CS232274B1 - Rubber compound based on natural butadiene styrene rubber - Google Patents

Abstract

SUMMARY OF THE INVENTION The present invention provides rubber compositions which, when vulcanized at elevated temperature, provide high adhesion to zinc, galvanized or zinc-containing surfaces. In addition to the adhesive additives and conventional rubber chemicals, the blend also contains a thermoreactive phenol formaldehyde resin, which substantially increases the heat-aging resistance of the rubber-metal joint. The invention can be used in the manufacture of conveyor belts with galvanized steel ropes or in the manufacture of brazed steel cord tires.

Description

The subject of the invention is a special rubber mixture based on natural rubber, butadiene-styrene rubber or their combination, ensuring its connection with a zinc, galvanized or zinc-containing surface after vulcanization of the mixture at elevated temperature.

When joining vulcanizable rubber mixtures to zinc, galvanized and/or zinc-containing surfaces, for example according to patents NDR 50 302, NDR 50 303, USSR 107 337, Canada 1 024 835, Belgium 876 349, Japan 5 4052 188, AO 222 737, cobalt complex compounds of branched organic acids with a chain of 4 to 14 carbon atoms are mixed into the rubber mixture and this rubber mixture is then vulcanized at elevated temperature onto the metal surface. By adding these cobalt compounds, a relatively very good connection of rubber with metal is achieved, however, at the dosage necessary to achieve satisfactory cohesion, the physical-mechanical values of the rubber are reduced, which is an undesirable phenomenon from the point of view of the desired properties. Another negative phenomenon in the above method of joining rubber to metal is the resistance of the joint to thermal loading, where the addition of these compounds has a negative effect on the strength of the joint after its thermal loading. In this case, cobalt compounds act as a degrader of rubber and adhesive bonds, and the use of conventional antidegradants is not very effective in this case. A significant improvement is achieved by combining cobalt compounds with resorcinol formaldehyde resin, which largely eliminates the negative effects of cobalt in conditions of higher temperatures. The condition for the application of this resin is to maintain temperatures in the range of 80 to 90 °C, both during mixing of the mixture and during its further processing. However, this condition is unfulfillable for most rubber companies, because compliance with the above temperatures is possible only on special mixing machines and processing equipment. If the specified temperature is exceeded, polycondensation of the resin occurs and this circumstance will cause the loss of the positive effects of the resin on the strength of the joint, its heat resistance, or will accelerate the setting of the rubber mixture during its preparation or processing, which is unacceptable for further technological operations.

The shortcomings of the above-mentioned types of mixtures are eliminated by using a rubber mixture based on natural rubber, butadiene-styrene rubber or their combination, containing a cobalt complex salt of an organic acid, fillers, vulcanizing agents and other conventional rubber additives, into which 2 to 15 parts by weight of a thermosetting phenol-formaldehyde resin is mixed per 100 parts by weight of rubber. The mixture prepared in this way is vulcanized at elevated temperatures on a zinc, galvanized or zinc-containing surface, thereby achieving high adhesion between rubber and metal.

When using the mixture according to the invention, the resistance of the joint to thermal aging is increased and the decrease in the physical and mechanical values of the rubber is substantially eliminated. Furthermore, the temperature limit for the preparation and processing of these rubber mixtures is significantly shifted to the range of up to 120 °C, which is a temperature that can be maintained in rubber production without increased demands on temperature control and without demands on special mixing and processing equipment.

The following examples illustrate specific embodiments of the invention.

Example

Mixtures 1, 2 and 3 were mixed from natural and butadiene-styrene rubber in a laboratory mixer. Mixture 1 was prepared without the addition of phenol-formaldehyde resin, mixtures 2 and 3 contained the resin. The mixing temperature was 1.5 °C.

The composition of the rubber mixtures was as follows:

parts by weight

Natural rubber mixture no. 1 60.0 mixture no. 2 60.0 mixture no. 60.0 Styrene butadiene rubber. 40.0 40.0 40.0 Zinc oxide 20.0 20.0 20.0 Stearic acid 1.0 1.0 1.0 Antioxidant ’,5 ’,5 ’,5 HAF carbon black 50.0 50.0 50.0 Aromatic oil 4.0 4.0 4.0 Cobalt(II) octoate 8% Co 5.0 5.0 5.0 Lead oxide ’,6 ’,6 1.6 Phenol formaldehyde resin - 5.0 5.0 Hexamethylenetetramine - 2.0 Hexamethoxymethylmelemine - - 2,’ Sulfenamide accelerator 0.8 . 0.8 0.8 Ground sulfur 2.5 2.5 2.5

Test specimens were pressed from these mixtures and galvanized steel ropes with a diameter of 5.94 mm at a temperature of 150 °C to determine adhesion using the method according to DIN 22 131 (DK 621 867 21 622 647 21). Half of the test specimens from each mixture were subjected to thermal stress in a drying oven at a temperature of 140 °C for 150 minutes, the other half of the samples were tested without thermal aging. The following average values of the resistance to rope tearing from the rubber sample were measured for the individual mixtures:

a) samples without thermal stress:

mixture number 1 mixture number 2 mixture number 3 115 N.mm” 117 N.mm ^- ' 106 N.mm ^- ' b) samples after thermal stress of 140 °C/150 minutes: mixture number 1 - 85 N.mm ^- ' i.e. decrease by 26% mixture number 2 - 106 N.mm ^- ' i.e. a decrease of 9.4% mixture number 3 - 100 N.mm ^- ' i.e. decrease by 5.7% Example 2 From natural and butadiene styrene rubber were mixed in a laboratory mixer of the following composition: parts by weight mixture 1 mixture 2 Natural rubber 60.0 60.0 Styrene butadiene rubber 40.0 40.0 Zinc oxide 20.0 20.0 Stearic acid ’,o ’,o Antioxidant ’,5 ’,5 HAF carbon black 50.0 50.0 Aromatic oil 4.0 4.0 Cobalt(II) octoate 8% Co 5.0 5.0 Lead oxide 1.6 ’,6 Phenol formaldehyde resin - 5.0 Resorcinol 3.0 . - Hexamethylenetetramine 2.0 2.0 Sulfenamide accelerator 0.8 - 0.8 Ground sulfur 2.5 2.5

Both mixtures were divided into two equal parts after mixing. One part of each mixture was then subjected to thermal stress in a Brabender laboratory mixer at a temperature of 115 to 120 °C for 15 minutes at 50 revolutions per minute. Test specimens were prepared from the mixtures without and after thermal stress to determine the resistance to tearing of a galvanized steel rope with a diameter of 5.94 mm using the method according to DIN 22 131. The following values were determined during the tensile tests:

a) mixture without thermal loading

mixture number 1 mixture number 2 118 N.mm ^-1 115 N.mm ^-1 b) mixtures after thermal loading 115 to 120°C/15 minutes mixture number 1 - 80 N.mm ^-1 i.e. decrease by 32% mixture number 2 .11 N.mm ^-1 i.e. decrease by 3.5%

Example 3

Test specimens were prepared from rubber mixtures No. 1 and 2 according to Example 1 to determine some physical properties before and after thermal aging at 70 °C for 7 days. The following values were measured during tensile tests:

a) physical properties before heat aging of mixture No. 1

Tensile strength (MPa) 17.5

Elongation (%) 410

Shore A hardness (°ShA) 65

Modulus 200% (MPa) 7.2 mix no. 2 21.8

500

6.5

b) physical properties after heat aging 70 °C/7 days mixture no. 1

Tensile strength (MPa) 11.7

Elongation (%) 230

Shore A hardness (°ShA) 70

Modulus 200% (MPa) 9.6 mix no. 2 10.1

370

7.1

In general, a significant number of other variants of the listed recipes can be used, so the examples should not be considered as limiting the choice of their composition.

The invention can be used in the production of conveyor belts with galvanized steel ropes or in the production of tires with brass-plated steel cord.

Claims (1)

Rubber composition based on natural butadiene styrene rubber or a combination thereof with high adhesion to a zinc, zinc plated or zinc-containing surface, containing a cobalt complex compound salt, fillers, vulcanizing agents and other conventional rubber additives, characterized in that it contains a thermoreactive phenolformaldehyde resin amount from 2 to 15 parts by weight not 100 parts by weight of rubber.