CS265302B1 - Stabilizing agent for vulcanizates - Google Patents

Abstract

The solution concerns stabilization compositions for natural vulcanizates and / or synthetic rubbers of thermoplastic rubbers. Stabilization the composition comprises 35.0 to 85.0 wt. 2-tert-butyl-4- (alpha, alpha'-dimethylbenzyl) - % phenol and 15.0 to 65.0% by weight. 2-mercaptobenzimidazole.

Description

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

CS 265 302 Bl

The invention relates to a stabilizing composition for vulcanizates of natural and / or synthetic rubbers, optionally of thermoplastic rubbers, comprising 2-mercaptobenzimidazole and 2-tert-butyl-4- (alpha, alpha) dimethylbenzyl) phenol.

Current demands on the protection of rubber products - white or colored vulcanisers against thermo-oxidative degradation during their exploitation - are largely ensured by phenolic antioxidants. Types such as. styrene phenol, 2,6-di-tert-butyl-4-methylphenol, and the like. however, they do not provide the desired stabilizing effect as they are low molecular weight mononuclear phenols. Significantly higher effects were reported with 2-tert-butyl-4-cumylphenol (CS 235 169) and 2-tert-butylphenol. 2,4-dimethyl-6 / l-methylcyclohexyl / phenol. The relative highest efficiency in terms of thermo-oxidative stability is characterized by polynuclear phenols. In the industrial rubber industry, structures have become established. biesphenols, of which a more prominent position occupy e.g. 2,2'-methylene-bis (4-methyl-6-tert-butyl) phenol, 2,2-isobutylidene-bis (4,6-dimethyl) phenol, respectively. 4,4'-thiobis (3-methyl-6-tert-butyl) phenol, and the like. (caučík P. et al .: Additives for Plastics, Alfa, Bratislava, 1985).

However, the high efficiency of these substances is outweighed by their high cost, a suitable raw material base is not available for their production, despite their high technological demands, their application is limited by limited availability and most of them negatively affect the coloring of white vulcanizates during exploitation.

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

It is often used in combination with other agents (amines, quinolines, phenols) and synergistically activates their effect (Franta I. et al .: Rubber raw materials, SNTL, Prague 1979).

A more viable way to achieve improved thermo-oxidative stability of the vulcanizates and thus a longer product life is to utilize the synergistic effect of two or more components of the stabilizing system exhibiting effects that differ from the expected additivity of their action. It is not only a combination of heat stabilizers and antioxidants, but also a mixture of ingredients of the same class, with a particular interest in researching and a smooth synergistic effect as a prerequisite for reducing the cost of stabilizing and extending product lifetime when exploited due to higher resistance to heat and thermo-oxidation. aging.

Common and known combinations with synergistic effects for the protection of polyolefins are e.g. substituted phenols and acid esters. propionic acid, benzophenones and esters of acid. phosphorous, for the protection of polyvinyl chloride e.g. antimony stabilizers and acid esters phosphorous phosphate, substituted hydroxybenzothiazoles and N-acid. phosphorous acid. US 3,535,249 discloses an antioxidant blend for polymers consisting of phenolic antioxidants, another heavy metal neutralizing neutralizer and a reducing agent; CS 165 480 and CS 244 977 protect the synergistic combination of styrenated phenol with 2-mercaptobenzimidazole.

Good workability and solid shelf life are also most required of the additive due to high current demands on work hygiene and trouble-free product handling.

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

The stabilizing composition comprises 35 to 85 wt. % Of 2-tert-butyl-4- (alpha, alpha'-dimethylbenzyl) phenol and 15 to 65 wt. 2-mercaptobenzimidazole. If desired, it can be treated with a suitable inert filler with an active compound content of 50 to 80% by weight. 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 is added to the polymer substrate.

The use of the stabilizing composition of the invention has many advantages. Because they are solids, respectively. in the case of an already manufactured solids mixture, a semi- or fully automatic weighing system can be used to prepare the raw rubber mixtures, thereby substantially improving the hygiene of the working environment.

By combining two components - readily available stabilizers, a stabilizing composition can be obtained with a higher efficiency than the previously used binary combination according to CS 265 480 or 244 977 and significantly higher than the components alone. By applying the stabilizing composition, vulcanizates are obtained with increased resistance to thermo-oxidative aging.

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

The use of the stabilizing composition of the invention preserves the original color shade of white or light colored vulcanizates even after aging by light exposure, as opposed to the negative effect of bisphenols.

For practical purposes, it is possible to prepare a mixed stabilizer in powder form that is more effective than the bisphenols mentioned.

The stabilizer composition may be applied to the polymer substrate or through the individual components in an appropriate ratio, by adapting to the substrate, or as a mixed antidegradant at a constant ratio of the two components alone, optionally in combination with another antidegradant.

The stabilizer composition is applied together with other conventional additives for polymeric materials, incorporating it into the rubber mixture by conventional processing techniques as other additives.

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

These examples illustrate but do not limit the scope of the invention.

Example 1

The stabilizing compositions of Table 1 were prepared from 2-mercaptobenzimidazole and 2-tert-butyl-4- [alpha, alpha'-dimethylbenzyl] phenol.

Table 1

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

A vulcanizate of the following composition (parts by weight) 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 has stabilized 2.0 wt. parts of the stabilizing composition according to Table 1 and pressed to the optimum at 145 ° C.

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

Because the properties that were most noticeable during thermo-oxidative aging of natural rubber were tensile strength as a critical and additional elasticity, these are shown in Table 2 as the time required to decrease the strength to half (half-life) and as the maximum change in elasticity .

Table 2

Thermo-oxidative aging of vulcanizates (90 ° C)

Endpoint Unstabilized Vulcanizate stabilized by stabilizing comp.

1 2 3 4 5 6

half 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 started to show itself in the ratio of components 1: 4 (4: 1), with the most pronounced in the interval 3: 2 (2: 3).

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

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

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

9. 2,2'-Isobutilidene-bis (4,6-dimethyl) phenol

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

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

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

Table 3

Thermo-oxidative aging of vulcanizates (70 ° C)

Endpoint Unstabilized Vulcanizate stabilized. with a stabilizing composition

7 8 9 10 11 half tensile strength ^t 50, s (days) 13 24 23 20 19 18 half life elasticity ^t 50, (days) 17 27 26 22 20 21 ) u Ϊ k and 4 Dynamic fatigue of atabilisates Monitored parameter volatile vulcanized stabilize . with a stabilizing composition 7 8 9 10 11 Crack growth 2 to 12 mm according to de Mattia (kc) 21 58 46 42 49 40 7 days after aging 170 ° C (kc) 15 44 30 35 33 31 The tables show that vulcanizate most effectively protects i Stabilization composition no. > u 1k and 5 Change in whiteness of vulcanizates after exposure to UV Žiaran (Leukometer,% MgO) Exposure time (h) volatile vulcanized stabilize . stabilizing 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

A vulcanizate containing the present stabilizing composition having a degree of coloration obtained after exposure under a UV source does not distinguish it from that of the unprotected vulcanizate.

Example 3

Vulcanizate, prepared from chloroprene rubber according to recipe (parts by weight) chloroprene rubber, type WRT ............................... 100 acid. Stear ...................................... 0,5 Zinc oxide ...... ................................. 5 magnesium oxide .............. ........................ 4 titanium dioxide ....................... .............. 10 kaolin .................................. ........... 90 paraffin .................................... ......... 3

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

2,2'-dibenzothiazole disulfide ................................ 0.5 and stabilized by 3 wt. 12, 13 and 14, was prepared by compression molding 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 different stabilizers

Parameter Non-stabilized vulcanizate stabilized by stabilizer

12 13 14 residual elongation (%) 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 cracks - pre- 3.2 6.6 7.5 22.6

Lamination according to de Mattia, (kc)

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

Example 4

Acrylonitrile rubber vulcanizate according to recipe parts by weight:

acrylonitrile rubber ....................... 100 stearic acid ...................... ...... 0,5 zinc oxide ............................... 5 carbon black, type GPF ... ........................... 50 tetramethylthiuram disulphide ................... 4

2-mercaptobenzothiazole ........................ 1 and containing in each case 1.0 part by weight of stabilizer 14, 15 and 16, was prepared by pressing into the optimum at 160 [deg.] C.

Stabilization system used

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

16. Mixer stabilizer consisting of styrene phenol and 2-mercaptobenzimidazole in the ratio 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 tensile half life, 6.0 6.25 7.75 ^t 50, S (days) ductility half, ^ (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.