JP5803372B2 - Rubber composition for tire - Google Patents

Description

  The present invention relates to a rubber composition for tires, which contains carbon black with controlled colloidal characteristics, and has improved durability over a conventional level while reducing heat generation.

  The bead portion of the pneumatic tire has a gum finishing and / or rim cushion (hereinafter sometimes simply referred to as “rim cushion”) on its outer layer so that the tire is in close contact with the rim when the rim is assembled to the wheel. Is provided. The rim cushion must be in close contact with the rim flange to prevent rim displacement with respect to the rim and to maintain air sealing performance. However, the rim cushion suffers from problems such as cracking due to compression force and heat generation from the rim, and fatigue due to repeated deformation, resulting in a decrease in tire durability.

As a countermeasure, Patent Document 1 blends 40 to 60 parts by weight of carbon black having a nitrogen adsorption specific surface area of 90 m ² / g or more with respect to 100 parts by weight of a rubber component, and blends a sulfenamide vulcanization accelerator. It has been proposed to improve crack resistance by using a rubber composition. However, when the blending amount of carbon black having a nitrogen adsorption specific surface area of 90 m ² / g or more is increased, the crack resistance is improved, but there is a problem that the heat generation is increased.

  The increase in heat generation causes the rim cushion to become hot and lowers durability, and the rolling resistance of the pneumatic tire deteriorates. In particular, as the interest in global environmental problems is increasing, it is important to improve fuel efficiency, so it is important to reduce heat generation. Generally, 60 ° C. tan δ by dynamic viscoelasticity measurement is used as an index of exothermic property of the rubber composition. The smaller the tan δ (60 ° C.) of the rubber composition, the smaller the exothermic property.

  Examples of a method for reducing the tan δ (60 ° C.) of the rubber composition include reducing the compounding amount of carbon black and increasing the particle size of carbon black. However, as described above, when such a prescription is adopted for a rubber composition that forms a part that contacts the rim of a bead part such as a rim cushion, the rubber hardness, tensile strength and elongation at break are lowered, and crack resistance when formed into a tire. In other words, it has a conflicting problem that durability such as fatigue resistance is lowered.

JP 2005-171016 A

  An object of the present invention is to provide a rubber composition for a tire which is improved in durability to a conventional level or less while blending carbon black with controlled colloidal characteristics to reduce heat generation.

The tire rubber composition of the present invention that achieves the above object has a nitrogen adsorption specific surface area N ₂ SA of 55 to 81 m ² / g, DBP with respect to 100 parts by weight of diene rubber containing 15 to 80% by weight of butadiene rubber. 60 to 110 parts by weight of carbon black having an absorption amount of 120 to 150 ml / 100 g is blended, and the mode diameter Dst (nm) in the Stokes diameter mass distribution curve of the carbon black aggregate and the N ₂ SA The relationship is expressed by the following formula (1)
Dst = α (N ₂ SA) ^−0.61 (1)
(However, Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and α is a coefficient.)
The coefficient α is 1979 or more and 2215 or less .

The rubber composition for a tire of the present invention has a nitrogen adsorption specific surface area N ₂ SA of 55 to 81 m ² / g and a DBP absorption of 120 to 100 parts by weight of diene rubber containing 15 to 80% by weight of butadiene rubber. 0.99 ml / 100 g, and since the carbon black factor α is 1979 or more 2215 or less when expressed in relation of the formula (1) as blended 60 to 110 parts by weight, of the rubber composition tan [delta (60 ° C. ) And low exothermic property, while ensuring the rubber hardness, strength and elongation at break, durability such as crack resistance and fatigue resistance when made into tires can be improved over conventional levels. .

The coefficient alpha is by the range of 1979 ≦ α ≦ 2215, it is possible to suppress the production cost while ensuring excellent properties described above.

  The pneumatic tire comprising the bead portion in contact with the rim with the tire rubber composition of the present invention has improved durability such as crack resistance and fatigue resistance while reducing rolling resistance and improving fuel efficiency. It can be improved beyond the level. Examples of the bead portion include gum finishing and / or rim cushion.

It is sectional drawing which illustrates the structure of the bead part of the pneumatic tire for passenger cars. It is sectional drawing which illustrates the structure of the bead part of the pneumatic tire for trucks and buses. It is a graph showing the relationship between Dst and N ₂ SA of the carbon black used in the rubber composition for a tire of the present invention.

  The rubber composition for tires of the present invention can be suitably used for constituting pneumatic tires for passenger cars and trucks / buses. Particularly, it is suitable for constituting a portion of the bead portion of the pneumatic tire that comes into contact with the rim, that is, a rim cushion and / or gum finishing.

  FIG. 1 is an explanatory view illustrating a cross-sectional configuration of a bead portion of a pneumatic tire for a passenger car, and FIG. In addition, the rim | limb R which mounts a pneumatic tire was shown with the dashed-dotted line.

  In FIG. 1, a bead portion of the pneumatic tire for passenger cars is denoted by 1, and a sidewall portion is denoted by 2. Between the pair of left and right bead portions 1, a carcass layer 5 having a cord angle with respect to the tire circumferential direction of substantially 90 ° is mounted, and both end portions of the carcass layer 5 are embedded in the bead portions 1. The bead filler 4 is wound up from the inside to the outside so as to wrap around the bead filler 4. Further, a gum finishing 7 is disposed on the inner surface of the bead portion 1 in the tire radial direction, and a rim cushion 6 is disposed on the outer surface of the bead portion 1 in the tire width direction. It is configured.

  In FIG. 2, 1 is a bead part, 2 is a side wall part. A carcass layer 5 in which a plurality of steel cords are arranged is mounted between the left and right bead portions 1 of the pneumatic tire for trucks and buses. The carcass layer 5 is wound up from the tire inner side to the outer side around a pair of left and right bead cores 3 embedded in the bead portion 1. In the bead portion 1, a fiber reinforcement layer 8 formed by aligning a plurality of steel cords is disposed along the carcass layer 5. A lower bead filler 4a is disposed outside the bead core 3 in the tire radial direction, and an upper bead filler 4b is disposed adjacent to the lower bead filler 4a. Further, a gum finishing 7 is disposed on the inner surface of the bead portion 1 in the tire radial direction, and a rim cushion 6 is disposed on the outer surface of the bead portion 1 in the tire width direction. The gum finishing 7 and the rim cushion 6 are both provided. The tire is configured to be in close contact with the rim R when the rim is assembled.

  In the present specification, the rim cushion and the gum finishing are not limited to the members having such names, and as illustrated in FIGS. It shall include the member of the name. The rim cushion and gum finishing can be configured independently as illustrated above. Moreover, a rim cushion and gum finishing can be comprised integrally. The name of the member formed integrally with the rim cushion and the gum finishing may be a rim cushion, gum finishing or other names.

  In the rubber composition for tires of the present invention, the diene rubber contains butadiene rubber as an essential component. The content of butadiene rubber is 15 to 80% by weight, preferably 20 to 70% by weight, in 100% by weight of diene rubber. If the butadiene rubber content is less than 15% by weight, tire durability, particularly fatigue resistance, cannot be improved sufficiently. On the other hand, when the content of butadiene rubber exceeds 80% by weight, rubber hardness and strength required as a tire rubber composition constituting the bead portion may be lowered.

  The diene rubber other than butadiene rubber may be any rubber usually used in tire rubber compositions, and examples thereof include natural rubber, isoprene rubber, styrene-butadiene rubber, and acrylonitrile-butadiene rubber. Of these, natural rubber, isoprene rubber, and styrene-butadiene rubber are preferable. These diene rubbers can be used alone or as any blend.

The tire rubber composition of the present invention has a specific nitrogen adsorption specific surface area N ₂ SA and DBP absorption, and limits the relationship between the N ₂ SA and the mode diameter Dst in the mass distribution curve of the Stokes diameter of the aggregate. By blending the new carbon black, mechanical properties such as tensile strength, tensile elongation at break, rubber hardness, and abrasion resistance are not deteriorated while reducing tan δ (60 ° C.) of the rubber composition. The amount of carbon black is 60 to 110 parts by weight, preferably 65 to 100 parts by weight, based on 100 parts by weight of the diene rubber. When the blending amount of carbon black is less than 60 parts by weight, the rubber hardness and elastic modulus of the rubber composition are deteriorated. If the blending amount of carbon black exceeds 110 parts by weight, tan δ (60 ° C.) increases and tensile elongation at break decreases.

The carbon black used in the present invention has a nitrogen adsorption specific surface area N ₂ SA of 55 to 81 m ² / g. When N ₂ SA is less than 55 m ² / g, mechanical properties such as rubber hardness and dynamic elastic modulus of the rubber composition are lowered. When N ₂ SA exceeds 81 m ² / g, tan δ (60 ° C.) increases. N ₂ SA shall be measured according to JIS K6217-2.

Further, DBP absorption amount of carbon black is 1 20~150ml / 100g. If the DBP absorption is less than 120 ml / 100 g, tan δ (60 ° C.) increases. Moreover, since the molding processability of the rubber composition is lowered and the dispersibility of the carbon black is deteriorated, the carbon black cannot be sufficiently reinforced. If the DBP absorption exceeds 150 ml / 100 g, the hardness of the rubber composition becomes too high and the tensile elongation at break decreases. In addition, workability deteriorates due to an increase in viscosity. The DBP absorption amount shall be measured according to JIS K6217-4 oil absorption amount A method.

The carbon black used in the present invention has the above-mentioned colloidal characteristics, and the mode diameter Dst and the nitrogen adsorption specific surface area N ₂ SA in the mass distribution curve of the Stokes diameter of the aggregate are expressed by the following equation (1). When expressed, the coefficient α is 1979 or more and 2215 or less .
Dst = α (N ₂ SA) ^−0.61 (1)
(However, Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and α is a coefficient.)

Carbon black has the N ₂ SA and DBP absorption amounts described above, and the coefficient α is set to 1979 or more, so that the tan δ (60 ° C.) of the rubber composition is reduced and the rubber hardness, the dynamic elastic modulus, etc. It can be maintained and improved. The upper limit of the coefficient α is preferably 2215 or less from the viewpoint of productivity such as the yield and cost of carbon black. In the present invention, the mode diameter Dst in the mass distribution curve of the Stokes diameter of the aggregate refers to the mode diameter of the maximum frequency in the mass distribution curve of the Stokes diameter of the aggregate obtained by centrifugal sedimentation of carbon black. In the present invention, Dst is measured according to the method for obtaining the aggregate distribution by JIS K6217-6 disc centrifugal light sedimentation method.

FIG. 1 is a graph showing the relationship between Dst and N ₂ SA of carbon black used in the present invention. In FIG. 1, the horizontal axis represents N ₂ SA (m ² / g), and the vertical axis represents Dst (nm). Representative carbon black having the ASTM standard number was plotted with square marks, and carbon black obtained by trial production was plotted with circle marks and triangle marks. Here, numbers 1 to 13 that refer to carbon blacks CB1 to CB13 used in Examples and Comparative Examples described later are attached to the plots, respectively. As shown in FIG. 1, Dst and N ₂ SA of conventional standardized carbon black black generally satisfy the relationship of the following formula (2).
Dst = 1650 × (N ₂ SA) ^−0.61 (2)
(However, Dst represents the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, and N ₂ SA represents the nitrogen adsorption specific surface area (m ² / g).)
In FIG. 1, the relationship of the above formula (2) is represented by a dotted curve.

On the other hand, in the carbon black used in the present invention, Dst and N ₂ SA are plotted on the upper right from the curve (solid line) of the following formula (3).
Dst = 1979 × (N ₂ SA) ^−0.61 (3)
(However, Dst represents the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, and N ₂ SA represents the nitrogen adsorption specific surface area (m ² / g).)

That is, in the present invention, a new carbon black in which Dst is larger than Dst of conventional carbon black is used in the range of N ₂ SA of 55 to 81 m ² / g. Such carbon black means that the Stokes diameter of the aggregate is large and the form of the aggregate is close to a sphere even when N ₂ SA is at the same level as conventional carbon black. Thereby, in order to raise the reinforcement performance with respect to rubber | gum, mechanical characteristics, such as rubber hardness of a rubber composition and a dynamic elastic modulus, can be improved more than the conventional level.

  Carbon black having the colloidal characteristics described above is, for example, feedstock introduction conditions, fuel oil and feedstock supply rate, fuel oil combustion rate, reaction time (combustion from the last feedstock introduction position to reaction stoppage) in the carbon black production furnace. The production conditions such as gas residence time) can be adjusted.

  In the present invention, a reinforcing filler other than carbon black having the specific colloidal characteristics described above can be blended, and the balance between tan δ of the rubber composition and mechanical properties such as rubber hardness and strength can be adjusted. it can. Examples of the reinforcing filler include carbon black other than the above-described carbon black, silica, clay, calcium carbonate, talc, mica, and the like. In particular, silica is preferably blended as a reinforcing filler. By blending silica together with the carbon black having the specific colloidal characteristics described above, the heat resistance of the rubber composition can be further reduced and the rolling resistance when the tire is made can be further reduced.

  The tire rubber composition may contain various additives generally used in tire rubber compositions such as vulcanization or crosslinking agents, vulcanization accelerators, various oils, anti-aging agents, and plasticizers. Such an additive can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for tires of the present invention can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for tires of the present invention is suitably used for constituting a portion that comes into contact with a rim of a bead portion of a pneumatic tire, that is, a rim cushion or gum finishing. Since the pneumatic tire in which the bead portion is composed of the rubber composition for tires of the present invention has low heat generation during running, it can reduce rolling resistance and improve fuel efficiency. At the same time, tire durability such as crack resistance and fatigue resistance is excellent, and the life of the tire can be made longer than the conventional level.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

Sixteen rubber compositions (Examples 1 to 5 and Comparative Examples 1 to 11) were prepared using 13 types of carbon black (CB1 to CB13). Of these, eight types of carbon black (CB1, CB2, CB8 to CB13) are commercially available grades, and five types of carbon black (CB3 to CB7) are prototypes. Tables 1 and 2 show their colloidal characteristics. Further, in FIG. 1, the relationship between Dst and N ₂ SA of each of the carbon blacks CB1 to CB13 is plotted, and numbers for referring to the respective carbon blacks are attached.

In Tables 1 and 2, each abbreviation represents the following colloidal characteristics.
N ₂ SA: Nitrogen adsorption specific surface area measured based on JIS K6217-2 IA: Iodine adsorption amount measured based on JIS K6217-1 CTAB: CTAB measured based on JIS K6217-3 Adsorption specific surface area DBP: DBP absorption measured based on JIS K6217-4 (uncompressed sample) 24M4: 24M4-DBP absorption measured based on JIS K6217-4 (compressed sample) TINT: JIS Specific tinting strength measured based on K6217-5, Dst: Mode diameter, ΔD50, which is the maximum value of the mass distribution curve of the Stokes diameter of the aggregate by the disc centrifugal light sedimentation method measured based on JIS K6217-6 : Mass fraction of the Stokes diameter of the aggregate measured by the disc centrifugal light sedimentation method measured based on JIS K6217-6 In curves, the width of the distribution when its mass frequency is half height of the maximum point (half-width)
· Alpha: coefficient when the Dst and N ₂ SA fit to the relationship of the formula (1) described above alpha

In Tables 1 and 2, carbon blacks CB1, CB2, and CB8 to CB13 represent the following commercial grades, respectively.
・ CB1: Seest KHP made by Tokai Carbon
・ CB2: Toast Carbon Co., Ltd. Seast KH
・ CB8: Tokai Carbon Co., Ltd. Seest 300
・ CB9: Show Black 330T manufactured by Cabot Japan
-CB10: Niteron # 10N manufactured by Nippon Kayaku Carbon
・ CB11: Tokai Carbon Co., Ltd. Seest 3
・ CB12: Tokai Carbon Co., Ltd. Seest NH
CB13: Tokai Carbon Co. Seast 6

Production of carbon blacks CB3 to CB7 Using a cylindrical reactor, carbon black CB3 was changed by changing the total air supply amount, fuel oil introduction amount, fuel oil combustion rate, feedstock oil introduction amount, reaction time as shown in Table 3. -CB7 was produced.

Preparation and Evaluation of Tire Rubber Compositions 16 kinds of rubber compositions (Examples 1 to 5 and Comparative Example 1) having the compositions shown in Tables 4 and 5 using the 13 kinds of carbon blacks (CB1 to CB13) described above. In preparing -11), the components excluding sulfur and the vulcanization accelerator were weighed and kneaded in a 55 L kneader for 15 minutes, and then the master batch was discharged and cooled at room temperature. This master batch was subjected to a 55 L kneader, and sulfur and a vulcanization accelerator were added and mixed to obtain a tire rubber composition.

  Each of the obtained tire rubber compositions was vulcanized at 150 ° C. for 30 minutes in a mold having a predetermined shape to prepare a test piece, and fatigue resistance and crack resistance were evaluated by the following methods.

Fatigue resistance In accordance with JIS K6270, a test piece of dumbbell shape No. 3 (distance between marked lines 20 mm) was produced. For fatigue characteristics, 100% strain was repeatedly applied to each test piece, and the number of repetitions until the test piece broke (hereinafter referred to as “number of breaks”) was measured. The number of breaks was measured at n = 6, and the 50% residual probability based on the normal probability distribution was determined from the number of breaks. The obtained results are shown in the column of “Fatigue resistance” in Tables 4 and 5 with the index of Comparative Example 1 as 100. The larger this index, the longer the fatigue life and the better the fatigue resistance.

Crack resistance In accordance with JIS K6260, a dematcher bent crack growth test piece was produced. Using this test piece, crack growth [unit: mm] after a stroke of 57 mm, a speed of 300 ± 10 rpm, and a flexion number of 100,000 was measured. The obtained results were used as indexes for setting the reciprocal number of Comparative Example 1 to 100, and are shown in the “crack resistance” column of Tables 4 and 5. Larger index means smaller crack growth and better crack resistance.

  Further, a pneumatic tire having a tire size of 195 / 65R15, in which a rim cushion and a gum finishing were constituted by the obtained tire rubber composition, was vulcanized. The rolling resistance of the obtained 16 types of pneumatic tires was evaluated by the following method.

Rolling resistance The obtained pneumatic tire is assembled to a standard rim (size 15 × 6J wheel), filled with air with an air pressure of 210 kPa, and attached to an indoor drum testing machine (drum diameter 1707 mm) in accordance with JIS D4230. In accordance with the high-speed durability test described in “6.4 High-Speed Performance Test A”, a high-speed durability test was conducted, and the resistance force at a test load of 4.82 kN and a speed of 50 km / hour was measured. It was. The obtained results are obtained in the column of “Rolling resistance” in Tables 4 and 5 by calculating the reciprocal of the rolling resistance, setting Comparative Example 1 as 100. The larger this index, the smaller the rolling resistance and the better the fuel efficiency.

The types of raw materials used in Tables 4 and 5 are shown below.
NR: natural rubber, RSS # 3
SBR: styrene butadiene rubber, Nipol 1502 manufactured by Nippon Zeon
BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon
CB1 to CB13: Carbon black aroma oils shown in Tables 1 and 2 above: Process X-140 manufactured by Japan Energy
Zinc Hana: Zinc Oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: NOF Co., Ltd. Beads stearic acid wax: Ouchi Shinsei Chemical Industry Co., Ltd. Sunnock anti-aging agent: Flexis Corporation SANTOFLEX 6PPD
Vulcanization accelerator: Nouchira NS-P manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Co., Ltd.

  As is apparent from Table 4, it was confirmed that the pneumatic tires of Examples 1 to 5 had low rolling resistance and improved durability including fatigue resistance and crack resistance to the conventional level or more.

As is clear from Table 4, the pneumatic tire of Comparative Example 1 has a DBP absorption amount of carbon black CB9 of less than 120 ml / 100 g and a coefficient α of formula (1) of less than 1979. Rolling resistance is larger than that of a pneumatic tire, and fatigue resistance and crack resistance are inferior. The pneumatic tires of Comparative Examples 2 and 3 have poor fatigue resistance because the butadiene rubber content is less than 15% by weight.

  As is clear from Table 5, the pneumatic tires of Comparative Examples 4, 5, and 10 have a coefficient α of the formula (1) of carbon blacks CB1, CB2, and CB12 of less than 1979. It is impossible to achieve both improvement in durability consisting of fatigue resistance and crack resistance.

In the pneumatic tire of Comparative Example 6, since the DBP absorption amount of carbon black CB3 exceeds 150 ml / 100 g and the coefficient α of the formula (1) is less than 1979, the strength of the rubber composition is insufficient, and the fatigue resistance In addition, the crack resistance is inferior.

In the pneumatic tires of Comparative Examples 7 and 9, since the DBP absorption amount of carbon black CB8 and CB11 is less than 120 ml / 100 g and the coefficient α in the formula (1) is less than 1979, the rolling resistance is reduced and the fatigue resistance is increased. It is impossible to achieve both improvement in durability consisting of crack resistance.

Since the N ₂ SA of CB10 is less than 55 m ² / g and the coefficient α in the formula (1) is less than 1979, the pneumatic tire of Comparative Example 8 is deteriorated in fatigue resistance and crack resistance.

In the pneumatic tire of Comparative Example 11, N ₂ SA of the carbon black CB13 exceeds 81 m ² / g and the coefficient α is less than 1979, so that the durability is reduced by rolling resistance, fatigue resistance, and crack resistance. It is not possible to achieve both improvement of sex.

1 Bead part 2 Side wall part 3 Bead core 4, 4a, 4b Bead filler 5 Carcass 6 Rim cushion 7 Gum finishing R rim

Claims (3)

Carbon black having a nitrogen adsorption specific surface area N ₂ SA of 55 to 81 m ² / g and a DBP absorption of 120 to 150 ml / 100 g is added to 60 to 100 parts by weight of diene rubber containing 15 to 80% by weight of butadiene rubber. 110 parts by weight, and the relationship between the mode diameter Dst (nm) in the Stokes diameter mass distribution curve of the carbon black aggregate and the N ₂ SA is expressed by the following formula (1).
Dst = α (N ₂ SA) ^−0.61 (1)
(However, Dst is the mode diameter (nm) in the mass distribution curve of the Stokes diameter of the aggregate, N ₂ SA is the nitrogen adsorption specific surface area (m ² / g), and α is a coefficient.)
A rubber composition for tires, wherein the coefficient α is 1979 or more and 2215 or less . A pneumatic tire comprising the tire rubber composition according to claim 1 , wherein a portion of the bead portion that contacts the rim is formed. The pneumatic tire according to claim 2 , wherein a portion of the bead portion that contacts the rim is a gum finishing and / or a rim cushion.

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