KR100333408B1 - Rubber composition for tire steel cord - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for bonding a steel cord to tires, wherein the composition contains 1 to 3 parts by weight of cobalt salt based on 100 parts by weight of natural rubber or isoprene rubber as an anti-aging agent. 0.1 to 3 weights of one or more selected from -methyl-6-tert-butylphenol), 2,2'-isobutylidene-bis (4,6-dimethylphenol) and a polyphenolic compound based on 100 parts by weight of rubber It is made by addition, which can effectively inhibit the decomposition of the rubber crosslinked structure generally promoted by metal ions by forming a complex of a metal ion and a phenolic anti-aging agent, and when using a phenylenediamine compound By maximizing the life efficiency of the anti-aging agent and showing continuous heat aging resistance, it is possible to reduce the aging due to heat generated by the deformation of the severe state caused by the high load of the vehicle. The.

Description

Rubber composition for tire cord adhesion of tires

The present invention relates to a rubber composition for bonding a steel cord of a tire, and more particularly, to a rubber composition capable of providing a continuous anti-aging effect by forming a complex with a metal ion contained in a rubber by adding a phenolic anti-aging agent. It is about.

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 the vehicle load, it must withstand the deformation of the severe state compared to other parts. Therefore, a steel cord is used for the belt portion of the tire as a reinforcing material to withstand the load of the tire and to improve the mechanical strength.

On the other hand, the rubber undergoes 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. The heat accumulated in this way causes thermal aging of the rubber.

The thermal aging of the rubber caused as described above boils the bond between the rubber-rubber and the rubber-steel, which are crosslinked by sulfur, and the chain breakage is caused by the active radicals generated at the broken site. In particular, the cobalt salt is used to promote adhesion between the belt portion and the steel in bonding to the steel, unlike other parts of the belt portion.

For example, in Korean Patent No. 174588, a rubber composition for coating steel cord having high breaking energy of modulus and rubber is carbon black, cobalt salt, sulfur, resorcinol and formaldehyde in natural rubber or natural rubber and synthetic isoprene rubber blend. A rubber composition to which polycondensed resin and quatromethoxymethylmelamine or a derivative thereof is added is disclosed.

In addition, domestic patent application No. 195-35034 also consists of cobalt adhesive or cobalt, resorcinol formaldehyde resin and hexamethoxymethylmelamine mixed adhesive system, including carbon black, cobalt naphthenate, epoxide-based adhesive and sulfur It has been disclosed a rubber composition suitable for a tire belt by the addition of such.

In this way, the rubber of the belt portion contains a significant amount of inorganic metal ions such as Co, Fe, Cu, Mn, Zn and the like. These metal ions are easily activated by heat, and thus the activated metal ions accelerate radical reactions, thereby rapidly lowering the physical properties of the rubber.

For example, such a decrease in physical properties results in delamination between the belt rubber and the steel, i.e., a decrease in the physical properties of the rubber promoted by purely thermally deteriorated rubber and activation of cobalt metal and other inorganic metal ions. It can be seen as the dual aging process seen in the rubber composition for steel cords.

Conventional methods for reducing such physical property deterioration were intended to prevent thermal aging. Basically, the anti-aging agent was used to reduce the heat aging, but the anti-aging agent was easily moved to another site or volatilized while driving, and thus the sustainability of the effect could not be maintained. Of course, anti-aging agents have also been used to maintain this effect.

For example, Korean Patent Application No. 1998-2793 discloses a rubber composition for steel cords using N-1,3-dimethylbutyl-N'-phenylquinone diimine as an anti-aging agent. Unlike the usual, it reacts with the rubber backbone and remains inside the rubber instead of being moved to other parts of the tire, and it is combined with radicals generated during the use of the tire to disappear the activity of radicals, so that the rubber's heat aging performance is different. It has been disclosed that it can last longer than when an anti-aging agent is used.

However, such an effect of the anti-aging agent only considers the aging structure in the rubber composition, it does not consider the complex aging problem promoted by the various metal ions contained in the belt rubber.

On the other hand, attempts were made to reduce the deformation of the tire while driving, and attempts were made to reduce the amount of shear deformation of the rubber by increasing the modulus of the rubber.

For example, in Korean Patent No. 219942, a rubber / steel cord adhesive rubber of a tire using resorcinol and formaldehyde polycondensation resin and hexabutoxymethylmelamine and cobalt metal salt added to improve the modulus and breaking energy of the rubber The composition has been disclosed.

However, if the modulus of the rubber is too high, there is a problem in processing the rubber during manufacturing to reduce the productivity.

Accordingly, the present inventors are trying to find an anti-aging agent that can suppress the aging-promoting action by metal ions in a rubber composition having a relatively high metal ion content such as belt portion or carcass while reducing thermal aging. As a result of using the anti-aging agent, it was found that the formation of the complex with the metal ion effectively inhibits the decomposition of the rubber crosslinked structure promoted by the metal ion, thereby completing the present invention.

Accordingly, an object of the present invention is to provide a rubber composition for tire steel cord adhesion, which can effectively suppress decomposition of a rubber crosslinked structure promoted by metal ions and exhibit continuous heat aging resistance.

The rubber composition for tire steel cord adhesion of the present invention for achieving the above object is a rubber composition for tire steel cord adhesion containing 1 to 3 parts by weight of cobalt salt based on 100 parts by weight of natural rubber or isoprene rubber, wherein the anti-aging agent 2,2'-methylene-bis (4-methyl-6-tert-butylphenol), 2,2'-isobutylidene-bis (4,6-dimethylphenol) and polyphenols represented by the following general formula (1) It is characterized by containing 0.1 to 3 parts by weight of at least one selected from the compounds.

Wherein R is an alkyl group and x is an integer from 1 to 9.

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

The present invention is to add a phenolic anti-aging agent to the rubber composition for bonding the steel cord of pneumatic tires.

The rubber composition for affixing tire steel cord of this invention has a natural rubber or isoprene rubber as a main component, and is a conventional thing formed by adding a cobalt salt here.

In general, the cobalt salt has an excellent effect on preventing corrosion, and is a compound generally added to a rubber composition for attaching a steel cord to a tire by serving to prevent corrosion of the steel cord.

Cobalt salts include conventional cobalt salts such as cobalt naphthenate and certain cobalt boron complexes. In the case of cobalt boron complexes, the bond strength between B and O is weak, so that the borate portion and the cobalt salt may easily fall off. In addition to acting as an adhesion enhancer, which is a common cobalt salt, the borate portion acts as a buffer to adjust the pH (pH) at the rubber and steel cord interface to maintain a pH of about 7 to 9 It is more preferable to prevent corrosion.

Thus, cobalt salt is normally added at 1-3 weight part with respect to 100 weight part of main component rubber | gum.

In the conventional rubber composition in which cobalt salt is added to improve corrosion resistance, the present invention includes 2,2'-methylene-bis (4-methyl-6-tert, including polyphenol-based compound represented by Formula 1 as an anti-aging agent. Phenolic compounds such as -butylphenol) or 2,2'-isobutylidene-bis (4,6-dimethylphenol) are added to the antioxidant.

Such a phenolic anti-aging agent forms a complex with metal ions present in the rubber, the complex forming structure is represented by the following formula (2).

In Formula 2, M is Co, Fe, Cu, Mn or Zn.

Thus, by forming a complex with a metal ion, a phenolic anti-aging agent can effectively suppress decomposition of the rubber crosslinked structure promoted by the metal ion.

In the rubber composition of the present invention, it is preferable that the amount of the phenolic anti-aging agent added is 0.1 to 3 parts by weight with respect to 100 parts by weight of the main component rubber. If less than 0.1 part by weight, the effect of complexation with the metal ion is insignificant.

However, the phenolic antioxidants have low volatility, but the activity of the rubber crosslinked structure is slow to inhibit degradation, and in view of this, phenylenediamine antioxidants having a relatively high volatility in spite of high reactivity are mixed in an appropriate ratio. If you do, you can maximize the life efficiency of the antioxidant.

In view of this, in the rubber composition of the present invention, N-1,2-dimethylbutyl-N'-p-phenylenediamine or poly- (2,24) -trimethyl-1, It may further comprise 2-dihydroquinoline.

This compound is fixed to the rubber main chain to prevent radicals generated by heat from cutting off the rubber main chain, thereby preventing deterioration of the rubber.

When these phenylenediamine compounds are mixed with the phenolic anti-aging agent, the added amount thereof is preferably 0.1 to 3 parts by weight based on 100 parts by weight of the main component rubber.

As a result, when phenolic antioxidants are used in combination, metal ions and complexes that activate the formation of radicals that cause deterioration of rubber properties or aging are formed, which slows aging, and phenolic antioxidants are combined with diene structure. To maintain a certain level of elongation and modulus of rubber.

More specifically, as shown in Formula 2, the phenolic anti-aging agent forms a complex with the metal ion present in the rubber, and effectively inhibits the decomposition activation action of the rubber crosslink. In addition, the phenylenediamine compound used in combination with a phenolic anti-aging agent serves to directly remove radicals. The phenylenediamine-based compound reacts with the rubber backbone to remain in the rubber rather than move to other parts of the tire, binding to the radicals generated during tire use, resulting in the disappearance of radical activity.

However, since the persistence of the phenylenediamine compound is lower than that of the phenolic antioxidant, the effect of the phenolic antioxidant increases as aging progresses. The properties of such phenolic antioxidants are as shown in the formula (2), the substituents present in the ortho position relative to the complex formation position to form a ring, consequently the phenolic antioxidants have a large geometric hinderance effect (steric hinderance) ) To suppress volatility and to continuously express the effect.

In addition, it is a matter of course that the rubber composition of the present invention can use an additive used in a conventional rubber composition for tire steel cord bonding.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Examples 1-2 and Comparative Examples 1-4

As shown in Table 1 below, each component was combined to prepare a rubber composition.

Example Comparative Example One 2 One 2 3 4 Natural rubber 100 100 100 100 100 100 Carbon black 58 58 58 58 58 58 Zinc oxide 10 10 10 10 10 10 Stearic acid 0.5 0.5 0.5 0.5 0.5 0.5 N-1,2-dimethylbutyl-N'-p-phenylenediamine 2 2 One 2 One 2 Poly- (2,24-trimethyl-1,2-dihydroquinoline) One One One One One One Phenolic Anti-aging Agent 2,2'-methylene-bis (4-methyl-6-tert-butylphenol) - - - - - - 2,2'-isobutylidene-bis (4,6-dimethylphenol) - - - - - - Polyphenol-based antioxidant of formula (1) One One - - - - Cobalt salt Cobalt naphthenate 2.5 - 2.5 2.5 - - Cobalt Boro Neodecanoate - 1.14 - - 1.14 1.14 brimstone 8.0 8.0 8.0 8.0 8.0 8.0 Mercapto benzothiazole- or sulfenamide-based accelerators 0.80 0.80 0.80 0.80 0.80 0.80 Retardant (PVI) 0.25 0.25 0.25 0.25 0.25 0.25 Carbon Black Co., Ltd .: Carbon black with nitrogen adsorption surface area of 70-100 m 2 / g and DBP oil absorption of 60-100ml / 100g

Experimental Example

In order to measure the heat aging performance in the rubber compositions obtained according to Examples 1 to 2 and Comparative Examples 1 to 4, rubber specimens were prepared, and the obtained rubber specimens were vulcanized in a 150 ° C. vulcanization press for 30 minutes to have a thickness of 3 mm. Vulcanization specimens were prepared, cut into dumbbells, and left for 1 week and 2 weeks in an oven at 70 ° C., and then the tensile strength of the tensile tester (Model 4204) manufactured by Instron was measured to change the physical properties according to aging time. To determine the degree, the adhesion between rubber and steel cord was evaluated according to the ASTM D 2229-80 method. Examples 1 to 2 are examples in which the polyphenol-based antioxidant of Formula 1 is used as the phenol-based antioxidant.

Adhesion test was prepared by leaving the specimen in a 100 ℃ oven for 2 weeks to evaluate the heat aging adhesion (HA), 10 ℃ NaCl solution and 70 ℃ relative humidity 95% oven for corrosion resistance (MPA and SCR) evaluation After each specimen was left for 2 weeks, the adhesion test of the specimen was performed. In addition, the amount of rubber adhesion was also evaluated for the steel cord specimens in which the adhesion evaluation was completed.

Among these changes in physical properties, the degree of heat aging performance was evaluated based on the rate of change of breaking energy in the range of favorable adhesive strength in consideration of the adhesion between rubber and steel cord. The rate of change of breaking energy was expressed using a reduction rate per week based on the breaking energy (toughness) during 0, 1, 2 weeks.

Example Comparative Example One 2 One 2 3 4 Tensile Initial Properties 100% modulus 65 74 65 66 73 74 Elongation at Break (%) 334 323 332 328 320 315 Tensile strength (kgf / ㎠) 235 229 2528 234 230 234 Breaking energy (kgf / ㎡) 381 371 380 379 368 369 Tensile (70 degrees * 1 week) 100% modulus 93 105 106 97 105 109 Elongation at Break (%) 211 204 206 210 172 183 Tensile strength (kgf / ㎠) 187 195 196 197 170 177 Breaking energy (kgf / ㎡) 197 199 201 207 158 162 Tensile (70 ℃ x 2 weeks) 100% modulus 103 111 109 106 115 118 Elongation at Break (%) 188 172 155 168 149 135 Tensile strength (kgf / ㎠) 166 175 148 159 169 164 Breaking energy (kgf / ㎡) 156 150 121 129 128 131 Adhesive force (kgf) Early 125 126 126 121 129 122 HA 2 weeks 88 91 63 65 74 77 HWR 2 weeks 121 122 124 122 121 119 MPA 2 weeks 107 109 98 102 103 97 SCR 2 weeks 66 70 58 56 61 60 Rubber adhesion amount (%) Early 100 100 100 100 100 100 HA 2 weeks 90 96 78 76 78 78 HWR 2 weeks 95 97 95 95 96 95 MPA 2 weeks 98 99 99 99 98 99 SCR 2 weeks 95 59 45 49 52 56 Aging rate Breakage energy reduction rate per week (kgf / ㎡ / 1 week) 112 110 129 125 120 120

In the above evaluation, the breaking energy is toughness at break, and the steel cord structure used in the adhesion test is a 3 + 9 + 15 (0.22) +1 cord plated with brass.

Initial adhesion in the adhesion test is 150 ° C × 30 minutes vulcanization, over-curing: 160 ° C × 60 minutes vulcanization, HA is heat aging in an oven at 1000 ° C, HWR is hot water resistance in MPC at 70 ° C, MPA Is aging (moisture penentration adhesion) at 70 ℃, 95% relative humidity, SCR means aging (salt corrosion resistance) in 25 ℃, 10% NaCl aqueous solution.

From the results of Table 2, the rubber composition for bonding the steel cord using 1 part by weight of a phenolic anti-aging agent and cobalt naphthenate as an adhesive was measured to decrease the breaking energy of 112kgf / ㎜ / 1 week, Comparative Example 1 or It can be seen that the aging progressed by 15 kg / mm 2/1 week as compared to the case where the phenolic anti-aging agent was not used as in 2. In addition, the adhesive strength after thermal aging is 78, 76kgf in the case of Comparative Example 1 or 2 in comparison with the weight of 90kgf in Example 1, it can be seen that the heat-resistant adhesive strength was very improved. In addition, the corrosion resistance test shows a very improved result.

On the other hand, in the case of Example 2, which is a rubber composition for bonding steel cord using 1 part by weight of a phenolic anti-aging agent and cobalt boron complex salt as an adhesive, the reduction rate of the breaking energy was measured to 110kgf / ㎜ / 1 week, Comparative Example As shown in 3 or 4, less aging was progressed by 10 kgf / mm 2/1 week compared to the case where no phenolic antioxidant was used. In addition, in the case of Comparative Example 3 or 4, the adhesive strength after thermal aging was 78 kgf, whereas in Example 2, 96 kgf was considered, and it was found that the heat-resistant adhesive strength was greatly improved. In addition, the corrosion resistance test shows a very improved result.

As described in detail above, as a result of using a phenolic compound as an anti-aging agent in a rubber cord adhesive composition of a tire comprising a metal salt according to the present invention, a metal ion and a phenolic anti-aging agent form a complex, and thus generally In addition to effectively inhibiting the decomposition of the rubber crosslinked structure promoted by the phenylenediamine-based compound, it exhibits continuous heat aging resistance by maximizing the life efficiency of the anti-aging agent, and thus in a severe state due to the high load of the vehicle. Aging due to the heat generated by the deformation of the can be reduced.

Claims (2)

In the rubber composition for tire steel cord bonding, containing 1-3 parts by weight of cobalt salt with respect to 100 parts by weight of natural rubber or isoprene rubber, The composition is 2,2'-methylene-bis (4-methyl-6-tert-butylphenol), 2,2'-isobutylidene-bis (4,6-dimethylphenol) and the following formula (1) as an antioxidant Rubber composition for tire steel cord bonding, characterized in that it comprises 0.1 to 3 parts by weight based on 100 parts by weight of one or more selected from the polyphenol-based compound to be displayed. Formula 1 Wherein R is an alkyl group, x is an integer of 1-9. The composition according to claim 1, wherein the composition comprises N-1,2-dimethylbutyl-Np-phenylenediamine or poly- (2,24) -trimethyl-1,2-dihydroquinoline together with the anti-aging agent. A rubber composition for tire steel cord bonding, further comprising 0.1 to 3 parts by weight based on 100 parts by weight of the component.