Conventionally, natural rubbers have been used as materials for products requiring flexibility such as gloves for industrial, medical and food applications, balloons and condoms. However, nitrile rubbers are rapidly replacing natural rubbers because the natural rubbers cause side effects of serious protein allergies to users. In addition, nitrile rubbers are widely used in gloves used by operators handling organic solvents, medical gloves and food gloves because of superior oil resistance. In addition, nitrile rubber products are suitable for use by medical personnel who handle sharp masses or injection needles because they are not readily perforated by injection needles as compared to natural rubber products.
Recently, many glove manufacturers are changing natural rubber glove production lines into nitrile glove production lines due to unstable supply of natural rubber and nitrile disposable gloves are increasingly used in consideration of safety.
In response to these trends, glove manufacturers aim at producing groves that are slim, but do not readily tear and thus want latexes for dip-forming enabling production of gloves with superior tensile strength.
However, when contents of gels in latexes are increased in order to improve tensile strength, gloves may be stiff upon use due to increase in modulus at 300%.
Accordingly, there is a need for methods for producing globes that do not impair workability upon glove production from compositions for dip-forming, prevent stiffness upon use due to low modulus at 300% and do not readily tear in spite of small thickness due to superior tensile strength.
Meanwhile, a pH adjustor should be further added in order to increase pH because pH at which reaction is finished in the preparation of latex is considerably low. When the pH adjuster is added in a great amount, deodorization should be further performed due to low solid content of latex, thus causing increased latex preparation cost.
In addition, when a composition for dip-forming is prepared for production of gloves, a low concentration of sodium hydroxide, potassium hydroxide or ammonia water is often added as a pH adjuster to the latex to adjust a pH range to a high level of 9 to 11. The pH of the composition for dip-forming affects tensile strength, elongation, texture and the like of produced gloves. The pH of the composition for dip-forming is not maintained and decreased in the process of producing gloves. For this reason, inevitable addition of pH adjuster is inconveniently required.
Adjustment and maintenance of pH in the process of producing latexes are essential factors affecting physical properties of gloves. Production costs can be reduced when pH can be maintained at a predetermined level while minimizing addition of pH adjuster.