Dip forming latex composition and dip formed article

The present invention relates to a dip-forming latex composition and a dip-formed article, and especially relates to a dip-forming latex composition capable to give articles having excellent tensile strength and resistance to flexing fatigue, and a dip-formed article obtained by dip-forming of the composition.

Rubber globes are widely used for homemaking, food related industry, precision industry, healthcare, etc. Conventionally, as rubber gloves having high tensile strength and excellent oil resistance, there are often used dip-formed articles obtained by dip-forming of a latex composition comprising carboxylated acrylonitrile-butadiene copolymer latex, sulfur and a curing accelerator.

For example, Patent Document 1 discloses a rubber glove (dip-formed article) obtained by dip-forming of a latex composition comprising carboxylated acrylonitrile-butadiene copolymer latex, zinc oxide, sulfur and a curing accelerator. The glove of the document exhibits good softness of touch, but has a problem of poor retention ratio of stress, so that it reduces adhesiveness to hand and finger and hardly follows the movement of the back of user\'s hand and finger while wearing it, resulting in making fine manipulation difficult.

Further, Patent Document 2 discloses a rubber glove (dip-formed article) obtained by dip-forming of a latex composition comprising a carboxylated acrylonitrile-butadiene copolymer latex, sulfur and a curing accelerator but not zinc oxide. The glove of the document exhibits good softness of touch, but has a problem of significant reduction in tensile strength.

Patent Document 3 discloses a rubber glove (dip-formed article) obtained by dip-forming of a latex composition comprising an acrylonitrile-butadiene copolymer latex containing a specific amount of carboxyl groups, a small amount of zinc oxide, a relatively large amount of sulfur and a curing accelerator. According to the document, remaining stress of the glove is 50% to 70% after 6 minutes of 100% elongation. However, it is required to stir for aging for a long time, i.e., more than 16 hours, after adding the curing accelerator to the latex to achieve the above property (remaining stress of 50% to 70%). Therefore, it deteriorates productivity.

In addition, the above-mentioned rubber gloves of Patent Documents 1 to 3 containing sulfur and a curing accelerator as essential components cause problems that odor due to sulfur brings discomfort and that the glove itself suffers coloration, which significantly lowers its commercial value, when continuing operation for a long time with wearing it.

On the other hand, it is studied to use an organic peroxide as a crosslinker as a method to obtain a dip-formed article without using sulfur and a curing accelerator. For example, Patent Document 4 discloses a dip-formed article obtained by dip-forming of a latex composition comprising an organic peroxide such as dicumyl peroxide or di-t-butyl peroxide. It is required to crosslink in a chemically inactive solvent such as melted salt, so that crosslinking reaction is performed in melted salt bath at a considerably high temperature when obtaining a dip-formed article of the document 4. Therefore, a rubber glove as the dip-formed article disclosed in the document 4 has problems of coloration due to exposure to a high temperature during production. There is another problem that low resistance to flexing fatigue causes tiny cracks in crotch of fingers in use for 2 to 3 hours for instance.

[Patent Document 1] U.S. Pat. No. 5,014,362

[Patent Document 2] WO 97/48765

[Patent Document 3] WO 00/21451

[Patent Document 4] WO 01/77210

An object of the present invention is to provide a dip-forming latex composition capable to give an article, which exhibits good softness of touch and excellent in tensile strength and resistance to flexing fatigue; and which itself hardly suffers coloration especially when the article is worn as a glove for continuous operation for a long time and is hard to reduce fitting and following characteristics to hand while wearing it; and a dip-formed article obtained by dip-forming of such a dip-forming latex composition.

To attain the above object, according to the first aspect of the present invention, there is provided a dip-forming latex composition comprising a conjugated diene rubber latex and an organic peroxide, wherein residual effective activity of the organic peroxide, defined as a ratio of organic peroxide retaining reactivity to the whole organic peroxide included in the dip-forming latex composition, is 35% or higher.

Preferably, a pH value of the latex composition is 9 or lower in the first aspect.

Preferably, 10-hour half-life temperature of the organic peroxide is 150° C. or lower in the first aspect.

Preferably, a content of the organic peroxide included in the latex composition is 0.01 to 5 parts by weight based on 100 parts by weight of solid content of the conjugated diene rubber latex in the first aspect.

Preferably, the conjugated diene rubber latex is a carboxylated nitrile rubber latex in the first aspect.

Further, according to the first aspect of the present invention, there is provided a dip-formed article obtained by dip-forming of any of the above dip-forming latex compositions.