JP2007176417A - Studless tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a studless tire making scratching effect and steering stability compatible at a high level, while maintaining wear resistance, and having excellent on-ice performance. <P>SOLUTION: This tire has a tread part constituted of a tread rubber layer to be a single layer or a multiple layer and foaming rubber layers formed in a part or all regions of a tread face of the tread rubber layer. In the tread face, many sipes are formed, and the regions are ones including at least shoulder parts of the sipes. Shore A hardness A of the foaming rubber composing the foaming rubber layers and Shore A hardness B of the tread rubber composing a layer in contact with the foaming rubber layers of the tread rubber layer are set to satisfy a formula A≤B. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a studless tire excellent in wear resistance and on-ice performance.

  In order to improve the scratching effect, which is one of the performances on ice of a studless tire, many sipes are arranged in the conventional block. However, when a sipe is inserted into the block, there is a problem that the block rigidity is lowered and the steering stability is deteriorated. Therefore, in order to improve the decrease in block rigidity, the shape of the block can be supported against the collapse of the block caused by the sipe, such as a wave shape sipe or a wedge-shaped sipe having a wedge-shaped pattern in the sipe depth direction. Sipe is adopted. However, the width of these sipes (that is, the gauge) is about 0.4 mm at the minimum, and the sipe width cannot be further reduced.

  Patent Document 1 has, as a rubber composition suitable for a traveling body such as a tire, which maintains mud adhesion prevention performance and durability, has independent or / and continuous bubbles mainly composed of a diene rubber, A rubber composition for preventing mud adhesion having an Asker C hardness of 20 to 60 ° C. after vulcanization, a breaking strength of 3.0 MPa or more, and a breaking elongation of 250% or more has been proposed.

  In Patent Document 2, for the purpose of providing a tire capable of improving the performance on ice and snow without impairing the handling stability on a dry road surface, the tread rubber has a mean fiber diameter of 1 to 100 μm and an average length of diene rubber. Is composed of a rubber composition in which 0.1 to 5 mm of water-soluble short fibers are dispersed, the water-soluble short fibers are oriented in the tread thickness direction, and the complex elastic modulus in the tread thickness direction measured at 25 ° C. of the tread rubber. Studless tires have been proposed in which the ratio E1 / E2 of E1 and the complex elastic modulus E2 in the tire circumferential direction is 1 to 4.

  In Patent Document 3, a tread surface land ratio is 10% or more and 40% or less as a motorcycle tire that exhibits stable performance for a long time and exhibits excellent grip properties when necessary. A motorcycle tire having a ratio of a height H of a tread portion to a half of a width W (H / (W / 2)) of 0.25 to 0.40, the tread portion being a base layer and the base layer A tire for motorcycles, the base layer comprising a solid rubber having a hardness of 72 degrees or more, and the surface layer comprising a foamed rubber containing closed cells having an average diameter of 10 μm to 100 μm Has been proposed.

However, in the methods of Patent Documents 1 to 3, it is difficult to improve the decrease in block rigidity due to the collapse of the block due to the sipe, and in particular the tire while ensuring the scratching effect on the ice and the steering stability to a satisfactory level. There is a problem that it is difficult to maintain the wear resistance.
JP 2000-62413 A JP 2001-315504 A JP 2004-50963 A

  An object of the present invention is to solve the above-mentioned problems, and to provide a studless tire having excellent on-ice performance with a highly compatible scratching effect and steering stability while maintaining wear resistance.

  The present invention is a studless tire having a tread portion comprising a tread rubber layer that is a single layer or a multi-layer, and a foamed rubber layer formed in a part or all of the tread surface of the tread rubber layer, A large number of sipes are formed on the tread surface, and this region includes at least a shoulder portion of the sipe, and JIS-A hardness A of the foam rubber constituting the foam rubber layer, and foaming of the tread rubber layer. The present invention relates to a studless tire in which a JIS-A hardness B of a tread rubber constituting a layer in contact with a rubber layer is set so as to satisfy Formula A ≦ B.

  The present invention also relates to a studless tire in which the average thickness of the foamed rubber layer is in the range of 0.5 to 2.0 mm.

  The present invention also relates to a studless tire having the JIS-A hardness A of 35 or more and 62 or less.

  The present invention also relates to a studless tire in which the sipe width of the above sipe is 0.4 mm or less.

  The present invention also relates to a studless tire in which the tread rubber layer includes a cap layer and a base layer, and the tread rubber layer includes a solid rubber.

  In the present invention, the JIS-A hardness A, the JIS-A hardness C of the cap rubber constituting the cap layer, and the JIS-A hardness D of the base rubber constituting the base layer are represented by the formula A ≦ C ≦ The present invention relates to a studless tire set to satisfy D.

  According to the present invention, by arranging a foam rubber layer on the tread surface and narrowing the sipe width, it is possible to obtain a studless tire that has excellent scratching effect and steering stability while maintaining wear resistance and provides excellent on-ice performance. It becomes possible.

  In the studless tire according to the present invention, a tread rubber layer that is a tread rubber layer formed on a surface of the tread rubber layer and a tread rubber layer laminated on the surface of the tread rubber layer is formed in the tread portion. A large number of sipes are formed, and the foamed rubber layer is formed in part or all of the tread surface including at least the shoulder portion of the sipes. Here, the sipe of the tread surface is provided in order to improve the scratching effect which is one of the performances on ice.

  In the present invention, the tread rubber layer can have a multilayer structure of a cap layer and a base layer. In this case, by adjusting the composition of the cap rubber that constitutes the cap layer and the base rubber that constitutes the base layer, the desired balance between the wear resistance of the tire and the grip performance and handling stability due to the scratching effect is desired. It can be appropriately controlled according to

  The tread rubber layer of the present invention is preferably made of solid rubber. When the tread rubber itself is foamed rubber, it is difficult to reduce the sipe width because it is necessary to consider the dimensional stability of the tread portion. It is also difficult to impart sufficient wear resistance to the tread portion. However, solid rubber is used for the tread rubber itself, and when the foam rubber layer is formed in the area including at least the shoulder portion of the sipe, the foam rubber is vulcanized at the time of tire manufacture, and after taking out from the mold, Furthermore, since expansion of the foam rubber occurs, the sipe width can be further narrowed by the foam rubber layer while ensuring the dimensional stability and wear resistance of the tread portion by the solid rubber. By narrowing the sipe width, the resistance to falling of the block becomes better, so that block rigidity is imparted and the steering stability of the tire is improved.

  When the tread rubber layer is composed of a cap layer and a base layer, both the cap rubber and the base rubber are preferably solid rubber.

  In the present invention, the JIS-A hardness A of the foam rubber and the JIS-A hardness B of the tread rubber constituting the layer in contact with the foam rubber layer are set so as to satisfy the relationship of A ≦ B. That is, in the present invention, a foamed rubber layer is formed in a region including at least a shoulder portion of a sipe, and a tread rubber having a JIS-A hardness equal to or higher than that of the foamed rubber is formed on the tread body. While the effect of reducing the sipe width by rubber is ensured, the effect of maintaining the wear resistance and dimensional stability of the tire by tread rubber is also obtained.

  In addition, in this specification, when a tread rubber layer is comprised from a cap layer and a base layer, JIS-A hardness B of said tread rubber is tread rubber of the layer which contact | connects a foamed rubber layer, ie, JIS of cap rubber. -A hardness shall be pointed out.

  When the tread rubber layer is composed of a cap layer and a base layer, the JIS-A hardness A of the foam rubber, the JIS-A hardness C of the cap rubber, and the JIS-A hardness D of the base rubber are expressed by the formula A ≦ It is preferable to set so as to satisfy C ≦ D. In this case, wear resistance, grip performance, and steering stability can be achieved at a higher level.

  Further, when the JIS-A hardness is set so as to satisfy the formula A <C <D, a rubber having a relatively high rigidity is used for the base layer, and a rubber having a lower rigidity than the base layer is used for the cap layer. It is possible to improve grip performance, handling stability, and ride comfort performance while maintaining wear resistance, and to easily control the physical properties of the tread part according to the desired tire performance Is preferable.

  In particular, when the cap rubber has a JIS-A hardness in the range of 35 to 62 and the base rubber has a JIS-A hardness in the range of 55 to 65, wear resistance, ride comfort, and handling stability. It is preferable at the point from which the tire which is excellent in is obtained.

  The average thickness of the foamed rubber layer formed in the present invention is preferably in the range of 0.5 to 2.0 mm. When the average thickness is 0.5 mm or more, the effect of narrowing the sipe width is obtained satisfactorily, and the steering stability of the resulting tire is favorable, and when it is 2.0 mm or less, It is preferable in that the shape change during foaming is small and the thickness of the foamed rubber layer can be easily controlled according to the desired sipe width. The average thickness of the foamed rubber layer is more preferably 1.0 mm or more, and more preferably 1.5 mm or less.

  The foam rubber layer preferably has a JIS-A hardness of 35 or more. When the JIS-A hardness is 35 or more, the foamed rubber layer has a sufficiently high rigidity, and the wear resistance of the tire is not impaired. The JIS-A hardness is more preferably 40 or more. On the other hand, the JIS-A hardness is preferably 62 or less, more preferably 55 or less. When the JIS-A hardness is 62 or less, the foamed rubber layer is not too hard and the grip performance is good.

  In addition, JIS-A hardness described in this specification is a value measured by a method based on JIS K6253 spring type (type A).

  As the shape of the sipe formed in the studless tire of the present invention, a corrugated shape, a wedge shape or the like can be preferably employed. These shapes are excellent in improving the grip performance while maintaining good tire block rigidity.

  In the studless tire of the present invention, the sipe width is preferably set to 0.4 mm or less. In this case, the steering stability can be satisfactorily obtained by ensuring the block rigidity that can withstand the collapse of the block. The sipe width is more preferably 0.3 mm or less.

  In addition, the dimension of each part of the studless tire prescribed | regulated in this specification is a dimension at the time of measuring with a tire single-piece unless there is special mention.

  As the foam rubber and tread rubber used in the present invention, a rubber composition prepared by kneading or the like using the compounding components described below can be used.

  The rubber components include natural rubber, polyisoprene rubber, emulsion-polymerized styrene-butadiene copolymer rubber, solution-polymerized styrene-butadiene copolymer rubber (styrene content 10 to 50 wt%, 1, bond amount 10 to 70%), high transformer , Styrene-butadiene copolymer rubber, low cis polybutadiene rubber, high cis polybutadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, solution polymerized styrene-butadiene-isoprene copolymer rubber, emulsion polymerized styrene-acrylonitrile- Preferred examples include butadiene copolymer rubber. In particular, natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber or the like is preferable.

  In addition, the rubber composition may preferably contain a reinforcing material such as silica, carbon black, short fiber, resin powder, inorganic powder, organic powder, talc, clay, and silicon rubber.

  Among these, silica can be mix | blended within the range of 5-70 mass parts with respect to 100 mass parts of a rubber component. Examples of commercially available silica include silica VN3 manufactured by Degussa.

  Moreover, carbon black can be mix | blended within the range of 5-70 mass parts with respect to 100 mass parts of a rubber component. Examples of commercially available carbon black include “N220” manufactured by Mitsubishi Chemical Corporation.

  Moreover, as a short fiber, acrylic fiber, nylon fiber, fluorine fiber, polyurethane fiber, alumina fiber, glass fiber, ceramic fiber, etc. are mix | blended in the range of 1-30 mass parts with respect to 100 mass parts of a rubber component, for example. be able to.

  In addition, as the resin powder, ionomer resin, AAS resin, ABS resin, fluorine resin, polyacetal resin, polyamide resin, polystyrene resin, etc., as inorganic powder, zinc compound, aluminum compound, copper compound, silicon compound, fluorine compound, etc. Plant cellulose powder etc. can be mix | blended as organic substance powder.

  In the rubber composition, a crosslinking agent, a vulcanization accelerator, a vulcanization aid, an activator, a plasticizer, an antiaging agent, a process oil, and the like can be blended as other compounding agents.

  As the crosslinking agent, an organic peroxide or a sulfur-based vulcanizing agent can be used, and a mixture thereof can also be suitably 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.

  As the vulcanization accelerator, sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, xanthate can be used. These mixtures can also be preferably used. Examples of the sulfenamide-based vulcanization accelerator include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-tert-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl. Sulfenamide compounds such as 2-benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and N, N-diisopropyl-2-benzothiazolesulfenamide can be used. . Thiazole vulcanization accelerators include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, cyclohexylamine salt, 2- ( Thiazole compounds such as 2,4-dinitrophenyl) mercaptobenzothiazole and 2- (2,6-diethyl-4-morpholinothio) benzothiazole can be used. Thiuram-based vulcanization accelerators include TMTD (tetramethylthiuram disulfide), tetraethylthiuram disulfide, TMTM (tetramethylthiuram monosulfide), dipentamethylene thiuram disulfide, dipentamethylene thiuram monosulfide, dipentamethylene thiuram tetrasulfide. Thiuram compounds such as sulfide, dipentamethylene thiuram hexasulfide, tetrabutyl thiuram disulfide, pentamethylene thiuram tetrasulfide and the like can be used. Moreover, as a thiourea type | system | group vulcanization accelerator, thiourea compounds, such as a thiacarbamide, diethyl thiourea, dibutyl thiourea, a trimethyl thiourea, a diortolyl thiourea, can be used. As the guanidine vulcanization accelerator, guanidine compounds such as diphenyl guanidine, DOTG (diortolyl guanidine), triphenyl guanidine, orthotolyl biguanide, diphenyl guanidine phthalate can be used. Examples of the dithiocarbamate vulcanization accelerator include sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium di-n-butyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc di-n-butyldithiocarbamate, Zinc diamyldithiocarbamate, zinc dibenzyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, zinc ethylphenyldithiocarbamate, pipecoline methylpentamethylenedithiocarbamate, zinc butylphenyldithiocarbamate, zinc dipropyldithiocarbamate, hexadecyl (or octadecyl) Zinc isopropyldithiocarbamate, piperidine pentamethylenedithiocarbamate, dimethyldithiocarbamate Vammin selenium, may be used diethyldithiocarbamate tellurium, dithiocarbamate based compounds such as diamyl dithiocarbamate cadmium. Aldehyde-amine or aldehyde-ammonia vulcanization accelerators include aldehyde-amine or aldehyde-ammonia, such as acetaldehyde-aniline reactant, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde-ammonia reactant. System compounds can be used. As the imidazoline vulcanization accelerator, an imidazoline compound such as 2-mercaptoimidazoline can be used. Further, as the xanthate vulcanization accelerator, xanthate compounds such as zinc dibutylxanthate, sodium isopropylxanthate, zinc isopropylxanthate, and zinc butylxanthate can be used.

  As the vulcanization aid, stearic acid, zinc white or the like can be used. As the activator, diethylene glycol, polyethylene glycol and the like can be used. As plasticizers, DMP (dimethyl phthalate), DEP (diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate), DOP (dioctyl phthalate), DINP (diisononyl phthalate), DIDP (phthalate) Diisodecyl acid), BBP (butylbenzyl phthalate), DLP (dilauryl phthalate), DCHP (dicyclohexyl phthalate), hydrophthalic anhydride ester, TCP (tricresyl phosphate), TEP (triethyl phosphate), TBP (tributyl phosphate), TOP (trioctyl phosphate), TCEP (trichloroethyl phosphate), TDCPP (trisdichloropropyl phosphate), TBXP (tosibutoxyethyl phosphate), TCPP (tris (β-chloropropyl) phosphate , TPP (triphenyl phosphate), octyl diphenyl phosphate, trisisopropylphenyl phosphate, DOA (dioctyl adipate), DINA (diisononyl adipate), DIDA (diisodecyl adipate), D610A (dialkyl adipate 610), BXA (dibutyldi) Glycol adipate), DOZ (di-2-ethylhexyl azelate), DBS (dibutyl sebacate), DOS (dioctyl sebacate), acetyl triethyl citrate, acetyl tributyl citrate, DBM (dibutyl maleate), DOM (maleic acid) -2-ethylhexyl), DBF (dibutyl fumarate), and the like can be used.

  As the foam rubber used in the present invention, a rubber composition in which a foaming agent is blended in addition to the above blending components can be used. Preferred examples of the foaming agent include azodicarbonamide, azobisisobutyronitrile, dinitrosopentamethylenetetramine, hydrazodicarbonamide, p-toluenesulfonylacetone hydrazone, and the like.

  In the studless tire of the present invention, when the foamed rubber layer is formed in the entire region of the tread portion in the tire width direction, for example, by simultaneously extruding the respective unvulcanized rubber compositions of the base rubber, the cap rubber and the foamed rubber. A tire tread member can be manufactured by a method of forming and vulcanizing a green tire after being laminated with other tire constituent materials.

  FIG. 1 is a cross-sectional view showing the right half of a studless tire according to the present invention, and FIGS. 2 and 3 are enlarged views illustrating a tread portion 2 in the studless tire 1 according to the present invention. As shown in FIG. 1, the studless tire 1 according to the present invention has a tread portion 2, a sidewall portion 3, and a bead portion 4. A bead core 5 is embedded in the bead portion 4. Then, a carcass 6 is disposed from one bead portion 4 to the other bead portion so that both ends of the bead core 5 are folded back and locked, and a belt layer 7 made of two plies is disposed outside the crown portion of the carcass. Is arranged. The tread portion 2 is composed of one or more cap layers 2A on the ground surface side and one or more base layers 2B on the side adjacent to the belt layer. A bead apex 8 extending in the sidewall direction from the upper end of the bead core 5 is disposed in a region surrounded by the carcass 6 and the folded portion thereof. In FIG. 1, the average thickness of the base layer is indicated by G1, and the average thickness of the cap layer is indicated by G2. The tread portion 2 is provided with a number of grooves 9 and a number of sipes 10.

  The average thickness G1 of the base layer 2B means the average thickness when the thickness changes from the tire center to the end as shown in FIGS. A foamed rubber layer 2C is formed on the surface of the cap layer 2A. The average thickness of the foamed rubber layer 2C is indicated by H. FIG. 2 shows a case where the foamed rubber layer 2C is formed on the entire surface of the tread in the tire width direction, and FIG. 3 shows a case where the foamed rubber layer 2C is formed only on a part of the tread. That is, in the present invention, as shown in FIGS. 2 and 3, the foamed rubber layer may be formed on the entire surface in the tire width direction or only on a part of the tread. What is necessary is just to be formed in the area | region containing a shoulder part. The rubber on the tread surface is worn early by running, but the rubber at the shoulder portion between the sipes remains for a long time. By providing the foamed rubber layer on the shoulder portion, the block rigidity is ensured over a long period of time, and good steering stability is imparted to the tire. The shape of the studless tire of the present invention is not limited to that shown in FIGS.

  The studless tire of the present invention can be employed as various tires such as passenger car tires, light truck tires, truck bus tires and the like.

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

<Production of studless tire>
The blending components shown in Table 1 were each kneaded at 150 ° C. for 5 minutes to prepare unvulcanized rubber compositions of base rubber, cap rubber and foam rubber. The obtained unvulcanized rubber composition was extruded in a three-layer structure to form a tread member, and vulcanized in combination with constituent materials at other parts of the tire to produce a studless tire of size 195 / 65R15 DS1. .

(Average thickness)
Each thickness of the base layer, the cap layer, and the foamed rubber layer was measured with a microscope (× 50) by a cross section of a 1 cm ² sample cut out using a cutter.

(Rubber hardness)
The JIS-A hardness of each of the base layer, cap layer and foamed rubber layer was evaluated by cutting out a block of about 1 cm ³ according to JIS-K6253 and measuring with a hardness meter.

<Performance evaluation>
The studless tire produced above was mounted on an actual vehicle (Toyota Mark II), a running test was conducted on an ice test course, and the following was evaluated.

(Brake performance on ice)
Measure the braking distance from 40km / h to stop,
Braking performance = (braking distance of conventional example 1) / (braking distance of each example and each comparative example) × 100
Thus, the index was displayed with the conventional example 1 as 100. The larger the value, the better the braking performance. The results are shown in Table 2.

(Operation stability on ice)
A feeling test was conducted with two test drivers, and the grip performance and handling performance were evaluated according to the following criteria, and the conventional example 1 was displayed as an index, each 6.0. The results are shown in Table 2.
8.0 points: Feeling is very good compared to Conventional Example 1.
7.0 points: Feeling is better than Conventional Example 1.
6.5 points: Feeling is slightly better than Conventional Example 1.
6.0 points: Feeling is equivalent to Conventional Example 1.
5.5 points: Although the feeling is slightly inferior to that of Conventional Example 1, it is within the allowable range.
5.0 points: Feeling is inferior to Conventional Example 1.
4.0 points: Feeling is very inferior to that of Conventional Example 1.

(Abrasion resistance)
Run at 800 km under the general running speed condition of 80 km / h or less, visually observe the appearance of the tire after running, pass the one where no occurrence of abrasion is recognized, and the one where occurrence of abrasion is recognized as a poorly worn appearance. It was rejected as an unacceptable level. The results are shown in Table 2.

Note 1: NR is the product name “KR7” made in Indonesia.
Note 2: BR is a trade name “BR150B” manufactured by Ube Industries.
Note 3: Carbon black is “N220” manufactured by Mitsubishi Chemical Corporation.
Note 4: Oil is a trade name “Diana Process AH40” manufactured by Idemitsu Kosan Co., Ltd.
Note 5: The vulcanizing agent is trade name “sulfur” manufactured by Tsurumi Chemical Co., Ltd.
Note 6: The vulcanization accelerator is the trade name “Noxeller NS” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Note 7: The foaming agent is “Cellular GX” manufactured by Eiwa Kasei.
Note 8: The anti-aging agent is a trade name “Ozonon 6C” manufactured by Seiko Chemical Co., Ltd.
Note 9: Wax is the trade name “Sannok N” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Note 10: Stearic acid is a product name “Kiri” manufactured by NOF Corporation.
Note 11: Zinc Hana is a trade name “Ginbae R” manufactured by Toho Zinc Co., Ltd.

  From the results shown in Table 2, in Comparative Example 1 in which rubber harder than the cap layer was formed as the foamed rubber layer, although the on-ice grip performance was good due to the good block rigidity, the on-ice grip performance was not sufficient. Further, in Comparative Examples 2 and 3 in which no sipes are provided, the foamed rubber layer has a relatively thin foam thickness of 0.4 mm. In Comparative Example 2, the braking performance on ice, the grip performance on ice, and the handling performance on ice are not sufficient. In Comparative Example 3 having a relatively thick thickness of 2.2 mm, braking performance on ice and grip performance on ice are good, but handling performance on ice and wear resistance are not sufficient. On the other hand, in Examples 1 to 4, by providing a foam rubber layer that is equal to or lower in hardness than the cap layer, the braking performance on ice, the grip performance on ice, the handling performance on ice and the wear resistance are all good. I know that there is. In particular, in Example 2, the thickness of the foam rubber layer is 1 mm within the range of 0.5 to 2 mm, the rubber hardness is lower in the foam rubber layer than the cap layer, and the wear resistance is maintained well. On the other hand, braking performance on ice, grip performance on ice, and handling performance on ice are all good.

  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.

  In the studless tire of the present invention, it is possible to narrow the sipe width while maintaining wear resistance, and therefore, grip performance and steering stability on ice are particularly good. The studless tire of the present invention is used for passenger cars. It can be suitably applied as various tires for light trucks, truck buses and the like.

It is sectional drawing which shows the right half of the studless tire which concerns on this invention. It is a figure expanding and explaining tread part 2 in studless tire 1 concerning the present invention. It is a figure expanding and explaining tread part 2 in studless tire 1 concerning the present invention.

Explanation of symbols

  1 Studless tire, 2 tread part, 2A cap layer, 2B base layer, 2C foam rubber layer, 3 side wall part, 4 bead part, 5 bead core, 6 carcass, 7 belt layer, 8 bead apex, 9 groove, 10 sipe.

Claims (6)

A studless tire having a tread portion composed of a tread rubber layer that is a single layer or a multi-layer, and a foam rubber layer formed in a part or all of the tread surface of the tread rubber layer,
A large number of sipes are formed on the tread surface,
The region is a region including at least a shoulder portion of the sipe, and
The JIS-A hardness A of the foam rubber constituting the foam rubber layer and the JIS-A hardness B of the tread rubber constituting the layer in contact with the foam rubber layer among the tread rubber layers satisfy the formula A ≦ B. Studless tire set to.   The studless tire according to claim 1, wherein an average thickness of the foamed rubber layer is in a range of 0.5 to 2.0 mm.   The studless tire according to claim 1, wherein the JIS-A hardness A is 35 or more and 62 or less.   The studless tire according to claim 1, wherein the sipe width of the sipe is 0.4 mm or less.   The studless tire according to claim 1, wherein the tread rubber layer includes a cap layer and a base layer, and the cap layer and the base layer include a solid rubber.   The JIS-A hardness A, the JIS-A hardness C of the cap rubber constituting the cap layer, and the JIS-A hardness D of the base rubber constituting the base layer satisfy the formula A ≦ C ≦ D. The studless tire according to claim 5, wherein

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