WO2009101855A1

WO2009101855A1 - Tire

Info

Publication number: WO2009101855A1
Application number: PCT/JP2009/051267
Authority: WO
Inventors: Daigo Yonemoto
Original assignee: Bridgestone Corporation
Priority date: 2008-02-12
Filing date: 2009-01-27
Publication date: 2009-08-20
Also published as: JP2009190437A

Abstract

Disclosed is a tire, which is excellent in on-ice performance, high in wear-resistance and low in rolling resistance. The tire is characterized in that its tread portion is made of tread rubber, in which ΔE' defined by the following formula (1) is 7.0 MPa or less: Δ E' = 0.1 %E' - 2 %E' (1), [wherein 0.1 %E' and 2 %E' indicate the dynamic storage elastic moduli which were measured for a frequency of 52 Hz and a tensile dynamic strain of 0.1 % or 2 % under the conditions of an initial load of 1.57 N and a temperature of 26 ºC]. The tire is characterized in that the average center-line roughness (Ra) of the worn face of the tread rubber after a run of 8000 Km on the asphalt road surface is 12 to 40 μm, and in that the ratio (Rz/Ra) between an average ten-point roughness (Rz) and the average center-line roughness (Ra) is 15 or more.

Description

tire

The present invention relates to a tire, in particular, a tire having good performance on ice, high wear resistance, and low rolling resistance.

Heavy duty pneumatic tires used for trucks and buses must have sufficient performance on ice from the viewpoint of safety and sufficient wear resistance from the viewpoint of economy.

In recent years, tires with reduced rolling resistance have been demanded as the above heavy duty tires without impairing on-ice performance and wear resistance. Here, among the tires, the tread rubber generates heat by repeatedly undergoing a large deformation during traveling, and therefore has a particularly large influence on the rolling resistance of the tire.

Conventionally, as a technique for improving the on-ice performance of a tire, a technique for improving the edge component of the tread pattern is known, but in this case, the movement of the block is increased, so that the low loss performance is impaired (that is, hysteresis). There is a problem that the rolling resistance of the tire increases and the improvement of the performance on ice and the reduction of the rolling resistance cannot be achieved at the same time (see Japanese Patent Application Laid-Open No. 2004-238619).

Therefore, an object of the present invention is to provide a tire that solves the above-mentioned problems of the prior art, has good performance on ice, has high wear resistance, and has low rolling resistance.

As a result of intensive studies to achieve the above object, the inventor of the present invention (1) reduces the rolling resistance of the tire by setting ΔE ′ of the tread rubber under a specific condition to a specific value or less, and (2) The ratio between the ten-point average roughness (Rz) and the centerline average roughness (Ra) is not less than a specific value while keeping the centerline average roughness (Ra) of the tread rubber worn surface after traveling a certain distance within a specific range. It is possible to improve the on-ice performance of the tire, and further satisfy (1) and (2) at the same time to obtain a tire having high on-ice performance and low rolling resistance while having high wear resistance. The headline and the present invention have been completed.

That is, the tire of the present invention has the following formula (I):
ΔE '= 0.1% E'-2% E' (I)
[Where 0.1% E ′ and 2% E ′ represent the dynamic storage modulus measured at an initial load of 1.57 N, a temperature of 26 ° C., a frequency of 52 Hz, and a tensile dynamic strain of 0.1% or 2%, respectively. The tread rubber having ΔE ′ defined by
The centerline average roughness (Ra) of the worn surface of the tread rubber after traveling 8000 km on the asphalt road surface is 12 to 40 μm, and the 10-point average roughness (Rz) and the centerline average roughness (Ra) The ratio (Rz / Ra) is 15 or more. The tire of the present invention is particularly suitable as a heavy load studless tire.

In the tread rubber of the tire of the present invention, ΔE ′ defined by the above formula (I) is preferably 4.0 μM or less. In this case, the rolling resistance of the tire is further reduced.

In the tire of the present invention, the rubber composition used for the tread rubber is preferably a rubber composition in which 3 to 30 parts by mass of silica is blended with 100 parts by mass of the rubber component.

In a preferred example of the tire of the present invention, the tread rubber has closed cells. Here, the tread rubber preferably has a foaming ratio in the range of 5 to 30%. The rubber composition used for the tread rubber is preferably a rubber composition obtained by blending 0.1 to 10 parts by mass of polyethylene short fibers with 100 parts by mass of the rubber component.

In another preferred embodiment of the tire of the present invention, the rubber component of the tread rubber is composed of natural rubber and a diene synthetic rubber, and the mass ratio (natural rubber / diene synthetic rubber) is 80/20 to 40/60. is there. Here, as the natural rubber, the total nitrogen content obtained from the latex obtained by partially deproteinizing the protein in the natural rubber latex by a mechanical separation technique is more than 0.1 mass% and 0.4 mass% or less. Natural rubber and modified natural rubber containing a polar group in the natural rubber molecule are preferred. The diene synthetic rubber is preferably a modified polybutadiene rubber having a nitrogen-containing functional group, and the nitrogen-containing functional group is preferably derived from hexamethyleneimine.

According to the present invention, (1) ΔE ′ of the tread rubber under a specific condition is not more than a specific value, and (2) the center line average roughness (Ra) of the tread rubber worn surface after traveling a certain distance is in a specific range. In addition, the ratio of the ten-point average roughness (Rz) to the centerline average roughness (Ra) is equal to or higher than a specific value, providing excellent on-ice performance, high wear resistance, and low rolling resistance. can do.

Hereinafter, the present invention will be described in detail. The tire according to the present invention includes a tread rubber having ΔE ′ defined by the above formula (I) of 7.0 μMPa or less in a tread portion, and an average center line of the wear surface of the tread rubber after running on an asphalt road surface for 8,000 km. The roughness (Ra) is 12 to 40 μm, and the ratio (Rz / Ra) of ten-point average roughness (Rz) to centerline average roughness (Ra) is 15 or more.

When the ΔE ′ of the tread rubber is 7.0 μM or less, the low loss property is improved (that is, the hysteresis loss is reduced), and the tire rolling resistance can be reduced. Also, the ratio of the 10-point average roughness Rz to the centerline average roughness (Ra) (with the centerline average roughness (Ra) of the tread rubber wear surface after traveling 8000 km on the asphalt road surface being 12-40 μm) By setting Rz / Ra) to 15 or more, the maximum wear is larger than the average wear, the ground contact area of the tire and the drainage volume are balanced, and the performance on ice can be improved. Furthermore, by combining these characteristics, it is possible to simultaneously achieve high wear resistance, good on-ice performance, and low rolling resistance.

Here, when ΔE ′ of the tread rubber exceeds 7.0 μMa, the low loss property is deteriorated (that is, the hysteresis loss is increased), and the rolling resistance of the tire is increased. From the viewpoint of further reducing the rolling resistance of the tire, ΔE ′ of the tread rubber is preferably 4.0 MPa or less, and more preferably 3.5 MPa or less. In addition, since ΔE ′ is an index of dispersibility, it is preferably as low as possible. Also, as ΔE ′ is low, the low loss property is favorable.

Also, if the centerline average roughness (Ra) of the tread rubber wear surface after traveling 8000 km on an asphalt road surface is less than 12 μm, the performance on ice will decrease, and if it exceeds 40 μm, the performance on ice will decrease. From the viewpoint of further improving the on-ice performance of the tire, Ra is preferably in the range of 20 to 40 μm, and more preferably in the range of 25 to 35 μm. In addition, when traveling on an asphalt road surface for 8,000 km, the tread surface is worn by about 1 mm and the foam surface is exposed.

Furthermore, even if the ratio (Rz / Ra) of the ten-point average roughness (Rz) to the centerline average roughness (Ra) of the worn surface of the tread rubber after traveling 8000 km on the asphalt road surface is less than 15, the performance on ice is good. descend. That is, even if the surface is too rough, the contact area is small, so the performance on ice is reduced. Also, if the surface is too small, the drainage volume is small, so the performance on ice is reduced. When / Ra is small, the drainage volume becomes small for the surface roughness, so the performance on ice is degraded. From the viewpoint of performance on ice (surface running water resistance), Rz / Ra is preferably 40 or less, and from the viewpoint of drainage volume, running water resistance, and wear resistance, Rz / Ra is in the range of 15-20. Is more preferable.

The tread rubber of the tire of the present invention preferably has closed cells. When the tread rubber has closed cells, the drainage volume of the tire is increased and the performance on ice is improved. Further, the expansion ratio of the tread rubber having closed cells is preferably in the range of 5 to 30%. When the foaming ratio of the tread rubber is less than 5%, the effect on improving the performance on ice is small, whereas when it exceeds 30%, the wear resistance tends to be lowered. The foaming rate (Vs) can be calculated by the following formula.
Vs = (ρ ₀ / ρ ₁ −1) × 100 (%)
Wherein, [rho ₁ represents the density of the tread rubber ^{(g / cm 3), ρ} 0 represents the density of the solid phase portion of the tread rubber (g / cm ^3)]. The density of the tread rubber and the density of the solid phase portion of the tread rubber are calculated from the mass in ethanol and the mass in air. The foaming rate can be changed as appropriate depending on the type and amount of the foaming agent and foaming aid. Examples of the foaming agent include azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), and dinitrosopentastyrene. Tetramine and benzenesulfonylhydrazide derivatives, p, p'-oxybisbenzenesulfonylhydrazide (OBSH), ammonium bicarbonate that generates carbon dioxide, sodium bicarbonate, ammonium carbonate, nitrososulfonylazo compounds that generate nitrogen, N, N ' -Dimethyl-N, N′-dinitrosophthalamide, toluenesulfonyl hydrazide, p-toluenesulfonyl semicarbazide, p, p′-oxybisbenzenesulfonyl semicarbazide and the like, and foaming aids include urea, zinc stearate, Zinc benzenesulfinate and zinc Hana, and the like.

The rubber component of the tread rubber is preferably composed of natural rubber and diene synthetic rubber, and the mass ratio (natural rubber / diene synthetic rubber) is preferably 80/20 to 40/60. In this case, it is easy to achieve both on-ice performance and wear resistance of the tire. In addition, when the ratio of natural rubber exceeds 80% by mass of the rubber component (when the ratio of diene synthetic rubber is less than 20% by mass of the rubber component), there is a tendency that the wear resistance and the performance on ice tend to be reduced. When the ratio of rubber is less than 40% by mass of the rubber component (when the ratio of diene synthetic rubber exceeds 60% by mass of the rubber component), workability tends to decrease.

Examples of the natural rubber include natural rubber having a total nitrogen content of more than 0.1% by mass and 0.4% by mass or less obtained from latex obtained by partially deproteinizing protein in natural rubber latex by mechanical separation technique. preferable. The partially deproteinized natural rubber can improve the dispersibility of fillers such as carbon black, and can improve the flexibility of the tread rubber at low temperatures. Here, the content of the partially deproteinized natural rubber in the rubber component is preferably in the range of 40 to 80% by mass.

The partially deproteinized natural rubber is obtained by converting the latex after tapping and before coagulation into a solid component in a general natural rubber production process, that is, in the order of latex tapping, coagulation, washing, dehydration, drying, and packing. After the partial deproteinization treatment by a mechanical separation method, preferably, centrifugal concentration method, so that the total nitrogen content in the above range, the obtained natural rubber latex is coagulated, washed, It can be obtained by drying using a normal dryer such as a vacuum dryer, air dryer, drum dryer or the like. In addition, the natural rubber latex used as a raw material is not particularly limited, and a field latex, a commercially available latex, or the like can be used.

In addition, as a deproteinization treatment method, a degradation treatment method using a proteolytic enzyme, a method of repeatedly washing with a surfactant, a method of using an enzyme and a surfactant in combination, and the like are known. However, although the protein in the solid rubber is reduced, at the same time, active ingredients such as tocotrienol having an anti-aging action are lost, so that the natural aging resistance inherent in natural rubber is lowered. On the other hand, in the mechanical separation method, since the active ingredient such as tocotrienol is hardly lost, the heat resistance can be maintained almost equal to that of the conventional natural rubber.

The total nitrogen content in the natural rubber is an index of protein content, and can be controlled by adjusting the centrifugation conditions (rotation speed, time, etc.) of the raw natural rubber latex. Here, the conditions for the centrifugation are not particularly limited, but it is preferable that the centrifugation is repeated several times at a rotational speed of about 7500 rpm. When the total nitrogen content is 0.1% by mass or less, the heat aging resistance is lowered. On the other hand, when the total nitrogen content exceeds 0.4% by mass, a sufficiently low exothermic property may not be obtained. The total nitrogen content in the natural rubber is preferably in the range of 0.2 to 0.4% by mass.

As the natural rubber, a modified natural rubber containing a polar group in the natural rubber molecule is also preferable. The modified natural rubber can also improve the dispersibility of fillers such as carbon black, and can improve the flexibility of the tread rubber at low temperatures. Here, the content of the modified natural rubber in the rubber component is preferably in the range of 40 to 80% by mass.

The modified natural rubber was obtained by adding a polar group-containing monomer to natural rubber latex, graft-polymerizing the polar group-containing monomer to natural rubber molecules in the natural rubber latex, and further coagulating and drying. Modified natural rubber is preferred. The natural rubber latex used for the production of the modified natural rubber is not particularly limited. For example, field latex, ammonia-treated latex, centrifugal concentrated latex, deproteinized latex treated with a surfactant or an enzyme, and combinations thereof are combined. A thing etc. can be used. In the modified natural rubber, the graft amount of the polar group-containing monomer is preferably in the range of 0.01 to 5.0% by mass, more preferably in the range of 0.1 to 3.0% by mass with respect to the rubber component in the natural rubber latex. The range of 0.2 to 1.0% by mass is even more preferable.

The polar group-containing monomer added to the natural rubber latex is not particularly limited as long as it has at least one polar group in the molecule and can be graft-polymerized with the natural rubber molecule. Here, the polar group-containing monomer preferably has a carbon-carbon double bond in the molecule for graft polymerization with a natural rubber molecule, and is preferably a polar group-containing vinyl monomer. . Specific examples of the polar group include amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, and oxycarbonyl. Preferred examples include groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, nitrogen-containing heterocyclic groups, oxygen-containing heterocyclic groups, alkoxysilyl groups, and tin-containing groups. These monomers containing a polar group may be used singly or in combination of two or more.

Examples of the monomer containing an amino group include N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dipropylaminoethyl (meth) acrylate, N, N N-dioctylaminoethyl (meth) acrylate and the like can be mentioned. Examples of the monomer containing a nitrile group include (meth) acrylonitrile and vinylidene cyanide. Examples of the monomer containing a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and the like. Examples of the monomer containing a carboxyl group include (meth) acrylic acid and maleic acid. Examples of the monomer containing an epoxy group include (meth) allyl glycidyl ether, glycidyl (meth) acrylate, and 3,4-oxycyclohexyl (meth) acrylate. Examples of the monomer containing the nitrogen-containing heterocyclic group include 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 5-methyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine, and the like. Is mentioned. Examples of the monomer having a tin-containing group include allyltri-n-butyltin and allyltrimethyltin.

The graft polymerization of the polar group-containing monomer onto the natural rubber molecule is preferably carried out by emulsion polymerization. Here, in the emulsion polymerization, generally, the polar group-containing monomer is added to a solution obtained by adding water and, if necessary, an emulsifier to a natural rubber latex, and a polymerization initiator is further added. It is preferable to polymerize the polar group-containing monomer by stirring at the temperature. As the emulsifier, a nonionic surfactant such as polyoxyethylene lauryl ether can be used. The polymerization initiator is preferably a redox polymerization initiator such as benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, or di-tert-butyl peroxide. It is preferable to use a combination of a peroxide and a reducing agent such as tetraethylenepentamine, mercaptans, acidic sodium sulfite, reducing metal ions, ascorbic acid or the like. Each component described above is charged into a reaction vessel and reacted at 30 to 80 ° C. for 10 minutes to 7 hours to obtain a modified natural rubber latex in which the polar group-containing monomer is graft copolymerized with natural rubber molecules. The modified natural rubber latex is coagulated, washed, and then dried using a dryer such as a vacuum dryer, an air dryer, a drum dryer or the like to obtain a modified natural rubber. Here, the coagulant used for coagulating the modified natural rubber latex is not particularly limited, and examples thereof include acids such as formic acid and sulfuric acid, and salts such as sodium chloride.

As the diene synthetic rubber, a modified polybutadiene rubber having a nitrogen-containing functional group is preferable. The modified polybutadiene rubber can improve the dispersibility of fillers such as carbon black, and can improve the flexibility of the tread rubber at low temperatures. Further, the modified polybutadiene rubber can improve the wear resistance of the tire. Here, the content of the modified polybutadiene rubber in the rubber component is preferably in the range of 20 to 60% by mass.

The modified polybutadiene rubber has a nitrogen-containing functional group at the active end after polymerizing 1,3-butadiene or synthesizing polybutadiene having an active end using a polymerization initiator having a nitrogen-containing functional group. It can be synthesized by a known method such as modification with a modifying agent. Here, the nitrogen-containing functional group is preferably a functional group derived from hexamethyleneimine (for example, a hexamethyleneimino group). The above-mentioned polymerization initiator having a nitrogen-containing functional group may be used in a polymerization reaction by preliminarily preparing lithium hexamethyleneimide or the like from a lithium compound such as n-butyllithium and a secondary amine such as hexamethyleneimine. May be produced in the polymerization system. Examples of the modifying agent include tin-containing compounds such as tin tetrachloride, N, N′-dimethylimidazolidinone, N-methylpyrrolidone, 4-dimethylaminobenzylideneaniline, and 4,4′-bis (N, N-dimethyl). Nitrogen-containing compounds such as amino) benzophenone, silicon tetrachloride, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, N- (1-methylpropylidene) -3- (triethoxysilyl) -1-propanamine, N- (1,3-dimethylbutylidene) -3- (triethoxysilyl) -1-propanamine, N- (3-triethoxysilylpropyl) -4,5-dihydroimidazole, 3 Examples include silicon-containing compounds such as 3-methacryloyloxypropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, and 3-triethoxysilylpropyl succinic anhydride. That.

In the tire tread rubber of the present invention, it is preferable to use a rubber composition in which 3 to 30 parts by mass of silica is blended with 100 parts by mass of the rubber component. By using a rubber composition containing silica as a tread rubber, it is possible to achieve both on-ice performance (flexibility at low temperatures) and wear resistance while reducing rolling resistance of the tire. If the amount of silica is less than 3 parts by mass, it is difficult to achieve both of the above while reducing rolling resistance. On the other hand, if it exceeds 30 parts by mass, the wear resistance is reduced.

In the tread rubber of the tire of the present invention, it is also preferable to use a rubber composition in which 0.1 to 10 parts by mass of polyethylene short fibers are blended with 100 parts by mass of the rubber component. When a rubber composition containing polyethylene short fibers is used for a tread rubber, the polyethylene short fibers melt or soften during vulcanization, while the gas generated during vulcanization in the rubber matrix melts or softens. As a result of staying inside the polyethylene, long bubbles are generated where the polyethylene short fibers were present. The long air bubbles exist independently (as independent air bubbles) in the tread rubber and can function as a micro drainage groove, so that the on-ice performance of the tire can be improved. In addition, when the blending amount of the polyethylene short fiber is less than 0.1 parts by mass, sufficient drainage effect may not be obtained. On the other hand, when it exceeds 10 parts by mass, the elastic modulus may increase and the performance on ice may be deteriorated. .

The tire of the present invention is a rubber composition comprising, for example, a rubber component made of natural rubber and a diene synthetic rubber and a compounding agent such as a filler such as carbon black or silica, a short polyethylene fiber, a foaming agent, and a foaming aid. The rubber composition can be used as a tread rubber and vulcanized according to a conventional method. As described above, the tire of the present invention has low rolling resistance, excellent performance on ice and wear resistance, and can be used as a studless tire for various vehicles, but is particularly suitable as a heavy duty studless tire. .

<< Example >>
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

<Example of production of partially deproteinized natural rubber>
The natural rubber latex (CT-1) added with 0.4% by mass of ammonia was concentrated by centrifuging at a rotational speed of 7500 rpm for 15 minutes using a latex separator SLP-3000 (manufactured by Saito Centrifuge Co., Ltd.). The concentrated latex was further centrifuged at 7500 rpm for 15 minutes. The resulting concentrated latex is diluted to about 20% as a solid content, then formic acid is added, and after standing overnight, the rubber content obtained by coagulation is dried at 110 ° C. for 210 minutes to partially deproteinize natural rubber Manufactured. It was 0.15 mass% when the total nitrogen content of the obtained natural rubber was measured by the Kjeldahl method.

<Example of production of modified natural rubber>
The field latex was centrifuged at a rotational speed of 7500 rpm using a latex separator (manufactured by Saito Centrifugal Industries) to obtain a concentrated latex having a dry rubber concentration of 60%. 1000 g of this concentrated latex is put into a stainless steel reaction vessel equipped with a stirrer and a temperature control jacket, and 10 mL of water and 90 mg of emulsifier [Emulgen 1108, manufactured by Kao Corporation] are added in advance to N, N-diethylaminoethyl methacrylate. The emulsion added in addition to 3.0 g was added with 990 mL of water, and these were stirred at room temperature for 30 minutes while purging with nitrogen. Next, 1.2 g of tert-butyl hydroperoxide and 1.2 g of tetraethylenepentamine were added as polymerization initiators and reacted at 40 ° C. for 30 minutes to obtain a modified natural rubber latex. Formic acid was added to the modified natural rubber latex to adjust the pH to 4.7 to coagulate the modified natural rubber latex. The solid thus obtained was treated five times with a creper, passed through a shredder and crushed, and then dried at 110 ° C. for 210 minutes with a hot air dryer to obtain a modified natural rubber. From the mass of the modified natural rubber thus obtained, it was confirmed that the conversion rate of N, N-diethylaminoethyl methacrylate added as a monomer was 100%. In addition, the modified natural rubber was extracted with petroleum ether and further extracted with a 2: 1 mixed solvent of acetone and methanol, but when the extract was analyzed, the homopolymer was not detected. It was confirmed that 100% of the added monomer was introduced into the natural rubber molecule. Accordingly, the polar group content of the resulting modified natural rubber is 0.027 mmol / g with respect to the rubber component in the natural rubber latex.

<Production example of modified polybutadiene rubber>
In a 800 mL pressure-resistant glass container that has been dried and purged with nitrogen, cyclohexane solution of 1,3-butadiene (16%), cyclohexane solution of styrene (21%), 40 g of 1,3-butadiene and 10 g of styrene Then, 0.12 mmol of 2,2-ditetrahydrofurylpropane was injected, and 0.4 mmol of lithium hexamethyleneimide was added thereto, followed by polymerization reaction in a warm water bath at 50 ° C. for 1.5 hours. The polymerization conversion rate at this time was almost 100%. Next, 0.1 mmol of tin tetrachloride was added as a modifier to the polymerization reaction system, and a modification reaction was further performed at 50 ° C. for 30 minutes. Thereafter, 0.5 mL of an isopropanol solution (BHT concentration: 5 mass%) of 2,6-di-t-butyl-p-cresol (BHT) was added to the polymerization reaction system to stop the polymerization reaction, and further according to a conventional method. By drying, a modified polybutadiene rubber (modified BR) was obtained. The obtained modified BR had a bound styrene content of 20% by mass, a vinyl bond content of 58%, and a weight average molecular weight (Mw) without modification termination of 290,000.

<Preparation and evaluation of rubber composition>
Rubber compositions having the formulations shown in Tables 1 and 2 were prepared according to a conventional method. The resulting rubber composition was vulcanized at 145 ° C. for 33 minutes to prepare a sample having a width of 4.7 mm, a thickness of 2 mm, and a length of 40 mm, and an initial load of 1.57 N using a spectrometer made by Kamijima. The dynamic storage elastic modulus (E ′) was measured at a temperature of 26 ° C., a frequency of 52 Hz, and a tensile dynamic strain of 0.1% or 2%, and the difference (ΔE ′) was calculated. Further, the loss tangent (tan δ) of the sample was measured under the conditions of an initial load of 1.57 N, a temperature of 26 ° C., a frequency of 52 Hz, and a tensile dynamic strain of 2% using the spectrometer. The results are shown in Tables 1-2.

<Production and evaluation of tire>
Using the above rubber composition as a tread rubber, a heavy duty studless tire having a size of 11R22.5 was manufactured, and after running on an asphalt road surface for 8000 km, the centerline average roughness (Ra) of the wear surface of the tread rubber according to JIS B0601 And ten-point average roughness (Rz) was measured. Furthermore, the rolling resistance, performance on ice and wear resistance of the tire were evaluated by the following methods. The results are shown in Tables 1-2.

(1) Rolling resistance The rolling resistance was measured by running on a drum at a speed of 80 km / h. The rolling resistance of the tire of Comparative Example 1 was indicated as 100 and indicated as an index. It shows that rolling resistance of a tire is so small that an index value is small.

(2) Performance on ice On a flat surface on ice, the vehicle was accelerated from a stationary state, and the lap time until 100 m traveled was measured. The larger the index value, the shorter the arrival time, and the better the acceleration on ice.

(3) Abrasion resistance Measure the groove depth of the tire when the above test tire is mounted on a vehicle and run for 50,000 km, and the travel distance / (groove depth of the tire before running minus the tire after running) The value of the groove depth) was calculated, and indexed with Comparative Example 1 as 100. It shows that it is excellent in abrasion resistance, so that an index value is large.

* 1 Partially deproteinized natural rubber produced by the above method
* 2 Modified natural rubber produced by the above method
* 3 Made by Ube Industries, BR150L
* 4 Modified polybutadiene rubber produced by the above method
* 5 NIPSEAL AQ made by Nippon Silica Industry
* 6 Azodicarbonamide
* 7 Made of Tile, Melting point = 125 ° C, Fiber diameter = 3.6 d, Average diameter = 0.023 mm, Average length = 2 mm
* 8 Made by Nippon Walnet, Soft Grip # 46

From the results in Table 1, it can be seen that the tires of the examples have good performance on ice, high wear resistance, and low rolling resistance.

On the other hand, the tire of Comparative Example 2 in which ΔE ′ of the tread rubber exceeded 7.0 kg MPa had increased rolling resistance and deteriorated wear resistance as compared with the tire of Comparative Example 1.

Also, the tires of Comparative Examples 3 and 4 in which the Ra of the wear surface of the tread rubber after traveling 8000 km on the asphalt road surface was less than 12 μm had deteriorated performance on ice as compared with the tire of Comparative Example 1.

Further, the tire of Comparative Example 5 in which the ratio of Rz to Ra (Rz / Ra) of the worn surface of the tread rubber after traveling 8000 km on the asphalt road surface is less than 15 is higher on the ice than the tire of Comparative Example 1. The performance was deteriorated and the wear resistance was greatly deteriorated.

In addition, since the rolling resistance of the tires of Examples 5 to 8 in which ΔE ′ of the tread rubber is 4.0 MPa or less is very small, it is understood that ΔE ′ of the tread rubber is preferably 4.0 MPa or less.

Claims

Formula (I) below:
ΔE '= 0.1% E'-2% E' (I)
[Where 0.1% E ′ and 2% E ′ represent the dynamic storage modulus measured at an initial load of 1.57 N, a temperature of 26 ° C., a frequency of 52 Hz, and a tensile dynamic strain of 0.1% or 2%, respectively. The tread rubber having ΔE ′ defined by
The centerline average roughness (Ra) of the worn surface of the tread rubber after traveling 8000 km on the asphalt road surface is 12 to 40 μm, and the 10-point average roughness (Rz) and the centerline average roughness (Ra) A tire having a ratio (Rz / Ra) of 15 or more.
The tire according to claim 1, wherein the tread rubber has a ΔE 'defined by the above formula (I) of 4.0 MPa or less.
The tire according to claim 1, wherein the tread rubber has closed cells.
The tire according to claim 3, wherein the tread rubber has a foaming ratio in the range of 5 to 30%.
The rubber component of the tread rubber is composed of natural rubber and diene-based synthetic rubber, and the mass ratio (natural rubber / diene-based synthetic rubber) is 80/20 to 40/60. tire.
The natural rubber is a natural rubber having a total nitrogen content of more than 0.1% by mass and 0.4% by mass or less obtained from a latex obtained by subjecting a protein in natural rubber latex to partial deproteinization by a mechanical separation method, or The tire according to claim 5, wherein the tire is a modified natural rubber containing a polar group in a natural rubber molecule.
The tire according to claim 5, wherein the diene-based synthetic rubber is a modified polybutadiene rubber having a nitrogen-containing functional group.
The tire according to claim 7, wherein the nitrogen-containing functional group is derived from hexamethyleneimine.
The tire according to claim 1, wherein a rubber composition obtained by blending 3 to 30 parts by mass of silica with 100 parts by mass of a rubber component is used for the tread rubber.
The tire according to claim 3, wherein a rubber composition comprising 0.1 to 10 parts by mass of polyethylene short fibers per 100 parts by mass of the rubber component is used for the tread rubber.
The tire according to any one of claims 1 to 10, wherein the tire is a heavy load studless tire.