Method of making a conductive polymer sheet

• US 4,885,457 A
• Filed: 09/30/1988
• Issued: 12/05/1989
• Est. Priority Date: 09/30/1988
• Status: Expired due to Term

• Current Assignee: Tyco Electronics Corporation (TE Connectivity Ltd. (United Kingdom))
• Original Assignee: Raychem Limited (TE Connectivity Limited)
• Inventors: Au, Andrew N.
• Primary Examiner(s): Pellinen, A. D.
• Assistant Examiner(s): Fuller, Leon K.
• Application Number:
  US07/252,229
• Time in Patent Office: 431 Days
• Field of Search: 219/548, 219/528, 219/538, 219/504, 219/505, 219/553, 219/549, 264/104, 264/105, 264/209.3, 264/211, 264/148, 264/146
• US Class Current: 219/548
• CPC Class Codes: B29C 2793/0063 Cutting longitudinally
• CPC Class Codes: B29C 2948/92133 Width or height
• CPC Class Codes: B29C 2948/92142 Length
• CPC Class Codes: B29C 2948/92438 Conveying, transporting or storage of articles
• CPC Class Codes: B29C 2948/92628 Width or height
• CPC Class Codes: B29C 2948/92638 Length
• CPC Class Codes: B29C 2948/92933 Conveying, transporting or storage of articles
• CPC Class Codes: B29C 48/0022 combined with cutting
• CPC Class Codes: B29C 48/022 characterised by the choice of material
• CPC Class Codes: B29C 48/07 Flat, e.g. panels
• CPC Class Codes: B29C 48/08 flexible, e.g. films
• CPC Class Codes: B29C 48/92 Measuring, controlling or regulating
• CPC Class Codes: B29K 2995/0005 Conductive
• CPC Class Codes: H01C 17/065 by thick film techniques, e.g. serigraphy
• CPC Class Codes: H05B 2203/006 using interdigitated electrodes
• CPC Class Codes: H05B 3/146 Conductive polymers, e.g. polyethylene, thermoplastics
• CPC Class Codes: H05B 3/20 Heating elements having extended surface area substantially in a two-dimensional plane, e.g. plate-heater H05B3/62, H05B3/68, H05B3/78, H05B3/84 take precedence

Abstract

A method of making a conductive polymer sheet in which a hollow conductive polymer extrudate is slit and flattened. The resulting sheet may have improved resistivity uniformity over conventionally extruded sheet. The sheet is useful in producing electrical devices such as heaters and circuit protection devices.

Claims

1. A method of making a conductive polymer sheet, which method comprises

(1) melt-extruding a conductive polymer composition through a die to produce a hollow extrudate;

and

(2)slitting the extrudate axially to form a sheet, wherein the sheet has a length p measured in the machine direction of extrusion where the machine direction is the direction parallel to the extrusion direction, a width w measured in the transverse direction at right angles to the direction of extrusion, and a thickness t, and if the sheet is divided at right angles to the machine direction into equal transverse segments, each transverse segment having a width equal to the smaller of (a) 0.2p and (b) as close to 1 inch as division into equal segments will allow, the resistivity measured in the machine direction of each transverse segment is from 0.7 R_m to 1.3 R_m, where R_m is the resistivity in the machine direction of the sheet.

2. A method according to claim 1 wherein the resistivity measured in the machine direction of each transverse segment is from 0.8 R_m to 1.2 R_m.

3. A method according to claim 1 wherein the resistivity of the sheet in the normal direction, R_n, is at least 2 times the resistivity of the sheet in the machine direction, R_m.

4. A method according to claim 3 wherein R_n is at least 5 times R_m.

5. A method according to claim 4 wherein R_n is at least 10 times R_m.

6. A method of making a conductive polymer sheet, which method comprises

(1) melt-extruding a conductive polymer composition through a die to produce a hollow extrudate;

and

(2) slitting the extrudate axially to form a sheet, wherein the sheet has a length p measured in the machine direction of extrusion where the machine direction is the direction parallel to the extrusion direction, a width w measured in the transverse direction at right angles to the direction of extrusion, and a thickness t, and if the sheet is divided in the machine direction into equal longitudinal segments, each segment having a width equal to the smaller of (a) 0.2w and (b) as close to 1 inch as division into equal segments will allow, the resistivity measured in the transverse direction of each longitudinal segment is from 0.7 R_t to 1.3 R_t, where R_t is the resistivity in the transverse direction of the sheet.

7. A method according to claim 6 wherein the resistivity measured in the transverse direction of each longitudinal segment is from 0.8 R_t to 1.2 R_t.

8. A method according to claim 6 wherein the resistivity of the sheet in the normal direction, R_n, is at least 2 times the resistivity of the sheet in the machine direction, R_m.

9. A method according to claim 8 wherein R_n is at least 5 times R_m.

10. A method according to claim 9 wherein R_n is at least 10 times R_m.

11. An electrical device which comprises

(1) a conductive polymer component which has been prepared by a method which comprises

(a) melt-extruding a conductive polymer composition through a die to produce a hollow extrudate,

(b) slitting the extrudate axially to form a sheet, and

(c) dividing the sheet into a plurality of components;

and

(2) at least two electrodes which can be connected to a source of electrical power to cause current to flow through the component,

wherein the component has a length p measured in the machine direction of extrusion where the machine direction is the direction parallel to the extrusion direction, a width w measured in the transverse direction at right angles to the direction of extrusion, and a thickness t, and if the component is divided at right angles to the machine direction into equal transverse segments, each transverse segment having a width equal to the smaller of (a) 0.2p and (b) as close to 1 inch as division into equal segments will allow, the resistivity measured in the machine direction of each transverse segment is from 0.7 R_m to 1.3 R_m, where R_m is the resistivity in the machine direction of the component.

12. A device according to claim 11 wherein the conductive polymeric component exhibits PTC behavior.

13. A device according to claim 12 wherein the device is a heater which has a surface area of at least 2 in².

14. A device according to claim 13 wherein the heater has a surface area of at least 5 in².

15. A device according to claim 13 wherein the conductive polymer composition has a resistivity of at least 100 ohm-cm.

16. A device according to claim 15 wherein the conductive polymer composition has a resistivity of at least 1000 ohm-cm.

17. A device according to claim 16 wherein the conductive polymer composition has a resistivity of at least 10,000 ohm-cm.

18. A device according to claim 11 wherein the device is a circuit protection device which has a surface area of less than 2 in².

19. A device according to claim 11 wherein the resistivity of the component in the normal direction, R_n, is at least 2 times the resistivity in the machine direction, R_m.

20. A device according to claim 19 wherein R_n is at least 5 times R_m.

21. A device according to claim 19 wherein R_n is at least 10 times R_m.

22. An electrical device which comprises

(1) a conductive polymer component which has been prepared by a method which comprises

(a) melt-extruding a conductive polymer composition through a die to produce a hollow extrudate,

(b) slitting the extrudate axially to form a sheet, and

(c) dividing the sheet into a plurality of components;

and

(2) at least two electrodes which can be connected to a source of electrical power to cause current to flow through the component, wherein the component has a length p measures in the machine direction of extrusion where the machine direction is parallel to the direction of extrusion, a width w measured in the transverse direction at right angles to the direction of extrusion, and a thickness t, and if the component is divided in the machine direction into equal longitudinal segments, each segment having a width equal to the smaller of (a) 0.2w and (b) as close to 1 inch a division into equal segments will allow, the resistivity measured in the transverse direction of each longitudinal segment is from 0.7 R_t to 1.3 R_t, where R_t is the resistivity in the transverse direction of the component.

23. A device according to claim 22 wherein conductive polymeric component exhibits PTC behavior.

24. A device according to claim 23 wherein the device is a heater which has a surface area of at least 2 in².

25. A device according to claim 24 wherein the heater has a surface area of at least 5 in².

26. A device according to claim 24 wherein the conductive polymer composition has a resistivity of at least 100 ohm-cm.

27. A device according to claim 26 wherein the conductive polymer composition has a resistivity of at least 1000 ohm-cm.

28. A device according to claim 27 wherein the conductive polymer composition has a resistivity of at least 10,000 ohm-cm.

29. A device according to claim 22 wherein the device is a circuit protection device which has a surface area of less than 2 in².

30. A device according to claim 22 wherein the resistivity of the component in the normal direction, R_n, is at least 2 times the resistivity in the machine direction, R_m.

31. A device according to claim 30 wherein R_n is at least 5 times R_m.

32. A device according to claim 31 wherein R_n is at least 10 times R_m.