WO2012085587A1

WO2012085587A1 - Elastomeric films

Info

Publication number: WO2012085587A1
Application number: PCT/GB2011/052569
Authority: WO
Inventors: Jayasundara Mudiyanselage Chamila BANDARA; Chigullapalli RADESH; Mikhail Kassam
Original assignee: Midas Safety, Inc.; Tridel Limited
Priority date: 2010-12-23
Filing date: 2011-12-22
Publication date: 2012-06-28
Also published as: GB201021903D0

Abstract

Processes for preparation of elastomeric films are disclosed, the processes comprising using a formulation of polychloroprene and nitrite rubber latex 0,1 to 50% by weight and dipping a fabric in the formulation to coat the fabric. Also disclosed are elastomeric formulations comprising an aqueous mixture of polychloroprene and 0.1 to 50% by weight nitrite rubber latex and gloves coated by such formulations. The elastomeric films have advantageous abrasion properties.

Description

EIASTOMERIC FILMS

The present invention relates to processes for producing eiastomeric films, to formulations for use in such processes and to eiastomeric films obtainable by such processes.

Eiastomeric films have uses in many areas of industry. One of the more important uses of eiastomeric films is as coatings on garments for protection and other applications. For example, work gloves are often coated with an eiastomeric layer especially on the palm and fingers for improvement of grip and protection to the wearer of the glove both against liquid chemical ingress and physical injury.

Generally, work gloves with eiastomeric coatings consist of a liner (e.g. a knitted, or cut and sewn finer) which is dipped in a formulation of the polymer coating to be formed on the glove to form a coating on the liner. Such gloves are disclosed in, for example, US-A-4,359,7.83, There have been other prior art discussions of such elastomer coated gloves including in European Patent Application No. 1016141.7 and European Patent Application No. 09172796.6.

Suitable eiastomeric materials for the coating include polyvinyl chloride pla-stisoi, rubber or polyurethane.

One of the more popular coatings is based upon rubber, including natural rubber (i.e. polyisopre.ne), nitrile rubber (formed from nitrite rubber latex which is generally a co-polymer containing precursors of at least acryionitrife (AGN) and butadiene) or other synthetic rubbers for exampie polych!oroprene (a family of synthetic rubbers produced by polymerization of chloroprene, often known by the Du Pont trade mark Neoprene). Polyurethane latex has also been used as an e!astGmeric coating.

Formulations used for dip coating gloves generally comprise an aqueous latex of one of these elastomers also containing suitable additives, for exampie rheoSogical control additives, fillers, processing additives and curing agents. Po!ychloroprene is usually used where good oil and chemical stability and resistance is required and other advantages include that it maintains efasiomeric stability and flexibility over a wide temperature range.

Nitrite rubber tends to have extremely good abrasion resistance but some other aspects of the rubber are not ideal for the use in gloves, including inflexibility, plastic feel and in some circumstances grip. The chemical resistance of nitrite rubber is often very good and depends to a large extent on the amount of nitr!le within the copolymer (i.e. the amount of ACN compared to butadiene).

Rubber latexes which form different rubber coatings have very different properties including both physical and chemical properties, especially pH, They require different processing and differing cure conditions and concentrations. Consequently a choice has to be made as to which of the available rubbers are appropriate for the use to which the eSastomeric film is to be put.

However, there are a number of properties required for gloves, in particular, (for example abrasion resistance) which are difficult to achieve whilst retaining other advantageous properties (e.g. good flexibility) and relatively low cost

For this reason, coatings on gloves have been modified using additives or foam coating (wherein the coating has a relatively open structure which often improves flexibility and grip in both wet and dry conditions).

However, problems still arise because it is often difficult to achieve both good feel for the user, safety, grip and also to provide good abrasion resistance in the same polymer coating.

it is an aim of the present invention to address this problem and to provide for an efasiomeric film which addresses the problems of the prior art.

The present Invention accordingly provides a process for preparation of an e!asfomeric film, the process comprising

a) providing a formulation comprising an aqueous mixture of

polychioroprene, and nitrile rubber latex in an amount in the range 0.1 to 50% by dry weight of the e!astomeric component, b) drying at least a portion of the aqueous mixture, c) curing the dry mixture.

Surprisingly, a mixture of poiych!oroprene and nitrite rubber latex has been found (despite expectations because of the differing pH and curing requirements of the two latexes) to be stable enough for the production of dip coated products,

It is preferred if the amount of nitriie latex in the aqueous mixture is in the range of 0.1 to 35% by dry weight in the elastomeric component, or preferably in the range of 0.1 to 25% by dry weight of the elastomeric component more preferably in the range of 0.1 to 21 % by dry weight of the elastomeric component and most preferably in the range of 0.1 to 15% by weight of the elastomeric component. It has surprisingly been found by the inventors that amounts of nitriie rubber latex in these ranges are stable when combined with polychloroprene latex and it is possible to produce cured elastomeric films with these amounts of nitriie rubber latex combined with a polychloroprene latex.

The total solids content of the formulation will usually be in the range 3 to 60 weight %, preferably 3% to 58%.

Usually, the elastomeric components in the formulation will comprise nitriie rubber latex in the amounts discussed above with the balance being polychloroprene (i.e. two elastomeric components only). However, in certain circumstances it may be advantageous to add a third (or more) elastomeric component to achieve beneficial properties. Such additional elastomeric components may include natural rubber.

The amount of nitrite latex in these ranges provides, surprisingly, significantly increased abrasion resistance of the elastomeric film once produced compared to polychloroprene alone even with very small amounts of nitriie latex.

in addition the tensile strength of the mixed elastomer is significantly better than for polychloroprene alone.

This is advantageous because a formulation comprising both polychforoprene and nitriie rubber latex according to the invention surprisingly provides elastomeric coatings on gloves having excellent feel for the user, good wet grip, chemical and oil resistance but also provides exceptionally improved abrasion resistance even with a very small amount of nifriie rubber latex in the mixture. Furthermore, the formulation may be (and preferably is) silicone free, may use a non hazardous solvent system and usually has a neutral odour (as does the elastomeric film when produced).

The fabric will usually comprise a component of a garment which may be, preferably, a liner for a glove. The liner will preferably be a knitted (e.g. weft knitted) glove liner or a "cut and sewn" liner comprising yarns selected from one or more of nylon, aramid (meta and/or para), cotton, polyester, glass and/or steel fibre (for added cut resistance) or other yarns used to produce garments.

Usually, the fabric, before the drying step, will previously have been contacted with a coagulant solution so that coagulant is present among the fibres of the fabric. Suitable coagulants include salts such as calcium nitrate.

The formulation may be used in order to coat a garment with elastomeric film of relatively high density, Alternatively, if desired, the aqueous mixture may be aerated by vigorous mixing (usually under high sheer) or by addition of blowing agents, in order to produce a formulation comprising a foam for foam coating, or as described in the Applicant's copending European Patent .Application No. 1016141 ,7 and European Patent Application No. 09172796.6.

The process according to the first aspect of the invention makes use of a formulation.

Thus, in a second aspect, the present invention provides an elastomeric latex formulation comprising, an aqueous mixture of potychioroprene and nitrite rubber latex In an amount in the range of 0.1 to 50% by dry weight of the elastomeric component

The nifriie latex in the formulation may further comprise one or more additional precursor components, for exampie acrylic acid and/or methacrylie acid. The formulation may aiso further comprise one or more additives, for example additives to promote curing, dispersing agents, thickeners (to increase viscosity), for example polyvinyl alcohol, polyvinyl acetate, polyacryiate (e.g. sodium polyacryiate or Methocel), Theology control agents, surfacfants (e.g. anionic, neutral or cationic), anti-microbia! agents and/or fillers. The formulation wili also usually comprise sulphur for subsequent vulcanisation.

The formulation may advantageously further comprise grains of polymeric materia!, preferably rubber material. Addition of these grains to the formulation results in the grains being present in the e!astomeric film when produced which can, when used as a glove coating provide even further enhanced grip.

Formulations as described according to the second aspect may, of course, be used in the process according to the first aspect of the invention.

In a third aspect, the present invention provides an eiastomenc film comprising polychloroprene and nitrsle rubber in an amount of 0.1 to 50% by weight of the eiastomenc component.

The process, formulation and films of the present invention find uses in many areas of rubber technology. However, a most important use is likely to be in providing gloves coated with elastomeric film by dip, shower, spray, knife or other types of liquid coating of a glove.

The invention is illustrated by the attached drawings in which:

Figure 1 illustrates the abrasion resistance (average weight loss of multiple samples} for Examples 6 to 10 and 100 nitrsle rubber after 250 cycles as a function of nitrite rubber content,

Figure 2 illustrates the abrasion resistance (average weight loss) of Example 11

Figure 3 illustrates the abrasion resistance (average weight loss) of Example 12

Figure 4 illustrates the abrasion resistance (average weight loss) of Example 13 The invention is further illustrated by the examples in which elastomeric films were produced from mixtures of poiychioroprene and nil rile rubber latexes.

Examples 1 to 5

in Example 1 to 5, unsupported films of elastomer were prepared by casting the formulation on a substrate of porcelain, leaching, drying and curing and subsequently removing the film.

The formulations used were mixture of poiychioroprene latex (Lipren T obtained from Polymer Latex) which is a colloidal dispersion with solids content of 58 weight %, pH value about 12 and nitrite butadiene rubber latex (HVT - LA obtained from Polymer Latex) which is a colloidal dispersion with solids content of 45 weight %, pH value about 8.2 of a carboxyfated ^'butadiene-acrylonitrile co-polymer with medium aoryloniiriie level {approximately 28% acrylonitrile) and medium amounts of methaerylic acid.

The formulation also comprised the following components (as aqueous dispersions) as described in table 1 in addition to the eiastomenc components (elastomeric components total of 100 parts by dry weight.)

Table 1

The parts by dry weight of the polychloroprene arid nitriie rubber in the elastomeric component for each formulation of Example 1 to 5 are as described in Table 2.

Table 2

Unsupported films were prepared from each formulation by casting on a former and coagulating the formulation using a 20% by weight aqueous solution of calcium nitrate followed by leaching for 20 min at 50°C and oven heating for 30 min at 120°C, the dry thickness of each film was 0,1 mm, Finally the films were dry tumbled at 60°C for 30 mins.

Results of tensile strength measurement, elongation, stress and breaking force as well as swelling in toiuene are described in table 4. The mixed elastomer films have excellent tensile properties with even small amounts of nitriie rubber whilst retaining good flexibility and feel.

Examples 6 to 10

Supported eiastomeric films were produced by dip coating 15 gauge knitted nylon glove liners in formulations according to the invention. Formulations with the proportion of elastomeric components as in Table 2 were prepared (except that Synthomer 8322 was used as nitriie component) with the other components as indicated in Table 3 (Table 3 includes reference to the elastomeric components of Example 10 of 10% nitrile 90% polychioroprene).

Table 3

Generally, for supported coated gloves a process for dip coating of a glove liner is as follows using the formulations according to the invention:

1 . Load liner on a hand-shaped former.

2. Dip former In pre-coagulant. Which is preferably 0.5-2% (usually 1.2%) w/w calcium nitrate solution in alcohol.

3. Drain the former and liner for 30 to 60 seconds fingers down.

4. Drain fingers up for 30 to 60 seconds.

5. Dip in the formulation after adjustment to a viscosity of 500 cps (0.5 Pas).

6. Allow to ge!i for a gelling time 120 seconds fingers down, 120 seconds fingers up.

7. Dry at 80°C for 45 mins.

8. Cure at 125°C for 15 mins. The abrasion resistance of the samples was tested using a Martindale abrasion tester generally according to EN388 but using Grit 120 Emery paper (which is much more abrasive and more consistent than the F1 glass paper specified in EN388), The samples were weighed initially, and re-weighed after abrasion, The results of weight loss after 250 cycles are illustrated for Example 6 to 10 in Figure 1 as a function of dry weight % (elastomeric component) nitrile rubber. The abrasion resistance of the samples is dramatically better with only a smail amount of nitrile, approaching the abrasion resistance of 100% nitrile whilst retaining the beneficial properties of polychloroprene. Examples 11, 12 and 13

Examples 11, 12 and 13 were prepared by dipping the compound onto a Nylon liner in the same way as Examples 8 to 10 but with % by dry weight of nitrile rubber of 10%, 15% and 20% with the balance of the elastomeric component being poiychloroprene. The nitrite rubber component NBR was obtained from Polymer Latex (NVT-LA), The polychloroprene component was CR Lipren T also from Polymer Latex,

Supported glove samples were tested for abrasion resistance as discussed above, The results after 50 to 250 cycles are illustrated in Figure 2, 3 and 4 for 10%, 15% and 20% nitriie respectively. Again the presence of nitrile produces dramatic improvement In abrasion resistance. In the legends of Figures 2, 3 and 4, "NUT" refers to the nitrile rubber component

Table 4

Claims

1. A process for preparation of an eiastomeric film, the process comprising

a) providing an formulation comprising an aqueous mixture of polychloroprene, and nitrile rubber iatex in an amount in the range 0:1 to 50% by dry weight of the eiastomeric component, b) dipping a fabric in the formulation to at least partially coat the fabric with a film,

c) optionally drying the film,

c) curing the film.

2. A process as claimed in claim 1, wherein the amount of nitrile rubber latex in the formulation is in the range 0.1 to 25% by weight of the eiastomeric component, preferably wherein the amount of nitrile rubber latex in the formulation is in the range 0,1 to 21% by weight of the eiastomeric component.

3. A process as claimed in either claim 1 or claim 2, wherein the fabric comprises a liner for a garment, preferably wherein the liner is a glove finer.

4. A process as claimed in any one of the preceding claims, wherein the total solids content of the formulation is in the range 3 to 58 weight %,

5. A process as claimed in any one of the preceding claims, wherein the fabric, before the dipping step, has previously been contacted with a coagulant solution.

6. A process as claimed in any one of the preceding claims, wherein at least part of the formulation comprises a foam.

7. An eiastomeric latex formuiation comprising, an aqueous mixture of polychloroprene and nitrite rubber latex in an amount in the range of 0.1 to 50% by dry weight of the eiastomeric component

8. A formulation as claimed in claim 7, wherein the nitrite rubber latex further comprises one or more additional precursor components.

9. A formulation as claimed in claim 8, wherein an additional precursor component comprises methacrylic acid,

10. A formuiation as claimed in any one of claims 7 to 9, further comprising one or more additives, preferably additives to promote curing, dispersing agents, thickeners, rheology control agents, surfactants, anti microbial agents and/or fillers.

11. A formulation as claimed in any one of the preceding claims 7 to 10 further comprising grains of cured polymeric material, preferably cured rubber material.

12. An eiastomeric film comprising polychloroprene and nitrife rubber in an amount of 0.1 to 50% by weight of the eiastomeric component

13. A glove coated with an eiastomeric film as claimed in claim 12.

14. A process for producing a coated glove, the process comprising

a) providing an formulation comprising an aqueous mixture of polychloroprene, and nitrite rubber iatex in an amount in the range 0.1 to 50% by dry weight of the eiastomeric component, b) providing a fabric glove finer

c) optionally applying a coagulant solution to the liner,

d) applying a portion of the formulation to at least a part of the gfove liner, e) gelling the formulation on the liner to provide a poiymer coating, f) optionally drying the liner, and

g) curing the poiymer coating.