Nitrile rubbers

Abstract

An improved polymerization and work-up process makes it possible to produce specific nitrile rubbers which have a particular ion index which is responsible for an excellent vulcanization rate and leads to vulcanizates having an advantageous property profile.

Description

FIELD OF THE INVENTION[0001]The invention relates to a nitrite rubber, a process for producing it, vulcanizable mixtures based on this nitrite rubber, also a process for producing vulcanizates from these mixtures and the vulcanizates obtained in this way.BACKGROUND OF THE INVENTION[0002]For the purposes of the present invention, nitrite rubbers, also referred to as “NBRs” for short, are rubbers which are copolymers or terpolymers of at least one α,β-unsaturated nitrite, at least one conjugated diene and optionally one or more further copolymerizable monomers.[0003]Such nitrile rubbers and processes for producing such nitrite rubbers are known, see, for example, W. Hofmann, Rubber Chem. Technol. 36 (1963) 1 and Ullmann's Encyclopedia of Industrial Chemistry, VCH Verlagsgesellschaft, Weinheim, 1993, pp. 255-261, This publication gives no indication as to whether and if appropriate how the vulcanization rate of such rubbers and the property profile, in particular the value of the modul...

AI Technical Summary

Benefits of technology

[0025]It was therefore an object of the present invention to provide a process which gives nitrite rubbers which allow fast initial and full vulcanization in subsequent processing and leads to vulcanizates having a good property profile.

[0026]It has surprisingly been found that nitrite rubbers having an excellent vulcanization rate and outstanding vulcanizate properties are obtained when the emulsion polymerization is carried out using specific molecular weight regulators and at the same time the coagulation of the latex is carried out in such a way that the nitrite rubbers have a specific content of cations.

Problems solved by technology

Even small amounts of residual electrolytes rive turbid and cloudy pressed and injection-moulded parts, impair the electrical properties and increase the water absorption capacity of the finished product” (citation).

Rather, it is said that a rubber whose vulcanizate properties are not impaired and are fully satisfactory is obtained.

This is presented as surprising since it is said that impairment of the rubber properties is frequently observed when polymers are precipitated from dispersions by means of polyvalent metal ions such as calcium or aluminium ions.

However, this is undesirable and, according to the teachings of U.S. Pat. No. 4,920,176, water-soluble cationic polymers are used instead of inorganic salts in the coagulation of nitrile rubber latices for the purpose of obtaining very pure nitrile rubber.

In particular, the residue emulsifier contents of these nitrite rubbers are very low.

It is clearly pointed out here that the use of the conventional known tert-dodecyl mercaptan as regulator gives nitrite rubbers having poorer properties.

In practice, short scorch times are not always desirable, since the corresponding rubber mixtures cannot be processed reliably because of such a fast initial vulcanization.

Particularly in injection moulding, rapid initial vulcanization is not satisfactory.

However, according to EP-A-0 692 496, these measures are not satisfactory (p.