Winding tape and method of making winding tape

1. A method for producing a winding tape from unsintered polytetrafluoroethylene wherein polytetrafluoroethylene powder is mixed with a lubricating or slip agent, the material is molded into a cylindrical blank and the blank is first extruded as a strand with small outer dimensions and subsequently calendered into tape form, wherein the strand extruded from the blank is a round rope that is calendered into the winding tape by compression in the radial direction such that the quantity of material remaining in the compressed center area made of polytetrafluoroethylene and lubricating or slip agent is greater than the quantity of material remaining in the areas approaching the tape edges.

2. The method in accordance with claim 1 , wherein the elongation of the calendered tape length with respect to the length of the pressed round rope is a factor of 1 to 3, preferably 1.2 to 2.2.

3. The method in accordance with claim 1 , wherein the distribution of material quantities across a winding tape cross-section that takes place during calendering is accomplished by one-sided or two-sided flattening of the curvature of the circumferential surface of the round rope in the central area that is subjected to compression.

4. The method in accordance with claim 1 , wherein the round rope is calendered into an oval cross-section with edge regions that taper to a point.

5. The method in accordance with claim 1 , wherein the round rope is calendered into a flat profile with edge regions that taper from the middle to a point on each side and with uniform edges.

6. The method in accordance with claim 1 , wherein the width of the calendered winding tape corresponds to at least 6 times and preferably 8 to 14 times the diameter of the round rope.

7. A method for producing a winding tape from unsintered polytetra-fluoroethylene wherein polytetrafluoroethylene powder is mixed with a lubricating or slip agent, the material is molded into a cylindrical blank and the blank is first extruded as a strand with small outer dimensions and subsequently calendered in the forming gap of a pair of rolls into the winding tape, wherein the surface of at least one roll of said pair of rolls is deformed under compression during the calendering of the round rope into the winding tape.

8. The method in accordance with claim 7 , wherein the degree of deformation of the roll surface is controlled as a function of the relevant diameter of the round rope.

9. The method in accordance with claim 8 , wherein the control of the deformation is accomplished by compression of the roll body.

10. The method in accordance with claim 7 , wherein the deformation of the roll surface as a function of the diameter of the round rope is accomplished by the latter itself.

11. The method in accordance with claim 7 , wherein the round rope passes through a guide nozzle immediately ahead of the forming gap of the roll pair.

12. The method according to claim 1 , wherein the winding tape is designed as a flat profile with edge regions tapering to a point from the center to both sides and with uniform tape contours at the edges.

13. The method according to claim 1 , wherein the edges of the tape are wide, wherein the edge width on both sides of the center region, which determines the tape thickness, is at least 45%, preferably 50 to 80% of the total width of the winding tape.

14. The method according to claim 1 , wherein the tape has the approximate shape in cross-section of a rectangle that is extended in the direction of the narrow sides, wherein the tape thickness decreases continuously from the tape center to the sides at both edges of the tape.

15. The method according to claim 1 , wherein the tape has the approximate shape in cross-section of a flattened dish, wherein the tape thickness decreases continuously from the tape center to the sides at both edges of the tape.

16. The method according to claim 1 , wherein the tape thickness is 20 to 200 μm, preferably 40 to 160 μm, and tapers to 5 μm and less at the edges.

17. The method according to claim 1 , wherein the width of the tape is from 5 to 50 mm, preferably 10 to 30 mm.

18. The method according to claim 1 , wherein the winding tape, when wound, forms a substantially planar surface thereby substantially eliminating protruding edges formed by the winding of the winding tape.

19. The method according to claim 18 , wherein the wound winding tape is subjected to a sintering process to thereby eliminate the protruding edges.