by a smooth, uniform swirl-free and indent-free surface, wherein a substantially uniform foamable mixture of water and a melted thermoplastic resin is formed in an extruder and said mixture is advanced under a predetermined pressure from the extruder to an accumulator and subsequently to a cavity in a mold, which cavity is at a lower pressure than the pressure applied to the foamable mixture in the extruder and in the accumulator, whereby the water in the form of steam causes the melted thermoplastic resin to foam and expand to completely fill the cavity in the mold, the method comprising controlling the quantity of said water present in said melted thermoplastic resin in said extruder within a range of about 0.1 to about 0.5 weight percent of the charge weight in the extruder.
Claim 8
Dependent Claim
12 words
The method according to claim 5 in which the thermoplastic is polystyrene.
Claim 9
Dependent Claim
34 words
The method according to claim 5 in which the accumulation zone melt temperature is from about 250° to about 600° F. and the accumulation zone pressure is from about 1200 to about 5000 psi.
Claim 10
Dependent Claim
18 words
The method according to claim 7 in which the mold temperature is no more than about 120° F.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1979-02-23 | 1979-08-25 | 1980-02-24 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1983-02-23 | 1983-08-25 | 1984-02-24 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1987-02-23 | 1987-08-25 | 1988-02-24 | $7700.00 | Window Closed / Lapsed |