JP7242003B2 - Rubber composition for tire tread and tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tire tread rubber composition and a tire having a tread made of the rubber composition.

In addition to excellent wear resistance, automobile tires must have good braking performance, driving performance, and excellent steering stability on various road surfaces, such as dry and wet roads, in order to improve driving safety. Tires satisfying these demands have been studied and various proposals have been made. For example, in Patent Document 1, the tread has a tan δ at 0° C. of 0.25 to 0.55, a difference between tan δ at 30° C. and tan δ at 60° C. of −0.02 to 0.07, and dynamic strain. 1%, formed using a rubber composition having a specific physical property that the dynamic storage elastic modulus at 0 ° C. is 4 to 20 MPa, and for the tread, the circumferential groove and the non-circumferential direction with respect to the contact area of the tread A tire having a groove area ratio set within a specific range is disclosed.

Furthermore, especially in recent years, in order to improve the fuel efficiency of automobiles, there has been an increasing demand for a reduction in the rolling resistance of automobile tires, and various proposals have been made. For example, Patent Document 2 discloses a method of forming a tread using a rubber composition using a diene rubber (modified rubber) modified with an organosilicon compound containing an amino group and an alkoxy group to reduce rolling resistance. disclosed.

JP 2016-193687 A JP-A-2000-344955

The tire described in Patent Document 1 is said to exhibit excellent braking and driving performance on various road surfaces such as dry and wet road surfaces, as well as excellent steering stability. Further, the tire described in Patent Document 2 is supposed to reduce rolling resistance. However, in recent years, the demand for fuel efficiency and steering stability of automobiles has become more sophisticated, and in particular, it is desired to reduce rolling resistance and further improve steering stability at high speeds such as 120 km / h. It is rare.

The present invention provides a rubber composition for a tire tread which has excellent wear resistance and the like, and which can be used to manufacture a tire having low rolling resistance during high-speed running and excellent steering stability during high-speed running. is the subject.
The present invention also provides a tire manufactured using the rubber composition for a tire tread, which has excellent wear resistance and the like, low rolling resistance during high-speed running, and steering stability during high-speed running. An object of the present invention is to provide a tire excellent in

As a result of intensive studies to achieve the above object, the present inventors have found that by forming a tread using a rubber composition having a specific composition, a tire made of a tread rubber having a small tan δ at 20°C can be produced. It was found that the rolling resistance during high-speed running can be improved. Furthermore, by using the rubber composition having the specific composition to form a tread in which the ratio of the circumferential groove area and the lateral groove area to the ground contact area is within a specific range to produce a tire, It has been found that rolling resistance can be improved and steering stability can also be improved. The present invention has been completed based on these findings.

The first aspect of the present invention is
[1] A rubber component containing 50% by mass or more of isoprene rubber, 10% by mass or more of SBR rubber, and 10% by mass or more of BR rubber, and 60 parts by mass or more of silica per 100 parts by mass of the rubber component and a mercapto-based coupling agent, and having a tan δ at 20°C of 0.1 or more and 0.4 or less measured under conditions of an initial strain of 2%, a dynamic strain of 1%, and a frequency of 10 Hz. A tread made of the composition, the tread having circumferential grooves extending continuously in the tire circumferential direction and lateral grooves extending in the width direction, the ratio of the circumferential groove area to the contact area of the tread being 9. % or more and 16% or less, and a lateral groove area ratio of 8% or more and 14% or less (Claim 1).

[2] In the tire tread rubber composition of [1], the SBR rubber contains SBR having a styrene content of 20 mol% or more and 45 mol% or less and a vinyl content of 20 mol% or more and 60 mol% or less. A tire tread rubber composition characterized by:

[3] Among the tire tread rubber composition of [1] or [2], the content of the mercapto-based coupling agent is 4% by mass or more and 20% by mass or less with respect to the content of the silica. A rubber composition for a tire tread is preferred, which is characterized by:

[4] Among the tire tread rubber compositions of [1] to [3] above, a tire tread rubber composition in which the silica contains silica having a BET of 180 or more is preferable.

[5] Among the tire tread rubber compositions of [1] to [4], a tire tread rubber composition containing 80 parts by mass or less of the silica with respect to 100 parts by mass of the rubber component is preferable.

[6] Among the tires of [1] to [5] above , the tread has a central region defined by two circumferential grooves positioned furthest outward in the tire width direction among the circumferential grooves, and and two side regions located outside the central region in the tire width direction, and the ratio of the lateral groove area to the tread contact area in the two side regions is the ratio of the lateral groove area to the tread contact area in the central region. Tires characterized by greater than percentages are preferred.

[ 7 ] In the tire of [ 6 ], the central region and the side regions have lateral grooves (lug grooves) with a groove width of 4 mm or more, and do the lateral grooves communicate with the adjacent circumferential grooves? Alternatively, a tire characterized by communicating with the circumferential groove in a state where a part of the groove bottom is raised is preferable.

[ 8 ] Among the tires of [ 6 ] or [ 7 ], preferred is a tire characterized in that lug grooves are provided in lateral regions and the lug grooves do not communicate with circumferential grooves.

[ 9 ] Among the tires of the above [ 6 ] to [ 8 ], the central region and/or the side regions are a plurality of widthwise regions that are open to the circumferential grooves and do not communicate with other adjacent circumferential grooves. Tires characterized by having striations are preferred.

[ 10 ] Among the tires of [6] to [ 9 ], a tire characterized by having two circumferential grooves is preferable.

The present invention provides a rubber composition for a tire tread that has excellent wear resistance, low rolling resistance during high-speed running, and excellent steering stability during high-speed running.
Further, by using the rubber composition for a tire tread and forming a tread with the predetermined tread pattern, the tire has excellent wear resistance, low rolling resistance during high-speed running, and steering stability during high-speed running. also provides excellent tires.

1 is a partial development view showing a tread pattern of a tire of an example. FIG. 1 is a partial development view showing a tread pattern of a tire of an example. FIG. 1 is a partial development view showing a tread pattern of a tire of an example. FIG. 1 is a partial development view showing a tread pattern of a tire of an example. FIG. 1 is a partial development view showing a tread pattern of a tire of an example. FIG.

1. Rubber composition for tire tread of the present invention A first aspect of the present invention is a rubber component containing 50% by mass or more of isoprene rubber, 10% by mass or more of SBR rubber, and 10% by mass or more of BR rubber, and the rubber component. 60 parts by mass or more of silica and a mercapto-based coupling agent with respect to 100 parts by mass of the initial strain 2%, dynamic strain (dynamic strain amplitude) 1%, frequency 10 Hz, 20 ° C. The tire tread rubber composition is characterized by having a tan δ of 0.1 or more and 0.4 or less.

In the rubber composition of the present invention, isoprene-based rubber is the main component, and SBR-based rubber, which is more polar than isoprene-based rubber, and BR-based rubber, which is less polar than isoprene-based rubber, are blended in a specific range of composition. By using isoprene-based rubber as a main component (50% by mass or more), excellent abrasion resistance can be obtained, and rolling resistance can also be improved.
Furthermore, a highly reactive mercapto-based coupling agent is blended. Silica is inherently difficult to disperse in isoprene-based rubber, but it was found that by blending a mercapto-based coupling agent, even if a large amount of silica is blended, it can be uniformly dispersed. By blending a rubber component with a composition within a specific range, a large amount of silica, and a mercapto-based coupling agent, tan δ at 20°C can be made smaller than before. It is possible to improve the rolling resistance when running at low speed), and by adopting a predetermined tread pattern, it is also possible to improve steering stability.

(1) Rubber Component The rubber component constituting the rubber composition for a tire tread of the present invention is characterized by including a rubber component including isoprene-based rubber, SBR-based rubber, and BR-based rubber as an essential component.

(Isoprene rubber)
The isoprene-based rubber includes synthetic rubber and natural rubber obtained by polymerizing isoprene. Natural rubber is almost pure polyisoprene with cis-1,4 bonds, but synthetic rubber obtained by polymerizing isoprene is also high cis-1,4 polyisoprene rubber containing 90% or more of cis-1,4 bonds. is preferred.
The molecular weight of the isoprene-based rubber is preferably 500,000 or more, more preferably 1,000,000 or more, in terms of Mw measured by GPC and calculated by standard polystyrene conversion. Moreover, 2 million or less are preferable and 1,500,000 or less are more preferable.

The isoprene-based rubber is contained in the rubber component in an amount of 50% by mass or more, preferably 60% by mass or more. By setting the content ratio of the isoprene rubber to 50% by mass or more, the Tg of the rubber composition is reduced, the tan δ at around 20°C is lowered, heat generation during tire running can be suppressed, and rolling resistance is reduced. can do. In addition, isoprene rubber, particularly natural rubber (NR), has a high molecular weight, and thus can improve wear resistance. Furthermore, steering stability during high-speed running can also be improved. If the content ratio of the isoprene-based rubber is 60% by mass or more, rolling resistance can be further reduced, and wear resistance and steering stability during high-speed running can be further improved.

(SBR rubber)
The SBR rubber means a copolymer of styrene and butadiene (styrene-butadiene rubber, SBR), a modified SBR, or the like. SBR is not particularly limited, and solution polymerization SBR (S-SBR), emulsion polymerization SBR (E-SBR) and the like can be mentioned. Furthermore, modified SBR obtained by modifying the terminal and/or the main chain of the above S-SBR or E-SBR, such as modified SBR coupled with tin, a silicon compound or the like, can also be used. Among them, S-SBR is preferable. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) and the like can also be used. These SBRs may be used alone or in combination of two or more.

In order to obtain good tire grip performance, the styrene content of SBR is preferably 10 mass % or more, more preferably 15 mol % or more, and even more preferably 20 mol % or more. On the other hand, if the styrene content is too high, the change in performance with respect to temperature changes becomes large, and stable grip performance during running may not be obtained satisfactorily. 50 mol % or less is more preferable, and 45 mol % or less is even more preferable.

The vinyl bond content (vinyl content) of SBR is preferably 10 mol% or more in mol% measured by infrared absorption spectrometry from the viewpoint of ensuring reactivity with silica, rubber strength and abrasion resistance. 15 mol % or more is more preferable, and 20 mol % or more is even more preferable. In order to prevent an increase in temperature dependence, obtain good grip performance, durability, and wear resistance, it is preferably 70 mol % or less, more preferably 65 mol % or less, and even more preferably 60 mol % or less.

The weight average molecular weight of SBR is preferably 200,000 or more, more preferably 300,000 or more, more preferably 500,000 or more, in terms of Mw measured by GPC and calculated by standard polystyrene conversion in order to obtain good wear resistance and grip performance. is particularly preferred. Also, it is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less.

The SBR-based rubber is contained in the rubber component in an amount of 10% by mass or more. By setting the content ratio of the SBR rubber to 10% by mass or more, the glass transition point (Tg) of the rubber composition can be increased, and braking performance on dry road surfaces and steering stability can be improved. If the content of the SBR rubber is less than 10% by mass, good grip performance on wet road surfaces cannot be obtained.
On the other hand, the content ratio of the SBR-based rubber in the rubber component is 40% by mass or less, preferably 30% by mass or less. If the content ratio of the SBR rubber increases, the content ratio of the isoprene rubber decreases, and it becomes impossible to sufficiently achieve reduction in rolling resistance, improvement in wear resistance performance, and improvement in steering stability during high-speed running.

(BR-Based Rubber) Butadiene Rubber The BR-based rubber means butadiene rubber (BR), which is a polymer of butadiene. BR is not particularly limited, and for example, low-cis BR having a cis-1,4 bond content of less than 50%, high-cis BR having a cis-1,4 bond content of 90% or more, rare earth element-based catalysts and SPB-containing BR containing syndiotactic polybutadiene crystals, which are commonly used in the manufacture of tires.
Furthermore, modified BR (high-cis modified BR, low-cis modified BR) can also be used. This modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and the terminal of the modified BR molecule is bound by a tin-carbon bond ( tin-modified BR), butadiene rubber having a condensed alkoxysilane compound at the active terminal of butadiene rubber (modified BR for silica), and the like.

In order to obtain good wear resistance and grip performance, etc., the standard polystyrene conversion weight average molecular weight Mw of BR measured by GPC is preferably 300,000 or more, more preferably 400,000 or more, and even more preferably 450,000 or more. Moreover, Mw is preferably 2,000,000 or less, more preferably 1,000,000 or less.

The content ratio of BR in the rubber component is 10% by mass or more. If the content is less than 10% by mass, the wear resistance tends to be insufficient. Further, the content ratio of BR in the rubber component is 40% by mass or less, but when the content ratio of BR is increased, the content ratio of isoprene rubber and SBR rubber decreases. If the content ratio of isoprene rubber decreases, it becomes impossible to sufficiently achieve reduction in rolling resistance, improvement in wear resistance performance, and improvement in steering stability during high-speed running. The content ratio of BR in the rubber component is preferably 20% by mass or less because good grip performance on wet road surfaces cannot be obtained.

(2) Silica Silica is a filler compounded to improve fuel efficiency (reduction of rolling resistance) and wear resistance. It is possible to improve wear resistance, reduce rolling resistance, and improve braking performance on wet road surfaces without impairing performance.
Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like, which are commonly used in the manufacture of tires. From the viewpoint of properties and elongation at break, wet silica and dry silica are preferable, and wet silica is particularly preferably used.
As such silica, commercial products such as "Nipsil AQ" and "Nipsil KQ" manufactured by Tosoh Silica Co., Ltd., and "Ultrasil VN3" manufactured by Degussa can be used. Also, one type of silica may be used alone, or two or more types may be used in combination.

Silica preferably has a BET specific surface area of 80 m ² /g or more, more preferably 180 m ² /g or more, as measured by the BET method according to ASTM D3037-93.
Since fine particles of silica increase the specific surface area, the bonding between the mercapto-based coupling agent and silica increases, resulting in a stronger network in the rubber composition and improved abrasion resistance. In particular, fine particle silica having a BET specific surface area of 180 m ² /g or more is preferable because it has a large effect of improving abrasion resistance.
Silica preferably has a BET specific surface area of 300 m ² /g or less, more preferably 250 m ² /g or less. By setting the BET specific surface area within the above range, both the effect of improving wear resistance and the dispersibility in the rubber composition can be achieved.

The content of silica in the rubber composition is 60 parts by mass or more with respect to 100 parts by mass of the rubber component. Silica is inherently difficult to disperse in isoprene-based rubber, but by blending a mercapto-based coupling agent, it can be uniformly dispersed even when blended in an amount of 60 parts by mass or more.
By setting the silica content to 60 parts by mass or more, sufficient effects of reducing rolling resistance and improving wear resistance can be obtained, and good grip performance on wet road surfaces can be obtained.
On the other hand, the content of silica is preferably 80 parts by mass or less with respect to 100 parts by mass of the rubber component. If the silica content exceeds 80 parts by mass, the dispersion of silica in the rubber becomes insufficient, which tends to reduce fuel efficiency and wear resistance, and may increase the viscosity of the rubber and make processing difficult. .

(3) Mercapto-based coupling agent A mercapto-based coupling agent means a silane coupling agent having a mercapto group. By using a mercapto-based coupling agent together with the rubber component and silica, kneading at a higher temperature becomes possible and silica dispersion can be improved. And, as mentioned above, it is possible to incorporate a large amount of silica into the rubber composition. As a result, tan δ can be lowered, that is, rolling resistance can be reduced, and wear resistance can be improved.

Mercapto-based coupling agents include, for example, a compound represented by the following formula (1) and a compound containing a bonding unit represented by the following formula (2).

(Wherein, R1 to R3 may be the same or different, and are linear or branched alkyl groups having 1 to 12 carbon atoms, linear or branched alkoxy groups having 1 to 12 carbon atoms, or - O—(R11—O)z—R12 (z represents an integer of 1 to 30. The z R11 may be the same or different, and may be linear or branched and have 1 to 30 carbon atoms. R12 represents a linear or branched alkyl group having 1 to 30 carbon atoms, a linear or branched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group having 7 to 30 carbon atoms.) represents a group represented by R4 represents a linear or branched alkylene group having 1 to 6 carbon atoms.)

(Wherein, y is an integer of 1 or more. R5 is a hydrogen atom, a halogen atom, a linear or branched C 1-30 alkyl group, a linear or branched C 2-30 alkenyl , a linear or branched alkynyl group having 2 to 30 carbon atoms, or a group in which the terminal hydrogen atom of the alkyl group is substituted with a hydroxyl group or a carboxyl group, where R6 represents the number of carbon atoms in the linear or branched chain. represents an alkylene group of 1 to 30, a linear or branched alkenylene group having 2 to 30 carbon atoms, or a linear or branched alkynylene group having 2 to 30 carbon atoms, where R5 and R6 form a ring structure; You may.)

Examples of the compound represented by the above formula (1) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-mercaptopropyl Mention may be made of dimethoxymethylsilane.
Commercially available products such as NXT-Z30, NXT-Z45, and NXT-Z60 manufactured by Momentive can be used as the compound containing the bonding unit represented by the above formula (2).
One of the mercapto-based coupling agents may be used alone, or two or more may be used in combination.

Mercapto-based coupling agents include, in addition to the mercapto-based coupling agents described above, protected mercapto-based coupling agents in which the mercapto group is blocked with a protecting group.
When a coupling agent in which the mercapto group is not blocked is used, depending on the conditions of use, the high reactivity of the mercapto group causes the formation of a gel when the rubber composition is kneaded, resulting in a high rubber composition. It tends to become viscous and tends to deteriorate the tire fabric, and its processability has sometimes been a problem.

By using a protected mercapto-based coupling agent, the highly reactive mercapto group is blocked (protected), which suppresses the formation of gel, preventing the viscosity of the rubber composition from increasing and the deterioration of the tire fabric. It is possible to improve workability.
As the protected mercapto-based coupling agent, commercially available products such as NXTsilane manufactured by Momentive can be used. Alternatively, a rubber composition containing an unprotected mercapto coupling agent may be added with an agent that reacts with the mercapto group to protect the mercapto group to obtain a protected mercapto coupling agent. Examples of the agent that reacts with the mercapto group include agents commercially available as processing aids and vulcanization accelerators, such as Rhenogran TP-50 manufactured by Rhein Chemie.

The content (mass) of the mercapto-based coupling agent in the rubber composition is preferably 4% by mass or more, more preferably 6% by mass or more, and even more preferably 8% by mass or more relative to the content of silica. By setting the content of silica to 4% by mass or more, the effect of reducing rolling resistance can be obtained, and the dispersibility of silica in rubber can be improved.
On the other hand, the content (mass) of the mercapto-based coupling agent is preferably 20% by mass or less, more preferably 15% by mass or less, relative to silica in order to prevent deterioration of rubber strength and abrasion resistance.

(4) Other components contained in the tread rubber composition of the present invention For example, reinforcing fillers such as carbon black, vulcanizing agents such as sulfur, various vulcanization accelerators, processing aids, oils, waxes, various anti-aging agents, softening agents, zinc oxide, stearic acid, etc. are appropriately blended. be able to. Moreover, a thermoplastic resin other than the rubber component can be further contained.

(Reinforcing filler)
As the carbon black, GPF, FEF, HAF, ISAF, SAF, and the like, which are generally used in the production of tires can be used, and these can be used alone or in combination of two or more. good.
Carbon black is preferably contained in an amount of 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. The content of carbon black with respect to 100 parts by mass of the rubber component is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less.

Other fillers include aluminum hydroxide, clay, alumina, talc, mica, kaolin, glass balloons, glass beads, calcium carbonate, magnesium carbonate, magnesium hydroxide, calcium carbonate, magnesium oxide, titanium oxide, potassium titanate, Those conventionally used in rubber compositions for treads, such as barium sulfate, can be mentioned.

(Vulcanizing agent, vulcanization accelerator)
Examples of the vulcanizing agent include sulfur, sulfur chloride, sulfur dichloride, morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide, selenium dimethyldithiocarbamate, etc. Among them, sulfur is preferred. Examples of vulcanization accelerators include compounds such as dithiocarbamates, thiurams, thiazoles, and thioureas.

(Thermoplastic resin)
Examples of the thermoplastic resin include styrene-based resins, coumarone-indene resins, C5-C9-based resins, dicyclopentadiene-based resins, rosin-based resins, alkylphenol-based resins, terpene-phenol-based resins, and the like. The C5-9 resin means a C5-9 synthetic petroleum resin.
Among the above thermoplastic resins, styrene resins, coumarone-indene resins, and C9 resins are preferred. In particular, the tire tread rubber composition contains one or more thermoplastic resins selected from the group consisting of styrene resins, coumarone-indene resins and C9 resins, and has an initial strain of 2%, a dynamic strain of 1%, A rubber composition for a tire tread is preferable in which the difference between tan δ at −20° C. and tan δ at 20° C. measured at a frequency of 10 Hz is 0.1 or more and 0.3 or less. By containing the thermoplastic resin, tan δ at low temperatures can be improved, so that the braking performance of the tire at low temperatures can be improved.

(Other ingredients)
Oils that can be contained in the rubber composition include, for example, petroleum softeners such as aromatic oil, paraffin oil, spindle oil, naphthenic oil, MES, TDAE, and SRAE, palm oil, castor oil, cottonseed oil, and soybean oil. and other vegetable softeners.

(5) Tan δ of the tire tread rubber composition of the present invention
The tire tread rubber composition of the present invention is characterized in that tan δ at 20°C measured under conditions of initial strain of 2%, dynamic strain of 1% and frequency of 10 Hz is 0.1 or more and 0.4 or less.
By forming a rubber composition having the composition described above using the materials described above, tan δ at 20°C can be in the range of 0.1 or more and 0.4 or less. By forming the tread from a rubber composition having a 20°C tan δ within the above range, it is possible to reduce the rolling resistance of the tire, especially when running at a high speed of about 120 km/h. Excellent braking performance on the road surface can be achieved.

(6) Method for producing tread rubber composition The tread rubber composition of the present invention can be produced using a known method. For example, using a rubber kneading device such as an open roll, a Banbury mixer, a kneader, or an internal kneader, the components other than the vulcanizing agent and the vulcanization accelerator are kneaded (kneading step 1), and then A vulcanizing agent and a vulcanization accelerator are added and further kneaded (kneading step 2) to obtain an unvulcanized tread rubber composition, which is then vulcanized (vulcanizing step).
As a specific example, in kneading step 1, after kneading for 1 to 10 minutes at a discharge temperature of 150 to 160 ° C., in kneading step 2, a vulcanizing agent and a vulcanization accelerator are added using an open roll or the like. The tread rubber composition of the present invention can be produced by kneading and vulcanizing at 150 to 170° C. for 10 to 35 minutes after kneading step 2.

2. The tire of the present invention The second aspect of the present invention is
A tread composed of the first tire tread rubber composition of the present invention,
The tread has circumferential grooves extending continuously in the tire circumferential direction and lateral grooves extending in the width direction, the ratio of the circumferential groove area to the ground contact area being 9% or more and 16% or less, and the ratio of the lateral groove area to the ground contact area. is 8% or more and 14% or less.

Owing to the above-described characteristics, this tire exhibits excellent wear resistance and the like, as well as low rolling resistance, particularly during high-speed running, and excellent steering stability during high-speed running.

The tire is characterized by having both circumferential grooves and lateral grooves. By having circumferential grooves, characteristics such as high maneuverability and straight running stability, low rolling resistance, good drainage, and resistance to skidding can be obtained. By having grooves, characteristics such as excellent driving force and braking force and high traction force on unpaved roads can be obtained.

The tread pattern of this tire is characterized in that the ratio of the circumferential groove area to the contact area is 16% or less and the ratio of the lateral groove area is 14% or less. That is, it is a tread pattern in which the ratio of the groove area to the contact area is small, especially the ratio of the area of the lateral grooves is small, and this pattern increases the rigidity of the tire.
On the other hand, this tire is characterized by being composed of the tire tread rubber composition, and the tire tread rubber composition is a composition that exhibits excellent wear resistance and flexibility during high-speed running. .
It is believed that high rigidity due to the tread pattern and flexibility due to the rubber composition improve rolling resistance while exhibiting high steering stability during high-speed running.

In the tread pattern of this tire, the ratio of the circumferential groove area to the contact area is 9% or more, and the ratio of the lateral groove area is 8% or more. By setting the ratio of the groove area to the above lower limit or more, it is possible to secure good braking performance (grip performance) and drainage performance, especially braking performance and cornering performance on wet road surfaces.
The ground contact area is the total area of the tire that comes into contact with the road surface when it is mounted on the applicable rim and filled with the specified internal pressure and rolled with a load corresponding to the maximum load capacity. It means the area of the outer peripheral surface over the circumference.

(1) Preferred Embodiment of the Tire of the Present Invention Among the tires of the present invention, the tread has a central region ( Region A in FIG. 1) and two side regions (region B in FIG. 1) located outside the central region in the tire width direction, and the ground contact area of the tread in the two side regions A tire is preferred, characterized in that the ratio of the lateral groove area is greater than the ratio of the lateral groove area to the contact area of the tread in said central region.
That is, the tire has a tread in which the proportion of the portion other than the lateral grooves (central land portion) in the central region is greater than the proportion of the portion other than the lateral grooves (lateral groove land portion) in the side regions. Since the rigidity of the central region particularly contributes to the improvement of steering stability, while keeping the area ratio of the lateral grooves in the entire tire within a predetermined range, the ratio of the land portions (parts other than the lateral grooves) in the central region is increased. By increasing the rigidity of , steering stability can be further improved without deteriorating drainage and braking performance.

Among the tires of the present invention, a tire characterized by having lateral grooves (lug grooves) with a groove width of 4 mm or more in the central region and the side regions is preferable.
The lateral grooves include lug grooves with a groove width (indicating the opening width to the tread contact surface; hereinafter the same) of 4 mm or more and width direction fine grooves of less than 4 mm. Examples of the narrow grooves in the width direction include sipes with a groove width of 1.5 mm or less and notch grooves with a groove width of 1.5 to 3.5 mm.
In order to ensure good braking performance (grip performance) and drainage performance, it is desired that the side regions have lug grooves, but in order to achieve the above effects, the central region should also have lug grooves. is preferred.

Among the tires described above, a tire characterized in that lug grooves are provided in lateral regions and the lug grooves do not communicate with circumferential grooves are preferable. Since the lug grooves provided in the side regions do not communicate with the circumferential grooves, the rigidity of the land portion of the tread can be further ensured while providing the lug grooves.

Among the tires described above, a tire characterized by having a plurality of narrow grooves in the width direction that are open to the circumferential grooves and do not communicate with other adjacent circumferential grooves is preferable. By providing the widthwise fine grooves, the rigidity of the tread can be ensured, and the water film removing effect of each fine groove can improve damp braking performance.

Although the number of circumferential grooves is not particularly limited, two circumferential grooves are preferable from the viewpoint of improving cornering power.

(2) Tread Pattern Hereinafter, examples of the tread pattern of the tire of the present invention will be described with reference to the drawings. 1 to 5 are partial development views showing examples (embodiments) of the tread pattern of the tire of the present invention, that is, diagrams schematically showing the pattern of a part of the tread of the tire in the circumferential direction.

(Tread pattern in Fig. 1)
1a, 1b, and 1c represent circumferential grooves, and in the example of this figure, three circumferential grooves are provided. A region defined by two circumferential grooves 1a and 1b located on the outermost side in the tire width direction of the three circumferential grooves (region represented by A in FIG. 1) is a central region. The two regions B located on the outside in the tire width direction of the regions are the side regions. 2a represents a lug groove and 3 represents a sipe. Also, 4 is a central land portion and 5 is a side land portion.
In the example of FIG. 1, the central region A is provided with a sipe 3 (thin groove in the width direction), and the side region B is provided with a sipe 3 (thin groove in the width direction) and a lug groove 2a having a groove width of 4 mm or more. It is As is clear from the figure, the ratio of the lateral groove area in the side regions B is much larger than the ratio of the lateral groove area in the central region A. FIG. The lug groove 2a in the lateral region B does not communicate with the circumferential grooves 1a and 1b. The sipe 3 in the central region A opens in one of the circumferential grooves 1a and 1b and does not communicate with the other circumferential grooves. The sipes 3 in the lateral region B do not communicate with the circumferential grooves 1a, 1b.

(Tread pattern in Fig. 2)
The lug grooves 2b provided in the lateral regions communicate with the circumferential grooves 1a or 1b (unlike the lug grooves 2a of FIG. 1). Others are the same as the tread pattern of FIG.

(Tread pattern in Fig. 3)
The lug grooves 2c provided in the lateral regions communicate with the circumferential grooves 1a or 1b (unlike the lug grooves 2a of FIG. 1). However, unlike the lug groove 2b of FIG. 2, the groove width decreases from the outside in the tire width direction toward the center in the tire width direction. When the lug grooves provided in the lateral regions communicate with the circumferential grooves, the width of the grooves is reduced from the outside in the tire width direction toward the center in the tire width direction, thereby providing the lug grooves while maintaining the land of the tread. The rigidity of the part can be secured more. The tread pattern of FIG. 3 is the same as the tread pattern of FIG. 1, except as noted above.

(Tread pattern in Fig. 4)
In this pattern, the central region A is provided with a lug groove 2d that opens into the circumferential groove 1a or 1b and does not communicate with the other circumferential grooves. Also, the sipe 3 in the central region A opens into the central circumferential groove 1c and does not communicate with the circumferential grooves 1a or 1b. The tread pattern is the same as the tread pattern of FIG. 1 except for the above points.

(Tread pattern in Fig. 5)
This pattern has two circumferential grooves 1a and 1b. The tread pattern is the same as that of FIG. 1 except that the central circumferential groove 1c is not provided.

(3) Manufacturing method of the tire of the present invention The tire of the present invention can be manufactured by a conventional method using the rubber composition for tread. That is, an unvulcanized rubber composition obtained by blending the above-mentioned other components with the above-mentioned rubber component is extruded according to the shape of a tread with a predetermined pattern, and is placed on a tire building machine. , tire members other than the tread portion; inner, ply, breaker, band, bead, sidewall, etc. are adhered together and molded by a normal method to form an unvulcanized tire (green tire). Thereafter, the unvulcanized tire can be produced by heating and pressurizing it in a vulcanizer to vulcanize it.
Tire members other than the tread; materials such as inner, ply, breaker, band, bead, and sidewall are the same as those of conventional tires and can be obtained by the same method.

(4) Uses of the Tire of the Present Invention The tire of the present invention has a tread with a predetermined pattern composed of the rubber composition for a tread, and is a tire for passenger cars, a high-performance tire for passenger cars, a tire for two-wheeled vehicles, and the like. It can be used for tires in general, and is particularly suitable for use as a tire for light passenger vehicles.

EXAMPLES Hereinafter, aspects of the present invention will be described in more detail based on examples, but the present invention is not limited only to these examples.

1. Raw Materials Used in Examples and Comparative Examples Various raw materials used in Examples and Comparative Examples are listed below. Some raw materials are indicated by abbreviations in Tables 1 and 2, and the abbreviations are shown in parentheses after each raw material name.

・Natural rubber (NR): TSR20
・SBR1:
Modified SBR produced in Production Example 1 below (styrene content: 30% by mass, vinyl content: 52% by mass, Mw: 250,000, Tg: -23°C)
SBR2: SPRINTAN SLR6430 (S-SBR manufactured by TRINSEO, styrene content: 40% by mass, vinyl bond content: 18 mol%, Mw: 1,460,000, Tg: -39°C, oil content: 37.0% per 100 parts by weight of rubber component Oil extended product containing 5 parts by weight)
・Butyl rubber (BR): butadiene rubber (BR150B) manufactured by Ube Industries, Ltd.
Carbon black (CB): Show Black N220 (N ₂ SA: 111 m ² /g) manufactured by Cabot Japan Co., Ltd.
Silica: Ultrasil VN3 (N ₂ SA: 172 m ² /g) manufactured by Evonik Degusa
・Mercapto-based coupling agent: NXT-Z45 manufactured by Momentive
- Protected mercapto-based coupling agent: NXTsilane manufactured by Momentive
・Processing aid: Zinc dithiophosphate (manufactured by Rhein Chemie)
・WAX: Ozoace 0355 (paraffin type) manufactured by Nippon Seiro Co., Ltd.
Anti-aging agent 1: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Anti-aging agent 2: Anti-aging agent RD (quinoline-based anti-aging agent): Nocrack 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
・Stearic acid: Bead stearic acid Tsubaki manufactured by NOF Corporation
・Zinc oxide: zinc oxide No. 1 manufactured by Mitsui Kinzoku Mining Co., Ltd.
・ Oil: Diana process oil AH-24 (aroma process oil) manufactured by Idemitsu Kosan Co., Ltd.
・ Sulfur: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd.
- Vulcanization accelerator 1: Noxeler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide (CBS)) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
・ Vulcanization accelerator 2: Noxceler D (N,N'-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

(Production example 1)
A nitrogen purged autoclave reactor was charged with cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene. After adjusting the temperature of the contents of the reactor to 20° C., n-butyllithium was added to initiate the polymerization. Polymerization was carried out under adiabatic conditions, and the maximum temperature reached 85°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and after further polymerizing for 5 minutes, N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier. reacted. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol was added. Then, the solvent was removed by steam stripping and dried with a hot roll adjusted to 110° C. to obtain SBR1.

2. Manufacture of Tire Chemicals other than sulfur and vulcanization accelerators were compounded according to the compositions shown in Tables 1 and 2, and kneaded at about 150° C. for 5 minutes using a Banbury mixer. After that, sulfur and a vulcanization accelerator were added to the resulting kneaded product according to the compositions shown in Tables 1 and 2, and kneaded at about 80 ° C. for 5 minutes with a twin-screw open roll to obtain an unvulcanized rubber composition (compound example) was obtained.
The unvulcanized rubber composition thus obtained is molded into the tread shape (represented in FIGS. 1 to 5) shown in Tables 1 to 4 by strip winding, and is laminated with other tire members. did After that, the mixture was vulcanized for 35 minutes at 150° C. and 25 kgf to produce studless tires for trucks and buses (tire size: 11R22.5), which were used in the following tests.

3. Evaluation content, evaluation method [tan δ at 20 ° C., rolling resistance]
A strip-shaped test piece having a width of 4 mm, a length of 20 mm, and a thickness of 2 mm was punched out from the tread portion of the produced tire and subjected to the test. Using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd., the tan δ of the strip-shaped test piece was measured at an initial strain of 2%, a dynamic strain amplitude of 1%, a frequency of 10 Hz, and 20°C. column. The value of the reciprocal of tan δ is indexed with Comparative Example 1 as 100 (fuel economy index=rolling resistance index), and is shown in the "rolling resistance" column of Tables 1-4. The larger the value of the rolling resistance index, the smaller the rolling resistance and the better the fuel efficiency.
(Rolling resistance index) = [(tan δ of Comparative Example 1)/(tan δ of each formulation)] × 100

[Abrasion resistance performance]
The test tires were mounted on a 660 cc domestically produced FF vehicle, and the actual vehicle was run on a dry asphalt test course. Measure the groove depth of the tire tread after running 10,000 km, calculate the running distance when the tire groove depth is reduced by 1 mm, and display it as an index (wear resistance index) according to the following formula. 4 "Abrasion resistance performance" column. The larger the index, the better the wear resistance.
(Abrasion resistance index) = [(running distance of each formulation) / (running distance of Comparative Example 1)] × 100

[High-speed steering stability]
The handling characteristics of each test tire were evaluated in an actual vehicle test on a dry road surface, based on the feeling of going straight, changing lanes, and accelerating and decelerating when the test driver was driving at 120 km/H. Taking the handling characteristics of the control tire (Sample 1: Comparative Example) as 100, and indexing according to the following criteria, the average value in the above three cases was calculated, and the index value is shown in Tables 1 to 4 as "high-speed steering stability ” column. A larger index value indicates better handling characteristics and superior high-speed steering stability.

(Standard for handling characteristics)
120: The level was as good as never seen before 110: The test driver judged that the performance was clearly improved 105: The test driver felt that it was somewhat good 100: Standard

4. Experimental Results The results of the experiments are shown in Tables 1-4.

As is clear from the results in Tables 1 to 4, a rubber component containing 50% by mass or more of isoprene rubber, 10% by mass or more of SBR rubber, and 10% by mass or more of BR rubber, and 100 parts by mass of the rubber component 60 parts by mass or more of silica and a mercapto-based coupling agent, and the tan δ at 20 ° C. measured under the conditions of 2% initial strain, 1% dynamic strain, and a frequency of 10 Hz is 0.1 or more and 0 The tires of Examples in which the tread was formed from the rubber composition for tire treads having a value of .4 or less exhibited better performance than Comparative Example 1 in terms of rolling resistance, wear resistance, and high-speed steering stability. has been achieved. As is clear from Table 3, this result is the same for any of the tread patterns shown in FIGS.

On the other hand, Comparative Example 1, which uses a rubber composition containing less than 50 parts by mass of isoprene rubber (NR), is inferior to any of the Examples in terms of rolling resistance, wear resistance, and high-speed steering stability. In Comparative Example 2, in which the content of SBR rubber is less than 10% by mass in the rubber component, the high-speed steering stability is inferior to the standard (index of 100), and the content of BR rubber is 10 mass% in the rubber component. %, the rolling resistance is inferior to the standard (index of 100) (rolling resistance is large), the silica content is less than 60 parts by mass with respect to 100 parts by mass of the rubber component, and the temperature is 20 ° C. In Comparative Example 4, in which tan δ is less than 0.1, the high-speed steering stability is inferior to the standard (index 100), and in Comparative Example 5, which does not contain a mercapto-based coupling agent, the wear resistance performance is lower than the standard (index 100). and high-speed steering stability are inferior, and the object of the present invention is not achieved.

From the results of the above examples and comparative examples, in order to achieve the object of the present invention, the content of isoprene rubber, SBR rubber and BR rubber in the rubber component should be 50% by mass or more and 10% by mass, respectively. % by mass or more and 10% by mass or more, the content of silica needs to be 60 parts by mass or more per 100 parts by mass of the rubber component, and a mercapto-based coupling agent is included. shown to be necessary.

Among the comparative examples, Comparative Example 6 in which the ratio of the circumferential groove area to the tread contact area is less than 9%, Comparative Example 7 in which the ratio of the circumferential groove area to the tread contact area is greater than 16%, and the tread contact area In Comparative Example 8 , in which the ratio of the lateral groove area to the tread contact area is less than 8%, and in Comparative Example 9 , in which the ratio of the lateral groove area to the contact area of the tread is greater than 14% or less, rubber compositions having the same formulation as these are formed, Compared to Examples 4 and 12, in which the ratio of the circumferential groove area to the ground contact area of the tread is within the range of 9% or more and 16% or less, and the ratio of the lateral groove area is within the range of 8% or more and 14% or less, the high speed Poor steering stability. These results show that the ratio of the circumferential groove area to the contact area of the tread is preferably in the range of 9% or more and 16% or less, and the ratio of the lateral groove area is preferably in the range of 8% or more and 14% or less. .

Further, Example 4 in which the ratio of the lateral groove area to the tread contact area in the side regions is larger than the ratio of the lateral groove area to the tread contact area in the central region is compared with Example 12 in which it is smaller. As a result, Example 12 is inferior to Example 4 in high-speed steering stability, although the formulation and tread pattern are the same. This result indicates that the ratio of the lateral groove area to the tread contact area in the lateral regions should preferably be greater than the ratio of the lateral groove area to the tread contact area in the central region.

1a, 1b, 1c circumferential grooves 2a, 2b, 2c, 2d lug grooves (lateral grooves)
3 Sipe 4 Central land portion 5 Lateral land portion A Central region B Lateral region

Claims (10)

A rubber component containing 50% by mass or more of isoprene rubber, 10% by mass or more of SBR rubber, and 10% by mass or more of BR rubber, 60 parts by mass or more of silica per 100 parts by mass of the rubber component, and mercapto and a tire tread rubber composition having a tan δ at 20°C of 0.1 or more and 0.4 or less, measured under conditions of an initial strain of 2%, a dynamic strain of 1%, and a frequency of 10 Hz. The tread has circumferential grooves extending continuously in the tire circumferential direction and lateral grooves extending in the width direction, and the ratio of the circumferential groove area to the contact area of the tread is 9% or more. % or less, and a lateral groove area ratio of 8% or more and 14% or less. The tire according to claim 1, wherein the SBR rubber contains SBR having a styrene content of 20 mol% or more and 45 mol% or less and a vinyl content of 20 mol% or more and 60 mol% or less. 3. The tire according to claim 1, wherein the content of the mercapto-based coupling agent is 4% by mass or more and 20% by mass or less with respect to the content of the silica. The tire according to any one of claims 1 to 3, wherein the silica contains silica having a BET of 180 or more. 5. The tire according to any one of claims 1 to 4, comprising 80 parts by mass or less of said silica with respect to 100 parts by mass of said rubber component. The tread has a central region defined by two circumferential grooves positioned on the outermost side in the tire width direction of the circumferential grooves, and two side regions positioned on the outer side of the central region in the tire width direction. and wherein the ratio of the lateral groove area to the tread contact area in the two lateral regions is larger than the ratio of the lateral groove area to the tread contact area in the central region . A tire according to any one of the above . The central region and the side regions have lateral grooves with a groove width of 4 mm or more, and the lateral grooves do not communicate with the adjacent circumferential grooves, or the groove bottoms are partly raised to form the circumferential grooves. 7. Tire according to claim 6 , characterized in that it communicates with the directional grooves. 8. Tire according to claim 6 or 7 , characterized in that lug grooves are provided in the lateral regions, said lug grooves not communicating with the circumferential grooves. 8. The central region and/or the side regions have a plurality of widthwise fine grooves that open to the circumferential grooves and do not communicate with other adjacent circumferential grooves. A tire according to any one of the above. A tire according to any one of claims 6 to 9 , characterized in that there are two circumferential grooves.

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