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
2001-07-11
2004-03-16
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S193000, C525S194000, C525S196000
Reexamination Certificate
active
06706816
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to latex formulations that do not contain accelerators, thiurams, or carbamates, and also relates to methods of making such formulations and to articles made from such formulations.
BACKGROUND OF THE INVENTION
Thiurams, accelerators and carbamates in natural and synthetic latex articles have historically been associated with type IV chemical allergic reactions in humans. The likelihood of such reactions is lessened when the article goes through a pre-leach and post leach process. However, those people who are hypersensitive may still react to accelerators, thiurams and carbamates not extracted during the leaching process.
Producing dipped natural or synthetic latex products is labor intensive, time consuming and expensive. As a result, many producers experience lower profit margins. High scrap rates from articles being stuck together or to molds and compounding errors also contribute to increased manufacturing costs. The energy required to produce a product may fluctuate based on weather, inconsistencies in compounding and mechanical failures. This is also reflected in the quality of the finished product and profitability.
For the purposes of cost reduction and improved chemical resistance, many polymers are laminated or over dipped with other polymers. However, due to differences in physical properties and chemical structure these polymers do not adhere well to each other. Over dipped goods often delaminate easily when subjected to stress or upon aging. This creates hazards to the end user that relies upon the integrity of the films for protection. The manufacturer is also subjected to increased liability when product failure occurs. This problem is particularly applicable to the glove industry. Glove manufacturers often face increased scrap rates when the product delaminates in the stripping and post processing stages. To overcome this problem it is often necessary for the manufacturer to blend the polymers and then overdip. This increases operating cost and reduces the chemical resistance of the prevalent polymer.
SUMMARY OF THE INVENTION
The present invention solves the above-described problems by providing natural or synthetic latex formulations that do not include accelerators, thiurams or carbamates. As a result, type IV chemical allergic reactions associated with these compounds are prevented. In addition, the latex formulations of the present invention provide improved adhesion between dissimilar polymers used in latex articles. The latex formulation of the present invention comprises a base polymer comprising carboxylate groups, a carboxylic acid or derivatives thereof, a divalent or trivalent metal, an amine or amino compound, and a neutralizing agent in an amount sufficient to neutralize at least a portion of the carboxylate groups in the base polymer.
The method of the present invention includes making an elastomeric material by mixing a base polymer comprising carboxylate groups with a carboxylic acid or derivatives thereof, a divalent or trivalent metal, an amine or amino compound, and a sufficient amount of a neutralizing agent to neutralize at least a portion of the carboxylate groups in the base polymer. Without desiring to be bound by a theory of operation, it is believed that the carboxylic acid or derivatives thereof provides a level of carboxyl groups to crosslink with the base polymer and complex with the divalent or trivalent metal without the use of an accelerator, thiuram or carbamate. The elastomeric material is formed into a latex article.
More particularly, the base polymer is acrylonitrile and the carboxylic acid derivative is preferably ethylene acrylic acid. In addition, the divalent or trivalent metal is preferably zinc, preferably in the form of zinc oxide, and the neutralizing agent is preferably potassium hydroxide.
The method of the present invention is useful in producing various latex articles including gloves.
The present invention is also directed to an article made from an elastomeric material comprising a base polymer having carboxylate groups, a carboxylic acid or derivatives thereof, a divalent or trivalent metal, an amine or amino compound, and a neutralizing agent to neutralize at least a portion of the carboxylate groups in the base polymer. The carboxylic acid or derivative thereof provides a level of carboxyl groups to crosslink with the base polymer and complex with the divalent or trivalent metal. The elastomeric material does not contain an accelerator, thiuram or carbamate.
The elastomeric material is further characterized by preferably having a tensile strength from about 2000 psi to about 2500 psi, and a 500% modulus from about 400 psi to about 800 psi. In addition, the elastomeric material preferably has an elongation from about 600% to about 700%.
Other objects, features and advantages of this invention will become apparent upon reading the following detailed description in conjunction with the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As summarized above, the present invention is directed to improved latex formulations and to methods of making improved latex formulations and articles made there from that do not contain thiurams, accelerators or carbamates, thereby significantly reducing type IV chemical allergic reactions normally associated with natural and synthetic latex. In addition, substantial improvements in operating efficiency are realized by the utilization of lower oven temperatures in the present invention, ease of compounding and inherent strength of the resulting article when dried.
As used herein, the term “polymer” includes homopolymers, copolymers, terpolymers and modifications thereof.
The term “tensile strength” as used herein means the energy required to stretch a material to the breaking point.
The term “elongation” as used herein means the percent stretch of a material at the breaking point.
The term “500% modulus” as used herein means the amount of energy it takes to stretch a material 500% of a predetermined length.
The present invention includes an elastomeric material formed from a latex formulation containing a base polymer. The base polymer is combined with a carboxylic acid, or derivatives thereof, a divalent or trivalent metal, an amine or amino compound and a neutralizing agent. The latex formulation is based on the dry weight of the base polymer being used. The number of carboxylate groups on the base polymer will vary with the amount of unsaturated acid groups present in the polymer. The pH of the base polymer usually varies from about 8.0 to about 8.5, with a pH of 8.4 being typical. In addition, the base polymer generally has an acid number from about 4 to about 8. Typically, the acid number of the base polymer is about 6.
Examples of suitable base polymers include, but are not limited to natural latex rubber and synthetic latex polymers, such as, acrylonitrile, butadiene rubber such as synthetic butadiene rubber and carboxylated butadiene rubber, neoprene, isoprene, polychloroprene, and copolymers, blends and mixtures thereof. Preferably, the base polymer is acrylonitrile. Suitable acrylonitrile base polymers include Reichhold 68074, Reichhold 68077, DP3040 and BP2000, all available from Reichhold of Research Triangle Park, NC. Dupont neoprene 750 or 761, available from Dupont Dow Elastomers LLC of Hockessin, Del. may also be used as the base polymer in the present invention.
A neutralizing agent is used to neutralize the carboxylate groups on the base polymer. Sufficient neutralizing agent is used such that all of the carboxylate groups or only a portion of the carboxylate groups on the base polymer may be neutralized. The latex formulation preferably contains from about 0.1 to about 1.0 part neutralizing agent based on the total dry weight of the base polymer. More preferably, the latex formulation contains from about 0.2 to about 0.7 part neutralizing agent based on the total dry weight of the base polymer. The neutralizing agent is used to adjust the pH of the base polymer to between about 8.7 and about 9.2. Desirably,
Cleveland Joyce Lee
Williams William Andrus
Best Manufacturing Company
Kilpatrick & Stockton LLP
Nutter Nathan M.
LandOfFree
Accelerator free latex formulations, methods of making same... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Accelerator free latex formulations, methods of making same..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Accelerator free latex formulations, methods of making same... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3223604