Stock material or miscellaneous articles – Composite – Of natural rubber
Reexamination Certificate
2000-09-15
2004-02-17
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of natural rubber
C428S500000, C428S036800, C264S306000
Reexamination Certificate
active
06692840
ABSTRACT:
The present invention relates to the use of a polymeric coating composition for rubber articles. In particular the polymeric coating composition is useful for the inside coating of latex gloves.
BACKGROUND OF THE INVENTION
As used herein, the terms latex glove or latex article refer to a glove or article made of natural or synthetic rubber. Conventional medical gloves made from natural or synthetic rubber are difficult to don without a lubricant. Generally, said gloves are manufactured with a powdered coating, such as corn starch, over the inner surface of the glove so that the gloves can be more easily put on. The powder coating is a known nuisance, as loose powder can become airborne. The powder tends to absorb proteins found in natural rubber latex and the powder is easily dislodged during donning and use, contaminating the surrounding environment and causing allergies and other negative effects. Further, the protein/powder complex serves as a food source for bacteria, allowing them to proliferate. Recently, there has been a growing demand for powder-free natural and synthetic rubber gloves, which do not use loose powder for donning and mold release.
Glove manufacturers have tried to find alternatives to using starch powder to coat gloves. Some latex glove manufacturers use a chlorination process to provide the slippage necessary to facilitate donning of the gloves. In this case, calcium carbonate is used as a mold release agent and washed away prior to chlorination. Although this reduces the tack and friction of the rubber, this process makes the rubber less pliant and reduces the shelf life of the glove.
Manufacturers have looked at polymer based coatings. To be an effective substitute for starch, the inner surface coating must not only reduce friction between the rubber and the hand to allow convenient donning, but also must allow the rubber to stretch without coating delamination, i.e. have a high coefficient of elongation combined with low tack and a low coefficient of friction. Further, the coating should be deliverable from an aqueous solution, which should be stable in extreme environmental conditions, and meet any relevant regulatory requirements.
Several types of coatings have been developed, primarily based on polyurethanes: U.S. Pat. No. 5,088,125 discloses gloves modified by an ionic polyurethane; U.S. Pat. No. 5,272,771 discloses gloves modified by an ionic polyurethane containing fully reacted isocyanate groups; and U.S. Pat. No. 5,534,350 discloses gloves in which the outer glove coating contains a polyurethane dispersion and the inside glove coating contains a polyurethane containing a silicone emulsion.
Other coatings which have been developed include emulsion copolymers, particularly core-shell, containing low surface energy monomers and hard monomers as disclosed in U.S. Pat. Nos. 5,691,069 and 5,700,585; or containing two monomers selected from styrene, methyl or butyl acrylates, methacrylic or acrylic acid and a silicone oligomer, with glass transition temperatures of less than 0° C. and from 0 to 100° C. respectively as disclosed in U.S. Pat. No. 5,712,346. These sequential emulsion polymerizations lead to substantially linear copolymers. Copending U.S. patent application Ser. No. 09/400,488 describes the use of star polymers as coatings for latex gloves.
Other coatings have been developed containing a slip conferring component: U.S. Pat. Nos. 4,070,713 and 4,143,109 disclose a medical glove with particulate matter securely embedded in, and randomly distributed throughout the inner layer; U.S. Pat. No. 5,395,666 discloses a flexible article coated with a binder and porous absorbent microparticles having average diameters of from 4 to about 20 microns and an oil adsorption greater than 180 g/100 g of powder.
Surprisingly, it has now been discovered that a formulation containing a high Tg polymer, a dispersant, and microspheres provides an excellent slip conferring coating to latex gloves and other natural and synthetic rubber articles. While a high Tg polymer alone can provide a good coating, it tends to precipitate, especially in the dilute solutions preferred in the glove industry. While not intending to be bound to any particular theory, it is believed that the addition of a dispersant to a composition containing a high Tg polymer and microspheres results in a stabilization of the high Tg polymer, and a stabilization and uniform dispersion of particles. The dispersant also assists in uniform or continuous film formation.
SUMMARY OF THE INVENTION
The present invention is directed to the use of a polymer coating composition having a dispersant, microspheres, and a high Tg polymer as a coating for rubber articles, particularly for the inner surface of latex gloves.
The dispersant serves to distribute the individual components within the coating composition. It can be polymeric or non-polymeric, preferably being a star polymer.
Microspheres are small beads having diameters below 60 microns. The microspheres decrease the area of contact with the rubber article, and thus reduce the friction.
The high Tg polymer is one having a Tg of from −10° C. to 120° C. The high Tg polymer acts as a friction-reducing agent and a binder.
Other embodiments of the invention are methods of making a glove in which a polymer coating composition having a dispersant, microspheres, and a high Tg polymer, is applied to the glove as the inner glove coating.
The coating is resistant to water and can be delivered from an aqueous solution.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to the use of a polymer coating composition having a dispersant, microspheres, and a high Tg polymer, as a coating for rubber articles, particularly for the inner coating of latex gloves.
Dispersants of the present invention promote the uniform distribution and stability of individual components within the polymer formulation. Preferably the dispersant is present at from 0.1 to 5% by weight, and most preferably from 0.5 to 3% by weight. The dispersant may be a polymer, a non-polymer, or a mixture thereof. Non-polymeric dispersants useful in the present invention include, but are not limited to, anionic, cationic, nonionic, and amphoteric surfactants.
Polymeric dispersants include both linear and star polymers. Linear polymers useful in the present invention include, but are not limited to, poly(vinyl alcohol); partially hydrolyzed poly(vinyl alcohol); poly(acrylic acid); poly(methacrylic acid); copolymers of acrylic acid and/or methacrylic acid with compatible ethylenically unsaturated monomers such as alkyl esters of (meth)acrylic acid, hydroxyalkyl esters of (meth)acrylic acid, alpha-methyl styrene, styrene, and derivatives thereof, vinyl acetate, crotonic acid, esters of crotonic acid, and acrylamide, and derivatives thereof. Other suitable linear polymeric dispersants include but are not limited to poly(maleic acid) and copolymers of maleic acid with compatible ethylenically unsaturated monomers such as mono- and diesters of maleic acid, (meth)acrylic acid, alkyl esters of (meth)acrylic acid, hydroxyalkyl esters of (meth)acrylic acid, alpha-methyl styrene, styrene, and derivatives thereof, vinyl acetate, crotonic acid, esters of crotonic acid, and acrylamide, and derivatives thereof. Other suitable linear polymeric dispersants include, but are not limited to, polystyrene sulfonates, which are typically obtained by sulfonating poly(styrene) or copolymers of styrene with compatible ethylenically unsaturated monomers including, but not limited to, (meth)acrylic acid, esters of (meth)acrylic acid, maleic acid, and mono- and diesters of maleic acid; condensates including but not limited to naphthalenesulfonic acid-formaldehyde condensate and melamine-formaldehyde condensate. Certain natural or naturally derived polymers useful in the present invention include but are not limited to tannins, lignins, lignosulfates, alginates, dispersed or soluble starches and modified starches, and cellulosic polymers.
Star or radial polymers, as used herein, is intended to describe polym
Li Zhixin
Mukherjee Apala
Petrash Stanislaw
Thomaides John S.
Xiao Chaodong
Bernatz Kevin M.
National Starch and Chemical Investment Holding Corporation
Roland Thomas F.
Thibodeau Paul
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