CS239744B1 - Rubber compounds with high adhesion to brass or brass surface - Google Patents

Abstract

The subject of the invention are special rubber mixtures, which allow achieving high adhesion to brass or brass-plated surfaces after vulcanization at elevated temperatures. The adhesive effects of these mixtures are achieved by using pre-polycondensed thermosetting resin and formaldehyde or methylene donor, which, together with fillers, vulcanizing additives and other common rubber chemicals, are mixed into the relevant elastomer or combination of elastomers at a temperature of up to 120 °C. The invention can be used primarily in the production of tires, hoses or V-belts reinforced with brass-plated steel cord. It can also be used in the production of conveyor belts with brass-plated steel ropes, or other rubber products reinforced with brass or brass-plated metal materials.

Description

The rubber has a high adhesion to brass or copper, which is achieved after vulcanization of the metal surface.

Recently, the reinforcement of some rubber products, such as tires, hoses and belts, with steel cord has become widely used. This reinforcing material is used in larger quantities for and against classic textile materials such as viscose, cotton or polyester, i.e. in the case when the steel cord is coated with brass, most often a mixture of Kf li dl i-1% Copper and a bl ni li% Zinc. Joto Hložišimi míjsukí gives nojlepuí udhíbaí vldsiiícubí ke ('íi»íi<Jk:/,η ,,ν&ΐ . In the above-mentioned deposition jo longer ndhesi influenced already his ttlouĚtkou náópii o ehoťbklí-j’Hí>i mobíízó layer.

The influence of the above-mentioned quantities _is that the materials are provided with a coating that guarantees the achievement of high adhesive properties. The situation is fundamentally different in the matter of the composition of the rubber compound used in connection with the surface. Here, manufacturers are trying to develop a recipe for an adhesive mixture that will ensure the best adhesion to the brass surface and at the same time meet technological, economic and health and hygiene requirements.

Currently, adhesive systems based on resorcinol formaldehyde resins, resorcinol melanin resins, cobalt compounds or systems containing a combination of resins and cobalt salts, as well as resins with an increased concentration of sulfur, are known and commonly used.

Each of these adhesive systems has its specific advantages and disadvantages and the manufacturer therefore chooses the adhesive system that best suits his production and economic conditions and possibilities. In this context, however, it can be stated that the most commonly used rubber mixtures contain an adhesive system based on resorcinol formaldehyde resins, designated in technical practice by the symbol HRH.

The system consists of resorcinol, hexamethylantetramine and active silicic acid.

For easy mixing into rubber mixtures, these basic substances are treated with additional additives, ensuring good dispersion, which also positively affects the resulting adhesion. The system shows relatively high cohesion values, even after thermal aging or after overvulcanization of the mixture.

A certain drawback of the HRH system is the very low thermal processability limit of the rubber adhesive mixture, as the reactivity of both resin components is strongly dependent on temperature.

The reaction of resin formation occurs very rapidly between 90 and 100 °C, so the temperature during mixing and processing of the mixture must not exceed 90 °C. In practice, the temperature is required to be as low as possible.

However, many rubber companies cannot normally meet this requirement without special mixing and processing equipment and without extraordinary technological measures and procedures. Another serious drawback of the HRH system is the formation of ammonia, which is released during the vulcanization of the adhesive mixture, when, among other things, polycondensation between resorcinol and formaldehyde occurs.

Ammonia then acts as a strong corrosive agent on the brass-plated steel cord, especially in places where the rubber mixture has not completely flowed in. The formation of exhalations escaping during the processing of the adhesive mixture is also not negligible, as it has been proven that these exhalations have a toxic effect on the operator.

When using a rubber sealant with an adhesive system containing resorcinol, hexamethoxymethylalanine or another methylene group donor and active silicic acid, known in technical practice as RFS, the thermal decomposition limit of the mixture is increased to H5 °C and the formation of ammonia is eliminated, but we will not achieve such high cohesion values as with the HRH system.

This fact has been proven by a number of experimental works comparing the two systems in terms of adhesion values. Rubber adhesive mixtures with cobalt additives or with increased sulfur content show a significantly greater decrease in adhesion after heat aging or after overvulcanization of the mixture when compared to the HRH and RFS systems.

In addition, in a system with an increased sulfur concentration, there is increased sulfur bloom on the surface of the mixture, which is negatively reflected in reduced assembly adhesion in rubberized co-adhesive semi-finished products. When using rubber mixtures with a combined adhesive system containing resin and cobalt compound, some of the aforementioned shortcomings of the cobalt, HRH and/or RFS systems are overcome.

The degree of defects then depends on the type of resin or cobalt compound used and their ratio in the rubber mixture.

The above-mentioned shortcomings are eliminated by using a rubber mixture according to the invention, which achieves high adhesion to brass or brass-plated surfaces and which is prepared on the basis of natural, isoprene, butadiene, butadiene-styrene rubber or their combination containing longer fillers, vulcanizing additives and other rubber chemicals, into which 2 to 6 parts by weight of prepolycondensed thermosetting phenol-formaldehyde resin and 0.4 to 2 parts by weight of hexamethylenetetramine or hexamethoxymethylmelamine are mixed per 100 parts by weight of rubber.

The rubber mixture containing the said adhesive agents is vulcanized at elevated temperature onto a brass-plated steel cord, thereby achieving high adhesion between the rubber and the metal.

When using the rubber mixture according to the invention, the heat processability limit of the rubber mixture is reached up to 120° C. This limit will enable the preparation and processing of the mixture under normal operating conditions on commonly used production and processing equipment.

In experimental laboratory tests, in which the thermal limit of resin processability was determined in a temperature-controlled drying oven at various temperatures, it was found, for example, that the resin begins to crosslink at a temperature of 120 °C after 20 minutes of tempering and at a temperature of 130 °C it is cured after 20 minutes.

At temperatures lower than 120 °C, resin crosslinking was not detected even after 30 minutes of tempering its solution in industrial alcohol. Another advantage is a significant reduction in ammonia evolution during the vulcanization of the mixture, compared to the HRH system.

This significant advantage is due to the fact that the pre-polycondensed phenol-formaldehyde resin is pre-crosslinked into a linear structure during its production and therefore desulfurization into a spatial structure requires 3 to 5 times less formaldehyde donor than with resorcinol-based resin. The greater part of the ammonia is therefore split off during the production of the pre-polycondensed phenol-formaldehyde resin outside the rubber mixture.

For this reason, rubber mixtures with pre-polycondensed phenol-formaldehyde resin exhibit significantly lower corrosive effects on brass-plated steel cord than mixtures with the HRH system. In rubber mixtures according to the invention, containing a chidonor of methylene groups, higher cohesion values are achieved than in adhesive mixtures with the RFS system.

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The higher adhesion values can be explained by the fact that the pre-polycondensation of the resin into a linear structure is carried out during its preparation with formaldehyde, with which the adhesive ^mixtures show better adhesion results than when using a donor of methylene groups.

One of the most important advantages of the adhesive system according to the invention is the almost negligible formation of exhalates during the preparation and processing of mixtures containing this system, this property is precisely given by the linear structure of the resin and it prevents the formation of resin exhalates up to a temperature of 120 °C, which is important from a hygienic and health point of view.

The practical implementation of the adhesive rubber mixtures according to the invention is illustrated by the following examples. »

Example

A base mixture of the following composition was mixed from natural rubber:

Natural rubber 100.0 parts by weight Stearic acid 0.5 parts by weight Zinc oxide 8.0 parts by weight Arjaatic oil 2.0 parts by weight HAF carbon black 60.0 parts by weight Antioxidant 2.0 parts by weight Silicic acid 5.0 parts by weight Sulfenamide accelerator 0.8 parts by weight Sulfur N 4.0 parts by weight

The mixture was mixed in a larger quantity and divided into 5 equal weight parts.

the following amounts of adhesive additives were then mixed into the individual parts: No. 5 mixture no. 1 No. 2 ¢. 3 No. 4 Resorcinol 2.5 - - - - Hexamethylenetetramine 1.5 0.4 0.5 0.8 1.0 Phenolform. resin - 3.5 5.0 5.0 6.0

The dosage of adhesive additives is given in parts by weight per 100 parts by weight of rubber in the base mixture. Test specimens for adhesion testing by the ASTM D 2229 - 75 method were prepared from mixtures No. 1 to No. 5.

Adhesion was monitored on a coated steel cord of construction 7 x 4 x 0.22 + 1 at a working length of 25 mm. The samples were vulcanized at a temperature of 150 °C for 25 and 45 minutes. The vulcanization time of 45 minutes was chosen with regard to the operating conditions during tire vulcanization and the time of 25 minutes as the optimum vulcanization. The following cohesion values in N.mm ^-1 were measured during the tests:

mixture no. 1 No. 2 No. 3 No. 4 No. 5 vulcanization 25 minutes 55 48 50 53 52 vulcanization 45 minutes 50 50 54 54 55 Example 2 To 5 equal parts by weight of the base rubber compound according to example 1 were mixed in

adhesive additives in the following quantities:

mixture no. 6 No. 7 No. 8 No. 9 No. 10 Hexamethoxyethylmelamine 0.4 0.8 1.2 1.6 2.0 Phenolform. resin 2.0 2.5 3.8 5.0 6.0

The dosage of adhesive additives is again given in parts by weight per 100 parts by weight of rubber in the base of the mixture according to Example 1. Test specimens for laboratory cohesion tests were prepared from the mixtures using the method according to Example 1. The following values in N.ma”' were found during the tests.

mixture no. 6 No. 7 No. 8 No. 9 No. 10 vulcanization 25 minutes 35 44 48 52 52 vulcanization 45 minutes 36 46 47 53 5,

Example 3

Rubber mixtures of the following composition were mixed from butadiene, butadiene-styrene and isoprene rubber in a laboratory kneading machine at a temperature of 105 to 115 °C:

mixture no. 11 8. 12 No. 13 Butadiene rubber 100.0 - - mass parts Styrene butadiene rubber - 100.0 - mass parts Isoprene rubber - - 100.0 mass parts Stearic acid 0.7 0.7 0.7 mass parts Zinc oxide 10.0 10.0 10.0 mass parts Aromatic oil 4.0 4.0 4.0 mass parts HAF carbon black 65.0 65.0 65.0 mass parts Antioxidant ' 2.0 2.0 2.0 mass parts Silicic acid 6.0 6.0 6.0 mass parts Sulfenamide accelerator 1.2 1.2 1.2 mass parts Phenolform. resin 5.0 5.0 5.0 mass parts Hexamethylenetetramine 0.8 0.8 0.8 mass parts Sulfur li 4.0 4.0 4.0 mass parts

Test samples were prepared from the above-mentioned rubber mixtures at a temperature of 150 °C and a vulcanization time of 30 minutes. The testing was carried out using the method according to example 1. The following adhesion values were measured in N.mm ^- ':

mixture no. li no. 12 no. 13 vulcanization 30 minutes 45 49 51 .Example 4

Rubber mixtures of the following composition were mixed from natural, butadiene, butadiene-styrene and isoprene rubber in a laboratory kneading machine at a temperature of 110 °C to 120 °C:

mixture no. 14 . No. 15 No. 16 No. 17 Natural rubber 60.0 70.0 40.0 50.0 mass parts Butadiene rubber - 30.0 - 20.0 mass parts Styrene Butadiene Rubber 40.0 . - - - mass parts Isoprene rubber - - 60.0 30.0 mass parts Stearic acid 0.6 0.6 0.7 0.7 mass parts Zinc oxide 8.0 8.0 8.0 8.0 mass parts Aromatic oil 3.0 3.0 3.0 3.0 mass parts HAF carbon black 60.0 60.0 60.0 60.0 mass parts Antioxidant 1.5 1.5 1.5 1.5 mass parts Silicic acid 6.0 6.0 6.0 6.9 mass parts Sulfenamide accelerator 1.0 1.0 1.0 1.0 mass parts Phenolform. resin 5.0 5.0 5.0 5.0 mass parts Hexaaethylenetetramine ' 0.8 0.8 0.8 0.8 mass parts Sulfur N 4.0 4.0 4.0 4.0 mass parts

Test specimens were prepared from these rubber mixtures for adhesion tests using the ASTM D 2229-75 method. The test specimens were vulcanized at 150°C for 30 minutes.

The following were measured during the burst tests: values in N.mm” : mixture no. 14 4' No. 15 6. 16 No. 17 vulcanization 30 minutes 55 52 54 54

In general, a wide range of other adhesive compositions can be used, and the examples given should not be considered as limiting the scope of the invention.

The invention can be used in the production of tires, hefdics or V-belts reinforced with brass-plated steel cord. It can also be used in the production of conveyor belts whose skeleton consists of brass-plated steel ropes.

Claims (1)

High-adhesion rubber mixtures with a brass or brass surface prepared on the basis of natural, butadiene, isopranous, butadiene-styrene rubber or combinations thereof, containing fillers, vulcanizing agents and other rubber additives, characterized in that they contain 2 to 6 parts by weight of pre-polycondensated thermoreactol resin and 0.4 to 2 parts by weight of hexamethyleneteramine or hexamethoxymethylmelamine per 100 parts by weight of rubber.