KR19990068892A - Rubber composition for pneumatic tire steel cord with improved heat aging resistance - Google Patents

Abstract

The present invention relates to a rubber composition for pneumatic tire steel cord with improved heat aging resistance, and more specifically, with respect to 100 parts by weight of natural rubber, the nitrogen adsorption surface area is 70 to 100 m 2 / g, DBP oil absorption 60 to 100 40 to 80 parts by weight of carbon black (ml / 100g), the cobalt boron complex of the following formula 1 0.01 to 3 parts by weight based on the pure cobalt content, N-1,3-dimethylbutyl-N'-phenyl quinone The present invention relates to a rubber composition for tire steel cords containing 0.4 to 9 parts by weight of diimine and an additive used in a conventional rubber composition for tire steel cords.

Structural Formula 1

In the above, X is a fatty acid or naphtanic acid.

Structural Formula 2

Description

Rubber composition for pneumatic tire steel cord with improved heat aging resistance

The present invention relates to a rubber composition for pneumatic tire steel cord with improved heat aging resistance, and more particularly, to prevent corrosion of the steel cord by using a cobalt boron complex and to deterioration of rubber by adding a quinone-imine-based antioxidant. It relates to a rubber composition for pneumatic tire steel cord that can prevent the.

Pneumatic tires are mounted on a vehicle to withstand high loads and deformations during use. In particular, the belt part of the tire supports most of the vehicle load, and is in a condition that must withstand more deformation than other parts while driving. Since rubber is a viscoelastic material, when such deformation is applied externally, heat is generated due to the viscosity of rubber. This heat is accumulated in the tire without dissipating out because the rubber is a non-conductor, and the accumulated thermal energy causes thermal aging of the rubber.

The thermal aging of rubber refers to the breakage of the main chain or crosslinked sulfur of the rubber by heat generated inside the rubber to generate active radicals. These active radicals again attack the main chain or crosslinked sulfur of the rubber to reduce the length of the rubber main chain. It refers to the phenomenon of reducing and changing the crosslinked structure. In order to reduce the thermal aging of the rubber, a method of reducing the amount of heat generated by reducing the amount of deformation received during tire use by increasing the modulus of the rubber has been conventionally attempted. In this case, however, if the modulus of the rubber is too high, processing problems occur during rubber production, thereby lowering productivity.

Attempts have been made to reduce this aging phenomenon by using anti-aging agents, but due to the phenomenon that the anti-aging agent for steel cords is moved to other parts of the tire while the tire is running, the effect decreases rapidly and the intended effect was not greatly obtained.

In the present invention, the cobalt boron complex, which has been excellent in preventing corrosion, is used to prevent corrosion of the steel cord, as well as to add a quinone-imine-based antioxidant having a certain reactivity with rubber to react this antioxidant to the rubber main chain. It can be fixed to prevent radicals generated by heat from cutting off the rubber backbone, thereby preventing deterioration of the rubber.

In addition, in the present invention, by using such a reactive antioxidant in combination with a boron-based cobalt salt, it is possible to further improve the durability of the steel cord portion of the tire.

The present invention is based on 100 parts by weight of natural rubber, nitrogen adsorption surface area of 70 to 100 m 2 / g, 40 to 80 parts by weight of carbon black having a DBP oil absorption of 60 to 100ml / 100g, the cobalt boron complex of the following structural formula 1 0.01 to 3 parts by weight based on the cobalt content, 0.4 to 9 parts by weight of N-1,3-dimethylbutyl-N'-phenyl quinone diimine of the following structural formula 2 and the additives used in the rubber composition for a conventional tire steel cord It is a rubber composition for tire steel cords to contain.

Structural Formula 1

In the above, X is a fatty acid or naphtanic acid.

Structural Formula 2

Hereinafter, the present invention will be described in detail.

In the present invention, 40 to 80 parts by weight of carbon black having a nitrogen adsorption surface area of 70 to 100 m 2 / g and a DBP oil absorption of 60 to 100 mm / 100 g is used.

The cobalt boron complex (hereinafter referred to as "CBC") used in the present invention has a structure different from the cobalt salt (Y-Co-Y structure, where Y is a fatty acid or naphtanic acid) commonly used. However, due to the weak bonding force between B and O, the borate and cobalt salts can easily fall off, which can serve as an adhesion enhancer, which is a common cobalt salt, and the borate portion is a kind of acidity (pH) at the rubber and steel cord interface. It acts as a buffer to adjust the pH to maintain a pH of about 7 to 9 to prevent corrosion of the steel cord.

N-1,3-dimethylbutyl-N'-phenyl quinone diimine (hereinafter referred to as "6QDI") of the formula 2 used in the present invention is a reactive antioxidant, N-1,3-dimethylbutyl-N Obtained by oxidizing '-p-phenylene diamine. The reaction is shown in the following scheme.

Unlike ordinary antioxidants, 6QDI reacts with the rubber backbone and remains inside the rubber rather than moving to other parts of the tire, binding to the radicals generated during tire use to dissipate radical activity. As a result, the heat-resistant aging performance of the rubber can be maintained for a long time compared with the case of using other general road agent.

When the CBC and the reactive antioxidant 6-QDI are used at the same time, both the corrosion resistance and the heat aging performance are excellent.

Antioxidants or antioxidants used in the present invention prevent the cleavage of the rubber backbone from oxygen or ozone and eliminate the activity of the radicals generated by heat, thereby preventing the rubber backbone from being cleaved.

Moreover, in this invention, the additive used for the rubber composition for ordinary tire steel cords is used.

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

Example

To prepare a rubber specimen by mixing the rubber composition as shown in Table 1. In order to compare the heat aging performance, rubber specimens were vulcanized in a 150 ° C. vulcanization press for 30 minutes to prepare vulcanization specimens having a thickness of 3 mm, which were cut into dumbbells to obtain strength and strength in a tensile tester (Model 4204) manufactured by Instron. In comparison, the degree of change in physical properties according to the aging time was determined, and the evaluation of adhesion between rubber and steel cord was performed according to ASTM D 2229-80 method.

The specimens for adhesion were first prepared by aging for 1 to 3 weeks in an oven at 100 ° C. for evaluation of heat aging adhesive strength, and the specimens were placed in an oven at 20% NaCl solution and 95% relative humidity of 95% for corrosion resistance evaluation. After standing for 3 weeks, the adhesion test of the specimen was performed. In addition, the rubber adhesion amount of the steel cord specimens in which the adhesion evaluation was completed was also evaluated.

Table 2 shows the physical test results of the rubber composition.

Comparative Examples 1 to 7

Each rubber specimen was prepared by blending a rubber composition as shown in Table 1 below. Physical properties of each rubber specimen were tested in the same manner as in Example, and the results are shown in Table 2.

Comparative Example 1 is a case in which neither 6-QDI nor CBC is added to the rubber composition, Comparative Examples 2 to 4 are cases in which CBC is added, and Comparative Examples 5 to 7 are cases in which 6-QDI is added.

Example Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Natural Rubber Carbon Black Covalent Zinc Oxide Stearic Acid General Preservative ¹ 6-QDI ² Co-Naph ³ CBC ⁴ Sulfur Promoter ⁵ Retardant ⁶ 10040582-4-1.332.510.5 100405824-3-2.510.5 100405824--1.332.510.5 100405824--4.432.510.5 100405824--0.12.510.5 10040582-43-2.510.5 10040582-0.33-2.510.5 10040582-103-2.510.5

1 general preservatives are amine or quinoline preservatives

2 6-QDI: N-1,3-dimethylbutyl-N'-phenylquinone diimine

3 Co-Naph: Cobalt Naphthenate (Cobalt Content 10%)

4 CBC: Cobalt Boron Complex (Cobalt Content 22.5%)

5 Accelerator: mercapto benzothiazole type or sulfenamide type

6 retardant: PVI

Example Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Initial Properties 100% M200% M300% MEb (%) Ts (kgf / ㎠) 49114180315191 50110170310185 48109169320189 62123181308193 46105160330182 52115173315191 50111170305183 3897152380189 100 ℃ × 48 hours Aging 100% M200% M300% MEb (%) Ts (kgf / ㎠) 53118184310193 68129-250155 58118-290179 82137-280183 56115-280162 60125183305192 58120180300181 45104159360192 Adhesive strength (kgf / 0.5in) Initial HA 1 week HA 2 weeks HA 3 weeks MPA 1 week MPA 2 weeks MPA 3 weeks SCR 1 week SCR 2 weeks SCR 3 weeks 53463933463730433732 52382820423224362618 52403226443527433630 50383022423326413226 46403225403329362720 53463932453628423530 52362519403123352518 48423529403227362821 Initial rubber 1% HA 2 weeks HA 3 weeks MPA 1 week MPA 2 weeks MPA 3 weeks SCR 1 week SCR 2 weeks SCR 3 weeks 100959187959287898479 100857565887971654520 100867667908580868073 100857467928882888275 100837262867568604018 100959086959085706054 100807060857467654218 100959390959288706052

* Steel cord structure used for adhesion test: 2 + 2 (0.25) high tensile cord with brass plating

* 100 (200, 300)% M: Stress value applied to the specimen at 100 (200, 300)% tension

Eb: Elongation at break (%)

* Ts: Fracture Strength (kgf / ㎠)

* HA: heat aging (heat aging in 100 ℃ oven)

* MPA: Moisture Penetration Adhesion (Aging in Oven with 75 ℃, 96% Relative Humidity)

* SCR: Salt corrosion resistance (aging in 20% NaCl aqueous solution)

* Changes in tensile properties due to thermal aging showed only test results of specimens left for 48 hours in an oven at 100 ° C.

In terms of the change in tensile properties according to aging, Examples and Comparative Examples 5 and 7 using a quinone-diimine-based anti-aging agent were shown to have a smaller change in physical properties compared to Comparative Example 1 when using a general spray agent. The change in elongation after aging is shown to be very small compared to the conventional rubber. However, in Comparative Example 6, the amount thereof is so small that the anti-aging effect is not sufficiently exhibited. In Comparative Example 7, the addition amount is too high and the strength (modulus) is too low to be suitable for rubber for steel cords.

The rubber using the cobalt-boron complex does not have a significant effect on the tensile property change after aging compared to the conventional rubber, but slightly improved compared to the conventional rubber. The reason why the quinone-diimine-based anti-aging agent is superior to the general anti-aging agent is that it retains physical properties. This is because the city can fully exhibit the effect of the roadwork. In order to confirm the reactivity of the rubber main chain and the quinone-diimine-based preservative, rubber obtained by mixing acetone and a quinone-diimine-based preservative was mixed with rubber, and the results of the extraction using acetone are shown in Table 3.

The results of evaluation of the rubber-steel cord adhesion of each example show that the adhesive strength after thermal aging of the quinone-diimine-based lubricating agent is much better than that of the general lubricating agent. Able to know. In addition, the rubber using the cobalt-boron complex is superior to the adhesive strength after aging of water and brine, compared to the case of using naphic acid-based cobalt salt. This suggests that the cobalt-boron complex is excellent in preventing corrosion by water and brine. This corrosion protection effect is because the boron anion present in the cobalt salt has the effect of preventing corrosion. In particular, in the case of the embodiment, it can be seen that the cobalt-boron complex and the quinone-diimine-based preservative are used at the same time as well as the heat aging performance of the rubber as well as excellent corrosion resistance effect.

In addition, when using the reactive antioxidant and 6-QDI at the same time as in the embodiment it can be seen that both the corrosion resistance and heat aging performance is excellent.

Acetone extraction rate of vulcanized rubber (when added to natural rubber) Additive Agent Amount Extraction amount Vulcanized Rubber Extraction Rate N-isopropyl-N'-phenyl-p-phenylene diamine 5 4.65 93% N-1,3-dimethylbutyl-N'-phenyl-p-phenylene diamine 5 4.75 95% Poly-2,2,4-trimethyl-1,2,4-dihydroquinoline 5 4.45 89% N-isopropyl-N'-phenyl-p-quinone diimine 5 3.3 66% N-1,3-dimethylbutyl-N'-phenylquinone diimine 5 3.2 64%

As shown in Table 3 above, the general preservative is extracted by 90% or more by acetone, while the extraction rate of the quinone-diimine preservative is about 60%.

The cobalt boron complex, which has an excellent effect on corrosion protection according to the present invention, is used to prevent corrosion of the steel cord, as well as to add a quinone-imine-based antioxidant having a certain reactivity with rubber, thereby adding this antioxidant to the rubber main chain. Reaction fixation prevents radicals generated by heat from cutting off the rubber main chain, thereby preventing deterioration of the rubber and further improving the durability of the steel cord portion of the tire.

Claims (1)

With respect to 100 parts by weight of natural rubber, 40 to 80 parts by weight of carbon black having a nitrogen adsorption surface area of 70 to 100 m 2 / g and a DBP oil absorption of 60 to 100 ml / 100 g, and the cobalt boron complex of the following structural formula 1 to the pure cobalt content Tires containing 0.01 to 3 parts by weight, 0.4 to 9 parts by weight of N-1,3-dimethylbutyl-N'-phenylquinone diimine of the following structural formula 2, and an additive used in a rubber composition for a conventional tire steel cord Rubber composition for steel cords. Structural Formula 1 In the above, X is a fatty acid or naphtanic acid. Structural Formula 2