JP2007176267A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire simultaneously satisfying on-ice gripping performance and on-ice steering stability. <P>SOLUTION: This pneumatic tire is provided with a side wall part constituted of two layers or more including at least inner layer and outer layer. The outer layer forms the surface of the side wall, and the inner layer has an exposed part to the surface of the tire. Rubber hardness of the inner layer is made lower than that of the outer layer. It is desirable that JIS-A hardness of the inner layer is in the range of 35 to 62. The side wall part is constituted of an inner layer and an outer layer. It is desirable that a layer thickness ratio at a tire maximum width position in a state in which the tire is mounted on a normal rim and stipulated internal pressure is filled is in the range of the outer layer/inner layer =90/10 to 20/80. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pneumatic tire having a sidewall portion composed of two or more layers and highly compatible with on-ice grip performance and on-ice handling stability.

  In recent years, studless tires have been made to reduce the hardness of tread rubber for the purpose of improving the grip performance on ice. However, when the hardness of the tread rubber is excessively lowered, the steering stability may be lowered. In the so-called SOT structure in which the sidewall rubber extends to at least a part of the tread portion, there is a case where a rubber flow is generated in which the sidewall rubber flows toward the tread when the tire is vulcanized. In particular, when the side wall is a single layer, a phenomenon in which the grip performance on ice is deteriorated may occur when the side wall rubber, which is usually harder than the tread rubber, flows on the tread surface.

In view of this, a method has been proposed in which the side wall rubber is composed of two layers, an inner layer and an outer layer, and even if a rubber flow occurs in the inner layer, the steering stability can be maintained by the presence of the outer layer. In Patent Document 1, for the purpose of providing a studless tire that reduces the amount of uneven wear at the initial stage of wear and provides a high level of tire performance when running on icy and snowy roads, an inner rubber layer mainly composed of a tread that forms a block pattern and a thickness thereof are disclosed. is composed of two layers of an outer rubber layer made of the skin of 0.5 mm to 3 mm, the inner rubber layer is 50% modulus consisted rubber ^{10kgf / cm 2 ~25kgf / cm 2} , 50% modulus of the outer rubber layer Has proposed a studless tire made of rubber that is 1.2 times or more of the inner rubber layer.

  In Patent Document 2, for the purpose of providing a studless tire capable of improving wear resistance performance and handling stability at the start of use, a tread rubber disposed on the tread portion is disposed on the tread surface with a small thickness. And a base rubber layer other than the surface rubber layer, the base rubber layer is made of a soft rubber layer suitable for running on ice and snow roads, and the surface rubber layer is made of soft rubber of the base rubber layer. Is made of a hard rubber having a large JIS A hardness, the thickness h of the surface rubber layer is 0.2 mm or more and less than 1.0 mm, and the JIS A hardness (Ha) of the hard rubber is greater than 50 degrees. A studless tire characterized by being smaller than 65 degrees has been proposed.

  In Patent Document 3, for the purpose of obtaining a pneumatic tire in which the rolling resistance of the entire tire is reduced, a low heat-generating rubber having a loss factor smaller than that of the tread rubber is used as a sidewall rubber, and the regular rim is used. In the meridional section of the tire in a reference low internal pressure state in which a rim is assembled and an internal pressure of 10 kPa is applied, the maximum width point at which the length W between the points where the tire axial line intersects the tire outer surface in the sidewall portion is the maximum value Wb The sidewall upper region radially outward from B is formed using a substantially arc-shaped and / or substantially straight contour line whose outer surface is convex outward, and the sidewall upper region has a low heat generation property. In the range made of rubber, the contour line is characterized in that it has a protruding area that forms an outwardly convex bent part for facilitating the bending of the sidewall part. The pneumatic tire has been proposed.

However, the tires proposed in Patent Documents 1 to 3 cannot be said to be at a satisfactory level in terms of achieving both on-ice grip performance and on-ice handling stability.
Japanese Unexamined Patent Publication No. 7-117411 JP-A-11-278015 JP 2003-136918 A

  An object of the present invention is to solve the above-mentioned problems and to provide a pneumatic tire that satisfies the on-ice grip performance and the on-ice handling stability at the same time.

  The present invention is a pneumatic tire provided with a sidewall portion comprising at least two layers including at least an inner layer and an outer layer, the outer layer forming a sidewall surface, and the inner layer having an exposed portion on the tire surface. In addition, the present invention relates to a pneumatic tire in which the rubber hardness of the inner layer is lower than the rubber hardness of the outer layer.

  The present invention also relates to a pneumatic tire in which the inner layer has a JIS-A hardness of 35 to 62.

  In the present invention, the layer thickness ratio at the tire maximum width position in a state where the sidewall portion is composed of an inner layer and an outer layer and is mounted on a regular rim and filled with a specified internal pressure is an outer layer / inner layer = 90 / 10-20 / The present invention relates to a pneumatic tire in the range of 80.

  The present invention also relates to a pneumatic tire in which a tread portion including a cap layer, a base layer, and a wing portion is provided as a tread portion.

  The present invention also relates to a pneumatic tire in which short fibers are contained in the inner layer.

  According to the present invention, in the sidewall portion including two or more layers including the inner layer and the outer layer, a part of the inner layer is exposed to the tire surface, and the rubber hardness of the inner layer is set lower than the rubber hardness of the outer layer. As a result, it is possible to ensure steering stability due to the contribution of the high-rigidity outer layer and to improve on-ice grip performance due to the contribution of the low-rigidity inner layer. Thereby, it is possible to obtain a pneumatic tire with good on-ice grip performance and on-ice handling stability.

  The sidewall portion provided in the pneumatic tire of the present invention includes at least an inner layer and an outer layer, the outer layer forms a sidewall surface, the inner layer has an exposed portion on the tire surface, and the inner layer has a rubber hardness. It is made lower than the rubber hardness of the outer layer. FIG. 1 is a diagram illustrating the right half of a cross-sectional view of a pneumatic tire according to the present invention, and FIGS. 2 and 3 are enlarged cross-sectional views showing examples of shoulder portions of the pneumatic tire according to the present invention. . The pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends thereof, and a bead portion 4 positioned at an inner end of each sidewall portion 3. A carcass 5 is bridged between the bead portions 4 and 4, and a belt layer 6 having a tagging effect is disposed on the outer side in the radial direction of the carcass 5.

  The carcass 5 is formed of one or more carcass plies in which the carcass cord is arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator. The carcass ply is connected to the bead portion from the tread portion 2 through the sidewall portion 3. 4 around the bead core 7 is folded back from the inner side to the outer side in the tire axial direction and is locked by the turned-up portion 5a. A bead apex 8 extending in the sidewall direction from the upper end of the bead core 7 is disposed in a region surrounded by the carcass 5 and the folded portion 5a. The belt layer 6 includes two or more belt plies in which belt cords are arranged at an angle of, for example, 45 ° or less with respect to the tire equator, and the belt cords are stacked in different directions so that the belt cords cross each other. . Further, a band layer (not shown) may be provided outside the belt layer 6. At this time, the band layer is formed by a continuous ply spirally wound with a low modulus organic fiber cord substantially parallel to the tire equator.

  In the present invention, the sidewall portion 3 has a structure of two or more layers having at least an inner layer 3a and an outer layer 3b. As shown in FIGS. 1-3, the inner layer 3a has an exposed part in the shoulder part of a tire. In the pneumatic tire of the present invention, the inner layer 3a has an exposed portion on the tire surface, preferably a portion of the tire surface that is a contact surface with the road surface, and the outer layer 3b has a relatively high rigidity necessary for the sidewall. The inner layer 3a has a lower hardness than that of the outer layer 3b, and has a configuration capable of imparting on-ice grip performance to the tire. As a result, a pneumatic tire that satisfies the on-ice grip performance and the on-ice handling stability at the same time can be obtained. In the present invention, as shown in FIG. 3, a wing portion 9 may be provided between the base layer 2b and the inner layer 3a. The structure of the pneumatic tire according to the present invention is not limited to that described above.

  The sidewall portion in the pneumatic tire of the present invention may have a two-layer structure of an inner layer and an outer layer, but within a range in which the object of the present invention can be achieved, the inner layer is further inside and between the inner layer and the outer layer. Another layer may be interposed in at least one of them.

  In the present invention, the JIS-A hardness of the inner layer is preferably in the range of 35 to 62. When the JIS-A hardness of the inner layer is 35 or more, the wear resistance is good, and when it is 62 or less, the effect of improving the on-ice grip performance is good. The inner layer has a JIS-A hardness of 55 or less, more preferably 50 or less. In addition, all values of JIS-A hardness described in this specification are based on ISO-7619 in a tire maximum width position in a state where a pneumatic tire is mounted on a regular rim and filled with a specified internal pressure. It is a value measured at 25 ° C.

  In the present invention, short fibers may be included in the inner layer of the sidewall portion. In this case, a better grip performance on ice is imparted to the pneumatic tire. Here, the short fiber means an organic or inorganic fiber finely cut into a predetermined shape. Specifically, acrylic fiber, acetate fiber, copper ammonia fiber, nylon, pulp, viscose rayon, vinylidene fiber, Vinylon, fluorine fiber, promix fiber, non-woven fabric, polyacetal fiber, polyurethane fiber, polyester fiber, polyethylene fiber, polyvinyl chloride fiber, polyclar fiber, polynosic fiber, polypropylene fiber, alumina fiber, glass fiber, ceramic fiber, silicon carbide fiber, A cut material such as carbon fiber is preferably exemplified. The average diameter of the short fibers is particularly preferably in the range of 10 to 100 μm, and the average length is particularly preferably in the range of 200 to 5000 μm.

  The short fiber content is preferably in the range of 1 to 30 parts by mass with respect to 100 parts by mass of the rubber component of the inner layer. When the content is 1 part by mass or more, the effect of improving the grip performance on ice is good, and when the content is 30 parts by mass or less, a decrease in durability due to poor dispersion of short fibers is prevented well. The content of the short fiber is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, and more preferably 25 parts by mass or less with respect to 100 parts by mass of the rubber component.

  In the pneumatic tire of the present invention, the ratio of the thickness of the inner layer to the total thickness of the sidewall portion at the tire maximum width position when the tire is mounted on the rim and filled with the specified internal pressure is in the range of 5 to 90%. It is preferable to be within. When the ratio is 5% or more, the effect of improving the grip performance on ice at the exposed portion of the tire surface is good, and when it is 90% or less, the thickness of the outer layer can be sufficiently secured, and the steering stability on ice is good. . The ratio is more preferably 10% or more, more preferably 85% or less, and still more preferably 80% or less. In particular, the sidewall portion is composed of two layers, an outer layer and an inner layer, and the ratio of the layer thicknesses is in the range of outer layer / inner layer = 90 / 10-20 / 80, and further in the range of 85 / 15-25 / 75. It is preferable.

  In the pneumatic tire of the present invention, the tread portion may have a single-layer structure. For example, as shown in FIGS. 1 to 3, the cap layer 2 a forming the tread surface, and the inner side in the tire radial direction from the cap layer The base layer 2b provided on the substrate may have a multilayer structure including two or more layers. When the tread portion has, for example, a two-layer structure of a cap layer and a base layer, it is preferable to adjust the rubber hardness of both layers so that the rubber hardness of the cap layer is smaller than the rubber hardness of the base layer. The cap layer provides good on-ice grip performance, and the base layer provides good steering stability, thereby further improving the on-ice performance of the tire. It is also preferable that the cap layer is designed to have a JIS-A hardness of 40 to 65 and a base layer of JIS-A hardness of 50 to 65.

  In the present invention, it is preferable that the rubber hardness of the inner layer of the sidewall portion is lower than the rubber hardness of the cap layer of the tread portion. In this case, by setting the rubber hardness of the cap layer within a range where the wear resistance can be secured while maintaining the grip performance on ice, the rubber hardness of the inner layer of the sidewall portion is set lower than that of the cap layer. For example, better grip performance on ice can be imparted by the contribution of the inner layer while maintaining the basic performance of the tire such as wear resistance. Specifically, a combination in which the JIS-A hardness of the cap layer is in the range of 40 to 65 and the JIS-A hardness of the inner layer is in the range of 35 to 50 can be preferably exemplified.

  The following components may be appropriately blended in the rubber composition constituting the sidewall portion and the tread portion of the pneumatic tire of the present invention. First, the rubber component is preferably natural rubber (NR) and / or diene synthetic rubber. Diene-based synthetic rubbers include styrene-butadiene rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR). Butyl rubber (IIR) and the like, and rubber components containing one or more of these are preferred. The ethylene-propylene-diene rubber (EPDM) is an ethylene-propylene rubber (EPM) containing a third diene component. Examples of the third diene component include non-conjugated dienes having 5 to 20 carbon atoms such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, and 2,5-dimethyl-1,5. -Hexadiene and 1,4-octadiene, cyclic dienes such as 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene, 2-methallyl-5 Preferred examples include alkenyl norbornene such as -norbornene and 2-isopropenyl-5-norbornene. In particular, dicyclopentadiene, 5-ethylidene-2-norbornene and the like can be preferably used.

  As a filler, for example, silica can be blended in an amount of 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the rubber component. As the silica, those generally used for general-purpose rubber can be used, and examples thereof include dry method white carbon, wet method white carbon and colloidal silica used as a reinforcing material. Among these, wet method white carbon mainly containing hydrous silicic acid is preferable. When the compounding amount of silica is 5 parts by mass or more, the tire composition has good wear resistance by sufficiently obtaining a reinforcing effect on the rubber composition, and when it is 100 parts by mass or less, the rubber composition is not yet manufactured. It is possible to prevent deterioration in processability and excessive increase in cost due to an increase in viscosity of the vulcanized rubber composition.

Nitrogen adsorption specific surface area (BET method) of silica used in the above, for example 50 to 300 m ² / g, it is preferably further in the range of 100 to 200 m ² / g. When the nitrogen adsorption specific surface area of silica is 50 m ² / g or more, the tire has good wear resistance due to a sufficient reinforcing effect on the rubber composition. On the other hand, when the nitrogen adsorption specific surface area is 300 m ² / g or less, the processability of the rubber composition is good and the steering stability is also good. Here, the nitrogen adsorption specific surface area is a value measured by the BET method according to ASTM D3037-81.

  When silica is blended in the rubber composition, it is preferable to blend a silane coupling agent, preferably a sulfur-containing silane coupling agent, for example, at 1% by mass or more and 20% by mass or less with respect to the silica mass. The abrasion resistance and steering stability of the tire can be improved by blending the silane coupling agent. When the blending amount of the silane coupling agent is 1% by mass or more with respect to the silica mass, the abrasion resistance and steering stability. The improvement effect of can be favorably obtained. Moreover, when the compounding quantity of a silane coupling agent is 20 mass% or less with respect to the silica mass, there is little risk that the rubber | gum kneading | mixing and the burning (scorch) in an extrusion process will arise. As sulfur-containing silane coupling agents, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazole tetrasulfide, triethoxysilylpropyl-methacrylate-monosulfide, dimethoxymethyl Examples include silylpropyl-N, N-dimethylthiocarbamoyl-tetrasulfide, bis- [3- (triethoxysilyl) -propyl] tetrasulfide, 3-mercaptopropyltrimethoxysilane and the like.

  Other silane coupling agents include vinyltrichlorosilane, vinyltris (2-methoxyethoxy) silane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ- (2-aminoethyl) Aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and the like can be used.

  In the present invention, other coupling agents such as aluminate coupling agents and titanium coupling agents can be used alone or in combination with a silane coupling agent depending on the application.

  In addition, the rubber composition constituting the sidewall portion and the tread portion is provided with a filler such as carbon black, clay, alumina, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium oxide, and titanium oxide. It can be used alone or in combination of two or more.

Here, the carbon black is preferably blended in an amount of 10 to 150 parts by mass with respect to 100 parts by mass of the rubber component. Here, the physical properties of carbon black are such that the nitrogen adsorption specific surface area (BET method) is in the range of 70 to 300 m ² / g, the DBP oil absorption is in the range of 5 to 300 ml / 100 g, and the iodine adsorption is in the range of 146 to 152 mg / g. The inner one is preferable in terms of the reinforcing effect on the rubber composition.

  In the present invention, the effect of improving the steering stability in the sidewall portion can be ensured by the contribution of the outer layer, and in this case, the inner layer does not necessarily require high rigidity. Therefore, it is possible to further improve the grip performance on ice by containing foamed rubber or the like in the inner layer. Examples of the foamed rubber include rubber foamed using a foaming agent such as N, N'-dinitrosopentamethylenetetramine, azodicarbonamide, 4,4'-oxybis (benzenesulfonylhydrazide). Among these, as a commercial item of N, N′-dinitrosopentamethylenetetramine, for example, “Cellular GX” manufactured by Eiwa Kasei Co., Ltd. may be mentioned. When foam rubber is contained in the inner layer, the inner layer may be entirely formed of foam rubber, or the inner layer may be formed of a solid rubber phase and a foam rubber phase. Note that foamed rubber may be applied to each layer of the other sidewall portion or tread portion.

  In addition to the above, a vulcanizing agent, a vulcanization accelerator, a softening agent, a plasticizer, an antiaging agent, an anti-scorch agent, and the like can be added to the rubber composition constituting the sidewall portion and the tread portion. is there.

  As the vulcanizing agent, an organic peroxide or a sulfur vulcanizing agent can be used. Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2, 5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne- 3 or 1,3-bis (t-butylperoxypropyl) benzene, di-t-butylperoxy-diisopropylbenzene, t-butylperoxybenzene, 2,4-dichlorobenzoyl peroxide, 1,1-di- t-butylperoxy-3,3,5-trimethylsiloxane, n-butyl-4,4 And the like can be used di -t- butyl peroxy valerate. Of these, dicumyl peroxide, t-butylperoxybenzene and di-t-butylperoxy-diisopropylbenzene are preferred. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example. Of these, sulfur is preferred.

  Vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Those containing at least one of them can be used.

  Examples of the sulfenamide system include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (Nt-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl-2- Examples thereof include sulfenamide compounds such as benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and N, N-diisopropyl-2-benzothiazolesulfenamide.

  Examples of the thiazole type include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, cyclohexylamine salt, 2- (2,4-dinitro). Phenyl) mercaptobenzothiazole, 2- (2,6-diethyl-4-morpholinothio) benzothiazole and the like.

  Examples of thiurams include TMTD (tetramethyl thiuram disulfide), tetraethyl thiuram disulfide, tetramethyl thiuram monosulfide, dipentamethylene thiuram disulfide, dipentamethylene thiuram monosulfide, dipentamethylene thiuram tetrasulfide, dipentamethylene thiuram hexasulfide. , Tetrabutyl thiuram disulfide, pentamethylene thiuram tetrasulfide and the like.

  Examples of thiourea compounds include thiourea compounds such as thiacarbamide, diethyl thiourea, dibutyl thiourea, trimethyl thiourea, and diortolyl thiourea.

  Examples of guanidine compounds include guanidine compounds such as diphenyl guanidine, diortolyl guanidine, triphenyl guanidine, orthotolyl biguanide, and diphenyl guanidine phthalate.

  Examples of dithiocarbamate include zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc diamyldithiocarbamate, zinc dipropyldithiocarbamate , Complex salt of zinc pentamethylenedithiocarbamate and piperidine, zinc hexadecyl (or octadecyl) isopropyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate, piperidine pentamethylenedithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, diamyl Di, such as cadmium dithiocarbamate Such Okarubamin acid compounds.

  Examples of the aldehyde-amine system or aldehyde-ammonia system include acetaldehyde-aniline reaction product, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde-ammonia reaction product, and the like.

  As the anti-aging agent, amine-based, phenol-based, and imidazole-based compounds, carbamic acid metal salts, waxes, and the like can be appropriately selected and used.

  In the present invention, a softener may be used in combination in order to further improve kneading processability. Softeners include process oil, lubricating oil, paraffin, liquid paraffin, petroleum asphalt, petroleum jelly such as petroleum jelly, fatty oil softener such as castor oil, linseed oil, rapeseed oil, coconut oil, tall oil, , Waxes such as beeswax, carnauba wax and lanolin, and fatty acids such as linoleic acid, palmitic acid, stearic acid and lauric acid.

  As plasticizers, DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl phthalate), DIDP (phthalate) Acid diisodecyl), BBP (butyl benzyl phthalate), DLP (dilauryl phthalate), DCHP (dicyclohexyl phthalate), hydrophthalic anhydride, DOZ (di-2-ethylhexyl azelate), DBS (dibutyl sebacate), DOS (Dioctyl sebacate), acetyl triethyl citrate, acetyl tributyl citrate, DBM (dibutyl maleate), DOM (2-ethylhexyl maleate), DBF (dibutyl fumarate) and the like.

  Further, as a scorch inhibitor for preventing or delaying scorch, for example, organic acids such as phthalic anhydride, salicylic acid and benzoic acid, nitroso compounds such as N-nitrosodiphenylamine, N-cyclohexylthiophthalimide and the like can be used. .

  The pneumatic tire of the present invention is obtained by vulcanizing and molding an unvulcanized rubber composition obtained by kneading and molding the above-described blended components to the sidewall portion and tread portion of the tire. be able to. The pneumatic tire of the present invention can be preferably applied to various vehicles such as passenger cars, trucks, buses, and heavy machinery.

[Example]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

  Of the blending components shown in Table 1, the components excluding sulfur and the vulcanization accelerator were kneaded at about 150 ° C. for 5 minutes using a banbury, and further added with sulfur and the vulcanization accelerator and about 80 using a biaxial open roll. A rubber composition was obtained by kneading at 5 ° C. for 5 minutes. A rubber sheet is produced using the rubber composition, molded as a tread and a sidewall of a tire, vulcanized under the conditions of 170 ° C., 15 minutes, 25 kgf (245.16625N), and a size of 195 / 65R15 DS1 Test tires were prepared. The layer structure of the sidewall portion in the conventional example, the example and the comparative example is as shown in Table 2. The tread portion has the same configuration having a two-layer structure of the cap layer and the base layer in all conventional examples, examples, and comparative examples, and all the conventional examples, examples, and comparative examples also in the outer layer of the sidewall portion. The same configuration was used. The thicknesses of the layers constituting the sidewall portion and the tread portion are as shown in Table 1. The thickness of each layer is a value measured at the tire maximum width position in a state where the tire is mounted on a regular rim and filled with a specified internal pressure.

(JIS-A hardness)
The JIS-A hardness of each layer of the tread part and the sidewall part shown in Table 1 was measured according to JIS 6253. The results are shown in Table 1.

(Brake performance on ice)
The test tire produced above is mounted on the Toyota Mark II, and the braking distance from 40 km / h to stopping is measured on the ice test course. The braking performance on ice in each of the conventional examples, examples and comparative examples is as follows. The formula of
On-ice braking performance = (braking distance of conventional example 1) / (braking distance of each example or each comparative example) × 100
Accordingly, the braking performance on ice of Conventional Example 1 was set as 100 and displayed as an index. The larger the value, the better the braking performance on ice. The results are shown in Table 2.

(sensory evaluation)
The test tires produced above were mounted on the Toyota Mark II, run at 40-100 km / h on an ice test course, and sensory evaluation was performed for each of grip properties and handling properties by a feeling test. The evaluation represents the average value of the two drivers based on the following criteria for each feeling of grip properties and handling properties based on 6.0 points. The larger the value, the better the grip or handling. The results are shown in Table 2.
8.0 points: Very good compared to Conventional Example 1.
7.0 points: Good compared to Conventional Example 1.
6.5 points: Slightly better than Conventional Example 1.
6.0 points: equivalent to Conventional Example 1.
5.5 points: Slightly inferior to Conventional Example 1.
5.0 points: Inferior to Conventional Example 1.
4.0 points: Very inferior to Conventional Example 1.

(Abrasion characteristics)
The actual tire wear test was carried out by attaching the test tire produced above to the Toyota Mark II and comparing the standard tire and the test tire produced above on the same vehicle. The appearance of the tire is visually checked to evaluate the wear appearance, and those that do not show uneven wear, early wear, or poor appearance such as abrasion, for example, are good. At least one of these wear appearances What was recognized was evaluated as defective. The results are shown in Table 2.

Note 1: NR is “RSS # 3” made in Thailand.
Note 2: BR is “BR150B” manufactured by Ube Industries.
Note 3: Carbon black ISAF is “N220” manufactured by Mitsubishi Chemical Corporation.
Note 4: Carbon black FEF is “N550” manufactured by Mitsubishi Chemical Corporation.
Note 5: The oil is “Diana Process AH40” manufactured by Idemitsu Kosan Co., Ltd.
Note 6: Anti-aging agent is “Ozonon 6C” manufactured by Seiko Chemical Co., Ltd.
Note 7: Wax is “Sannokk Wax” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Note 8: Stearic acid is “paulownia” manufactured by NOF Corporation.
Note 9: Zinc oxide is “Ginbae R” manufactured by Toho Zinc Co., Ltd.
Note 10: Sulfur is manufactured by Tsurumi Chemical.
Note 11: The vulcanization accelerator is “Noxeller NS” (Nt-butyl 2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Note 12: Glass fiber is glass fiber (diameter 15 μm) manufactured by Nippon Sheet Glass Co., Ltd.

  In Comparative Example 1 in which the rubber hardness of the inner layer of the sidewall portion is larger than that of the outer layer, the grip performance is not sufficient, and the braking performance on ice, grip performance, handling performance and wear resistance are not satisfied at the same time. In Examples 1 to 3, inner layers 1 to 3 having a rubber hardness smaller than that of the outer layer are blended as the inner layer of the sidewall portion, and the grip performance is not significantly impaired on braking performance on ice, handling properties and wear resistance. Has been improved. That is, in Examples 1 to 3, it can be seen that the grip performance on ice and the steering stability on ice are satisfied at the same time.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  According to the present invention, a pneumatic tire satisfying both on-ice grip performance and on-ice steering stability can be obtained, and the pneumatic tire is suitable as a tire for various vehicles such as passenger cars, trucks, buses, and heavy machinery. Can be applied to.

It is the figure which illustrated the right half of the sectional view of the pneumatic tire concerning the present invention. It is an expanded sectional view showing an example of a shoulder part of a pneumatic tire concerning the present invention. It is an expanded sectional view showing an example of a shoulder part of a pneumatic tire concerning the present invention.

Explanation of symbols

  1 pneumatic tire, 2 tread part, 2a cap layer, 2b base layer, 3 side wall part, 3a inner layer, 3b outer layer, 4 bead part, 5 carcass, 5a folded part, 6 belt layer, 7 bead core, 8 bead apex, 9 Wing club.

Claims (5)

A pneumatic tire provided with a sidewall portion comprising at least two layers including at least an inner layer and an outer layer,
The outer layer forms a sidewall surface, and the inner layer has an exposed portion on the tire surface;
A pneumatic tire in which the rubber hardness of the inner layer is lower than the rubber hardness of the outer layer.   The pneumatic tire according to claim 1, wherein the inner layer has a JIS-A hardness of 35 to 62.   The side wall portion is composed of the inner layer and the outer layer, and the layer thickness ratio at the maximum tire width position when the tire is mounted on a normal rim and filled with a specified internal pressure is the outer layer / the inner layer = 90 / 10-80 / 20. The pneumatic tire according to claim 1, which is within a range.   The pneumatic tire according to claim 1, wherein a tread portion including a cap layer, a base layer, and a wing portion is provided as the tread portion.   The pneumatic tire according to claim 1, wherein short fibers are contained in the inner layer.

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