JPH10338771A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition, excellent in reinforcing properties, abrasion resistance and heat buildup characteristics useful for various rubber products such as hoses or mechanical belts including large-sized tires for trucks or buses and having especially the well balanced abrasion resistance and heat buildup characteristics. SOLUTION: This rubber composition is obtained by compounding 100 pts.wt. at least one rubber selected from the group consisting of a natural rubber and/or a diene-based synthetic rubber with 5-45 pts.wt. carbon black having a nitrogen specific surface area [N2 SA] within the range of 70-160 m<2> /g and a 24M4DBP oil absorption volume within the range of 50-120 mL/ 100 g and further surface functional groups of >=200 μ equiv./g hydroxyl groups, >=200 μequiv./g carboxyl groups and <=100 μ equiv./g quinone groups by oxidation treatment, 5-45 pts.wt. silica heat-treated at 250-450 deg.C temperature and 2-12 wt.% silane coupling agent based on the silica.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for various rubber products such as hoses and mechanical belts, such as large tires such as trucks and buses, and has improved reinforcing properties, abrasion resistance and heat generation characteristics. The present invention relates to a rubber composition having a good balance of heat generation characteristics.

[0002]

2. Description of the Related Art There are various types of carbon black for rubber reinforcement depending on the characteristics of the rubber components. Since the characteristics of these types are the main factors that determine various properties of a rubber composition to be compounded, the rubber component At the time of compounding, carbon black having a variety of characteristics suitable for the use of the member is selected and used. In recent years, fuel-efficient tires have been actively developed in order to meet social demands for resource saving and energy saving.

[0003] In general, when a soft carbon black having a large particle diameter is blended with a rubber component in a relatively small proportion, a rubber composition having low heat generation and high rebound resilience can be obtained.
There is a disadvantage that the reinforcing property and the wear resistance are reduced. On the other hand, a rubber composition containing a hard carbon black having a small particle diameter and a large specific surface area has a high degree of reinforcement and abrasion resistance, but has a disadvantage of increasing heat generation characteristics.

For this reason, in addition to basic properties such as particle diameter, specific surface area and structure, various properties of hard carbon black are evaluated more microscopically, and carbon black having specific selective properties is compounded in a rubber component. A number of techniques have been developed and proposed to improve the reinforcing property, wear resistance and heat generation characteristics by performing such techniques (for example,
No.-53978, JP-A-59-140241, JP-A-63-1126
No. 38, No. 63-179941, No. 63-225639,
63-297439, JP-A-1-201367, etc.).

In addition, in order to improve dispersibility and improve abrasion resistance, attention is paid to the surface chemical properties of carbon black particles and the chemical reaction with rubber molecules during kneading with a rubber component. A rubber composition containing carbon black having a high surface state has also been proposed. For example, JP-A-61-207452 discloses that the nitrogen adsorption specific surface area [N ₂ SA] is in the range of 100 to 200 m ² / g, the 24M4DBP oil absorption is in the range of 70 to 120 ml / 100 g, and
The amount of hydrogen generated (D) expressed in m-mol as the amount of hydrogen generated at 0 ° C. converted to 1 g of carbon black is represented by the formula D ≧
There is disclosed a rubber composition for a tire tread containing carbon black having a relationship of −3.30 × 10 ⁻³ × N ₂ SA + 0.89 (m-mol / g).

Japanese Unexamined Patent Publication (Kokai) No. 62-18446 discloses that the nitrogen adsorption specific surface area [N ₂ SA] is 70 to 200 m ² / g,
A carbon black having an oil absorption in the range of 80 to 130 ml / 100 g, wherein a phenolic hydroxyl group is mainly introduced into the surface of the carbon black by low-temperature plasma treatment, or after the introduction of a carboxyl group and a phenolic hydroxyl group, Carbon black 30 with neutralized base
There has been proposed a rubber composition containing dispersibility-improved carbon black to which -150 parts by weight is added.

Further, Japanese Patent Application Laid-Open No. 1-92247 discloses that
Nitrogen adsorption specific surface area [N ₂ SA] is 65 to 160 m ² / g, 24
A carbon black having an M4DBP oil absorption of 70 to 140 ml / 100 g, wherein the concentration of phenolic hydroxyl groups introduced on the surface of the carbon black is 3.0 × 10 ¹² to
8.1 × 10 ¹⁴ particles / m ² , 30 to 80 parts by weight of a reinforcing carbon black having a pH value of 3 to 5;
There is disclosed a rubber composition in which 0 parts by weight and a silane coupling agent are added and mixed in an amount of 5 to 20% by weight based on the total amount of carbon black and silica. This is to improve the abrasion resistance by forming a strong bond between the carbon black surface and the rubber polymer by the silane coupling agent.

[0008]

As a result of further detailed research on the relationship between the functional group present on the surface of carbon black and the physical properties of the compounded rubber composition, the present inventors have found that a quinone group as a functional group is a hydroxyl group. Or if it is significantly more than carboxyl groups, tensile strength, abrasion resistance,
It has been found that rubber properties such as heat generation properties are reduced, and that when hydroxyl is present in combination with silica, hydroxyl groups present on the surface are a factor for reducing these rubber properties, unlike carbon black.

The carbon black is appropriately oxidized on the surface to control the functional groups present on the surface to a specific range,
It was also confirmed that the silica used in combination was heat-treated to remove the hydroxyl group and that the use of a silane coupling agent could improve the rubber properties.

The present invention has been completed on the basis of the above findings, and its purpose is to provide reinforcement, wear resistance and heat generation useful for various rubber products such as large tires such as trucks and buses, hoses, and mechanical belts. It is an object of the present invention to provide a rubber composition having excellent properties, particularly having a good balance between abrasion resistance and heat generation properties.

[0011]

Means for Solving the Problems The rubber composition according to the present invention for achieving the above-mentioned object comprises 100 parts by weight of at least one kind of rubber selected from the group consisting of natural rubber and / or diene-based synthetic rubber. , Nitrogen adsorption specific surface area [N ₂ SA]
Is 70-160 m ² / g, 24M4DBP oil absorption is 50-12
It is within the range of 0ml / 100g, hydroxyl group is more than 200μeq / g and carboxyl group is 200μeq by oxidation treatment.
/ g or more, a quinone group having a surface functional group of 100 μeq / g or less 5 to 45 parts by weight, 250 to 450 parts by weight
The composition is characterized in that 5 to 45 parts by weight of silica heat-treated at a temperature of ° C. and a silane coupling agent are blended in a ratio of 2 to 12% by weight of silica.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As the rubber component used in the rubber composition of the present invention, natural rubber, styrene-butadiene rubber,
One type of diene-based synthetic rubber such as polybutadiene rubber and acrylonitrile-butadiene rubber, or a mixed rubber obtained by blending these is used.

The carbon black to be blended in the rubber composition of the present invention has an N ₂ SA of 70 to 160 m ² / g, 24M4
The DBP oil absorption is in the range of 50 to 120 ml / 100 g,
Hard carbon blacks such as SAF, ISAF and HAF are targeted. N ₂ SA value of 70 m ² / g and 24M4D
When the value of BP oil absorption is less than 50 ml / 100 g, the dispersibility in the rubber component is reduced and the heat generation increases, and the value of N ₂ SA is 160 m ² / g and the value of 24M4DBP oil absorption is 120 ml / 100 g.
If it exceeds g, the amount of functional groups per unit surface area of the carbon black will be small, and it will not be possible to sufficiently improve the reinforcing properties, abrasion resistance and heat generation properties.

As these characteristic values, values obtained by the following measuring methods are used. Nitrogen adsorption specific surface area [N ₂ SA]: ASTM D303
7-88 “Standard Test Method for Carbon Black-Su
rface Area by Nitrogen Adsorption "Method B. The measured value of IRB # 6 by this method is 76 m ²
/ g. 24M4DBP oil absorption: ASTM D3037-88
“Standard Test Method for Carbon Black-n-Dibutyl
Phthalate Adsorption Number of Compressed Sample ”
by. The measured value of IRB # 6 by this method is 8
It is 7 ml / 100 g.

By oxidizing these carbon blacks under appropriate conditions, the type and amount of functional groups present on the surface are controlled and controlled. Oxidation treatment is ozone, oxygen, N
Normal methods such as gas-phase oxidation with O gas or the like, wet oxidation with nitric acid, aqueous hydrogen peroxide, acetic acid, etc. can be applied, but under strong oxidation treatment conditions, the hydroxyl group and carboxyl group are changed to quinone groups. It is preferable to carry out under mild conditions. For example, by immersing carbon black in a mixed solution of aqueous hydrogen peroxide and glacial acetic acid for an appropriate time, washing with water, and drying, a large number of hydroxyl groups can be generated as functional groups on the surface of carbon black. Further, carbon black is placed in a nitric acid solution, refluxed and circulated at an appropriate temperature with a reflux condenser, washed with water, and dried, whereby a large amount of carboxyl groups can be generated as functional groups on the surface of carbon black. Thus, carbon black having a surface functional group having a hydroxyl group of 200 μeq / g or more, a carboxyl group of 200 μeq / g or more, and a quinone group of 100 μeq / g or less is prepared.

The amount of functional groups on the surface of carbon black is 200 μeq / g or more for hydroxyl groups and 200 μeq / g for carboxyl groups.
The reason for setting the quinone group to a value of 100 μeq / g or less, because the hydroxyl group is less than 200 μeq / g and the carboxyl group is less than 200 μeq / g, the exothermicity increases when the rubber composition is used. This is because wear resistance and tensile strength are reduced. Furthermore, the hydroxyl group is 200 μeq / g
As described above, even if the carboxyl group is 200 μeq / g or more,
When the quinone group exceeds 100 μeq / g, the tensile strength is remarkably reduced.

The silica used in the rubber composition of the present invention is preferably in the form of fine particles produced by a wet method, and the hydroxyl groups have been removed by heat treatment at a temperature of 250 to 450 ° C. in air. Things are used. If the heating temperature is lower than 250 ° C., the removal of hydroxyl groups is not sufficient, so that rubber properties such as abrasion resistance and exothermic characteristics are deteriorated. If the heating temperature is higher than 450 ° C., reagglomeration easily occurs in the rubber component and the rubber compounding time is long. This is because not only is the tensile strength lowered, but also the tensile strength is reduced.

These carbon blacks and silicas are
The rubber component is blended in a ratio of 5 to 45 parts by weight of carbon black and 5 to 45 parts by weight of silica with respect to 100 parts by weight of rubber. If the compounding ratio of carbon black is less than 5 parts by weight, the reinforcing effect is low, and if it exceeds 45 parts by weight, the heat generation characteristics are deteriorated. On the other hand, if the compounding ratio of silica is less than 5 parts by weight, the heat generation characteristics cannot be maintained at a low level, while if it exceeds 45 parts by weight, the reinforcing property is reduced. The silane coupling agent is a component added for firmly bonding the rubber component and silica, and is blended in an amount ratio of 2 to 12% by weight based on silica. If the addition ratio of the silane coupling agent is less than 2% by weight, the coupling effect is small, and 12% by weight.
If it exceeds, not only gelation of the rubber polymer occurs but also disadvantages in cost.

In the rubber composition of the present invention, in addition to the above-described carbon black, silica and a silane coupling agent,
Necessary rubber chemicals such as vulcanizing agents, vulcanization accelerators, anti-aging agents, vulcanization aids, softeners, plasticizers and the like which are commonly used
The rubber composition of the present invention is obtained by compounding and kneading at a ratio of 20 to 100 parts by weight with respect to parts by weight.

[0020]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

(1) Preparation of carbon black sample: ISA
Using F (N220) and HAF (N330, N351) grade carbon black, surface oxidation treatment was performed by the following method to prepare carbon black samples having different surface functional groups. Surface oxidation treatment: 50 g of carbon black and 20% of 35% hydrogen peroxide solution
After being immersed in a mixed solution of 00 ml and 2000 ml of glacial acetic acid at room temperature for 48 hours, it was washed with water until neutral and dried. 50 g of carbon black was added to a 35% nitric acid aqueous solution 700
The mixture was treated with a reflux condenser at 110 ° C. for 5 hours, washed with water until neutral, and dried. 50 g of carbon black is added to a 60% aqueous nitric acid solution 200
After being immersed at room temperature for 48 hours, the mixture was washed with water until it became neutral and dried.

For each of the obtained carbon black samples, the amount of surface functional groups was measured by the following method, and the characteristics are shown in Table 1. a hydroxyl group; 2,2'-Diphenyl-1-picrylhydra
zyl (DPPH) is dissolved in carbon tetrachloride and the concentration is 5 × 10 ^-4
A 0.1 mol / l solution was prepared, 0.1 to 0.6 g of carbon black was added to the solution, and the mixture was stirred in a thermostat at 60 ° C. for 6 hours. Thereafter, carbon black was separated from the reaction solution by filtration, and the filtrate was measured with an ultraviolet absorption spectrophotometer to calculate the amount of hydroxyl groups. b Carboxyl group: 2 to 5 g of carbon black was added to 50 ml of 0.976N sodium hydrogen carbonate, and the mixture was shaken for 6 hours. Then, the carbon black was filtered off from the reaction solution, and the filtrate was subjected to a titration test to calculate the amount of carboxyl group. did. c quinone group; sodium borohydride aqueous solution (6.87 × 10
^{-3 ~7.94 × 10 -3 mol / l} ) was shaken for 3 hours by the addition of carbon black 1~4g in and then filtered to remove the carbon black from the reaction solution, generated by dropping a small amount of 12N sulfuric acid to the filtrate The amount of quinone group was calculated from the amount of hydrogen gas.

[0023]

[Table 1]

Examples 1 to 6, Comparative Examples 1 to 3 (2) Styrene butadiene rubber compounding: Carbon black samples shown in Table 1 and Nipsil-AQ manufactured by Nippon Silica Industry Co., Ltd.
Was heated at 400 ° C. in the air, and SI-69 manufactured by Degussa was used as a silane coupling agent, and styrene-butadiene rubber [JSR1712 manufactured by Nippon Synthetic Rubber Co., Ltd.] was used at a compounding ratio shown in Table 2. ].

[0025]

[Table 2]

The rubber properties obtained by vulcanizing these compounds at a temperature of 145 ° C. for 50 minutes were measured for rubber properties by the following methods and conditions. The results are shown in Table 3. Tensile strength: measured according to JIS-6301. Abrasion test; ASTM D2 using pico abrasion tester
The wear loss was measured according to 228. Exothermic; Visco Elastic Spectrom manufactured by Iwamoto Seisakusho
According to the tester, a slab sheet with a thickness of 2 mm and a width of 5 mm was used for the test piece, the distance between the test piece sandwiches was 20 mm, and the initial load was 12
0 g, dynamic distortion: 2%, frequency: 20 Hz, temperature: 6
The loss factor (tan δ) was measured at 0 ° C.

[0027]

[Table 3] (Note) * 1 Sample number of carbon black shown in Table 1

Examples 7 to 12, Comparative Examples 4 to 6 (3) Compounding of natural rubber: Carbon black samples shown in Table 1 and Nipsil-AQ manufactured by Nippon Silica Kogyo Co., Ltd.
Silica heat-treated at a temperature of 0 ° C., and SI-69 manufactured by Degussa as a silane coupling agent, were blended with natural rubber (RSS # 1) at a blending ratio shown in Table 4. About the rubber composition obtained by vulcanizing these compounds at a temperature of 145 ° C. for 40 minutes, the rubber properties were measured by the same method and conditions as in Examples 1 to 6, and the results are shown in Table 5. .

[0029]

[Table 4]

[0030]

[Table 5] (Note) * 1 Sample number of carbon black shown in Table 1

From the results shown in Tables 3 and 5, the rubber compositions of the respective examples in which styrene butadiene rubber or natural rubber was blended with carbon black having the surface functional group content specified in the present invention had a surface functional group content of It can be seen that the tensile strength is higher and the amount of pico abrasion is smaller than that of the rubber composition of each comparative example in which the corresponding carbon black which deviates from the requirements specified in the present invention is blended. Further, it is recognized that the value of the loss coefficient (tan δ) indicating the heat generation characteristics is small, and the heat generation characteristics are also excellent.

[0032]

As described above, according to the rubber composition of the present invention, carbon black having a hydroxyl group, carboxyl group and quinone group amount controlled as specific functional groups on the surface by oxidation treatment is used as a rubber. By blending it with the component, the nitrogen adsorption specific surface area of carbon black [N ₂ S
A], the amount of 24M4DBP oil absorption and the heat-treated silica and silane coupling agent function synergistically to provide high reinforcement and to provide high abrasion resistance and low heat generation in a well-balanced manner. Therefore, it is possible to provide a rubber composition that can be suitably used for various rubber products such as hoses and mechanical belts, as well as large tires such as trucks and buses.

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Claims (1)

[Claims] 1. A nitrogen adsorption specific surface area [N ₂ SA] of 70 to 160 m ² per 100 parts by weight of at least one rubber selected from the group consisting of natural rubber and / or diene synthetic rubber.
/ g, 24M4DBP oil absorption is in the range of 50-120ml / 100g, hydroxyl group is 200μeq by oxidation treatment
/ g or more, carboxyl group 200 μeq / g or more, quinone group 5 to 45 parts by weight of carbon black having a surface functional group of 100 μeq / g or less, silica heat-treated at a temperature of 250 to 450 ° C. 5 to 45 parts by weight, And a silane coupling agent in an amount of 2 to 12% by weight of silica.