JPH08300904A - Pneumatic tire - Google Patents

Abstract

PURPOSE: To provide a studless tyre for all seasons in the true sense having a sufficient brake property and driving property, not only on dry-on-ice but on wet-on-ice, after ensuring steering stability, durability and a low fuel consumption property sufficiently in summer. CONSTITUTION: A tread is provided with a foamed rubber whose hardness measured by ASTM shore D is 40 deg. or more and average grain diameter is 10-400μm and which contains a resin which can form a polymer alloy with a rubber or crosslink with the rubber by 5-30 weigh parts per 100 weight parts of a rubber component and whose foamed ratio is 5-30% and having a closed cell, the average grain diameter of whose resin is 0.5-5 times an average cell diameter and whose storage elasticity (E') at -20 deg.C is within the range of 6.0×10<7> to 20×10<7> dyn/cm<2> .

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a pneumatic tire,
More specifically, the driving performance, braking performance and maneuverability when traveling on ice and snowy road surfaces without impairing the steering stability, durability and wear resistance required in the summer (hereinafter simply referred to as "ice and snow performance") The present invention relates to an all-season studless pneumatic tire that has been significantly improved.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for so-called all-season tires that can be used in the same manner as in summer without tire replacement even in winter. This type of tire has the same dry grip, wet grip, steering stability, durability, and fuel economy as in the summer, and has sufficient drivability and braking even on ice or snow. Is.

Conventional tread rubbers used in such tires are required to have a low hardness at low temperatures of tread rubbers for summer, and polymers having a low glass transition point are used, or elastic moduli at low temperatures are used. There is known a method of using a softening agent capable of properly maintaining

[0004]

However, in the former method, due to the hysteresis characteristic of this polymer,
Even if some performance is exhibited in the ice and snow temperature region, there is a problem that braking performance and maneuverability on wet road surfaces and dry road surfaces are not sufficient, and the latter method is also disclosed in JP-A-55-13.
5149, JP-A-58-199203, JP-A-60
No. 137945, etc., any of the methods has a problem that the improvement in the performance on ice and snow has a great adverse effect on wear resistance and durability when traveling on a general road. Has been pointed out.

In addition, whichever technique is used, the ice-snow performance of so-called dry-on-ice is certainly good in a relatively low temperature range of -5 ° C or lower, but it is about 0 ° C. In the wet condition, that is, the so-called wet-on-ice performance on snow and snow, it is difficult to say that a sufficient friction coefficient is obtained, and the drivability, braking performance and steering stability are sufficiently improved.

Therefore, an object of the present invention is to ensure sufficient steering stability, durability, and fuel efficiency in the summer, and not only for dry on ice, but also for wet on ice. It is to provide a true all-season studless tire having braking performance and drivability.

[0007]

Means for Solving the Problems As a result of intensive studies on the performance of tread rubber of studless tires for all seasons on ice and snow, the inventors have found that the matrix rubber of the tread portion has a specific hardness and particle size. By mixing a special resin having an affinity with the matrix rubber and setting the storage elastic modulus (E ′) of the matrix rubber as a foamed rubber having a specific foaming ratio and a foaming diameter within a specific range, Confirm that the performance can be improved significantly and that it does not impair the driving stability, durability, etc. required for running in summer or on ordinary road surfaces.
The present invention has been completed.

That is, the pneumatic tire of the present invention is
A resin having a hardness of 40 ° or more and an average particle diameter of 10 to 400 μm as measured by STM Shore D, which is capable of forming a polymer alloy with rubber or a resin which can be co-crosslinked with rubber, is added to 5 parts by weight of a rubber component. A foamed rubber containing 30 to 30 parts by weight, a foaming ratio of 5 to 30%, and an average particle diameter of the resin being 0.5 to 5 times the average foamed diameter, and having closed cells, wherein Storage elastic modulus (E ') is 6.0 × 10 ⁷
It is characterized in that the tread is provided with foamed rubber in the range of up to 20 × 10 ⁷ dyn / cm ² .

Examples of the above resins include ultrahigh molecular weight polyester resins having a molecular weight of 1,000,000 to 10,000,000 which form a polymer alloy as they are, and resins which are co-crosslinked as they are, such as styrene-butadiene resin. The most preferable resin from the viewpoint of improving
It is a crystalline syndiotactic-1,2-polybutadiene resin (hereinafter simply referred to as "syn-1,2PB") having a temperature of 0 ° C or higher.

Examples of the polymerization catalyst for the syn-1,2PB resin include soluble cobalt such as cobalt octoate, cobalt 1-naphthate, and cobalt benzoate, and organic aluminum compounds such as trimethylaluminum, triethylaluminum, tributylaluminum, and triphenyl. Examples thereof include a catalyst system composed of aluminum and the like and carbon dioxide. Specific polymerization methods include JP-B-53-39917 and JP-B-54-54.
Although the methods described in Japanese Patent Publication No. 36 and Japanese Patent Publication No. 56-18005 can be used, the polymerization method is not particularly limited to the methods described therein.

In the present invention, the above resin and the resin 10
0.3 to 5.0 parts by weight of sulfur with respect to 0 parts by weight, and
Particle size 1 obtained by blending 1 to 7.0 parts by weight of a vulcanization accelerator
It is preferable that a resin composite masterbatch having a thickness of 0 to 400 μm is prepared in advance and is blended with the rubber composition forming the matrix portion of the tire tread portion.

The resin composite has the following formula: 0 <X + 10Y <1300 (where X is the nitrogen adsorption specific surface area (m ² / g), and Y is the number of parts of carbon black compounded with 100 parts by weight of the above resin ( It is preferable that carbon black or an anti-scorch agent satisfying the relation represented by (part by weight) is blended.

Such a resin composite can be easily produced by kneading with a conventional kneader such as a kneader, Banbury mixer, or roll at a temperature higher than the melting point of the resin, and then pulverizing to a desired particle size, No special conditions are required.

The rubber component of the rubber composition forming the matrix portion of the tread portion may be a conventional polymer type used in conventional pneumatic tires for all seasons, such as natural rubber and butadiene rubber. A mixed rubber or a mixed rubber in which styrene-butadiene rubber is further added can be used.

The method of mixing the resin composite and the rubber composition of the tread portion-forming matrix is not particularly limited, and the same effect can be obtained by a wet blending method in a solvent or a dry blending method using a Banbury mixer or the like. .

The rubber composition forming the matrix portion contains an inorganic filler such as silica, a softening agent such as aroma oil and spindle oil, an antioxidant, a vulcanizing agent, a vulcanization accelerator, and a vulcanization accelerating aid. It goes without saying that an appropriate amount of a compounding agent that is usually compounded, such as an agent, can be appropriately compounded.

In the present invention, in order to obtain a foamed rubber having the above-mentioned specific foaming ratio and average foaming diameter, after blending a foaming agent with the above-mentioned rubber composition, heating and pressurization may be carried out according to a usual tire manufacturing method. . Examples of the foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, aromatic sulfonyl hydrazide compounds such as benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, and oxy-bis-benzenesulfonyl hydrazide. Can be used. Among these, azodicarbonamide is preferable from the viewpoint of fine foaming. In addition, dinitrosopentamethylenetetramine is preferable in terms of large foam diameter.

[0018]

The resin used in the present invention has a hardness of 40 ° or more, preferably 70, as measured by ASTM Shore D.
It must be above °. If it is less than 40 °, a sufficient scratching effect cannot be obtained. The concrete measuring method of ASTM Shore D was based on JIS K 7215.

The average particle size of the resin, or the average particle size when the resin is a resin composite, is 10 to 400 μm.
It is necessary to be within the range. If the particle size is smaller than 10 μm, the improvement in the on-ice and snow performance targeted by the present invention is not sufficient, and conversely, if it is larger than 400 μm, some effect is observed in the on-snow and snow performance, but the wear resistance. It is not preferable because it deteriorates other performances required for the tire, such as occurrence of cracks at the groove bottoms.

The resin is generally crystalline, but the melting point of its crystal part is preferably 110 ° C. or higher. If the melting point is lower than 110 ° C., the resin may be softened and deformed or part or all thereof may be melted when the resin is added in a composite form and kneaded during compounding. It becomes impossible to maintain the particle size of the above, and it becomes difficult to obtain the intended effect of improving the performance on ice and snow.

In the present invention, it is necessary to mix the above resin or resin composite in the matrix rubber composition forming the tread portion within the range of 5 to 30 parts by weight with respect to 100 parts by weight of the rubber. If the blending amount is less than 5 parts by weight, the desired effect of improving the performance on ice and snow is hardly recognized, while if it exceeds 30 parts by weight, other performance required for the tire such as abrasion resistance is remarkably increased. Not only does it hurt,
The workability during tire production also deteriorates significantly, making it unusable for practical use.

Next, in the present invention, in order to obtain an excellent performance on ice and snow, it is necessary that the rubber constituting the tread is a foamed rubber and the foaming rate thereof is within the range of 5 to 30%. If the foaming rate is less than 5%, the effect of foaming is not sufficient, while if it exceeds 30%, the rigidity of the tread is insufficient, resulting in a decrease in wear resistance and the occurrence of cracks in the groove bottom.

The relationship between the average foam diameter of the foamed rubber and the average particle diameter of the resin or resin composite is such that the average particle diameter of the resin or resin composite is 0.5 to 5 of the average foam diameter.
It needs to be doubled. If this ratio is less than 0.5 times, the desired performance on ice and snow cannot be obtained, while if it exceeds 5 times, the wear resistance is greatly reduced, which is not preferable. Preferably 1.0 to 4 times, most preferably 1.5 to 2.5
It is twice.

Further, in the present invention, the storage elastic modulus (E ') of the tire tread rubber at -20 ° C is controlled by controlling the compounding system of the rubber composition or the foaming conditions.
It is required to be in the range of 0 × 10 ^{7 to} 20 × 10 ⁷ dyn / cm ² , preferably 8.0 × 10 ^{7 to} 12 × 10 ⁷ dyn / cm ² . This value is 6.0 × 10 ⁷ dyn /
If it is less than cm ^2, the block of the tire pattern may be deformed or the sipes may be opened, resulting in deterioration of performance on ice and snow. On the other hand, when it exceeds 20 × 10 ⁷ dyn / cm ² , the tire installation area is reduced and the performance on ice and snow is also deteriorated.

In the present invention, when the resin is compounded in the form of a composite, if the content of sulfur is less than 0.3 part by weight, the crosslinking bond between the resin and the rubber forming the matrix of the tread part is formed. Is not sufficiently obtained, and on the other hand, when it exceeds 5.0 parts by weight, the workability during the production of the composite is remarkably reduced,
Not preferred.

Further, in this case, if the compounding amount of the vulcanization accelerator is less than 0.1 parts by weight, the adhesiveness due to crosslinking becomes insufficient, while if it exceeds 7.0 parts by weight, workability is problematic. Cause It is preferably in the range of 0.3 to 5.0 parts by weight.

Further, when carbon black is added to such a composite, X + 10Y (where X is the nitrogen adsorption specific surface area (m ² / g), and Y is the number of parts of carbon black based on 100 parts by weight of the resin (weight: If the value of (indicated by part) exceeds 1300, the processability during the production of the resin composite is significantly reduced, which is not preferable.

In a preferred embodiment of the present invention, the resin is previously made into a composite form with a specific carbon black, sulfur and a vulcanization accelerator as described above. This allows
Crosslinking between the resin and the matrix rubber for forming the tread portion is sufficiently performed, and as a result, the resin is less likely to drop from the tread portion, and the effect of improving the performance on ice and snow becomes remarkable.

[0029]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. First, as follows, syn-1,2
A PB resin was prepared. Volume 2 with air replaced with nitrogen gas
760 cc of dehydrated benzene was put into a 1-liter autoclave to dissolve 74 g of 1,3-butadiene. To this, 1 mmol of cobalt octoate (using a benzene solution with a concentration of 1 mmol / cc) was added, and 1 minute later, 2 mmol of triethylaluminum (a benzene solution with a concentration of 1 mmol / cc) was added, and the mixture was stirred and then added in an appropriate amount. Acetone was added. After 1 minute, 0.6 mmol of carbon disulfide (benzene solution having a concentration of 0.3 mmol / cc) was added, and the mixture was stirred at 10 ° C for 60 minutes,
Polymerization of 1,3-butadiene was performed.

0.75 g of 2,4-ditert-butyl-p-cresol was added to the resulting syn-1,2PB resin production liquid. Next, the syn-1,2PB resin production liquid was added to 1000 cc of methanol, and the syn-
The 1,2PB resin was precipitated. This syn-1,2
PB was further washed with methanol, filtered to remove methanol, and then dried in vacuum.

The obtained syn-1,2PB resin was mixed with carbon black in accordance with the compounding contents shown in Table 1 below.
The mixture was kneaded in a 50 cc Labo Plastomill at a temperature equal to or higher than the melting point of the resin for 1 minute, and then sulfur, a vulcanization accelerator and a scorch inhibitor were added and kneaded for 30 seconds. Obtained syn-
The 1,2PB resin composites were pulverized according to a usual method to obtain syn-1,2PB resin composites (A to F) having respective average particle diameters shown in Table 1.

[0032]

[Table 1] 1) N-oxydiethylene-2-benzothiazolylsulfenamide

In Table 1, the nitrogen adsorption specific surface area N ₂ SA of carbon black was measured according to the ASTM D3037-84 B method.

Examples 1 to 13 and Comparative Examples 1 to 8 Using the various syn-1,2PB resin composites described above, rubber compositions for tread rubber were prepared with the compounding contents shown in Tables 2 and 3 below. The storage elastic modulus (E ′) of the rubber composition at −20 ° C. was measured. Then, using these rubber compositions as a tread rubber, the tire size P
Small test tires of SR165SR13 were manufactured, and the foaming rate, average foaming diameter, braking performance on ice, and abrasion resistance of these tires were evaluated.

These measuring methods and evaluation methods are as follows. B) Storage elastic modulus (E ') Vulcanization conditions of 160 ° C. × 15 minutes, a sample with a width of 5 mm and a length of 20 mm cut out from a slab sheet with a gauge of 2 mm was used for initial measurement using a spectrometer manufactured by Iwamoto Manufacturing Co., Ltd. The measurement was performed under the conditions of a load of 150 g, a dynamic strain of 1%, a frequency of 50 Hz, and a set temperature of -20 ° C.

(B) Foaming ratio The foaming ratio V _S is expressed by the following equation, V _S = {(ρ ₀ −ρ _g ) / (ρ ₁ −ρ _g ) −1} × 100 (%) (1), and ρ _l is the density of the foamed rubber (g / cm ³ ), ρ ₀
Is the density (g / cm ³ ) of the solid phase portion of the foamed rubber, ρ
_g is the density (g / cm ³ ) of the gas portion in the bubbles of the foamed rubber
Is. The foamed rubber is composed of a rubber solid phase portion and a cavity (closed cell) formed by the rubber solid phase portion, that is, a gas portion in the bubble. Since the density ρ _{g of the} gas portion is extremely small, close to zero, and extremely small with respect to the density ρ _l of the rubber solid phase portion, the above equation (1) can be expressed by the following equation. V _S = (ρ ₀ / ρ _l −1) × 100 (%) (2) Actually, a block-shaped sample from the foamed rubber phase of the tread of the test tire that was left to stabilize for one week after vulcanization was used. A thin piece having a thickness of 5 mm was formed, the density was measured, and the density of the tread of non-foamed rubber (solid phase rubber) was also measured, and the foaming rate V _S was obtained using the above formula (2).

C) Average foam diameter A block-shaped sample was cut out from the foamed rubber phase of the tread of the test tire, photographed with an optical microscope at a magnification of 100 to 400, and the bubble diameter of 200 or more closed cells was measured and calculated arithmetically. Expressed as an average value. D) Braking performance on ice First, after performing a 50km normal run as a leveling run,
It used for the following measurement tests. First, four test tires were mounted on a passenger car with a displacement of 1500 cc, and the braking distance was measured on ice with an outside air temperature of -5 ° C. The tire of Comparative Example 1 was indexed to 100. The larger the value, the better the braking.

(E) Abrasion resistance After running in the same manner as for wet skid resistance, two test tires were mounted on the drive shaft of a passenger car with a displacement of 1500 cc, and the test road was tested on the concrete road surface. It was run at the speed of. The amount of change in groove depth was measured, and the tire of Comparative Example 1 was set to 100 and displayed as an index.
The larger the value, the better the wear resistance. The obtained results are also shown in Tables 2 and 3 below.

[0039]

[Table 2] 1) dibenzothiazyl disulfide 2) N-cyclohexyl-2-benzothiazylsulfenamide 3) a mixture of dinitrosopentamethylenetetramine (DPT) and urea with a mixing ratio of DPT / urea = 57/43
Is.

[0040]

[Table 3] 1) Same as Supplementary Note 3) in Table 2 above 2) Azodicarbonamide

[0041]

As described above, in the pneumatic tire of the present invention, the tread rubber contains a predetermined amount of a specific resin having a specific hardness and an average particle diameter, and a specific foaming ratio,
Sufficient handling stability, durability, and low fuel consumption in the summer are obtained by using foamed rubber with closed cells of average foaming diameter and by setting the storage elastic modulus (E ') at -20 ° C of this foamed rubber to a specific range. After securing the
Not only in ice, but also in wet-on-ice, sufficient braking performance and drivability are exhibited, and an effect of having excellent performance on ice and snow can be obtained.

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Claims (4)

[Claims] 1. A rubber component comprising 100 parts by weight of a resin capable of forming a polymer alloy with rubber or a resin capable of co-crosslinking with rubber, having a hardness of 40 ° or more and an average particle diameter of 10 to 400 μm as measured by ASTM Shore D. A foamed rubber containing 5 to 30 parts by weight with respect to 10 parts by weight, a foaming rate of 5 to 30%, and closed cells having an average particle size of the resin of 0.5 to 5 times the average expanded diameter, A pneumatic tire characterized in that a tread is provided with a foamed rubber having a storage elastic modulus (E ′) at −20 ° C. within a range of 6.0 × 10 ^{7 to} 20 × 10 ⁷ dyn / cm ² . 2. The pneumatic tire according to claim 1, wherein the resin is a crystalline syndiotactic-1,2-polybutadiene resin having a melting point of 110 ° C. or higher. 3. The resin is blended with 0.3 to 5.0 parts by weight of sulfur and 0.1 to 7.0 parts by weight of a vulcanization accelerator with respect to 100 parts by weight of the resin. Average particle size 10-400
The pneumatic tire according to claim 1 or 2, wherein the resin composite has a thickness of µm, and the resin composite is mixed with the rubber component. 4. The resin composite is added to the following formula: 0 <X + 10Y <1300 (where X is a nitrogen adsorption specific surface area (m ² / g), Y is the number of parts by weight of carbon black based on 100 parts by weight of the resin (weight: The pneumatic tire according to claim 3, further comprising carbon black satisfying a relationship represented by (part)).