Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2001-06-15
2004-08-31
Resan, Stevan A. (Department: 1773)
Electric heating
Metal heating
For bonding with pressure
C425S089000, C106S038350, C428S515000
Reexamination Certificate
active
06784397
ABSTRACT:
The present invention relates to the use of a polymeric release composition for molds and formers used in the production of natural and synthetic rubber articles. In particular the polymeric release composition is useful for the formation of latex gloves, and also for preventing blocking on the outer surface of such gloves. The release composition of the present invention has the advantage of being easily cleaned from molds and formers, and is compatible with coagulant currently used in many manufacturing processes, eliminating the need for an extra step to coat the mold or former with a release coating.
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. Articles made from natural or synthetic rubber are elastic materials having low glass transition temperatures. The surfaces of these materials are tacky and tend to adhere to each other. For example, latex gloves are difficult to strip from glove formers at the end of the manufacturing process, and they tend to stick together, or block, when packaged for distribution and sale.
There are currently several approaches to solving the problem. One method involves the use of a particulate or powder material, such as starch, talc, or calcium carbonate. The particulate can be blended into a coagulant solution to form a barrier between the latex rubber and the surface of the former. The powder facilitates the stripping of gloves from the formers, and also prevents blocking. Unfortunately, the powder coating is a known nuisance, as loose powder can become airborne. Starch powder tends to adsorb proteins found in natural rubber latex and the powder is easily dislodged during 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.
Another approach is the use of a chlorination process to provide the necessary anti-blocking properties, as described in U.S. Pat. No. 4,851,266. 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 rubber article. Also, chlorination leaves the article quite slippery, which makes it difficult to handle objects with chlorinated gloves. To address this problem, chlorinated gloves are often textured.
Yet another approach is the use of silicone materials. These materials facilitate removal of gloves from the formers, and also reduce blocking. Unfortunately, the residue of this material is rather hard to clean from the former in preparation for the next dipping cycle.
Talc-free mold release agents using surfactants are described in U.S. Pat. No. 4,310,928.
Polymeric mold release agents have also been disclosed in the art. Formulated polychloroprenes are described in EP 0 640623, Urethane dispersions in U.S. Pat. No. 5,534,350, and Styrene/acrylates containing silicone in U.S. Pat. Nos. 5,993,923; 5,691,069; 5,700,585; and 5,712,346. Copending U.S. patent application Ser. No. 09/400,488, and copending U.S. Patent Application, submitted Sep. 15, 2000 describe the use of star polymers as inner coatings for latex gloves.
Surprisingly it has been found that a release composition containing a water-borne high Tg polymer formed from at least one hydrophobic monomer and at least one hydrophilic monomer provides a powder-free mold release agent, provides anti-blocking in the finished article, and also aids in providing a smooth latex deposition on the formers. Additionally, the release composition is dispersible in high electrolyte coagulant, making it compatible with current manufacturing processes.
SUMMARY OF THE INVENTION
The present invention is directed to a mold or former for natural or synthetic rubber articles having on its surface a release composition comprising a water-borne polymer formed from at least one hydrophobic monomer and at least one hydrophilic monomer, where the polymer has a Tg of at least −10° C.
Other embodiments of the invention are methods of making a latex glove in which a release composition, containing a water-borne polymer, having a Tg of at least −10° C., and formed from at least one hydrophobic monomer and at least one hydrophilic monomer, is applied to a former as a release coating.
Still another embodiment of the invention is a natural or synthetic rubber article having on its surface a coating comprising a polymer having a Tg of at least −10° C., and formed from a hydrophobic monomer and a hydrophilic monomer.
Still another embodiment of the invention is a latex coagulant, comprising a release composition, comprising a polymer having a Tg of at least −10° C., and formed from a hydrophobic monomer and a hydrophilic monomer, which is used in manufacturing powder-free rubber articles.
While not wishing to be bound to any particular theory, it is believed that the key performance characteristics desirable for a release coating are: a high Tg polymer, which provides anti-blocking; ease of cleaning from a former; wettability of the film, for smooth latex deposition; an affinity to the latex surface; the ability to impart an anti-blocking character to the article formed from a mold or former.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a mold or former for the production of natural and synthetic rubber articles, having on its surface a release composition comprising a water-borne high Tg polymer formed from at least one hydrophobic monomer and at least one hydrophilic monomer.
Natural and synthetic rubber articles, as used herein, refer to articles made from low-Tg, tacky polymeric materials. Examples of such materials include, but are not limited to, butyl rubber, natural latex rubber, polyvinyl chloride, neoprene, nitrile, viton, styrene butadiene copolymers, polyurethanes, or interpenetrating polymer network emulsion polymers, or combinations of these.
The water-borne polymer of the present invention is one which is water-borne, and formed by means known in the art, such as emulsion polymerization and suspension polymerization.
By high Tg polymer is meant a polymer having a Tg of at least −10° C., preferably from 25 to 200° C., and most preferably from 40 to 150° C. Monomers useful in forming the polymer of the present invention are ethylenically unsaturated monomers or mixtures thereof. Particularly useful hydrophobic monomers include (meth)acrylates, vinyl acetate, ethylene, and styrene. A preferred hydrophobic monomer is styrene.
The polymer of the present invention is also formed from a hydrophilic monomer. The hydrophilic monomer is present in the polymer at from 10-90 percent, based on the weight of the polymer. Suitable hydrophilic monomers include those monomers that are ionic, e.g. anionic, cationic, or zwitterionic, or have sufficient nonionic polar functionality, e.g. hydroxyl or amido groups to render them hydrophilic. Examples of such monomer include, but are not limited to hydroxyethyl acrylate, acrylonitrile, 2-(dimethylamino)ethyl (meth)acrylate, [3-(methacryloylamino)propyl]trimethylammonium chloride, 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (a.k.a. AMPS), [2-(acryloyloxy)ethyl]trimethylammonium chloride. Preferred hydrophilic monomers are acrylic acid and methacrylic acid.
The polymer may optionally contain a cross-linker. The cross-linker is present at from 0 to 10 percent, and preferably from 0.5 to 5 percent by weight, based on the weight of the polymer. The cross-linker is preferably a di-functional cross-linker, such as divinylbenzene, diallyl maleate, ethylene glycol dimethacrylate, vinyl crotonate and diallyl phthalate. Multi-functional cross-linkers, such as allyl and vinyl sucrose ethers, pentaerythritol tetra(meth)acrylate, tri
Gardner Joseph B.
Gore Christopher G.
Li Zhixin
Petrash Stanislaw
Thomaides John S.
Falasco Louis
National Starch and Chemical Investment Holding Corporation
Resan Stevan A.
Roland Thomas P.
LandOfFree
Mold release and anti-blocking coating for powder-free... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Mold release and anti-blocking coating for powder-free..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Mold release and anti-blocking coating for powder-free... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3283807