JPH11181152A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pneumatic tire improved in braking, driving, and operating performances during running on an icy road by using a rubber compsn. contg. a metal dithiophosphate for a solid rubber part of a foamed rubbr. SOLUTION: This pneumatic tire has a bilayered tread section comprising a cap rubber layer installed at the outside of the radial direction and a base rubber layer installed at the inside of the radial direction, and the cap rubber layer has a foamed rubber layer which has closed cells and a foaming ratio of 5-50% and is attached at least to the side being brought into contact with a road surface. The solid phase part of the foamed rubber is formed from a rubber compsn. prepd. by compounding 100 pts.wt. rubber component comprising 20-70 wt.% natural rubber and 30-80 wt.% butadiene rubber with 0.1-5.0 pts.wt. metal dithiophosphate of the formula (wherein R<1> and R<2> are each a linear, branched, or cyclic alkyl group or a 6-10C aryl; M<1> is Zn, Sb, Fe, or Cu; and (n) is the valence of a metal bonded).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly, to a braking performance when traveling on icy and snowy roads.
The present invention relates to a pneumatic tire having excellent driving performance and steering performance.

[0002]

2. Description of the Related Art With the regulation of spiked tires, there is a strong demand for studless tires having excellent driving performance, braking performance and maneuvering performance (hereinafter simply referred to as "ice and snow performance") when traveling on icy and snowy roads. Many studies have been made focusing on patterns, tread rubber members, and the like.

[0003] As an example of a tire in which ice and snow performance is improved by a tire tread rubber member, a so-called foam using a rubber composition mainly comprising a natural rubber / butadiene rubber and carbon black provided on a tread rubber is provided. A tire (JP-A-62-283001) is known. This foamed tire has excellent ice and snow performance, and is an excellent technology that has cleared the technical difficulties of controlling the vulcanization reaction and foaming reaction during vulcanization in order to manufacture this tire. Japanese Patent Application Laid-Open No. Hei 7-186633 discloses a method for forming microscopic grooves on a rubber surface.

[0004] However, these tires have the problem that even if the performance on ice at the initial stage can be improved, the hardening of the tread rubber due to running cannot be suppressed, and the performance on ice cannot be maintained until the end of running. there were.

[0005]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a pneumatic tire having excellent ice and snow performance from the beginning to the end of running of the tire.

[0006]

Means for Solving the Problems The present inventors have proposed a rubber component and a filler of a rubber composition (hereinafter, simply referred to as "rubber composition of a foamed rubber layer") in a solid phase rubber portion of a foamed rubber layer of a tire tread. Focusing on compounding agents such as vulcanization accelerators, their composition, etc., and as a result of intensive studies taking into account the control of the vulcanization reaction in the tire during running, as detailed below In the rubber composition of the foamed rubber layer, it has been found that by adding an appropriate amount of a metal dithiophosphate, the progress of the vulcanization reaction in the tire during running is rather suppressed, leading to the completion of the present invention. Was.

That is, (1) The pneumatic tire of the present invention has a tread portion composed of two layers, a cap rubber layer disposed radially outside and a base rubber layer disposed radially inside. A pneumatic tire provided with a foamed rubber layer containing closed cells on at least a surface of a rubber layer substantially in contact with a road surface, wherein the foamed rubber layer has a thickness of 5 to 5 mm.
A rubber composition having a foaming rate of 0% and constituting a solid phase rubber part of the foamed rubber is mixed with a metal dithiophosphate represented by the following general formula (I) based on 100 parts by weight of a rubber component. 0.1 to 5.0 parts by weight.

[0008]

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(Wherein R ¹ and R ² are each independently an alkyl group having 1 to 10 carbon atoms,
Represents an aryl group of 0. This alkyl group may be linear, branched or cyclic. M ¹ is a Zn atom, Sb
Represents an atom, an Fe atom, or a Cu atom. n represents the number of valences of the metal to be bonded. (2) The metal dithiophosphate represented by the general formula (I) described in the above item (1) is preferably a metal dithiophosphate represented by the following general formula (II).

[0010]

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(Wherein, M ² represents a Zn atom or an Sb atom, and n represents the number of valences of the metal to be bonded.) (3) The solid-phase rubber portion described in the above item (1) The rubber composition to be formed contains 30 to 80 parts by weight of a filler composed of silica and carbon black with respect to 100 parts by weight of a rubber component composed of 20 to 70 parts by weight of natural rubber and 30 to 80 parts by weight of butadiene rubber, 0 to 90% by weight of the filler is silica, and the silane coupling agent is added in an amount of 5 to 90% of the silica amount.
The carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 50 to 150 m ² / g and a dibutyl phthalate (DBP) oil absorption of 100 to 200.
It is preferred to have the characteristics of cm ^3/100 g. (4) It is preferable that the rubber composition of the base rubber layer described in the above item (1) contains the metal dithiophosphate represented by the general formula (I).

According to the present invention, as described above, the metal dithiophosphate represented by the following general formula (I) is added to the solid rubber portion of the foamed rubber of the tire tread, and the rubber component 100 of the solid rubber is used.
There is a great feature in that 0.1 to 5.0 parts by weight is contained with respect to parts by weight. In a pneumatic tire, crosslinking is performed by vulcanization after tire molding to impart rubber elasticity as a tire, but an unreacted vulcanizing agent remains in the tire, and the vulcanization reaction occurs due to heat generated during traveling. Proceeds further, causing the tread rubber to harden. Therefore, from the viewpoint of maintaining the performance on ice until the end of traveling, it is necessary to suppress the progress of the vulcanization reaction in the tire during this traveling, and to suppress the curing of the tread rubber. Conventional vulcanization accelerators also accelerate the vulcanization reaction during running, but the metal dithiophosphate of the present invention is not suitable for vulcanization in the vulcanization step after tire molding. Although it acts as an agent, it forms a stable cross-linked form and thus plays a role as a re-crosslinking inhibitor that suppresses the progress of the subsequent vulcanization reaction. That is, the pneumatic tire of the present invention was obtained by blending such a metal dithiophosphate.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The tire of the present invention has a tread portion comprising two layers, a cap rubber layer disposed radially outward and a base rubber layer disposed radially inward. A foamed rubber layer containing closed cells is provided in the layer. The foamed rubber layer may be provided on at least the surface of the cap rubber layer substantially in contact with the road surface in order to obtain the effect of improving the ice and snow performance, but the entire cap rubber layer is formed of the foamed rubber layer (foamed rubber layer 100).
%). The foamed rubber layer includes a solid phase rubber portion (non-foamed rubber portion) and a cavity (closed cell) formed in the solid phase rubber portion, that is, a bubble portion. By adopting such a structure, water generated during traveling on ice is efficiently removed, and ice and snow performance is improved.

The foaming ratio of the foamed rubber layer of the present invention is obtained from the density of the foamed rubber, the density of the solid phase rubber portion of the foamed rubber, and the density of the gas portion in the bubbles of the foamed rubber according to the following equation (1). Foaming rate Vs. _{Vs = {(ρ 0 -ρ g} ) / (ρ 1 -ρ g) -1} × 100 (%) ·· formula (1) (wherein, [rho ₁ is the density of the foamed rubber (g / cm ^3), ρ ₀ represents the density (g / cm ³ ) of the solid phase rubber portion of the foamed rubber, and ρ _g represents the density (g / cm ³ ) of the gas portion in the foamed rubber bubble.) The density ρ _g is extremely small,
Equation (1) is approximated by the following equation (2) because it is nearly zero and extremely small with respect to the density ρ ₀ of the solid phase rubber portion. Vs = (ρ ₀ / ρ ₁ -1) × 100 (%) (2)

[0015] In the foamed rubber layer of the present invention, the foaming ratio is 5 to 50%, preferably 10 to 35%. If the foaming ratio is less than 5%, sufficient initial on-ice performance cannot be obtained in the obtained tire, and if it is more than 50%, the wear resistance of the tire is significantly reduced.

The metal dithiophosphate represented by the general formula (I) of the present invention is used together with a vulcanizing agent such as sulfur.
In the vulcanization step after tire molding, it acts as a vulcanization accelerator, but, as described above, plays a role in suppressing the progress of the vulcanization reaction during running and suppressing the curing of the tread rubber. is there.

R ¹ and R ² of the metal dithiophosphate represented by the general formula (I) each independently have 1 to 8 carbon atoms.
An alkyl group or an aryl group having 6 to 10 carbon atoms,
This alkyl group may be linear, branched or cyclic. M ¹ is a Zn atom, Sb atom, Fe atom or Cu atom, and n is the number of valences of the metal to be bonded. Among them, R ¹ and R ² are preferably an alkyl group having 3 to 4 carbon atoms. Metal dithiophosphates having an alkyl group having 2 or less carbon atoms tend to have low solubility in rubber, and if the number of carbon atoms is 5 or more, the effect cannot be further improved. Is not always effective. As the metal, a Zn atom or an Sb atom is preferable. That is, a metal dithiophosphate represented by the formula (II) is preferable.

The metal dithiophosphate used in the present invention includes, for example, O, O'-dipropyldithiophosphate,
O, O'-diisopropyldithiophosphoric acid, O, O'-di-n-butyldithiophosphoric acid, O, O'-di-sec-butyldithiophosphoric acid, O, O'-di-t-butyldithiophosphoric acid, O, O O'-diphenyldithiophosphoric acid, O, O'-
And metal salts such as dicyclohexyldithiophosphoric acid.

The dithiophosphoric acid compound represented by the general formula (I) is used in an amount of 0.1 to 100 parts by weight of the rubber component.
It is necessary to contain 1 to 5.0 parts by weight. If the amount is less than 0.1 parts by weight, the performance on ice after running cannot be suppressed, and the performance cannot be reduced to 5.0.
If the amount is more than the weight part, the scorch time becomes extremely short, that is, the vulcanization proceeds early and becomes hard, and the subsequent refining,
This causes a problem of scorching in the extrusion process.

The metal dithiophosphate of the present invention can be used in combination with other vulcanization accelerators.
Thiazole vulcanization accelerators such as 2-mercaptobenzothiazolyl disulfide, Nt-butylbenzothiazolylsulfenamide, N-cyclohexylbenzothiazolylsulfenamide and tetra (2 -Ethylhexyl) thiuram vulcanization accelerators such as thiuram disulfide and tetramethylthiuram disulfide can be appropriately compounded. Each compounding amount of other vulcanization accelerators,
The amount is preferably 0.1 to 3.0 parts by weight based on 100 parts by weight of the rubber component. If it is less than 0.1 part by weight, sufficient vulcanization properties cannot be obtained, and if it exceeds 3.0 parts by weight, the scorch becomes extremely short, which is not preferable.

Sulfur is used as the vulcanizing agent, and the compounding amount is preferably 0.5 to 3.0 parts by weight based on 100 parts by weight of the rubber component. If the amount is less than 0.5 part by weight, it is difficult to obtain a required elastic modulus, and if it exceeds 3.0 parts by weight, it is not preferable in terms of heat aging.

As the rubber component used in the rubber composition of the foamed rubber layer of the present invention, styrene-butadiene rubber, natural rubber, butadiene rubber, butyl rubber, and the like can be used. Natural rubber 20 ~
A blend rubber blended in a ratio of 70 parts by weight and butadiene rubber in a proportion of 30 to 80 parts by weight is preferably used.
More preferably, it is a blend rubber having a ratio of 30 to 70 parts by weight of natural rubber and 70 to 30 parts by weight of butadiene rubber. If the butadiene rubber is less than 30 parts by weight, the hardness of the rubber on the ice and snow road surface increases, and the ice and snow performance becomes insufficient. If the butadiene rubber exceeds 80 parts by weight, the WET performance is greatly reduced. In particular, cis-1,4-polybutadiene is preferred because it has a low glass transition temperature and a large effect on ice and snow performance.

The rubber composition of the foamed rubber layer of the present invention preferably contains a filler composed of silica and carbon black. As the silica used in the present invention, all available ones are used and are not particularly limited,
Dry process silica (silicic anhydride) and wet process silica (hydrous silicic acid) are included, and wet process silica is preferable. The silica used has a nitrogen adsorption specific surface area (N ₂ SA) of 150 m ² / g.
It is preferable that it is above. Preferable examples of the wet process silica include Nipsil AQ (trade name) manufactured by Nippon Silica Co., Ltd., and the like.

The carbon black used in the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 50 to 150 m.
² / g and dibutyl phthalate (DBP) oil absorption of 1
And it has a feature of 00~200cm ³ / 100g is preferably used. Specific examples of carbon black include SAF, ISAF-HM, ISAF-LM, and ISAF-
HS and the like.

The amount of the filler comprising silica and carbon black is 30 parts by weight based on 100 parts by weight of the rubber component.
It is preferably from 80 to 80 parts by weight, more preferably from 40 to 70 parts by weight. Further, it is preferable that 0 to 90% by weight of the filler is silica, and 30 to 80% by weight is more preferable. If the content is more than 90% by weight, inconveniences such as burning in an extrusion step or the like during production occur.

With respect to this foaming, it is additionally stated that stable foaming can be obtained by controlling a competitive reaction between the foaming reaction and the vulcanization reaction. If a difference occurs between the respective rates of the foaming reaction and the vulcanization reaction, it is difficult to obtain the desired average cell diameter and foaming ratio. It is known that silica inherently tends to reduce the vulcanization rate. For this reason, in foamed tires, the use of silica is usually difficult to consider, but the amount of silica is set to a predetermined amount, and the vulcanization rate is controlled in conjunction with the increase in the amount of a vulcanization accelerator described below. This makes it possible to balance the foaming reaction and the vulcanization reaction.

It is preferable to use a silane coupling agent together with silica in the rubber composition of the foamed rubber layer of the present invention. As the silane coupling agent used in the present invention,
Those represented by the following general formula are preferred. _{Y 3 -Si -Cn H 2 n-} A formula (wherein, Y is an alkyl group having 1 to 4 carbon atoms, an alkoxyl group or a chlorine atom, three of Y may be the same or different, n Represents an integer of 1 to 6, and A represents -Sm-CnH
_A group selected from the group consisting of ₂ n-Si-Y ₃ groups, X groups, and SpZ groups, wherein the X group is a nitrile group, a mercapto group, an amino group, an epoxy group, a vinyl group, a chlorine atom,
Or an imide group, Z is a group represented by the following formula, m and p each represent an integer of 1 to 6, and Y is as described above. )

[0028]

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Specifically, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylpropyl) tetrasulfide
Trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-nitropropyltrimethoxysilane, 3-
Nitropropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-
Chloroethyltriethoxysilane, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,
N-dimethylthiocarbamoyltetrasulfide, 2-
Triethoxysilylethyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-trimethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-tri Methoxysilylpropyl methacrylate monosulfide and the like are preferable, and bis (3-triethoxysilylpropyl) tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide and the like are preferable.

Further, bis (3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, 3-nitropropyldimethoxymethylsilane, 3-chloropropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N, N Silane coupling agents such as dimethiocarbamoyltetrasulfide and dimethoxymethylsilylpropylbenzothiazole tetrasulfide;

The compounding amount of the silane coupling agent is 5 to 2 with respect to silica from the viewpoint of securing reinforcing property of silica and maintaining rigidity.
0% by weight, preferably 8 to 15% by weight. If the amount of the silane coupling agent is less than 5% by weight, the coupling effect is small, so that the rubber strength is low and the abrasion resistance is poor,
If it exceeds 20% by weight, a remarkable increase in the elastic modulus occurs, no improvement in the strength of the rubber is observed, and this is not preferable from the viewpoint of cost increase.

In the rubber composition of the foamed rubber layer of the present invention, other components such as an antioxidant, zinc white, stearic acid, a softener, and WAX which are commonly used do not impair the effects of the present invention. It can be appropriately compounded within the range, and if necessary, a filler such as magnesium carbonate, calcium carbonate, glass fiber, aluminum hydroxide, clay, whisker and the like can be added.

The foamed rubber used for the pneumatic tire according to the present invention is formed when heating and pressurizing using a foaming agent in accordance with a usual tire manufacturing method.

Examples of the blowing agent used in the present invention include azo compounds such as ammonium bicarbonate and sodium bicarbonate which generate carbon dioxide, azodicarbonamide and azobisisobutyronitrile which generate nitrogen, and N, N '-
Nitroso compounds such as dinitrosopentamethylenetetramine, N, N'-dimethyl-N, N'-dinitrosophthalamide, benzenesulfonylhydrazide, toluenesulfonylhydrazide, other aromatic sulfonylhydrazides, derivatives thereof, and pp'- Sulfonyl hydrazide compounds such as oxybis (benzenesulfonyl hydrazide), p-toluenesulfonyl semicarbazide, p, p '
-Oxy-bis (benzenesulfonyl semicarbazide)
And the like, and these can be appropriately selected and used according to the vulcanization temperature. Among these, dinitrosopentamethylenetetramine is preferred from the viewpoint of controlling the foaming diameter. Urea or the like is used as a foaming aid.

As the rubber composition of the base rubber layer of the tire of the present invention, a filler composed of carbon black is used in an amount of 30 to 100 parts by weight of a rubber component composed of a diene rubber.
It is preferable that the rubber composition is 80 parts by weight and further contains the metal dithiophosphate. By blending the metal dithiophosphate in the rubber composition of the base rubber layer, the curing of the base rubber can be suppressed, and the performance on ice can be maintained higher until the end of running.

The other rubber composition for a pneumatic tire of the present invention can be obtained by kneading using a kneading machine such as a roll, an internal mixer, a Banbury mixer or the like according to a usual method. It is vulcanized and used for tire treads and the like.

[0037]

The present invention will be described more specifically with reference to the following examples, but the contents of the present invention are not limited to the examples. The measurement of the properties of the foamed rubber and the evaluation of the tire performance were performed by the following methods.

(Measurement of Characteristics of Foamed Rubber and Evaluation of Tire Performance) (1) Foaming Rate The foaming rate Vs is obtained by cutting a block-shaped sample from the foamed rubber layer of the tread of the test tire and obtaining the density ρ ₁ of the block-shaped sample. (G / m ³ ), and the density ρ ₀ of the non-foamed rubber (solid phase rubber) was measured and determined using the above equation (2). (2) Initial ice / snow performance The ice / snow performance is represented by its braking performance on ice as an index. 18
Four new 5 / 70R13 size test tires were mounted on a 1600 cc passenger car, and braking performance was measured on ice at -1 ° C and -8 ° C. The performance on ice was indicated by an index according to the following equation. The larger the value, the better the braking performance. Initial performance on ice = (braking distance of control tire (Comparative Example 1) / braking distance of test tire) × 100 The minimum inter-sipe length of this test tire is 3 mm. (3) After-running ice and snow performance Four 185 / 70R13 sizes were mounted on a passenger car in the same manner as in (2), and the actual road was 10,000 km and 200 km.
After traveling 00 km, the braking performance was measured on ice as in (2). After traveling 10,000 km, the base rubber is not yet exposed, but after traveling 20,000 km, the base rubber is exposed. The performance on ice was indicated by an index according to the following equation.
The larger the value, the better the braking performance. Performance on ice after running = (braking distance of control tire (Comparative Example 1) / braking distance of test tire) × 100 Also, for comparison with the initial performance on ice of control tires, the performance on ice after running represented by the following formula Is also described. Performance on ice after running = (initial braking distance of control tire (Comparative Example 1) / braking distance of test tire) × 100

[Examples 1 to 3, Comparative Example 1] According to the compounding recipe shown in Table 1 below, the obtained compounded rubber was foamed using the combination shown in Table 2 for the cap rubber layer and the base rubber layer in the tread portion. A tire was manufactured, the characteristics of the foamed rubber were measured, and the tire performance was evaluated. The results are shown in Tables 1 and 2.
Shown in

[0040]

[Table 1]

[0041]

[Table 2]

According to the examples, the pneumatic tire of the present invention
Not only has good initial ice and snow performance, but also 10,000
It can be seen that ice and snow performance is maintained even after traveling km. In addition, it can be seen that when a suitable amount of the metal dithiophosphate of the present invention is added to the base rubber layer, the ice and snow performance is maintained at a higher rate.

As described above, according to the present invention, it is possible to provide a pneumatic tire capable of achieving both the initial performance on ice and the performance on ice after traveling.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 3/36 C08K 3/36 5/5398 5/5398

Claims (4)

[Claims] 1. A tread portion comprising two layers, a cap rubber layer disposed radially outside and a base rubber layer disposed radially inside, and at least a surface of the cap rubber layer substantially in contact with a road surface, A pneumatic tire provided with a foamed rubber layer containing closed cells, wherein the foamed rubber layer has a foaming rate of 5 to 50%, and comprises a solid phase rubber portion of the foamed rubber. A pneumatic tire containing 0.1 to 5.0 parts by weight of a metal dithiophosphate represented by the following general formula (I) based on 100 parts by weight of a rubber component. Embedded image (Wherein, R ¹ and R ² each independently represent a carbon atom of 1
Represents an alkyl group having 10 to 10 or an aryl group having 6 to 10 carbon atoms. This alkyl group may be linear, branched or cyclic. M ¹ represents a Zn atom, Sb atom, Fe atom, or Cu atom. n represents the number of valences of the metal to be bonded. ) 2. The pneumatic tire according to claim 1, wherein the metal dithiophosphate represented by the general formula (I) is a metal dithiophosphate represented by the following general formula (II). Embedded image (Wherein, M ² represents a Zn atom or an Sb atom. N
Represents the number of valences of the metal to be bonded. ) 3. The rubber composition constituting the solid phase rubber part comprises 20 to 70 parts by weight of natural rubber and butadiene rubber 3
A filler consisting of silica and carbon black was added to 100 parts by weight of a rubber component consisting of 0 to 80 parts by weight.
0 to 80 parts by weight, wherein 0 to 90% by weight of the filler is silica, and the silane coupling agent is used in an amount of 5 to 2 parts by weight of silica.
0% by weight, the carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 50 to 150 m ² / g and a dibutyl phthalate (DBP) oil absorption of 100 to 200 c.
The pneumatic tire according to claim 1 or 2, characterized by having the properties of m ^3/100 g. 4. The rubber composition of the base rubber layer contains a metal dithiophosphate represented by the general formula (I). Pneumatic tires.