JP2015124258A - Rubber composition for tire sidewall and pneumatic tire using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire sidewall for overcoming problems of worsening conductivity of the sidewall, generating radio noise and reducing various properties such as flexural fatigue resistance of the sidewall or cutting resistance with means for blending large particle diameter carbon black or the like for achieving reducing heat generation of the tire sidewall.SOLUTION: A rubber composition for a tire sidewall is obtained by blending, with respect to 100 pts.mass of a rubber composition consisting of natural rubber of 30 to 70 pts.mass and other diene rubber of 70 to 30 pts.mass, 3 to 15 pts.mass of conductive zinc oxide having an amount of oil absorption of 25 to 50 (ml/100 g), bulk specific volume of 400 to 1000 (ml/100 g) and volume resistivity of 1×10(Ω cm) or less, and 30 to 60 pts.mass of carbon black having an amount of DBP oil absorption of 80 to 120 (cm/100 g).

Description

  The present invention relates to a rubber composition for a tire sidewall and a pneumatic tire using the rubber composition, and more specifically, it has excellent heat conductivity, low heat generation resistance, bending fatigue resistance, and cut resistance. The present invention relates to a rubber composition for a tire sidewall in which generation of radio noise and the like are suppressed, and a pneumatic tire using the same.

  With the recent increase in environmental awareness, there is a need to improve the fuel efficiency of tires. The rubber composition for tire sidewalls also has such a requirement, and in order to reduce the heat generation of the sidewall, a large particle size carbon black is blended (Patent Document 1) or the blending amount of the carbon black is reduced. However, it is difficult to dissipate the static electricity generated in the car body and tire of the automobile through the tire tread, which causes problems such as radio noise. There was a point. In addition, the above-described means causes deterioration of various characteristics such as bending fatigue resistance and cut resistance of the sidewall.

JP-A-61-106686

  An object of the present invention is to provide a rubber composition for a tire sidewall that has excellent heat resistance, bending fatigue resistance, cut resistance, good electrical conductivity, and suppressed generation of radio noise and the like. It is to provide a pneumatic tire.

As a result of intensive studies, the present inventors have blended a specific amount of conductive zinc oxide having specific characteristics and a specific amount of carbon black having specific characteristics with a rubber component having a specific composition, It was found that the above problems could be solved, and the present invention could be completed.
That is, the present invention is as follows.

1. The amount of oil absorption is 25 to 50 (ml / 100 g) and the specific volume is 400 to 1000 (ml / 100 ml) with respect to 100 parts by weight of the rubber component consisting of 30 to 70 parts by weight of natural rubber and 70 to 30 parts by weight of other diene rubbers. 100g) and a volume resistivity of ^{1 × 10 6 (Ω · cm} ) of the conductive zinc oxide or less 3-15 parts by blending, further, DBP oil absorption amount of carbon black 80 to 120 ^(cm 3 / 100g) 30 to 60 parts by mass of a rubber composition for tire sidewalls.
2. 10 to 30 parts by mass of the conductive zinc oxide, 3 to 18 parts by mass of stearic acid, and 20 to 35 parts by mass of the carbon black are blended with respect to 100 parts by mass of the rubber component, and (a) the conductive zinc oxide And (b) the blending ratio (b) / (a) with the stearic acid is 0.3 to 0.6, and the volume fraction of the carbon black × the DBP oil absorption / 100 is 15 to 30. 2. The rubber composition for a tire sidewall according to 1 above, wherein the master batch adjusted to 1 is blended.
3. A pneumatic tire using the rubber composition according to 1 or 2 as a sidewall.

According to the present invention, since a specific amount of conductive zinc oxide having specific characteristics and a specific amount of carbon black having specific characteristics are blended with a rubber component having a specific composition, low heat build-up, bending fatigue resistance It is possible to provide a rubber composition for a tire sidewall that has excellent electrical properties and cut resistance, has good electrical conductivity, and suppresses generation of radio noise and the like, and a pneumatic tire using the rubber composition.
In addition, by blending a master batch having a specific composition, excellent dispersibility of the conductive zinc oxide and carbon black can be obtained, and the effects can be further enhanced.

  Hereinafter, the present invention will be described in more detail.

(Rubber component)
The rubber component used in the present invention requires the use of natural rubber (NR). In addition to NR, any diene rubber that can be blended in the rubber composition for a tire sidewall can be used. For example, isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer Examples include coalesced rubber (SBR) and acrylonitrile-butadiene copolymer rubber (NBR). These may be used alone or in combination of two or more. The molecular weight and microstructure of the diene rubber are not particularly limited, and may be terminal-modified with an amine, amide, silyl group or the like.
In the present invention, when the rubber component is 100 parts by mass, the NR needs to be 30 to 70 parts by mass, and preferably 40 to 60 parts by mass.
Cut resistance deteriorates that the compounding quantity of NR is less than 30 mass parts. Conversely, when it exceeds 70 mass parts, exothermic property and bending fatigue resistance will deteriorate.
The diene rubber used other than NR is particularly preferably BR from the viewpoint of the effect of the present invention.

(Conductive zinc oxide)
The conductive zinc oxide used in the present invention has an oil absorption of 25 to 50 (ml / 100 g), a specific volume of 400 to 1000 (ml / 100 g), and a volume resistivity of 1 × 10 ⁶ (Ω · cm). It is necessary that: If the oil absorption is outside the above range, the cut resistance is not improved and the conductivity is also deteriorated. When the specific volume is outside the above range, the cut resistance is not improved and the conductivity is also deteriorated. If the volume resistivity exceeds 1 × 10 ⁶ (Ω · cm), desired conductivity cannot be obtained.
More preferably, the oil absorption is 35 to 45 (ml / 100 g).
Furthermore, the said specific volume of the said palm is 700-900 (ml / 100g).
More preferably, the volume resistivity is 1 × 10 ⁵ (Ω · cm) or less.
The conductive zinc oxide can be prepared by a known means such as doping of zinc oxide with ions. As the ^{ions, Li +, Na +, K} +, Rb +, Cs +, Ti 4+, Zr 4+, Ta 5+, V 5+, Nb 5+, Al 3+, B 3+, Ga 3 ⁺ , In ³⁺ , Tl ³⁺ , C ⁴⁺ , Si ⁴⁺ , Ge ⁴⁺ , Sn ⁴⁺ , Pb ⁴⁺ , N ³⁻ , P ³⁺ , As ³⁺ , Sb ³⁺ , Bi ³⁺ , O ²⁻ , S ²⁻ , Se ²⁻ , Te ^{2− and the} like can be mentioned. Moreover, what is marketed can be utilized for electroconductive zinc oxide, for example, Mitsui Kinzoku Mining Co., Ltd. product 23-K, Hakusuikku Co., Ltd. passet CK etc. are mentioned.
The amount of oil absorption and the specific volume of the bulk can be measured according to JIS K5101. The volume resistivity is a value obtained by putting 10 g of the test powder into a cylinder with an inner diameter of 25 mm processed with a polytetrafluoroethylene resin and pressurizing it at 10 MPa, and measuring the volume resistivity of the green compact with a volume resistivity measuring device.

(Carbon black)
Carbon black used in the present invention must have a DBP oil absorption in the range of 80~120 ^(cm 3 / 100g). When the DBP oil absorption is outside this range, low heat build-up cannot be obtained, and the bending fatigue resistance is also deteriorated. Further preferred DBP oil absorption amount is in the range of 100~115 ^(cm 3 / 100g).
The DBP oil absorption is a value determined based on the JIS K6217-4 oil absorption A method.

(Combination ratio of rubber composition for tire sidewall)
The rubber composition for a tire sidewall according to the present invention includes 3 to 15 parts by mass of the conductive zinc oxide and 100 to 30 parts by mass of the carbon black with respect to 100 parts by mass of the rubber component. It is characterized by that.
When the blending amount of the conductive zinc oxide is less than 3 parts by mass, the blending amount is too small to achieve the effects of the present invention. Conversely, if it exceeds 15 parts by mass, low heat build-up cannot be obtained, and bending fatigue resistance and cut resistance deteriorate.
Cut resistance deteriorates that the compounding quantity of the carbon black is less than 30 parts by mass. On the other hand, if it exceeds 60 parts by mass, low exothermic property cannot be obtained, and the bending fatigue resistance deteriorates.

A more preferable blending amount of the conductive zinc oxide is 6 to 12 parts by mass with respect to 100 parts by mass of the rubber component.
A more preferable blending amount of the carbon black is 40 to 50 parts by mass with respect to 100 parts by mass of the rubber component.

The rubber composition for a tire sidewall of the present invention can obtain excellent dispersibility of the conductive zinc oxide and carbon black by blending a master batch having a specific composition, and can further enhance the effect. it can.
That is, the masterbatch used in the present invention is 10 to 30 parts by mass of the conductive zinc oxide, 3 to 18 parts by mass of stearic acid, and 20 to 35 parts by mass of the carbon black with respect to 100 parts by mass of the rubber component. (A) the blending ratio (b) / (a) of the conductive zinc oxide and (b) the stearic acid is 0.3 to 0.6, and the volume fraction of the carbon black × the above The value of DBP oil absorption / 100 is adjusted to 15-30.
If the blending ratio (b) / (a) is less than 0.3, the dispersion of the conductive zinc oxide is deteriorated, which is not preferable. On the other hand, if it exceeds 0.6, the amount of stearic acid is excessive, and the effect of improving conductivity is reduced, which is not preferable.
When the value of volume fraction of carbon black × DBP oil absorption / 100 is less than 15, the effect of improving conductivity is reduced, which is not preferable. Conversely, if it exceeds 30, the effect of improving low heat build-up is reduced, which is not preferable.
The volume fraction of carbon black can be calculated by (volume of carbon black to be blended / volume of master batch) × 100.
The master batch can be prepared by, for example, using a known rubber kneader, such as a Banbury mixer, a kneader, or a roll, and kneading each component according to the above formulation. Subsequently, the composition of the present invention can be prepared by kneading the obtained master batch and other remaining components with the kneader.

(Other ingredients)
In addition to the above-described components, the rubber composition for tire sidewall used in the present invention includes a vulcanization or crosslinking agent; a vulcanization or crosslinking accelerator; various fillers such as silica, clay, talc, and calcium carbonate. Various oils, anti-aging agents, various additives generally added to rubber compositions such as plasticizers, and the like, and these additives are kneaded by a general method to form a composition. It can be used for sulfurization or crosslinking. The blending amounts of these additives can be set to conventional general blending amounts as long as the object of the present invention is not violated.

  The rubber composition for a tire sidewall of the present invention can be used to form a sidewall of a pneumatic tire according to a conventional method for producing a pneumatic tire.

The sidewall formed by the rubber composition for a tire sidewall of the present invention has, for example, an electric resistance of 1 × 10 ⁴ to 1 × 10 ⁷ (Ω · cm) (double ring electrode method (IEC60093, ASTM D257). , JIS K6911, JIS K6271)), excellent conductivity. In addition, the conductive zinc oxide is less susceptible to friction between the two, and can be uniformly entangled in the carbon black having a large particle size, increasing the dispersibility of both, low heat buildup, bending fatigue resistance, cut resistance Can be improved at the same time.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited to the following example.

Examples 1-7 and Comparative Examples 1-7
Preparation of sample In the formulation (parts by mass) shown in Table 1, the components except the vulcanization accelerator and sulfur were kneaded for 4 minutes with a 1.7 liter closed Banbury mixer, and then released to the outside of the mixer at about 160 ° C. Cooled to room temperature. Subsequently, a vulcanization accelerator and sulfur were added to the composition and kneaded with an open roll to obtain a rubber composition. Next, the obtained rubber composition was press vulcanized in a predetermined mold at 170 ° C. for 10 minutes to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece were measured by the following test method.

  In the examples where the master batch was blended, the master batch was kneaded for 4 minutes with a 1.7 liter closed Banbury mixer according to the formulation shown below, and then released to the outside of the mixer at about 160 ° C. And cooled at room temperature. Next, the obtained master batch was mixed with other components, and a vulcanized rubber test piece was obtained according to the preparation of the sample.

Exothermic property (tan δ (60 ° C.)): Using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., the dynamic elasticity was measured at a static strain of 10%, a dynamic strain of ± 2%, and a frequency of 20 Hz. Tan δ was measured. The result was expressed as an index with the value of Comparative Example 1 as 100. A smaller value means lower heat generation.
Cut resistance: Hardness was measured according to JIS K 6253. The result was expressed as an index with the value of Comparative Example 1 as 100. It means that it is excellent in cut resistance, so that this value is large.
Bending fatigue resistance: In accordance with JIS K6260, a bending test was performed 300 times per minute at room temperature, and the number of bendings until the crack length reached 20 mm was determined. The results are shown as an index with the value of Comparative Example 1 being 100. It means that it is excellent in bending fatigue resistance, so that this value is large.
Conductivity: The electric resistance value was measured according to JIS K6911.
The results are also shown in Table 1.

* 1: NR (RSS # 1)
* 2: BR (Nipol 1220 manufactured by Nippon Zeon Co., Ltd.)
* 3: Masterbatch-1 (based on 100 parts by mass of rubber component, (a) 10 parts by mass of the following conductive zinc oxide, (b) 5 parts by mass of the following stearic acid, and 20 parts by mass of the following carbon black (The blending ratio (b) / (a) is 0.5, and the value of carbon black volume fraction × DBP oil absorption / 100 is 15.)
* 4: Masterbatch-2 (100 parts by mass of rubber component (a) 10 parts by mass of the following conductive zinc oxide, (b) 5 parts by mass of the following stearic acid, and 10 parts by mass of the following carbon black (The blending ratio (b) / (a) is 0.5, and the value of carbon black volume fraction × DBP oil absorption / 100 is 8.)
* 5: Carbon Black -1 (Tokai Carbon Co., Ltd. Seast SO, nitrogen adsorption specific surface area ^{_{(N 2 SA) = 42m 2}} / g, DBP oil absorption ^{= 115 (cm 3 / 100g)} )
* 6: Carbon black 2 (Cabot Japan Ltd. SHOWBLACK N234, the nitrogen adsorption specific surface area ^{_{(N 2 SA) = 118m 2}} / g, DBP oil absorption ^{= 125 (cm 3 / 100g)} )
* 7: Conductive zinc oxide-1 (Pastran, Mitsui Mining & Smelting Co., Ltd., oil absorption = 40 (ml / 100 g), bulk specific volume = 800 (ml / 100 g), volume resistivity = 1 × 10 ² (Ω・ Cm))
* 8: Conductive zinc oxide-2 (23-K manufactured by Hakusuitec Co., Ltd., oil absorption = 20 (ml / 100 g), specific volume of bulk = 250 (ml / 100 g), volume resistivity = 1 × 10 ² (Ω・ Cm))
* 9: Zinc oxide (3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.)
* 10: Stearic acid (beef stearic acid manufactured by NOF Corporation)
* 11: Oil (Extract No. 4 S manufactured by Showa Shell Co., Ltd.)
* 12: Sulfur (Tsurumi Chemical Industry Co., Ltd., Jinhua Ink Fine Powdered Sulfur * 13: Vulcanization accelerator (Ouchi Shinsei Chemical Co., Ltd. Noxeller CZ-G)

As is apparent from Table 1 above, the rubber compositions prepared in the examples were obtained by adding a specific amount of conductive zinc oxide having specific characteristics and carbon black having specific characteristics to rubber components having specific compositions. As a result, it was proved that the heat resistance, the bending fatigue resistance, and the cut resistance were superior to those of the conventional representative comparative example 1 and that they had good conductivity.
On the other hand, Comparative Examples 2 and 3 could not obtain the desired conductivity because the oil absorption and bulk specific volume of the conductive zinc oxide were outside the ranges defined in the present invention. Moreover, the effect of improving cut resistance could not be confirmed.
In Comparative Example 4, since the amount of NR was less than the lower limit specified in the present invention, the cut resistance was deteriorated.
In Comparative Example 5, since the blending amount of carbon black exceeded the upper limit specified in the present invention, low exothermic property could not be obtained, and bending fatigue resistance was deteriorated.
In Comparative Example 6, since the DBP oil absorption amount of carbon black was outside the range specified in the present invention, low exothermic property could not be obtained, and bending fatigue resistance deteriorated.
In Comparative Example 7, since the blending amount of the conductive zinc oxide exceeds the upper limit specified in the present invention, low exothermic property cannot be obtained, and bending fatigue resistance and cut resistance deteriorated.

Claims (3)

The amount of oil absorption is 25 to 50 (ml / 100 g) and the specific volume is 400 to 1000 (ml / 100 ml) with respect to 100 parts by weight of the rubber component consisting of 30 to 70 parts by weight of natural rubber and 70 to 30 parts by weight of other diene rubbers. 100g) and a volume resistivity of ^{1 × 10 6 (Ω · cm} ) of the conductive zinc oxide or less 3-15 parts by blending, further, DBP oil absorption amount of carbon black 80 to 120 ^(cm 3 / 100g) 30 to 60 parts by mass of a rubber composition for tire sidewalls.   10 to 30 parts by mass of the conductive zinc oxide, 3 to 18 parts by mass of stearic acid, and 20 to 35 parts by mass of the carbon black are blended with respect to 100 parts by mass of the rubber component, and (a) the conductive zinc oxide And (b) the blending ratio (b) / (a) with the stearic acid is 0.3 to 0.6, and the volume fraction of the carbon black × the DBP oil absorption / 100 is 15 to 30. The rubber composition for a tire side wall according to claim 1, wherein the master batch adjusted to the above is blended.   A pneumatic tire using the rubber composition according to claim 1 or 2 as a sidewall.