Nitrile rubber article having natural rubber characteristics
View Patent ↗An improved process and material for making elastomeric nitrile rubber articles is disclosed. In particular, the process and material formulation can produce nitrile rubber based articles, which exhibit force-strain characteristics that are comparable to those of natural rubber latex articles, while maintaining the tensile strength properties of nitrile rubber. The process includes an accelerator composition at the pre-cure stage having a dithiocarbamate, a thiazole, and a guanidine compound. The invention also includes an elastomeric nitrile rubber product made by the process, such as examination, surgical, or work gloves.
1. A process for making an elastomeric article, the process comprising:
a) preparing a compounded carboxylated nitrile-butadiene terpolymer latex formulation containing, in terms of parts per 100 dry parts of rubber consisting of the carboxylated nitrile-butadiene terpolymer, between 0-1.5 parts of an alkali agent that provides monovalent ions and 0.5-1.5 parts of zinc oxide wherein the total combined amount of the alkali agent and zinc oxide is greater than 1.0 part per 100 dry parts of rubber, a stabilizer and, one or more accelerator from a group including a guanidine, dithiocarbamate, and optionally a thiazole compound, and adjusting the pH of the formulation to about 8.5 or higher;
b) dipping a former into said compounded carboxylated nitrile-butadiene terpolymer latex formulation rubber composition; and
c) curing said compounded nitrile-butadiene terpolymer latex formulation rubber to form said elastomeric article.
2. The process according to claim 1 , wherein said accelerator composition comprises: zinc diethyldithiocarbamate (ZDEC), zinc 2-mercaptobenzithiazole (ZMBT), and diphenyl guanidine (DPG).
3. The process according to claim 1 , wherein said guanidine, dithiocarbamate, and thiazole, are in a ratio of about 2:1:1, respectively.
4. The process of claim 1 , wherein the alkali agent is selected from potassium hydroxide, ammonium hydroxide, or the like and combinations thereof.
5. The process of claim 1 , wherein the pH is adjusted as the last step in the compounding sequence.
6. The process of claim 1 , wherein the pH of the formulation is 9-12.5.
7. The process of claim 1 , wherein the formulation is a latex containing 15-25% total solids content.
8. The process of claim 1 , wherein the article is an elastomeric glove.
9. The process of claim 8 , wherein the article has:
an elastic modulus in the range of 3 MPa to 6 at MPa at 300% stretch-elongation, and a tensile strength at break in the range of 30 MPa to 55 MPa.
10. A process for making an elastomeric article, the process comprising:
a) preparing a compounded formulation containing: (i) a carboxylated nitrile-butadiene random terpolymer latex having an acrylonitrile content of between about 17 wt. % to 45 wt. %, a carboxylic acid content of up to about 15 wt. %, and the remaining balance of the terpolymer being butadiene, (ii) in terms of parts per 100 dry parts of rubber consisting of the carboxylated nitrile-butadiene random terpolymer, between 0-1.5 parts of an alkali agent that provides monovalent ions and 0.5-1.5 parts of a metallic oxide wherein the total combined amount of the alkali agent and metallic oxide is greater than 1.0 part per 100 dry parts of rubber, (iii) a stabilizer and, (iv) one or more accelerator from a group including a guanidine, dithiocarbamate, and optionally a thiazole compound; adjusting the total solids content of the formulation to about 15 to 25%, and adjusting the pH of the formulation to about 8.5 or higher;
b) dipping a former into the compounded carboxylated nitrile-butadiene latex formulation; and
c) curing said compounded nitrile-butadiene latex formulation to form said elastomeric article.
11. The process according to claim 10 , wherein said accelerator composition comprises: zinc diethyldithiocarbamate (ZDEC), zinc 2-mercaptobenzithiazole (ZMBT), and diphenyl guanidine (DPG).
12. The process according to claim 10 , wherein said guanidine, dithiocarbamate, and thiazole, are in a ratio of about 2:1:1, respectively.
13. The process of claim 10 , wherein the alkali agent is selected from potassium hydroxide, ammonium hydroxide, or the like and combinations thereof and the metallic oxide is zinc oxide.
14. The process of claim 10 , wherein the pH is adjusted as the last step in the compounding sequence.
15. The process of claim 10 , wherein the pH of the formulation is 9-12.5.
16. The process of claim 10 , wherein the formulation is a latex containing 15-25% total solids content.
17. The process of claim 10 , wherein the article is an elastomeric glove.
18. The process of claim 17 , wherein the article has:
an elastic modulus in the range of 3 MPa to 6 at MPa at 300% stretch-elongation, and a tensile strength at break in the range of 30 MPa to 55 MPa.
19. A process for making an elastomeric article, the process comprising:
a) preparing a compounded formulation containing a blend of: (i) a first carboxylated nitrile-butadiene random terpolymer latex, (ii) a second carboxylated nitrile-butadiene random terpolymer latex, the compositional ratio ranging, respectively, from about 60:40 to about 40:60, wherein the blend of the first and second latexes have an acrylonitrile content of between about 17 wt. % to 45 wt. %, a carboxylic acid content of up to about 15 wt. %, and the remaining balance of the terpolymer being butadiene, (iii) in terms of parts per 100 dry parts of rubber consisting of the carboxylated nitrile-butadiene random terpolymer, between 0-1.5 parts of an alkali agent that provides monovalent ions and 0.5-1.5 parts of a metallic oxide wherein the total combined amount of the alkali agent and metallic oxide is greater than 1.0 part per 100 dry parts of rubber, (iv) a stabilizer and, (v) one or more accelerator from a group including a guanidine, dithiocarbamate, and optionally a thiazole compound; adjusting the total solids content of the formulation to about 15 to 25%, and adjusting the pH of the formulation to about 8.5 or higher;
b) dipping a former into the compounded carboxylated nitrile-butadiene latex formulation; and
c) curing said compounded nitrile-butadiene latex formulation to form said elastomeric article.