JP2006124504A - Rubber composition for tire and pneumatic tire by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire, gentle to the earth, achieving static electricity-preventing performance and improving abrasion resistance, rolling resistance characteristic and wet grip performance in a good balance for preparing the future reduction of the supplying amount of petroleum. <P>SOLUTION: This rubber composition for the tire is provided by containing a rubber component and carbon black and showing >10<SP>8</SP>and ≤10<SP>11</SP>Ω. cm volume resistivity measured by impressing 1,000 V electric voltage within 10-50°C temperature and 15-100 % humidity range, or containing the rubber component and carbon black having ≤30 nm mean particle diameter and ≤0.5 % volatile matter, and showing ≤10<SP>11</SP>Ω. cm volume resistivity measured by impressing 1,000 V electric voltage within 10-50°C temperature and 15-100 % humidity range. The pneumatic tire consisting of each of the rubber compositions for the tire is also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-performance tire rubber composition and a pneumatic tire using the same.

  Carbon black or silica has been mainly used as the filler used in the tire rubber composition. In particular, due to the recent social demand for lower fuel consumption of automobiles, silica is used instead of part or all of carbon black to reduce the rolling resistance of tires.

  However, if the blending amount of the carbon black is reduced to a certain amount or less, the electrical conductivity of the tire is lowered, and there is a problem that static electricity is accumulated in the tire and a vehicle equipped with the tire. The accumulation of static electricity generates static electricity when getting in and out of a car, causing discomfort, obstructing radio wave reception, or causing a fire during refueling.

  In order to solve these problems, high molecular weight polymer antistatic agents having ionic conductivity are used, and further, unsaturated groups such as carbon-carbon double bonds are introduced into the polymer antistatic agents. Thus, a rubber composition that can be fixed during vulcanization has been proposed. In particular, as a polymer imparting ionic conductivity, a polyether copolymer composed of ethylene oxide, propylene oxide, and unsaturated epoxide (more specifically, ethylene oxide-propylene oxide-allyl glycidyl ether copolymer (EO-PO- It has been reported that by adding AGE copolymer)) to the rubber composition, the affinity between the copolymer and silica is increased to form a composite, and the electrical resistance can be reduced by adding a smaller amount. (See Patent Documents 1 and 2).

  However, even with these techniques, the polymer has a very large polarity, and is poorly compatible with styrene butadiene rubber, butadiene rubber, natural rubber, butyl rubber, halogenated butyl rubber, etc., which are generally used in tires. By adding such a polymer, there is a problem that the wear resistance tends to be lowered, there is still room for improvement, and the resistance value at low temperature and low humidity increases. In particular, a problem due to an increase in electrical resistance value in a dry winter season when the air temperature is 10 ° C. or lower is likely to occur.

  From the above, in order to obtain a sufficiently low electric resistance value, a method in which a required amount of carbon black and silica are used in combination is generally used at present. However, in this case, by adding carbon black, tan δ near 70 ° C. is increased, and generally the low fuel consumption characteristics of the vehicle are deteriorated, and the tire wear resistance may be decreased.

By the way, the tires currently on the market are composed of raw materials made up of petroleum resources with more than half of the total weight, but in recent years, environmental issues have come to be emphasized, CO ₂ emission suppression regulations have been strengthened, In addition, since petroleum raw materials are limited and the supply amount is decreasing year by year, the oil price is expected to rise in the future, and there is a limit to the use of raw materials consisting of petroleum resources.

  For this reason, rubber made of non-petroleum resources such as natural rubber is being used for rubber components that account for more than half of the total weight of the tire.

For example, as disclosed in Patent Document 3, it is desired to reduce the ratio of raw materials made of petroleum resources as much as possible because of environmental problems, CO ₂ emission regulations, fear of exhaustion of petroleum resources, and the like.

JP-A-10-147668 JP 2000-239445 A JP 2003-63206 A

  The present invention provides a tire rubber composition capable of producing a tire that suppresses the use of petroleum raw materials as much as possible, achieves antistatic performance, and improves the wear resistance, rolling resistance characteristics, and wet grip performance in a well-balanced manner. The purpose is that.

The first aspect of the present invention includes a rubber component containing epoxidized natural rubber and carbon black, and volume resistance measured by applying a voltage of 1000 V within a temperature range of 10 to 50 ° C. and humidity of 15 to 100%. The rate is 10 ⁸ Ω. greater than cm and 10 ¹¹ Ω. It is related with the rubber composition for tires which is cm or less.

The second aspect of the present invention contains a rubber component and carbon black having an average particle size of 30 nm or less and a volatile content of 0.5% by weight or less, in a temperature range of 10 to 50 ° C. and a humidity of 15 to 100%. The volume resistivity measured by applying a voltage of 1000 V is 10 ¹¹ Ω. It is related with the rubber composition for tires which is cm or less.

  In the second embodiment, the average particle size of the carbon black is preferably 30 nm or less and the volatile content is 0.5% by weight or less.

  The rubber component preferably further contains natural rubber and / or a modified product thereof.

  Furthermore, the rubber composition for tires preferably contains 5 parts by weight or more of calcium carbonate surface-treated with an organic substance with respect to 100 parts by weight of the rubber component.

  The present invention also relates to a pneumatic tire using the tire rubber composition.

  According to the first aspect of the present invention, epoxidized natural rubber is used as a rubber component, and by defining the volume resistivity of the obtained tire rubber composition, the use of petroleum raw materials is suppressed as much as possible, and antistatic performance is achieved. In addition, the wear resistance, rolling resistance characteristics and wet grip performance can be improved in a balanced manner.

  According to the second aspect of the present invention, the antistatic performance is achieved by defining the volume resistivity of the obtained rubber composition for tires using carbon black that defines the average particle size and the volatile content. In addition, the wear resistance, rolling resistance characteristics, and wet grip performance can be improved in a well-balanced manner.

  The rubber composition for tires according to the first aspect of the present invention comprises a rubber component containing epoxidized natural rubber and carbon black.

  Epoxidized natural rubber has a large interaction with silica, and an interaction such as intermolecular force or hydrogen bond is exerted between the epoxy group and the silanol group on the silica surface or the surface functional group of carbon black. Therefore, by using silica and carbon black in combination with epoxidized natural rubber, it is possible to exhibit extremely good vehicle fuel efficiency and tire grip performance. In addition, since it has a polyisoprene structure, excellent wear resistance can be obtained by crystallization of the epoxidized natural rubber by stretching caused by the structure.

  The epoxidized natural rubber may be a commercially available epoxidized natural rubber or an epoxidized natural rubber. Examples of a method for epoxidizing natural rubber include a method of reacting natural rubber with an organic peracid such as peracetic acid or performic acid.

  The epoxidation rate of the epoxidized natural rubber is preferably 5 mol% or more, preferably 10 mol% or more, and more preferably 20 mol% or more. When the epoxidation rate is less than 10 mol%, the modification effect on the epoxidized natural rubber is small, and therefore, it tends to be difficult to obtain good fuel efficiency characteristics and grip performance. The epoxidation rate is preferably 80 mol% or less, more preferably 60 mol% or less, and further preferably 55 mol% or less. If the epoxidation rate exceeds 80 mol%, the polymer component gels or the crosslinking efficiency deteriorates, so that the fuel efficiency and repeated fatigue strength tend to deteriorate. By satisfying the numerical range of the epoxidation rate, both good tire grip performance and vehicle fuel efficiency can be achieved.

  The content of the epoxidized natural rubber in the rubber component is preferably 20% by weight or more, more preferably 30% by weight or more, further preferably 50% by weight or more, and 70% by weight or more. Most preferred. If the content is less than 20% by weight, good grip performance and wear resistance tend to be difficult to obtain. The content of the epoxidized natural rubber can be 100% by weight.

  As rubber components other than epoxidized natural rubber, the compatibility with the low volatile carbon black that can be used in the present invention is particularly excellent, and excellent abrasion resistance and reinforcement by crystallization at the time of stretching of such rubber In view of the grip performance, the rubber is preferably a rubber having a polyisoprene structure in a proportion of 50 mol% or more or a modified product thereof. Such rubber is preferably natural rubber or a modified product thereof (hydrogenated natural rubber, acid-modified natural rubber, etc.) because excellent fuel efficiency and grip performance can be obtained. In addition, the ratio of resources other than petroleum can be increased as much as possible, and environmentally friendly tires can be manufactured.

  The rubber composition for tires according to the first aspect of the present invention preferably contains conductive carbon black as carbon black. Specific examples of conductive carbon black include acetylene black, graphitized carbon, and ketjen black. Among them, good low fuel consumption characteristics can be obtained, and the reason for its high affinity with natural rubber, etc. Therefore, acetylene black or graphitized carbon is preferable.

  As conductive fillers other than conductive carbon black, natural graphite, artificial graphite, metal oxide, metal powder, carbon black for general tires, and the like can be used.

  The average primary particle size of carbon black is preferably as small as possible. However, in view of industrial mass productivity and cost, it is generally about 10 nm or more or 20 nm or more. The average primary particle size of carbon black is preferably 30 nm or less, more preferably 28 nm or less, further preferably 26 nm or less, and particularly preferably 24 nm or less. When the average primary particle diameter exceeds 30 nm, it tends to be difficult to improve the wear resistance and grip performance.

Preferably the nitrogen adsorption specific surface area of the carbon black is 55m ² / g or more, more preferably 80 m ² / g or more, further preferably 95 m ² / g or more. If the nitrogen adsorption specific surface area is less than 55 m ² / g, the average primary particle size generally tends to be too large, and it tends to be difficult to improve wear resistance and grip performance. Further, the nitrogen adsorption specific surface area of carbon black is preferably 900 m ² / g or less, more preferably 800 m ² / g or less, and further preferably 500 m ² / g or less. When the nitrogen adsorption specific surface area exceeds 900 m ² / g, excessive pores are present on the surface, the adhesion between the carbon black surface and the rubber is deteriorated, and the wear resistance tends to be remarkably lowered.

Dibutyl phthalate (DBP) oil absorption of carbon black is preferably at 80 cm ^3/100 g or more, more preferably 95cm ^3/100 g or more, still more preferably 180cm ^3/100 g or more, 200 cm ^3/100 g The above is particularly preferable. In less than 80 cm ^3/100 g DBP oil absorption, low degree of structure of the development, inferior in electrical conductivity and thermal conductivity, they tend not sufficiently low fuel consumption characteristics are obtained with respect to the car. Further, DBP oil absorption of carbon black is preferably 450 cm ^3/100 g or less, more preferably 400 cm ^3/100 g or less, and more preferably not more than 300 cm ^3/100 g. When the DBP oil absorption exceeds 450 cm ^3/100 g, the hardness of the resulting rubber composition is increased significantly, car fuel economy characteristics and wet grip performance of the tire tends to be lowered.

  The pH of carbon black is preferably 6 or more, more preferably 7 or more, further preferably 7.5 or more, and particularly preferably 8.5 or more. When the pH is less than 6, there is a tendency to delay the vulcanization of the compounded rubber, and there is a tendency that acidic functional groups such as -COOH increase on the carbon black surface and the conductivity is lowered. The pH of the carbon black is preferably 12 or less, more preferably 11 or less, and even more preferably 10 or less. When the pH exceeds 12, the compounded rubber tends to be burnt and tends to be difficult to process. Here, the pH means a value measured by the method described in JIS K6221 or the like.

  The volatile content of carbon black is preferably 0.5% by weight or less, more preferably 0.4% by weight or less, further preferably 0.3% by weight or less, and 0.2% by weight or less. Is particularly preferred. If the volatile content exceeds 0.5%, the conductivity will decrease, so the amount of carbon black added to achieve antistatic will tend to increase, and in addition, good fuel efficiency and natural rubber will be good. Tend to be difficult to obtain. By satisfying the range of the upper limit of the volatile matter, it becomes a carbon black that is particularly excellent in conductivity, so that the amount of carbon black required for antistatic is reduced, and a large amount of silica composed of resources other than petroleum can be blended. This makes it possible to consider the environment and improve the low fuel consumption characteristics of vehicles and the wet grip characteristics of tires. Also, by using carbon black with low volatile content, affinity with low polar rubbers (NR, IR, BR, low styrene SBR) such as natural rubber is improved, and tan δ around 0 ° C. can be increased. Furthermore, the fuel efficiency and wet grip characteristics can be improved. Here, the volatile content of carbon black is measured by a method described in JIS K6221 or the like.

  When the carbon black used in the first aspect of the present invention satisfies the above characteristics, the surface is highly crystallized, the structure is well developed, and the conductivity imparting performance is improved.

  The total content of the carbon black is preferably 2 parts by weight or more, more preferably 4 parts by weight or more, and still more preferably 10 parts by weight or more based on 100 parts by weight of the rubber component. 15 parts by weight or more is most preferable. When the carbon black content is less than 2 parts by weight, the carbon black does not impart conductivity, and in particular, there is a tendency that the antistatic performance cannot be exhibited effectively. The carbon black content is preferably less than 35 parts by weight, more preferably 30 parts by weight or less, and even more preferably 20 parts by weight or less. When the content is 35 parts by weight or more, there is a tendency that good low fuel consumption characteristics of the silica compound are impaired or wear resistance is deteriorated.

  In the present invention, silica, calcium carbonate, aluminum hydroxide and the like can be suitably used as the reinforcing filler.

  The compounding amount of silica is preferably 30 parts by weight or more with respect to 100 parts by weight of the rubber component, more preferably 35 parts by weight or more, further preferably 40 parts by weight or more, and 45 parts by weight or more. It is particularly preferable that it is 50 parts by weight or more. When the amount of silica is less than 30 parts by weight, the rubber composition is not sufficiently reinforced, and particularly when used for a tread, the wear resistance becomes insufficient. Tend to get worse. The amount of silica is preferably 100 parts by weight or less, more preferably 90 parts by weight or less, still more preferably 80 parts by weight or less, and particularly preferably 70 parts by weight or less. When the blending amount of silica exceeds 100 parts by weight, the hardness becomes too high, which may hinder the use as a tire, or the processability at the time of unvulcanized rubber tends to be poor and the mass productivity tends to be impaired.

  The total amount of carbon black and silica is preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and still more preferably 70 parts by weight or more with respect to 100 parts by weight of the rubber component. When the total amount is less than 60 parts by weight, the rubber composition is not sufficiently reinforced, and particularly when used for a tread, the wear resistance tends to be insufficient. Further, the total blending amount is preferably 140 parts by weight or less, more preferably 120 parts by weight or less, and further preferably 80 parts by weight or less. When the total blending amount exceeds 140 parts by weight, the hardness becomes too high, and there is a tendency to hinder use as a tire.

  The surface of calcium carbonate is preferably treated with an organic substance (surface-treated calcium carbonate). Examples of such organic substances include fatty acids, resin acids, lignins, surfactants, etc., but it is particularly preferred that they are treated with fatty acids because of their good affinity for natural rubber and / or modified products thereof.

The nitrogen adsorption specific surface area of calcium carbonate is preferably 5 to 100 m ² / g. When the nitrogen adsorption specific surface area is less than 5 m ² / g, the reinforcing property is lowered, the breaking strength tends to be lowered, and the corrosion resistance tends to be lowered. The larger the nitrogen adsorption specific surface area of calcium carbonate, the better. However, in view of the manufacturing cost, it is generally about 100 m ² / g or less.

  The compounding amount of calcium carbonate is preferably 5 parts by weight or more, more preferably 7 parts by weight or more, and further preferably 15 parts by weight or more with respect to 100 parts by weight of the rubber component. When the blending amount of calcium carbonate is less than 5 parts by weight, the effect of reinforcing the natural rubber and / or modified product thereof and improving the fuel efficiency characteristics tends not to appear so much. Further, the blending amount of calcium carbonate is preferably 40 parts by weight or less, more preferably 30 parts by weight or less, and further preferably 25 parts by weight or less. When the compounding amount of the surface-treated calcium carbonate exceeds 40 parts by weight, it is necessary to reduce the compounding amount of silica or carbon black, and the wear resistance tends to be lowered depending on the content of the compounding.

  The total amount of silica and calcium carbonate is preferably 50 parts by weight or more, more preferably 55 parts by weight or more, and still more preferably 60 parts by weight or more with respect to 100 parts by weight of the rubber component. If the total blending amount is less than 50 parts by weight, it tends to be difficult to obtain good fuel consumption characteristics particularly when used for treads. Further, the total blending amount is preferably 110 parts by weight or less, more preferably 90 parts by weight or less, and further preferably 75 parts by weight or less. When the total blending amount exceeds 110 parts by weight, the hardness becomes too high, and there is a tendency to hinder the use as rubber for tires.

  The total amount of carbon black and calcium carbonate is preferably 10 parts by weight or more, more preferably 15 parts by weight or more, and still more preferably 20 parts by weight or more with respect to 100 parts by weight of the rubber component. . If the total blending amount is less than 10 parts by weight, it is difficult to obtain sufficient antistatic performance, and the processability in the unvulcanized rubber state tends to be slightly deteriorated. The total amount is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and further preferably 30 parts by weight or less. When the total blending amount exceeds 50 parts by weight, the wear resistance tends to deteriorate.

  The total amount of silica, carbon black, and calcium carbonate is preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and 70 parts by weight or more with respect to 100 parts by weight of the rubber component. Further preferred. When the total blending amount is less than 60 parts by weight, a sufficient reinforcing effect cannot be obtained, so that wear resistance tends to deteriorate and bending fatigue characteristics tend to deteriorate. Further, the total blending amount is preferably 140 parts by weight or less, more preferably 120 parts by weight or less, and further preferably 80 parts by weight or less. When the total blending amount exceeds 140 parts by weight, the hardness becomes too high, and there is a tendency to hinder use as a rubber for tires.

  In addition to the rubber component and the reinforcing filler, the tire rubber composition according to the first aspect of the present invention includes a general softener, stearic acid, zinc oxide, anti-aging agent, vulcanizing agent in the tire industry, A vulcanization accelerator or the like can be appropriately blended.

  As the softener, vegetable oil is preferable, and palm oil, soybean oil, rapeseed oil and the like are more preferable. Of these, it is preferable to use soybean oil as the softening agent because there is little deterioration in the performance of the rubber composition due to the addition of the softening agent.

  When vegetable oil is used as the softening agent, the iodine value of the vegetable oil is preferably 50 to 150, and more preferably 50 to 135. Vegetable oils having an iodine value of less than 50 are generally difficult to obtain. On the other hand, if it exceeds 150, the tan δ of the compounded rubber increases, the hardness decreases, the rolling resistance increases, and the steering stability tends to decrease.

  The blending amount of the softening agent is preferably 5 to 30 parts by weight with respect to 100 parts by weight of the rubber component. If the blending amount is less than 5 parts by weight, sufficient grip performance cannot be obtained, and the workability tends to deteriorate, and if it exceeds 30 parts by weight, the wear resistance tends to decrease.

  In the tire rubber composition according to the first aspect of the present invention, an ion conductive conductivity imparting agent may be blended. Specific examples of the ion conductivity-based conductivity-imparting agent include EO-PO-AGE copolymers and epichlorohydrin rubber. These have a moderate compounding amount dependency, can easily control the volume resistivity to an appropriate value, and can further improve rolling resistance characteristics and the like as necessary. Further, in the present invention, by adding a specific additive salt described later to the above-described ionic conductive copolymer or rubber, the antistatic performance at low temperature and low humidity, which was a drawback of the conventional ionic conductive system, is improved. You can also

  The compounding amount of the ionic conductive conductivity imparting agent is preferably 1 to 15 parts by weight, more preferably 2 to 10 parts by weight with respect to 100 parts by weight of the rubber component. If the blending amount is less than 1 part by weight, the conductivity imparting effect when blended tends to be insufficient, and if it exceeds 15 parts by weight, the wear resistance tends to deteriorate or the cost tends to increase more than necessary. is there.

The first rubber composition for a tire of the aspect of the present invention, lithium trifluoromethanesulfonate, bis (trifluoromethanesulfonyl) imide lithium, etc., -F and / or -SO ₂ - can be compounded salts containing.

  The compounding amount of the salt is preferably 0.01 to 3 parts by weight with respect to 100 parts by weight of the rubber component. If the blending amount is less than 0.01 parts by weight, sufficient conductivity imparting performance tends not to be obtained, and the effect of improving the antistatic performance particularly at low temperature and low humidity tends to be small, exceeding 3 parts by weight. Then, the cost tends to rise more than necessary, or depending on the type of salt, there is a tendency to bloom.

The rubber composition for a tire according to the first aspect of the present invention has a volume resistivity of 10 ⁸ Ω.measured by applying a voltage of 1000 V within a temperature range of 10 to 50 ° C. and a humidity of 15 to 100%. cm, preferably 10 ^8.5 Ω. cm or more, more preferably 10 ^9.0 Ω. cm or more. Volume resistivity is 10 ⁸ Ω. Below cm, the amount of carbon black added is unnecessarily high, resulting in poor fuel consumption characteristics and wear resistance, or the amount of ion conductive conductivity imparting agent is increased more than necessary, so no cost is required. May rise. The volume resistivity is 10 ¹¹ Ω. cm or less, preferably 10 ^10.5 Ω. cm or less, more preferably 10 ¹⁰ Ω. cm or less. Volume resistivity is 10 ¹¹ Ω. If it exceeds cm, the antistatic performance is insufficient, and there is a risk of adverse effects due to static electricity. The volume resistivity can be measured by, for example, a digital ultra-high resistance microammeter R-8340A manufactured by Advantest Corporation, Hiresta UP or Loresta GP manufactured by Mitsubishi Chemical Corporation, It is possible to measure using various probes according to the size and shape in combination.

  The tire rubber composition in the second embodiment of the present invention comprises a rubber component and carbon black.

  Examples of the rubber component include styrene-butadiene rubber (SBR) and polybutadiene rubber (BR) that are generally used as a rubber component in the tire industry, and carbon black having a low volatile content that can be used in the present invention. The rubber having a polyisoprene structure in a proportion of 50 mol% or more, or its modification, because it exhibits excellent wear resistance, reinforcement and grip performance due to crystallization when the rubber is stretched, in addition to being particularly excellent in compatibility with It is preferable that it is a thing. Such rubber is preferably natural rubber or a modified product thereof (hydrogenated natural rubber, acid-modified natural rubber, etc.) because excellent fuel efficiency and grip performance can be obtained. In addition, the ratio of resources other than petroleum can be increased as much as possible, and environmentally friendly tires can be manufactured.

  As the rubber component, epoxidized natural rubber can be blended and has a large interaction with silica. Intermolecular force, hydrogen bond, etc. between the epoxy group and the silanol group on the silica surface or the surface functional group of carbon black Exerts the interaction. Therefore, by using silica and carbon black in combination with epoxidized natural rubber, it is possible to exhibit extremely good vehicle fuel efficiency and tire grip performance. In addition, since it has a polyisoprene structure, excellent wear resistance can be obtained by crystallization of the epoxidized natural rubber by stretching caused by the structure.

  The epoxidized natural rubber may be a commercially available epoxidized natural rubber or an epoxidized natural rubber. Examples of a method for epoxidizing natural rubber include a method of reacting natural rubber with an organic peracid such as peracetic acid or performic acid.

  The epoxidation rate of the epoxidized natural rubber and the content of the epoxidized natural rubber in the rubber component are the same as those of the epoxidized natural rubber of the first aspect of the present invention.

  The average primary particle diameter of carbon black is 30 nm or less, preferably 28 nm or less, more preferably 26 nm or less, and further preferably 24 nm or less. When the average primary particle diameter exceeds 30 nm, it is difficult to improve the wear resistance and grip performance.

  The volatile content of carbon black is preferably 0.5% by weight or less, more preferably 0.4% by weight or less, further preferably 0.3% by weight or less, and 0.2% by weight or less. Is particularly preferred. If the volatile content exceeds 0.5%, the conductivity will decrease and the amount of carbon black added to achieve anti-static will tend to increase. In addition, good fuel efficiency characteristics, natural rubber, etc. It tends to be difficult to obtain a good affinity. By satisfying the range of the upper limit of the volatile matter, it becomes a carbon black that is particularly excellent in conductivity, so that the amount of carbon black required for antistatic is reduced, and a large amount of silica composed of resources other than petroleum can be blended. This makes it possible to consider the environment and improve the low fuel consumption characteristics of vehicles and the wet grip characteristics of tires. Also, by using carbon black with low volatile content, affinity with low polar rubbers (NR, IR, BR, low styrene SBR) such as natural rubber is improved, and tan δ around 0 ° C. can be increased. Furthermore, the fuel efficiency and wet grip characteristics can be improved. Here, the volatile content of carbon black is measured by a method described in JIS K6221 or the like.

  As carbon black, carbon black having an average primary particle size of more than 30 nm and 600 nm or less is used in combination with carbon black having an average primary particle size of 30 nm or less and a volatile content of 0.5% by weight or less. May be.

  It is preferable to use conductive carbon black as the carbon black. Specific examples of conductive carbon black include acetylene black, graphitized carbon, and ketjen black. Among them, good low fuel consumption characteristics can be obtained, and because of its high affinity with natural rubber, etc. Acetylene black or graphitized carbon is preferred.

  As conductive fillers other than conductive carbon black, natural graphite, artificial graphite, metal oxide, metal powder, carbon black for general tires, and the like can be used.

The nitrogen adsorption specific surface area, dibutyl phthalate oil absorption, pH and content of carbon black are the same as those of the carbon black in the first aspect of the present invention. As the reinforcing filler in the second aspect of the present invention, silica, Calcium carbonate, aluminum hydroxide, and the like can be suitably used, and their characteristic values and contents are the same as those in the first embodiment of the present invention.

  In addition to the rubber component and reinforcing filler, the tire rubber composition according to the second aspect of the present invention includes a softener, stearic acid, zinc oxide, anti-aging agent, vulcanizing agent, and the like commonly used in the tire industry. Vulcanization accelerators and the like can be blended as appropriate, and their characteristic values and contents are the same as in the first embodiment of the present invention.

In the rubber composition for a tire according to the second aspect of the present invention, the volume resistivity measured by applying a voltage of 1000 V within a range of a temperature of 10 to 50 ° C. and a humidity of 15 to 100% is 10 ¹¹ Ω. cm or less, preferably 10 ^10.5 Ω. cm or less, more preferably 10 ¹⁰ Ω. cm or less. Volume resistivity is 10 ¹¹ Ω. If it exceeds cm, the antistatic performance is insufficient, and there is a risk of adverse effects due to static electricity. The volume resistivity is 10 ⁸ Ω. preferably greater than cm, 10 ^8.5 Ω. more preferably greater than or cm, 10 ^9.0 Ω. It is especially preferable that it is cm or more. Volume resistivity is 10 ⁸ Ω. If it is less than cm, the blending amount of carbon black increases more than necessary, so that fuel efficiency and wear resistance tend to deteriorate, or costs tend to increase unnecessarily. The volume resistivity can be measured by, for example, a digital ultra-high resistance microammeter R-8340A manufactured by Advantest Corporation, Hiresta UP or Loresta GP manufactured by Mitsubishi Chemical Corporation, It is possible to measure using various probes according to the size and shape in combination.

  As a use of the rubber composition for a tire in the first aspect and the second aspect of the present invention, it is preferably used as an element constituting a pneumatic tire, particularly for a tread (base tread, cap tread). When the tread is used, the structure and the manufacturing method are simplified, and the manufacturing cost can be reduced. However, the present invention is not limited to this. For example, the tire rubber composition of the present invention can be used for a portion where conductivity is required, such as a conductive strip described in Japanese Patent No. 2944908.

  The tire rubber composition according to the first and second aspects of the present invention can also be suitably used as a tire member such as a tread of a studless tire or a sidewall. Furthermore, it can be suitably used as a rubber for tire production, particularly as a tire bladder.

  The pneumatic tire of the present invention can produce a tire containing a tread composed of the rubber composition for a tire according to the first aspect and the second aspect of the present invention by an ordinary method. That is, the tire rubber composition of the present invention is formulated with a rubber component and a reinforcing filler, and, if necessary, a softener, stearic acid, zinc oxide, an anti-aging agent, a vulcanizing agent, a vulcanization accelerator, and the like. The unvulcanized tire is formed by extruding in accordance with the shape of the tire member at an unvulcanized stage and molding the tire member by a normal method on a tire molding machine. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

  EXAMPLES The present invention will be described more specifically with reference to the following examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

The various chemicals used in the examples and comparative examples are shown below.
Natural rubber (NR): RSS # 3
Epoxidized natural rubber: GUTHRIE POLYMER SDN. BHD ENR-25 (epoxidation rate 25 mol%)
SBR: Nipol NS116R manufactured by ZEON CORPORATION
EO-PO-AGE copolymer: ZSN8030 manufactured by Nippon Zeon Co., Ltd.
Salt: 3M Fluorad HQ-115 (compound name: bis (trifluoromethanesulfonyl) imidolithium) manufactured by Sumitomo 3M Co., Ltd.
Silica: Ultrasil VN3 manufactured by Degussa (nitrogen adsorption specific surface area of 175 m ² / g)
Silane coupling agent: Si69 manufactured by Degussa
Soybean oil: Soybean white oil (S) manufactured by Nisshin Oilio Co., Ltd. (iodine value 131, fatty acid component 84.9% having 18 or more carbon atoms)
Stearic acid: Tungsten zinc oxide manufactured by Nippon Oil & Fats Co., Ltd .: Two types of zinc oxide manufactured by Mitsui Metal Mining Co., Ltd. Anti-aging agent: NOCRACK 6C manufactured by Ouchi Shinsei Chemical Co.
Surface-treated calcium carbonate: Hakucho Hana CC manufactured by Shiraishi Calcium Co., Ltd. (surface treatment with fatty acid, nitrogen adsorption specific surface area 26 m ² / g)
Untreated calcium carbonate: Light calcium carbonate manufactured by Maruo Calcium Co., Ltd. (nitrogen adsorption specific surface area of 3 m ² / g)
Clay: Hard clay crown carbon black manufactured by South Eastern 1: Denka black (granular, acetylene black) manufactured by Denki Kagaku Kogyo Co., Ltd.
Carbon Black 2: Ketjen Black EC600JD manufactured by Ketjen Black International Co., Ltd.
Carbon Black 3: Denka Black FX-35 (granular, small particle size acetylene black) manufactured by Denki Kagaku Kogyo Co., Ltd.
Carbon black 4: # 4000B (graphitized carbon black) manufactured by Mitsubishi Chemical Corporation
Carbon Black 5: Printex XE2B manufactured by Degussa
Aroma oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. BBS: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator DPG: Noxeller D manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

  The characteristic values of carbon black are listed in Table 1.

Examples 1 to 23 and Comparative Examples 1 to 23
Based on the formulations shown in Tables 2 to 7 excluding sulfur and the vulcanization accelerator, various chemicals were used using a 1.7 liter small Banbury manufactured by Kobe Steel Co., Ltd. and kneaded for 7 minutes. Then, sulfur and a vulcanization accelerator are added, mixed at 60 ° C. using a biaxial open roll, and the rubber removed from the open roll is formed into a sheet shape and charged into a mold, 170 Press vulcanized for optimum time at ℃. The pressure during vulcanization was 20 MPa. The vulcanization time was measured with a curast meter or the like, and was appropriately adjusted based on a 95% torque rise time t ₉₅ [minute].

  Thus, a vulcanized rubber slab sheet for evaluating volume resistivity and viscoelastic properties having a thickness of about 2 mm × 130 mm × 130 mm was obtained. In parallel, a vulcanized rubber test piece for wear test and a rubber test piece (thickness 10 mm × 120 mm × 175 mm) for thermal conductivity measurement were also produced. The following tests were performed using the produced sheet and rubber test piece.

(Rolling resistance characteristics)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), tan δ of each vulcanized rubber slab sheet was measured under conditions of a temperature of 70 ° C. and an initial strain of 10% and a dynamic strain of 2%. The rolling resistance characteristics were index-evaluated by the following formula, where tan δ of Comparative Example 14, Comparative Example 16 and Comparative Example 20 was 100 respectively. The larger the index, the lower the rolling resistance and the better the rolling resistance characteristics.
(Rolling resistance characteristic index) =
(Tan δ of Comparative Example 1, 14, 16, or 20 / tan δ of each formulation) × 100

(Abrasion resistance)
Measure the amount of Lambourn wear on the vulcanized rubber specimens at a temperature of 20 ° C, a slip rate of 20%, and a test time of 5 minutes using a Lambourn wear tester, and calculate the volume loss of each compound from the obtained wear. The loss amounts of Comparative Example 1, Comparative Example 14, Comparative Example 16, and Comparative Example 20 were set to 100, and the wear resistance was indicated by an index using the following formula. The higher the index, the better the wear resistance.
(Abrasion resistance index) =
(Loss amount of Comparative Example 1, 14, 16, or 20) / (loss amount of each formulation) × 100

(Volume resistivity)
The volume resistivity was measured on a vulcanized rubber slab sheet using a digital ultrahigh resistance microammeter R-8340A manufactured by Advantest Corporation. The normal temperature and normal humidity conditions represent a constant temperature and humidity condition of a temperature of 23 ° C. and a relative humidity of 55%, and the low temperature and low humidity conditions represent a constant temperature and humidity condition of a temperature of 10 ° C. and a relative humidity of 15%. The applied voltage was 1000 V, and the sample was measured in a measurement atmosphere for 5 hours or longer before measurement. For other items, the volume resistivity measurement method described in JISK 6911 was followed. Note that the volume resistivity is the common logarithm log ₁₀ R [Ω. cm]].

  Furthermore, in order to perform evaluation in an actual vehicle, an unvulcanized fun tread is prepared using the rubber composition having the blending contents described in each of the examples and comparative examples, and is pasted and molded on a raw cover. A 175 / 70R13 size tire was produced under the conditions and method of vulcanizing at 20 kgf for 10 minutes and used in the following tests. The tread was not made of two layers, a cap tread and a base tread, but was made in the form of a single layer structure.

(Antistatic performance in actual vehicles)
A rim made of steel was assembled on the tire. Next, a load of 450 kg is applied with an air pressure of 2.0 Ksc, and the electrical resistance value between the central portion of the rim and the conductive plate made of steel with which the tire is grounded is measured at an applied voltage of 1000 V to provide antistatic properties. evaluated.
○: No antistatic performance problem ×: Antistatic performance problem

  In addition, evaluation with an actual vehicle was performed under conditions of normal temperature (22.5 ± 2.5 ° C.) and, if necessary, low temperature (10 ° C. ± 2.5 ° C.). The relative humidity at the time of evaluation at room temperature was 55 ± 10%, and the relative humidity at the time of evaluation at low temperature was 15 ± 10%.

(Wet skid test)
Using a portable skid tester manufactured by Stanley, the maximum wear coefficient was measured according to the method of ASTM E303-83, and the measured values of Comparative Example 1, Comparative Example 14, Comparative Example 16 and Comparative Example 20 were taken as 100 and Wet skid performance was displayed as an index. The larger the index, the better the wet grip performance.
(Wet skid performance index) =
(Numerical value of each formulation) / (Numerical value of Comparative Example 1, 14, 16, or 20) × 100

(Thermal conductivity)
It measured using Kyoto Electronics Industry Co., Ltd. rapid thermal conductivity meter Chemtherm QTM-D3.

(Non-oil resource ratio)
The non-petroleum resource ratio (% by weight) of each formulation of Examples and Comparative Examples is shown.

  Test results are shown in Tables 2-7.

Claims (6)

Contains rubber components including epoxidized natural rubber and carbon black,
The volume resistivity measured by applying a voltage of 1000 V in the range of temperature 10 to 50 ° C. and humidity 15 to 100% is 10 ⁸ Ω. greater than cm and 10 ¹¹ Ω. The rubber composition for tires which is cm or less. Containing a rubber component, and carbon black having an average particle size of 30 nm or less and a volatile content of 0.5% by weight or less,
The volume resistivity measured by applying a voltage of 1000 V in the temperature range of 10 to 50 ° C. and humidity of 15 to 100% is 10 ¹¹ Ω. The rubber composition for tires which is cm or less. The tire rubber composition according to claim 1, comprising carbon black having an average particle size of 30 nm or less and a volatile content of 0.5% by weight or less as carbon black. The rubber composition for a tire according to claim 1, 2 or 3, wherein the rubber component further contains natural rubber and / or a modified product thereof. Furthermore, the rubber composition for tires of Claim 1, 2, 3 or 4 which contains 5 weight part or more of calcium carbonate surface-treated with organic substance with respect to 100 weight part of rubber components. A pneumatic tire using the tire rubber composition according to claim 1, 2, 3, 4 or 5.