US4577998A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Production of PVC irrigation pipe and the pipe so produced
Assignee: Imperial Chemical Industries Ltd
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Filing: 1982-10-04
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Granted: 1986-03-25
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Expires: 2002-10-04
Abstract
Abstract Process for producing flexible PVC irrigation pipe by extruding a plasticized PVC composition containing a melt strength-enhancing aid and a chemical blowing agent and (a) the extruded melt being expanded by foaming thereof immediately on leaving the die into a substantially closed-cell extrudate of outer diameter greater than the die orifice with the extrudate surfaces being substantially unpunctured, (b) drawing down the extrudate in the atmosphere causing rupturing of the foam cell walls of the extrudate to form a substantially open-cell extrudate having punctured surfaces, and (c) when the extrudate has been drawn down to a degree which is prior to any cellular collapse which would lead to the formation of water-impervious pipe, cooling the extrudate by passing it through a cooling means in order to prevent said collapse. Preferably the extrudate passes through a tubular guide into a water bath in step (c). The pipe thus produced is suitable for irrigation applications and may be used for long periods without exhibiting an unacceptable decrease in water-permeability.
Inventors
- 👤 Clive Dorrn
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 09:32
CPC Classifications
A; A01; A01G; A01G25/00; A01G25/06; B; B29; B29C; B29C44/00; B29C44/34; B29C44/36; B29C44/46; B29C44/50; B29C44/507; B29K; B29K2027/00; B29K2027/06; B29L; B29L2023/00; B29L2023/22; Y; Y10; Y10S; Y10S138/00; Y10S138/09; Y10S264/00; Y10S264/08; Y10S264/13
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
166 words
A process for producing water-permeable flexible PVC pipe suitable for irrigation applications which process comprises extruding a plasticised PVC composition, containing a melt strength-enhancing aid and a chemical blowing agent system, using an extruder equipped with a pipe-forming die, wherein said extrusion comprises (a) the extruded melt being expanded by foaming thereof immediately on leaving the die into a substantially closed-cell extrudate of greater outer diameter than the outer diameter of the die exit orifice with the surfaces of the extrudate being substantially unpunctured, said expansion being into the surrounding atmosphere, (b) drawing down the extrudate in the atmosphere causing rupturing of the foam cell walls of the extrudate to form a substantially open-cell extrudate having punctured surfaces, and (c) when the extrudate has been drawn down in the atmosphere to a degree which is prior to any cellular collapse which would lead to the formation of substantially water-impervious pipe, cooling the extrudate by passing it through a cooling means in order to prevent said collapse.
Claim 2
Dependent Claim
166 words
A process for producing water-permeable flexible PVC pipe suitable for irrigation applications which process comprises extruding a plasticised PVC composition, containing a melt strength-enhancing aid and a chemical blowing agent system, using an extruder equipped with a pipe-forming die, wherein said extrusion comprises (a) the extruded melt being expanded by foaming thereof immediately on leaving the die into a substantially closed-cell extrudate of greater outer diameter than the outer diameter of the die exit orifice with the surfaces of the extrudate being substantially unpunctured, said expansion being into the surrounding atmosphere, (b) drawing down the extrudate in the atmosphere causing rupturing of the foam cell walls of the extrudate to form a substantially open-cell extrudate having punctured surfaces, and (c) when the extrudate has been drawn down in the atmosphere to a degree which is prior to any cellular collapse which would lead to the formation of substantially water-impervious pipe, cooling the extrudate by passing it through a cooling means in order to prevent said collapse.
Claim 3
Dependent Claim
21 words
A process according to claim 1 wherein the die used is an annular die which yields pipe of annular cross section.
Claim 4
Dependent Claim
35 words
A process according to claim 1 wherein in step (c), the extrudate is drawn down in the atmosphere to a preselected outer diameter which is greater than the outer diameter of the die exit orifice.
Claim 5
Dependent Claim
17 words
A process according to claim 1 wherein in step (c), the cooling means is a cooling bath.
Claim 6
Dependent Claim
33 words
A process according to claim 4 wherein in step (c), the extrudate enters the cooling bath through a guide, the guide being a cylindrical tube in the case of using an annular die.
Claim 7
Dependent Claim
55 words
A process according to claim 4 wherein in step (c) the extrudate enters the cooling bath through a guide and is drawn down to a preselected outer diameter which is greater than the outer diameter of the die exit orifice, the inner diameter of the guide being substantially equal to the preselected outer extrudate diameter.
Claim 8
Dependent Claim
18 words
A water-permeable PVC pipe suitable for irrigation purposes which is produced by a process according to claim 1.
Claim 9
Dependent Claim
24 words
A PVC pipe according to claim 7 having an initial water seepage rate at 1 bar water pressure of at least 1 liter/meter length/hour.
Claim 10
Dependent Claim
24 words
A PVC pipe according to claim 7 having an initial water seepage rate at 1 bar water pressure of 10 to 200 liters/meters length/hour.
References Cited (Backward Citations)
US2807505A
Cited
GB971567A
Cited
US3403203A
Cited
US3300366A
Cited
GB1100727A
Cited
DE1629423A1
Cited
US3634564A
Cited
GB1237097A
Cited
US3539666A
Cited
US3954928A
Cited
GB1393680A
Cited
US3874965A
Cited
GB1554373A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-03-24 | 1989-09-23 | 1990-03-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-03-24 | 1993-09-23 | 1994-03-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-03-24 | 1997-09-23 | 1998-03-25 | $7700.00 | Window Closed / Lapsed |