Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1994-08-18
1996-01-09
Cain, Edward
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525349, C08F 830
Patent
active
054830060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to processes for curing chloroprene/sulfur copolymers which do not form nitrosamines.
2. Background Art
Conventional chloroprene/sulfur-copolymers are in general made by radical induced emulsion polymerization of chloroprene (2-chloro-1,3-butadiene) in the presence of elementary-sulfur and, if required for certain applications, of a copolymerizable diene such as 2,3 dichloro-1,3-butadiene or an acrylic derivative. The highly viscous polymers so formed are plasticized by treating the latex with a peptization system. Such systems are usually based on thiurams (1) and/or dithiocarbamates (2), which are known to form carcinogenic nitrosamines (3) during processing and storing of the rubber, the compounds and the final article. ##STR1##
U.S. Pat. No. 3,984,609 to Branlard et al. describes the peptization of chloroprene/sulfur copolymers, made in the presence of a modifying agent such as iodoform or a dialkylxanthogen disulfide, by adding to alkaline latexes of such copolymers a modifying agent which is a thiol of the formula R-SH wherein R includes, amongst other groups, an arylthiazole so as to give mercaptobenzothiazole as the modifying agent. The curing systems used with these copolymers use a nitrosamine forming accelerator, i.e., 2-mercaptoimidazoline.
Nitrosamine formation with the above systems can be avoided by curing the copolymers with metal oxides alone or omission of 2-mercaptoimidazoline as an accelerator. However, in these cases there is an insufficient cure.
A goal in the rubber industry is to provide the outstanding processability of conventional chloroprene/sulfur copolymers, which use thiurams as peptizing agents, while at the same time avoiding the formation of nitrosamines. The processability of such copolymers is characterized by (1) further peptizability during compounding and curing, (2) reasonably long storage stability for safe handling and low scorch, and (3) high rate and final state of cure when cured by metal oxides only. The present invention meets this goal.
SUMMARY OF THE INVENTION
According to the present invention there is provided a process for curing a chloroprene/sulfur copolymer peptized in an alkaline dispersion by a xanthogen disulfide alone or in combination with mercaptobenzothiazole which comprises curing said copolymer in the presence of N-cyclohexyl-2-benzothiazyl-sulfenamide or mercaptobenzothiazole disulfide as an accelerator and in the absence of nitrosamine forming additives.
DETAILED DESCRIPTION OF THE INVENTION
A realistic alternative to the peptization of sulfur/chloroprene copolymers by conventional thiurams and dithiocarbamates is the use of a xanthogen sulfide (XS) added directly to the polymerization emulsion. Xanthogen sulfides (4) have the formula: ##STR2## An XS acts as a modifier during polymerization and as a peptizing agent after polymerization during ageing of the latex, by breaking down the sulfur chains of the copolymer.
For low sulfur copolymers the effectiveness of low levels of XS is significantly enhanced by mercaptans, such as mercaptobenzothiazole (5), or their alkali metal salts.
Simple alkylmercaptans are not as effective as 5 (MBT): ##STR3## A xanthogen sulfide (4) may also be added after stabilization to a latex modified only by sulfur in combination with (5) to reduce the viscosity of the copolymer. Typically, about 0.15-1.5 parts of XS per hundred parts of monomer (phm) are used, preferably 0.2-1 phm. At the low end of this range (i.e., less than 0.4), the XS is used in combination with MBT at a concentration of 0.05-0.3 phm, preferably 0.1-0.2 phm.
The Mooney viscosity of the isolated polymer and the level of ultimate peptizability are determined by the polymerization conditions, the order in which plasticizer is added, the sulfur/XS/MBT-level and the ageing conditions of the polymer latex.
Copolymers peptized as described above have different processability and cure properties than standard chloroprene/sulfur copolymers. For example, when cured with conve
REFERENCES:
patent: 4695609 (1987-09-01), Stevenson et al.
patent: 5254635 (1993-10-01), Stevenson et al.
patent: 5326828 (1994-07-01), Rowland et al.
T. L. Jablonowski, "Tetrabenzylthiuram disulfide and N-cyclohexylbis-(2-benzothiazolesulfen)amide as Alternative Accelerators to Reduce the Generation of Hazardous Nitrosamines", Paper No. 41, Presented at ACS Rubber Div. Meeting, Oct. 8-11, 1991.
Bromels Marilyn H.
Cain Edward
E. I. Du Pont de Nemours and Company
LandOfFree
Nitrosamine-free curing of chloroprene/sulfur copolymers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nitrosamine-free curing of chloroprene/sulfur copolymers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nitrosamine-free curing of chloroprene/sulfur copolymers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1303636