Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-03-12
2004-12-07
Wu, David (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S326100, C524S025000, C524S399000, C524S565000, C428S036800
Reexamination Certificate
active
06828387
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of elastomeric articles used in the medical field. In particular, the invention relates to improvements to the process of making elastomeric polyisoprene articles for medical applications.
BACKGROUND OF THE INVENTION
The manufacturing process for producing elastomeric articles from natural or synthetic rubber latex involves a curing step during which cross-linking or vulcanization through sulfur groups occurs between the polymer units. Conventional processes for making elastomeric articles from natural or synthetic latex typically involve preparing a latex dispersion or emulsion, dipping a former in the shape of the article to be manufactured into the latex and curing the latex while on the former. Desirable properties of certain elastomeric articles such as tensile strength are substantially affected by the cross-linking and curing stages of the manufacturing process.
The use of vulcanizing or sulfur cross-linking accelerator compounds in the manufacture of rubber articles is well-known. Conventional vulcanization accelerators include dithiocarbamates, thiazoles, guanidines, thioureas, amines, disulfides, thiurams, xanthates and sulfenamides. The use of vulcanization accelerators in the manufacture of polyisoprene rubber is disclosed in D'Sidocky et al., U.S. Pat. No. 5,744,552 and Rauchfuss et al., U.S. Pat. No. 6,114,469. Certain fields in which elastomeric articles are needed, such as the medical field, utilize specific types of equipment and processing techniques which accommodate the specific performance and regulatory requirements of the particular article produced.
The use of natural rubber latex in the manufacture of certain articles such as medical gloves has been associated with disadvantageous properties, such as allergic reactions believed by some to be caused by natural proteins or allergens present within the natural rubber latex and the final product. Of increasing interest in the medical field, particularly in the field of gloves, are synthetic elastomeric products and manufacturing processes which altogether reduce, or altogether avoid, the likelihood of potential adverse reactions of the user or wearer.
Synthetic elastomeric polyisoprene articles such as gloves are known and are of interest in the art as an alternative to the use of natural latex. Commercially available synthetic gloves include those elastomers composed of polychloroprene (neoprene), carboxylated acrylonitrile butadiene (nitrile), styrene-isoprene-styrene/styrene-ethylene-butylene-styrene block co-polymers, polyurethane, and polyisoprene. Polyisoprene is one of the most preferred polymers due to its chemical similarity to natural rubber as well as its physical properties such as feel, softness, modulus, elongation and tensile strength. One such polyisoprene glove is commercially available from Maxxim Medical (Clearwater, Fla.).
A majority of glove manufacturing processes are water-based dipping systems. It is known that solvent-based systems are possible for polyisoprene, although such systems are poorly suited for the manufacture and molding of elastomeric articles for medical applications. One difficulty in the field of gloves, for example, is the design of processes and materials which will produce a thin elastomeric article having desirable properties such as high tensile strength. Another disadvantage of solvent-based systems is solvent toxicity. Process and materials which would obviate or reduce the need for the use of toxic solvents while at the same time yielding a product having desirable properties for medical applications are thus still being explored.
Accordingly, there exists a need in the medical device field for improved manufacturing processes for making synthetic elastomeric articles. Especially desirable would be processes which can produce polyisoprene articles, such as surgical gloves, which possess the desirable properties found in the natural rubber counterpart, while at the same time permitting economical and cost-effective manufacturing.
SUMMARY OF THE INVENTION
Applicants have discovered a three-part accelerator composition for sulfur cross-linkable polyisoprene latex which can be used with latex in a process for making elastomeric articles having the desirable properties (e.g., tensile strength) similar to that of natural rubber but without the presence of natural rubber latex proteins and allergens. Another advantage is that the accelerator system is suitable for medical applications where thin molded elastomeric articles are required, such as gloves. Furthermore, the accelerator composition and process of the invention permits the use of a solvent-free, water-based process system, as opposed to a solvent-based process system. The resultant article has properties similar to those produced using the solvent-based system. Accordingly, the use of solvents can be reduced or avoided and solvent toxicity can likewise be avoided using the invention.
Another advantage of the invention is that conventional manufacturing equipment and most readily-available materials can be used in accordance with the invention to make the synthetic polyisoprene glove without the need for new or costly additional materials or equipment. Further, no complicated new process steps are required by the invention and the invention can be readily incorporated into existing glove making processes and systems.
Another aspect of the invention is that the compounded (or ready to use) polyisoprene latex composition formulated in accordance with the invention exhibits prolonged storage stability. For example, the pre-cure storage stability of the compounded polyisoprene latex composition (i.e., the time period prior to the use of the compounded polyisoprene latex composition in the dipping and curing stages) can extend up to about 8 days, in contrast to the typical current 3 to 5 day time period. By extending storage life of the latex, the amount of wasted latex can be significantly reduced and greater flexibility in scheduling manufacturing processes is permitted.
Yet another advantage is that the process of the invention allows for significantly reduced pre-cure process parameters (lower temperature and shorter time periods than conventionally used) and lower dipping temperatures in the manufacturing process. Accordingly, significant cost and resource advantages are provided over conventional manufacturing practices.
The invention provides for a process of making a synthetic elastomeric polyisoprene article comprising the steps of: a) preparing a compounded polyisoprene latex composition containing an accelerator composition containing a dithiocarbamate, a thiazole and a guanidine compound; b) dipping a former into said compounded polyisoprene latex composition; and c) curing said compounded polyisoprene composition on said former. Additionally, the initial pre-cure processing (i.e., prior to storage and article manufacture) can be performed at temperatures of less than 35° C. and in time periods as short as ranging from about 90 minutes (1.5 hours) to about 150 minutes (2.5 hours), preferably about 120 minutes (2.0 hours). The compounded polyisoprene latex composition can be stored for periods up to about 8 days at ambient temperatures (ranging from about 15° C. to about 20° C.). Lower temperatures can be used for the latex dipping step as well.
The invention also provides for a synthetic elastomeric polyisoprene article made by a process comprising the steps of: a) preparing a compounded polyisoprene latex composition comprising an accelerator composition comprising a dithiocarbamate, a thiazole and a guanidine compound; b) pre-curing said compounded polyisoprene latex composition c) dipping a former into said compounded polyisoprene latex composition; and d) curing said compounded polyisoprene composition on said former. Elastomeric articles made by the process of the invention can exhibit tensile strengths of over 3000 psi (as measured in accordance with ASTM D412) even after as much as 7 days of latex storage prior to use in the arti
Wang Shiping
Weicheong Wong
Wenig Randell
Yeh Yun-Siung Tony
Allegiance Corporation
Hu Henry S.
Rozycki Andrew G.
Wu David
LandOfFree
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