Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-12-17
2001-09-04
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S301000, C526S321000, C526S324000, C526S325000, C526S328500, C526S329000, C526S347000, C428S036800, C428S451000, C428S492000, C428S520000, C428S522000
Reexamination Certificate
active
06284856
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to articles formed of natural or synthetic rubber having thereon a powder-free polymeric coating that enables or enhances mold- or substrate-stripping and donning.
BACKGROUND OF THE INVENTION
Rubber articles made from natural or synthetic rubber include surgical gloves, physician examining gloves, industrial work gloves, prophylactics, catheters, balloons, tubing, sheeting and the like. Some of these articles, and in particular gloves, require the ability of donning, that is, the ability of the rubber article to be slid on and off skin surfaces without undue clinging or friction. Surgical gloves require wet donning, that is, the ability to be slid over wet skin surfaces, while physician examining and industrial work gloves require the ability to be slid over dry skin surfaces. Other rubber articles, like catheters and tubing, require some means to isolate the rubber from body fluids and tissue.
While this invention pertains to polymeric coatings for all rubber articles, discussion of the invention will focus on gloves, which are the most complex of rubber articles in terms of use and manufacture. To achieve acceptable donning properties, the surface of rubber a glove that comes in contact with skin or tissue has to be modified to reduce friction.
Surgeons' gloves, as of today, desire the donning surface to be sufficiently hydrophilic to absorb moisture that may be present on the surface of skin or tissue when the article is donned. Hydrogel coatings, as described, for instance, in U.S. Pat. No. 3,813,695, incorporated herein by reference, have been employed to achieve this property.
Examination and other gloves, by contrast, do not have a hydrophilicity requirement but still require the ability of the rubber article to be slid over dry skin surfaces with minimal drag or friction. Traditionally, this had been achieved by applying talc or other powdered materials, such as modified corn starch, over the skin or tissue-contacting surface of the glove. However, talc can no longer be used, and other powders can contaminate the field of work. The same problems arise for gloves used by workers in dust-free environments, such as clean rooms used in the manufacture of computer chips and other electronic articles.
With reference to
FIG. 1
, the conventional way of manufacturing rubber gloves has been to dip a mold or former, having the shape of the article to be formed, into a powder/coagulant slurry containing calcium nitrate and calcium carbonate. After drying, the mold is immersed in a rubber emulsion (latex) for a time sufficient for the rubber to coagulate and form a coating of desired thickness. The formed coagulated rubber article is then oven-cured. Water leaching is generally employed as the next step in order to remove rubber impurities. Once the leaching process has been completed, the rubber article is then dipped into a starch slurry. The starch-coated surface is then dried to provide a powder coat on the surface of the glove. After cooling, the rubber article is stripped from the mold. This turns the glove inside out. The mold is then cleaned and recycled.
Methods and materials used for glove manufacture are described, for instance, in U.S. Pat. Nos. 3,411,982 and 3,286,011 to Kavalier et al., both incorporated herein by reference, “Polyurethane Latexes for Coagulation Dipping,” Sadowski et al., Elastomerics, August 1979, pp. 17-20, incorporated herein by reference, and “Dipping with Natural Rubber Latex,” Pendler et al., Natural Rubber Technical Bulletin, 1980, also incorporated herein by reference.
Halogenation, for example, chlorination, and other chemical surface treatments have been used to eliminate the need for a powder coat that improves the dry donning characteristics of the final product. While effective, such treatments are expensive and have the shortcoming of reducing the shelf life of the rubber articles formed. It would be desirable to provide a rubber article with a powder-free donning surface without resorting to the expensive and article-deteriorating practices now popular. Such a process could substantially reduce the cost of manufacture and maximize the shelf life of the rubber article.
U.S. Pat. No. 4,302,852 to Joung, incorporated herein by reference, proposed covalently bonding an RTV silicone coating to the interior surface of a rubber surgeons glove after formation of the glove. This is said to reduce but not eliminate the need for a donning powder.
U.S. Pat. No. 4,304,008 also to Joung and incorporated herein by reference, applies a covalently bonded silicone or urethane to the outer surface of the glove, and halogenates the inner surface. The halogenated inner surface eliminates the need for a donning powder.
U.S. Pat. No. 4,310,928, also to Joung and incorporated herein by reference, teaches the deposition of a lipo compound (lipid or lipophilic substances) in place of a powder of mineral origin in combination with a surfactant in a coagulant solution to form a uniform film on a glove mold onto which the rubber is coagulated. The lipo compound and surfactant enable stripping of a formed glove from its mold.
These and other proposals have not achieved commercial acceptance.
SUMMARY OF THE INVENTION
The present invention provides acrylic-based copolymers to coat, firmly adhere to, and in some instances, be absorbed on the surface of a rubber article. The copolymers may either be deposited as a slurry during the coagulation of the rubber article, or deposited onto a preformed rubber article. The copolymers improve the properties of mold-stripping (release from the mold) of the formed rubber article. They also improve the dry and wet donning characteristics of the rubber article, without requiring further chemical treatment. Such donning characteristics and mold stripping properties may be achieved by depositing the same or a different acrylic-based copolymer on opposed surfaces of the formed rubber article.
The acrylic-based copolymers of the present invention are preferably emulsion-based copolymers polymerized from a monomer mixture that includes at least one reactive (copolymerizable) low surface energy monomer, preferably a silicone oligomer; at least one alkyl acrylate; at least one reactive (copolymerizable) aliphatic urethane oligomer; and at least one reactive (copolymerizable) hard monomer. As used herein, the term “monomer mixture” refers to a mixture of monomers and/or oligomers that can be copolymerized to form the desired copolymer. The hard monomers (described below) should be present in a total amount sufficient to form a non-tacky copolymer directly or by blending of copolymers. Preferably, a sequential polymerization process using two different monomer mixture emulsions is used to produce the coating emulsion. The first monomer mixture should yield a first copolymer that exhibits at least one dominant glass transition temperature (T
g
) peak below about 0° C., while the second monomer mixture should yield a second copolymer exhibiting at least one dominant glass transition temperature peak above about 0° C. More preferably, the first copolymer exhibits a glass transition temperature peak between about −50° C. and −10° C., and the second copolymer exhibits a glass transition temperature peak between about 12° C. and 65° C.
The presently preferred copolymers are prepared from silicone oligomers, butyl acrylate, methyl acrylate, methacrylic acid, acrylic acid, styrene, and an aliphatic urethane oligomer.
The addition of a urethane oligomer to the monomer mixture provides a number of benefits. First, it permits the copolymer to withstand higher cure temperatures such that the copolymer can be cured at a temperature that is more compatible with the cure temperatures for the rubber emulsions generally used for making formed rubber articles. This permits the copolymer coating and the rubber to be cured simultaneously. Second, a copolymer that includes a urethane oligomer can be used with a broader class of latexes and rubbers than a copolymer without a urethane oligomer. Speci
Avery Dennison Corporation
Christie Parker & Hale LLP
Pezzuto Helen L.
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