Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2002-01-22
2004-07-20
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S492000, C428S517000, C428S519000, C428S520000
Reexamination Certificate
active
06764731
ABSTRACT:
The present invention relates to a two-side treated rubber article having on its outside surface a polymer coating and having a chlorinated inner surface. The invention is also related to an in-line process for forming such an article, and in particular forming a latex glove.
BACKGROUND OF THE INVENTION
Rubber articles are elastomeric materials having low glass transition temperatures (Tg). Surfaces of the low Tg articles tend to stick together. In particular, in a rubber or latex glove, the inside of the glove must allow for good donning, while the outside of the glove (which is in contact with a former during manufacturing) must be able to be easily released from the former, and must not stick to other gloves when packaged (must have good anti-blocking properties). Both of these problems have been solved in the past by coating the inside and outside of a glove with a powder, such as starch, talc or calcium carbonate.
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.
One alternative to a powdered glove is a powder-free glove using chlorination of both the inner and outer surfaces to reduce the tack and friction of the rubber. An additional advantage of this process is a reduction in the protein level of the latex. A disadvantage is that the chlorination process makes the rubber less pliant, and reduces the shelf life of the glove. Chlorination of both surfaces of a glove is very labor intensive process, since the glove must be stripped from the former to chlorinate the outer surface.
Another method for producing a powder-free glove is the use of polymer coatings. Several types of polymer 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. Copending U.S. patent applications Ser. Nos. 09/663,468 and 09/882,222 describe polymer coatings and polymer mold release compositions useful for inner and outer glove coatings respectively, and are incorporated herein.
It has now been found that a continuous in-line process for two-side treated rubber articles, involving chlorination of the inner surface and a polymer-coated outer surface, advantageously combines the positive features of both technologies to produce a powder-free glove. An in-line outer coating process combined with off-line chlorination allows for chlorination to occur for extended time periods not limited by the line speed, and also allows chlorination to occur in a closed system to control chlorine emmisions.
SUMMARY OF THE INVENTION
The present invention is directed to a two-sided treated rubber article having a polymer coating on the outer surface, and a chlorinated inner surface.
The invention is also directed to a process for making a glove comprising
a) immersing a glove former in a coagulant solution comprising a release composition comprising a polymer to produce a coated former;
b) immersing the coated former into a rubber latex to coat the former with said latex;
c) chlorinating the latex on the coated former;
d) curing the chlorinated latex on the coated former; and
e) removing the finished glove from the former.
The invention is further directed to a process for making a glove comprising
a) immersing a glove former in a coagulant solution comprising a release composition comprising a polymer to produce a coated former;
b) immersing the coated former into a rubber latex to coat the former with said latex;
c) curing the latex on the coated former;
d) chlorinating the latex on the coated former; and
e) removing the finished glove from the former.
DETAILED DISCRIPTION OF THE INVENTION
The present invention is directed to two-sided treated rubber article having a polymer coating on the outer surface; and a chlorinated inner surface; and a process for producing said glove.
A rubber article, as used herein, refers to an article made of a natural or synthetic, low-Tg, elastomeric polymer or mixture of polymers. Examples of such polymeric 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 polymer coating on the outer surface of the rubber article serves both as a mold-release agent and also as an anti-blocking agent. The polymer of the invention preferably has a Tg of greater than −10° C., preferably from 25 to 200° C. and most preferably from 40 to 150° C. For ease of use in a glove manufacturing process, the polymer should be water-borne.
A preferred polymer for the outer coating is a copolymer formed from at least one hydrophobic monomer. The polymer may, and preferably does, also contain at least one hydrophilic monomer, though a useful polymer may be formed without a hydrophilic monomer. Monomers useful in forming the polymer of the present invention are ethylenically unsaturated monomers or mixtures thereof.
A preferred method of producing the polymer of the outer coating is described in copending U.S. patent application Ser. No. 09/882,222.
The polymer used as the outer coating of the rubber article may be formulated with other optional ingredients, such as dispersants, surfactants, microspheres, and rheology modifiers.
Preferably the outside polymer coating contains no silicones, however the addition of a silicone to the composition can also be advantageous. A problem with having silicon compounds in the composition is that they can remain on a mold or former, making the mold or former more difficult to clean.
The polymer coating composition may also contain microspheres. Microspheres are useful in reducing the surface contact area, and thus the adhesion between the coated rubber article and the mold, former, or other object. This improves both the release and anti-blocking characteristics.
A dispersant may optionally be added to aid in dispersion of the microspheres into the aqueous polymer composition. Dispersants useful in the present invention include, but are not limited to, surfactants and polymeric dispersants including amphiphilic linear and star copolymers.
A rheology modifier is optionally present in the release composition.
The outside polymer composition may also contain other additives known in the art, such as adhesion promoters, crosslinking agents, biocides, low surface energy compounds, fillers, and antifoaming agents.
The polymer composition for the outer surface of a rubber article is made by combining each of the ingredients to form an aqueous dispersion, by means known in the art.
A preferred method of formulating the polymer of the out
Gardner Joseph B.
Li Zhixin
Savoca Ann C.
National Starch and Chemical Investment Holding Corporation
Nolan Sandra M.
Roland Thomas F.
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