Method for the manufacturing of a low shrinkage flexible sheet

Patent metadata

Field	Value
Publication number	US-9522518-B2
Application number	US-201013501305-A
Country	US
Kind code	B2
Filing date	Oct 12, 2010
Priority date	Oct 12, 2009
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

The invention relates to a method for the manufacturing of a low shrinkage flexible sheet, said sheet comprising a fabric containing polyolefin fibers, said method comprising the steps of: a) depositing a molten plastomer layer on at least one surface of the woven fabric to form a sheet having a thickness approximately equal with the sum of the thicknesses of said molten plastomer layer and of said fabric; and b) impregnating said fabric with at least part of the molten plastomer layer by drawing the sheet into a gap between two calendaring rollers at a temperature of between the melting temperature of the plastomer and the melting temperature as determined by DSC of the polyolefin fibers, said gap having a width smaller than the thickness of the sheet; wherein the width of the gap is chosen to apply an impregnation pressure on the sheet of at least 20 bars.

First claim

The invention claimed is:

1. A method for the manufacturing a flexible sheet which comprises a fabric containing polyolefin fibers, wherein the method comprises the steps of:
(a) forming a layer of molten plastomer onto at least one surface of a woven fabric by extruding molten plastomer as a layer into contact with the at least one surface of the woven fabric to form a preform sheet having a thickness approximately equal with a sum of thicknesses of the molten plastomer layer and the woven fabric; and
(b) impregnating the fabric with at least part of the molten plastomer layer by drawing the preform sheet into a gap between two calendering rollers at a temperature of between a melting temperature of the plastomer and a melting temperature of the polyolefin fibers as determined by Differential Scanning calorimetry (DSC) to thereby form a low shrinkage flexible sheet, wherein
step (b) includes adjusting the gap between the two calendering rollers to provide a gap width which is smaller than the thickness of the preform sheet prior to being drawn into the gap to thereby cause the calendering rollers to apply an impregnation pressure on the preform sheet of at least 20 bars.

2. The method of claim 1 , wherein step (a) comprises applying the molten plastomer layer onto the fabric at a plastomer temperature above a melting temperature of the plastomer to a temperature of at most 180° C.

3. The method of claim 2 , wherein the molten plastomer layer is deposited at a plastomer temperature between 120° C. and 150° C.

4. The method of claim 1 , wherein step (b) includes adjusting the gap width so that the calendering rollers apply an impregnation pressure of at least 30 bars.

5. The method of claim 1 , wherein step (b) is practiced at a calandering temperature between 80° C. and 160° C.

6. The method of claim 1 , wherein step (a) comprises preheating the woven fabric before depositing the molten plastomer layer thereon.

7. The method of claim 6 , wherein the woven fabric is preheated to a temperature between 50° C. and 130° C.

8. The method of claim 1 , further comprising subsequent to the impregnation step (b), a further compression step (c) which comprises heating the flexible sheet to a heating temperature, and compressing the heated flexible sheet by application of a compression pressure.

9. The method of claim 8 , wherein the thickness of the flexible sheet after the compression step (c) is reduced by at least 2%.

10. The method of claim 1 , wherein the plastomer is a semi-crystalline copolymer of ethylene or propylene and one or more C2 to C12 α-olefin co-monomers, and wherein the plastomer has a density of between 880 and 930 kg/m 3 .

11. The method of claim 1 , wherein the plastomer is a thermoplastic copolymer of ethylene or propylene and containing as co-monomers one or more α-olefins having 2-12 C-atoms.

12. The method of claim 1 , wherein the amount of the plastomer is chosen to yield a flexible sheet having an areal density (AD) that is at least 20% higher than the AD of the woven fabric.

13. The method of claim 1 , wherein the polyolefin fibers are polyethylene fibers.

14. The method of claim 1 , wherein the woven fabric is selected from the group consisting of plain weaves, basket weaves, crow feet weaves, satin weaves and triaxial weaves.

15. The method of claim 1 , wherein step (b) is practiced at a calendering temperature between 90° C. and 150° C.

16. The method of claim 13 , wherein step (b) comprises compressing the flexible sheet while heating the flexible sheet at a heating temperature between the melting temperature of the plastomer and the melting temperature of the polyethylene fibers as determined by DSC.

17. The method of claim 8 , wherein the heating temperature of the compression step (c) is between 60 and 150° C.

18. The method of claim 13 , wherein the polyethylene fibers are high molecular weight polyethylene (HMWPE) fibers having a weight average molecular weight between 20,000 and 600,000 g/mol.

19. The method of claim 18 , wherein the polyethylene fibers are ultrahigh molecular weight polyethylene (UHMWPE) fibers.

20. The method claim 18 , wherein the HMWPE fibers have a weight average molecular weight between 60,000 and 200,000 g/mol.

21. A method for manufacturing a plastomer-coated flexible sheet comprised of a fabric formed of polyolefin fibers and a plastomer coated on a surface of the fabric, wherein the method comprises the steps of:
(a) forming a molten layer of plastomer by extruding a plastomer melt into a first gap defined between opposed surfaces of first and second counter-rotating rollers, wherein the first and second rollers are heated to a temperature which is above a melting temperature of the plastomer so as to maintain the plastomer in a molten state with the second roller heated to a temperature which is greater than the temperature of the heated first roller so that the molten layer of plastomer adheres to the surface of the second roller when drawn through the first gap;
(b) providing a second gap between the heated second roller and an opposed counter-rotating third roller maintained at a temperature between the melting point of the plastomer and the melting point of the polyolefin fibers;
(c) directing the molten layer of plastomer to the second gap while simultaneously introducing the fabric into the second gap such that one surface of the fabric is positioned against a surface of the third roller and an opposite surface of the fabric is in contact with the molten layer of plastomer;
(d) drawing the molten layer of plastomer in contact with the fabric through the second gap to thereby apply pressure to the molten layer of plastomer and fabric to cause at least a part of the molten plastomer layer to impregnate the fabric and form a molten plastomer-coated fabric preform; and thereafter
(e) cooling the plastomer-coated preform to a temperature below 50° C. to obtain the plastomer-coated flexible sheet.

22. The method according to claim 21 , wherein step (e) is practiced to cool the plastomer-coated preform to a temperature between 10° C. and 30° C.

23. The method of claim 21 , wherein step (c) comprises applying the molten plastomer layer onto the fabric at a plastomer temperature above the melting temperature of the plastomer to a temperature of at most 180° C.

24. The method of claim 23 , wherein the molten plastomer layer is deposited at a plastomer temperature between 120° C. and 150° C.

25. The method of claim 21 , wherein step (d) includes adjusting the second gap width so that the second and third rollers apply an impregnation pressure of at least 30 bars.

26. The method of claim 21 , wherein step (d) is practiced at a temperature between 80° C. and 160° C.

27. The method of claim 21 , which further comprises preheating the woven fabric before depositing the molten layer of plastomer thereon.

28. The method of claim 27 , wherein the woven fabric is preheated to a temperature between 50° C. and 130° C.

29. The method of claim 21 , further comprising a further compression step which comprises heating the plastomer-coated flexible sheet to a heating temperature, and compressing the heated plastomer-coated flexible sheet by application of a compression pressure.

30. The method of claim 29 , wherein the plastomer-coated flexible sheet has a thickness after the further

Assignees

• Wienke Dietrich
• Marissen Roelof
• Jacobs Martinus Johannes Nicolaas
• Welzen Leonardus Jacobus Johannes Wilhelmus
• Dsm Ip Assets Bv

Inventors

• Wienke Dietrich
• Marissen Roelof
• Jacobs Martinus Johannes Nicolaas
• Welzen Leonardus Jacobus Johannes Wilhelmus

Classifications

• B32B2439/06

  Bags, sacks, sachets · CPC title

• B32B2439/46

  Bags · CPC title

• B32B2307/72

  Density · CPC title

• B32B5/024

  Woven fabric · CPC title

• B32B27/12 Primary

  next to a fibrous or filamentary layer · CPC title