JPH09124842A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition high in wear resistance, suitable especially for a tire tread, by blending a rubber with carbon black excellent in dispersibility in rubber and processability. SOLUTION: This rubber composition for tire tread is obtained by blending 100 pts.wt. of at least one rubber selected from the group consisting of a natural rubber and/or a diene-based synthetic rubber with 20-100 pts.wt. of carbon black having 100-160m<2> /g specific surface area of nitrogen absorption [N2 SA], 50-100ml/100g 24M4DBP oil absorption and a value of a surface free energy [γDs ] mJ/m<2> satisfying the relationship of the following formula. 0.582×[N2 SA]+47.5<=[CDs]<=0.914+19.1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition containing carbon black having excellent dispersibility in rubber and having high abrasion resistance, and particularly suitable for tire treads.

There are various varieties of carbon black for rubber reinforcement depending on the characteristics of the rubber, and these characteristics of varieties are major factors that determine the various performances of the rubber composition to be blended. At the time of compounding, carbon black having a variety of characteristics suitable for the material application is selected and used. For example, for rubber members that require a high degree of wear resistance under severe running conditions such as tire treads,
Hard type carbon black such as SAF (N110) and ISAF (N220) is applied.

However, since these carbon blacks have a small particle size and a large specific surface area, the rubber component becomes highly viscous and the hardness increases during the kneading process during rubber compounding, and the carbon black can be uniformly dispersed in the rubber component. It will be difficult.
For this reason, the quality characteristics of the compounded rubber deteriorate, and this causes a decrease in wear resistance, which is particularly important as a tire tread.

Further, in the method of improving the wear resistance by increasing the blending amount of carbon black, not only the elastic modulus of the blended rubber becomes high and the workability is impaired, but also the cut resistance during tire running and This will lead to a decrease in chipping resistance.

[0005]

Therefore, a rubber composition having improved wear resistance by improving the dispersibility of carbon black in a rubber component has been developed. For example, the applicant has focused on carbon black particle agglomerates, and a rubber composition for tire tread containing carbon black having a broadened aggregate size distribution (JP-A-63-112638), aggregate size distribution. A rubber composition (Japanese Unexamined Patent Publication (Kokai) No. 63-179941) containing carbon black having two maximum points in a specific range was proposed.

Further, the present applicant has found that the nitrogen adsorption specific surface area [N
₂ SA] belongs to the hard system region of 140 m ² / g or more, and the particle aggregate void diameter (nm) is 59.182-0.236 ×
Carbon black having a characteristic value equal to or more than the value calculated by the formula [N ₂ SA (m ² / g)] is 3 per 100 parts by weight of the rubber component.
A rubber composition has been developed which is compounded at a ratio of 5 to 100 parts by weight (Japanese Patent Laid-Open No. 64-136). According to this technology,
By setting the voids of the particle aggregates per constant specific surface area of the carbon black to be relatively large, it is possible to improve the dispersion processability in the kneading process with the rubber component.

Further, in order to improve the dispersibility and wear resistance, paying attention to the surface chemical properties of the carbon black particles and the chemical reaction with the rubber molecules during the kneading with the rubber component, the reactivity with the rubber is considered. A rubber composition containing carbon black having a high surface state has also been proposed. For example, in JP-A-61-207452, the nitrogen adsorption specific surface area [N ₂ SA] is 100 to 200 m ² / g, the 24M4DBP oil absorption is in the range of 70 to 120 ml / 100 g, and 120
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 ≧
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) is disclosed.

[0008]

However, focusing only on specific radicals existing on the surface of carbon black particles means that the influence of other radicals will be ignored, and the chemical reactivity with rubber molecules will be considered comprehensively. There are difficulties that cannot be evaluated.

The inventor of the present invention targets a hard carbon black having a small particle size of carbon black, that is, a large nitrogen adsorption specific surface area [N ₂ SA], and a parameter indicating interfacial reactivity with a hydrocarbon component of a rubber molecule. As a result of the search, it was found that the reactivity can be quantitatively grasped by the surface free energy of the carbon black particles, that is, the difficulty of the dispersion workability of carbon black can be evaluated.

The present invention has been completed on the basis of the above findings, and its object is to improve the dispersibility of carbon black in a rubber component so that a tire tread having excellent wear resistance can be obtained. To provide a rubber composition suitable as.

[0011]

A rubber composition for a tire tread according to the present invention for achieving the above object comprises at least one rubber 100 selected from the group consisting of natural rubber and / or diene synthetic rubber. Nitrogen adsorption specific surface area [N ₂ SA] is 100 to 160 (m ² / g) in parts by weight, 24M4D
Carbon black having a BP oil absorption of 50 to 100 (ml / 100g) and a surface free energy [γ ^D _S ] (mJ / m ² ) satisfying the following formula (1) is 20 to
The composition is characterized in that 100 parts by weight is blended. 0.582 x [N ₂ SA] + 47.5 ≤ [γ ^D _S ] ≤ 0.914 x [N ₂ SA] + 19.1 (1)

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a rubber component used in the present invention, one kind of a diene-based synthetic rubber such as natural rubber, butadiene rubber, styrene-butadiene rubber or isoprene rubber,
Alternatively, a hydrocarbon rubber such as a mixed rubber obtained by blending these may be used.

Among the carbon black characteristic items specified in the present invention, the nitrogen adsorption specific surface area [N ₂ SA] is 100 to 1
60m ² / g particle characteristics and 24M4DBP oil absorption of 50 ~
The range of structure characteristics of 100 ml / 100 g is SAF (N110), ISAF (N220, N23) of normal varieties.
1, N234) and the like, which is a prerequisite for imparting a high degree of wear resistance for tire treads. Nitrogen adsorption specific surface area [N
₂ SA] is less than 100 m ² / g, abrasion resistance is not sufficient,
On the other hand, if it exceeds 160 g m ² / g, the carbon black particles become finer and the dispersibility in the rubber component deteriorates, and the wear resistance and the reinforcing property decrease. Also, 24M4DBP oil absorption is 50ml / 100
If it is less than g, wear resistance will be impaired and 100 ml / 100
If it exceeds g, the elastic modulus increases, resulting in a decrease in fatigue property and deterioration of workability.

According to the present invention, the value of the surface free energy [γ ^D _S ] is the nitrogen adsorption specific surface area [N
₂ SA], the main constituent requirement is to satisfy the value of the following expression (1). 0.582 x [N ₂ SA] + 47.5 ≤ [γ ^D _S ] ≤ 0.914 x [N ₂ SA] + 19.1 (1)

The surface free energy is a parameter indicating the activity of the surface properties of carbon black particles, that is, the rate of chemical reactivity with rubber molecules and the degree of strength and weakness, and the magnitude of the surface free energy is carbon. It is also related to the particle size and specific surface area of the black particles, and for example, the larger the specific surface area, the larger the surface free energy value. The surface free energy [γ ^D specified in the present invention
_The carbon black having _S ] set to a value of 0.582 × [N ₂ SA] +47.5 or more has a relatively high surface free energy value with respect to the nitrogen adsorption specific surface area as compared with the carbon black of the usual type. It is characterized by that. Therefore, when the nitrogen adsorption specific surface area is the same, since it has more surface activity that is rich in chemical reactivity with rubber molecules, it becomes easier to disperse it in the rubber component, and a strong reaction layer with rubber molecules is obtained. As a result, the wear resistance is improved.

However, when the surface free energy increases, the value of the loss coefficient (tan δ) of the physical properties of the compounded rubber tends to increase, and the impact resilience and heat generation characteristics tend to deteriorate. Especially, the surface free energy [γ ^D _S ] is 0.914 × [N
₂ SA] ＋ 19.1 Exceeding the equation value, loss factor (tan δ)
Becomes extremely large, so it is necessary to set the value below the same value. For this reason, as an appropriate value of the surface free energy [γ ^D _S ] that can effectively improve the wear resistance while suppressing the increase of the loss coefficient (tan δ), the above formula (1) is used. To be specified in the range.

The rubber composition of the present invention is intended for SAF and ISAF grade hard carbon black having a large specific surface area, and has a relatively large surface free energy per constant nitrogen adsorption specific surface area and a loss coefficient (tan δ). By setting the upper limit within a range in which the increase of) is allowed, it functions synergistically with the characteristics of the nitrogen adsorption specific surface area and the 24M4DBP oil absorption, which are prerequisites, and the carbon black content in the kneading process with the rubber component is The dispersibility in the rubber component is remarkably improved. As a result, it becomes possible to effectively prevent the deterioration of the abrasion resistance of the rubber composition due to the decrease in the dispersibility.

The characteristic values of the above carbon black are
The values obtained by the following measurement 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 Absorption "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.

Surface free energy [γ ^D _S ]: Carbon black is filled in a Teflon tube having an outer diameter of 4 mm and an inner diameter of 3 mm, the total surface area is 10 m ² , an adsorption layer is prepared, and a gas chromatographic analysis is conducted. The analysis conditions for gas chromatography were: injection temperature 200 ° C, column temperature 100 ° C, detector temperature 250 ° C, helium gas was used as a carrier gas, and a flow rate of 30 ml / min (measured with soap membrane flowmeter) was set. To do. As a probe, C
5 (n-pentane), C6 (n-hexane) and C7 (n-heptane) are used.

Under the above-mentioned certain conditions, each probe was set to 0.1, 0.075, 0.05, 0.
Inject 025, 0.01 μl and measure the retention time of each. The retention volume of the sample is calculated by multiplying the measured retention time by the carrier gas flow rate, and the infinite dilution retention volume (V _n ) of each probe is estimated by a fourth-order polynomial. By substituting the estimated value of the retention volume (V _n ) in this infinitely diluted state into the following formula (2), the change amount of the adsorption energy per 1 mol of the methyl group (CH ₂ group) is calculated, and the freeness about the CH ₂ group is calculated. Energy change ΔG
_(CH2) (J / mol) is calculated. However, V _{(n + 1)} is an infinite dilution retention volume of a linear alkane having one carbon number more than V _(n) . ΔG _(CH2) = RT × ln [V _{(n + 1)} / V _(n) ] (2)

Next, the surface free energy [γ ^D _S ] (mJ / m ² ) is calculated from the following equation (3). [Gamma ^D _{S] ^{= (ΔG (CH2)) 2}} /4 · N A 2 · a 2 (CH2) · γ (CH2) ... (3) In addition, in (3), N _A is Avogadro's number [6. 02
2 × 10 ²³ ] (mol ⁻¹ ), a ₍ CH _{2 )} is a contact area per one CH ₂ group [0.06 × 10 ^-18 ] (m ² ), and γ _{(C H2)} is C
Dispersive interaction of surface free energy of H ₂ group [35.
6 + 0.058 (298-T)] (J / m ² ), T is temperature (K)
It is.

The carbon black having the surface free energy [γ ^D _S ] of the present invention can be obtained by subjecting SAF and ISAF grade furnace blacks, which are generally used as a hard type for rubber reinforcement, to an oxidation treatment. . The oxidation treatment can be modified into carbon black having a predetermined surface free energy by oxidizing under appropriate treatment conditions by a method such as gas phase oxidation or liquid phase oxidation. For example, a method of heat-treating carbon black in an oxygen-containing atmosphere such as air or an ozone atmosphere, or a method of heating and stirring carbon black in a nitric acid solution or a hydrogen peroxide solution is preferably applied.

These carbon blacks, along with the necessary components such as a vulcanizing agent, a vulcanization accelerator, an antiaging agent, a vulcanization aid, a softening agent and a plasticizer, are used in accordance with a conventional method, as well as natural rubber, diene-based synthetic rubber and the like. 20 parts to 100 parts by weight of the rubber component of
The rubber composition of the present invention is obtained by compounding and kneading at a ratio of -100 parts by weight.

[0024]

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

Examples 1 and 2 and Comparative Examples 1 to 3 As samples, SAF (N110) grade carbon black [“SEAST 9” manufactured by Tokai Carbon Co., Ltd., N ₂ SA: 142]
m ² / g, 24M4DBP: 96 ml / 100 g], and put carbon black in an amount corresponding to 1/10 of the column volume in a gas phase fluidized bed connected to an ozone generator, and an ozone flow rate of 2.0 Nm ³ / hr Ozone concentration was 10 g / Nm ³ and oxidation treatment was performed at room temperature for different times. The surface free energy of each of these oxidized and untreated carbon blacks was measured and shown in Table 1 together with the calculated values of the formula (1).

[0026]

[Table 1]

Examples 3 to 6 and Comparative Examples 4 to 9 As a sample, ISAF (N220) grade carbon black ["SEAST 6" manufactured by Tokai Carbon Co., Ltd., N ₂ SA: 1
17m ² / g, 24M4DBP: 98ml / 100g] and ISA
F (N219) grade carbon black ["Seast 600" manufactured by Tokai Carbon Co., Ltd., N ₂ SA: 106 m ² / g,
24M4DBP: 70ml / 100g], thinly laid in a heat-resistant bat to a thickness of about 2mm, and put in an electric furnace in the atmosphere for 5
The temperature was raised to 350 ° C. at a heating rate of 0 ° C./hr, and the holding time was changed to perform the oxidation treatment. Then, naturally cooled, the surface free energy of each obtained carbon black is measured, (1)
It is shown in Table 2 together with the calculated value of the formula.

[0028]

[Table 2]

The carbon blacks of Tables 1 and 2 were blended with styrene-butadiene rubber in the weight ratios shown in Table 3.

[0030]

[Table 3] (Table Note) * 1 JSR1712 manufactured by Japan Synthetic Rubber Co., Ltd.

A rubber composition obtained by vulcanizing these compounds at a temperature of 145 ° C. for 50 minutes was subjected to an abrasion test and a loss coefficient (tan δ) measurement. The results are shown in Table 4. The measurement was performed by the following method and conditions.

Abrasion test Using a Lambourn abrasion tester (mechanical slip mechanism),
The measurement was performed under the following conditions. The results show that Run Nos. 1 to 5 are indexes [(wear amount of Comparative Example 1 / wear amount of sample) x 100] when the wear amount of the carbon black of Comparative Example 1 (N110) is 100.
As Run Nos. 6 to 10, Comparative Example 4 (N220) was used,
unNos. 11 to 15 are each shown as an index when the abrasion amount of the carbon black of Comparative Example 7 (N219) is 100.
Therefore, the larger this value is, the better the abrasion resistance is. Test piece: thickness 10 mm, outer diameter 44 mm Emery wheel: GC type, grain size # 80, hardness H added carborundum powder: grain size # 80, addition amount about 9 g / min Relative slip ratio between emery wheel surface and test piece: 24
%, 60% Test piece rotation speed: 535 rpm Test load: 4 kg

Loss coefficient (tan δ) It was measured under the following conditions using a Visco Elastic Spectrometer manufactured by Iwamoto Seisakusho. The measurement results are Run Nos. 1 to 5 which are indexes when the measurement value of the loss coefficient (tan δ) of the carbon black of Comparative Example 1 (N110) is set to 100.
10 is Comparative Example 4 (N220), and Run Nos. 11 to 15 are indexes with the loss factor (tan δ) of the carbon black of Comparative Example 7 (N219) being 100. Loss factor (t
anδ) is an index of exothermicity, and the smaller this value is, the lower exothermicity is. Test piece: Thickness 2 mm, length 30 mm, width 5 mm Frequency: 50 Hz Dynamic strain rate: 1.2% Temperature: 60 ° C

[0034]

[Table 4] (Note) * 1 Slip rate 24%, * 2 Slip rate 60%

From the results shown in Table 4, the rubber composition containing the carbon black satisfying the characteristic requirements of the present invention has a smaller amount of abrasion than the corresponding rubber composition of Comparative Example and is excellent in abrasion resistance. I understand. In addition, the value of the surface free energy [γ ^D _S ] is 0.914 × [N ₂ SA] +19.1.
When carbon black exceeding the calculated value of is added, the wear resistance of the rubber composition is high, but the loss factor (tan
δ) becomes large, and remarkable deterioration of heat generation characteristics is recognized.

[0036]

As described above, according to the rubber composition of the present invention, the surface free energy [γ ^D _S ] of the carbon black particles which functions to disperse in the rubber component is determined by the corresponding nitrogen adsorption specific surface area [ N ₂ SA] and the loss factor (tan
Suitable for tire treads with high wear resistance because it has a good dispersion workability in the rubber component because it contains carbon black with an upper limit set to an appropriate range that allows an increase in δ). It is possible to provide a different rubber composition.

Claims (1)

[Claims] 1. A nitrogen adsorption specific surface area [N ₂ SA] of 100 to 160 is added to 100 parts by weight of at least one rubber selected from the group consisting of natural rubber and / or diene synthetic rubber.
(M ² / g), 24M4DBP oil absorption 50-100 (ml / 100
g) and a surface free energy [γ ^D _S ] (mJ / m ² ) of 20 to 100 parts by weight of carbon black that satisfies the relationship of the following formula (1). A rubber composition for a tire tread. 0.582 x [N ₂ SA] + 47.5 ≤ [γ ^D _S ] ≤ 0.914 x [N ₂ SA] + 19.1 (1)