JP2002079808A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire suitable for racing managing both gripping property including not only gripping in earlier part of traveling but also gripping in later part, and wear resistance. SOLUTION: The pneumatic tire has a tread comprising two layers, a surface layer of thickness 0.5 to 1.5 μm and an inner layer of rubber composition including filler agent more than 70 weight part against 100 weight part of rubber component, and having a ratio of stress of the rubber composition constructing the surface layer to stress of the rubber composition constructing the inner layer at 300% stretch in a tensile test greater than 70%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pneumatic tire,
In particular, it is related to pneumatic tires for competition that can achieve both grip characteristics and wear resistance.

[0002]

2. Description of the Related Art Tread rubber required for racing tires for racing vehicles and the like requires grip characteristics during running, traction and cornering, and increases the coefficient of friction generated between the road surface and the tread surface. Therefore, usually, a region having a small distortion (0.3 to 5)
A rubber having low elastic modulus and high tan δ when measuring viscoelasticity at 0% dynamic strain) is desired. Both properties are important, and it is important to increase tan δ / modulus.

In order to satisfy the required characteristics, it is usual to use a polymer having a high glass transition temperature (Tg), increase the amount of a filler or a softening agent, or reduce the amount of sulfur. Have been.

[0004] However, when the elastic modulus is lowered and tan δ is increased by the usual means as described above, a large force is applied to the tread surface due to braking and cornering during running.
By repeated deformation, abrasion wear occurs.

[0005] When a large force is applied to rubber, the rubber is softened and continuously deforms in a certain direction. Ablation wear is corrugated wear that occurs in the vertical direction of the force. In this case, as the interval and depth of the waves are larger, not only the appearance becomes worse, but also the contact area between the rubber and the road surface becomes smaller and the performance is reduced. Empirically, it has been found that rubber having a low elastic modulus in a strain region where large deformation occurs easily causes abrasion wear. That is, there is a correlation between the elastic modulus at 300% elongation measured in the tensile test and the interval between waves of abrasion wear.

In general, when the amount of a filler or a softener is increased in order to increase the grip force, the elastic modulus is reduced, and t
Although an δ can be increased, the elastic modulus at 300% elongation also decreases.

[0007] Even when a low elastic modulus is achieved by reducing the amount of sulfur or the amount of the vulcanization accelerator, the elastic modulus at 300% elongation is reduced. For this reason, it was difficult to achieve both wear resistance and grip characteristics with the conventional technology.

When focusing only on the grip characteristics, tan δ /
By simply increasing E ′ (elastic modulus in a region where the distortion is small), that is, simply by lowering the elastic modulus, the grip characteristics in the initial stage of traveling are improved, but the grip characteristics in the latter period are not necessarily sufficiently improved. Further, as the wear progresses, the grip condition is significantly reduced due to a change in the wear state.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pneumatic tire which is particularly suitable as an athletic tire having both grip characteristics including a grip at an early stage as well as a grip at a later stage and a wear resistance. Is to do.

[0010]

Means for Solving the Problems A tire was trial-produced by combining a rubber having a two-layer structure in which the surface layer used in the initial stage of running was soft and the inner surface layer was hard.
It is important to increase nδ / E ′ (elastic modulus in a region where the strain is small), and it has been found that even if the stress (M300) at 300% elongation is relatively low, abrasion resistance does not matter. As for the inner surface layer, it is necessary to withstand running after the surface is worn away, and it is considered that a relatively high M300 is required.

Therefore, the ratio of M300 of the surface layer to M300 of the inner layer is set to 70% or less, and by combining the two layers, it is possible to improve the initial grip characteristics without impairing the latter-stage grip characteristics and wear resistance. did.

That is, according to the present invention, the thickness is 0.5-1.
5 mm surface layer and 70 parts by weight of rubber component
In the tensile test, the ratio of the ratio M300 of the rubber composition constituting the surface layer to the ratio M300 of the rubber composition constituting the inner surface layer is composed of two layers, namely, an inner layer composed of a rubber composition containing at least one part by weight of a filler. A pneumatic tire having a tread of 70% or less.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, a pneumatic tire has a pair of bead portions, a pair of sidewall portions, and a tread portion connected to both sidewall portions.

The pneumatic tire of the present invention has a tread composed of two layers, a surface layer and an inner layer.

The rubber composition constituting both layers contains a rubber component. The rubber component can be used without particular limitation as long as it is generally used in a tread rubber composition for a tire.

Specific examples of the rubber component include, for example, natural rubber (NR), various butadiene rubbers (BR),
Various styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrilobutadiene rubber, chloroprene rubber, ethylene-propylene copolymer rubber, ethylene-propylene-
Diene copolymer rubber, styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber,
Examples include isoprene-butadiene copolymer rubber, chlorosulfonated polyethylene, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluorine rubber, urethane rubber, and EXXPRO90-10 (trade name). These may be used alone or as a mixture of two or more. The mixing ratio when mixing is not particularly limited.

The rubber composition constituting both layers may further contain a filler.

As the filler, for example, silica,
Clay, alumina, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide,
Examples include magnesium oxide, titanium oxide, and carbon black. These may be used alone or as a mixture of two or more. Examples of carbon black include, for example, HAF, ISAF, SAF, etc., but are not particularly limited.

The rubber composition (cap rubber) constituting the surface layer is, for example, 70 parts by weight per 100 parts by weight of the rubber component.
It can contain more than 1 part by weight, preferably 100 to 170 parts by weight of filler.

The rubber composition (base rubber) constituting the inner surface layer contains 70 parts by weight or more, more preferably 90 parts by weight or more, and further preferably 100 to 170 parts by weight of a filler with respect to 100 parts by weight of the rubber component. Including.

When the amount of the base rubber filler is less than 70 parts by weight, the grip characteristics in the latter half of the run are insufficient, and
If the amount exceeds 70 parts by weight, a large amount of process oil must be added to adjust the hardness of the rubber, so that the abrasion wear resistance tends to decrease.

The rubber composition constituting both layers may contain, in addition to the rubber component and the filler, components and additives generally used in the production of a tread rubber composition for a tire, in an amount usually used as necessary, Can be included. Specific examples of the components and additives include, for example, process oils (paraffin-based process oil, naphthene-based process oil, aromatic-based process oil, etc.), vulcanizing agents (sulfur, sulfur chloride compounds, organic sulfur compounds, etc.), Vulcanization accelerators (guanidine, aldehyde-amine, thiourea, thiuram,
Dithiocarbamate compounds, xandate compounds, etc.),
Crosslinking agents (radical generators such as organic peroxide compounds and azo compounds, oxime compounds, nitroso compounds, polyamine compounds, etc.), reinforcing agents (high impact polystyrene resin, phenol-formaldehyde resin, etc.), antioxidants or antioxidants ( Amine derivatives such as diphenylamine and p-phenylenediamine, quinoline derivatives, hydroquinone derivatives, monophenols, diphenols, thiobisphenols, hindered phenols, phosphites, etc.), wax, stearic acid, oxidation Examples include zinc, a softener, and a plasticizer.

The amount of the vulcanizing agent in each rubber composition (cap rubber and base rubber) is 0.1 to 3 parts by weight per 100 parts by weight of the rubber component in each rubber composition (cap rubber and base rubber). Parts by weight, more preferably 0.3 to 2 parts by weight.
If the amount of the vulcanizing agent is less than 0.1 part by weight, the abrasion resistance tends to decrease, and if it exceeds 3 parts by weight, the grip properties tend to decrease.

The amount of the vulcanization accelerator in each rubber composition (cap rubber and base rubber) is preferably 1.5 to 1.5 parts by weight based on 100 parts by weight of the rubber component in each rubber composition (cap rubber and base rubber). It is preferably 14 parts by weight, more preferably 0.5 to 25 parts by weight. If the compounding amount of the vulcanization accelerator is less than 0.5 part by weight, the abrasion resistance tends to deteriorate, and if it exceeds 25 parts by weight, the grip characteristics deteriorate or the rubber scorches (burns) during rubber processing. Tend.

The amount of the softener in each rubber composition (cap rubber and base rubber) is 50 to 200 parts by weight based on 100 parts by weight of the rubber component in each rubber composition (cap rubber and base rubber). Preferably, it is 90 to 170 parts by weight. If the amount of the softening agent is less than 50 parts by weight, the rubber tends to be hard, so that the grip characteristics tend to be insufficient. If the amount exceeds 200 parts by weight, the abrasion resistance tends to deteriorate.

In the pneumatic tire of the present invention, in a tensile test, the ratio of M300 of the rubber composition (cap rubber) constituting the surface layer to M300 of the rubber composition (base rubber) constituting the inner layer of the tread is 70. % Or less,
Preferably 20-70%, more preferably 40-60%
It is.

If the ratio of M300 exceeds 70%, the initial grip properties become insufficient, and if the ratio of M300 is less than 20%, the abrasion wear resistance becomes insufficient, and the base is hard and the late grip characteristics become insufficient. .

The ratio of M300 is determined by the M300 of the cap rubber.
, Or by increasing the base rubber M300. Cap rubber M3
00 can be reduced by lowering the crosslinking density, increasing the blending amount of the filler, using an inorganic filler having low reinforcing properties, or using a softener. M300 of the base rubber can be increased by a method such as increasing the crosslink density.

As the base rubber, for example, the ratio (tan tan) of the loss tangent (tan δ) to the dynamic viscoelastic modulus (E ′) in a viscoelasticity (50 ° C., 2.5% dynamic strain) test is used.
[delta] / E ') is 0.08~2.50 (MPa) ^-1, can be preferably used a rubber composition of 0.11~0.22 (MPa) ^-1.

As the cap rubber, for example, tan
A rubber composition having δ / E ′ of 0.12 to 0.30 (MPa) ⁻¹ , preferably 0.15 to 0.25 (MPa) ⁻¹ can be used.

The thickness of the surface layer is 0.5 to 1.5 mm, preferably 0.5 to 1.0 mm. If the thickness of the surface layer is less than 0.5 mm, the effect of improving the initial grip characteristics is reduced, and if it exceeds 1.5 mm, the abrasion resistance is deteriorated.

The tread of the present invention is obtained by kneading the components constituting the cap rubber and the base rubber with a usual processing device, for example, a roll, a Banbury mixer, a kneader or the like, and forming a sheet into a predetermined shape. Or extruded into two or more extruders and formed into two layers at the head outlet of the extruder.

The pneumatic tire of the present invention has excellent grip characteristics and abrasion resistance, and can be suitably used as a competition tire.

[0034]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 5 and Comparative Examples 1 to 4 (1) The reagents used in the examples and the comparative examples, the method for producing tires, and the method for producing test samples are summarized below.

(Reagent) Wax: Sannoc N antioxidant 6C manufactured by Ouchi Shinko Chemical Co., Ltd. Santoflex 1 manufactured by Flexis
3 Anti-aging agent 224: Nocrack 224 manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Tung Zinhua manufactured by Nippon Yushi Co., Ltd. Zinc oxide manufactured by Mitsui Kinzoku Kogyo Co., Ltd. Sulfur: Tsurumi Chemical Co. ) Powder sulfur Vulcanization accelerator: Noxeller N manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
S SBR: Toughden 4350, manufactured by Asahi Kasei Corporation, 39% of bound styrene in the rubber component, polymer having an oil extension of 50 parts by weight based on 100 parts by weight of the rubber component Aromatic oil: Process X-260 manufactured by Japan Energy Filler: SAF carbon (diamond black A manufactured by Mitsubishi Chemical Corporation) Hard clay: Southeast clay (Southeas)
tern Clay Company) Crown Clay

(Production method) Reagents other than sulfur and the vulcanization accelerator shown in Table 1 were kneaded at 145 ° C. for about 3 minutes using a BR type Banbury mixer and discharged (base kneading). The obtained rubber composition, sulfur and a vulcanization accelerator were kneaded with an open roll for about 5 minutes to prepare a sheet having a predetermined thickness, and a sheet was bonded to a predetermined shape to prepare a tread. 10 * 4.
A prototype of a 00-5 size cart tire was produced and evaluated as follows. In Comparative Examples 1 and 4, the tread was constituted by one layer made of a base rubber.

[0038]

[Table 1]

(Vulcanization of Test Sample) The sheet prepared under the above production conditions was vulcanized at 170 ° C. for 12 minutes in a mold specified in the following sections (hardness), (tensile test) and (viscoelasticity).

(2) The evaluation methods used in Examples and Comparative Examples will be summarized below. (Hardness) A sample vulcanized with a mold for producing a rubber sample having a thickness of 4 mm was measured with a JIS-A hardness meter.

(Tensile Test) A rubber sample having a thickness of 2 mm was vulcanized, and a test was performed using a sample punched out with a dumbbell No. 3 based on JIS K6251 (tensile test method).
The value of M300 (stress at 300% elongation) was evaluated by indexing M300 of the base rubber of Comparative Example 1 to 100. The larger the M300, the better the abrasion resistance.

(Viscoelasticity) Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., at a temperature of 50 ° C. and an initial strain of 10
%, Dynamic elastic modulus (E ') under the measurement conditions of dynamic strain 2.5%
And loss tangent (tan δ) were measured. E ', tan
δ and tan δ / E ′ were evaluated by indexing each with the base rubber of Comparative Example 1 as 100.

The lower the index of E ', the higher the index of tan δ, the better the grip.
The higher the index of E ', the better the grip.

(Actual vehicle test) 10 * 4.00-
Five prototype tires were mounted, and the vehicle traveled 10 laps on a course of about 2 km per lap, and the following evaluations were made. 1) Grip characteristics The grip feeling of the tire of Comparative Example 1 was evaluated as 3 points (reference), out of 5 points. The evaluation was divided into the first five laps and the last five laps. 2) Wear Appearance The wear appearance was visually checked after 5 laps and 10 laps of the abrasion wear (interval between the peaks of the generated waves), and the wear appearance of the tire of Comparative Example 1 was evaluated at 3 points (standard). )age,
The evaluation was made out of 5 points.

(3) Table 2 shows the experimental results.

Compared to the base rubber of Comparative Example 1, the base rubber of Comparative Example 4 was reduced in the amount of sulfur to lower E ′ and increased the grip coefficient (tan δ / E ′). With this method, the initial grip properties could be improved, but the abrasion resistance was low, and the grip properties in the later stages were reduced.

Examples 1 and 2 were prepared by reducing the amount of sulfur to lower the crosslink density, and Example 3 was prepared by increasing the amount of softener (aromatic oil).
In Example 4, the thickness was increased from 0.5 to 1.5 m by increasing the amount of the filler (hard clay) to increase the grip coefficient.
m cap rubber was used. In this method, the grip characteristics did not decrease in the latter stage even when the base rubber layer came out or approached the tire surface.

In Example 5, the same cap rubber as in Example 3 was used, and a base rubber having an increased M300 by increasing the amount of sulfur to increase the crosslink density was used. This keeps the initial grip properties, and
The grip characteristics in the latter half due to abrasion were particularly improved.

In Comparative Example 2, a cap rubber having a thickness of 2 mm or more and a high grip coefficient was used. When the cap rubber was thick, the effect of the base rubber was not obtained, and the wear resistance was reduced.

M30 of cap rubber to base rubber
In Comparative Example 3 in which the ratio of 0 exceeded 70%, the effect of improving grip characteristics and abrasion resistance was small.

[0051]

[Table 2]

[0052]

According to the present invention, it is possible to provide a pneumatic tire which improves not only the grip characteristics at the beginning of running but also the grip characteristics at the latter stage, and is particularly suitable as a racing tire having no problem of wear.

Claims (1)

[Claims] 1. A surface layer having a thickness of 0.5 to 1.5 mm,
In the tensile test, the stress of the rubber composition constituting the inner layer at 300% elongation in a tensile test is composed of two layers: a rubber composition containing 70 parts by weight or more of a filler with respect to 100 parts by weight of the rubber component. A pneumatic tire having a tread having a stress ratio of the rubber composition constituting the surface layer to 70% or less.