GB2156394A

GB2156394A - Improving adhesion of coatings to textile fabrics

Info

Publication number: GB2156394A
Application number: GB08506613A
Authority: GB
Inventors: James Ronald Holker; Anthony John Grant Sagar
Original assignee: Shirley Institute
Current assignee: Shirley Institute
Priority date: 1984-03-28
Filing date: 1985-03-14
Publication date: 1985-10-09
Also published as: GB8408024D0; GB8506613D0

Abstract

The invention provides improved adhesion by treating the fabric, prior to coating, with a polymeric carboxylic acid which may react with the fabric. The coating may be of a polyurethane & the fabric be of nylon.

Description

SPECIFICATION Adhesion of coatings to textile fabrics This invention relates to the improvement of adhesion of coatings to textile fabrics.

It is now quite common practice to coat textile fabrics with a thin layer of plastics, for example in order to obtain a waterproof fabric suitable for making up into foul weather clothing. One of the problems with coatings applied to flexible substrates like textile fabric is in obtaining adequate adhesion between the coating and the textile fabric so that they do not separate when the fabric is flexed. The lack of adhesion can be particularly marked with synthetic fabrics for example of nylon.

The present invention has been made from a consideration of this problem.

According to one aspect of the invention there is provided a method for improving adhesion between a fabric and a coating comprising treating the fabric with a polymeric carboxylic acid prior to coating.

Preferably the fabric to be treated will be one made from synthetic fibres, such as polyamide, which will react, at least partially with the acid. It is known that certain acids will react with polyamide fabrics to stiffen the fabric but it was not appreciated that adhesion between the fabric and a coating could also be improved by such treatment.

The polymeric carboxylic acid that is applied is preferably one which will react with the fabric. Typical acids are homopolymers of unsaturated carboxylic acids such as polyacrylic acid, polymethacrylic acid, polyitaconic acid, and copolymers for example of an unsaturated carboxylic acid with an olefin or an unsaturated ether such as a copolymer of maleic acid with ethylene or with methyl vinyl ether.

The treatment of the fabric with the acid may be carried out at ambient or elevated temperature, for example by immersion of the fabric in a solution or dispersion of the acid. The treated fabric is dried followed by exposure to elevated temperature for example above 100 C but preferably not above the heat setting temperature and finally washed to remove unreacted acid.

The treated fabric can be coated with any suitable coating of for example plastics, natural or synthetic rubber or silicone. Typical coatings of plastics materials with which good adhesion can be obtained are polyurethanes, polyvinylchlorides and acrylics. Particularly good results can be obtained using polyurethanes of the kind described in our Patent Application No.8037510 (Serial No.2087909).

The adhesion between the coating and fabric treated in accordance with the invention is maintained or even improved when the fabric is wetted and re-dried.

In another aspect of the invention, a polymer coating is modified by incorporation of groups that promote adhesion to a fabric substrate. For example a polymer coating such as a polyurethane containing a proportion of carboxylic acid side-chains exhibits better adhesion to a nylon fabric than a polymer of similar structure not containing carboxylic acid side-chains. Furthermore, coatings such as polyurethane coatings, containing a plurality of basic groups also adhere better to nylon when the fabric is pretreated with polyacrylic acid. Dry adhesion of coatings actually increases if the coating fabrics are wetted with water and then redried.

The following Examples further illustrate the invention: Example I A nylon 6.6 fabric (120 g/m2) was treated with a solution of polyacrylic acid (0.075% w/v) and a nonionic surfactant (0.05% w/v), dried and cured simultaneously at 190"C for 150 sec. Any unbound polymer was then washed off with water. The treated fabric and an untreated control were then direct-coated (knife-on-roll) with some commercially available polyurethanes, together with a standard cross-linking agent (Imprafix TH). Peel strengths were then measured (BS 3424, Method 9).

Polyacrylic Coating Peel Strength (N/5 cm) acid treated Weight Dry Wet Water zglm2) t2% Na Soaked, oleate) Redried Impranil C No 25 39 34 39 Yes 31 100 59 91 Impranil CHW No 36 36 27 Yes 43 68 48 73 Witoflex 635 No 36 47 40 Yes 45 57 48 Example Il Improved adhesion has also been observed when carboxylic acid side-chains were introduced into a polyurethane used to coat unmodified nylon fabric. Thus, a control polymer was synthesised by the successive reaction of 4,4'-diisocyanato-dicyclohexylmethane (2.0 mol) with butane -1,4-diol (1.0 mol) and polycaprolactone diol (MW 1250) (1.0 mol); a second polymer was then prepared in which 0.25 mol of the butane -1,4-diol was replaced by 2,2-bis-hydroxy-methylpropionic acid.Both polymers plus a standard cross-linked agent (13% wlw), were then coated onto a filament-woven nylon fabric (120 gim2). The dry peel adhesion of the modified coating was 57N/5 cm compared with 40N/5 cm for the control polymer.

The same control and polyacrylic acid (PAA) treated (0.075 w/v bath) nylon fabrics as described in Example I were next coated with a group of polyurethanes based on a control polymer derived from isophorone diisocyanate (2 mol), butane -1,4-diol (1 mol), and polycaprolactone (MW 2000) (1 mol). In these polymers, the parent hard-segment diol was replaced by a basic diol, N-methyldiethanolamine (NMDEA) in progressively increasing amounts, as shown in the following Table. Each polymer, together with a standard cross-linking agent, was then coated (25-33 g/m2) on to the nylon fabrics and their dry and wet peel adhesion was measured.

Proportion of NMDEA (mol) Peel Adhesion .0 0.25 0.5 0.75 1.0 (N15 cm) Control fabric Dry 21 26 26 26 25 Wet (Na oleate) 20 29 27 28 23 Wet (water) 27 28 22 34 22 Redried - - 35 39 38 PAA-treated fabric Dry 53 32 36 37 45 Wet (Na oleate) 61 50 38 37 35 Wet (water) 60 49 33 31 36 Redried - 58 43 43 88 Dry peel adhesion to the control fabric was not affected by changes in polymer composition. Aithough all the polymers adhered better to PAA-modified fabric than to untreated fabric, the effect was greatest with the unmodified polymer, i.e. containing no NMDEA. Wet peel adhesion in sodium oleate and in water was for the most part at least as good as dry peel adhesion, and on certain PAA-treated fabrics it was significantly better.When the water-wetted specimens were redried, dry peel adhesion was actually greater (ca. 100% in one example) than the original dry adhesion. It has been observed that the polymers containing NMDEA all had very good adhesion to glass, even when wetted. That may be because of polar interactions between basic centres in the polymer and the glass surface.

Example 111 Nylon fabric (120 g/m2) was treated with polyacrylic acid solution (0.1% w/v) and dried. The treated fabric was coated using a knife-on-roll with a medium viscosity unpigmented polyvinylchloride plastisol to a coating weight of 130 g/m2 and with a high viscosity, pigmented polyvinylchloride plastisol to a coating weight of 173 g/m2. The peel strength of the product was from 250 to 300% better than that of an untreated nylon fabric having the same coating whilst the tear strength was of the same order.

Claims

1. A method for improving adhesion between a fabric and a coating composition comprising treating the fabric with a polymeric carboxylic acid.

2. A method as claimed in Claim 1, wherein the polymeric carboxylic acid is one that reacts with the fabric.

3. A method as claimed in Claim 1 or Claim 2, wherein the polymeric carboxylic acid is a homopolymer of an unsaturated carboxylic acid or a copolymer of an unsaturated carboxylic acid with an olefin or an unsaturated ether.

4. A method as claimed in Claim 3, wherein the carboxylic acid is polyacrylic acid, polymethacrylic acid, polyitaconic acid, a copolymer of ethylene and maleic acid or a copolymer of methyl vinyl ether and maleic acid.

5. A method as claimed in any preceding claim, wherein the fabric comprises synthetic fibres.

6. A method as claimed in any preceding claim, wherein the fabric is treated with the polymeric carboxylic acid at ambient temperature.

7. A method as claimed in any of Claims 1 to 5, wherein the fabric is treated with the polymeric carboxylic acid at elevated temperature.

8. A method as claimed in any preceding claim wherein the polymeric carboxylic acid is applied to the fabric in the form of a solution or dispersion.

9. A method as claimed in any preceding claim, wherein after treatment with the polymeric carboxylic acid and prior to coating the fabric is dried.

10. A method as claimed in Claim 9, wherin after treatment with the polymeric carboxylic acid and prior to coating the fabric is heated.

11. A method as claimed in any preceding claim, wherein the coating is of plastics material, rubber or silicone.

12. A method as claimed in Claim 11, wherein the coating is of polyurethane, polyvinylchloride or an acrylic based polymer.

13. A method as claimed in Claim 11 or Claim 12, wherein the coating material is a polymer having groups which promote adhesion to the fabric.

14. A method as claimed in Claim 13, wherein the coating material is a polyurethane having carboxylic acid side chains or a plurality of basic groups.

15. A method as claimed in any preceding claim, wherein the coated fabric is wetted and then dried.

16. A method for improving the adhesion between a fabric and a coating composition substantially as described herein with reference to any one of the Examples.

17. Coated fabric produced by the method as claimed in any preceding claim.