JP4976736B2 - Rubber composition for tire sidewall and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition for a tire sidewall used for a sidewall portion of a pneumatic tire, and a pneumatic tire.

  Conventionally, it has been known to reduce the heat resistance of a tread rubber, which accounts for the majority of the hysteresis loss of a tire, and thereby reduce the rolling resistance of the tire in order to achieve a reduction in fuel consumption when driving a car. However, reducing the heat generation property of the tread rubber simultaneously reduces the grip performance. Therefore, it is desirable to reduce the rolling resistance at a portion other than the tread portion, and such a proposal has been made.

For example, in Patent Document 1 below, in a rubber composition for a tire sidewall, 5 to 50 parts by weight of carbon black having a specific average particle diameter, a compressed DBP oil absorption amount and a CTAB surface area with respect to 100 parts by weight of a diene rubber. Rolling resistance by blending 10 to 60 parts by weight of precipitated silica having a DBP oil absorption of 200 ml / 100 g or more and a BET nitrogen adsorption specific surface area of 180 m ² / g or less, and a specific amount of a silane coupling agent. It is described that a tire having a small electrical resistance, excellent wear resistance and WET performance, and low electrical resistance can be obtained.

Incidentally, in Patent Document 2, relative to 100 parts by weight of the rubber component, the ratio DBP of CTAB specific surface area of 80~150m ² / g, CTAB specific surface area DBP oil absorption amount to the ^{(m 2 / g) (cm} 3 / 100g) / CTAB is 1.3 or more, and Δthermal weight reduction rate (%), which is a value obtained by subtracting the reduction rate at 150 ° C. from the reduction rate at 1000 ° C. in thermogravimetry, and the CTAB specific surface area (m ² / G) 5 to 120 parts by weight of silica satisfying a predetermined relational formula, and 2 to 25 parts by weight of a coupling agent with respect to 100 parts by weight of the silica. Is disclosed. However, this rubber composition is used for tire treads, and its purpose is to improve fuel efficiency and low temperature performance without impairing wear resistance and wet grip properties, which is different from the present invention. It is.
JP 10-36559 A JP 2003-155383 A

  The present inventor has focused on parts other than the tread portion for reducing fuel consumption, and considers that the sidewall portion contributes most to lower fuel consumption, and reducing the heat generation property of the sidewall portion contributes to lower fuel consumption of the tire. I thought it was an effective method. And, silica was used to achieve low heat generation in the side wall part, and the formulation of large particle size silica was examined for further heat generation, but mere large particle size silica is still not enough to reduce fuel consumption. Moreover, it has been found that there is a demerit such as a decrease in cut resistance when large particle size silica is used.

  The present invention has been made in view of the above points, and while suppressing a decrease in cut resistance as much as possible, a rubber composition for a tire sidewall capable of reducing the rolling resistance of a tire and achieving low fuel consumption, And providing a pneumatic tire using the same.

The rubber composition for a tire sidewall according to the present invention has a DBP oil absorption (cm ³ ) with respect to 100 parts by weight of a diene rubber with a CTAB specific surface area of 80 to 130 m ² / g and a CTAB specific surface area (m ² / g). / 100 g) ratio DBP / CTAB is 1.3 or more, and Δthermal weight reduction rate (%) which is a value obtained by subtracting the reduction rate at 150 ° C. from the reduction rate at 1000 ° C. in thermogravimetry 5 to 70 parts by weight of silica whose relationship with the CTAB specific surface area (m ² / g) satisfies the following formula (1), and 0 to 70 parts by weight of carbon black, silica / carbon black = 0.2 / 1 to 1 / 0 weight ratio, and further, 2 to 25 parts by weight of a coupling agent is blended with respect to 100 parts by weight of silica.
ΔThermal weight reduction rate ≧ 0.0283 × CTAB specific surface area + 0.6 (1)

  Moreover, the pneumatic tire according to the present invention has a sidewall made of the rubber composition.

  According to the present invention, by using specific silica having a relatively large particle size and a large surface activity as described above in the rubber composition for a sidewall, a simple large particle size silica having an equivalent particle size can be obtained. Compared with the case where it is used, it is possible to further reduce the exothermic property and reduce the rolling resistance of the tire, and to reduce the margin for reduction in cut resistance. Therefore, it is possible to reduce the rolling resistance of the tire and reduce fuel consumption while suppressing the reduction in cut resistance as much as possible.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  As the diene rubber used in the tire sidewall rubber composition of the present invention, various rubbers used in tire sidewall portions can be used. For example, natural rubber, isoprene rubber, butadiene rubber, styrene butadiene Examples thereof include rubber and ethylene propylene rubber. These may be used alone or in combination of two or more.

The silica (hydrous silicic acid) used in the rubber composition for a tire sidewall of the present invention has a relatively large particle size with a CTAB specific surface area (cetyltrimethylammonium bromide adsorption specific surface area) in the range of 80 to 130 m ² / g. Silica. Here, the CTAB specific surface area means that the smaller the value, the larger the particle diameter of the silica. By using such a relatively large particle size silica, the heat generation can be reduced and the rolling resistance can be reduced. A more preferred lower limit of the CTAB specific surface area is Ru ^90m 2 / g der.

The silica may also ratio DBP / CTAB of DBP for CTAB specific surface ^(m 2 / g) ^(dibutyl phthalate) oil absorption ^(cm 3/100 g) is high structure product is 1.3 or more. A more preferable range of DBP / CTAB is 1.4 to 2.4. In general, DBP oil absorption is used alone as a structure index, but in the present invention, DBP / CTAB, which is a ratio to a CTAB specific surface area, is used as a structure index. This is because the smaller the particle size, the larger the number of particles in a constant weight and the higher the DBP oil absorption, and the DBP oil absorption alone does not express the degree of structure as it is.

The above silica also has a relationship between Δthermal weight reduction rate (%), which is a value obtained by subtracting the reduction rate at 150 ° C. from the reduction rate at 1000 ° C. in thermogravimetry, and the CTAB specific surface area (m ² / g). Satisfies the formula (1).

ΔThermal weight reduction rate ≧ 0.0283 × CTAB specific surface area + 0.6 (1)
In the thermogravimetric measurement, the volatile matter at 150 ° C. is due to adhering moisture, and the volatile matter at 1000 ° C. is mainly the one in which the surface silanol groups are volatilized as moisture. The rate of decrease is an indicator of how much silanol groups (Si-OH) are present on the silica surface. The larger the Δthermal weight reduction rate, the more silanol groups on the silica surface, that is, the greater the surface activity of the silica.

  This formula (1) is defined in order to increase the surface activity and improve the low heat buildup and cut resistance while using silica having a relatively small specific surface area. That is, when the formula (1) is not satisfied, the silica having a relatively large particle size as in the present invention has a small amount of bonding with a polymer, a low tear strength, and a significant reduction in cut resistance. Become. Also, the low exothermic property is inferior due to the small amount of bonding with the polymer.

  The Δthermal weight reduction rate tends to increase as the CTAB specific surface area increases because it is the amount of volatile matter on the silica surface. However, in the conventional rubber composition for a tire sidewall, the high Δheat as described above with respect to the CTAB specific surface area. Silica with a weight loss rate is not used. The silica usually used in the conventional rubber composition for tire sidewall has a Δthermal weight reduction rate of about 0.0283 × CTAB specific surface area or less, and is clearly different from the silica used in the present invention. is there.

  As described above, the colloidal characteristics of silica have a relatively small specific surface area, but have a high structure and a large surface activity, so that the silica is physically or chemically bonded to the polymer to generate heat. Can be greatly reduced. Moreover, compared with the silica with an equivalent particle diameter, it is possible to reduce the drop in tear strength and to suppress the deterioration of cut resistance.

  In the rubber composition for a tire sidewall of the present invention, the silica is blended in an amount of 5 to 70 parts by weight based on 100 parts by weight of the diene rubber. When the blending amount of silica is less than 5 parts by weight, the above-described effects of the present invention cannot be sufficiently exhibited, and when it exceeds 70 parts by weight, a sufficient exothermic reduction effect cannot be obtained. As for the more preferable compounding quantity of a silica, a minimum is 20 weight part and an upper limit is 60 weight part.

  The rubber composition for a tire sidewall of the present invention may contain carbon black, although not essential, together with silica, and the carbon black is blended in an amount of 0 to 70 parts by weight with respect to 100 parts by weight of the diene rubber. . Silica and carbon black are blended at a ratio of silica / carbon black = 0.2 / 1 to 1/0. When the ratio of silica is less than this range, the effect of improving fuel efficiency becomes insufficient.

  The coupling agent used in the rubber composition for a tire sidewall of the present invention binds silica and a diene rubber, for example, sulfide, amino group, mercapto group, vinyl group, methacryl group, epoxy group, etc. And an organic silane compound having an organic moiety capable of reacting with the above polymer and a halogen or an alkoxy group. Preferably, a sulfide silane represented by the following general formula (2) or a protected mercaptosilane represented by the general formula (3) is used.

_{(C 2 H 5 O) 3} Si-C 3 H 6 -S x -C 3 H 6 -Si (OC 2 H 5) 3 ... (2)
In formula (2), x is 2-4. Incidentally, -S x in the formula _- per, x is has a normal distribution, i.e., generally sold on the market as a mixture of several of sulfur chain binding different, x is representative of the average value. Specific examples of such silane coupling agents include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, and the like.

_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 ... (3)
In formula (3), n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9. This silane coupling agent is a protected mercaptosilane in which a hydrogen atom of a mercapto functional group is substituted, and can be produced, for example, according to the method described in JP-T-2001-505225. By using such a protected mercaptosilane, fuel efficiency can be further improved, and deterioration of tear strength can be further suppressed.

  The coupling agent is blended in an amount of 2 to 25 parts by weight, preferably 4 to 15 parts by weight, based on 100 parts by weight of silica. The coupling agent may be preliminarily treated with silica, and the treated silica may be added to and mixed with the diene rubber.

  In addition to the above-described components, the rubber composition for a tire sidewall of the present invention includes various additives such as a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, a softening agent, a plasticizer, an activator, and a lubricant. It can be added as necessary.

  The tire sidewall rubber composition of the present invention comprising the above is used as a rubber composition for a sidewall portion of a pneumatic radial tire, and is formed by vulcanization molding according to a conventional method. Can do.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to these Examples.

1. Silica As the silica, five types of silica shown in Table 1 below were used. Among them, silica (1) is “Nip Seal AQ” made by Nippon Silica, which is widely used as silica to be blended in the tire rubber composition. Silica (2) is “Zeosil 1115MP” manufactured by Rhodia, and silica (3) is “Ultrasil VN3” manufactured by Degussa.

Silica (4) and (5) form an initial bottom product containing sodium silicate and sodium sulfate in accordance with Japanese Patent No. 3304097, and sulfuric acid is added to the bottom product to react at a pH of 7 or higher. A product is obtained, and sodium silicate and sulfuric acid are simultaneously added to the obtained reaction product for reaction, and then aluminum sulfate and then sodium hydroxide solution are added and aged to prepare a suspension of precipitated silica. And the silica prepared by separating and drying the resulting suspension. However, the specific surface area, structure and surface activity were adjusted by reducing the amount of aluminum sulfate added and aging at pH 7 to 10 to obtain silica having the characteristics shown in Table 1.

  The measuring method of silica characteristics is as follows.

CTAB specific surface area: Measured according to the method described in ASTM D3765-92. However, since this method is a measurement method for carbon black, it was changed. That is, without using the carbon black standard ITRB (83.0 m ² / g), a CTAB (cetyltrimethylammonium bromide) standard solution was prepared separately, whereby aerosol OT (di-2-ethylhexylsulfosuccinic acid) was prepared. (Sodium) solution was standardized, and the specific surface area was calculated from the amount of CTAB adsorbed, assuming that the adsorption cross-section per molecule of CTAB on the silica surface was 35 square angstroms.

-DBP oil absorption: measured in accordance with JIS K-5101.

-Δ thermogravimetric reduction rate: Thermogravimetric measurement was performed at a temperature rising rate of 10 ° C / min from ambient temperature using air with an atmospheric gas as a thermogravimetric measuring device manufactured by TA Instruments Inc. The difference between the two was determined from the decrease rate at 150 ° C. and the decrease rate at 150 ° C.

2. Preparation and Evaluation of Rubber Composition Using a Banbury mixer, a rubber composition was prepared according to the formulation shown in Table 2 below. Details of each component in Table 2 are as follows.

Natural rubber: RSS # 3 (glass transition point Tg = −60 ° C.)
Isoprene rubber: “IR2200” manufactured by JSR (glass transition point Tg = −59 ° C.),
-Butadiene rubber: Ube Industries high cis butadiene rubber "BR150B" (1,4-cis butadiene unit amount = 97 wt%, glass transition point Tg = -104 ° C),
・ Carbon black: "Seast V" made by Tokai Carbon
・ Oil: JOMO “Process X140”
Coupling agent (1): Degussa “Si-75” (polysulfide silane represented by the above formula (2) (x = 2 (average value)),
Coupling agent (2): “NXT” manufactured by GE Silicones (protected mercaptosilane represented by the above formula (3) (n = 2, m = 3, k = 7).

  In each rubber composition, 2 parts by weight of stearic acid (“Lunac S-20” manufactured by Kao) and zinc white (“Zinc Hana 1 type” manufactured by Mitsui Metals) are used as a common formulation with respect to 100 parts by weight of diene rubber. ) 3 parts by weight, anti-aging agent (“Antigen 6C” manufactured by Sumitomo Chemical) 2 parts by weight, 2 parts by weight of wax (“Sannok N” manufactured by Ouchi Shinsei Chemical), vulcanization accelerator (“Sokucinol CZ” manufactured by Sumitomo Chemical) 1.0 part by weight and 2.0 parts by weight of sulfur (“powder sulfur” manufactured by Tsurumi Chemical) were blended.

  For each rubber composition, the Mooney viscosity was measured, and the dynamic elastic modulus and tear strength were measured. Further, each rubber composition was used as a sidewall rubber and vulcanized and molded according to a conventional method to produce a 205 / 65R159H radial tire for passenger cars, and the rolling resistance was measured. Each measurement / evaluation method is as follows.

Mooney viscosity (workability): Mooney viscosity was measured in accordance with JIS K6300, and displayed as an index with the value of Comparative Example 1 being 100. A smaller index indicates a lower viscosity, that is, better workability.

-Dynamic elastic modulus: A test piece having a predetermined shape (vulcanized and molded at 160 ° C for 15 minutes) was measured using a dynamic viscoelasticity measuring device manufactured by UBM, at a temperature of 25 ° C, a static strain of 10%, The loss factor tan δ was measured under the conditions of a strain of 0.1% and a frequency of 10 Hz, and displayed as an index with the value of Comparative Example 1 as 100. A smaller index indicates a lower exothermic property.

-Tear strength (cut resistance): A sample obtained by punching a vulcanized rubber sample (vulcanized at 160 ° C. for 15 minutes) in the crescent form of JIS K6252 and making a notch of 0.50 ± 0.08 mm in the center of the indentation Was teared at a tensile speed of 500 mm / min with a tensile tester manufactured by Shimadzu Corporation, and the tear strength was measured. The value of Comparative Example 1 is expressed as an index, and the larger the index, the higher the tear strength and the better the cut resistance.

Rolling resistance (low fuel consumption): Rolling resistance when running at 23 ° C and 80 km / h on a rolling resistance measuring drum with tires mounted with a rim of 15 x 6.5 JJ and an air pressure of 230 kPa and a load of 450 kgf Was measured. The value of Comparative Example 1 is expressed as an index, and the smaller the index is, the smaller the rolling resistance is, and thus the better the fuel efficiency is.

  As shown in Table 2, in Examples 1, 2, and 4 using silica (4), (5) satisfying the colloidal characteristics of the present invention, Comparative Example 1 containing no silica and small particle size silica were blended. In comparison with Comparative Examples 2 and 5, the rubber composition itself was reduced in heat generation, and the rolling resistance as a tire was also greatly reduced. Further, in Comparative Example 3 in which mere large particle size silica was blended, the tear strength was greatly reduced, whereas in Examples 1, 2 and 4 using silica having a large particle size and high surface activity, tearing was performed. The drop in strength was small and the cut resistance was improved. In Examples 1, 2 and 4, the rolling resistance was further improved compared to Comparative Example 3, and the Mooney viscosity was low and the processability was excellent.

  FIGS. 1 and 2 illustrate this point. FIG. 1 shows the relationship between tear strength (cut resistance) and rolling resistance (low fuel consumption), and FIG. 2 shows Mooney viscosity (workability) and rolling resistance. The relationship with (low fuel consumption) is shown respectively. The directions indicated by arrows A and B in the figure are preferred directions, and Examples 1, 2, and 4 are improved in the preferred direction in both of the above relationships with respect to Comparative Example 3.

  Further, in Example 3, by combining protected silica (4) with a protected mercaptosilane as a coupling agent, the processability, cut resistance and fuel efficiency are greatly improved compared to Examples 1 and 2. As shown in FIGS. 1 and 2, it was improved in a preferable direction as compared with Comparative Example 4 in which mere large particle size silica and protected mercaptosilane were combined.

  As described above, according to the present invention, it is possible to reduce the rolling resistance of the tire and reduce fuel consumption while suppressing a reduction in cut resistance as much as possible. Therefore, various pneumatic tires including radial tires for passenger cars are used. Can be used.

It is a graph which shows the relationship between the tearing strength and rolling resistance of an Example and a comparative example. It is a graph which shows the relationship between the Mooney viscosity of an Example and a comparative example, and rolling resistance.

Claims (3)

To diene rubber 100 parts by weight, a CTAB specific surface area of 80~ 130 ^m 2 / g, DBP oil absorption amount to the CTAB specific surface area ^{(m 2 / g) (cm} 3 / 100g) ratio DBP / CTAB of 1.3 or more The relationship between ΔC weight reduction rate (%), which is a value obtained by subtracting the reduction rate at 150 ° C. from the reduction rate at 1000 ° C. in thermogravimetry, and the CTAB specific surface area (m ² / g) 5 to 70 parts by weight of silica satisfying the following formula (1) and 0 to 70 parts by weight of carbon black are blended at a weight ratio of silica / carbon black = 0.2 / 1 to 1/0, and further coupling is performed. A rubber composition for a tire sidewall obtained by blending 2 to 25 parts by weight of an agent with respect to 100 parts by weight of silica.
ΔThermal weight reduction rate ≧ 0.0283 × CTAB specific surface area + 0.6 (1) The rubber composition for a tire sidewall according to claim 1, wherein the coupling agent is represented by the following general formula (2) or general formula (3).
_{(C 2 H 5 O) 3} Si-C 3 H 6 -S x -C 3 H 6 -Si (OC 2 H 5) 3 ... (2)
(In the formula, x is 2 to 4.)
_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 ... (3)
(In the formula, n is an integer of 1 to 3, m is an integer of 1 to 5, and k is an integer of 5 to 9.)   A pneumatic tire having a sidewall made of the rubber composition according to claim 1.

Images