NONWOVEN COMPOSITE STRUCTURE WITH EXCELLENT WATER VAPOUR PERMEABILITY

Abstract

The present invention relates to a composite comprising a nonwoven fabric being the substrate of the composite, wherein the nonwoven fabric comprises a polymer (A) selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and polyamide; and a coating layer, wherein the coating layer comprises a polymer (B), wherein said polymer is an ethylene copolymer, preferably a polar ethylene copolymer; whereby the coating layer overlays at least one surface of the nonwoven fabric; and whereby the composite has a water vapor transmission rate (WTVR) according to ASTM E-96 ((water cup method) at 38° C. at 50% RH at the outside of the sample and 100% RH at the inside of the samples) of more than 50 g/[m.sup.2/24 h], preferably of more than 100 g/[m.sup.2/24 h].

Claims

1. Composite comprising a nonwoven fabric being the substrate of the composite, wherein the nonwoven fabric comprises a polymer (A) selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate and polyamide; and a coating layer, wherein the coating layer comprises a polymer (B), wherein said polymer is an ethylene copolymer, wherein said polymer (B) is free of fillers and/or wherein the coating layer is free of pores, and wherein the coating layer has a weight per unit area of from 0.1 to 30 g/m.sup.2; whereby the coating layer overlays at least one surface of the nonwoven fabric; whereby the composite has a water vapor transmission rate (WVTR) according to ASTM E-96 ((water cup method) at 38° C. at 50% RH at the outside of the sample and 100% RH at the inside of the samples) of more than 50 g/[m2/24 h]; and wherein no adhesive between the coating layer and the nonwoven fabric is present.

2. Composite according to claim 1, wherein polymer (B) is an ethylene copolymer, comprising at least one polar comonomer selected from a comonomer containing at least one polar group.

3. Composite according to claim 1, wherein polymer (B) comprises a comonomer selected from the group consisting of acrylates and methacrylates.

4. Composite according to claim 1, wherein polymer (B) has a comonomer content of from 1 to 80 wt. %, based on the total amount of polymer (B).

5. Composite according to claim 1, wherein the melt flow rate, MFR.sub.2, determined according to ISO 1133 with loading of 2.16 kg, at 190° C. for polyethylene and 230° C. for polypropylene, of the coating layer is from 1 to 100 g/10 min.

6. Composite according to claim 1, wherein polymer (B) is the only polymer within the coating layer.

7. Composite according to claim 1, wherein the coating layer (a) is non-stretched, and/or (b) has a weight per unit area of from 0.5 to 15 g/m.sup.2.

8. Composite according to claim 1, wherein the nonwoven fabric has a weight per unit area of from 1 to 500 g/m.sup.2.

9. Composite according to claim 1, wherein the nonwoven fabric is a spunbonded fabric, preferably said spunbonded fabric comprises a polypropylene having (a) a melt flow rate MFR.sub.2 (230° C., 2.16 kg) measured according to ISO 1133 in the range of from 8 to 80 g/10 min; and/or (b) a molecular weight distribution (MWD) measured according to ISO 16014 of not more than 6.0.

10. Composite according to claim 1, wherein polymer (A) is a polypropylene homo- or copolymer.

11. Composite according to claim 1, wherein the coating layer is an extrusion coating layer.

12. Process for the preparation of a composite as defined in claim 1 comprising the steps of (a) extruding polymer (B); and (b) coating the nonwoven fabric with the extruded polymer (B).

13. Process according to claim 12, wherein a line speed in step (b) is at least 60 m/min.

14. A method for using a polymer (B), comprising: coating a nonwoven fabric with the polymer (B); wherein the polymer (B) is an ethylene copolymer that is free of fillers.

15. A hygiene or medical product, roofing material, housing material, or construction material comprising the composite of claim 1.

16. The composite of claim 1, wherein the polymer (B) is a polar ethylene copolymer.

17. The composite of claim 1, wherein the composite has a WVTR of more than 100 g/[m.sup.2/24 h].

18. The composite of claim 2, wherein the at least one polar comonomer contains hydroxyl group(s), alkoxy group(s), carbonyl group(s), carboxyl group(s), ether group(s), silane group(s) or ester group(s), or a mixture thereof.

19. The composite of claim 3, wherein the comonomer is selected from the group consisting of vinyl acrylate, methyl acrylate and ethyl acrylate.

20. The composite of claim 10, wherein polymer (A) is a propylene homopolymer.

Description

EXAMPLES

[0156] The spunbonded fabric was produced on a Reicofil 4 machine as described in WO 2017/118612 A1.

[0157] A nonwoven substrate being a spunbonded fabric with a weight per unit area of 13 g/m.sup.2 has been extrusion coated with different polymers (B-1 to B-3) and coating weights at a line speed of 80 m/min.

[0158] Obtained composites (CE1-CE3 & IE) have been evaluated for water vapour permeability, WVTR, according ASTM E-96 (water cup method) at 38° C. at 50% RH at the outside of the sample and 100% RH at the inside of the samples.

[0159] Each sample has been tested 4 times and the average and standard deviation have been calculated.

[0160] Results of WVTR tests are shown in Table 1.

TABLE-US-00001 TABLE 1 Weight per unit Polymer Weight per unit WVTR Sam- area Substrate of coating area Coating g/[m.sup.2- Stand. ple [g/m.sup.2] layer layer [g/m.sup.2] day] dev. CE 1 13 B-1 3 89 4 CE 2 13 B-1 4 53 8 CE 3 13 30% B-1 + 7 26 2 70% B-2 IE 13 B-3 4 605 22

[0161] As can be derived from table 1 the inventive example (IE) shows an extremely high WVTR for a coating weight of 4 g/m.sup.2. This is a much better WVTR than all comparative examples 1 to 3 (CE1-CE3) show.

[0162] Comparative Examples 1 to 3 demonstrate that a higher coating weight might result in a lower WTVR. However, IE shows that the coating weight is not the main issue, in fact, the structure of the coating layer seems to play a crucial role in water permeability of the composite.