JP3461396B2 - Rubber composition for tire tread - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition suitable as a tire tread member for passenger cars and light trucks, and more particularly to an excellent wear resistance effective for fuel-efficient tires. The present invention relates to a low-heat-generating rubber composition having a high rebound resilience while maintaining the same. 2. Description of the Related Art There are various types of carbon black for rubber reinforcement depending on the characteristics of the rubber, and the characteristics of these types are the main factors for determining various properties of a composition compounded in rubber. Becomes For this reason, when compounding with rubber, a means for selecting and using carbon black having a variety of characteristics suitable for the purpose of the member is generally used. [0003] For example, in recent years, fuel-efficient tires have been actively developed to meet the social demands for resource saving and energy saving, but such fuel-efficient tires have a relatively small particle size. A rubber composition having low heat build-up and high rebound resilience in which a large variety of carbon black is blended in a relatively small amount into a rubber component is effective. However, rubber compounding of carbon black with a large particle diameter and a small specific surface area is effective for the purpose of improving fuel economy performance,
Deterioration of surface characteristics such as braking performance and abrasion resistance on wet road surfaces is inevitable. Therefore, if carbon black having a small particle size and a large specific surface area can be simultaneously imparted to a compounded rubber with high abrasion resistance and low heat generation giving high rebound resilience, a tire tread intended for low fuel consumption can be provided. It becomes ideal as a rubber member for use. [0004] The applicant of the present invention adds the above-mentioned reciprocal rubber performance to the characteristic aspects of the carbon black to be compounded, in particular, to the basic properties such as particle diameter, specific surface area, structure and the like, as well as more microselective properties. We have systematically continued the research to make this compatible, and have already made the following development proposals. (1) Nitrogen adsorption specific surface area (N ₂ SA) is 60m ² / g or more, compression D
A carbon black having a BP of at least 112 ml / 100 g and a compounded rubber in which the Stokes mode diameter and the distribution of aggregates are maintained at a certain value or more can simultaneously impart high reinforcement performance and high rebound resilience (Japanese Patent Publication No. −53978
No.). (2) N ₂ SA is 60m ² / g or more, DBP is 108ml / 100g
Above, the true specific gravity value per specific surface area is set to a specific range significantly lower than that of the known carbon black, and the coloring power and the distribution width per aggregate mode diameter are blended with the carbon black that maintains the specific width or more. Rubber composition having both high abrasion resistance and high rebound resilience
No. -70746). (3) N ₂ SA is 65 to 84 m ² / g, and the ratio of N ₂ SA / absorbed iodine (IA) is in the range of 1.10 to 1.35;
Carbon black that can simultaneously impart high abrasion resistance and high rebound resilience to a compounded rubber in which a relational expression value with BP, blackness, iodine adsorption amount and aggregate mode diameter as variables are set to be equal to or more than a certain value JP-A-63-225639). (4) N ₂ SA is 75 to 105 m ² / g, compressed DBP is 110
In the case of ml / 100g or more, the specific gravity value per specific surface area is set to a specific range lower than that of known carbon black, and the distribution width per particle aggregate void diameter and aggregate mode diameter is maintained at a specific value or more. Carbon black (Japanese Unexamined Patent Publication No. Hei. 1-201367) which allows the compounded rubber to have both high wear resistance and high rebound resilience. (5) Carbon black having a N ₂ SA of 60 to 100 m ² / g and a mode diameter Dp of the pores between the aggregates and a relational expression with the particle aggregate mode diameter (Dst) set to a certain value or less was blended. A rubber composition having both high rebound resilience and high abrasion resistance (Japanese Patent Laid-Open No. 4-209640). In addition, US Pat. No. 4,360,627 discloses N ₂ SA85-95 for tire tread rubber.
^{m 2 / g, 24M4DBP100~104ml / 100g} , Tint 95
１０５105%, distribution of aggregate Stokes mode diameter (ΔD
₅₀ ) is 180 nm or more, a carbon black achieving high abrasion resistance and high rebound resilience is disclosed, and U.S. Pat. No. 4,548,980 discloses a low rolling resistance and a high degree of hardness required for an energy-saving tire tread rubber. As carbon black characteristics for obtaining wet grip performance,
N ₂ SA75 to 105 m ² / g, N ₂ SA-IA ≧ 15, N
₂ SA-CTABSA ≦ 5, 24M4DBP ≦ 110, Tin
t 90 to 110 and ΔTint ≦ −3 are shown. [0006] However, the demand for materials for fuel-efficient tires is becoming more and more advanced, and it is currently difficult for the rubber composition according to the prior application to meet the recent required performance. The present inventor has proceeded with research under such a background, and found that the nitrogen adsorption specific surface area (N ₂ SA) is 75 to 12
Furnace carbon black belonging to a hard region of 5 m ² / g and a compressed DBP of 100 to 130 ml / 100 g,
The half-width of the Stokes diameter of the aggregate is in the range of the constant relational expression in relation to the Stokes mode diameter, and the half-width of the pore diameter distribution between aggregate grains is constant in the relation to the mode diameter of the pore diameter distribution. The present inventors have clarified the fact that a rubber composition containing carbon black within the range of the formula value can obtain suitable rubber physical properties as a tire tread for passenger cars and light trucks, and proposed the same as Japanese Patent Application No. 5-348207. [0007] According to the above prior art (Japanese Patent Application No. 5-348207), various properties of the specified carbon black act comprehensively to give the rubber composition excellent resistance. It is possible to impart low heat build-up having high rebound resilience while maintaining abrasion. The present inventor has continued research on the relationship between the form of the carbon black aggregate and the properties of the compounded rubber. As a result, when the shape anisotropy of the aggregate is small, that is, the Stokes mode diameter (Ds
In the relationship between t) and the average circle diameter (De) of the aggregate determined from the projected area of the two-dimensional projected image observed by the transmission electron microscope, carbon black having a value of Dst equal to or greater than a certain relational expression value is blended. It has been found that the obtained rubber composition shows high rebound resilience and low heat build-up without abrasion resistance. The present invention has been developed on the basis of the above findings, and has as its object to provide a low tread member having both high abrasion resistance and high rebound resilience suitable as a tread member for fuel-efficient tires of passenger cars and light trucks. An object of the present invention is to provide an exothermic rubber composition. [0010] The rubber composition for a tire tread according to the present invention for achieving the above object has a nitrogen adsorption specific surface area (N ₂ SA) of 75 to 100 m ² / g, and a compressed DBP. Is a hard carbon region of 105 to 120 ml / 100 g, and has a Stokes mode diameter (Dst) of the aggregate having selective properties according to the following relational formula: 35 to 100 parts by weight with respect to 100 parts by weight of the rubber component. Is a structural feature. Dst ≧ 0.62 × De + 28.0 where Dst is the Stokes mode diameter of the carbon black aggregate measured by the disc centrifuge (DCF), and De is the two-dimensional projection image by the transmission electron microscope. The figure shows the circle-converted average diameter of the projected area of the carbon black aggregate obtained by image analysis. The values obtained by the following measuring methods are used as the characteristics of the carbon black in the above-described configuration. Nitrogen adsorption specific surface area (N ₂ SA); ASTM D3037-88
“Standard Test Method for Carbon Black-SurfaceAre
a by Nitrogen Absorption "Method B. The measured value of IRB # 6 by this method is 76 m ² / g. Compressed DBP; ASTM D3493-85a“ Standard Tes
t Method for Carbon Black- Dibutyl Phthalate Absorp
The measurement value of IRB # 6 by this method is 87 ml / 100 g. Dst (Stokes mode diameter of aggregate); JIS K6221 (1982) 5 "How to make dry sample" A carbon black sample dried based on the above is mixed with a 20% by volume aqueous ethanol solution containing a small amount of a surfactant to prepare a dispersion having a carbon black concentration of 50 mg / l. I do. 80 Disk Centrifuge (Joyes Lobel, UK)
The rotation speed is set to 00 rpm, 10 ml of a spin solution (2% by weight glycerin aqueous solution, 25 ° C.) is added, and 1 ml of a buffer solution (20% by volume ethanol aqueous solution, 25 ° C.) is injected. Then, a carbon black dispersion at a temperature of 25 ° C. was added.
After adding 5 ml with a syringe, centrifugal sedimentation was started, and at the same time, the recorder was operated and the distribution curve shown in FIG. 1 (horizontal axis: elapsed time after adding the carbon black dispersion with the syringe, vertical axis: carbon black) (Absorbance at the measurement point changed with the centrifugal sedimentation). Each time T is read from this distribution curve and substituted into the following equation (Equation 1) to calculate the Stokes equivalent diameter corresponding to each time. ## EQU1 ## In Equation 1, η is the viscosity of the spin liquid (0.93
5 cp), N is the disk rotational speed (8000 rpm), r ₁ is the carbon black dispersion injection point radius (4.56cm), r ₂ is the radius to the absorbance measuring point (4.82cm), ρ _CB is carbon black density ( g / cm ^3), ρ _l is the density of the spin fluid (1.00178g / c
m ³ ). The Stokes equivalent diameter having the maximum frequency in the Stokes equivalent diameter and absorbance distribution curve (FIG. 2) obtained in this manner is defined as the Dst mode diameter (nm). The Dst mode diameter of IRB # 6 according to this measurement method is 92 nm. De (average diameter of the aggregate in terms of yen);
It is an average diameter obtained by converting a projected area obtained by image analysis of a two-dimensional projected image of carbon black aggregate by a transmission electron microscope into a circle, and is measured by the following method. 2 mg of a dried carbon black sample was precisely weighed and placed in a test tube in accordance with JIS K6221 (1982) 5 "How to make a dried sample", and 1.5 ml of chloroform was added thereto, treated with ultrasonic waves for 60 seconds, and dispersed. Liquid 0.5
Then, 2 ml of chloroform is added and treated with ultrasonic waves for 60 seconds to be sufficiently dispersed. This dispersion was immediately fixed on a carbon black support film, photographed with a transmission electron microscope (direct magnification: 20,000 times), and the projection area of 1000 carbon black aggregates was randomly determined from the obtained two-dimensional projection image of 100 visual fields. (A) is measured by an image analyzer (LUZEX5000 manufactured by NIRECO), and a circle-converted diameter is obtained from the equation De = (4A / π) ^1/2 , and the arithmetic average diameter of 1000 aggregates is defined as De (nm). . Among the characteristic items of the furnace carbon black specified in the present invention, the nitrogen adsorption specific surface area (N ₂ SA) is 75%.
~ 100m ² / g, compressed DBP oil absorption is 105 ~ 120ml / 1
The particle property of 00 g belongs to the hard system region, and is a prerequisite for maintaining the compounded rubber with high abrasion resistance and low heat generation with high rebound resilience. That is, the nitrogen adsorption specific area
If (N ₂ SA) is less than 75 m ² / g, sufficient abrasion resistance cannot be obtained,
On the other hand, when it exceeds 100 m ² / g, the heat buildup increases, and when the compressed DBP is less than 105 ml / 100 g, the wear resistance decreases,
If it exceeds 120 ml / 100 g, the viscosity becomes high at the time of compounding with the rubber component, resulting in a decrease in processability. The range of the Dst mode diameter specified in the present invention is an important constituent element of the present invention, and this value is (0.62 × De + 28.30) in relation to the circle-converted average diameter (De).
If the value is less than the value calculated from 0), high rebound resilience and heat build-up cannot be significantly reduced without reducing the wear resistance. That is, the nitrogen adsorption specific area (N ₂ SA) is 75 to 1
00m ² / g, the compressed DBP is in the range of 105 to 120 ml / 100 g, and when the relational expression of Dst ≧ 0.62 × De + 28.0 is satisfied, the rubber composition has relatively excellent wear resistance and high wear resistance. It is possible to simultaneously provide resilience and low heat generation. Furnace carbon black having the characteristics of the present invention is provided in a combustion chamber having a tangential air supply port at the furnace head and a combustion burner mounted in the furnace axis direction, and a combustion chamber provided coaxially with the combustion chamber. An oil furnace furnace comprising a two-stage narrow-diameter reaction chamber having a single-stage narrow-diameter reaction chamber and a second-stage narrow-diameter reaction chamber having an inner diameter smaller than that of the first-stage narrow-diameter reaction chamber, and comprising a successive wide-diameter reaction chamber Using, the raw material oil amount and fuel oil to be introduced into each narrow-diameter reaction chamber by simultaneously injecting and introducing the raw oil into each narrow-diameter reaction chamber of the first-stage narrow-diameter reaction chamber and the second-stage narrow-diameter reaction chamber,
It can be manufactured by adjusting the supply amount of combustion air and the like and further changing the conditions such as the addition of oxygen gas as appropriate. The above-mentioned furnace carbon black is blended with an elastomer such as natural rubber, styrene butadiene rubber, polybutadiene rubber, isoprene rubber, butyl rubber, other various rubbers which can be reinforced with conventional carbon black, and mixed rubber according to a conventional method. The compounding ratio of carbon black is set to 35 to 100 parts by weight based on 100 parts by weight of the rubber component. If the carbon black compounding ratio is less than 35 parts by weight, sufficient abrasion resistance is not imparted to the compounded rubber,
If the amount exceeds 100 parts by weight, the viscosity of the compound increases, so that the kneading processability decreases. When blending,
Vulcanizing agents, vulcanization accelerators, antioxidants, vulcanization aids, softeners,
The rubber composition for a tire tread of the present invention is obtained by kneading with a necessary component such as a plasticizer. The carbon black specified in the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 75 to 100 m ² / g and a compressed DBP of 1
Aggregate-Stokes mode diameter (Ds) for carbon black with a characteristic of 0.5 to 120 ml / 100 g
The value of t) is equal to or greater than the value of the relational expression of [0.62 × De + 28.0] with respect to the circle-equivalent average diameter (De) of the aggregate. The carbon black aggregate is a particle aggregate having a complicated morphology in which primary particles of the carbon black are fused and bonded in a three-dimensionally linked manner in the process of producing the carbon black, and the Stokes mode diameter of the aggregate ( Dst) is the Stokes equivalent diameter at the maximum frequency in the Stokes equivalent diameter distribution curve measured by the centrifugal sedimentation method, and is an index indicating the size of the aggregate. The aggregate equivalent diameter of the aggregate (De) is 100
The arithmetic mean diameter measured by converting the projected area of the two-dimensional projected image obtained for zero aggregates into a circle,
e The Dst value per average diameter is an index indicating the shape anisotropy of the aggregate. That is, when the aggregates are centrifugally sedimented, even if the aggregates have the same size (mass), if the form is different, the fluid resistance will be different, resulting in a difference in sedimentation speed, and the measured value of the Stokes mode diameter (Dst) will be different. Change. For example, an aggregate in which the three-dimensional connection of the particle aggregates is small has a small fluid resistance, and the apparent Stokes mode diameter has a large value. On the other hand, if the size (mass) of the aggregate is the same, the projected area of the two-dimensional projected image of the aggregate will be a substantially constant value even if the form is different. The magnitude of the Dst value when (De) is fixed is related to the shape anisotropy of the aggregate. As described above, the Stokes mode diameter (Dst) of the aggregate and the average circle-converted diameter (De) show a certain correlation. According to the study of the present inventors, the hard carbon black marketed generally has [Dst = (0.62 × De +1)
8.0) ± 9.5]. That is, the Dst value is a value between [0.62 × De + 8.5] and [0.62 × De + 27.5]. In the present invention, Dst is higher in relation to De than the value calculated from the above-mentioned relational expression, in other words, the circle-equivalent average diameter (De) of the aggregate.
Is constant, the value of the Stokes mode diameter (Dst) is relatively large, and the shape anisotropy of the aggregate is small. In particular, when the value of Dst is [0.62 × D
e + 28.0] or more, the compounded rubber can be provided with low heat build-up having high rebound resilience without abrasion resistance. According to the present invention, the above-mentioned various properties of the carbon black function comprehensively to provide a nitrogen adsorption specific surface area (N ₂ SA).
When the ratio is constant, the compounded rubber composition can have a well-balanced combination of abrasion resistance, rebound resilience and heat generation suitable as a member for a tire tread of a passenger car or a light truck. EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Examples 1 to 5 and Comparative Examples 1 to 5 A combustion chamber (diameter 800 mm, length 800 m) having a tangential air supply port at the furnace head and a combustion burner mounted in the furnace axis direction
m), a first-stage narrow-diameter reaction chamber (diameter 250 mm, length 500 mm) and a second-stage narrow-diameter reaction chamber (diameter 200 mm, each having a raw material injection nozzle coaxially connected to the combustion chamber and penetrating the furnace wall.
450mm in length), followed by a large-diameter reaction chamber (40mm in diameter)
0 mm). The feedstock had a specific gravity (15/4 ° C.) of 1.073, a viscosity of 40 ° (20 ° C.) and a toluene insoluble content of 0.03.
%, An aromatic hydrocarbon oil having a correlation coefficient (BMCI) of 140, and a specific gravity (15/4 ° C.) 0.903 and a viscosity (Cst
/ 50 ° C) 16.1 A hydrocarbon oil having a residual carbon content of 5.4% and a flash point of 96 ° C was used. Using the above-mentioned reactor, raw oil and fuel oil, the feed oil supply amount, fuel oil amount, air supply amount, and the presence or absence of oxygen gas in the first-stage narrow-diameter reaction chamber and the second-stage narrow-diameter reaction chamber 10 conditions (Examples 1 to 5, Comparative Example 1
~ 5) Furnace carbon black was produced. Table 1
Table 2 shows the conditions for forming the carbon black and the characteristics of the obtained carbon black. Table 3
Shows the characteristics of commercially available hard carbon black varieties as Reference Examples 1 to 4. [Table 1] [Table 2] [Table 3] [Table Note] Reference Example 1; N351 [Tokai Carbon Co., Ltd., Seast NH] Reference Example 2; N347 [Tokai Carbon Co., Ltd., Seast 3H] Reference Example 3; N339 [Tokai Carbon Co., Ltd., Seast KH] Reference Example 4; N220 (Shiest 6 manufactured by Tokai Carbon Co., Ltd.) Next, these carbon black samples were mixed at a compounding ratio shown in Table 4 with styrene-butadiene rubber [JSR1712 manufactured by Nippon Synthetic Rubber Co., Ltd.] ]. [Table 4] Each rubber composition obtained by vulcanizing the compound of Table 4 at a temperature of 145 ° C. for 50 minutes was subjected to various rubber tests according to the following method, and the measured results were shown in Table 5 (Examples). 6 (Comparative Example) and Table 7 (Reference Example).
FIG. 3 shows the relationship between N ₂ SA and wear resistance (24% slip), and FIG. 4 shows the relationship between N ₂ SA and tan δ.
The relationship between δ and wear resistance (24% slip) is shown in FIG.
FIG. 6 shows the relationship between δ and wear resistance (60% slip). The abrasion resistance was represented by the reciprocal of the ratio, with the abrasion amount of each sample taken as 100 for the abrasion amount of each sample.
Therefore, the larger the numerical value of wear resistance, the smaller the amount of wear,
Indicates excellent wear resistance. Further, tan δ (loss coefficient) is an index of heat build-up, and a smaller value indicates a lower heat build-up. Using a wear amount Lambourn abrasion tester (mechanical slip mechanism),
The measurement was performed under the following conditions. Test piece: thickness 10 mm, outer diameter 44 mm Emery wheel: GC type, particle size # 80, hardness H Carborundum powder with addition: particle 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 tan δ (loss coefficient) It was measured under the following conditions using a Visco Elastic Spectrometer manufactured by Iwamoto Seisakusho. Test piece: thickness 2 mm, length 30 mm, width 5 mm Frequency: 50 Hz Dynamic strain rate: 1.2% Temperature: 60 ° C. Other characteristics According to JIS K6301 (1975) “Vulcanized rubber physical test method”. [Table 5] [Table 6] [Table 7] The following is clear from Tables 5 to 7 and FIGS. In general, as N ₂ SA increases, the wear resistance improves. However, from the graph of the relationship between N ₂ SA and wear resistance (24% slip) in FIG. All have higher abrasion resistance per constant N ₂ SA than the rubber compositions of Comparative Examples and Reference Examples. That is,
Excellent wear resistance. Although tanδ increases with increasing N ₂ SA, rubber compositions of Examples from the relationship graph of the N ₂ SA and tanδ in Figure 4 as compared to Comparative Examples, the rubber composition of Example constant N tanδ per ₂ SA is in the low, low exothermic property. As described above, when the wear resistance is improved, tan δ is increased, that is, the heat generation is increased. From the graphs of FIGS. 5 and 6 showing the relationship between tan δ and wear resistance, the rubber compositions of Examples are comparative. When the tan δ is the same level as in the rubber compositions of Examples and Reference Examples, the abrasion resistance is high, and when the abrasion resistance is the same level, the tan δ is low and the heat build-up is low. Furthermore, the rubber compositions of the examples also have higher rebound resilience than the rubber compositions of the comparative examples and reference examples, and it is recognized that the rubber compositions exhibit high rebound resilience. From the above results, the rubber composition of the example satisfying the characteristic requirements specified in the present invention has the same level of particle properties (nitrogen adsorption specific surface area, compressed DBP) as the rubber composition of the comparative example. In addition to maintaining high abrasion resistance while having a reduction in tan δ (loss coefficient), which is an index of exothermicity, and improving rebound resilience, it is found that these characteristics are compatible with a good balance. Further, as compared with the reference example, it is apparent that the characteristics are significantly improved, and that other reinforcing characteristics are also maintained at a high level. According to the present invention, a low heat build-up rubber composition having both excellent wear resistance and high rebound resilience can be obtained by selectively controlling the micro characteristics of carbon black different from the prior art. Can be provided. Therefore,
The present invention can be applied to a tire tread member for a passenger car or a light truck to achieve effective fuel saving.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a distribution curve showing changes in absorbance due to centrifugal sedimentation of carbon black and the time elapsed since the carbon black dispersion was added. FIG. 2 is a distribution curve showing the relationship between Stokes equivalent diameter (Dst) and absorbance, and an explanatory diagram of a Dst mode system. FIG. 3 is a graph showing the relationship between N ₂ SA and abrasion resistance (24% slip) for the rubber compositions of Examples, Comparative Examples, and Reference Examples. FIG. 4 is a graph showing the relationship between N ₂ SA and tan δ for the rubber compositions of Examples, Comparative Examples, and Reference Examples. FIG. 5 is a graph showing the relationship between tan δ and abrasion resistance (24% slip) for the rubber compositions of Examples, Comparative Examples, and Reference Examples. FIG. 6 is a graph showing the relationship between tan δ and abrasion resistance (60% slip) for the rubber compositions of Examples, Comparative Examples, and Reference Examples.

Claims (1)

(57) [Claims 1] A nitrogen adsorption specific surface area (N ₂ SA) of 75 to 100
Furnace carbon black, which belongs to a hard region of m ² / g and a compressed DBP of 105 to 120 ml / 100 g, and has a Stokes mode diameter (Dst) of an aggregate having selective properties according to the following relational formula, 100 parts by weight of a rubber component A rubber composition for a tire tread, characterized in that the rubber composition is blended in an amount of 35 to 100 parts by weight with respect to the weight of the rubber composition. Dst ≧ 0.62 × De + 28.0 where Dst is the Stokes mode diameter of the carbon black aggregate measured by the disc centrifuge (DCF), and De is the two-dimensional projection image by the transmission electron microscope. The figure shows the circle-converted average diameter of the projected area of the carbon black aggregate obtained by image analysis.