GB2292384A - Coating composition, method of using it and article coated with same - Google Patents

Abstract

An aqueous composition comprises a natural rubber modified with a graft-polymerised methylmethacrylate polymer such as a graft-polymerised methylmethacrylate an acrylic polymer, such as a poly(acrylonitrile/ butadiene/carboxylate) latex, an acrylonitrile synthetic rubber and optionally other ingredients. The other ingredients may be a quaternary ammonium surfactant and a polysiloxane. The composition is applied to an article such as of natural and/or synthetic rubber to effect coating. The process is especially suited to coating of gloves intended for industrial, medical or domestic applications. The gloves may be coated on one surface and chlorinated on the other.

Description

COATING COMPOSITION, METHOD OF USING IT AND ARTICLE COATED WITH SAME The present invention relates to a coating composition, to a method of applying the composition to an article and to an article coated with said composition. The composition is especially, although not exclusively, suited to application to a glove e.g. made of natural or synthetic rubber and for use in such applications as medical, food, industrial or domestic environments.

The past ten years or more have seen an increased demand for hand protection in various industries, such as in the medical profession, chemical industry, engineering, as well as domestic applications. For example, current legislation requires employers to provide hand protection to their staff who may come into contact with noxious chemicals as part of their work. Practitioners in the medical and dental professions require a skin barrier to prevent crossinfection between their patients and themselves, hence the vast increase in the demand for disposable natural-rubber medical gloves.

As the demand for these gloves has increased, so their service requirements have become stricter. Thus all articles for sale in the USA for medical applications must conform to the US-FDA standards. Different regulations apply in other countries. In addition, there are further demands that may be either necessary or desirable, depending on the intended use, and these may be summarised as follows: - for medical applications, many users require a pale (white/off-white) colour; - the gloves must be compatible with the skin, i.e.

non-allergenic; - the gloves must have the necessary physical properties, such as tensile strength, tear strength, elongation-at-break, modulus, and be free of faults such as holes, embedded dirt, stains, irregular thickness, etc; - the gloves should be free of particulate matter, so that in use no particles of dusting or lubricant powder are left behind on the surface that has been handled; this is especially important for electronic assembly use but is also highly desirable in medical products; - the gloves should be made of such a material that will provide chemical resistance to the environment that is being contacted, petroleum oil, grease, fatty deposits, etc and this is especially important in industrial gloves; the products should have adequate shelf-life ageing characteristics; - the gloves should have a zero or low free protein level when prepared from natural rubber latex or blends containing it.

Two aspects of the above require further elaboration: skin-compatibility and chemical resistance. Gloves for the medical industry are dominated by those based on natural rubber polymer (cis 1. 4 polyisoprene), and are generally satisfactory.

However, they are known to be deficient in terms of their chemical resistance and in some cases show unacceptable reactions to sensitised skins, due to antigens derived from certain proteins naturally present in natural rubber latex. Concerning skin-compatibility, there is obvious interest in making gloves from polymers which either do not contain protein or having minimum extractable levels and are not therefore able to give allergic reactions as in the case of some natural rubber gloves.

With regard to the latter aspect, it is known that gloves based on natural rubber have inadequate resistance to non-polar solvents such as hexane, decane, petroleum oil, kerosene, toluene, etc., in which contact with the solvent results in rapid and marked swelling of the rubber film, a loss of physical properties, and often catastrophic break-through. It is also reported that long-term surgical operations may result in fat absorption by the glove film with consequent weakening.

These aspects are common knowledge and where they are critical, for example in chemical handling, it is necessary to use gloves that are based on polymers such as poly(acrylonitrile-butadiene), or poly(chloroprene).

Whilst these polymers have different stress/strain characteristics compared with natural rubber, e. g.

poly(acrylonitrile-butadiene) gloves are more stiffer or have an inherent higher extension modulus their molecular composition ensures superior resistance to solvents as described above compared with those made from natural rubber and thus are preferred. In the past these gloves were used primarily for industrial applications and were thick (e.g. 0. 5-2mm) and sometimes made with a cotton liner. Currently, thinner ones without fabric liners are being used for some medical and industrial applications.

The invention in its various embodiments or examples fulfils one or more of the aforementioned requirements.

It is aimed at providing superior type of coating composition and glove coated with same, in particular a rubber glove. The glove itself may be made of synthetic or natural rubber, or a blend of synthetic and natural rubbers, although for reasons already mentioned, synthetic rubber will sometimes be preferred. Gloves according to the invention are superior with regard to its processing and/or surface finish.

Gloves according to the present invention may be fabricated for any particular use or application, for example any as hereinbefore described. However, one preferred application is a medical glove. The term "medical glove" is used herein to define all types of medical hand protection normally known in the industry as "examination gloves", "procedure gloves", "surgeons' gloves", "post-mortem gloves", "dental care gloves" and so on. Preferably, these gloves are made totally from natural rubber or blends of polymers in which natural rubber is the predominant ( > 50%) polymer. As used herein, the term "rubber" means any natural or synthetic rubber or natural rubber and polymer blend unless specifically stated to the contrary.

The special needs of these gloves need to be considered further. A good white colour is easy to produce but will be lost to a greater or lesser extent on chlorination and ageing (q. v. ).

Compatibility with human skin is generally a pre-requisite especially in the case where gloves are worn for long periods during extended medical procedures, and this property is sometimes termed l'hypoallergenicity''. This property is conventionally provided by the selection of non-irritant chemicals in the formulation and ensuring that during fabrication, adequate washing is given to remove unwanted chemicals resulting from the processing. However, it has been found that for some medical personnel even gloves described in this way may on repeated use give rise to irritation or even dermatitis. To overcome the latter problem, it is desirable to provide a barrier that separates the rubber from the skin. Such a barrier would need to be innocuous and not affect the skin.

Shelf-life ageing is also an important factor. All rubber products degrade on ageing but this process is very slow if the product is properly formulated, processed and stored under the correct conditions.

However, in the context of the present invention a new type of glove which will age with greater retention of properties compared with a normal product would be preferred.

The conventional method of manufacturing medical gloves is to treat the inherently sticky rubber surface with a bio-compatible powder such as starch. Without this material, the gloves could not be easily donned or removed, and finger manipulation would be severely restricted. However, the presence of powder on the surface of the glove means that in use, some of the powder is likely to be left behind in or on the patient.

There are two alternatives currently in use. The first entails treatment of either or both surfaces of the glove with an aqueous dilute solution of chlorine.

This modifies the rubber surface chemically and provides a low friction surface for easy processing and use.

Whilst this is a simple process, this treatment is deleterious to the physical properties of the glove. It darkens the film colour and impairs the shelf-life ageing characteristic, especially after sterilisation.

The second alternative involves processing the glove in such a way that a different polymeric film is deposited on the rubber surface to give the donning, removal and manipulative qualities that are required.

Examples of this process are described in the following patent specifications, namely US-A-4 499 154, US-A-5 132 129, EP-A-O 413 467, EP-A-O 198 514 and EP-A-O 455 323.

The polymer used for such an applied film must be easy to apply and have the suitable properties, i. e. it should be flexible, adhere to the rubber surface, allow satisfactory manipulation and be non-irritant.

Recent studies of allergenicity have shown that medical rubber gloves with relatively high (500 ppm or more) of free or extractable protein can give rise to anaphylactic shock in sensitised patients. Whilst these represent a very small proportion of people, it is plainly advisable to make gloves with as low a free protein level as possible. It is one object of the present invention to provide a medical glove wherein the free protein level, as measured using a standard test procedure, is as low as possible when based on natural rubber, or zero, when applied to a synthetic glove.

The basic manufacturing technique for making gloves from polymer latex (either natural or synthetic) is well known, e.g. as described in US-A-5 014 362 or US-A-5 084 514.

The gloves are made by the batch or chain process in which formers are dipped into a coagulant solution, usually a calcium salt, dried1 then into the latex compound, followed by drying, beading, washing or leaching, vulcanisation and stripping. After this, some finishing operations, inspection, and packing take place. Gloves made in this way have a natural surface tack, and this impairs donning, doffing and general manipulation. This surface tack is normally overcome by the use of a lubricant powder such as talc or, in the case of medical gloves, bio-absorbable cornstarch which is applied during the production on-line or as an off-line process. In some cases, the gloves are treated with a dilute aqueous solution~of chlorine, which reacts with the rubber surface to improve its smoothness.

However, this process is relatively expensive, elaborate to operate, and may give rise to a discoloured product with a reduced shelf-life or inferior ageing characteristics.

Regarding medical gloves in particular, there are two commonly used methods of manufacture. Both methods rely on dipping suitably shaped formers into a coagulant, then into a rubber latex compound, followed by steps of drying, washing (leaching), and drying/vulcanisation and finally stripping. Further off-line processes may then be effected, for example extra drying, powdering, chlorination, etc. The two methods differ only in the way in which the dipping is performed. One method entails batch dipping, in which a batch of formers is dipped in one operation before passing onto the next stage. The other utilises chain line dipping, in which the formers attached to a continuous chain are dipped consecutively in the various coagulant and latex baths. Gloves made in accordance with the present invention can be formed according to either of these known methods.It can be carried out either on-line or off-line.

The inner or outer surface or both surfaces of the glove may be with a coating composition according to the system which gives unique properties in terms of good donning and doffing, good manipulation and finger sensitivity, a surface with a non-irritant polymeric layer bonded to the rubber, very low or zero available protein, excellent pale colour, and better ageing shelf-life characteristics than conventional products.

If required, this novel process can be combined with an existing finishing process, such as chlorination, so that one side of the glove is treated with the polymeric film and the other side is chlorinated. Of course, it is also possible to have one side powdered and the other side polymer treated.

The polymeric system that is used in this invention is a blend of water-based polymers which would not be expected to give the required properties, but surprisingly has been found after extensive development work, to fulfil this aim.

Thus, a first aspect of the present invention provides an aqueous coating composition comprising a natural rubber modified with a graft-polymerised methacrylate type polymer, an acrylic polymer, an acrylonitrile synthetic rubber and optionally, minor ingredients.

Preferably, the graft-polymerised methylmethacrylate polymer used to modify the natural rubber is a graft-polymerised polymethylmethacrylate or a graft-polymerised polyethylmethacrylate.

Preferably, also the amount of methacrylate-type graft polymer modified natural rubber is from 0. 1$ to 10%, more preferably from 0. 5% to 4. 0%, and especially from 1.0% to 2. 0%. The level of graft polymer is preferably from 35% to 60%, e.g. nominally at about 40% though variations are possible.

Preferably, the amount of the acrylic polymer is from 0. 1% to 10%, more preferably from 0. 5% to 8. 0%, (e.g. 0.5% to 6.0%) and especially from 1.0% to 4.0%.

This may be acrylic polymer latex of the type commonly used in the manufacture of emulsion paints. A wide range of such acrylic polymer emulsions are suitable, based on monomers such as vinyl acetate, methyl acrylate, or monomer blends of acrylic esters with styrene, ethylene, methacrylate ester, vinyl chloride, and the like.

Preferably, the amount of the acrylonitrile synthetic rubber is from 0. 1$ to 5%, more preferably from 0. 5% to 3. 0%, and especially from 1.0% to 2.0%.

The acrylonitrile polymer is a polymer which is formed of at least acrylonitrile monomer units, but preferably also incorporates other monomer species such as butadiene and/or carboxylic monomers. A particularly preferred acrylonitrile polymer is prepared from a terpolymer of acrylonitrile, butadiene and a carboxylic monomer which contains, for example, from 30% to 40% acrylonitrile e.g. to resemble the base glove polymer.

Preferably, the amount of the polysiloxane is from 0. 05% to 10%, more preferably from 0. 1% to 5.0%, and especially from 1.0% to 3.0%. One preferred polysiloxane is polydimethyl siloxane of a molecular weight in the range 12000-15000, incorporated as an emulsion.

Preferably, the amount of the quaternary ammonium surfactant is from 0. 05% to 5%, more preferably from 0. 1% to 2. 0%, and especially from 0. 5% to 1. 5%.

Preferred quaternary ammonium surfactants include cetyltrimethylammonium bromide, or the chloride salt or a mixture thereof.

Although not essential to this invention, sometimes it has been found to give superior handling if from 0. 1% to 3. 0%, preferably from 0. 5% to 2. 0%, of a lubricant such as an aqueous dispersion of a stearate, such as zinc stearate or calcium stearate is added to the polymeric system given above. It may be queried that this represents a powder addition when the final gloves are regarded as "powderless"; however, it is believed that excess powder is removed from the glove surface during the drying/tumbling process and what is left dissolves in the rubber during the heat of drying so that the rubber surface is powder-free as measured using a standard method.

The percentages quoted above all represent the total solids content of the polymeric systems as normally determined. Unless specifically indicated to the contrary, all percentages recited herein are percentages by weight.

Gloves made of natural and/or synthetic rubber may be coated by several different processes. These will now be described in outline.

A first process is applicable to natural rubber gloves and to rubber gloves made from a commercially available polychlorprene latex or a poly(acrylonitrile/ butadiene/carboxylate latex). The gloves are made in the conventional way using a batch-line process fitted with wet stripping (high pressure water jets). The gloves from the wet stripping are charged into a glove tumbler resembling an industrial washing machine commonly known in the art and tumbled to remove excess water for ten to twenty, e.g. ten to fifteen minutes.

The excess water is drained, and the aqueous polymeric system added. The gloves are then tumbled again for ten to twenty minutes, and the excess mixture then drained.

The gloves are then transferred to a tumble dryer and dried thirty to sixty minutes at 60'C to 80'C in hot air. The gloves are then ready for checking and packing.

A second process is suitable for both natural rubber gloves and gloves made of poly(acrylonitrile/butadiene/ carboxylate) or polychloroprene latex. They are prepared by the normal chain line process. To facilitate stripping, it is normal to add some powder in this process both in the coagulant and in the post-oven slurry bath. Bio-absorbable starch is the normal agent. However, in this process the powder is calcium carbonate. The special treatment is then as follows.

The gloves are charged into the tumbler and 0. 5% acetic acid is added and tumbling commenced until all the powder is neutralised and washed off, about ten minutes is normally sufficient. The acid is drained and the polymeric system is added; the same procedure is followed as in the first example given above. In both these two cases, the polymeric system is the same on both sides of the gloves.

It will be noted that in the above three processes, the polymeric system is the same on both sides of the glove. In the case of special requirements in the feel, donning, etc., this invention allows different polymeric systems to be coated on each side of the glove. This is illustrated in a third process which also shows how an extra off-line process can be oviated, if desired. This is also applicable to both natural and synthetic rubber gloves. In other words, it optionally obviates the need for an extra off-line step and is suitable for batch and chain-line operation. Here, the normal aqueous coagulant mixture with a calcium salt such as nitrate is augmented with the polymeric system.In this case it is necessary to add 2.0% to 4.0% of a nonionic surfactant to the polymeric system to maintain colloidal stability in the coagulant and best to use the lowest levels of a polyorganosiloxane such as polydimethyl siloxane emulsion or to omit it entirely. This modification of the coagulant will require some minor adjustment of the dipping and oven parameters as is common in the art.

The process may be further modified so that the on-line powder slurry bath is replaced by the aqueous polymeric system so that on stripping the products contain a polymeric coating on both sides without an extra off-line process.

In this process, the gloves are dipped in coagulant and latex in the normal way and after the main oven, dipped in the polymeric system, dried, and stripped dry. Thus, by modifying the coagulant bath and the slurry, it is possible to alter the coating systems so that each side has a different finish.

As described above, it is possible to make hybrid coating systems, such that one side is polymer finished and the other side is chlorinaèd. This is illustrated in a fourth process suitable for natural rubber gloves or gloves made from a poly(acrylonitrile/butadiene/ carboxylate) latex. Gloves are made on a batch or chain-line are dipped in the aqueous polymeric mixture with a conventional coagulant containing some calcium carbonate dusting powder, but using an aqueous polymeric bath to replace the slurry bath, dried, and stripped.

They are then chlorinated by the usual method and everted. The chlorinated layer is then inside the glove and the polymer surface is on the outside. Such a system does not possess all the advantages of the two-sided polymeric coating in terms of excellent colour, and the best unaged and aged tensile properties.

A fifth process is also suitable for gloves made from natural and/or synthetic latex. It is also of the hybrid treatment and resembles the fourth process. The chain line is modified to provide on-line chlorination after the main oven and this is combined with the use of a polymeric coagulant as given in the third process.

This method obviates the need for off-line processing, thus giving products ready for inspection and packing.

The present invention will now be explained in more detail by way of the following description of non-limiting Examples.

Example 1 Natural rubber gloves (40kg weight) from a batch line were taken from the wet stripping stage were placed in a tumbler of capacity 800 litres, rotated for ten minutes to remove excess water, and the following polymeric mixture added.

Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer, 50. 0% total solids content ................ 32. 0 kg Acrylic polymer latex, 48% total solids content . 16. 7 kg Polybutadiene acrylonitrile carboxylated latex, 52% total solids content . 15. 4 kg Polydimethyl siloxane emulsion, total solids content 36% . ..... . ........ ........... 66.7 kg Cetyl trimethylammonium bromide, total solids content 10% . . ............... 8.0 kg Water, softened or deionised .. 661. 2 kg All parts are by weight of solids. The mixture was prepared prior to addition to the glove tumbler.

The gloves were tumbled with the mixture for twenty minutes and the polymeric system drained out. It may be used again for further treatment of gloves with slight topping up. The gloves were tumbled for a further ten minutes to remove excess, and dried in a rotatory drier for 30-60 minutes at 60'C. The weight increase per glove was between 0. 5% and 3.0% by weight. The properties of the gloves made in this way compared with those finished conventionally from the same type of latex are shown in Tables 1 and 2. The advantages of the new coating system are clearly seen. The polymer-coated gloves were easy to don and doff, and gave excellent grip and sensitivity when in use.

Polymer-coated gloves were tested for skin irritation and sensitivity and found satisfactory, using the method in B. S. 5736 parts 6, 8.

Example 2 Gloves (40kg) prepared from poly(acrylonitrile/ butadiene/carboxylate) latex using a batch line were taken from the wet stripping stage and placed in a 800 litre capacity tumbler, rotated for ten minutes to remove excess water, and the following polymeric mixture added: Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer, 50% total solids content . ........................................ 32.0kg Acrylic polymer latex, 48% total solids content . 16. 7kg Poly(acrylonitrile/butadiene/carboxylate) latex, 52% total solids content ......................... 14. 4kg Polydimethylsiloxane emulsion, total solids content 36% . . . ... . . 66. 7kg Cetyltrimethylammonium bromide, total solids content 10% . . . 8. Okg Deionised water . . 661. 2kg All parts are by weight of solids.The above mixture was blended prior to addition to the tumbler.

The gloves are tumbled with the mixture for twenty minutes and the polymeric system drained off. this can be used for subsequent treatments with slight topping up. The gloves are further tumbled for ten minutes to remove excess polymer, and transferred to a rotatory drier for drying 30-60 minutes at 70-80'. The weight increase per glove was between 0. 5% and 3. 0% of the original weight. the physical properties are given in Table 3. The polymer coated gloves were easy to don and doff and gave excellent sensitivity and grip when in use. The polymeric layer was bonded to the rubber surface and could not be removed with normal glove operations. The gloves coated with the polymeric system were tested for skin irritation and sensitivity according to B.S. 5736 Parts 6 and 8, and found satisfactory.Test results of physical properties of gloves according to this example are given in Table 3 hereinbelow.

Example 3 This Example has two variants, one using natural rubber gloves and the other using gloves prepared from poly(acrylonitrile/butadiene/carboxylate) latex. In each case, gloves (40kg weight) from a batch line were taken from the wet stripping stage and were placed in a tumbler of capacity 800 litres; rotated for ten minutes to remove excess water, and the following polymeric mixture added: Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer, 50. 0% total solids content . . 16.0 kg Acrylic polymer latex, 48% total solids content . 33. 3 kg Polybutadiene acrylonitrile carboxylated latex, 52% total solids content ........................ 15.4 kg Polydimethyl siloxane emulsion, total solids content 36% ........... ... ... ..... 44.4 kg Cetyl trimethylammonium bromide, total solids content 10% ..... ..... . 8. 0 kg Water, softened or deionised .. . 682. 9 kg All parts are by weight of solids. The mixture was prepared prior to addition to the glove tumbler.

The gloves were tumbled with the mixture for twenty minutes and the polymeric system drained out. It may be used again for further treatment of gloves with slight topping up. The gloves were tumbled for a further ten minutes to remove excess, and dried in a rotatory drier for 30-60 minutes at 60'C. The weight increase per glove was between 0. 5% and 3. 0% by weight. The properties of these natural rubber gloves made in this way were compared with those finished conventionally from the same type of latex are shown in Tables 1 and 2. The physical properties of the synthetic latex gloves were similar to those described in Example 2.

The advantages of the new coating system are clearly seen. The polymer-coated gloves were easy to don and doff, and gave excellent grip and sensitivity when in use.

Example 4 Natural rubber gloves (40kg weight) from a batch line were taken from the wet stripping stage were placed in a tumbler of capacity 800 litres, rotated for ten minutes to remove excess water, and the following polymeric mixture added: Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer, 50. 0% solids content .............................. 32.0 kg Acrylic polymer latex, 48% total solids content . 66. 7 kg Polybutadiene acrylonitrile carboxylated latex, 52% total solids content ........................ 7. 7 kg Polydimethyl siloxane emulsion, total solids content 36% ..................................... 44. 4 kg Cetyl trimethylammonium bromide, total solids content 10% ..................................... 80. 0 kg Aqueous dispersion of zinc stearate, total solids content 35% .............................. 45. 7 kg water, softened or deionised .... ............ 523.5 kg All parts are by weight of solids. The mixture was prepared prior to addition to the glove tumbler.

The gloves were tumbled with the mixture for twenty minutes and the polymeric system drained out; it may be used again for further treatment of gloves with slight topping up. The gloves were tumbled for a further ten minutes to remove excess, and dried in a rotatory drier for 30-60 minutes at 60'C. The weight increase per glove was between 0. 5% and 3. 0% by weight. The properties of the gloves made in this way were compared with those finished conventionally from the same type of latex are shown in Tables 1 and 2. The advantages of the new coating system are clearly seen. The polymer-coated gloves were easy to don and doff, and gave excellent grip and sensitivity when in use.

Example 5 This Example also has two variants, respectively using natural rubber and synthetic rubber gloves. In each case, the gloves were made on a chain line using the conventional method with 5% calcium carbonate in the coagulant and in the slurry after the main oven of 9% calcium carbonate to coat the outer surface of the gloves before stripping. The dry stripped gloves (40kg) were charged into the wet tumbler and 400 litres of 0. 5% acetic acid added. The gloves were agitated for 10 minutes. The acid was drained, and the gloves washed with water for 5 minutes.The water was drained and the following mixture added: Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer, 50. 0% total solids content ............................ 24. 0 kg Acrylic polymer latex, 48% solids content ....... 58. 3 kg Polybutadiene acrylonitrile carboxylated latex, 52% total solids content ........................ 30. 8 kg Polydimethyl siloxane emulsion, total solids content 36% ...................................... 44. 4 kg Cetyl trimethylammonium bromide, total solids content 10% ...................................... 40.0 kg Aqueous dispersion of zinc stearate, total solids content 35% .............................. 2. 3 kg Water, softened or deionised ................... 600. 2 kg The gloves were tumbled in the above polymeric mixture for 15 minutes, and then drained for 10 minutes, and dried for 60 minutes at 60'C.

The natural rubber gloves have these characteristics: Appearance . . good Colour . . white Polymer coating .. . ..... .... adhered Feel, flexibility . . excellent Donnability . good Doffability ....... ........ .......... good Grip ......... ......... excellent Physical properties ........... ..... excellent (as in Tables 1 and 2) Ageing excellent Ageing, sterilised excellent The synthetic rubber gloves had similar properties to those of Example 2.

Example 6 This is a method of preparing natural rubber gloves with a polymeric layer on both sides using a batch or chain line process in which, as described in Example 4 above, the coagulant is modified to contain the polymer which will form the inner layer of the glove when dipped but the outer layer in use, since eversion usually occurs on stripping. The following coagulant was prepared for an 800 litre coagulant tank: - Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer, 50. 0% total solids content ..................................... 32. 0 kg Acrylic polymer latex, 48% total solids content . 66. 7 kg Polybutadiene acrylonitrile carboxylated latex, 52% total solids content . ................. 15.4 kg Nonionic surfactant, such as polyoxyethylene condensate of a long chain alcohol of 12 carbon atoms or more, with at least 12 molecules of ethylene oxide polymerised, total solids content 10% . . . 16.8 kg Cetyl trimethylammonium bromide, total solids content 10% . . . 8. 0 kg Water, softened or deionised . . 261. 1 kg The above mixture was prepared and then blended with a mixture of: Calcium nitrate hydrate . ..... 80.0 kg Water ......................... .... .. 320.0 kg The normal batch or chain line dipping process was followed except that for ease of stripping at the end of the process, it was found that the last stage in the former cleaning process should be a dip into a 1.0% potassium oleate, prior to drying before coagulant dipping.After the main oven the formers were dipped into a blend of: Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer 50. 0% total solids content ............................ 32. 0 kg Acrylic polymer latex, 48% total solids content . 66. 7 kg Polybutadiene acrylonitrile carboxylated latex, 52% total solids content ........................ 15. 4 kg Polydimethyl siloxane emulsion, total solids content 36% ...................................... 44. 4 kg Cetyl trimethylammonium bromide, total solids content 10% .......................... .......... 80.0 kg Aqueous dispersion of zinc stearate, total solids content 35% .............................. 2. 3 kg Water, softened or deionised ................... 559. 2 kg The gloves were then dried, stripped, inspected, and packed. The properties of these gloves resemble those given above.

Example 7 This describes a method of-preparing synthetic gloves with a polymeric layer on both sides using a batch or chain line process without additional off-line processing in which the inner layer is formed, as described above, by modifying the coagulant to coat the former surface and using a polymeric bath on line to coat the air surface. The following coagulant was prepared for a 800 litre coagulant tank: - Polymethylmethacrylate graft polymer natural rubber latex with 40% of graft polymer, 50% total solids content . . 32. Okg Acrylic polymer latex, 48% total solids content . . 66. 7kg Poly(acrylonitrile/butadiene/carboxylate) latex, 52% total solids content ............... 15. 4kg Nonionic surfactant, such as a polyethylene oxide condensate of a long-chain alcohol of 12 carbon atoms or more, with at least 12 molecules, preferably 30 molecules, of condensed ethylene oxide, total solids content 10% ........... .......................... 16.8 kg Cetyltrimethylammonium bromide, total solids content 10% ...................................... 8. Okg Deionised water ................................. 181.1 kg The above mixture is prepared in the order stated, and then blended with a mixture of: Calcium Nitrate hydrate ........ . 120. Okg Deionised water . .... ... ..... ..... ... 360.0 kg The normal production process is followed but for ease of stripping at the end of the process it was found beneficial to dip the clean formers prior to drying in a 2% aqueous potassium oleate solution.After the main oven, the gloves on the formers were dipped into the same polymeric slurry used for dipping the gloves of Example 6. the gloves had similar properties to those of Example 2.

The natural rubber gloves of Examples 1, 3 and 4 were further tested in comparison with conventional gloves as described in Tables 1 and 2 hereinbelow.

Corresponding results for gloves of synthetic latex are shown in Table 3.

TABLE 1 properties of Conventional and Polymer Coated Natural Rubber Gloves Glove Unaged Aged, 14 days/70 Aged, 22h/100 Type T. S. E. B. M 300% T. S E. B M 300% T. S. E. B. M 300% (MPa) (%) (MPa) (MPa) (%) (MPa) (MPa) (%) (MPa) P, 32 1 865 1 52 31 9 1011 1 31 34.2 956 1.28 non-s (99%) (107%) P, 33.2 882 1.61 26.3 969 1.11 24.4 987 1.14 s (79%) (74%) C, 31.0 855 1.69 6.2 857 0.86 8.4 957 0.88 non-s (20%) (27%) C, 30.6 873 1.71 0 0 0 4.2 831 0.76 s (14%) P1, 33.2 888 1.63 29.8 917 1 68 29.0 915 1.68 non-s (90%) (87%) P1, 32.8 885 1.58 29.5 866 1.56 30.8 963 1.44 s (90%) (94%) P2, 33.7 885 @ 1 58 31 8 942 1 50 33.1 905 1.62 non-s (94%) (98%) P2, 30.4 935 1.32 28.1 785 1.66 28.6 951 1.46 s (92%) (94%) P3, 34.7 883 1 62 31 5 988 1 56 33.2 862 1.60 non-s (91%) (96%) P3, 30.3 947 1.31 30.0 833 1 59 31.5 931 1.53 s (99%) (104%) Key to abbreviations: T.S. = tensile strength; E. B. = Elongation-at-break, M 300% = 300% modulus Tensile testing carried out according to B. S. 903 part A2; P. = powdered; non-s = non-sterilised; s = radiation sterilised; C. = chlorinated; P1 = polymer coated as in Example 1; P2 = polymer coated as in Example 2; P3 = polymer coated as in @Example 3.

TABLE 2 Powder and Extractable Protein Contents Glove Type Powder Extractable Level, mg/glove protein, ppm Powdered 218. 0 166 Chlorinated 2. 8 20 Example 1 0. 5 17 Example 2 0. 2 6 Example 3 3. 1 5 Powder levels were determined using the French standard method NF S90-000.

Protein levels were determined using the Lowry method modified by the Rubber Research Institute of Malaysia; see J. Nat. Rubb. Res. 7 (3), 206-218 (1992).

Table 3 Physical properties and performance of gloves with different finishes made by dipping from poly(acrylonitrile/butadiene/carboxylate) latex Test Conventional powdered Polymer coated Polymer/Chlorinated Unaged Tensile Strength, Mpa 27.4 30.6 28.5 Elongation-at-break % 660 643 620 Modulus, 300%, Mpa 3.13 4.20 4.04 Aged 22h/100 Tensile Strength, Mpa 27.4 27.9 27.9 Elongation-at-break, % 604 633 630 Modulus, 300%, Mpa 4.43 3.40 3.77 Powder level, ppm 107.1 3.0 2.2 Grip poor-moderate excellent excellent Donning ease good excellent excellent Doffing ease good excellent excellent Coating adherence - excellent excellent Feel powdery powder-free powder-free Sensitivity moderate excellent excellent Powder residue after use bad none none Tensile test procedure, according to ISO 37-1977 (E).

Powder level, US-FDA-ASTM test method.

In the light of this disclosure, modifications of the described Examples, as well as other Examples, all within the scope of the present invention as defined by the appended claims, will now become apparent to persons skilled in the art.

Claims (36)

CLAIMS:

1. An aqueous coating composition comprising a natural rubber modified with a graft-polymerised methacrylate-type polymer, an acrylic polymer, an acrylonitrile synthetic rubber and optionally, minor ingredients.

2. A composition according to claim 1, also comprising optional minor ingredients in the form of a polysiloxane and a quaternary ammonium surfactant.

3. A composition according to claim 2, wherein the polysiloxane is polydimethyl siloxane with an average molecular weight of from 12,000 to 20,000.

4. A composition according to claim 2 or claim 3, wherein the amount of the polysiloxane is from 0. 05% to 10% by weight of the total solids content.

5. A composition according to any of claims 2 to 4, wherein the quaternary ammonium surfactant is selected from cetyltrimethylammonium bromide and cetyltrimethylammonium chloride and mixtures thereof.

6. A composition according to claim 2 or claim 5, wherein the amount of the quaternary ammonium surfactant is from 0. 05% to 5% by weight of the total solids content.

7. A composition according to any preceding claim, wherein the amount of the natural rubber modified with graft-polymerised methacrylate polymer is from 0. 1% to 10% by weight of the total solids content.

8. A composition according to any preceding claim, wherein the graft-polymerised methacrylate-type polymer is a graft polymerised methyl methacryl ate.

9. A composition according to any preceding claim, wherein the amount of graft-polymer in the natural rubber modified with graft-polymerised methyl methacryl ate polymer is from 35% to 45% by weight.

10. A composition according to any preceding claim, wherein the amount of the acrylic polymer is from 0. 1% to 10% by weight of the total solids content.

11. A composition according to any preceding claim, wherein the acrylic polymer is an acrylic polymer synthetic latex.

12. A composition according to any preceding claim, wherein the amount of the acrylonitrile synthetic rubber is from 0. 1% to 5% by weight of the total solids content.

13. A composition according to any preceding claim, wherein the acrylonitrile synthetic rubber is a polybutadiene acrylonitrile carboxylated polymer.

14. A composition according to claim 13, wherein the poly(acrylonitrile/butadiene/carboxylate) polymer is in its latex form.

15. A composition according to=any preceding claim, further containing a lubricant.

16. A composition according to claim 14, wherein the amount of the lubricant is from 0. 1% to 3% by weight of the total solids content.

17. A composition according to claim 15 or claim 16, wherein the lubricant is zinc stearate.

18. An aqueous coating composition substantially as hereinbefore described with reference to any of the examples.

19. A method of coating an article, the method comprising applying to said article, an aqueous coating composition according to any of claims 1 to 18.

20. A method according to claim 18, the method comprising treating the wet-stripped article after stripping with said composition and then drying.

21. A method according to claim 19 or claim 20, wherein calcium carbonate powder is used for effecting dry-stripping.

22. A method according to any of claims 19 to 21, wherein said composition is applied by dipping the article after heating of said article.

23. A method according to any of claims 19 to 22, wherein the article is made from a material comprising a natural rubber.

24. A method according to any of claims 19 to 22, wherein the article is made from a material comprising a synthetic rubber.

25. A method according to claim 24, wherein the synthetic rubber comprises a poly(acrylonitrile/ butadiene/carboxylate) polychloroprene polymer.

26. A method according to any of claims 23-25, wherein said article is a glove.

27. A method according to claim 26, wherein a coagulant is applied during manufacture of said glove, and a composition according to any of claims 1 to 15 is incorporated with the coagulant.

28. A method according to claim 26 or claim 27, wherein said composition is applied to one side of the glove whilst the other side of the glove is subjected to a chlorination treatment.

29. A method according to claim 26 or claim 27, wherein said composition is applied to one side of the glove and a powder treatment is applied to the other side.

30. A method of coating a glove, the method being substantially as hereinbefore described with reference to any of the examples.

31. An article coated with a composition according to any of claims 1 to 18.

32. An article according to claim 31, the article being made of a material comprising a natural rubber.

33. An article according to claim 31, the article being made of a material comprising a synthetic rubber.

34. An article according to claim 33, wherein the synthetic rubber comprises a poly(acrylonitrile/ butadiene/carboxylate) polymer.

35. An article according to any of claims 32-34, the article being a glove.

36. A coated glove substantially as hereinbefore described with reference to any of the examples.