JP2007031522A - Rubber composition for tire tread and pneumatic radial tire for truck/bus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire treads making abrasion resistance compatible with heat build-up properties at much higher levels than those of conventional compositions and to provide a pneumatic radial tire for trucks/buses using the composition. <P>SOLUTION: The rubber composition is obtained by compounding 100 pts.wt. of a diene rubber with 30-50 pts.wt. of carbon black having 110-130 m<SP>2</SP>/g CTAB (cetyltrimethylammonium bromide) adsorption specific surface area, ≥0.85 24M4DBP (compressed DBP oil absorption)/CTAB adsorption specific surface area and ≥1.05 N<SB>2</SB>SA (nitrogen adsorption specific surface area)/IA (iodine adsorption). The pneumatic radial tire for the trucks/buses is prepared by using the rubber composition in a cap rubber and has ≥12 MPa 300% tensile stress of both the cap rubber and the base rubber measured at 80°C. Loss tangents tanδc and tanδb of the cap rubber and the base rubber measured at 80°C satisfy the relationship of 0.12>tanδc>tanδb, respectively. Furthermore, the ratio of the thickness of the base rubber to the whole thickness of the tread rubber is set within the range of 0.20-0.50. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread and a pneumatic radial tire for trucks and buses using the rubber composition.

  In heavy-duty tires used for trucks and buses, it has become important to improve the wear resistance of the tread portion and to reduce rolling resistance, but these are generally in a trade-off relationship.

  Conventionally, for example, as a technique for improving wear resistance, a high cis type having a high cis-1,4 content is used for butadiene rubber used as a rubber component, or a small amount of carbon black as a filler is used. Measures such as using particles having a particle size, using a structure having a high structure, or increasing the amount added are proposed.

For example, the following Patent Document 1, with respect to the diene ^{rubber, CTAB = 110~170m 2 / g,} 24M4DBP = 100~130ml / 100g, TINT = 130~150, N 2 SA / IA = 1.00~1. 20, carbon having characteristics of {(2540 + 71 × DBP) / N ₂ SA} /Dst≧−5.35×10 ⁻³ × CTAB + 2.014, Vp = 115 to 150 (cc / 100 g), DBP-24M4DBP <32. A rubber composition for tires containing black has been proposed.

  With these conventional methods, the wear resistance can be expected to improve, but the heat generation required for tread rubber for heavy-duty tires deteriorates, resulting in loss of rolling resistance and heat durability, and low tire The fuel efficiency and renewability will be affected.

Therefore, proposals for achieving both wear resistance and heat generation have been made. For example, in the following Patent Document 2, as a tread cap rubber, a molecular weight distribution (Mw / Mn) represented by a ratio of a weight average molecular weight (Mw) to a number average molecular weight (Mn) is 1.5 to 3.0. A rubber composition comprising 45 to 65 parts by weight of carbon black having a CTAB adsorption specific surface area of 135 to 160 m ² / g per 100 parts by weight of diene rubber containing cis-1,4-polyptadiene rubber is used. In addition, the track rubber in which a rubber composition having a 300% tensile stress of 16 MPa or more is used as the base rubber, and the ratio of the thickness of the base rubber to the total thickness of the tread rubber is set in a range of 0.25 to 0.40. Radial tires for buses have been proposed.

  In Patent Document 3 below, the dynamic elastic moduli E′c and E′b of the cap rubber and the base rubber are set to E′c> E′b ≧ 8.5 MPa, respectively, Loss tangent tan δc and tan δb of tan δc> 0.12 ≧ tan δb, and the ratio of the thickness Tb of the base rubber at the tire shoulder to the total thickness Ta of the tread rubber 0.25 <Tb / Ta <0.70 Pneumatic radial tires for trucks and buses have been proposed.

Furthermore, in the following Patent Document 4, CTAB = 115 to 145 m ² / g, 24M4DBP (ml / 100 g) / CTAB (m ² /g)=0.75 to 0.92, CTAB (m ^{2 /} g) / IA (mg / g) = 0.97 to 1.25, TINT (%) ≧ −46.787 (24M4DBP / CTAB) +168 Proposed.
Japanese Patent Laid-Open No. 5-230290 Japanese Patent Laid-Open No. 7-118443 Japanese Patent Laid-Open No. 6-1557829 JP 2000-344945 A

  In view of the above, the present invention provides a rubber composition for a tire tread capable of achieving both a high level of wear resistance and heat generation, and a pneumatic radial tire for trucks and buses using the same. The purpose is to provide.

The rubber composition for a tire tread according to the present invention, with respect to the diene rubber 100 parts by weight, CTAB adsorption specific surface area of 110~130m ² / g, compression DBP oil absorption for CTAB adsorption specific surface area (CTAB) (24M4DBP ) Ratio 24M4DBP (ml / 100 g) / CTAB (m ² / g) is 0.85 or more, and ratio of nitrogen adsorption specific surface area (N ₂ SA) to iodine adsorption amount (IA) N ₂ SA (m ² / g) / IA (mg / g) is 30 to 50 parts by weight of carbon black having a value of 1.05 or more.

  In the rubber composition of the present invention, the diene rubber is preferably composed of 95 to 50% by weight of natural rubber and / or isoprene rubber and 5 to 50% by weight of butadiene rubber. Further, the butadiene rubber has a cis-1,4 bond content of 95% or more, and a ratio T-cp / ML1 + 4 of a toluene solution viscosity (T-cp) at 25 ° C. to a Mooney viscosity (ML1 + 4) at 100 ° C. The value is 2.0 or more, and the molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) is in the range of 2.0 to 3.0. A certain butadiene rubber is preferable.

  The pneumatic radial tire for trucks and buses according to the present invention is a pneumatic radial tire for trucks and buses in which the tread rubber has a two-layer structure of a cap rubber and a base rubber, and the cap rubber is a rubber composition for the tire tread. 300% tensile stress of the cap rubber and the base rubber measured at 80 ° C. is 12 MPa or more, and the loss tangent tan δc and tan δb of the cap rubber and the base rubber measured at 80 ° C. are 0.12 > Tan δc> tan δb is satisfied, and the ratio of the thickness of the base rubber to the total thickness of the tread rubber is set in a range of 0.20 to 0.50.

According to the present invention, the carbon black to be blended in the rubber composition for a tire tread is set as a structure index after setting the CTAB adsorption specific surface area serving as a particle size index within a range of 110 to 130 m ² / g. By using 24 M4DBP / CTAB as 0.85 or more and a high structure, N ₂ SA / IA as an index of surface activity is defined as 1.05 or more and a high surface activity material is used. While maintaining the wear resistance, it is possible to suppress the deterioration of the heat generation, and therefore, it is possible to achieve both high wear resistance, rolling resistance and heat generation durability.

  Further, by using a rubber composition containing a specific butadiene rubber together with the specific carbon black as a cap rubber, and further defining the physical properties of the cap rubber and the base rubber, and specifying the thickness ratio of the base rubber, A pneumatic radial tire for trucks and buses having good wear resistance and heat generation can be obtained.

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

  In the rubber composition of the present invention, examples of the diene rubber used as the rubber component include natural rubber, and diene synthetic rubbers such as isoprene rubber, butadiene rubber, and styrene-butadiene rubber. It may be used alone or in combination of two or more.

  Preferably, the diene rubber is composed of 100 to 50% by weight of natural rubber and / or isoprene rubber and 0 to 50% by weight of butadiene rubber. That is, natural rubber and / or isoprene rubber alone or a blend of this with butadiene rubber is preferable. When blended, the natural rubber and / or isoprene rubber is preferably 50% by weight or more and the butadiene rubber is preferably 50% by weight or less, more preferably, the natural rubber and / or isoprene rubber is 50 to 95% by weight, Butadiene rubber is 5 to 50% by weight, more preferably natural rubber and / or isoprene rubber is 50 to 90% by weight, and butadiene rubber is 10 to 50% by weight.

  As the butadiene rubber, a high cis type rubber having a cis-1,4 bond content of 95% or more is preferable for improving wear resistance. Here, the cis-1,4 bond content is a value measured by an infrared absorption spectrum method (Morello method).

  Moreover, it is preferable that ratio T-cp / ML1 + 4 of the toluene solution viscosity (T-cp) in 25 degreeC and the Mooney viscosity (ML1 + 4) in 100 degreeC is 2.0 or more. This ratio is related to the linearity of the polybutadiene rubber, and a larger value means higher linearity, that is, higher linearity tendency. In addition, when specified only by the toluene solution viscosity, the higher the toluene solution viscosity, the better the wear resistance, but the heat generation and workability may be inferior, and it is specified by the ratio with the Mooney viscosity as in the present invention. And by making the ratio 2.0 or more, exothermic property and workability can be improved while improving wear resistance. The upper limit of T-cp / ML1 + 4 is not particularly limited, but is usually 6 or less. Here, the toluene solution viscosity (T-cp) is a value of a 10% by weight toluene solution viscosity at 25 ° C. measured by a Brookfield (BL) viscometer. The Mooney viscosity (ML1 + 4) is a value measured at a temperature of 100 ° C. for 1 minute of preheating, 4 minutes of measurement, according to JIS K6300.

  The butadiene rubber preferably has a molecular weight distribution (Mw / Mn) represented by a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) in the range of 2.0 to 3.0. . If Mw / Mn is less than 2.0, the workability deteriorates. Conversely, if Mw / Mn exceeds 3.0, the hysteresis loss increases and the heat generation temperature rises. Here, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values measured by gel permeation chromatography (GPC) using tetrohydrofuran (THF) as a developing solvent. Specifically, for polystyrene with a known molecular weight, a calibration curve was created for the relationship between the peak position of the GPC spectrogram and the molecular weight, and the spectrogram of butadiene rubber measured by GPC was compared with the calibration curve of polystyrene with a known molecular weight. It is determined by calculating the weight average molecular weight and the polystyrene equivalent number average molecular weight.

  The carbon black used in the rubber composition of the present invention satisfies the following (1) to (3).

(1) CTAB adsorption specific surface area of 110 to 130 m ² / g,
(2) Compressed DBP oil absorption (24M4DBP) / CTAB adsorption specific surface area (CTAB) ≧ 0.85,
(3) Nitrogen adsorption specific surface area (N ₂ SA) / iodine adsorption amount (IA) ≧ 1.05.

The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area (hereinafter sometimes simply referred to as “CTAB”) in (1) above is a value measured according to ASTM D3765, and is the particle size of carbon black. It is an indicator. CTAB in the present invention is intended to use a relatively small particle diameter is 110~130m ² / g, is less than 110m ² / g, it is impossible to obtain good abrasion resistance as the tread rubber of heavy duty tire . On the other hand, if it exceeds 130 m ² / g, the exothermic property is deteriorated.

  The 24M4DBP / CTAB in (2) above serves as an index of the structure of carbon black, and in the present invention, a high structure product having this ratio of 0.85 or more is used. Wear resistance can be improved by using such a high structure product. The upper limit of this ratio is not particularly limited, but is usually 1.0 or less. Here, the compressed DBP (dibutyl phthalate) oil absorption (24M4DBP) is measured according to ASTM D3493. The compressed DBP is preferably 100 ml / 100 g or more in order to obtain good wear resistance. The upper limit of the compressed DBP is not particularly limited, but is preferably 120 ml / 100 g or less.

N ₂ SA / IA of (3) above serves as an index of the surface activity of carbon black, and in the present invention, a high surface active product having this ratio of 1.05 or more is used. By using such a high surface active product, excellent effects in improving wear resistance and heat generation can be obtained. More specifically, the higher the structure, the better the wear resistance, but at the same time the exothermicity deteriorates and adversely affects hysteresis and durability, but the surface activity represented by N ₂ SA / IA. By making the height higher, exothermic deterioration can be suppressed while maintaining good wear resistance. The upper limit of the N ₂ SA / IA ratio is not particularly limited, but is usually 1.40 or less. Here, the nitrogen adsorption specific surface area (N ₂ SA) is a value measured according to ASTM D3037, and the iodine adsorption amount (IA) is a value measured according to ASTM D1510.

  The compounding amount of the carbon black is 30 to 50 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of the carbon black is less than 30 parts by weight, the wear resistance is deteriorated, and when it exceeds 50 parts by weight, the exothermic property is deteriorated.

  In addition to the components described above, the rubber composition of the present invention is generally used in a tread rubber composition for heavy duty tires such as anti-aging agent, zinc white, stearic acid, softening agent, vulcanizing agent, and vulcanization accelerator. Various additives can be blended.

  The pneumatic radial tire for trucks and buses of the present invention includes a tread rubber having a two-layer structure of a cap rubber and a base rubber, and the cap rubber is made of the above-described rubber composition for a tire tread. In this tire, the 300% tensile stresses of the cap rubber (c) and the base rubber (b) measured at 80 ° C. are M300c and M300b, respectively, and the loss tangent of each rubber at the same temperature is tanδc and tanδb, respectively. When satisfying the following relationship.

(4) M300c ≧ 12 MPa,
(5) M300b ≧ 12 MPa,
(6) 0.12> tan δc> tan δb.

  The 300% tensile stress in the above (4) and (5) is a value measured at 80 ° C. in accordance with JIS K6251. If M300c does not satisfy the above (4), the wear resistance deteriorates. Further, if M300b does not satisfy the above (5), since rigidity is low, distortion of the entire tread is concentrated on the base rubber, heat generation is deteriorated, and good wear resistance is not obtained. The upper limit of M300c is not particularly limited, but is usually 20 MPa or less. The upper limit of M300b is not particularly limited, but is usually 23 MPa or less.

  The loss tangent tan δ of (6) above is obtained by using a viscoelastic spectrometer (manufactured by UBM), with a sample having a width of 5 mm, a thickness of 1 mm, and a length of 20 mm, initial strain of 10%, dynamic strain of 3%, frequency of 15 Hz, and temperature. It is a value measured under the condition of 80 ° C. Generally, tan δb of the base rubber is smaller than tan δc of the cap rubber. However, in the present invention, not only the base rubber but also the cap rubber can improve the heat generation property of the entire tire by making tan δ less than 0.12. it can. Moreover, good abrasion resistance can be maintained by using a rubber composition containing the above-mentioned specific carbon black as the cap rubber. The lower limit of tan δb is not particularly limited, but is usually 0.03 or more. The lower limit of tan δc is not particularly limited, but is usually 0.05 or more.

  In the tire of the present invention, the ratio of the thickness of the base rubber to the total thickness of the tread rubber is set in the range of 0.20 to 0.50, thereby obtaining good wear resistance and heat generation. be able to. If the thickness of the base rubber relative to the total thickness of the tread is thin, the heat generated by the tire is increased without sufficiently canceling the heat generated by the cap rubber. On the contrary, if the thickness of the base rubber is increased, it is advantageous for heat generation, but the wear resistance of the base rubber is inferior to that of the cap rubber, so that the wear life as a tire is reduced.

In the rubber composition constituting the base rubber, the rubber component can be used as long as it is a rubber component composed of at least one of diene synthetic rubber in addition to natural rubber. Natural rubber having excellent properties is most preferable. Moreover, in order to adjust the 300% tensile stress of the base rubber to 12 MPa or more, usually, carbon black having a CTAB in the range of 100 to 130 m ² / g is used, and the blending amount is 35 to 35 parts by weight per 100 parts by weight of rubber. This is achieved by adjusting in the range of 50 parts by weight. In addition to the above components, commonly used compounding agents such as vulcanizing agents, vulcanization accelerators, vulcanization accelerating aids, anti-aging agents, process oils, and other processing aids can be added as appropriate. Needless to say.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Examples 1-5 and Comparative Examples 1-7
As carbon black, nine types of carbon blacks CB-1 to 9 shown in Table 1 below were used. CB-1 is "Seast 9" made by Tokai Carbon, CB-2 is "Seast 6" made by Tokai Carbon, and CB-3 is "Seast 7HM" made by Tokai Carbon. CB-4 to 9 are multi-stages having a combustion chamber having an air supply port and a combustion burner mounted in the furnace axial direction at the furnace head, and a feed oil injection nozzle provided coaxially with the combustion chamber. Using an oil furnace furnace composed of a small-diameter reaction chamber and a large-diameter reaction chamber, feedstock introduction conditions, air introduction conditions, fuel oil introduction conditions so as to have the characteristics shown in Table 1 below. It was obtained by adjusting the cooling conditions.

As the butadiene rubber, three types of polybutadienes BR-1 to 3 shown in Table 2 below were used.

  Using a Banbury mixer, tire tread rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 7 were prepared according to the composition shown in Table 3 below. NR in Table 3 is natural rubber (RSS3). In each rubber composition, 3 parts by weight of zinc white (Mitsui Kinzoku “Zinc Hana 1”), 3 parts by weight of stearic acid (manufactured by Nippon Oil & Fats), aging are used for 100 parts by weight of the rubber component. 1 part by weight of an inhibitor (“6PPD” manufactured by Monsanto), 2 parts by weight of sulfur (manufactured by Shikoku Kasei), and 1 part by weight of a vulcanization accelerator (“TBBS” manufactured by Sanshin Chemical) were blended.

  Each rubber composition was subjected to a tensile test to measure 300% modulus, breaking strength and elongation at break, and to evaluate wear resistance and heat generation. Each evaluation method is as follows.

-Tensile test: 300% modulus, breaking strength and breaking elongation were measured in accordance with JIS K6251 (dumbbell shape No. 3), and displayed as an index with the value of Comparative Example 1 being 100.

-Abrasion resistance: Measured according to Lambone method in accordance with JIS K6264 under standard conditions: slip rate of 30%, load load of 40 N, amount of falling sand of 20 g / min, and displayed as an index with the value of Comparative Example 1 as 100. It shows that it is excellent in abrasion resistance, so that a numerical value is large.

Exothermic property: Using a Toyo Seiki spectrometer, the viscoelastic property tan δ at 80 ° C. was measured with a frequency of 10 Hz, an initial elongation of 10%, and a strain amplitude of 2%. It shows that it is excellent in exothermic property, so that a numerical value is small.

  As shown in Table 3, in Comparative Examples 2 to 7, good abrasion resistance and heat generation were not obtained as compared with Comparative Example 1. In particular, in Comparative Examples 2 and 3, since butadiene rubber having low linearity was used, and in Comparative Example 6, carbon black had a low structure, so that neither of them had good wear resistance. Moreover, although the comparative example 7 was excellent in abrasion resistance, since the carbon black with low surface activity was used, exothermic property deteriorated significantly. On the other hand, in Examples 1 to 5, since the particle size, structure, and surface activity were considered in a well-balanced manner, good wear resistance was obtained while suppressing deterioration in heat generation. Even when the amount of carbon black was varied and compared at the same modulus, good wear resistance was obtained in Example 5, and the heat generation was further improved.

Example 6 and Comparative Examples 8-14
A rubber composition for tire treads was prepared according to the composition shown in Table 4 below using a Banbury mixer. Comparative Examples 8 to 11 are the same as the rubber composition of Comparative Example 1 described above, and Comparative Examples 13 and 6 are the same as the rubber composition of Example 4 described above. The common compound described above was added to the rubber compositions of Comparative Examples 12 and 14.

  Using each rubber composition as a cap rubber, a radial tire for trucks having a tire size of 11R22.5 was produced according to a conventional method. At that time, the ratio Tb / Ta of the base rubber thickness (Tb) to the total thickness (Ta) of the tread rubber was as shown in Table 4. The rubber composition of the base rubber is as shown in Table 4, and each rubber composition contains 3 parts by weight of zinc white ("Zinc Flower No. 1" manufactured by Mitsui Metals) as a common compound with respect to 100 parts by weight of the rubber component. Parts, stearic acid (manufactured by NOF Corporation) 3 parts by weight, anti-aging agent (Monsanto "6PPD") 2 parts by weight, sulfur (Shikoku Kasei) 1.5 parts by weight, vulcanization accelerator (Sanshin Chemical "TBBS" ") 1 part by weight and 45 parts by weight of carbon black (" Seast 7HM "manufactured by Tokai Carbon Co., Ltd.). The aroma oil in Table 4 is “Aroma Oil No. 4” manufactured by Showa Shell Sekiyu.

  About the obtained tire, abrasion resistance and exothermicity were measured by the following methods.

・ Abrasion resistance: After mounting a tire on the rear wheel of the truck and traveling 100,000 km, the remaining groove of each tire was measured, and the difference in groove depth before and after traveling was evaluated as the wear amount. Expressed with an index of 100. It shows that it is excellent in abrasion resistance, so that a numerical value is large.

Exothermic property: The tire was run on a drum under high-speed durability test conditions, the surface temperature of the outermost layer belt in the shoulder portion was measured, and displayed as an index with Comparative Example 8 taken as 100. It shows that it is excellent in exothermic property, so that a numerical value is small.

As shown in Table 4, in Comparative Example 9, since the base rubber thickness was thin, the heat generation was deteriorated. On the contrary, in Comparative Example 10, the wear resistance was greatly deteriorated because the base rubber was thick. In Comparative Example 11, since the rigidity of the base rubber was low, the distortion of the entire tread was concentrated on the base rubber and the heat generation was deteriorated. In Comparative Example 12, the wear resistance deteriorated because the tensile stress of the cap rubber was small. Further, in Comparative Examples 13 and 14, the same carbon black as in Example 6 was used, but since the base rubber thickness was thin or butadiene rubber having low linearity was used, the effect of improving wear resistance was small. In contrast, in Example 6, the wear resistance was significantly improved without impairing the heat generation.

Claims (3)

For 100 parts by weight of diene rubber,
The CTAB adsorption specific surface area is 110 to 130 m ² / g, and the ratio of the compressed DBP oil absorption (24M4DBP) to the CTAB adsorption specific surface area (CTAB) is 24M4DBP (ml / 100 g) / CTAB (m ² / g) is 0.85 or more. And a ratio of nitrogen adsorption specific surface area (N ₂ SA) to iodine adsorption amount (IA) N ₂ SA (m ² / g) / IA (mg / g) is 1.05 or more. A rubber composition for a tire tread characterized by containing -50 parts by weight. The diene rubber comprises 95 to 50% by weight of natural rubber and / or isoprene rubber and 5 to 50% by weight of butadiene rubber.
The butadiene rubber has a cis-1,4 bond content of 95% or more, and has a ratio T-cp / ML1 + 4 of a toluene solution viscosity (T-cp) at 25 ° C. to a Mooney viscosity (ML1 + 4) at 100 ° C. Butadiene having a molecular weight distribution (Mw / Mn) in the range of 2.0 to 3.0, which is 2.0 or more and represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) The rubber composition for tire tread according to claim 1, wherein the rubber composition is rubber. A tread rubber is a pneumatic radial tire for trucks and buses having a two-layer structure of a cap rubber and a base rubber, and the cap rubber comprises the rubber composition for a tire tread according to claim 1 or 2 and measured at 80 ° C. The cap rubber and the base rubber both have 300% tensile stress of 12 MPa or more, and the loss tangent tan δc and tan δb of the cap rubber and base rubber measured at 80 ° C. satisfy the relationship of 0.12> tan δc> tan δb. A pneumatic radial tire for trucks and buses, wherein a ratio of the thickness of the base rubber to the total thickness of the tread rubber is set in a range of 0.20 to 0.50.