JP2007231179A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire treads that highly enhances abrasion resistance and low heat build-up properties. <P>SOLUTION: The rubber composition for tire treads suitable for heavy-duty tire treads comprises 100 pts.wt. of a diene rubber and, incorporated therewith, 40-60 pts.wt. of carbon black having a CTAB adsorption specific surface area of 120-140 m<SP>2</SP>/g, a compressed DBP oil absorption (24M4DBP) of 100-120 mL/100 g and a ratio (N<SB>2</SB>SA/IA) of a nitrogen adsorption specific surface area (N<SB>2</SB>SA) to an iodine adsorption number (IA) of 1.20-1.30 m<SP>2</SP>/mg with the difference between the N<SB>2</SB>SA and the CTAB adsorption specific surface area of at most 5 m<SP>2</SP>/g. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread, and more particularly to a rubber composition for a tire tread suitable for a heavy load tire that has improved wear resistance and low heat build-up by using a specific carbon black.

  In heavy duty tires used for trucks and buses, it is important to improve the wear resistance of the tread portion. Conventionally, as a measure for improving the wear resistance, a high cis type having a high cis-1,4 content is used as a 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 have been proposed.

  Although these conventional measures are certainly expected to improve wear resistance, they do not satisfy the recent requirements for high wear resistance, and the low heat build-up required for tread rubber for heavy-duty tires There are drawbacks that adversely affect properties such as cut resistance / chip resistance.

  In the rubber composition for tire treads, various proposals have been conventionally made in order to achieve both wear resistance and low heat build-up (see Patent Documents 1 to 6 below). However, none of these documents disclose the specific carbon black used in the present invention, and by using the carbon black in a rubber composition for a tire tread, wear resistance and low exothermicity are disclosed. Is not disclosed that can be improved to a higher degree than before.

For example, in the following Patent Document 2, the CTAB adsorption specific surface area is 145 to 151 m ² / g and the compressed DBP oil absorption (24M4DBP) is 100 parts by weight of the diene rubber component containing 15 to 30% by weight of butadiene rubber. 104-110 ml / 100 g, ratio of CTAB to iodine adsorption amount (IA) (CTAB / IA) is 0.95-1.04 m ² / mg, nitrogen adsorption specific surface area (N ₂ SA) is 164-170 m ² / g There has been proposed a rubber composition for a tire tread that can improve wear resistance while maintaining good fuel economy by containing 50 to 56 parts by weight of certain carbon black. Table 3 discloses carbon A having CTAB of 130 m ² / g, 24M4DBP of 108 ml / 100 g, N ₂ SA of 131 m ² / g, and IA of 122 mg / g. This carbon A has a difference of 1 m ² / g between N ₂ SA and CTAB and has a small surface roughness, but N ₂ SA / IA which is an index of surface activity is as small as 1.07. Abrasion resistance and low heat build-up cannot be improved greatly.
JP 2004-256756 A JP 2004-59803 A JP 2001-123008 A Japanese Patent Laid-Open No. 2001-2835 JP-A-6-184362 Japanese Patent Laid-Open No. 4-170448

  An object of this invention is to provide the rubber composition for tire treads which can improve abrasion resistance and exothermic property highly.

  As a result of intensive studies focusing on the characteristics of carbon black, the present inventor is able to highly improve low heat buildup and wear resistance by regulating surface roughness and suppressing surface roughness. As a result, the present invention has been completed.

That is, the tire tread rubber composition according to the present invention has a nitrogen adsorption specific surface area (N ₂ SA) ratio (N ₂ SA / IA) to iodine adsorption amount (IA) with respect to 100 parts by weight of the diene rubber. 40 to 60 parts by weight of carbon black having a difference of 1.20 to 1.30 m ² / mg and a difference of N ₂ SA and CTAB adsorption specific surface area of 5 m ² / g or less is blended. is there.

In the rubber composition of the present invention, the carbon black preferably has a CTAB adsorption specific surface area of 120 to 140 m ² / g and a compressed DBP oil absorption (24M4DBP) of 100 to 120 ml / 100 g.

  In the rubber composition of the present invention, the diene rubber is composed of 95 to 50% by weight of natural rubber and / or isoprene rubber and 5 to 50% by weight of butadiene rubber having a cis-1,4 bond content of 95% or more. Preferably it consists of.

According to the present invention, for the carbon black blended in the rubber composition for tire treads, N ₂ SA / IA, which is an index of surface activity, is increased to 1.20 to 1.30, thereby strengthening the network with the rubber polymer. By doing so, wear resistance and low heat build-up can be improved. Further, by defining the difference between N ₂ SA and CTAB adsorption specific surface area as an index of the surface roughness of carbon black to be small, the wear resistance and the low heat generation property are further improved. Thus, the combination of both can greatly improve wear resistance and low heat buildup.

  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.

  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).

The carbon black used in the rubber composition of the present invention has a ratio of nitrogen adsorption specific surface area (N ₂ SA) (m ² / g) to iodine adsorption amount (IA) (mg / g) (N ₂ SA / IA). Satisfies the property of 1.20 to 1.30 m ² / mg. This ratio is an index of the surface activity of carbon black, and in the present invention, a high surface activity product within the above numerical range is used. By using carbon black having a high surface activity in this way, the network with the rubber polymer can be strengthened, and the wear resistance and low heat build-up can be improved.

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 carbon black also satisfies the characteristic that the difference between N ₂ SA and CTAB adsorption specific surface area is 5 m ² / g or less. Here, the CTAB (cetyltrimethylammonium bromide) adsorption specific surface area is a value measured according to ASTM D3765, and serves as an index of the particle size of carbon black. Further, N ₂ SA is an indicator of the total surface area of carbon black, whereas the CTAB adsorption specific surface area is an indicator of the external surface area of carbon black. Therefore, the difference between the two represents the surface roughness of carbon black. As an index, the smaller the difference, the fewer pores and the smaller the surface roughness. In the present invention, wear resistance and low heat build-up can be further improved by using carbon black having a small surface roughness with a difference between them of 5 m ² / g or less. This difference is preferably as small as possible, and more preferably 3 m ² / g or less.

The carbon black is a SAF grade carbon black having a CTAB adsorption specific surface area of 120 to 140 m ² / g and a compressed DBP (dibutyl phthalate) oil absorption (24M4DBP) of 100 to 120 ml / 100 g. Is preferred. 24M4DBP serves as an index of the structure of carbon black, and is measured according to ASTM D3493. In the present invention, a high-structure product within the above numerical range is used. The SAF grade carbon black is a 100th order small particle size carbon black classified and coded according to the particle diameter in ASTM D1765. By using carbon black having such a small particle size and a high structure, it is possible to further eliminate wear resistance and low heat buildup.

  The compounding amount of the carbon black is 40 to 60 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 40 parts by weight, the reinforcing property is not sufficient and the wear resistance is lowered.

  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.

  According to the rubber composition of the present invention composed of the above, since wear resistance and heat generation can be improved to a high degree, it can be suitably used as a tread rubber for pneumatic tires, and particularly used under high loads. And is suitably used for heavy load tire treads that require high wear resistance.

  Such a rubber composition can be prepared using various mixers such as a Banbury mixer, a roll, a kneader, and the kneaded rubber composition is used as a tire tread rubber and vulcanized according to a conventional method. Thus, a pneumatic tire can be manufactured.

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

Examples 1-4 and Comparative Examples 1-6
The rubber composition for tire treads of Examples 1 to 4 and Comparative Examples 1 to 6 was prepared using a Banbury mixer. The composition of each rubber composition is as follows.

Natural rubber (RSS 3) 80 parts by weight butadiene rubber (cis 1,4 bond = 95%, “BR01” manufactured by JSR) 20 parts by weight carbon black Zinc flower (Mitsui Kinzoku Co., Ltd. “Zinc flower 1” 3) parts by weight stearic acid (manufactured by NOF Corporation) 3 parts by weight anti-aging agent (“6PPD” manufactured by Monsanto) 1 part by weight sulfur (manufactured by Tsurumi Chemical Co., Ltd.) 2 parts by weight vulcanization accelerator (Sanshin Chemical Co., Ltd.) "TBBS" manufactured) 1 part by weight.

  The characteristics of carbon black are as shown in Table 1 below. The carbon blacks of Comparative Examples 1 to 3 are all commercially available ASTM grade SAF and ISAF grade carbon blacks. Comparative Example 1 is “Seast 9” manufactured by Tokai Carbon Co., and Comparative Example 2 is “Seast 6” manufactured by Tokai Carbon Co. Comparative Example 3 is “Seast 7HM” manufactured by Tokai Carbon.

  Further, the carbon blacks of Comparative Examples 4 to 6 and Examples 1 to 4 are connected to a combustion chamber having an air supply port and a combustion burner mounted in the furnace axial direction at the furnace head, and are coaxially connected to the combustion chamber. The conditions for introducing the feedstock oil so as to have the characteristics shown in Table 1 below, using an oil furnace furnace comprising a multistage small reaction chamber having a feedstock injection nozzle and a large reaction chamber. It is obtained by adjusting the air introduction condition, the fuel oil introduction condition, and the cooling condition. In addition, the carbon black of Example 3 and Example 4 is the same product.

  Each rubber composition was subjected to a tensile test to measure 300% modulus, breaking strength and elongation at break, and evaluated wear resistance and low heat build-up. 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.

Low exothermic property: Using a Toyo Seiki spectrometer, the viscoelastic property tan δ at 60 ° 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 low exothermic property, so that a numerical value is small.

  The results are as shown in Table 1, and the carbon blacks of Comparative Examples 1 to 4 are small particle size products, but have low surface activity, so the effect of improving wear resistance and low heat generation is low. It was insufficient. In Comparative Example 5, since the surface activity of carbon black was high, both wear resistance and low heat build-up were improved, but the surface roughness of carbon black was large, so that the improvement effect was small. Further, in Comparative Example 6, the surface roughness of the carbon black is small, and therefore, the wear resistance is improved, but the effect is not always sufficient because the surface activity is small, and particularly the improvement of low heat generation. Almost no effect was obtained.

On the other hand, in the carbon blacks of Examples 1 to 4, the value of N ₂ SA / IA that is an index of surface activity is as high as 1.20 or more, and the relationship with the structure is also high by breaking the balance of the proportional relationship. The wear resistance and low heat build-up were improved. Further, since the surface roughness of the carbon black is suppressed, the wear resistance and the low heat buildup have been further improved. In Example 4, even when the blending amount of carbon black was reduced and the modulus was evaluated at the same place, sufficient wear resistance was obtained, and further lower heat generation was achieved.

  The rubber composition for a tire tread of the present invention can be used as a tread rubber for various pneumatic tires, and is particularly preferably used as a tread rubber for a large tire used for a truck or a bus, that is, a heavy load tire. it can.

Claims (3)

For 100 parts by weight of diene rubber,
Ratio of nitrogen adsorption specific surface area (N ₂ SA) to iodine adsorption amount (IA) (N ₂ SA / IA) is 1.20 to 1.30 m ² / mg, and N ₂ SA and CTAB adsorption specific surface area 40 to 60 parts by weight of carbon black having a difference of 5 m ² / g or less is blended. A rubber composition for a tire tread, characterized by comprising: ^{2. The} rubber composition for a tire tread according to claim 1, wherein the carbon black has a CTAB adsorption specific surface area of 120 to 140 m ² / g and a compressed DBP oil absorption (24M4DBP) of 100 to 120 ml / 100 g. The diene rubber is composed of 95 to 50% by weight of natural rubber and / or isoprene rubber and 5 to 50% by weight of butadiene rubber having a cis-1,4 bond content of 95% or more. Or the rubber composition for tire treads of 2.