JP2017100671A - Tire rubber composition and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire rubber composition that has a low temperature dependency of piezoelectric properties and also has excellent performance such as elongation at break, durability, and breakdown resistance, and a pneumatic tire prepared therewith.SOLUTION: A tire rubber composition satisfies the following formulas (1)-(3): d33(25°C)≥25pC/N (1), (d33(x°C) is piezoelectric properties at temperature x°C); 0.5×d33(0°C)≤d33(100°C)≤5×d33(0°C) (2); and EB(%)≥100 (3), (EB(%) is an elongation at break measured in accordance with JIS K6251).SELECTED DRAWING: None

Description

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

Piezoelectric materials such as inorganic materials such as piezoelectric ceramics and organic materials such as polyvinylidene fluoride are known, and it has been proposed to apply such piezoelectric materials to tires. For example, Patent Document 1 discloses a rubber composition for a tread that contains polyvinylidene fluoride and describes that the grip performance is improved.

However, polyvinylidene fluoride has problems such as insufficient heat resistance when applied to tire applications, and also has poor rubber properties, so that durability when incorporated in a tire is also insufficient. .

On the other hand, in recent years, there are increasing demands for various performances other than driving such as wear resistance, rolling resistance, etc., as well as air pressure and deflection monitoring, decorative lighting, etc. Therefore, it is also required that the temperature dependence of various performances is low.

For example, Patent Document 2 discloses a tire in which a power generation tool using a piezoelectric element is used as a power source for a tire air pressure sensor or the like. However, temperature dependency, power generation performance, elongation at break, durability, and resistance to fracture are disclosed. There is still room for improvement in various performances such as rolling resistance.

JP 2010-143963 A JP 2014-83957 A

The present invention solves the above-mentioned problems, and provides a rubber composition for a tire excellent in performance such as elongation at break, durability, fracture resistance, and the like, and a pneumatic tire using the same. The purpose is to provide.

The present invention relates to a tire rubber composition satisfying the following formulas (1) to (3).
d33 (25 ° C.) ≧ 25 pC / N (1)
(D33 (x ° C.) represents the piezoelectric characteristics at the temperature x ° C.)
0.5 × d33 (0 ° C.) ≦ d33 (100 ° C.) ≦ 5 × d33 (0 ° C.) (2)
EB (%) ≧ 100 (3)
(EB (%) represents elongation at break measured according to JIS K6251.)

The rubber composition is preferably one in which a piezoelectric material is oriented in a rubber matrix.

The present invention also relates to a pneumatic tire using the rubber composition as a material for a tire sensor, and a pneumatic tire using the rubber composition as a material for tire decoration power generation.

According to the present invention, since the rubber composition for tires satisfies the formulas (1) to (3), by using the rubber composition, the temperature dependence of piezoelectric characteristics is small, the elongation at break, and the durability. It is possible to provide a pneumatic tire excellent in performance such as fracture resistance.

The tire rubber composition of the present invention satisfies the following formulas (1) to (3).
d33 (25 ° C.) ≧ 25 pC / N (1)
(D33 (x ° C.) represents the piezoelectric characteristics at the temperature x ° C.)
0.5 × d33 (0 ° C.) ≦ d33 (100 ° C.) ≦ 5 × d33 (0 ° C.) (2)
EB (%) ≧ 100 (3)
(EB (%) represents elongation at break measured according to JIS K6251.)

Here, the piezoelectric constant d33 is an index indicating the amount of deformation of the material in the voltage direction when a voltage is applied to the material. The larger the piezoelectric constant d33, the larger the displacement.

The rubber composition of the present invention has a displacement amount (piezoelectric characteristics) of a predetermined value or more, satisfying the formula (1), that is, the piezoelectric constant d33 at 25 ° C. of 25 pC / N or more. Furthermore, d33 at 0 ° C. and 100 ° C. satisfies 0.5 × d33 (0 ° C.) ≦ d33 (100 ° C.) ≦ 5 × d33 (0 ° C.), and the displacement at 100 ° C. is 0 It stays within the range of 0.5 to 5 times the displacement at 0 ° C. and has little temperature dependence. In addition, the rubber composition has a characteristic that the elongation at break EB is 100%.

Therefore, since it has the desired piezoelectric characteristics (Equation (1)), it can be suitably used as a sensor material for tire pressure and deflection monitoring, and it can also be used as a power source material to add decorative properties such as tire lighting. it can. Since the temperature dependence is small (Equation (2)), it can be used in a very wide temperature range, and is less affected by changes in road surface temperature, heat generation due to use, and the like. Furthermore, since it has EB more than a predetermined value and high flexibility (Equation (3)), the piezoelectric performance is exhibited following the tire strain, and the durability of good piezoelectric performance is obtained. Further, peeling from other tire members and the like are prevented, and good fracture resistance is obtained. Therefore, by using the rubber composition, it is possible to provide a pneumatic tire having a small temperature dependency of piezoelectric characteristics and excellent properties such as elongation at break, durability, and fracture resistance.

The rubber composition satisfies the following formula (1).
d33 (25 ° C.) ≧ 25 pC / N (1)
If it is 25 pC / N or more, a sufficient piezoelectric effect is obtained, and it functions as a tire sensor or an electric decoration application. 30 pC / N or more is preferable, and 35 pC / N or more is more preferable. The upper limit is not particularly limited.

The rubber composition satisfies the following formula (2) (unit: pC / N).
0.5 × d33 (0 ° C.) ≦ d33 (100 ° C.) ≦ 5 × d33 (0 ° C.) (2)
When the formula (2) is satisfied, the temperature dependence from 0 ° C. to 100 ° C. is small, and it can be applied to a wide temperature range.
Preferably, 0.6 × d33 (0 ° C.) ≦ d33 (100 ° C.) ≦ 3 × d33 (0 ° C.), more preferably 0.7 × d33 (0 ° C.) ≦ d33 (100 ° C.) ≦ 1.5 × d33 (0 ° C.).

The rubber composition satisfies the following formula (3).
EB (%) ≧ 100 (3)
If the EB is less than 100%, minute damage (voids) may occur in the rubber composition due to repeated deformation, and the piezoelectric performance may be deteriorated. EB is preferably 150% or more, and more preferably 200% or more. The upper limit is not particularly limited.

In the present invention, d33 (x ° C.) is a value measured by applying a load of clamping force 8N or more and dynamic force 0.4N or more, and other conditions are measured according to JIS R1696. The EB (%) is the elongation at break measured according to JIS K6251. d33 (x ° C.) and EB (%) can be measured, for example, by the method of Examples described later.

In the present invention, the characteristics of the above formulas (1) and (2) can be imparted by a known material having a high piezoelectric effect, use of a piezoelectric material having a small temperature dependency, a preferred orientation of the piezoelectric material, and the like. The characteristic of the formula (3) is that a known rubber composition having a high EB is used (for example, use of rubber components such as natural rubber, butadiene rubber, epoxidized natural rubber, epoxidized butadiene rubber, etc., predetermined DBP oil absorption amount) Or carbon black with a nitrogen adsorption specific surface area, use of softener such as oil, use of appropriate amount of cross-linking agent, etc.) use of piezoelectric material with a predetermined average particle diameter, blending of appropriate amount of piezoelectric material, etc. Can be granted.

The rubber composition preferably contains a piezoelectric material (piezoelectric substance) from the viewpoint that the effects of the present invention can be obtained satisfactorily.

A piezoelectric material is a material capable of mutual conversion between mechanical energy and electrical energy, and has a property (piezoelectricity) in which a voltage is generated when a force is applied and a displacement and a force are generated when a voltage is applied.

In the rubber composition, the content of the piezoelectric material is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 5 parts by mass, the effect of the present invention tends to be insufficient. Content of this piezoelectric material becomes like this. Preferably it is 100 mass parts or less, More preferably, it is 70 mass parts or less, More preferably, it is 50 mass parts or less. If it exceeds 100 parts by mass, the fracture resistance and the like may be reduced.

When a granular material is used as the piezoelectric material, the average particle size is preferably 30 μm or less, and more preferably 10 μm or less. If it exceeds 30 μm, the fracture characteristics of the rubber composition may be deteriorated. The average particle size is preferably 0.01 μm or more, more preferably 0.1 μm or more. If it is less than 0.01 μm, the piezoelectric performance may be inferior. In this specification, the average particle diameter of the piezoelectric material (in the case of the polymer composite piezoelectric material described later, the polymer composite piezoelectric material) is observed with a transmission electron microscope, and the primary particles observed in the field of view are It can be determined by measuring 400 or more and averaging them.

Examples of the piezoelectric material include known ceramic-based and polymer-based piezoelectric materials.
Ceramic piezoelectric materials include barium titanate (BT), lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), lead titanate (PT) -lead zirconate (PZ) A three-component system or a four-component system based on can be suitably used. Three-component and four-component elements include Nb, Mg, Ni, Zn, Mn, Co, Sn, Fe, Cd, Sb, Al, Yb, In, Sc, Y, Ta, Bi, W, Te, Re Etc. Representative examples include barium titanate (BaTiO ₃ (BT)), strontium titanate (SrTiO ₃ ), lithium niobate (Li ₂ NbO ₃ ), lithium titanate (LiTiO ₃ ), lead titanate (PbTiO ₃ ), Lead barium titanate ((Ba, Pb) TiO ₃ ), barium calcium titanate ((Ba, Ca) TiO ₃ ), potassium sodium niobate ((K, Na) NbO ₃ ), lithium potassium niobate ((K, Li) NbO ₃ ), lead zirconate titanate (Pb (Zr, Ti) O ₃ (PZT)), and the like can be used. Note that it is desirable to use a piezoelectric material that does not contain lead from an environmental aspect.

As the polymer piezoelectric material, polyvinylidene fluoride, polytetrafluoroethylene, iodinated polyvinyl acetate, polyurea, polylactic acid, or the like can be used. A ceramic-based piezoelectric material is preferable from the viewpoint that good piezoelectric performance can be obtained.

In the present invention, as a piezoelectric material, a matrix made of an organic polymer resin, and a piezoelectric body made of a perovskite oxide having a composition represented by the following general formula contained in the matrix (which may contain inevitable impurities): A polymer composite piezoelectric material containing can also be suitably used.
_{(Bi x, A 1-x} ) (B y, C 1-y) O 3
(In the formula, A is an A site element having an average ion valence of 2 other than Pb, B is a B site element having an average ion valence of 3 and C is a B site element having an average ion valence of 3 or more.) A, B and C are each one or more metal elements, O is oxygen, B and C have different compositions, 0.6 ≦ x ≦ 1.0, x−0 2 ≦ y ≦ x The ratio of the total number of moles of the A-site element and the total number of moles of the B-site element to the number of moles of oxygen atoms is 1: 3, respectively, but may have a perovskite structure. It may deviate from 1: 3 within the range.)

The matrix (polymer matrix) is not particularly limited as long as it is an organic polymer resin. For example, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene (PTFE), ABS resin (acrylonitrile butadiene styrene resin). General-purpose plastics such as acrylic resin; Engineering plastics such as polyamide, polycarbonate, polyethylene terephthalate (PET), and thermoplastic polyimide; Synthetic rubbers such as acrylic rubber, acrylonitrile butadiene rubber, isoprene rubber, urethane rubber, butadiene rubber, and silicone rubber; Piezoelectric polymers such as vinylidene fluoride (PVDF) and copolymers thereof; thermosetting resins such as phenol resins, epoxy resins, melamine resins, and polyimides; It is below.

As for the piezoelectric body made of the perovskite oxide, as represented by the formula, the A-site element may be Bi alone, or the A-site element A having an average ion valence other than Pb and having a bivalence may be included. Examples of the A site element A include at least one metal element selected from the group consisting of Mg, Ca, Sr, Ba, (Na, Bi), and (K, Bi).

Since the main component of the A site (60 mol% or more) is Bi with an ionic valence of 3, the B site element B is a metal element with an average ionic valence of 3 and having a small mass. preferable. Examples of the B site element B include at least one metal element selected from the group consisting of Al, Sc, Cr, Mn, Fe, Co, Ni, Cu, Ga, Y, In, and Re (rare earth element). .

When A site element A is included, A has an average ionic valence of 2, and therefore, it is preferable that B site element C contains the same number of moles of a metal element having an average ionic valence of 4 as an average ion valence. When the number of moles is more than the same, the B site element C functions as a donor / dopant, but may be contained up to 20% or less. The B site element C may contain an element having an average ion valence greater than four. In this case, the element C having an average ion valence greater than 4 functions as a donor / dopant even in the same number of moles as the element A. The B site element C as a dopant may be contained up to 20% or less. When the A site element A is not included, the B site element C functions as a donor / dopant when the average ion valence is 4 or more. As the B site element C as a dopant, Nb, Mn and the like are preferable.

Further, instead of the perovskite oxide, a polymer composite piezoelectric material using PZT-based piezoelectric ceramics (piezoelectric material) can also be used.

These polymer composite piezoelectric materials include, for example, those having a configuration in which a piezoelectric material is disposed in a polymer matrix, and can be manufactured by a normal manufacturing method. Specifically, it can be produced by a method of producing an arrayed columnar piezoelectric body using a die casting method or a multi-blade wafer ring saw for producing a wafer, and pouring a polymer resin into a gap between the arrays.

The piezoelectric material in the present invention is preferably oriented in the rubber matrix in that good piezoelectric performance can be obtained. The method for aligning is not particularly limited, and a known method can be used, and examples thereof include a method in which a rubber component is extruded before being cured by vulcanization or the like, a method in which vulcanization is performed while applying a voltage, and the like. Specifically, in the latter method, an unvulcanized rubber composition is vulcanized while applying a DC voltage of 0.5 to 5.0 kV / mm within a range of 120 to 180 ° C. The piezoelectric material can be oriented.

The rubber composition of the present invention preferably contains a conductive material. Examples of the conductive material include metal particles such as copper powder and silver powder, surface-treated products obtained by treating the metal particles with an inorganic substance, zinc oxide powder made of N-type semiconductor by doping zinc oxide or the like with a different element, carbon Examples thereof include black, carbon nanofiber, and metal fiber. Among these, conductive carbon black is particularly preferable from the balance of fuel efficiency, elastic modulus, and processability.

As the conductive carbon black, known materials such as graphitized carbon black, acetylene black, and ketjen black can be used.

Among them, conductive carbon black, dibutyl phthalate (DBP) oil absorption of 100 cm ^3/100 g or more, a nitrogen adsorption specific surface area _(N 2 SA) of ^{40 m} 2 / g or more, at least volatile content below 1.0 wt% It is preferable to blend those having one characteristic. In addition to reducing rolling resistance by itself, it has a conductive effect in a small amount, and the hardness of rubber can be increased. Therefore, the amount of carbon black blended when the same hardness is reduced can be reduced, and rolling resistance can be further reduced. Furthermore, since the developed structure of conductive carbon black causes a change in resistance value due to a load, it can be provided with an ON-OFF switch function and is useful for use in a load sensor or the like.

The dibutyl phthalate (DBP) oil absorption amount of the conductive carbon black is preferably 120 ml / 100 g or more, more preferably, because the conductivity is improved and tan δ which is an index of rolling resistance is reduced and the hardness is increased. It is 160 ml / 100 g or more, more preferably 200 ml / 100 g or more, and particularly preferably 300 ml / 100 g or more. Although an upper limit is not specifically limited, Preferably it is 1000 ml / 100g or less, More preferably, it is 600 ml / 100g or less.

The nitrogen adsorption specific surface area (N ₂ SA) of the conductive carbon black is preferably 50 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 150 m ² / g or more. Carbon black generally has improved conductivity when N ₂ SA is high, and especially those having a large number of pores on the surface have further improved conductivity, and N ₂ SA of carbon black tends to be higher. Therefore, those having the above N ₂ SA are preferable. Although an upper limit is not specifically limited, Preferably it is 1500 m < ² > / g or less, More preferably, it is 1300 m < ² > / g or less.

The volatile content of the conductive carbon black is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and still more preferably 0.5% by mass or less. Since there are fewer functional groups on the surface of the carbon black and the more carbon, the better the conductivity, and at the same time the volatile content of the carbon black tends to decrease. Therefore, the decrease in the volatile content can be used as an index for improving the conductivity. Since the volatile content is small, the conductivity becomes good.

In this specification, the DBP oil absorption and volatile content of carbon black are values measured by the method described in JIS K6221 (1982), and N ₂ SA is a value measured by the A method of JIS K6217.

The content of the conductive carbon black is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and further preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 5 parts by mass, there is a possibility that the conductivity cannot be imparted by carbon black. Moreover, this content becomes like this. Preferably it is 100 mass parts or less, More preferably, it is 70 mass parts or less, More preferably, it is 50 mass parts or less. If it exceeds 100 parts by mass, the elongation at break, durability, and resistance to fracture may be reduced.

The rubber composition of the present invention preferably contains a diene rubber in view of rubber elasticity, durability, and strength. The diene rubber is not particularly limited. For example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber ( EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), epoxidized natural rubber (ENR), epoxidized butadiene rubber (EBR) and the like.

Of these, isoprene-based rubbers such as NR and ENR, butadiene-based rubbers such as BR and EBR, and SBR are preferable. Further, from the viewpoint of low fuel consumption and durability due to a strong bond with a filler, a modified diene rubber having a polar functional group in the molecule is desirable. The cis content of the butadiene rubber is preferably 90% by mass or more, more preferably 95% by mass or more. 1-50 mass% is preferable and, as for the epoxidation rate of epoxidized diene rubbers, such as EBR and ENR, 2-25 mass% is more preferable. The cis content can be measured by infrared absorption spectroscopy, and the epoxidation rate can be measured by nuclear magnetic resonance spectroscopy.

When an isoprene-based rubber such as NR is used as the rubber component, the amount of isoprene-based rubber may be appropriately selected according to the rubber physical properties, but the content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 10 to 10%. It is 70 mass%, More preferably, it is 30-50 mass%.

When a butadiene rubber such as BR or EBR is used as the rubber component, the BR amount may be appropriately selected according to the rubber physical properties, but the content of the butadiene rubber in 100% by mass of the rubber component is preferably 30 to It is 90 mass%, More preferably, it is 50-70 mass%.

In addition to the above components, the rubber composition of the present invention contains compounding agents generally used in the production of rubber compositions, such as vulcanizing agents, stearic acid, various anti-aging agents, anti-ozone degradation agents, oils and waxes. Further, a vulcanization accelerator and the like can be appropriately blended.

When blending an oil such as an aromatic process oil, the blending amount of the oil is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1.0 part by mass, the elongation at break may be reduced. The amount of the oil is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5.0 parts by mass or less. If it exceeds 20 parts by mass, the durability may decrease.

When sulfur is compounded as a vulcanizing agent, the amount of sulfur is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.2 parts by mass, the crosslink density becomes low, and there is a possibility that the elongation at break and the fracture resistance cannot be secured sufficiently. The amount of sulfur is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and still more preferably 2.0 parts by mass or less. If it exceeds 5.0 parts by mass, the crosslinking density increases, and there is a possibility that rubber properties such as elongation at break cannot be obtained sufficiently.

As the vulcanization accelerator, a sulfenamide vulcanization accelerator such as Nt-butyl-2-benzothiazylsulfenamide can be suitably used. When the sulfenamide-based vulcanization accelerator is blended, the blending amount is preferably 0.2 to 2.5 parts by mass, more preferably 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the rubber component. Part.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading each component such as a rubber component, a piezoelectric material, and conductive carbon black with a Banbury mixer, a kneader, an open roll, etc., and then vulcanizing.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, a rubber composition containing the above components is extruded in accordance with the shape of a tire member such as a tread at an unvulcanized stage, and is molded together with other tire members by a usual method on a tire molding machine. Thus, an unvulcanized tire is formed. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire. As described above, by applying a method of applying pressure before curing (vulcanizing), a method of vulcanizing while applying voltage, and the like, a tire member and a tire in which a piezoelectric material is oriented in a rubber matrix are applied. Can be manufactured.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

The various chemicals used in the examples are described below.
NR: TSR20
BR: Ubepol BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass)
EBR: Production Example 1 below
Carbon Black 1: Ketjen Black EC600JD (DBP: 495 ml / 100 g, N ₂ SA: 1270 m ² / g, volatile content: 0.7% by mass) manufactured by Ketjen Black International Co., Ltd.
Carbon Black 2: Dia Black N550 manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 41 m ² / g, DBP: 115 ml / 100 g, volatile content: 0.5% by mass)
Piezoelectric ceramics 1-3: Production Examples 2-4 below
Oil: X-140 (aromatic process oil) manufactured by Japan Energy Co., Ltd.
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads stearic acid anti-aging agent manufactured by NOF Corporation: NOCRACK 6C (N-phenyl-) manufactured by Ouchi Shinsei Chemical Co., Ltd. N ′-(1,3-dimethylbutyl) -p-phenylenediamine) (6PPD)
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Synthesis of peracetic acid solution>
To a 300 ml Erlenmeyer flask, 57 g of glacial acetic acid and 107 g of hydrogen peroxide solution were added, and after stirring, the mixture was allowed to stand for 24 hours while being kept at 40 ° C. in a constant temperature bath to obtain a peracetic acid solution.

(Production Example 1 Synthesis of EBR (epoxidized butadiene rubber))
A stainless steel polymerization reactor with an internal volume of 2 liters equipped with a stirrer was washed, dried, and then replaced with dry nitrogen. To this, 300 g of cyclohexane and 50 g of 1,3-butadiene were added, and 5.2 mmol of n-butyllithium (n-BuLi) was further added, followed by carrying out a polymerization reaction at 50 ° C. for 5 hours. Thereafter, 0.5 mL of an isopropanol solution (BHT concentration: 5% by mass) of 2,6-di-t-butyl-p-cresol (BHT) was added to the polymerization reaction system to stop the polymerization reaction. 100 ml of an aqueous solution containing 5 g of a surfactant was added to the reaction solution, 100 ml of the above-mentioned peracetic acid solution was added, and the mixture was irradiated with ultrasonic waves with vigorous stirring to carry out an epoxidation reaction for 0.5 hours under emulsifying conditions. The organic layer was separated, the solvent was removed, and drying under reduced pressure was performed to obtain EBR. The obtained EBR was Mw 5.2 × 10 ⁵ , epoxidation rate 5 mass%, vinyl content 26 mass%, trans content 42 mass%, and cis content 32 mass%.

(Production Example 2 Synthesis of Piezoelectric Ceramics 1)
As a raw material so as to have a composition of (Ba _0.2 , Bi _0.8 ) (Ti _0.2 , Fe _0.78 , Nb _0.01 , Mn _0.01 ) O ₃ , BaTiO ₃ , Bi ₂ O ₃ , Fe ₂ O ₃ , Mn ₂ O ₃ and Nb ₂ O ₅ were prepared. At this time, Bi ₂ O ₃ was 0.5 mol% excess. The blended raw material powder was wet mixed in a ball mill in ethanol to produce a mixed powder. After mixing, drying and molding, calcining was performed at 750 ° C. for 3 hours, and then pulverized and press-molded using PVA (polyvinyl alcohol) as a binder.
The obtained molded body was fired at 930 ° C. for 10 hours and then pulverized to obtain a piezoelectric ceramic 1 (polymer composite piezoelectric body) having an average particle diameter of 1.7 μm. The composition was the target composition and was a single perovskite phase

(Production Example 3 Synthesis of Piezoelectric Ceramics 2)
Production example except that the composition of the piezoelectric ceramic is Pb (Ti _0.48 , Zr _0.52 ) O ₃ , the raw material is PbO, TiO ₂ , ZrO _2, and the raw material is prepared with PbO in excess of 0.5 mol%. In the same manner as in Example 2, PZT piezoelectric ceramics 2 (polymer composite piezoelectric material) having an average particle size of 1.2 μm were obtained.

(Production Example 4 Synthesis of Piezoelectric Ceramics 3)
A piezoelectric ceramic 3 (polymer composite piezoelectric material) having an average particle size of 200 μm was obtained in the same manner except that the pulverization conditions of Production Example 3 were changed.

<Examples 1 and 2 and Comparative Example 1>
According to the blending contents shown in Table 1, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 5 minutes at 80 ° C. using a biaxial open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was vulcanized for 30 minutes at 150 ° C. while applying a DC voltage of 2 kV / mm to obtain a vulcanized rubber composition.

<Comparative example 2>
According to the blending contents shown in Table 1, a vulcanized rubber composition was obtained in the same manner as in Comparative Example 1 except that no DC voltage was applied during vulcanization.

The following evaluation was performed about the obtained vulcanized rubber composition. The results are shown in Table 1.

<Piezoelectric performance>
Piezoelectric properties (piezoelectric constant) d33 at 25 ° C., 0 ° C., and 100 ° C. of the vulcanized rubber composition were measured using a d33 meter (PM-300 manufactured by PIEZO TEST). The piezoelectric property d33 was measured under the conditions of a frequency of 110 Hz, a clamping force of 15N, and a dynamic force of 0.5N, and the other conditions were measured in accordance with JIS R1696.

<Piezoelectric durability>
Using the vulcanized rubber composition, a sample was prepared based on JIS K6260 “Vulcanized Rubber and Thermoplastic Rubber—Dematcher Flexural Crack Test Method” and subjected to a durability test. The degree of deterioration of piezoelectric performance after bending the rubber sheet by repeating 50% elongation 1000 times was evaluated by the following formula.
(Piezoelectric durability) = d33 after durability test (25 ° C.) / New d33 (25 ° C.) × 100

<Tensile test>
In accordance with JIS K6251 “How to determine tensile properties of vulcanized rubber and thermoplastic rubber”, tensile tests were conducted in each direction against roll extrusion using a No. 3 dumbbell, and the vulcanized rubber composition had an elongation at break (EB). The tensile strength (TB) at break was measured. EB (%) is shown in Table 1 as an index of rubber flexibility.
Further, TB × EB / 2 was used as an indicator of the breaking strength, and the breaking strength of the reference comparative example was taken as 100, and the breaking strength of each formulation was indicated by an index according to the following formula. The larger the index, the better the fracture resistance.
(Fracture resistance index) = (TB of each formulation × EB / 2) / (TB of reference comparative example × EB / 2) × 100

In the example, the difference in d33 between 0 ° C. and 100 ° C. was small, and the temperature dependence of the piezoelectric characteristics was low. In addition, the piezoelectric properties were excellent in durability, elongation at break EB, and fracture resistance. Therefore, it was revealed that the rubber compositions of the examples can be suitably used as tire sensor materials and decorative materials.

Claims (4)

A rubber composition for tires that satisfies the following formulas (1) to (3).
d33 (25 ° C.) ≧ 25 pC / N (1)
(D33 (x ° C.) represents the piezoelectric characteristics at the temperature x ° C.)
0.5 × d33 (0 ° C.) ≦ d33 (100 ° C.) ≦ 5 × d33 (0 ° C.) (2)
EB (%) ≧ 100 (3)
(EB (%) represents elongation at break measured according to JIS K6251.) The tire rubber composition according to claim 1, wherein a piezoelectric material is oriented in the rubber matrix. A pneumatic tire using the rubber composition according to claim 1 or 2 as a tire sensor material. A pneumatic tire using the rubber composition according to claim 1 or 2 as a tire decoration power generation material.