Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-06-30
2004-09-21
Zalukaeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S319000, C526S315000, C526S316000, C526S328000, C526S329500, C525S123000, C525S124000, C525S379000
Reexamination Certificate
active
06794475
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polymers and their latexes, solutions, dispersions and blends used to produce gloves and other articles having superior electrostatic dissipative properties.
BACKGROUND OF THE INVENTION
Polymeric materials for use in electrostatic discharge (“ESD”, “static dissipative” or “antistatic”) applications fall into two categories: rubbery or thermoplastic. Typically rubbery and thermoplastic materials are used in different applications and are made by different manufacturing methods. The ESD properties are achieved by incorporating hydrophilic moieties, such as various ethoxylates, or electroconductive fillers such as carbon black, metals, or salts. Many of these systems have shortcomings. Additives by their very nature can have widely variable results due to non-uniform dispersion in the matrix. They also can lose effectiveness if they extract from the matrix and/or deteriorate over time.
Achieving ESD properties in articles that are designed to be flexible rather than rigid provides further challenges. Some of the traditional ingredients in the prior art such as carbon black, metal powders and wires, electroconductive polymers, and inorganic fillers, can stiffen an article. This is not important in plastic applications, but will present a significant issue for articles that must be flexible.
In addition, ingredients in a flexible matrix, by their very nature, are more mobile than in a plastic matrix. Flexible articles such as gloves and papers are designed to bend, flex, and stretch under contact with moist skin. These conditions are more conducive to creating motion at the molecular level, which could increase the likelihood for water-soluble materials and fillers to bloom, transfer or flake off the surface. Any particulate matter coming off articles can potentially cause damage in a critical environment where antistatic properties are desired, such as “clean room” applications and electronics manufacturing.
Traditional materials for making ESD clean room articles incorporate conductive fillers, fibers, ionic materials, carbon black, or application of a surface coating. Shortcomings of these articles include extraction or deterioration over time, non-homogeneity, and a need for humidity to dissipate static charges effectively. Many articles such as gloves used in a clean room are manufactured under special conditions to minimize particulate contamination. For example, additional post-leach or water-soak processes in glove manufacturing will remove particulate contamination.
Current gloves used in clean room environments typically are made from latexes (also known as emulsions or latex emulsions) or dispersions of natural rubbers, acrylonitrile-butadiene rubbers, styrene-butadiene rubbers, polyvinylchlorides, polychlorobutadienes, and polyurethanes. Latexes typically are prepared by polymerization of monomers in a water medium, while dispersions are prepared by distribution of polymers in a water medium following polymerization. Gloves made from these polymers under current standard conditions of compounding and processing typically have a surface resistivity of 1×10
11
to 1×10
13
ohms/square and a static decay time greater than 1 second. Specialty gloves are currently on the market which offer antistatic or conductive features, incorporate additives such as carbon black during compounding, and have published surface resistivity values as low as 1×10
4
ohms/square.
The most accepted method of glove manufacturing is the coagulant dipping process, followed by subsequent leaching and curing cycles. In this process, a preheated and cleaned glove mold (also called a “former”) is dipped into a calcium nitrate salt solution, and dried to tackiness. This salt-coated mold is dipped into a compounded latex or polymer dispersion, causing the latex or polymer dispersion to coagulate on the mold and form a glove. The glove is then leached in water to remove the salt, dried and cured to achieve final properties. Thus, an essential property of the latex or polymer dispersion is its ability to coagulate, forming an article.
The most widely used approach to render polymers antistatic is incorporating a polyethyleneglycol (PEG) moiety into the backbone of the polymer. PEG is a hydrophilic material and attracts moisture into the article, thus reducing its resistivity. Since it is polymerized into the backbone of the polymer, it is not extractable. For example, U.S. Pat. No. 4,543,390 relates to graft copolymers prepared by emulsion polymerization of certain polyethyleneglycol monomers and optionally certain vinyl monomers in the presence of rubbers. The graft copolymers subsequently are blended with compatible thermoplastic resins. However, the polyethyleneglycol monomers which render polymers antistatic also yield polyvalent ion-stable polymer emulsions which are unsuitable for glove making by coagulant dipping processes. See R. H. Ottewill et al, Colloid & Polymer Science, Vol. 266, No. 6, p. 547 (1988), and R. H. Ottewill, Emulsion Polymerization and Emulsion Polymers (Editors: P. A. Lovell and M. S. El-Aaser), J. Wiley & Sons (1997). p. 104 (1997).
U.S. Pat. No. 4,302,558 and U.S. Pat. No. 4,384,078 relate to antistatic graft copolymers obtained by graft-polymerizing a vinyl or vinylidene monomer onto a rubber trunk polymer which comprises a polyalkylene oxide monomer comprising 4 to 500 alkylene oxide groups together with an ethylenic unsaturation, and a conjugated diene and/or an alkyl acrylate. However, as shown in the examples below, the graft copolymers are unsuitable for glove making by coagulant dipping processes.
SUMMARY OF THE INVENTION
Unexpectedly, this invention demonstrates that blends of certain PEG-containing latexes, solutions or dispersions with typical glove-making latexes or dispersions are suitable for making gloves and other articles by coagulant dipping processes. Also unexpectedly, certain PEG-containing latexes, solutions or dispersions are suitable for making gloves and other articles by coagulant dipping processes even in the absence of said typical glove-making latexes or dispersions. Further, articles made from the compositions of this invention are inherently static dissipative and will not bloom, rub-off or extract during use. In particular, articles such as gloves made from the compositions of this invention, and that meet ASTM examination standards for target tensile and elongation properties, will also have a surface resistivity value below 1×10
11
ohms/square per square, a static decay time of less than 1 second, or both.
The materials of the present invention suitable for making antistatic articles by coagulant dipping processes are blends of (A) one or more step (1) polymers (in latex, solution or dispersion form) of (a) at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transformation, (b) optionally, one or more ethylenically unsaturated monomers having at least one carboxylic acid group, and (c) optionally, one or more free radically polymerizable comonomers, and (B) one or more step (2) other polymer latexes or dispersions of such polymers as natural rubber, conjugated-diene-containing polymers, hydrogenated styrene-butadiene triblock copolymers, chlorosulfonated polyethylenes, ethylene copolymers, acrylic and/or methacrylic ester copolymers, vinyl chloride copolymers, vinylidene copolymers, polyisobutylenes, polyurethanes, polyureas, and poly(urethane-urea)s. The term “free-radical transformation” means being capable of reacting by a free-radical mechanism, examples including free-radically polymerizable monomers, chain transfer agents, or chain terminating agents.
Also suitable for making antistatic articles by coagulant dipping processes, even in the absence of said step (2) other polymer latexes or dispersions, are step (1) polymers (in latex, solution or dispersion form) of (a) at least one reactive macromer of at least one alkylene oxide having at least one functional group capable of free-radical transf
Bialke Julie Vaughn
Canady John B.
Hsu Shui-Jen Raymond
Lubnin Alexander V.
Masler, III William F.
Dunlap Thoburn T.
Hudak, Shunk & Farine Co. LPA
Noveon IP Holdings Corp.
Zalukaeva Tatyana
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