POLYURETHANE COATED FABRIC

Abstract

A method for making a polyurethane coated fabric, the method comprising: a) providing a fabric liner; b) applying a coating to at least part of the liner, said coating comprising a polyurethane resin and manganese ferrite dissolved in a polar aprotic solvent; c) at least partially gelling the coating with water or an aqueous solution, so that the polar aprotic solvent is extracted from the coating; d) leaching the at least partially gelled coating with water or an aqueous solution, so as to further reduce the level of the polar aprotic solvent in the coating; and e) drying and curing the coating. The coating may also contain a dark colour pigment. A composition suitable for use in the method is also provided. The method enables polyurethane coated fabric products, such as gloves, to be produced which are black or grey in colour and contain a reduced amount of residual polar aprotic solvent, such as N,N-dimethylformamide.

Claims

1-15. (canceled)

16. A method for making a polyurethane coated fabric, the method comprising: a) providing a fabric liner; b) applying a coating to at least part of the liner, said coating comprising a polyurethane resin and manganese ferrite dissolved in a polar aprotic solvent; c) at least partially gelling the coating with water or an aqueous solution, so that the polar aprotic solvent is extracted from the coating; d) leaching the at least partially gelled coating with water or an aqueous solution, so as to further reduce the level of the polar aprotic solvent in the coating; and e) drying and curing the coating.

17. The method as claimed in claim 16, wherein the polar aprotic solvent comprises N, N-dimethylformamide.

18. The method as claimed in claim 16, wherein the manganese ferrite is present in an amount of from 5-15% by weight.

19. The method as claimed in claim 16, wherein the coating also contains a dark colour pigment.

20. The method as claimed in claim 19, wherein the dark colour pigment comprises a green pigment.

21. The method as claimed in claim 19, wherein the dark colour pigment comprises a phthalocyanine.

22. The method as claimed in claim 19, wherein the proportion of the manganese ferrite to the dark colour pigment is from 10:0.001 to 10:1.0 by dry weight.

23. The method as claimed in claim 16, wherein the coating also contains carbon black and the proportion of manganese ferrite to carbon black is from 70:30 to 90:1 by weight.

24. The method as claimed in claim 16, wherein the coating is applied to the liner by dip coating, curtain coating, shower coating, spray coating and/or screen printing.

25. The method as claimed in claim 16, further comprising one or more washing and drying steps.

26. The method as claimed in claim 16, wherein the fabric is in the form of a glove.

27. A composition for use in a method for making a polyurethane coated fabric, said composition comprising manganese ferrite and a dark colour pigment.

28. The composition as claimed in claim 27, wherein the proportion of the manganese ferrite to the dark colour pigment is from 10:0.001 to 10:1.0 by dry weight.

29. The composition as claimed in claim 27, wherein the dark colour pigment comprises a green pigment.

30. The composition as claimed in claim 27, wherein the dark colour pigment comprises a phthalocyanine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention provides a method of manufacturing PU coated gloves, both black and grey in colour, wherein the typical active effect of carbon black pigment in the dipping compound is replaced with preferred neutral effect metallic oxide types, or a particularly preferred combination of manganese ferrite with a dark colour pigment and, in particular, a combination of manganese ferrite with organic dark green pigments.

[0035] The PU compound being used in the method is a substantially diluted PU resin to around 10-15% solids with preferred DMFa and/or other typical polar aprotic solvents, such as dimethyl sulphoxide or methyl ethyl ketone.

[0036] Typical carbon black pigments have a very strong affinity for these preferred organic solvents, many of which are known to be hazardous and so are not desirable in the finished product, which in the case of gloves are in direct contact with the human skin. The use of non-active effect pigments in the present invention has the advantage that it results in a much lower residual solvent content of the gloves after processing. The final product is hence much safer for its intended use.

[0037] While the following account refers largely to the dip coating process, it will be well understood by persons skilled in the art that the method and compositions of the present invention may also be used in other procedures for applying polymers to fabrics, such as spraying, curtain or shower coating, and screen printing.

[0038] The process of making dip coated PU gloves is relatively simple. Such dipping processes can be performed on a simple manual basis or go on up to massive automated manufacturing plants. However, the basic process fundamentals remain the same.

[0039] Typically, aluminium hand shaped formers are used. These are usually PTFE coated to allow for easy loading of fabric liners and then stripping of the finished PU gloves where the PU tends to substantially penetrate the fabric glove liner and during drying and curing stick to the former. Hence the need for a PTFE coating on the former to aid product release.

[0040] There is a huge range of fabric liners used in the mass glove production plants. Most typical gloves are simple machine knit nylons or polyesters, the majority being made on 15 gauge (15 needles per inch) automated knitting machines such as Shima Seiki flat bed machines. There are also many cut resistant liners made: from fine, thin 18 gauge knitted, to thicker, heavier shells made on 10 gauge knitting machines. These heavier 10 gauge glove liners are impregnated with more compound and which leads to heavier gloves that can be even more problematic with regards to retaining DMFa. Those practised in the art will realise that knitted glove shells are not limited to this version of various glove knitting machines.

[0041] The vast majority of the glove production is made using 15 gauge knitted shells based typically but not limited to nylon 6, nylon 66 and polyester. These shells are sometimes a knitted blend with elastane type yarns such as Lycra or Spandex to increase elasticity of the shell to enhance grip and comfort. Many of the heavier, tougher gloves are made of more technical cut resistant yarns which comprise, for example, ultra high molecular weight polyethylene (UHMWPE), such as Dyneema, or Tsunooga, or perhaps a meta-aramid, such as Nomex, or a para-aramid, such as Kevlar, or Twaron. These may be plied in conjunction with wrapping yarns or also concurring steel yarns and or glass fibre yarns. All to increase cut resistance. The shells can also be of a plaited nature where one side of the knitted material is of one yarn type and the reverse side is another yarn type, or have targeted yarn specific knitting back to back faces of the shell fabric with different yarns.

[0042] As will be well understood by those skilled in the art, the liner may be made of other types of fabrics or materials to those listed above. For example, it may be woven and/or made up of multiple pieces sewn together.

[0043] Typically, the initial stage of the process is to load the fabric liner/shell onto the hand shaped former.

[0044] The dressed hand shaped formers are then dipped in the viscous liquid PU compound. The PU resin and DMFa solvent percentages are balanced to give a target viscosity that will both give adequate fabric penetration during the dip and yet at the same time not all of the compound will drain off the glove in the process.

[0045] A set time is given for draining after dipping, typically 4-9 minutes, but more preferably 5-7 minutes, in the fingers pointing down position to allow the excess of the flowing compound to drain off the former. This is usually until the intermittent compound drips are occurring at the finger tips. The hand formers are then rotated to the fingers up position to allow the mobile compound to flow back down and so even out the compound distribution on the palm of the glove.

[0046] The coated glove is then rotated back down through 180 and is slowly immersed in the first water coagulation tank/leach tank. Typically, this initial tank contains between 5 and 15% DMFa and more preferably between 8 and 12% DMFa. It is at this point that a gelling reaction of the PU dipped compound happens. As the water enters the DMFa PU compound through osmosis it penetrates the PU and rapidly extracts the polar aprotic DMFa. The extraction occurs relatively quickly and results in the fluid PU/DMFa resin becoming a gelled semi-solid as water replaces the organic solvents, i.e. organic PU resin does not dissolve in water. This rapid extraction of the majority of free DMFa during gelation of the PU results in an excellent microporous coating which is a massive advantage for breathability and grip of the finished PU glove coating on which the PU glove market has based its success.

[0047] The PU dipped gloves then progress on through several separate water leaching tanks. Each time the glove formers leave a leach tank and move on to the next tank the percentage of DMFa in each leach tank gradually reduces from 10% in the initial tank down to typically no more than 1.0% (and more preferably near to 0%) in the last leach tank. This can also be performed in one long leach tank.

[0048] The leached gloved former leaves the last leach tank fingers down and drains for 5 minutes or so to allow the excess contaminated water to drain off. The formers then rotate around to the fingers up position and enter a drying oven where the temperatures are typically around 80-90 C. Over a period of an hour or so the temperatures are raised up to 100 C. to evaporate off most of the water and also evaporate off most of the DMFa, and cure the PU coating. At the exit of the oven the formers dressed with the finished dried cured gloves are allowed to cool slightly and then the PU coated glove is removed. A new knitted liner shell will then be placed on the former ready for the next dipping circuit.

[0049] FIG. 1 shows a brief schematic outline of the basics of the glove dipping process.

[0050] After the above on plant process there can often be additional processing to remove further DMFa from the gloves, such as multiple tumble washing, tumble drying and re-heating.

[0051] The compounds used for solvent based PU gloves are typically mixed and dissolved with polar aprotic solvents such as DMFa, dimethyl sulphoxide, dimethyl pyrrolidone, dimethyl acetamide, or methyl ethyl ketone. Particularly preferred is DMFa. A typical formulation will consist of PU resin, or resins that can be of various crosslinkable hardnesses. Often blends of resins are involved to get the right feel and performance of a glove. Those who are practised in the art will be aware of this fact. The resins are usually purchased predissolved in DMFa and come in at around 30% solids solutions. TG-1020 for instance. An example of a supplier is Heung-il Polychem Ltd, Song Jung-Dong, Kang Seo-Gu, Busan, South Korea. Also SW-2030, as supplied by Duksung Co Ltd.

[0052] The pigment is also usually predissolved in a ratio of PU resin and DMFa. A supplier of the carbon black pigment is Ilsam Co Ltd, Myongji Bldg, 135, Seosomoon-Dong, Jung-Gu, Seoul, Korea.

[0053] The formulations may also include processing aids of polysiloxane, such as HD 7. A supplier is Heung it Polychem Ltd.

[0054] A further typical component is a polyol addition, such as DS 600. A supplier being Duksung Co Ltd, Shin-Dong, Yeongtong, Suwon-Si, Kyungi-Do, Korea.

[0055] Those practised in the art will be aware of the materials and suppliers.

[0056] The present invention will now be illustrated by the following examples. Unless otherwise indicated, either in the preceding or following text, all parts are by weight.

Example 1

[0057] A typical carbon black standard pigment 25% solution/dispersion is as follows:

TABLE-US-00001 Parts 1. Carbon black dry powder 25 2. Polyurethane elastomer 25 3. DMFa 50

[0058] This is usually milled to make sure there is a fine dispersion/solution of the pigment particles.

Example 2

[0059] A preferred 30% pigment solution made with just manganese ferrite is as follows:

TABLE-US-00002 Parts 1. Manganese ferrite 10 2. 35% TG 1020 29 3. 100% DS 600 0.001 4. DMFa 60

[0060] This needs to be milled to create a fine particle solution. The manganese ferrite was supplied by Ferro Corporation of Kunlun Town, Zichuan District, Zibo, Shandong Province 255129, China.

Example 3

[0061] A pigment solution/dispersion made with manganese ferrite and a green pigment is as follows:

TABLE-US-00003 Parts 1. 100% Manganese ferrite 10 2. 35% TG 1020 29 3. 100% DS 600 0.001 4. 30% green WS38716A 0.15 5. DMFa 60

[0062] An example of a suitable green pigment dispersion is WS38716A as supplied by West and Senior Ltd, Milltown Street, Radcliffe, Manchester, England. This is a 30% solids dispersion in polyol.

Example 4

[0063] A typical glove dipping formulation that the pigments of Examples 1, 2 and 3 may be used with is as follows:

TABLE-US-00004 Parts (per hundred of polymer) 1. 30% TG1020 Resin 200.000 2. 25% SW-2030 160.000 3. 100% HD7 3.047 4. 100% DS 600 6.100 5. 25% Pigment 46.000 6. 100% DMFa 405.800

[0064] Typically the solvent DMFa is adjusted up or down to maintain a suitable dipping viscosity of possibly 700-1400 and more preferably 900-1100 centipoise. Those practised in the art will be familiar with this practice.

[0065] This dipping formulation was then used to produce gloves according to the process shown in FIG. 1, but with an additional washing and re-drying procedure. The knitted shell for the gloves was a 15 gauge nylon. The washing procedure was a 30 minute fresh water wash at 45 C., followed by a 5 minute rinse at room temperature and a centrifugal spin to remove excess water. The gloves were tumble dried for 90 minutes at 55 C. The gloves were tested (as described below) seven days after their manufacture.

Results

[0066] The use of the carbon black pigment dispersion of Example 1 in the formulation of Example 4 produces suitably commercial black coloured PU dipped gloves. However, there is the major problem of the residual DMFa in the gloves produced.

[0067] When the pigment dispersion of Example 2 is used in the formulation of Example 4, the jet blackness simply is not present in the gloves produced (as demonstrated in the shade depth analysis data below).

[0068] The black shade strength can be increased by using a combination of the pigment dispersion of Example 2 (manganese ferrite alone) and the pigment dispersion of Example 1 (carbon black), at a ratio of 80:20, which will yield gloves having a reasonable jet blackness (as shown in the shade depth analysis data below). However, the gloves have the disadvantage of a relatively high residual DMFa content.

[0069] When the pigment dispersion of Example 3 is used in the formulation of Example 4, however, it is surprisingly found that a considerably increased black jet tone is produced compared with the use of the pigment containing manganese ferrite alone of Example 2 (as shown in the shade depth analysis data below). A very commercially acceptable black shade is achieved.

Shade Depth Analysis

[0070] The tests were carried out on a Datacolor 110 spectrophotometer. The test method involved firstly scanning a standard production black dipped glove palm that had 12% of Example 1 pigment. The scanning was performed five times on each glove sample palm and the average recorded on the software. The first test was on a standard production glove made with carbon black and used as the reference as 100% black colour strength. Then each of the laboratory produced sample pigment combinations were tested against the reference.

[0071] % Colour Strength Against the Standard Production

TABLE-US-00005 1. 11.5% Standard carbon black 95.67% 2. 11.5% Manganese ferrite 68.35% 3. 11.5% Manganese ferrite + 3% carbon black 88.53% 4. 11.5% Manganese ferrite + 0.15% WS38617A 77.80%

[0072] By comparison, a sample of WS38617A alone gave approximately 35% black colour strength. These results clearly demonstrate the synergy between the manganese ferrite and the green based pigment (WS38617A). When they are used in combination a significantly darker black colouration is produced compared to when either of them is used alone.

Residual DMFa Analysis

[0073] The black PU gloves produced using i) the standard carbon black pigment and ii) the combination of manganese ferrite with WS38716A pigment have been analysed for residual DMFa content at Intertek Consumer Goods Gmbh, of Furth, Germany. The method used to extract the DMFa from the gloves is extensive and probably the most accurate measurement of DMFa content of a product. The extraction involves soaking a set amount (1 gram) of the glove material in a set amount (10 ml) of methanol, heating to 70 C. for an hour in an ultrasonic bath, then using GC/MS to establish the residual DMFa in the glove material. The results below of the comparison test are expressed in milligrams per kilogram, or parts per million (ppm). Essentially this is the same extraction method as specified in EN ISO 16778, but yet with a longer dwell time of material in the methanol extraction media of 60 minutes (compared to EN 16778 at 30 minutes).

Using Carbon Black Standard Dispersion (Example 1):

[0074] TEST REPORT FUTXP2014-16857 Residual DMFa is 240 mg/kg (ppm)

Using Manganese Ferrite and WS38716A (Example 3):

[0075] TEST REPORT FUTXP2015-03272 Residual DMFa is 6.9 mg/kg (ppm)

[0076] The results show that the PU coated gloves produced using a pigment that contains both manganese ferrite and a phthalocyanine green based pigment (such as WS38716A) have an acceptably dark black colouration and a very low residual DMFa content in comparison to PU coated gloves produced using a standard carbon black pigment.