CS225360B1 - Process for limiting of the rubber compositions reversion - Google Patents

Description

The ^y n ^and lies with tiýka. . of ^p Úsobí omezern reversion of the rubber compositions based on natural rubber or blends of natural and synthetic and ^{the c} u ^k u pomorn in NYC ^h o ^{d h} polymermch additives.

It is known that during the vulcanization of rubber with ^ME with ^P ° ^{to mares} r ^i, and ^d a ^{b o} ou vu anizac ^e fyzikálněm.echanické improve properties ^of the vulcanizate, staying ^and VaJ ^{s p} o However Urch ^d at a constant and ^b then they deteriorate again. The deterioration is the result of a reversal. ^N egativnl change ^of f ^y zi ^ka lnemechanic ^to ACTIVE properties vulkarnz ^ ^ ^b as claimed by reversion of great importance for the quality parameters of the final product.

To increase the reverse stability, vulcanization systems have been established to some extent in which the sulfur content is reduced and the vulcanization accelerator content is increased. Such systems became known under n ^a m invite system ^{E Y} E ^{V P} o ^p of ^{IP de} semi-EV (Beníšků, Rosner: Plaste und Kautschuk 25 (1978) 10). However, they have a number of disadvantages. Especially in ^y with ^Ké matenálov ^{Step C O} series and in most cases require a multistage mixing. In one GDR patent 27,611 describes the use of the emulsion copolymer butadin styrene block copolymer containing 10 to 20 weight percent bound styrene, to reduce reversion of mixtures based on natural rubber or synthetic cis-1,4-polyisoprene or mixtures thereof, ^T his method is disadvantageous _ ^{characterized} in that the change of the elastomeric bases are more or less strongly influenced by the individual physician ^{AL some} mec ^h anic ^Ké vlastnosh vu ^o aniseed ^and herein.

It is therefore desirable to find a method in the ESEM ^kt Byta reversal in direction ^of sich natural rubber or blends of natural and synthetic rubber is limited and not have the abovementioned disadvantages. Toho se. achieves a method of limiting the reversion of the natural rubber-synthetic rubber blends of the present invention in which they crosslink with sulfur and vulcanization activators within 10 to ²⁴⁰ minutes at ⁴⁵³ to 373 ^{K by} adding 100 parts by weight of rubber to the rubber blend 5 ^{parts by} weight ^of ahamelytetyrenic ohomer with carbodithio groups of the general formula

HSSC -

n - CSSH wherein n is 2 to 8, preferably 4 to 6.

The mixture was investigated by Kleemann: Plaste und Kautschuk, 25 (1978) 4. The results of the experiments are shown below.

Mixture 1 vulcanization time

In the process according to the invention, natural rubber and natural rubber in admixture with synthetic polymers of conjugated dienes or copolymers of such dienes, for example 1,4-cis-polyisoprene, 1,4-cis-polybutadiene, butadiene-styrene copolymers, butadiene- acrylonitrile,

The carbodithio-alpha-methylstyrene oligomer of the above structural formula (hereafter referred to as SAMS) is a fine powder which can be easily processed into said rubber compositions on known mixing devices. It is colored pink. SAMS is effective in conjunction with conventional sulfur-based vulcanization systems. The degradation of sulfur bridges, which can be observed at longer vulcanization times for both natural and synthetic rubber, is compensated for by the partial decomposition of SAMS with simultaneous discharge of sulfur, leading to the formation of new sulfur bridges.

The SAMS additive affects the physical-mechanical properties of the resulting vulcanizates only to a small extent and mostly positively. The delay of the reversion leads to better product properties, which is interesting for many applications.

The process according to the invention is further illustrated by the following examples of a specific embodiment.

Example 1

Natural rubber mixtures were prepared on a calender according to the formulas below and the test specimens were cured in a hydraulic laboratory press under the specified conditions.

(in minutes) 30 60 120 180 tensile strength MPa L70 166 161 143 modules MPa 83 83 80 78 protažní při breakage % 485 475 480 445 impact elasticity % 58 57 57 57 Shore A hardness 58 56 55 55 Λ T 16.5 16.5 17.5 18.0 alpha 0.199 0.199 0.218 0.230 Mixture 2 vulcanization time (in minutes) 30 60 90 120 tensile strength MPa 207 181 161 155 moduiaoo MPa 81 72 60 53 protažní při breakage % 545 535 530 530 impact elasticity % 59 58 55 53 Shore A hardness 55 52 51 50 A T 16.2 18.8 22.7 25.3 alpha 0.200 0.261 0.378 0.436

As can be seen from the module U3oo, AT and alpha values, the use of SAMS causes a significant reduction in reverse.

Example 2

Here, mixtures of natural and synthetic rubber were used, and their preparation and vulcanization proceeded as in Example 1.

Mixture no. 1 2 natural rubber 100.0 100.0 soot R 300 40.0 40.0 zinc oxide 5.0 5.0 stearic acid 2.5 2.5 plasticizer SE 6.0 6.0 sulfur 2.6 2.6 sulfenamide accelerator Sulfenax CB 0.7 0.7 SAMS 5.0 -

Data are in parts by weight.

Mix No. 3 4

natural rubber 17.36 17.91 Buna cis 13.02 13.43 Buna SB 150 H 13.02 13.43 soot R 300 17.36 17.91 stearic acid 0.87 0.89 zinc oxide 2.17 2.24 sulfur 1.08 1.12 Sulfenax CB 30 0.35 0.36 plasticizer SE 2.60 2.69 SAMS 2.17 -

The effect of SAMS on the reversal delay was investigated using module 300 and heat-build-up as a function of vulcanization time at a vulcanization temperature of 145 ° C. For this the thermostability coefficient was calculated:

The reversal constant R is obtained from the function alpha = alpha ₀ + R. t. The importance of the coefficient alpha and R as the criteria for determining the reverse

The following results were obtained.

Mix No. 3 vulcanization time (in minutes) 30 60 90 180 tensile strength MPa 112 104 110 111 moduiaoo MPa 83 85 85 83 protažní při breakage ° / o 370 340 375 300 impact elasticity % 62 62 62 62 Shore A hardness 60 60 60 60 Λ T 19.7 19.2 18.5 19.2 alpha 0.237 0.226 0.213 0.231

Mix No. 4 vulcanization time

(in minutes) 30 60 120 180 tensile strength MPa 127 130 124 116 tnodulooo MPa 66 66 57 54 protažní při breakage % 475 475 500 495 impact elasticity % 60 60 56 56 Shore A hardness 56 56 54 54 Δ T 22.8 23.7 26.8 28.8 alpha 0.345 0.359 0.470 0.533

From the results, it can be seen that even with natural and synthetic rubber mixtures, the addition of SAMS causes a significant reduction in reversion.

Claims (1)

Method for limiting the reversion of natural rubber-based rubber mixtures or mixtures of natural and synthetic rubber, which are crosslinked with sulfur and vulcanization activators within 10 to 240 minutes at 453 to 373 K, characterized in that 100 parts by weight of rubber are added to the rubber mixture 2 to 5 parts by weight of an alpha-methylstyrene oligomer with carbodithio groups of the general formula.