Coating processes – Medical or dental purpose product; parts; subcombinations;... – Fluid barrier or fluid transporting product – other than...
Reexamination Certificate
1995-08-30
2002-05-07
Wilson, Donald R. (Department: 1713)
Coating processes
Medical or dental purpose product; parts; subcombinations;...
Fluid barrier or fluid transporting product, other than...
C428S035200, C428S446000, C428S447000, C428S484100, C428S492000, C002S161700
Reexamination Certificate
active
06383552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention pertains to a sulphur free prevulcanized rubber latex, and to a method of producing same and articles produced therefrom. More particularly, the present invention pertains to a method of manufacturing sulfur-free, natural rubber latex and for forming same into thin walled articles such as gloves so that the resulting articles are not chemically reactive with other substances which may be contacted by the articles during subsequent use, and so that the articles are otherwise completely safe for substantially any application, including those involving with humans.
2. Description of Relevant Art
Rubber is a very common compound. It is available in many different compositions and forms such as rubber latex. In conventional processes for forming rubber, or for forming products from rubber, rubber is cured or vulcanized so as to join the modules within the rubber composition together giving the rubber composition desired strength and toughness. Most typically sulphur or sulphur donating compounds are used as the primary curing or vulcanizing agents.
For example, there are many publications available, including publications by Uniroyal, Vanderbilt and Monsanto describing start-formulas or for sulphur-cure natural rubber systems. Typically, these formulas will include sulphur or a partial substitute of sulphur such as TMTD, DIAK and Sulfasan (partial substitutes of sulfur being preferred especially when controlled release of available sulphur is required), a zinc-based cross linking agent such as zinc dithiocarbamate (ZDBC) and zinc diethylcarbamate (ZDEC), cure rate accelerators (primary and secondary) such as excessive sulphur, ZDBC and sodium diethylcarbamate (SDBC), and an antioxidant which are mostly phenolic or amine compounds.
Although products formed from such sulphur-cured natural rubber exhibits some very good qualities, including strength, toughness, elasticity, etc. and are used very effectively in many applications, there are some areas of applications where compatibility problems arise due to the chemicals incorporated into the rubber which react undesirably with foreign materials contacted by products formed from the rubber during the products'subsequent use. Particularly, the sulphur, sulphur compounds, dithiocarbamate compounds, zinc and its compounds which are present on and/or in the surfaces of products formed from the rubber may react with foreign materials contacted during use of the products, resulting in contamination, fouling, spoilage or discoloration of rubber products or of the materials contacted therewith (either directly or indirectly). Additionally, nitrosamine, which is often used as an antioxidant in conventional rubber compositions or is generated by the amine compounds used as antioxidants, is believed to be carcinogenic, and hence it is undesirable to use these compounds as antioxidants where products formed from the rubber composition are likely to be contacted by humans, such as with their skin, body fluids, or in their mouths.
A specific example of a problem which has arisen due to a chemical reaction between chemicals in a conventional rubber product and a foreign material contacted by the rubber product during use is in the field of latex examination gloves. Such gloves are almost always used by persons in the medical and dental field during any procedure requiring bodily contact with a patient, such use is even required by federal and/or state laws in many instances and such gloves are also being used in many other fields. Throughout the application the term “latex gloves” refers to any type of latex glove including examination gloves, surgical gloves, and all purpose gloves.
A common procedure involved in dental examinations is the taking of an impression of a patient's upper or lower dental arch, or of one or several teeth. Such impressions are formed using a gel-like dental impression material (DIM) in a metal or plastic container which is pressed against the dental structure to obtain a negative impression of the patient's teeth or arch. Upon removal of the impression material and container from the patient's oral cavity, it is allowed to cure and harden. Once hardened, a second material such as a flowable plaster is poured into the hardened, negative impression material to obtain a positive impression of the teeth or arch. One such DIM is vinyl polysiloxane distributed by 3M under the Trademark EXPRESS™.
The dental community has recently observed a re-occurring problem in forming negative impressions from the DIM caused by chemical reaction(s) with chemicals contained on/in conventional rubber latex gloves. Specifically, after a negative impression has been obtained of the patient's dental structure, portions of the exposed regions of the DIM which had been in contact (direct or indirect) with the gloves fail to sufficiently cure and harden. Instead, those regions remain uncured and retain their gel-like consistency. This is most undesirable when attempting to subsequently form the positive impression since the uncured regions of the negative impression do not sufficiently retain and transfer the structure and surface details of the patient's teeth or arch which had been previously contacted, to the positive impression material. Regions of the DIM remain uncured because chemicals on/in the latex gloves react with and tie up the platinum base catalyst of the DIM, which catalyst normally assures rapid curing and hardening of the DIM.
Previously, applicant has proposed to overcome such glove contamination problem through post treatment of the manufactured gloves to tie up and/orbarricade the offending chemicals on/inthe gloves. Particularly, applicant has proposed to tie up the offending chemicals by treating the exterior surfaces of the latex glove with an acidic suspension of metal particles, such as relatively dilute solution of phosphoric acid (0.25-2.0 molar) with finally divided copper and/or iron particles therein. The suspension is applied to the glove exterior in any appropriate manner such as spraying, brushing, wiping, dipping, etc. after which the treated gloves are allowed to dry. Alternatively, or additionally, a water resistant (preferably insoluble) barricade coating was applied to the exterior of the gloves, including such coating materials as silicone spray, polyethylene, PVC, polysilane, octyl acrylamid, acrylate copolymer VA, chrononates, vinyl neodecanoate copolymer, ethylester of polyvinyl, nathacrylate-methylacrylate copolymer, etc.
Although such post treatments of the conventional latex gloves were usually effective for overcoming undesirable chemical reactions between chemicals of the latex gloves and foreign materials such as the DIM contacted by the latex gloves during use, the treated gloves still undesirably reacted with the DIM approximately 10% of the time and this was an unacceptable failure rate. Further, such post treatments have other problems and disadvantages associated therewith, including the additional cost involved with the post treatments, shelf life and reliability of the post treated gloves, undesired reactions of the post treatment materials with other foreign materials subsequently contacted by the gloves, etc.
The curing and vulcanization of rubber compounds may be done at various stages relative to the formation or shaping of products from the rubber compounds. For example, in the manufacture of latex gloves from latex emulsions, it is conventional to vulcanize the composition after it has been shaped into gloves (post-vulcanization process), or the latex emulsion may be vulcanized before it is shaped into the gloves (pre-vulcanization). Typically, the chemicals used for vulcanizing the rubber compositions are consumed more efficiently in pre-vulcanization processes because vulcanization occurs with respect to a large mass of material over a longer length of time. On the other hand, pre-vulcanized gloves are known to be tacky and soft in comparison to the post-vulcanized gloves,
Hau Ho Teon
Noecker Audra
Blackman William D.
Carrier Joseph P.
Carrier, Blackman & Associates, P.C
Wilson Donald R.
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