KR100453282B1 - Coating composition for steel-cord - Google Patents

Abstract

The present invention can increase the modulus of the rubber to suppress cracking and growth of the rubber part of the belt due to the decrease in the amount of deformation, and also to improve the heat aging and the salt water adhesion without damaging the fatigue resistance due to the breaking energy and the modulus of the rubber. The present invention relates to a rubber composition for coating a tire steel cord, which is obtained by adding cobalt boron complex salt together with activated zinc oxide in a conventional rubber cord coating rubber composition.

Description

Rubber composition for tire steel cord coating {Coating composition for steel-cord}

The present invention relates to a rubber composition for coating a tire steel cord, and more particularly, to a rubber composition coated on the surface of the steel cord used as a reinforcing material in the belt portion of the radial tire.

Pneumatic tires are subjected to high loads and deformations of the vehicle while driving. In particular, since the belt portion of the tire supports most of such vehicle loads, it must withstand the deformation of harsh conditions compared to other parts of the tire.

At this time, the rubber subjected to deformation shows viscoelastic behavior, and heat is generated by the viscous characteristics. The heat generated in this way is not easily transferred to the outside due to the non-conductivity of the rubber and accumulates therein. Accumulated heat causes thermal aging of rubber. As the deformation and stress change continues, aging progresses, a crack is generated between the brass-coated steel cord and the rubber, and when the crack and the concentration of the strain and stress are continued, the crack grows gradually. This eventually leads to destruction, which causes serious problems with the stability of the tires.

Such cracking and growth of the rubber is known to be closely related to the deformation amount of the tire belt portion and the fatigue resistance of the rubber.

As a method for increasing the modulus of rubber, a method of adding a large amount of sulfur, increasing the amount of carbon black, and using a reinforcing resin to increase the modulus of rubber are used. However, excessive use of sulfur greatly reduces rubber fatigue, breaking energy, and heat aging resistance, and degrades adhesion due to the precipitation of sulfur during processing, and also greatly increases the viscosity of rubber, making processing difficult. . The use of reinforcing resins also has the disadvantage of causing viscosity increase during processing and weakening the fatigue resistance and strength of the rubber in terms of physical properties.

In addition, we tried to increase the modulus by applying activated zinc oxide whose surface area was much higher than that of general zinc oxide, but the effect was negligible. Rather, due to the high moisture content of activated zinc oxide, thermal aging and salt water adhesion between rubber and steel cord This showed a tendency to deteriorate. That is, the problem caused by the reduction of the basic adhesive force than the one to increase the modulus to reduce the deformation occurred.

Accordingly, the present invention solves the problems of the prior art to increase the modulus of the rubber to suppress the crack generation and growth of the rubber of the belt portion by reducing the amount of deformation, and also without damaging the fatigue resistance due to the breaking energy and the modulus of the rubber at all. In addition, while trying to develop a new steel cord coating rubber composition that can improve thermal aging and salt water adhesion, active zinc oxide is used in the conventional steel cord coating rubber composition, and cobalt naphthenate complex salts are replaced. As a result of using the cobalt boron complex salt in which the cobalt metal salt of the dog is coordinated with boron, it was found that the above object can be achieved.

Accordingly, an object of the present invention is to provide a rubber composition for coating a steel cord having high modulus and excellent fatigue resistance and improved heat aging and salt water adhesion.

The rubber composition for coating the steel cord to achieve the above object is made by adding carbon black, zinc oxide, stearic acid, cobalt naphthenate-based complex salts, antioxidants, sulfur and accelerators to the raw material rubber, wherein zinc oxide is BET Activated zinc oxide having a surface area of 6 to 120 m 2 / g alone or a mixture with conventional zinc oxide having a BET surface area of 5 m 2 / g or less and containing 2 to 15 parts by weight based on 100 parts by weight of the raw material rubber, wherein the cobalt naphthenate The cobalt boron complex salt in which three cobalt metal salts are coordinated with boron in place of the complex salt is characterized in that it contains 1 to 3 parts by weight based on 100 parts by weight of the raw material rubber.

The present invention will be described in more detail as follows.

The present invention is to provide a rubber composition for coating a steel cord having a high modulus and excellent fatigue resistance, and is used alone or conventional activated zinc oxide having a surface area of 6 to 120 m 2 / g in a conventional steel cord coating rubber composition. It is a mixture of general zinc oxide used in the rubber industry.

In the above classification of zinc oxide, conventional zinc oxide is zinc oxide produced by the dry method (direct method (US), indirect method (French)), and has a BET surface area of 10 m 2 / g or less, specifically 2 to 5 m 2 / It refers to zinc oxide which is g.

Activated zinc oxide refers to zinc oxide, which is produced in a wet manner and has a very large specific surface area compared to conventional zinc oxide, that is, a BET surface area of 6 to 120 m 2 / g or less. .

The content of such active zinc oxide alone or a mixture of active zinc oxide and general zinc oxide is 2 to 15 parts by weight based on 100 parts by weight of raw rubber, and when it exceeds 15 parts by weight, the dispersion of zinc oxide, deterioration of rubber properties and increase in specific gravity Compound cost rises may occur.

The belt portion of the radial tire may be deformed by repeated stresses while driving, which affects the durability of the tire and promotes crack generation and crack growth of the tire belt portion. The steel belt is used as a reinforcing material in the belt part of the tire, and cracks may occur at the rubber / steel cord interface or cracks may occur at the rubber / steel cord interface due to repeated deformation and fatigue occurring while driving. In order to prevent cracking at the rubber / steel interface, a method of generally maintaining the adhesive strength by inducing a chemical reaction between brass-sulfur-rubber by brass plating on the steel cord surface and adding a large amount of sulfur is common. Is being used.

A large amount of zinc oxide is used together with a large amount of sulfur. Zinc oxide reacts with sulfur, an accelerator, and stearic acid to assist in the formation of a crosslink and to maintain the size of the zinc oxide layer at the brass interface. The zinc oxide layer on this interface should be present at an appropriate thickness (about 100 kPa) to inhibit the surface elution of zinc in the brass components. In this process, the active zinc oxide having a very small particle size has a relatively large surface area as compared with the conventional zinc oxide, thus greatly improving the crosslinking efficiency and improving the modulus of the rubber, and also increasing the polysulfide structure formation rate in the crosslinking structure. It has been found to have a beneficial effect on fatigue resistance despite the modulus increase.

On the other hand, activated zinc oxide has a moisture content of about 10 times higher than that of general zinc oxide, which has a small surface area, so that a part of zinc oxide is formed of zinc hydroxide at the interface between rubber and steel, thereby combining sulfur with copper or zinc during thermal aging. It accelerates the reaction and develops a fragile structure as the thickness of the bonding interface grows excessively. In addition, the zinc oxide layer at the interface becomes thinner, and thus the interface protection ability by the saline is poor, resulting in much poorer adhesion results than the conventional zinc oxide.

Because of this problem, the efficiency was halved by the reduction of the most important adhesive force in the steel cord composition, rather than the deformation reduction effect which is an advantage of increasing the modulus in the composition to which the active zinc oxide is applied.

In order to solve this problem, the present invention replaces the existing cobalt naphthenate-based complex salts with cobalt boron complex salts and simultaneously applies them with active zinc oxide.

Here, the cobalt boron complex salt is a form in which three cobalt metal salts are coordinated to one boron, and the acid forming the salt in each cobalt is bound by neodecanoic acid or 2-ethylhexanoic acid, and cobalt metal It means that the content of about 20 to 25%.

Specific cobalt boron complex salts include cobalt borone etecanoate, cobalt boroacylate, and the like.

The content of cobalt boron complex salt is preferably 1 to 3 parts by weight with respect to 100 parts by weight of the raw material rubber. If the amount is more than 3 parts by weight, the tensile strength of the rubber is lowered and there is a problem of deterioration of fatigue resistance and heat aging resistance.

Using cobalt boron complex salt together with activated zinc oxide increases the modulus of the modulus and improves thermal aging and salt water adhesion by cobalt boron's high activity and stabilizing the interfacial layer under aging conditions by heat or brine. You can.

On the other hand, the rubber composition for coating the steel cord of the present invention is a raw material rubber used in conventional steel cord coating rubber composition, specifically, natural rubber alone or natural rubber and synthetic isoprene rubber blend, carbon black, stearic acid, anti-aging agent, Of course, it includes sulfur and accelerators. The content thereof depends on the blending ratio of the rubber composition for coating a conventional steel cord, and is not particularly limited.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Example 1

Example 1 relates to a rubber composition for a steel cord using 10 parts by weight of active zinc oxide and 1 part by weight of cobalt boron complex salt as an adhesive, the specific composition is shown in Table 1 below. Each of these components was combined to prepare a rubber composition.

In order to measure the heat aging performance, rubber specimens were prepared from this rubber composition, and the rubber specimens were vulcanized in a 150 ° C. vulcanization press for 30 minutes to prepare vulcanization specimens having a thickness of 3 mm. After cutting it into a dumbbell shape and leaving it for 1 week and 2 weeks in an oven at 70 ° C., tensile strength was measured by a tensile tester (Model 4204) manufactured by Instron, and the evaluation of adhesion between rubber and steel cord was evaluated. It was carried out according to the ASTM D 2229-80 method. The adhesion test was prepared by leaving the specimen in an oven at 100 ° C. for 2 weeks for evaluation of heat aging adhesion (HA), and a chamber of 70 ° C., 95% relative humidity and 10% NaCl aqueous solution for corrosion resistance (MPA and SCR) evaluation. After each specimen was left for 2 weeks, the specimen was subjected to the adhesion test.

In addition, the amount of rubber adhesion was evaluated for the steel cord specimens in which the adhesion evaluation was completed.

Specific experimental results are shown in Table 2 below.

Example 2

In the same manner as in Example 1, except that 6 parts by weight of active zinc oxide and 4 parts by weight of general zinc oxide were mixed as shown in Table 1 below.

Specific experimental results are shown in Table 2 below.

Comparative Examples 1 to 3

Next, rubber specimens were prepared in the same manner as in Example 1 with the compositions shown in Table 1, and physical properties were evaluated in the same manner. The results are as shown in Table 2.

Example Example One 2 One 2 3 Natural rubber 100 100 100 100 100 Carbon Black ⁽¹⁾ 58 58 58 58 58 Zinc Oxide ⁽²⁾ - 4 10 - 4 Activated Zinc Oxide ⁽³⁾ 10 6 - 10 6 Stearic acid 0.5 0.5 0.5 0.5 0.5 Cobalt naphthenate - - 2.5 2.5 2.5 Cobalt Voronededecanoate 1.14 1.14 - - - Anti-aging 2 2 2 2 2 brimstone 8.0 8.0 8.0 8.0 8.0 Accelerators ⁽⁴⁾ 0.80 0.80 0.80 0.80 0.80 Retardant ⁽⁵⁾ 0.25 0.25 0.25 0.25 0.25 (1) Carbon black: Carbon black with nitrogen adsorption specific surface area (N2SA) of 70 to 100 m 2 / g and DBP oil absorption of 60 to 100 ml / 100 g (2) Zinc oxide: ZnO prepared by dry method BET surface area: 3 m 2 / g) (3) Active zinc oxide: ZnO (BET surface area 70 m 2 / g) produced by a wet method (4) Accelerator: mercapto benzothiazole type or sulfenamide type (5) Delay agent: PVI

Example Comparative Example One 2 One 2 3 Tensile Initial Properties 100% modulus 78 77 65 72 71 Elongation at Break (%) 334 323 348 328 320 The tensile strength 235 233 221 231 228 Adhesive force (kgf / in) Early 125 126 126 124 125 HA 2 weeks 110 109 83 78 77 HWR 2 weeks 121 122 121 122 121 MPA 2 weeks 107 109 98 100 103 SCR 2 weeks 87 89 68 62 64 Rubber adhesion amount (%) Early 100 100 100 100 100 HA 2 weeks 94 94 78 68 69 HWR 2 weeks 95 97 95 95 96 MPA 2 weeks 98 99 98 98 98 SCR 2 weeks 85 89 65 47 50 Initial: 150 ℃ × 0 min vulcanization, HA: 100 ℃ Heat aging in oven WR: 70 ℃ Hot water resistance PA: 70 ℃, aging under 95% relative humidity (Moisture Pentration CR: Aging at 25 ° C, 10% NaCl solution (Salt Corrosion Resistance)

In Table 2, the steel cord structure used for the adhesion test is a brass plated 3 + 9 + 15 (0.22) + 1 cord.

From the results of Table 2, in the case of Example 1 compared to the conventional steel cord composition as in Comparative Example 1 showed a modulus 6kgf / ㎠ or higher than Comparative Example 2 applying only active zinc oxide. In the case of adhesive strength, thermal aging adhesive strength (HA) was improved by 27 kgf / in than Comparative Example 1. In addition, in the salt water adhesion strength 19kgf / in compared to Comparative Example 1, compared to 25kgf / in than the Comparative Example 2 showed an improved adhesive strength, after drawing, the rubber adhesion was much improved results. These results indicate that the modulus for reducing the deformation of rubber is somewhat increased in Comparative Example 2, in which active zinc oxide is used instead of ordinary zinc oxide, but the thermal aging and saline adhesion decrease, but cobalt boron complex salt The composition of Example 1 obtained by mixing the mixture shows that the aging resistance and the saline adhesion are greatly improved by the large activity of cobalt boron and the stabilizing effect of the interfacial layer.

In the case of Example 2, the modulus was 5 to 6kgf / ㎠ higher than the conventional steel cord composition as in Comparative Example 1 than 12kgf / ㎠, Comparative Examples 2 or 3 applying only active zinc oxide. In the case of adhesive strength, the thermal aging adhesive strength (HA) was improved by 26 kgf / in than Comparative Example 1, and improved by 31 to 32 kgf / in compared to Comparative Examples 2 and 3 in which the adhesive strength was reduced than that of Comparative Example 1. . In addition, the salt water adhesion was improved by 27 ~ 29kgf / in than 2kgf / in, Comparative Examples 2, 3 compared to Comparative Example 1. In addition, the rubber adhesion amount after drawing was much improved.

As described in detail above, when active zinc oxide is used in a conventional rubber cord coating rubber composition and cobalt boron complex salt is used in combination with the present invention, cracking and growth of the rubber part of the belt due to a decrease in the amount of deformation is increased. In addition, it is possible to suppress the fatigue resistance due to the increase in the breaking energy and modulus of the rubber and to increase the heat aging and the salt water adhesion.

Claims (2)

In the rubber composition for tire steel cord coating comprising carbon black, zinc oxide, stearic acid, cobalt naphthenate complexing salt, anti-aging agent, sulfur and accelerator in addition to raw material rubber, The zinc oxide is 2 to 15 parts by weight based on 100 parts by weight of the raw material rubber as an active zinc oxide alone having a BET surface area of 6 to 120 m 2 / g or a mixture with conventional zinc oxide having a BET surface area of 5 m 2 / g or less, Rubber for coating a tire steel cord, comprising cobalt boron complex salts in which three cobalt metal salts are coordinated with boron in an amount of 1 to 3 parts by weight based on 100 parts by weight of the raw material rubber in place of the cobalt naphthenate complex salt. Composition. The rubber composition for coating a tire steel cord according to claim 1, wherein the cobalt boron complex salt is selected from cobalt borone decanoate and cobalt boroacylate.