CS272924B1 - Curing system for rubber latex - Google Patents

Abstract

The production of dipped articles from rubber latex requires a short period of curing without using pressure and a relatively low temperature. Often it is necessary to pre-cure the latex mixture prior to processing to the given level of cross-linking so that, during processing at the given temperature and time, curing occurs to the required level. Pre-curing requires installation of storage tanks or boilers with energy feed and maintenance. The problem is solved with a curing system of latexes with higher speed and more effective curing. Per 100 mass parts polymer the system contains 0.l to 5 mass parts sulphur and 0.5 to 3 mass parts of a synergic mixture of accelerators based on tiuram disulphides and salts of dithiacarbamanes and/or mercaptobenzothiazoles. The mutual ratio of the compound of tiuram disulphide and compound containing the salt of dithiacarbamane and/or mercaptobenzothiazole is 3:7 to 7:3.

Description

The present invention relates to a rubber latex vulcanization system having a higher vulcanization rate and efficiency.

Of rubber latexes, which are naturally synthetic; are mainly produced thin-walled products - dipped goods, or products of low density - foam rubber. In these technologies, a short vulcanization time without applying pressure at a relatively low temperature is required. Therefore, accelerators from the group of fast and ultra-fast are used for sulfur vulcanization. In particular, they are the zinc salts of alkyl or aryldithiocarbamic acid; mercaptobenzothiazole either alone or in combination.

However, they are very fast accelerators; it is often desirable to pre-vulcanize the latex mixture (especially based on natural rubber) to a certain degree of cross-linking prior to processing so that vulcanization to a desired degree occurs at a certain temperature and time. Pre-vulcanization It is carried out in practice either by latexing the mixture for several hours to dnif or by pre-vulcanizing the mixture discontinuously in heated boilers for several hours. In the first case, the procedure requires the installation of additional storage tanks / in the second case of boilers requiring energy supply and operation. In addition, only latices stabilized by special and relatively expensive stabilizers can be processed. * In both cases, however, the need for pre-vulcanization imposes a burden on production by the need for additional equipment / labor and, above all, time.

Partial solutions to the problem of rapid vulcanization of rubber latexes are offered by the USSR Authorized Certificate 705,425. parts per ICO wt. 1 parts by weight of polyisoprene accelerator of the tiuram type; parts / optionally other accelerators and as a secondary accelerator diphenylfluoroacrylate * SmS3 vulcanizes rapidly; vulcanizates have increased strength and heat resistance. The major disadvantage of this solution, however, is the health aspect: products from a mixture containing thiourea are not suitable for contact with the human organism.

The disadvantages of these solutions are overcome by the vulcanization system of rubber latexes with a higher rate and efficiency of vulcanization according to the invention. The principle of the solution consists in that the vulcanization system contains per 100 wt. parts of polymer 0/1 to S wt. parts of sulfur and 0/5 to 3 wt. parts of a synergistic mixture of thiuram disulfide accelerators and a salt of dithiocarbamates and / or mercaptobenzothiazoles; wherein the ratio of component and component containing disulphide salt ditiokarbamanů and / ebo mercaptobenzothiazole _n is 3 to 7 to 7: 3. It is preferred to use tetrametyltiuraradisulfidu; zinc diethyldithiocarbamate and / or zinc mercaptobenzothiazole salts.

An advantage of the rubber latex vulcanization system of the present invention is that it achieves the desired degree of crosslinking while maintaining the temperature and vulcanization time without the need to pre-vulcanize the latex mixture. In addition, the sulfur dosage can be reduced in the mixture (since sulfur from tiuram disulfide is also involved in crosslinking).

The following example illustrates the invention.

An example of a natural rubber latex based composition with a sulfur content of 1 parts by weight per 100 parts by weight. Different types of accelerators and combinations thereof were mixed in the polymer parts. The composition of the individual mixtures (labeled A to H) is given in Table 1.

Table 1

Latex of natural rubber (dry matter content

166/5 165/5 166/5 166/5 16S / 5 166/5 166/5 166/5

CS 272 924 Bl

Continuation of Table 1

AND (B) C 0 E F G H Sodium ketylbisnaphthalenesulfonate 0.08 0/08 0; 08 0.08 0; 08 0.08 0/08 0; 08 Sulfur 1 1 1 1 1 1 1 1 Oietylditiokarbaman zinačnaté 1 - - - 0.5 - 0.5 ·· Fanyletylditiokarbaman zinc - 1 - - 0.5 - - Tetramethylthiuram- dioulfid - - 1 - 0.5 0/5 - 0/5 Zn-merkeptobenz- thiazole - and" 1 «· «· 0.5 0.5

The individual blends were vulcanized at 80 and 110 ° C. The degree of vulcanization was expressed by volume fraction of the rubber in the sample in toluene zbotnalóm - designation V ₂ «during cure was evaluated on the V ₂ at the time of vulcanization. Oak's rate of attainment of the vulcanized state was taken at the time at which 30% of the cross-linking was obtained - labeled ιθθ. The maximum degree of amplification is indicated by V _{2 raax <}

The results are shown in Table 2.

Table 2

Mixture AND (B) C 0 E F Vuikanizace při 80 ° C ^v 2 max. 0/138 - - 0/164 ^t 90 /min./ 70 > 90 »90 »90 50 > 90 Vulcanization at ^V 2 max. 1 0/150 0/104 aa - 0,160 0/130 110 C ^t 90 /min./ 12 11 »90 9/0 13/0 Further results are shown values in, depending 2 O8X « on time vulcanization 30, 60 / evant. 90 min at 80 and 110 ° C in the following table 3. Table 3 Mixture AND (B) C 0 E F G H temperature vulkani- zace time min 30 o; o8o 0/058 0/045 0/045 0/101 0/045 0,045 0/045 80 ° C 60 O; 126 0,087 0/045 0/045 0/1? 6 0/074 0/068 0/118 90 0/138 0/098 0/045 0/045 0/164 0/104 0,070 0/151 30 0/146 0/099 0/045 0/045 0/157 0,126 0.119 0/144 Mp 110 ° C 60 0/138 0/086 0/045 0/045 0.154 0/118 0/110 0/142 90 0/132 0/075 0/045 0/045 0/154 0,110 0/094 0.138

* i

CS 272 924- Bl

The results show that mixtures with the addition of tetramethylthiuramide amide exhibit higher vulcanization rates as well as a faster vulcanization (mixture A, Ej especially 3 mixture D; H). When applying tetramethylthiuram disulfide, the reversal at 110 ° C is lower / than using a single accelerator. In terms of speed / efficiency and cost, the combination of zinc diethyldithiocarbamate and tetramethylthiuram disulfide (mixture E) has the most beneficial effect.

Claims (2)

SUBJECT OF THE INVENTION A rubber latex vulcanization system having a higher vulcanization rate and efficiency, characterized in that it contains 0> 1 to 5 parts by weight of sulfur and 0.5 to 3 parts by weight of a synergistic mixture of thiuram disulfide accelerators and dithiocarbamates salt per 100 parts by weight of polymer; or mercaptobenzothiazoles, wherein the ratio of the tiuram disulfide component to the diocarbamate salt component and / or the mercaptobenzothiazole component is between 3 and 7 to 7: 3. 2. The latex vulcanization system of claim 1 wherein the synergistic accelerator mixture comprises tetramethylthiuram disulfide; zinc diethyldithiocarbamate and / or zinc salt of mercaptobenzothiazoles »