Coated fabric and process for forming a polymeric coating on a liner

Abstract

Fabrics are disclosed having a liner with a polymeric coating, the coating comprising 0.25 to 8 ridges per cm and pits at an area density of 20 to 2500 cm.sup.2. The fabrics provide good friction in oily conditions. Also disclosed are methods for producing such fabrics comprising applying to a liner a liquid comprising water and a precursor of a polymeric material, contacting the liquid on the liner with a water-sorbing material and curing the polymeric coating. The fabrics may find use in gloves.

Claims

1. A process for forming, on a liner, a polymeric coating having a surface containing ridges and pits, which process comprises the steps: a) providing a liner; b) applying to at least a portion of the liner a liquid comprising water and a precursor of a polymeric material to form a coating on the liner; c) applying to the surface of the coating on the liner particles of a water-absorbing material selected from the group consisting of a cellulose derivative and a smectite clay; d) allowing the particles of the water-absorbing material to absorb water from the coating on the liner thus causing shrinkage of the surface to form a wave-like pattern comprising ridges in the coating and coagulation of the precursor of the polymeric material around the particles to gel the ridges in the surface of the coating; e) curing the precursor of the polymeric material to form a cured polymeric coating having ridges on the surface of the liner; and f) leaching the cured polymeric coating with water to remove the particles of the water-absorbing material from the surface of the coating to leave pits in the surface of the cured polymeric coating.

2. The process as claimed in claim 1, wherein the polymeric coating comprises an elastomer.

3. The process as claimed in claim 1, wherein contacting the liquid with the water-sorbing material is by sprinkling the particles on the liquid, spraying the particles, shower coating with the particles or fluidised bed application.

4. The process as claimed in claim 2, wherein the elastomer is a rubber.

5. The process as claimed in claim 4, wherein the rubber is nitrile rubber.

6. The process as claimed in claim 1, wherein the cellulose derivative comprises hydroxy ethyl cellulose.

7. A fabric comprising a liner having a polymeric coating on at least a portion thereof, which is formed by the process as claimed in claim 1, wherein the polymeric coating comprises 0.25 to 8 ridges per cm and pits on the surface thereof at an area density of 20 to 2500 cm.sup.2.

8. The fabric as claimed in claim 7, wherein the polymeric coating comprises an elastomeric coating.

9. The fabric as claimed in claim 8, wherein the elastomeric coating is a rubber coating.

10. The fabric as claimed in claim 7, wherein the coating comprises 50 to 2000 pits cm.sup.2.

11. The fabric as claimed in claim 7, wherein the coating comprises 100 to 2000 pits cm.sup.2.

12. The fabric as claimed in claim 7, wherein the polymeric coating comprises 1 to 5 ridges per cm.

13. The fabric as claimed in claim 7, wherein the orientation of the ridges is substantially random.

14. The fabric as claimed in claim 7, wherein the ridges are of varying height.

15. The fabric as claimed in claim 7, wherein at least a portion of the ridges are of 4 mm height or less.

16. The process as claimed in claim 1, wherein the polymeric coating comprises 0.25 to 8 ridges per cm and pits on the surface thereof at an area density of 20 to 2500 cm.sup.2.

17. A glove comprising a fabric as claimed in claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In order that the present invention may be better understood, it will now be described by way of example with reference to the accompanying drawings in which:

(2) FIG. 1 is a detail of a photograph of prior art polymeric coated fabric produced according to the known crinkle process.

(3) FIG. 2a is a drawing of a glove produced according to invention.

(4) FIG. 2b is a detailed photograph of the surface of a fabric according to the present invention.

(5) FIG. 3 is a magnified schematic diagram illustrating a cross-section through a fabric according to the present invention.

(6) FIG. 4 is a schematic, perspective view of the surface (magnified) of a fabric according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 illustrates a fabric 2 according to the prior art which comprises crinkles 4 on its surface. These crinkles are produced by depositing a polymeric coating of natural rubber on a liner and subsequently treating the natural rubber with organic solvent (for example paraffin) before curing. The crinkles of the surface have a linear frequency/density of a approximately 7 to 10 crinkles/cm.

(8) FIG. 2a illustrates a glove 5 according to the present invention comprising a fabric 6 consisting of a polymeric coating of nitrile rubber with a ridged surface and a liner 12 of knitted nylon (15 gauge). The polymeric coating extends over the whole of the palm of the glove 5 and also the palm side thumb 8 and fingers 10 of the glove with some coating on the backside (not shown) of the glove. The glove liner 12 has a finishing portion 13 at the end of the wrist portion to prevent unravelling.

(9) FIG. 2b illustrates a detail 7 of the surface of the polymeric coating according to the present invention which comprises a number of randomly orientated ridges 16 raised above the surface of the fabric and also a number of pits 14 of very small size scattered across the surface of the polymeric coating on the fabric. The ridges typically have a frequency/linear density (measured using transects across the surface of the fabric) of approximately 1 to 3 per cm. The pits on the surface have an area density of approximately 240 to 400 cm.sup.2. The ridges 16 have varying heights of typically less than 4 mm.

(10) The height of each ridge may be calculated as the distance between the trough and crest of the ridge.

(11) FIG. 3 illustrates schematically a fabric according to the present invention comprising a polymeric coating 18 of e.g. nitrile rubber having a series of wave like ridges 16 across its surface. On both the ridges 16 and in between the ridges 16 the surface has microscopic pits 14. In combination the ridges 16 and pits 14 provide a very effective grip especially in oily conditions when, for example, the fabric is used in a glove. FIG. 4 illustrates a perspective view of the surface showing the wavelike ridges 16 and microscopic pits 14 as they are distributed (thought to be randomly) on the surface of the polymeric coating 18.

(12) The invention is further illustrated by the following Example in which a glove as illustrated in FIG. 2a was manufactured according to the process of the present invention in order to provide a glove and fabric according to the first aspect of the invention.

(13) The liner for the glove was a 15 gauge knitted nylon liner. The liner was dip processed to coat the palm side of the glove with a suitable elastomeric polymer coating. A carboxylated acrylonitrile butadiene polymer dipped coating would be a typical example of a preferred coating. Such a nitrile latex grade is 6322 commercially available from Synthomer Ltd, Kluang, Malaysia.

(14) A suitable formulation for the elastomeric polymer coating for the dipping process is: 1. Synthomer 6322 latex100.00 parts of rubber. 2. Anionic stabilizer0.20 parts per 100 parts of rubber (phr). 3. Pigment2.00 phr. 4. ZnO (zinc oxide)4.00 phr. 5. PVA thickener+/to achieve the predetermined required viscosity of around 1000 centipoise.

(15) The glove dipping process has the following steps: 1. Load the knitted shell on the dipping, hand-shape former. 2. Dip the former and liner into a pre-coagulant solution, preferably calcium nitrate in alcohol/water, where methanol is 94 parts, water is 5 parts and calcium nitrate is 1 part (coagulant solution is not necessary if the liner is cotton or cotton-based). 3. Withdraw the former and liner from the solution and allow it to semi-dry, fingers down draining for 60 seconds, followed by fingers up for 60 seconds. 4. Slowly dip the former and liner into the nitrile latex dipping compound at a rate of 0.5 to 1.0 cm per second. 5. Withdraw the former and liner from the nitrile compound slowly, preferably at a rate not faster than 1.0 cm per second, and at a steady rate sufficient to yield a coating having a uniform, predetermined thickness of about 0.25 mm to about 0.75 mm. 6. Allow excess latex to drain. 7. Sprinkle hydroxy ethyl cellulose powder on the wet surface. 8. Allow to react for 2-3 minutes. 9. Dry and cure the dipped glove for about 25 to 200 minutes at a temperature in the range of about 85 C. to about 125 C. 10. After curing leach in water for 5 mins at 50 C. on the former. 11. Strip off the finished glove and wash at 50 C. and repeat the process in water for 30 minutes, pre-dry with air and then dry at 110 C. for 20-25 minutes on a drying former.

(16) The hydroxy ethyl cellulose powder has a particle size such that 100% is retained on sieve mesh size 40 (400 m), 65% to 75% is retained on mesh 60 (250 m), 40% to 50% retained on mesh size 70 (210 m) and 20% to 25% on mesh size 140 (105 m).

(17) Gloves produced according to the Example were tested to determine the coefficient of friction in dry, wet (water) and oily conditions. Gloves with the same nitrile rubber coatings to which no further process was applied (i.e. smooth surface) and the crinkle process was applied were also tested for comparison.

(18) All the equipment used was calibrated.

(19) The apparatus used is designed to determine the coefficient of friction between two flat surfaces which are under a predetermined load. The measurements were taken at 500 mm/min at ambient temperature under dry, water wet and oil (10 W 40 commercial engine oil) contaminated.

(20) Each test specimen was taken from the palm of the glove (the area of maximum grip) as this was the only place that generally a significant amount of material could be obtained. The palm material was clamped and draped over a 30 mm diameter rubber button which was approximately 9 mm high and had an approximate harness of 55 IRHD. By clamping the test specimen at one end, the material became taut naturally during the test.

(21) The water wet and oil contaminated test specimens were conditioned in the respective fluids for a minimum of 30 minutes prior to testing.

(22) The bearing surface was a ground steel plate having a surface roughness of less than 1 m R.sub.a. The same bearing surface was used for the dry, the water wet and finely the oil test.

(23) With the test specimen mounted in the jig and adjusted so that it just touched the bearing surface, the load of 5 kg (49.1N) was applied to the test specimen/bearing surface assembly by means of a bearing mounted in a bell crank. The bearing surface was then drawn over the test specimen and the resulting force required measured. At the end of the 50 mm travel the load was removed, the bearing surface returned to the start position and the procedure repeated. Three results were obtained for each sample, the load for the Coefficient of Friction calculation was taken as the mean value from the straighter end portion of the graph, generally the 20 mm to 50 mm portion.

(24) TABLE-US-00001 TABLE 2 Sample Dry Wet (water) Oil Example 0.9 0.67 0.26 Nitrile rubber nitrile 1.54 0.84 0.13 crinkle glove Nitrile rubber untreated 1.99 1.84 0.06 (smooth) glove

(25) The results in Table 2 show that the gloves according to the invention have good dry and wet (water) function and much better function in oil compared to known smooth nitrile rubber or crinkle nitrile rubber gloves. In fact, the lower values in dry and wet (water) conditions than conventional gloves offer more comfort for the wearer because the stickinessfeel is reduced.