JPH1149892A - Tread rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tread rubber composition exhibiting excellent low electrical resistance and bleed resistance, and useful for tires of high fuel economy, by compounding a rubber component with a specified proportion of silica coated with a specific amount of an electroconductive material. SOLUTION: This tread rubber composition is obtained by compounding (A) 100 pts.wt. of a rubber component predominant in diene-based rubber with (B) 20-80 pts.wt. of silica coated with 2-50 pts.wt., based on 100 pts.wt. of the silica, of an electroconductive material [pref. a compound of the formula R- O-(CH2 -CH2 -O)n -H (R is H or a hydrocarbon group; (n) is >=1), e.g. a compound of the formula]. Tires using this tread rubber composition have the following advantages: the treat surface is hydrophilic, the water on roads or atmospheric moisture is absorbed onto the surface to effect improvement in the electroconductivity of the tire surface, leading to release of static electricity onto the ground and into the atmosphere, preventing automobiles from static electricity buildup, and affording sustainable electroconductive coating film on the silica surface because of good coating film formability of the tire tread.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire tread rubber composition having a low electric resistance and a low bleeding property of a conductive material.

[0002]

2. Description of the Related Art In recent years, low fuel consumption tires having reduced rolling resistance have been developed in response to low fuel consumption of automobiles. In order to reduce hysteresis loss, reinforcement used in tread rubber compositions for tires has been developed. It is common practice to replace part or all of carbon black as a material with silica.

[0003] However, if the amount of carbon black is reduced, the electric resistance of the obtained tire increases and static electricity accumulates in the automobile. For example, radio noise is generated or a spark is generated at a gas station to ignite. There is such a problem.

Accordingly, for example, International Publication No. 95/318
No. 88 pamphlet (1995) or JP-A-9-11
No. 1039 discloses a technique of blending a conductive material that is a nonionic surfactant having an oxyethylene unit in order to impart conductivity to a silica-containing rubber composition.

[0005] However, in the prior art, a rubber composition is obtained by simultaneously kneading a conductive material and other components such as a rubber component and silica, and the dispersibility of the conductive material is reduced. Not only is it low, but the electrical resistance cannot be reduced sufficiently unless the compounding amount is increased, and the bleeding of the conductive material is likely to occur due to the low solubility of the conductive material in the rubber component. There is.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a tread rubber composition having a low electric resistance (high electric conductivity) and a low bleeding property of a conductive material. .

[0007]

SUMMARY OF THE INVENTION The present invention provides a silica 100
A tread rubber composition comprising 20 to 80 parts by weight of a coated silica obtained by coating 2 to 50 parts by weight of a conductive material with respect to 100 parts by weight of a rubber component mainly composed of a diene rubber. About.

The conductive material has the formula (I): R—O—
The compound is preferably a compound having an oxyethylene unit represented by (CH ₂ —CH ₂ —O) _n —H (wherein, R is a hydrogen atom or a hydrocarbon group, and n is an integer of 1 or more).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The most important feature of the present invention is that silica to be blended in a rubber composition is previously coated with a conductive material. That is, in the present invention, coated silica having a conductive coating is blended with a rubber component mainly composed of a diene rubber. Thereby, the dispersibility of the conductive material in the obtained tread rubber composition is improved, and as a result, a tread rubber composition having low electric resistance and low bleeding property of the conductive material can be obtained.

In the present invention, it is necessary to disperse the conductive material constituting the coating on the silica surface almost uniformly with the silica in the obtained rubber composition. Therefore, the coating must be hardly separated from the silica surface at least when the coated silica and the rubber component are mixed and kneaded.

It is preferable that the coating is formed by uniformly covering the entire surface of the silica. However, depending on the type of conductive material forming the coating, a part of the silica surface can be substantially uniformly formed, and the effect of the present invention can be improved. Should be covered within a range that does not impair.

The conductive material that can be used in the present invention may be any of a liquid and a paste, as long as it can form a conductive film on the surface of silica. Any material may be used as long as it does not decrease the dispersibility of the silica and is not easily separated from silica at least at the time of compounding and kneading with the rubber component.

The tread rubber composition of the present invention has less bleeding of the conductive material even after being formed into a tread.
This is probably because the conductive coating is chemically bonded to, for example, the surface of silica, is supported by affinity on the surface of silica, or is physically supported on the surface of silica.

Examples of such conductive materials include: (1) compounds having an oxyethylene unit in a side chain, a main chain and / or a terminal; etc .; In the field, it is usually used as a nonionic surfactant, and those having a relatively high carbon number are usually used in the field of rubber compositions for tires as antistatic agents and conductive plasticizers. Further, these are supported on the surface of silica by affinity to form a film.

(2) Metal salts such as lithium perchlorate; these are commonly used in the field of rubber compositions for tires in combination with the above-mentioned (1) nonionic surfactant, antistatic agent or conductive plasticizer. used.

(3) Conductive polymers such as polyacetylene, poly-p-phenylene, polyphenylene sulfide, and polypyrrole; these are physically supported on the surface of silica to form a coating.

(4) An electron accepting molecule such as iodine or arsenic pentafluoride or an electron donating substance such as sodium metal is added to a main chain conjugated polymer such as polyacetylene, poly-p-phenylene, polyphenylene sulfide or polypyrrole. Doped conductive polymers such as those obtained by doping; these are physically supported on the surface of silica to form a coating.

Further, among the conductive materials (1) to (4), (1) because of high affinity with silica.
The conductive material of the formula (I): RO
— (CH ₂ —CH ₂ —O) _n —H ( _where R is a hydrogen atom,
Alternatively, a compound having an oxyethylene unit represented by a hydrocarbon group and n is an integer of 1 or more is preferably used. In this compound, since the ether bond portion of the compound having an oxyethylene unit is hydrophilic, the surface of the obtained tire tread becomes hydrophilic, and the hydrophilic surface absorbs water on the road and moisture in the atmosphere. As a result, the conductivity is increased and the conductivity is obtained by discharging the static electricity to the ground or the atmosphere, thereby preventing the static electricity from being accumulated in the automobile. Further, this compound has a good film-forming property, and a hydroxyl group present on the silica surface and a hydrophilic portion of the conductive material are combined to form a persistent conductive film. The compound having an oxyethylene unit has an oxyethylene unit on the side chain, main chain and / or terminal.

The range of n in the formula (I) may be an integer of 1 or more, but if it is too small, the effect of reducing the electric resistance is small, and if it is too large, the compatibility with the rubber component and the reinforcing property are reduced. Therefore, it is preferable that 2 ≦ n ≦ 16, and furthermore, it is preferable that 3 ≦ n ≦ 14 from the viewpoint of the balance between the electrical resistance reduction effect, the compatibility with the rubber component, and the reinforcing property.

In the formula (I), R is a hydrogen atom or a hydrocarbon group. The hydrocarbon group is not particularly limited as long as the effects of the present invention are not impaired, and examples thereof include an alkyl group and an aryl group. These hydrocarbon groups may be substituted and may be linear or branched. When the hydrocarbon group is substituted, it may be substituted with an oxyethylene unit from the viewpoint of an electric resistance reduction effect and an improvement in compatibility with a rubber component (in this case, a compound having an oxyethylene unit may be substituted). Also includes those having an oxyethylene unit in the side chain).

Among the compounds having an oxyethylene unit represented by the above formula (I), specific examples of the compound having an oxyethylene unit in the main chain include, for example, monoethylene glycol, diethylene glycol, triethylene glycol,

[0022]

Embedded image

(Rikemar A- manufactured by Riken Vitamin Co., Ltd.)
23, n = 8), C 12 H 25 O (CH 2 CH 2 O) 5 H ( manufactured by Riken Vitamin Co., Ltd. Rikemal B-205, n = 5)
Examples of the compound having an oxyethylene unit in the side chain include Sumiade 300G (n = 10) manufactured by Sumitomo Chemical Co., Ltd.

Next, the silica coated with the conductive material in the present invention may be any silica that has been conventionally used in the field of tires, but has a specific surface area from the viewpoint of reinforcement, handling and mixing. 150-300
Those having an m ² / g and an apparent specific gravity of 120 to 300 g / l are preferred.

Next, the method of coating the silica with the conductive material is not particularly limited, and may be appropriately selected depending on the type and properties of the conductive material. For example, a method of obtaining a coated silica by dripping the conductive material while stirring the silica in a stirring tank, and drying or spraying or spraying the conductive material while stirring the silica in the stirring tank. To obtain coated silica.

In the above-mentioned coated silica, silica 1
The weight ratio of the conductive material (coating) to 00 parts by weight is 2 to 50 parts by weight from the viewpoint that the effect of improving the conductivity is small when the amount is too small, and blooming occurs when the amount is too large. The amount is preferably 5 to 25 parts by weight from the viewpoint of preventing blooming.

The rubber component in the present invention mainly comprises a diene rubber. As such a diene rubber, any rubber may be used as long as it is conventionally used in the field of tires.
For example, natural rubber (NR), isoprene rubber (IR),
Examples thereof include styrene butadiene rubber (SBR), butadiene rubber (BR), halogenated butyl rubber (X-IIR), and butyl rubber (IIR), and these may be used alone or in any combination.

The rubber component other than the diene rubber constituting the rubber component in the present invention is a rubber component which is usually used in combination with a diene rubber in the field of tires and does not impair the effects of the present invention. I just need. The compounding ratio may be within a range that does not impair the effects of the present invention.

The tread rubber composition of the present invention is obtained by kneading the rubber component and the coated silica by a conventional method. In this case, the kneading ratio of the coated silica to the rubber component is 20 to 80 parts by weight with respect to 100 parts by weight of the rubber component from the viewpoint of achieving both reinforcement and low fuel consumption. Considering the balance, it is preferably 30 to 70 parts by weight.

Further, the tread rubber composition of the present invention comprises:
Carbon black may be blended within a range that does not impair the effects of the present invention. As such carbon black, any carbon black conventionally used in the field of tires may be used,
Preferably, those having a high reinforcing property such as SAF, ISAF, and HAF are desirable.

When carbon black is compounded, the kneading ratio to the rubber component may be within a range that does not impair the effects of the present invention.

The tread rubber composition of the present invention comprises:
Compounding agents usually used in the field of tires, for example, vulcanizing agents such as ions, vulcanization accelerators such as Nt-butyl-2-benzothiazolylsulfenamide (NS), zinc white (ZnO) and stearin Vulcanization aids such as acids, coupling agents, process oils, waxes, anti-aging agents, etc.
You may mix | blend as needed within the range which does not impair the effect of this invention.

Using the tread rubber composition of the present invention, a tread for a tire and a tire having the tread can be produced by an ordinary method.

[0034]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Production Examples 1-4 (Production of coated silica) Ultrasil VN3 manufactured by Degussa Co., Ltd. was used as silica A.
(Specific surface area: 210 m ² / g, apparent specific gravity: 220 g / g
Liter), using triethylene glycol manufactured by Mitsui Petrochemical Co., Ltd.
Of silica, 100 g of the conductive material A was dropped at a rate of 100 g / min with stirring, and then dried, whereby 100 parts by weight of the silica was coated with 2 parts by weight of the conductive material A. Silica 1 was obtained. Similarly, the amount of the conductive material A dropped was 500 g, 1000 g, and 2500 g, and the coated silica 2, 3 and 3 of the present invention in which the conductive material A was coated at 10, 20, and 50 parts by weight with respect to 100 parts by weight of silica, respectively. I got 4.

Examples 1 to 4 40 parts by weight of natural rubber and 60 parts by weight of SBR were used as the rubber components. The mixture was kneaded using a mixer to obtain a tread rubber composition of the present invention. This rubber composition was cured at 170 ° C. using a vulcanizing press.
Vulcanized tread rubber 1-4 by vulcanizing for 0 minutes
I got

The SBR is Nippon Synthetic Rubber Co., Ltd.
SL574 manufactured by Degussa, Inc .; Si69 (bis (3-triethoxysilylpropyl) tetrasulfen) manufactured by Degussa, Diana Process PS32 manufactured by Idemitsu Kosan Co., Ltd. as process oil, and Ouchi as wax. Sunnock wax manufactured by Shinko Chemical Industry Co., Ltd., and Ozonone 6 manufactured by Seiko Chemical Co., Ltd.
C, stearic acid as tung, manufactured by Nippon Oil & Fats Co., Ltd .; zinc flower, Ginrei R, manufactured by Toho Zinc Co., Ltd .; sulfur, sulfur manufactured by Tsurumi Chemical Co., Ltd .; vulcanization accelerator, Ouchi Emerging Co., Ltd. Noxeller NS manufactured by Chemical Industry Co., Ltd. was used.

The obtained tread rubbers 1 to 4 or the vulcanized tread rubbers 1 to 4 were evaluated according to the following methods. Table 1 shows the evaluation results.

[Evaluation Method] From the vulcanized tread rubbers 1-4, the length and width were determined to be 15
cm and a test piece with a thickness of 2 mm were prepared.
Using an electric resistance measuring instrument R8340A manufactured by ST Corporation, the volume specific resistance value: log σV (Ωcm) of each test piece was measured under the conditions of an applied voltage of 500 V, a temperature of 25 ° C., and a humidity of 50%. The smaller the value, the smaller the electrical resistance value of the obtained rubber composition and the higher the performance.

Viscoelasticity A test piece prepared in the same manner as in the case of the measurement of the volume resistivity was measured using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho under the conditions of a frequency of 10 Hz and a dynamic strain of 2.0%. Below, the loss factor (tan δ) at 70 ° C. was measured. The reciprocal of the obtained value was indicated by an index, with the value of Comparative Example 1 (containing no conductive material) described later being 100 as a reference. The larger the index, the lower the tan δ and the better the performance.

Abrasion Resistance A test piece prepared in the same manner as in the case of the measurement of the volume specific resistance value was subjected to a surface rotation speed of 50 m / min and a load by using a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. The amount of wear was evaluated under the conditions of 1.5 kg, slip rates of 30% and 50%, and falling sand of 15 g / min. Take the average of the values at the two slip rates, and take the average
The results are shown in an index with Comparative Example 1 (containing no conductive material) to be described later being 100 as a reference. The larger the index, the better the wear resistance.

Tire electric resistance Using the unvulcanized tire tread rubber compositions 1 to 4,
Make a tread and paste it on a tire cover.
A tire having a size of 195 / 65R15 was produced under the conditions and method of vulcanizing at 70 ° C. and 20 kgf for 10 minutes. With respect to the obtained tire, the electric resistance of the tire was measured according to the method for measuring the electric resistance of the tire under a load specified in Wdk flat3. FIG. 1 is a schematic explanatory view for explaining a method for measuring the electric resistance of a tire. As shown in FIG. 1, a tire 1 having a rim assembled to a standard rim 4 and having an air pressure of 20 kpa is installed on a steel plate 3 which is attached to a base plate 2 in an insulated state.
The resistance value between the central part of the rim and the steel plate 3 on which the tire 1 is grounded is determined by using a resistance measuring device 5 to apply an applied voltage of 500 V, a temperature of 25 ° C., and a humidity of 50%.
It measured on condition of.

Bleed resistance: From the vulcanized tire tread rubbers 1-4, a width of 10c
Specimens having a length of 10 cm, a length of 10 cm and a thickness of 2 mm were prepared and exposed to a sunny place without rain for 30 days. 30
A, 30 indicates that no bleed was observed after the passage of days.
B when bleed was observed after elapse of 20 days, C when bleed was observed after 20 days, C when bleed was observed after 10 days, and E when bleed was observed after 1 day. Was evaluated.

Comparative Examples 1 to 5 Comparative rubber compositions 1 to 5 were obtained and evaluated in the same manner as in Example 1 except that the mixing ratio was changed as shown in Table 1. Table 1 shows the results. Comparative Example 1 is an example in which the conductive material A was not blended, and Comparative Examples 2 to 5 are examples in which the conductive material A was simply mixed without being coated with silica.

[0045]

[Table 1]

As shown in Table 1, the tread rubber composition 1 of the present invention (Example 1) obtained by using silica previously coated with a conductive material is obtained by simply mixing the same amount of the conductive material and silica. Compared with the comparative tread rubber composition 2 (Comparative Example 2), the volume specific resistance and the electric resistance of the tire are reduced, and tan δ and bleed resistance are improved. The same can be said from Example 2 and Comparative Example 3, Example 3 and Comparative Example 4, and Example 4 and Comparative Example 5. In Examples 1 to 4, bleed resistance did not decrease due to an increase in the amount of conductive material used, but Comparative Examples 2 to 4 did not decrease.
In No. 5, it can be seen that the bleed resistance is reduced.

Example 5 and Comparative Examples 6 to 7 A tread rubber composition 5 of the present invention and comparative rubber compositions 6 to 7 were obtained in the same manner as in Example 1 except that the mixing ratios shown in Table 2 were used. Evaluation was performed in the same manner as in Example 1. Table 2 shows the results. In addition, N330 manufactured by Tokai Carbon Co., Ltd. was used as carbon black.

[0048]

[Table 2]

From Table 2, it can be seen that the tread rubber composition 5 (Example 5) of the present invention, even if it contains carbon black, is a comparative tread rubber composition 6 obtained by simply mixing a conductive material and silica. Compared with (Comparative Example 6), the volume specific resistance value and the electric resistance value of the tire are lower, and t
An δ and bleed resistance are improved. From Comparative Example 7, it can be seen that tan δ decreases when the volume specific resistance and the electric resistance of the tire are reduced by increasing the amount of carbon black without using a conductive material.

Production Examples 5 to 7 Monoethylene glycol (conductive material B) manufactured by Mitsui Petrochemical Co., Ltd. as a conductive material, and Riquemar A-23 (manufactured by Riken Vitamin Co., Ltd.)

[0051]

Embedded image

N = 8) (Conductive material C), Rikemar B-205 (C ₁₂ H ₂₅ O (CH ₂ ) manufactured by Riken Vitamin Co., Ltd.
CH ₂ O) ₅ H, n = 5) (Conductive material D), except that 10 parts by weight of conductive materials B to D were used for 100 parts by weight of silica A in the same manner as in Production Example 1. The coated silicas 5 to 7 of the present invention having a coating of

Examples 6 to 8 and Comparative Examples 8 to 10 The tread rubber compositions 6 to 8 and the comparative tread rubber compositions 8 to 8 of the present invention were prepared in the same manner as in Example 1 except that the mixing ratios shown in Table 3 were used. A rating of 10 and an evaluation were made. Table 3 shows the results. Table 3 shows Example 2 for comparison.
The results for the rubber composition obtained in Comparative Example 3 are also described.

[0054]

[Table 3]

According to Table 3, the conductive material B was used as the conductive material.
The tread rubber composition 6 (Example 6) of the present invention obtained by using (monoethylene glycol) and silica previously coating the conductive material has the same conductive material B
In comparison with Comparative Tread Rubber Composition 8 (Comparative Example 8) obtained by simply mixing silica and silica, the volume resistivity and the electrical resistance of the tire are reduced, and tan δ and bleed resistance are improved. Example 2 and Comparative Example 3 using conductive material A (triethylene glycol) as the conductive material, Example 7 and Comparative Example 9 using conductive material C (polyoxyethylene alkylphenyl ether) as the conductive material Example 8 and Comparative Example 1 using conductive material D (polyoxyethylene alkyl ether) as the conductive material
The same applies to the case of 0. That is, it is understood that the excellent effects of the present invention can be obtained even if the type of the conductive material is changed.

Production Examples 8 and 9 Nipsil VN3 manufactured by Nippon Silica Co., Ltd. (specific surface area: 170 to 220 m ² / g, apparent specific gravity: 120) was used as silica.
(Silica B) or Nipsil AQ manufactured by Nippon Silica Co., Ltd. (specific surface area: 170 to 220 m).
² / g, apparent specific gravity: 240 to 280 g / liter)
Except for using (silica C), coated silicas 8 and 9 of the present invention having a coating composed of 10% by weight of conductive material A with respect to silica B or C were obtained in the same manner as in Production Example 1.

Examples 9 to 10 and Comparative Examples 11 to 12 Tread rubber compositions 9 and 10 and comparative tread rubber compositions 11 and 11 of the present invention were prepared in the same manner as in Example 1 except that the mixing ratios shown in Table 4 were used. 12 and evaluation was performed. Table 4 shows the results. Table 4 also shows the results of the rubber compositions obtained in Example 2 and Comparative Example 3 for comparison.

[0058]

[Table 4]

As shown in Table 4, the tread rubber composition 9 of the present invention (Example 9) obtained by using silica B as the silica for coating the conductive material in advance is obtained by simply mixing the conductive material and the same silica B. Compared with the obtained comparative tread rubber composition 11 (Comparative Example 11), the volume specific resistance value and the electric resistance value of the tire are reduced, and tan δ and bleed resistance are improved. The same applies to Example 2 and Comparative Example 3 and between Example 10 and Comparative Example 12. That is, it can be seen that the excellent effects of the present invention can be obtained even if the type of silica is changed.

[0060]

According to the present invention, it is possible to obtain a tread rubber composition having low electric resistance, excellent bleed resistance, and suitable for a fuel-efficient tire.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view for explaining a method for measuring an electric resistance of a tire.

[Explanation of symbols]

 Reference Signs List 1 tire 2 base plate 3 steel plate 4 rim 5 resistance measuring instrument

Claims (2)

[Claims] 1. A coated silica obtained by coating 2 to 50 parts by weight of a conductive material with respect to 100 parts by weight of silica.
Parts by weight of a rubber component 100 containing a diene rubber as a main component
A tread rubber composition formulated in parts by weight. 2. The method according to claim 1, wherein the conductive material has the formula (I): R—O—
_{(CH 2 -CH 2 -O) n} -H ( wherein, R represents a hydrogen atom or a hydrocarbon radical, n is an integer of 1 or more) tread rubber according to claim 1, wherein the compound having oxyethylene units represented by Composition.