CS265302B1 - Stabilizing composition for vulcanizates - Google Patents

Abstract

The solution relates to a stabilizing composition for vulcanizates of natural and/or synthetic rubbers, or of thermoplastic rubbers. The stabilizing composition contains 35.0 to 85.0 wt. % of 2-tert.butyl-4-/alpha, alpha'-dimethylbenzyl/-phenol and 15.0 to 65.0 wt. % of 2-mercaptobenzimidazole.

Description

(57) The solution relates to a stabilizing composition for vulcanizates of natural and/or synthetic rubbers, or of thermoplastic rubbers. The stabilizing composition contains 35.0 to 85.0 wt. % of 2-tert.butyl-4-/alpha, alpha'-dimethylbenzyl/phenol and 15.0 to 65.0 wt. % of 2-mercaptobenzimidazole.

CS 265 302 Bl

The invention relates to a stabilizing composition for vulcanizates of natural and/or synthetic rubbers, or of thermoplastic rubbers, containing 2-mercaptobenzimidazole and 2-tert.butyl-4-[alpha, alpha']-dimethylbenzyl]phenol.

Current demands for the protection of rubber products - white or colored vulcanizers against thermo-oxidative degradation during their exploitation - are provided predominantly by phenolic antioxidants. Types such as styrene phenol, 2,6-ditert.butyl-4-methylphenol, etc., however, do not provide the desired stabilizing effect, since they are mononuclear phenols with low molecular weight. A significantly higher effect is recorded with 2-tert.butyl-4-cumylphenol (CS 235 169) or 2,4-dimethyl-6-/1-methylcyclohexyl/phenol. Polynuclear phenols are characterized by the relative highest efficiency in terms of thermo-oxidative stability. In industrial rubber practice, structures - the so-called bisphenols - have become established, of which e.g. 2,2'-methylene-bis/4-methyl-6-tert.butyl/phenol, 2,2-isobutylidene-bis/4,6-dimethyl/phenol, or 4,4'-thiobis/3-methyl-6-tert.butyl/phenol, etc. (P. caučík et al.: Přísady do plastov, Alfa, Bratislava, 1985).

The high efficiency of these substances is, however, offset by their high price; their production is not accompanied by a high technological complexity and there is no suitable raw material base available; their application is limited by limited availability and, moreover, most of them have a negative impact on the colouring of white vulcanizates during exploitation.

Another well-known and commonly used non-coloring type of antioxidant is 2-mercaptobenzimidazole, which gives vulcanizers good resistance to the effects of oxygen and dynamic fatigue.

It is often used in combination with other agents (amines, quinolines, phenols), synergistically activating their effect (Franta I. et al.: Gumárenské suroviny, SNTL, Prague 1979).

A more feasible way to achieve improved thermo-oxidative stability of vulcanizates and thus a longer product life is to use the synergistic effect of two or more components of the stabilization system, showing effects that differ from the expected additivity of their action. This concerns not only combinations of thermal stabilizers and antioxidants, but also mixtures of additives of the same class, while the synergistic effect is being studied and sought with particular interest as a prerequisite for reducing stabilization costs and extending the product life during their exploitation as a result of higher resistance to thermal and thermo-oxidative aging.

Common and known combinations with synergistic effects for the protection of polyolefins are, for example, substituted phenols and esters of propionic acid, benzophenones and esters of phosphorous acid, for the protection of polyvinyl chloride, for example, antimony stabilizers and esters of phosphorous acid, substituted hydroxybenzothiazoles and Ni-sol of phosphorous acid. US 3,535,249 discloses an antioxidant mixture for polymers, which consists of a phenolic antioxidant, further a neutralizer neutralizing the action of heavy metals and a reducing agent, CS 165,480 and CS 244,977 protect a synergistic combination of styrenated phenol with 2-mercaptobenzimidazole.

The most important requirements for a given ingredient are good processability and solid storage stability due to the high current demands for work hygiene and problem-free handling of the product.

It has now been found that the above claims include a stabilizing composition for vulcanizates of natural and/or synthetic rubbers, or of thermoplastic rubbers, comprising 2-mercaptobenzimidazole and 2-tert.butyl-4/alpha, alpha'-dimethylbenzyl/phenol according to the invention.

The essence of the invention lies in the fact that the stabilizing composition contains 35 to 85% by weight of 2-tert.butyl-4-/alpha, alpha'-dimethylbenzyl/phenol and 15 to 65% by weight of 2-mercaptobenzimidazole. If necessary, it can be modified with a suitable inert filler at an active substance content of 50 to 80% by weight. The polymer substrate is added in an amount of 0.3 to 5.0, preferably 1.0 to 3.0 parts by weight of the stabilizing composition per 100 parts by weight of rubber.

The use of the stabilizing composition according to the invention has many advantages. Since it is a solid substance, or in the case of an already produced mixture, a semi- or fully automatic mixing system can be used for the preparation of raw rubber mixtures, which significantly improves the hygiene of the working environment.

By combining two components - readily available stabilizers, it is possible to obtain a stabilizing composition with higher efficiency than in the case of the previously used binary combination according to CS 265 480 or 244 977 and significantly higher than when using the components alone. By applying the stabilizing composition, vulcanizates with increased resistance to thermo-oxidative aging are obtained.

The stabilizing composition according to the invention exhibits a significantly higher effect on improving the dynamic properties of vulcanizates than the previously used binary combination and commonly used bisphenols.

When using the stabilizing composition according to the invention, the original color shade of white or light colored vulcanizates is preserved even after aging under the influence of light, in contrast to the negative effect of bisphenols.

From the point of view of practical application, it is possible to prepare a mixed stabilizer in powder form, which is more effective than the aforementioned bisphenols.

The stabilizer composition can be applied to the polymer substrate or through individual components in the appropriate ratio, adapted to the given substrate, or as a mixed antidegradant at a constant ratio of both components - alone, or in combination with another antidegradant.

The stabilizer composition is applied together with other conventional additives for polymeric materials, and is incorporated into the rubber mixture using conventional processing methods like other additives.

The properties of raw rubber mixtures and vulcanizates were monitored and evaluated by common tests used in the technology of polymer materials, according to valid ČSN.

The examples given illustrate, but do not limit, the subject matter of the invention.

Example 1

Stabilizing compositions were prepared from 2-mercaptobenzimidazole and 2-tert-butyl-4-[alpha, alpha'-dimethylbenzyl]phenol according to Table 1.

Table 1

Stabilizing composition 1 2 3 4 5 6 2-mercaptobenzimidazole 0 20 40 60 80 100 (¾ weight) 2-tert.butyl-4-/alpha, alpha'-dimethylbenzyl/phenol (% wt.) 100 80 60 40 20 0

A vulcanizate of the following composition (parts by mass) was prepared from natural rubber:

natural rubber, type SMF-L 100 zinc oxide 10 titanium dioxide 10 stearic acid 1 light mineral filler 60 sulfur 2.5 tetramethylthiuram disulfide 0.5 which was stabilized with 2.0 parts by weight of the stabilizing composition according to Table 1 and pressed to the optimum at 145 °C.

The aging process of the vulcanizates prepared and stabilized in this way was monitored based on the change in the basic tensile and physical-mechanical properties of the test specimens in a stream of hot air at a temperature of 90 °C using the method according to ČSN 62 1511 for 1 to 7 days.

Since the properties that changed most significantly during thermo-oxidative aging of natural rubber were the tensile strength as a critical value and then elasticity, these are listed in Table 2 as the time required for the strength to decrease to half its value (half-life of strength) and as the maximum change in elasticity.

Table 2

Thermo-oxidative aging of vulcanizates (90 °C)

Monitored parameter Unstabilized Vulcanizate stabilized with stabilizing comp.

2 3 4 5 6

half-life of tensile strength, ^t 50,s (days) 1.0 1.5 2.3 3.6 3.0 2.1 1.7 change in elasticity after 7 days of aging (%) 32 15 13 9 10.0 15 18

The synergistic effect began to manifest itself at a ratio of components of 1:4 (4:1), while it was most pronounced in the interval 3:2 (2:3).

Example 2 □ To the vulcanizate of the composition according to Example 1, the following stabilizing compositions were added in an amount of 1.5 parts by weight:

7. 45% wt. 2-mercaptobenzimidazole + 55 i wt. 2-tert,butyl-4-/alpha, alpha'-dimethylbenzyl/phenol

8. 2,2'-methylene-bis/4-methyl-6-tert.butyl/phenol

9. 2,2'-isobutylidene-bis/4,6-dimethyl/phenol

10. 2,2'-methylene-bis/4-methyl-6-cyclohexyl/phenol

11. mixed stabilizer, consisting of styrenated phenol and 2-mercaptobenzimidazole in a ratio of 7:3

The results of thermo-oxidative aging, dynamic fatigue and whiteness change after exposure to UV radiation are presented in Tables 3, 4 and 5.

Table 3

Thermo-oxidative aging of vulcanizates (70 °C)

Monitored parameter Unstabilized Vulcanizate stabilized with stabilizing composition

7 8 9 10 11 half-life of tensile strength ^t 50,s (days) 13 24 23 20 19 18 half-life of elasticity ^t 50, (days) 17 27 26 22 20 21 ) u Ϊ k a 4 Dynamic fatigue of stabilizers Monitored parameter Unstabilized Vulcanizate stabilize . stabilizing composition 7 8 9 10 11 Crack growth 2 to 12 mm according to de Mattia (kc) 21 58 46 42 49 40 dtto after aging 7 days 170 °C (kc) 15 44 30 35 33 31 The tables show that vulcanizate most effectively protects i stabilizing composition No. > u 1 k a 5 Change in whiteness of vulcanizates after UV exposure radiation (Leucometer, % MgO) Exposure time (h) Unstabilized Vulcanizate stabilize . stabilization by composition 7 8 9 10 11 0 1 74 75 73 74 75 75 5 68 68 66 64 62 67 20 63 62 59 57 57 59

The vulcanizate containing the subject stabilizing composition, with the degree of coloration acquired after exposure under a UV radiation source, does not differ from the degree of coloration of the unprotected vulcanizate.

Example 3

Vulcanizate, prepared from chloroprene rubber according to the recipe (parts by weight) chloroprene rubber, type WRT ...................... 100 stearic acid ...................................... 0.5 zinc oxide ...................................... 5 magnesium oxide ...................................... 4 titanium dioxide ..................................... 10 kaolin .............................................. 90 paraffin ................................................ 3

2-mercaptoimidazoline ................................ 1

2,2'-dibenzothiazoledisulfide .......................... 0.5 and stabilized by 3 mass, with parts of stabilizers no. 12, 13 and 14, was prepared by pressing to the optimum at 160 °C.

Stabilizer

12. 4,4'-thiobis-[3-methyl-6-tert.butyl/phenol

13. 2,2'-methylene-bis/4-methyl-6-tert.butyl/phenol

14. Stabilizing composition: 50% 2-mercaptobenzimidazole and 50% 2-tert.butyl-4-[alpha, alpha'-dimethylbenzyl]phenol.

The results of thermo-oxidative aging are shown in Table 6.

Table 6

Properties of vulcanizates with various stabilizers

Parameter Vulcanizate not stabilized stabilized with stabilizer

12 13 14 residual ductility (%) exposure 120 °C, 40 86 82 87 1 day 3 days 15 57 69 68 5 days 10 38 48 49 7 days 5 23 28 32 crack formation - for- 3.2 6.6 7.5 22.6

lapping according to de Mattia, (kc)

The vulcanizate containing the stabilizing composition 14 does not differ in degree of coloring from the degree of coloring of the unprotected vulcanizate.

Example 4

Acrylonitrile rubber vulcanizate according to the recipe, parts by weight:

acrylonitrile rubber ....................... 100 stearic acid ............................ 0.5 zinc oxide ............................... 5 carbon black, type GPF .............................. 50 tetramethylthiuram disulfide ................... 4

2-mercaptobenzothiazole ........................ 1 and containing 1.0 part by weight of stabilizers 14, 15 and 16, was prepared by pressing to the optimum at 160 °C.

Stabilization system used

15. Mixed stabilizer consisting of styrenated phenol and 2-mercaptobenzimidazole in a ratio of 7:3

16. Mixed stabilizer consisting of styrenated phenol and 2-mercaptobenzimidazole in a ratio of 9.9:3.8

14. From example 3

Table 7

Thermo-oxidative aging of vulcanizates, GEER 130 °C, 1 to 10 days

Parameter Stabilization system

16 14 half-life of tensile strength, 6.0 6.25 7.75 ^t 50.S (days) half-life of ductility, ^(days) 3.0 3.5 4.8

Claims (3)

OBJECT OF THE INVENTION Stabilizing composition for vulcanizates of natural and / or synthetic rubbers / thermoplastic rubbers, based on 2-mercaptobenzimidazole and 2-tert-butyl-4- (alpha, alpha'-dimethylbenzyl) phenol, characterized in that it contains 35.0 to 85.0 wt. % Of 2-tert-butyl-4 [alpha], [alpha] -dimethylbenzyl] phenol and 15.0 to 65.0 wt. 2-mercaptobenzimidazole.