AN IMPROVED ACRYLIC BASED EMULSION COMPOSITION FOR COATING RUBBER ARTICLES FIELD OF THE INVENTION This invention relates to an improved powder- free acrylic based emulsion copolymer composition that can be used as a coating for rubber articles. The coating assists in the removal of the article from the mold and facilitates dry donning. BACKGROUND OF THE INVENTION Traditionally, rubber articles such as gloves were manufactured by dipping a former or mold into a rubber latex. These processes often. included the use of a powdered lubricant, such as talc, cornstarch, or clay. Typically, the powder was incorporated into either a coagulant or into a release slurry. A coagulant is a compound that coagulates a layer-forming emulsion or dispersion to form a thicker layer than it would normally do otherwise. A release slurry is a slurry containing powder which is applied to the article prior to removal from the former. The use of powder in the coagulant or release slurry served two important purposes. First, powder made it easier to strip the resulting article from the former. With respect to gloves, removal from the mold is often difficult because cured latex gloves tend to be tacky and adhere to the mold. However, the use of powder reduced the tackiness or stickiness of the gloves

and improved stripping. Second, powder facilitated donning in certain articles such as gloves.

While the use of powder in the manufacture of rubber articles solved many problems, it created many new ones as well.

The main problem was that the completed rubber article contained a great deal of residual powder. It is well known in the art that this residual powder can create numerous problems, particularly with respect to surgical gloves where there is a risk that the powder may escape from the glove and contaminate the surgical field. See Alexander's Care of the Patient in Surgery 9th Edition. Another problem commonly associated with the use of powder is that the process requires cleaning up the powder residue on the former after formation of each and every article, a tedious and time consuming operation. Because of these problems, numerous attempts have been made to eliminate the use of powder in the construction of articles. For a detailed description of making rubber articles see: Natural Rubber Dipping Technologies, Symposium on Latex as a Barrier Material, April 6 and 7, 1989, University of Maryland; Russell D. Culp and Bradley L. Pugh. This publication is incorporated herein by reference.

Several processes are known in the art for making powder-free articles.

PRIOR ART In one process to make the article powder-free, the article is halogenated, normally with chlorine, in a batch process. For example, U.S. Patents 3,411,982 and 3,740,262 disclose that the surface of a rubber glove can be halogenated to make it slippery. U.S. Patent 4,304,008 discloses that halogenation facilitates donning in rubber articles in lieu of powdered lubricants. U.S. Patent 3,740,262 discloses halogenating a glove to provide a powder-free rejecting outer surface and a powder- accepting inner surface.

Halogenation produces articles having a powder- free clean surface. In fact, chlorination is widely used to make clean-room gloves, powder-free surgical gloves and powder-free examination gloves. Although articles produced using chlorination are powder-free and exhibit good dry donning characteristics, they are economically more expensive to produce due to the number of chlorination steps, turning steps, and drying processes involved in the manufacture.

While halogenation can be used to facilitate donning, halogenated articles possess many disadvantages. Halogenated articles tend to discolor and age poorly both in storage and in use. In fact, discoloration can begin almost immediately, and within a month, the halogenated surface may become hard, brittle and brown in color.

Additionally, chlorine is considered to be a toxic chemical and disposal of materials containing this element presents numerous environmental issues. The disadvantages of chlorination are recognized in U.S. Patent 5,284,607. This patent discloses a process for making a multi-layered, powder-free medical glove. The glove is made with an acid-soluble powder, and once fully formed, stripped from the former and reversed so that the first layer is on the outside. The glove is then treated with an acid, such as nitric acid, to remove the acid-soluble powder. After the acid treatment, the glove is rinsed with water and treated with bleach to chlorinate the inner and outer glove surface. The bleach does not cause the glove to have the excessively slippery outer surface that typically results when chlorination is used.

U.S. Patent 4,310,928 discloses a talc free surgeon's glove. The glove is made by dipping a former into a coagulant solution containing a lipo compound and a surfactant and then into latex to form a glove.

U.S. Patent 4,499,154 discloses another method of making a powder-free article. This patent details a process for making a rubber article by dipping a former into compounded latex, leaching the article, priming the article with an acid, neutralizing the article with water or an aqueous

alkali, applying a hydrophilic coating, heating the article to fix the coating, curing the rubber, stripping the article from the former and applying a solution of surfactant materials and silicone. While this process produces a powder-free article, the number of steps involved makes the process unduly expensive and the low molecular weight components (surfactants and silicone) could cause contamination. U.S. Patent 5,138,719 discloses a method of making powder-free gloves, finger stalls and other protective articles constructed from latex and microcapsules. The microcapsules are dispersed and arranged in the latex to form a concentration gradient, with the concentration of the microcapsules increasing progressively from the outer surface to the inner surface of the article. The high concentration of the microcapsules at the inner surface provides good sliding properties and facilitates donning without the need for powder. In addition, the microcapsules may contain a pharmaceutically active substance such as nonoxynol, moroxydine hydrochloride, vidarabine to provide viricidal activity against diseases such as AIDS or herpes. See U.S. Patent 5,024,852.

EP 0574160A1 discloses a method for making a powder-free, wet and dry donnable, multi-layered article having a first layer formed from natural

rubber, a second layer formed from natural rubber, polyurethane, poly(acrylamide/acrylic acid) and polyethylene oxide, and a third layer of an acrylic copolymer and fluorocarbon telomer resin. A different process for making rubber gloves alleged to have good donning properties is disclosed in Kavalir et al., U.S. Patents 3,286,011 and 3,411,982. The disclosures of these patents are the same. These patents a coating composition comprising a mixed latex which is approximately 1:1 on a weight basis of a rubber latex and certain resinous polymer latices. One group of these polymer latices are certain acrylic ester latices. The compositions of the patent are suggested for use as being former coatings and as coatings for the inner surfaces of rubber gloves to impart improved donning characteristics. The acrylic ester latices used by the patentees in their process are mixtures of acrylic ester latices. These acrylic latices and their method of manufacture are described in detail as well in U.S. Patent 2,795,564 the disclosure of which is incorporated herein by reference.

One of the teachings of the Kavalir et al. patents is that high concentrations of coagulating salts may be incorporated into the coating compositions of the invention. The use of a water soluble non-ionic surfactants incorporated into the compositions of the patent allows for the

introduction of large quantities of coagulating salts such as calcium nitrate without resulting in the destabilization of the compositions. The patentees stress that the resinous polymer latices alone without the rubber latex are inoperative.

Other disadvantages become apparent from the study of these patents. Powders such as talc, are needed to provide former release. Also, the compositions of the patentees are high solids viscous compositions making them difficult to apply either to formers or articles formed thereon. Thus, while providing and interesting approach to improved glove making this patent still does not solve the problem of eliminating powders as lubricants. OBJECTS OF THE INVENTION

An object of the present invention is to provide an improved powder-free acrylic based emulsion composition for coating rubber articles. The improved coating composition of this invention allows for the easy removal of the articles from the former upon which they are produced. Gloves produced by using the improved composition of this invention exhibit excellent dry and some good wet donning characteristics. SUMMARY OF THE INVENTION

The present invention involves an improved powder-free acrylic based emulsion copolymer composition. The improved composition can be used

as a coating for rubber articles. As used in the specification and appended claims, "powder-free" mean that the composition has been manufactured to eliminate most, if not all, powder. The improved coating composition is prepared by copolymerization of a reactive silicone acrylate, an alkyl acrylate and a hard monomer. Such compositions are known in the art. However, an improved composition is obtained when a silicone emulsion is added to the composition.

Additionally, the composition can contain water-soluble surfactants, such as non-ionic surfactants. The surfactants can be used to stabilize the composition so that coagulating metal salts can be added to the composition without causing the composition to destabilize. By adding the coagulating metal salts to the composition, the composition is capable of coagulating latex once dipped and dried on a former. The improved composition of this invention can be used as a coating for rubber articles. When used as a coating for rubber articles, the composition can be coated on the inside and outside of the rubber article. The coating provides good dry donnability and some good wet donnability.

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a powder-free acrylic based emulsion copolymer coating composition

which can be used as a coating for rubber articles. The improvement in the coating over other coatings in the prior art is the addition of a silicone emulsion to the composition. Acrylic based emulsion copolymer compositions are known in the art. For example, the coating composition can prepared by copolymerizing a reactive silicone acrylate, an alkyl acrylate and a~ hard monomer. It is preferred that such copolymerization take place in the form of emulsions. Methods for preparing emulsions are well known in the art. However, a better and more improved coating is obtained when a silicone emulsion is added to the composition. Compositions such as those described in U.S.

Patent 5,234,736, hereby incorporated by reference, can be modified to provide good coatings for rubber articles. This composition comprises a "reactive silicone acrylate polymer." What is meant by a "reactive silicone acrylate polymer" is polymeric siloxanes and silicones which display an acrylate functionality including but not limited to acrylate polysiloxanes. The acrylate functionality is greater than 1. Examples of the multifunctional silicone acrylates that can be used include Tego ^® silicone acrylate RC 149, 300, 450, 710, 720, and 802 and ZMR1395 manufactured and sold be Goldschmidt Chemical Corporation of Hopewell, VA, which polymers

are linear dimethylpolysiloxanes with acrylate functionality and a molecular weight between 1000 and 20,000 g/mol and include dimethylpolysiloxanes with pentaertyritoltriacrylate. For use as a rubber coating for articles, the composition may contain less than about 10% by weight of the reactive silicone acrylate polymer.

The rest of the composition comprises at least one alkyl acrylate and at least one hard monomer. The alkyl acrylate that can be used in the composition can have the formula:

CH ₂ =C-COOR ^x

where R is hydrogen or a methyl group and R ^x represents, when R is methyl, a primary or secondary alkyl group of 5 to 18 carbon atoms, or when R is hydrogen, an alkyl group not over 18 carbon atoms, or better, of 2 to 12 carbon atoms. Typical compounds within the above definition are methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, sec. butyl acrylate, amyl acrylate, isoamyl acrylate, hexyl acrylate 2-ethylhexyl acrylate, octylacrylate, 3, 5, 5 trimethyl-hexyl acrylate, decyl acrylate, dodecyl acrylate, cetyl acrylate, octadecyl acrylate, n-amyl methacrylate, sec. -amyl

methacrylate, hexyl methacrylate, 2-ethylbutyl methacrylate, octyl methacrylate, 3, 5, 5- trimethylhexyl methacrylate, decyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, butoxyethyl acrylate, or methacrylate or other alkoxyethyl acrylate or methacrylate, etc.

The amount of alkyl acrylate that can be employed in the composition is 10 to 90% by weight. The balance of the composition comprises of a hard monomer. By "hard monomer" what is meant is monomers having a glass transition temperature (Tg) greater than 0°C. Examples of hard monomers that can be used in this composition styrene, methacrylate, ethyl acrylate, alkyl methacrylates having alkyl groups of not over four carbon atoms, also tert. - amyl methacrylate, tert . -butyl or tert. -amyl acrylate, cyclohexyl acrylate or methacrylate, acrylonitrile or methacrylonitrile, and unsaturated carboxylic acids. The resulting composition has a glass transition temperature above 35°C.

In addition to the above components, other additives such as free radical catalysts, chain transfer agents, antioxidants, etc. can be employed as needed.

It is preferred that the composition contain metal coagulating salts capable of coagulating latex. The amount of metal salt added to the

composition is at least 5-25% and preferably 10-20% by weight of coagulating salts. These coagulating salts are most commonly inorganic salts of mineral acids such as water soluble alkaline earth salts of hydrochloric, sulfuric or nitric acids. Typically, salts such as calcium chloride or calcium nitrate provide satisfactory coagulation of most rubber latices. Salts of zinc and aluminum may also be used. The salts when added to the coating composition can in certain instances cause destabilization. To preve.it this from taking place it is desirable that a stabilizing amount of a water soluble surfactant, preferably a non-ionic surfactant, be added to the latex-salt mixture. This stabilization technique is described in the Kavalir patents previously cited. The amount and type of surfactant can only be determined by experimentation since the components of the composition and particular coagulant salt will vary. Usually not more than a few percent of the stabilizer is necessary e.g. about from 0.1% to about 3% by weight. It will be understood that when the coating composition is used to form a coating on the inside of the finished article such as a glove it is not necessary nor desirable that it contain a coagulating salt. In a similar fashion it not necessary that the same latex used as the former

mold release coating be used in the formation of the donning coating.

The thickness of the coatings applied to the former or to the formed article will vary and can be optimized by routine experimentation. The thickness of the former release coating need not necessarily be the same thickness as a donning coating. As a general rule the thickness of the coatings should not be not be greater than 20% the thickness of the coating of the rubber latex article. Typically coatings as thin as 200 microns up to coatings of several mils may be used.

Improved results are achieved when the composition is modified to include silicone polymers. A preferred method of combining the silicone resin with the composition is to use silicone emulsions which contain in emulsion form polymers such as polydimethylsiloxane polymers. One such emulsion is sold by Dow Corning under the trade designation, Dow Corning Emulsion 365. While the amount of silicone resin in a dry weight basis may range between 0.001 to 3% by weight, typically, 0.1 to 2.5% will give good results. Amounts as great as 5% may be used, but too much may produce adverse effects. These emulsions may require modifications to render them compatible and stable when they are blended with the composition.

Optionally, the silicone emulsion can comprise silicone monomers having vinyl unsaturation which when mixed with silicone hydride containing crosslinkers is cured by a Group VIII metal catalyst, preferably a platinum catalyst. For example, a silicone emulsion, such as 400-E, available from Wacker Chemicals USA, Norwalk, CT, which contains an emulsified vinyl oil, a platinum catalyst, and a platinum inhibitor can be used. The emulsion can also contain reactive surfactants.

The preferred vinyl-addition silicone emulsions are mixtures of reactive vinyl silicone polymers of the formula:

CH, CH, CH, CH,

CH ₂ =CH-Si-0- (SiO)m- (SiO)n-Si-CH=CH ₂

CH ₃ CH ₃ CH ₂ CH ₃

CH ₃

where m and n are independent integers and silicone hydride cross linking polymers of the formula:

CH, CH, CH, CH,

CH ₃ -Si-0- (SiO)m- (Si _. 0)p-Si-CH ₃

CH ₃ CH ₃ H CH ₃

where and p are also independent integers. There may also be included conventional ingredients designed to modify the release properties.

Vinyl-addition silicone systems react by thermally induced addition-cure (hydrosilations between polydimethyl-hydrogen siloxane crosslinkers and reactive vinyl-functional silicone polymers) to furnish a cured silicone release composition.

The vinyl-functional silicone molecules are polydimethylsiloxanes, where some of the methyl groups have been substituted with vinyl groups or other alkyl groups containing vinyl unsaturation, i.e. the reaction takes place between a vinyl substituted polydimethylsiloxane and polydimethylhydrogen siloxane.

The whole hydrosiliation is catalyzed by silicone soluble complex compounds of Group VIII transition metals, particularly platinum. In normal use of vinyl-addition silicone systems, a small amount of inhibitor is added to prevent premature reaction between the silicone hydride and vinyl silicone groups following mixing of the existing components, before deposition onto the substrate. The inhibitor is removed or made ineffective during the thermal curing process. A suitable silicone emulsion system showing the practice of this invention can be obtained from Dow Corning, Rhone- Poulenc, and Wacker-Chemicals, USA, a division of Wacker-Chemie of Germany. The coating composition of this invention is made without the use of powder.

THE COATING PROCESS Once the improved coagulation-inducing, powder- free composition is prepared, the former is dipped or immersed in the composition to form a film or first layer and is then withdrawn. After the former is withdrawn from the composition, the first layer is allowed to stand and dry or is dried in an oven at 70°C for about 3 minutes to form a coherent film or layer. Once dried, the first layer is capable of inducing conventional coagulation when dipped or immersed into a latex compound.

After the formation of the first layer, the former is then dipped into a latex compound to form a second layer. The latex compound can be any coagulatable natural or synthetic latex compounds, coagulatable natural or synthetic rubber latices or styrenic block copolymer dispersions known in the art. Conventional formulations for the preparation of latex are well known in the art and those skilled in the art are readily able to vary the formulations and conditions of curing and the like to suit the particular latex being used as well as the final article desired. Precured or partially cured latex can be used; however, if non-cured' latex is used, it must be cured after forming. Additionally, the latex may contain conventional compounding ingredients commonly utilized. Specific examples are provided in U.S. Patent 3,411,982, hereby incorporated by reference.

When the former is immersed into the latex compound, the dried film induces coagulation of the latex to produce a uniform coagulated deposit of the latex on the former. The length of time the former is immersed in the latex determines the wall thickness of the article. The longer the dwell time period, the greater the wall thickness of the article, and vice versa. Articles produced according to the method of this invention typically have a thickness of between 4 to 15 mils .

The former is removed from the latex with a coating of gelled latex adhering to it. The former is placed in a water bath to leach out water soluble components such as proteins, electrolytes, etc. The temperature of the water bath is between 49-60°C.

After leaching, the second layer maybe dried or coated with a lubricating polymer. If dried, then the first and second layers are cured. As used in this invention, the term "curing" also includes "fusing" or "fusion" as some types of polymers require fusing instead of curing. For example, thermoplastic elastomers such as the copolymers poly(styrene-b-isoprene-b-styrene) (SIS) , poly(styrene-b-butadiene-b-styrene) (SBS) , and poly(styrene-b-ethylene propylene-b-styrene) (SEPS) require fusing. Typically, however, curing is employed. The length of time required for curing depends upon the polymers selected, however, most polymers can be cured in about 5 to 10 minutes at about 138°C. After curing, the resulting article is allowed to cool and is removed from the former.

When the composition is used as article coatings can be applied either before the drying of the second layer, after the drying of the second layer but before curing, or after curing. When applied, it will add additional layers to the already multi-layered article. After the acrylic ester latex is coated to the article, it is allowed

to stand and dry or is dried in an oven. One skilled in the art would recognize that the conditions required for drying the lubricating polymer in an oven vary based on the type of lubricating polymer employed. If the acrylic ester polymer is added to the article prior to curing, the polymer may be dried and the article cured in one step. If the polymer is applied after the article is cured, then it must be dried. Stripping of the article from the former turns the article inside out so that the first layer is on the outside and the latex or lubricating layer is on the inside. The stripping process does not require any powder to release the article from the former. Additionally, the resultant article is not tacky. In the practice of the invention with respect to gloves, the molds used are in a variety of sizes and shapes corresponding to the various hand sizes for which the gloves are intended. The preferred mold is a contoured mold having a textured to highly polished ceramic or porcelain surface or one having a fluorocarbon coating, however, other molds such as glass, hard woods, and plastic can also be used. Gloves produced using this improved composition are easily removed from a former are not tacky, exhibit good donning characteristics, and are powder-free.

EXAMPLE A coagulant emulsion was prepared by mixing 200 grams of an acrylic emulsion, IL-93-10-19, available from Avery Dennison Corporation, Pasadena, California, containing a reactive silicone acrylate an alkyl acrylate and a hard-monomer with 10 grams of a silicone emulsion. The silicone emulsion comprises 34.3 grams of 400 E, which is a vinyl oil that uses a vinyl oil and platinum catalyst and a platinum inhibitor available from Wacker Chemicals USA, Inc., Norwalk, CT, and 8.14 g of V-20, a silicon hydride cross-linker also available from Wacker Chemicals USA, Inc. Next, 40 grams of calcium nitrate and 40 grams of water were added. A ceramic mold was warmed to 80°C and dripped for about 4 seconds into the above emulsion and after drying dipped into the latex compound. The mold was then dipped into a warm water bath and leached. After leaching the mold is dipped into the acrylic emulsion (IL-93-10-19) without coagulant. The formed product is then cured at 138°C for 10 minutes and removed from the former.

CONCLUSION Although the invention has been described primarily in connection with the special and preferred embodiments, it will be understood that it is capable of modification without departing from the scope of the invention. The following claims

are intended to cover all variations, uses, or adaptions of the invention, following, in general, the principles thereof and including such departures from the present disclosure as come within known or customary practice in the field to which the invention pertains, or as are obvious to persons skilled in the field.