EP0198620A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Manufacture of low density, sintered polytetrafluoroethylene articles
Assignee: Carlisle Corp
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Filing: 1986-03-27
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Granted: —
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Expires: 2006-03-27
Abstract
Abstract A method for extruding, stretching and sintering polytetrafluoroethylene in a single pass operation to form tubular articles of low density, low matrix tensile strength, sintered polytetrafluoroethylene and articles such as electric cable having low density, low matrix tensile strength sintered polytetrafluoroethylene insulation applied about a conductor by such method. A high reduction ratio rating polytetrafluoroethylene powder with a lubricant is extruded by an extruder (14) having a low reduction ratio, and the extrudate is heated (16) to remove the lubricant and is stretched (17) prior to sintering (18) of the polytetrafluoroethylene tube (T) which is held in its previously stretched state during sintering.
Inventors
- 👤 Norman Ralph Harlow
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 10:21
CPC Classifications
H; H01; H01B; H01B3/00; H01B3/18; H01B3/30; H01B3/44; H01B3/443; H01B3/445; B; B29; B29C; B29C48/00; B29C48/022; B29C48/03; B29C48/06; B29C48/15; B29C48/25; B29C48/92; B29C55/00; B29C55/005; H01B13/00; H01B13/06; H01B13/14; H01B13/145; B29C2948/00; B29C2948/92; B29C2948/92009; B29C2948/92209; B29C2948/92314; B29C2948/92323; B29C2948/92361; B29C2948/92409; B29C2948/92504; B29C2948/9258; B29C2948/92609; B29C2948/92657; B29C2948/92819; B29C2948/92857; B29C2948/92904; B29C48/36; B29C48/475; B29K; B29K2027/00; B29K2027/12; B29K2027/18; B29L; B29L2031/00; B29L2031/34; B29L2031/3462
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
252 words
A method of forming an elongated tubular product of low density, low matrix tensile strength, polytetrafluoroethylene characterised by: A. forcing an extrusible mixture of unsintered, high reduction ratio rating polytetrafluoroethylene and extrusion aid through a die (14) of an extruder (12) with a low reduction ratio, while substantially reducing the cross-section of said mixture and forming a central opening in said mixture to extrude an elongated continuous tube (T) formed of said extrusible mixture, said high reduction ratio rating being at least 1000/1 and the reduction ratio of said extruder being less than said reduction ratio rating and less than 1000/1; B. controlling the linear speed of said tube (T) exiting from said die (14) to hold the volumetric rate thereof at approximately the volumetric rate of said mixture passing through said die; C. thereafter passing said tube (T) in sequence through an extrusion aid removal zone (16) and a stretching zone (17); D. drawing said tube (T) through said stretching zone (17) at a speed in excess of the linear speed of said mixture exiting from said die (14) to stretch the tube in said stretching zone; E. maintaining conditions in said extrusion aid removal zone (16) effective to remove the extrusion aid in said mixture as said tube (T) is passed through said extrusion aid removal zone (16); and F. heating said tube (T) in said stretching zone (17) to a temperature above that in said extrusion aid removal zone (16) but less than the sintering temperature of the polytetrafluoroethylene.
Claim 2
Independent Claim
252 words
A method of forming an elongated tubular product of low density, low matrix tensile strength, polytetrafluoroethylene characterised by: A. forcing an extrusible mixture of unsintered, high reduction ratio rating polytetrafluoroethylene and extrusion aid through a die (14) of an extruder (12) with a low reduction ratio, while substantially reducing the cross-section of said mixture and forming a central opening in said mixture to extrude an elongated continuous tube (T) formed of said extrusible mixture, said high reduction ratio rating being at least 1000/1 and the reduction ratio of said extruder being less than said reduction ratio rating and less than 1000/1; B. controlling the linear speed of said tube (T) exiting from said die (14) to hold the volumetric rate thereof at approximately the volumetric rate of said mixture passing through said die; C. thereafter passing said tube (T) in sequence through an extrusion aid removal zone (16) and a stretching zone (17); D. drawing said tube (T) through said stretching zone (17) at a speed in excess of the linear speed of said mixture exiting from said die (14) to stretch the tube in said stretching zone; E. maintaining conditions in said extrusion aid removal zone (16) effective to remove the extrusion aid in said mixture as said tube (T) is passed through said extrusion aid removal zone (16); and F. heating said tube (T) in said stretching zone (17) to a temperature above that in said extrusion aid removal zone (16) but less than the sintering temperature of the polytetrafluoroethylene.
Claim 3
Dependent Claim
44 words
a method according to claim 1 characterised in that, after passing said tube (T) through said extrusion aid removal zone (16), and through said stretching zone (17), the tube (T) is passed through a sintering zone (18) which is maintained at sintering temperature conditions.
Claim 4
Dependent Claim
39 words
A method according to claim 1 or 2 characterised by maintaining the linear speed of said tube (T) entering said sintering zone (18) at substantially the same speed as that of said tube (T) exiting said sintering zone (18).
Claim 5
Dependent Claim
39 words
A method according to claim 3 characterised in that said linear speed of said tube (T) exiting said die (14) is controlled by passage between a pair of pinch rolls (30,31) in peripheral rolling contact with said tube (T).
Claim 6
Dependent Claim
64 words
A method according to claim 1 or claim 2 characterised in that said extrusion aid is a volatile substance and said conditions in said extrusion aid removal zone (16) include a temperature sufficient to volatilize said extrusion aid as said tube passes through said extrusion aid removal zone, and said temperature of said tube (T) in said stretching zone is between 250OF and 450°F.
Claim 7
Independent Claim
17 words
A method according to calim 5 characterised in that said extrusion aid is V.M. & P. naphtha.
Claim 8
Independent Claim
17 words
A method according to calim 5 characterised in that said extrusion aid is V.M. & P. naphtha.
Claim 9
Dependent Claim
75 words
A method as set forth in claim 2-characterised in that said tube (T) is pulled at the downstream end of said sintering zone (18) by first pulling means (22) and is stretched in said stretching zone (17) by second pulling means (23a, 24a, 25a) intermediate said stretching zone (17) and said sintering zone (18) said second pulling means pulling said tube at substantially the same speed as it is pulled by said first pulling means.
Claim 10
Dependent Claim
69 words
A method as set forth in claim 1 or 2 characterised by this, that an indefinite length of material which is inextensible relative to said tube (T) is supplied to said central opening in said mixture and through said die (14) into said tube (T) and said tube (T) with said indefinite length of said material therein is drawn through said stretching zone (17) and said sintering zone (18).
Claim 11
Dependent Claim
21 words
A method as set forth in claim 8 characterised in that said indefinite length of material is an electric conductor (W).
Claim 12
Dependent Claim
38 words
A method as set forth in claim 1 or 2 characterised in that said reduction ratio rating is at least 2500/1 and the reduction ratio of said extruder is in the range from about 200/1 to about 800/1.
Claim 13
Dependent Claim
37 words
A method as set forth in claim 10 characterised in that the reduction ratio of said extruder (14) is less than one fourth of said reduction ratio rating and said tube (T) is stretched at least 150%.
Claim 14
Dependent Claim
50 words
An electric cable (C) comprising an elongated inner conductor (W) and a continuous layer (T) of low density polytetrafluoroethlyene surrounding and contacting said conductor characterised by said layer (F) having a uniform cross-section and density in both the longitudinal and radial directions and being substantially homogeneous as viewed in cross-section.
Claim 15
Dependent Claim
50 words
An electric cable (C) comprising an elongated inner conductor (W) and a continuous layer (T) of low density polytetrafluoroethlyene surrounding and contacting said conductor characterised by said layer (F) having a uniform cross-section and density in both the longitudinal and radial directions and being substantially homogeneous as viewed in cross-section.
Claim 16
Dependent Claim
20 words
A cable as set forth in claims 12 characterised in that said layer (F) of low density polytetrafluoroethylene is sintered.
Claim 17
Dependent Claim
18 words
A cable as set forth in claim 12 or 13 characterised in that said polytetrafluoroethylene contains 70% voids.
Claim 18
Dependent Claim
42 words
A cable as set forth in claim 14 characterised in that the electrical signal propagation velocity of said layer is at least 75% of the velocity of light and the matrix tensile strength of said layer is less than about 12,000 p.s.i.
Claim 19
Dependent Claim
41 words
A cable as set forth in claims 15 characterised in that said electrical signal propagation velocity is at least 80% of the velocity of light and said matrix tensile strength is in the range from about 2000 p.s.i. to 8000 p.s.i.
Claim 20
Dependent Claim
28 words
A cable as set forth in claim 16 characterised in that said layer has a density of from about 0.45 3 3 g/cm3 to about 1.9 g/cm .
References Cited (Backward Citations)
No citation records indexed.
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