JPWO2020121788A1 - Rubber composition, rubber composition for tread, and pneumatic tires - Google Patents

Abstract

Provided are a pneumatic tire having excellent steering stability and wet grip performance, and a rubber composition for obtaining the tire and a rubber composition for tread. The rubber composition contains a rubber component, silica, and a water-soluble inorganic filler having a whisker structure, and the mass ratio of the silica content (a) to the content (b) of the water-soluble inorganic filler. [(A) / (b)] is 2.5 to 40.

Description

The present invention relates to rubber compositions, tread rubber compositions, and pneumatic tires.

Conventionally, from the viewpoint of improving vehicle safety, various studies have been conducted in order to improve the braking performance, drivability, etc. of tires not only on dry road surfaces but also on various road surfaces such as wet road surfaces and icy and snowy road surfaces. It has been done.
For example, natural rubber and / or diene-based synthetics are used for the purpose of providing a rubber composition having excellent wet grip performance while maintaining electrical conductivity and low heat generation without deteriorating workability and abrasion resistance. 20 to 100 parts by weight of carbon black on which silica is immobilized and an average particle size of 0.1 to 10 μm and a BET specific surface area of 20 m ² / g or more as a reinforcing filler with respect to 100 parts by weight of rubber. It is disclosed that 5 to 30 parts by weight of aluminum is blended (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2000-281833

However, the rubber composition described in Patent Document 1 has insufficient wet grip performance.
An object of the present invention is to provide a pneumatic tire having excellent steering stability and wet grip performance, and a rubber composition for obtaining the tire and a rubber composition for tread, and it is an object of the present invention to solve the object. do.

<1> A mass ratio of the content (a) of the silica to the content (b) of the water-soluble inorganic filler containing a rubber component, silica, and a water-soluble inorganic filler having a whisker structure [(( A) / (b)] is a rubber composition of 2.5 to 40.

<2> The rubber composition according to <1>, wherein the mass ratio [(a) / (b)] is 2.5 to 15.
<3> The rubber composition according to <1> or <2>, wherein the water-soluble inorganic filler is basic magnesium sulfate.
<4> The water-soluble inorganic filler is any one of <1> to <3> having a whisker structure having an average fiber diameter of 0.1 to 1.0 μm and an average fiber length of 6 to 100 μm. The rubber composition according to.
<5> The water-soluble inorganic _{filler, MgSO 4 · 5Mg (OH)} 2 · nH 2 O (n = 0~3 integer) and (integer _{n = 0~8) MgSO 4 · 5MgO} · nH 2 O The rubber composition according to any one of <1> to <4>, which comprises at least one selected from the group consisting of.
<6> The rubber composition according to any one of <1> to <5>, wherein the total amount of the silica and the water-soluble inorganic filler is 65 to 100 parts by mass with respect to 100 parts by mass of the rubber component. It is a thing.

<7> A rubber composition for tread containing the rubber composition according to any one of <1> to <6>.
<8> A pneumatic tire using the rubber composition according to any one of <1> to <6>.

According to the present invention, it is possible to provide a pneumatic tire having excellent steering stability and wet grip performance, and a rubber composition for obtaining the tire and a rubber composition for tread.

<Rubber composition>
The rubber composition of the present invention contains a rubber component, silica, and a water-soluble inorganic filler having a whisker structure, and the content (a) of the silica relative to the content (b) of the water-soluble inorganic filler. The mass ratio [(a) / (b)] of is 2.5 to 40.
Hereinafter, the "water-soluble inorganic filler having a whisker structure" may be simply referred to as a "water-soluble inorganic filler".
Conventionally, vulcanized rubber obtained by vulcanizing a rubber composition by adding a large amount of filler to the rubber composition or making the network structure of the rubber component dense by giving priority to the steering stability of the tire. Sometimes the elastic modulus was increased. However, when the elastic modulus of the tire increases, the ground contact property of the tire deteriorates, and braking performance such as wet grip performance may deteriorate, and steering stability and wet grip performance are in a trade-off relationship. ..

On the other hand, a pneumatic tire using the rubber composition of the present invention (hereinafter, may be simply referred to as "tire") can achieve both excellent steering stability and wet grip performance.
This is presumed to be due to the following reasons.
The rubber composition of the present invention contains a predetermined amount of silica and a water-soluble inorganic filler having a Whisker structure as a filler.
The whisker structure refers to a fibrous crystal structure grown in a needle-like or whisker-like shape. By including the water-soluble inorganic filler having a whisker structure in the rubber composition together with the rubber component, the formation of a network between the rubber component and the water-soluble inorganic filler is developed as compared with the case where only the particulate filler is contained. It is considered easy. Further, it is considered that the inorganic filler is water-soluble, and when it is used in combination with silica, a network of the water-soluble inorganic filler and silica is formed. Therefore, it is considered that even if the content of the water-soluble inorganic filler in the rubber composition is small, the elastic modulus of the vulcanized rubber can be easily improved and the steering stability of the tire can be improved.
Furthermore, since the rubber composition contains a water-soluble inorganic filler, the tire surface obtained from the rubber composition also becomes more compatible with water and the ground contact property is improved, so that it is considered that the wet grip performance is improved. .. Further, even if the tire is worn away due to wear, the water-soluble inorganic filler contained in the tire is newly exposed on the tire surface, so that the wet grip performance is considered to be permanent.
From the above, it is considered that the tire using the rubber composition of the present invention is excellent in steering stability and wet grip performance.
Hereinafter, the details of the rubber composition of the present invention will be described.

[Rubber component]
The rubber component used in the rubber composition of the present invention is not particularly limited, and in addition to natural rubber (NR), polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), and the like. Synthetic rubbers such as ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), butyl halide rubber, and acrylonilittle-butadiene rubber (NBR) can be used. These rubber components may be used alone or in combination of two or more.
Of these, natural rubber, polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), and polybutadiene rubber (BR) are preferable, and natural rubber (NR) and styrene-butadiene copolymer rubber (SBR) are more preferable. Preferably, styrene-butadiene copolymer rubber (SBR) is even more preferred.

〔filler〕
The rubber composition of the present invention contains silica and a water-soluble inorganic filler having a whisker structure as a filler, and the mass of the silica content (a) with respect to the content (b) of the water-soluble inorganic filler. The ratio [(a) / (b)] is 2.5 to 40.
By using a water-soluble inorganic filler having a whisker structure and silica in the above amount range, the interaction between the two can be sufficiently obtained, the elastic modulus of the vulcanized rubber can be increased, and the steering stability of the tire can be improved. Can be done.
The rubber composition of the present invention may further contain another filler such as carbon black as the filler.

(silica)
The silica is not particularly limited, and can be used depending on the application, such as general grade silica and special silica surface-treated with a silane coupling agent or the like. As the silica, for example, wet silica is preferably used.
Silica is usually in the form of particles and is distinguished from a water-soluble inorganic filler having a whisker structure.
The content of silica in the rubber composition is preferably 30 to 120 parts by mass with respect to 100 parts by mass of the rubber component from the viewpoint of improving the elastic modulus of the tire and improving the steering stability. It is more preferably 120 parts by mass, and even more preferably 40 to 95 parts by mass.

(Water-soluble inorganic filler with whisker structure)
As described above, the water-soluble inorganic filler having a whisker structure means a water-soluble inorganic filler having a fibrous crystal structure grown in a needle-like or whisker-like shape, and specifically, the average fiber diameter is A structure having an average fiber length of 6 to 100 μm and 0.1 to 1.0 μm.
The water-soluble inorganic filler means an inorganic filler having a solubility in water of 0.01 g / L or more at 20 ° C.
The water-soluble inorganic filler preferably has an average fiber diameter of 0.5 to 1.0 μm and an average fiber length of 10 to 10 from the viewpoint of maintaining the whisker structure and enhancing network formation in the rubber composition. It is preferably 50 μm, more preferably 13 to 30 μm. The average aspect ratio (average fiber length [μm] / average fiber diameter [μm]) of the water-soluble inorganic filler is preferably 10 to 100, and more preferably 15 to 60.

Examples of the water-soluble inorganic compound that can constitute the water-soluble inorganic filler include alkali metal salts; beryllium, magnesium sulfate, and the like. Examples of the alkali metal salt include alkali metal chlorides, carbonates, hydrogen carbonates, sulfates, phosphates, borates, silicates, and the like. For example, sodium as an alkali metal is specified. Examples thereof include sodium sulfate, sodium chloride, sodium carbonate, sodium hydrogencarbonate, sodium tripolyphosphate, sodium pyrophosphate, sodium silicate and the like.
Among the above water-soluble inorganic compounds, the compound having a whisker structure can be the water-soluble inorganic filler having a whisker structure in the present invention. Among them, magnesium sulfate tends to have a whisker structure. As the water-soluble inorganic filler having a whisker structure, basic magnesium sulfate is preferable, and more specifically, ASTM No. The following expressive formulas described in 7-415 can be mentioned.
MgSO ₄ · _{5Mg (OH)} (an integer _{n = 0~3) 2 · nH 2} O.
Alternatively, those represented by the following demonstrative formulas can be mentioned.
_{MgSO 4 · 5MgO · nH 2 O} (n = 0~8 integer).
Basic magnesium sulfate has a hydroxyl group on the surface of the water-soluble inorganic filler and has a high interaction with silica, so that it is easy to form a network and increase the elastic modulus of the crosslinked rubber.

The water-soluble inorganic filler having a whisker structure may have a functional group capable of reacting with a rubber component. Since the water-soluble inorganic filler is modified with a compound having a functional group capable of reacting with the rubber component, the water-soluble inorganic filler and the rubber component form a chemical bond, and the abrasion resistance of the crosslinked rubber is formed. Can be improved.
Examples of the functional group capable of reacting with the rubber component include a group having a sulfur atom, and a group having a disulfide bond (—S—S—) is preferable.
Examples of the compound having a functional group capable of reacting with the rubber component include α-lipoic acid (thioctic acid), dithiodiglycolic acid, 3,3'-dithiodipropionic acid, 4,4'-dithiodibutyric acid and the like. Be done.

The content of the water-soluble inorganic filler having a whisker structure in the rubber composition is 0.5 to 30 with respect to 100 parts by mass of the rubber component from the viewpoint of improving steering stability and wet grip performance. It is preferably parts by mass, more preferably 1 to 25 parts by mass, further preferably 3 to 23 parts by mass, and even more preferably 5 to 20 parts by mass.

The mass ratio [(a) / (b)] of the silica content (a) to the content (b) of the water-soluble inorganic filler is 2.5 to 40, preferably 2.5 to 15. , 3.0 to 15, more preferably. It is considered that when the mass ratio is in the above range, the network of silica and the water-soluble inorganic filler is likely to develop, the elastic modulus is improved, the steering stability is improved, and the wet grip performance is improved.

(Carbon black)
The carbon black is not particularly limited and can be appropriately selected depending on the intended purpose. The carbon black is preferably, for example, FEF, SRF, HAF, ISAF, SAF grade, and more preferably HAF, ISAF, SAF grade.
The content of carbon black in the rubber composition is preferably 1 to 60 parts by mass and 5 to 50 parts by mass with respect to 100 parts by mass of the rubber component from the viewpoint of improving the elastic modulus of the vulcanized rubber. More preferably.

The total amount of silica in the rubber composition of the present invention and the water-soluble inorganic filler having a whisker structure is determined from the viewpoint of improving steering stability and wet grip performance by developing a network of silica and water-soluble inorganic filler. It is preferably 65 to 100 parts by mass, and more preferably 75 to 95 parts by mass with respect to 100 parts by mass of the component.
As described above, the rubber composition of the present invention contains a water-soluble inorganic filler excellent in forming a network between fillers and also contains silica, so that the elastic modulus of the crosslinked rubber is small even if the amount of the filler is small. It can be increased to 100 parts by mass or less with respect to 100 parts by mass of the rubber component. Further, by setting the amount to 65 parts by mass or more with respect to 100 parts by mass of the rubber component, the steering stability can be further improved and the wet grip performance can be further improved.

[Vulcanizing agent]
The rubber composition of the present invention preferably contains a vulcanizing agent.
The vulcanizing agent is not particularly limited, and sulfur is usually used, and examples thereof include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur.
In the rubber composition of the present invention, the content of the vulcanizing agent is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component. When this content is 0.1 part by mass or more, vulcanization can be sufficiently proceeded, and when it is 10 parts by mass or less, the aging resistance of the vulcanized rubber can be suppressed.
The content of the vulcanizing agent in the rubber composition is more preferably 0.5 to 7 parts by mass and further preferably 0.7 to 4 parts by mass with respect to 100 parts by mass of the rubber component.

In addition to the above components, the rubber composition of the present invention contains, if necessary, a compounding agent commonly used in the rubber industry, such as a softening agent (aromatic oil, etc.), stearic acid, an antiaging agent, and zinc oxide. (Zinc oxide), a vulcanization accelerator, etc. may be appropriately selected and contained within a range that does not impair the object of the present invention.

The rubber composition is produced by blending each component including a rubber component, silica, and a water-soluble inorganic filler having a whisker structure, and kneading them using a kneader such as a Banbury mixer, a roll, or an internal mixer. be able to.
The kneading of each component may be carried out in all one step, or may be carried out in two or more steps. When the kneading is divided into two or more stages, the components that are difficult to contribute to vulcanization or promotion of vulcanization of the rubber component, for example, rubber component, softener, filler, silane coupling agent, by the stage before the final stage. , Stearing agent, anti-aging agent and the like are kneaded, and at the final stage, the rubber component is vulcanized, and the component that promotes vulcanization is further blended and kneaded. The vulcanization of the rubber component or the kneading of the component that does not easily contribute to the promotion of vulcanization may be further divided into two or more steps.
Above all, from the viewpoint of maintaining the whisker structure of the water-soluble inorganic filler, it is preferable that the kneading is divided into two or more stages and the water-soluble inorganic filler is blended in the final stage.
When kneading in two stages, the maximum temperature in the first stage of kneading is preferably 140 to 160 ° C, and the maximum temperature in the second stage is preferably 90 to 120 ° C.

<Rubber composition for tread>
The rubber composition for tread of the present invention includes the above-mentioned rubber composition of the present invention.
A tire formed by vulcanizing the rubber composition of the present invention into a tire shape is excellent in steering stability and wet grip performance. Therefore, the rubber composition of the present invention is used for producing tread rubber for tires. Is excellent. Therefore, the rubber composition of the present invention is preferably a rubber composition for tread.

<Pneumatic tires>
The pneumatic tire of the present invention is made by using the rubber composition of the present invention.
A tire tread may be manufactured using the rubber composition for tread of the present invention, and a tire including the tire tread may be manufactured.
Since the tire of the present invention uses the rubber composition of the present invention having the above-described configuration, it is excellent in both steering stability and wet grip performance.
The tire may be obtained by vulcanizing after molding using an unvulcanized rubber composition, depending on the type and member of the tire to be applied, or the unvulcanized rubber composition is once subjected to a preliminary vulcanization step or the like. A semi-vulcanized rubber may be obtained from a product, molded using the rubber, and then further vulcanized.
For example, the rubber composition of the present invention containing various components is processed into a tire tread at an unvulcanized stage, and is pasted and molded on a tire molding machine by a usual method to form a raw tire. The raw tire is heated and pressurized in a vulcanizer to obtain a tire.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for the purpose of exemplifying the present invention and do not limit the present invention in any way.

<Preparation of rubber composition and preparation of tires>
According to the formulations shown in Tables 1 and 2, each component was blended and kneaded in two steps to obtain rubber compositions of Examples and Comparative Examples. Each of the obtained rubber compositions was vulcanized, and the steering stability and wet grip performance were evaluated. The evaluation results are shown in Table 2.

<Evaluation>
(1) Steering stability The storage elastic modulus (E') of the vulcanized rubber was measured using a spectrometer manufactured by Ueshima Seisakusho Co., Ltd. under the conditions of a temperature of 30 ° C., an initial strain of 2%, a dynamic strain of 1%, and a frequency of 52 Hz. The storage elastic modulus (E') of Comparative Example 3 was set to 100 and displayed exponentially.
The larger the index, the better the steering stability of the tire obtained from the vulcanized rubber.

(2) Wet grip performance (braking performance on wet road surface)
The wet skid resistance of the vulcanized rubber on a wet road surface was evaluated according to ASTM E303 using BPST (British Portable Skid Assessment Tester). The measured value of Comparative Example 3 was set as 100 and displayed as an index. The larger the index value, the better the wet skid resistance of the tire obtained from the vulcanized rubber.

The details of the components in Table 1 are as follows.
SBR: Solution-polymerized styrene-butadiene copolymer rubber manufactured by JSR Corporation, trade name "SL552"
Aromatic oil: Sankyo Yuka Kogyo Co., Ltd., trade name "A / O mix"
Carbon Black: Made by Tokai Carbon Co., Ltd., ISAF-HS, product name "Seast 7HM"
Silica: Made by Tosoh Silica Co., Ltd., Product name "Nipsil AQ"
Silane coupling agent: Evonik's silane coupling agent, trade name "Si75"
Anti-aging agent: Manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., trade name "Nocrack 6C"
Vulcanization accelerator DPG: Manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Sun Cellar D"
Vulcanization accelerator DM: Manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Suncellor DM"
Vulcanization accelerator NS: Manufactured by Sanshin Chemical Industry Co., Ltd., trade name "Sun Cellar NS"

Details of the inorganic fillers in Tables 1 and 2 are as follows.
Water-soluble inorganic filler A1: Ube Material Industries, Ltd., trade name "MOS-HIGE (powdered product)" _{(MgSO 4 · 5Mg (OH)} 2 · 3H 2 O, an average fiber diameter = 0.6 .mu.m, average fiber length = 16 μm, aspect ratio = 27, solubility in water (20 ° C) = 0.046 g / L)
Water-soluble inorganic filler A2: Inorganic filler obtained by modifying the water-soluble inorganic filler A1 with α-lipoic acid (average fiber diameter = 0.6 μm, average fiber length = 16 μm, aspect ratio = 27, solubility in water (20 ° C.)) = 0.046g / L)
Water-soluble inorganic filler A3: Water-soluble inorganic filler A1 is crushed with a ball mill to eliminate the structure (average fiber diameter = 0.6 μm, average fiber length = 5 μm, aspect ratio = 8, solubility in water (20). ° C.) = 0.046 g / L)

Water-soluble inorganic filler B: Ube Material Industries, Ltd., trade name "MOS-HIGE (P powdered product)" _{(MgSO 4 · 5Mg (OH)} 2 · 3H 2 O, an average fiber diameter = 0.6 .mu.m, the average fiber length = 14 μm, aspect ratio = 23, solubility in water (20 ° C.) = 0.046 g / L)
Water-soluble inorganic filler C: manufactured by Umai Chemical Co., Ltd., trade name "magnesium sulfate MN-00" (Then ₄ anhydrous salt, granular filler without whisker structure)
Water-insoluble inorganic filler D: manufactured by Showa Denko KK, trade name "Heidilite H-43M" (including aluminum hydroxide: 99.6%, sodium oxide: 0.40%, etc .; granules having no whisker structure) filler)

The water-soluble inorganic filler A2 (an inorganic filler obtained by modifying the water-soluble inorganic filler A1 with α-lipoic acid) was obtained as follows.
A water-soluble inorganic filler A1 (5.0 g) and α-lipoic acid (1.5 g) were added to toluene, mixed, stirred at 80 ° C., and suction filtered to obtain a solid content. The solid content was dissolved in toluene at 80 ° C. and suction-filtered to obtain a solid content. The purified crystal was used as a water-soluble inorganic filler A2.

The average fiber diameter, average fiber length, and aspect ratio of the water-soluble inorganic fillers A1, A2, A3, and B are obtained from a magnified image obtained by a scanning electron microscope (FE-SEM S-4800, manufactured by Hitachi High-Technologies Co., Ltd.). It can be calculated by measuring the fiber diameter and fiber length of 100 basic magnesium sulfates and obtaining the average value of the number thereof.

As can be seen from Table 2, when the rubber composition of Example is used, steering stability and wet grip performance are compared with the case of using the rubber composition of Comparative Example 3 using basic magnesium sulfate having no whisker structure. It turns out that it is excellent in both.
In Comparative Example 3, in Comparative Example 1 having the same configuration except that it did not contain basic magnesium sulfate, the steering stability was lowered, and in Comparative Example 2 in which 10 parts of silica was added instead of the addition of basic magnesium sulfate, steering was performed. Stability was improved, but wet grip performance was reduced. Further, in Comparative Example 3, in Comparative Example 4 in which an anhydrous salt of magnesium sulfate was used instead of the addition of basic magnesium sulfate, and Comparative Example 5 in which a water-insoluble inorganic filler was used, steering stability or wetness was also obtained. Grip performance has deteriorated.
As in Comparative Example 6, when (a) / (b) is less than 2.5 even if basic magnesium sulfate is contained, the steering stability evaluation is increased, but the wet grip performance evaluation is decreased.

Claims (8)

With rubber components
With silica
Contains a water-soluble inorganic filler having a whisker structure,
A rubber composition in which the mass ratio [(a) / (b)] of the silica content (a) to the content (b) of the water-soluble inorganic filler is 2.5 to 40. The rubber composition according to claim 1, wherein the mass ratio [(a) / (b)] is 2.5 to 15. The rubber composition according to claim 1 or 2, wherein the water-soluble inorganic filler is basic magnesium sulfate. The rubber composition according to any one of claims 1 to 3, wherein the water-soluble inorganic filler has a whisker structure having an average fiber diameter of 0.1 to 1.0 μm and an average fiber length of 6 to 100 μm. thing. The water-soluble inorganic _filler, the group consisting of _{MgSO 4 · 5Mg (OH) 2} · nH 2 O (n = 0~3 integer) and _{MgSO 4 · 5MgO · nH 2 O} (n = 0~8 integer) The rubber composition according to any one of claims 1 to 4, which comprises at least one selected from. The rubber composition according to any one of claims 1 to 5, wherein the total amount of the silica and the water-soluble inorganic filler is 65 to 100 parts by mass with respect to 100 parts by mass of the rubber component. A rubber composition for a tread containing the rubber composition according to any one of claims 1 to 6. A pneumatic tire using the rubber composition according to any one of claims 1 to 6.