JP6181431B2 - Pneumatic tire - Google Patents

Description

The present invention relates to a pneumatic tire having a foam rubber layer in a tread portion.

In recent years, there has been a demand for reducing the weight of tires in order to reduce the fuel consumption of automobiles. As a means for reducing the weight of tires, pneumatic tires having a foamed rubber layer in the tread portion have been manufactured and marketed. . The foamed rubber bubbles used in the tread remove the water film and stabilize the contact with the road surface. This foamed rubber can be obtained by adding a pyrolytic foaming agent to solid rubber and vulcanizing it. Since the heat source for vulcanization is outside the rubber, vulcanization proceeds in order from the outside. As a result, the bubbles on the surface are fine and the bubbles inside are large. This is because the rubber vulcanization precedes foaming at the surface to increase the viscosity, and the generation of bubbles is suppressed. Inside, foaming precedes vulcanization, so the foaming progresses while the viscosity is low. This is because the growth can be greatly increased (Patent Document 1 and Non-Patent Document 1).

However, there is a problem that the air bubbles in the surface portion become fine and the braking performance (wet braking performance) on the wet road surface due to the water absorption effect that is a feature of the foamed rubber cannot be sufficiently exhibited. Although it is possible to increase the overall bubble diameter, a large bubble diameter lowers the storage elastic modulus G ′ of the rubber, so that it is difficult to ensure sufficient steering stability when traveling at high speed.

Patent Document 2 discloses a tread rubber having a higher expansion ratio in the outer portion than in the inner portion. However, the outer side in the tire radial direction is heated and foamed at a higher temperature than the inner side. Therefore, there are a number of fine bubbles in the outer portion, and there is a problem that the wet braking performance cannot be sufficiently exhibited.

Japanese Patent Application Laid-Open No. 2012-3231 JP 2010-274785 A

Mitsuo Akiba et al., Japan Rubber Association, Vol. 74, 386-391.

An object of the present invention is to provide a pneumatic tire that can achieve both high wet braking performance and water handling stability due to water absorption without impairing the weight reduction effect due to foaming.

The present inventors examined a tire having a foamed rubber layer in the tread portion of the tire. As a result, the weight of the foam was ensured by increasing the average bubble diameter of the surface portion of the foamed rubber layer and decreasing the average bubble diameter inside. In addition, the present inventors have found that wet braking performance by water absorption and steering stability can be achieved at a high level, and the present invention has been completed.

That is, the present invention relates to a pneumatic tire using a foam rubber layer in a tread portion, wherein the average cell diameter inside the tread of the foam rubber layer is smaller than the tread surface portion.

The average bubble diameter of the foamed rubber layer is preferably 40 to 100 μm at the tread surface and 5 to 40 μm inside.

The tread surface portion is preferably 5 to 10 mm in the center direction from the tire surface, and the inside of the tread is preferably 1 to 7.5 mm in the center direction from the lowermost portion of the surface portion.

The vulcanization pressure in the vulcanization step is preferably 1.4 to 5.0 MPa.

The difference between the minimum value (ML) and the maximum value (MH) of the torque of the vulcanization rate curve at 160 ° C. (according to JIS K 6300 “Testing method for unvulcanized rubber”) of the rubber composition used for the foam rubber layer When (MH−ML) is ME, it is preferable that time t10 (minute) to reach ML + 0.1ME is slower than 2.5 minutes.

The foamed rubber is preferably produced using a pyrolytic foaming agent.

The foaming agent is preferably azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, 4,4′-oxobisbenzenesulfonyl hydrazide, or sodium bicarbonate.

The following formula summarizing the surface portion and the inside of the foamed rubber layer:
Foaming rate = (density of solid phase in vulcanized rubber / density of vulcanized rubber−1) × 100%
It is preferable that the foaming rate calculated by is 10 to 50%.

According to the present invention, the average bubble diameter of the foamed rubber layer can be ensured by making the inside of the tread smaller than the surface of the tread, so that water absorption can be secured, and the braking distance (wet braking on a wet road surface) can be ensured. Distance) can be shortened. In addition, by making the internal bubbles fine, it is possible to suppress a decrease in the storage elastic modulus G ′ and to ensure steering stability at high speeds.

The pneumatic tire of the present invention is a pneumatic tire using a foamed rubber layer in a tread portion, wherein the average cell diameter inside the tread of the foamed rubber layer is smaller in the tread surface portion than in the tread surface portion. .

The average cell diameter of the foamed rubber layer used for the tread portion is preferably 40 to 100 μm and more preferably 50 to 70 μm at the tread surface portion. If it is less than 40 μm, a sufficient water absorption effect cannot be obtained, and the braking performance on wet road surfaces tends to be difficult to obtain sufficiently. When the average cell diameter exceeds 100 μm, the wear resistance tends to deteriorate, and the wear performance as a summer tire tends to be unable to be ensured. On the other hand, 5-40 micrometers is preferable inside a tread, and 20-40 micrometers is more preferable. If it exceeds 40 μm, the storage elastic modulus G ′ tends to decrease and sufficient steering stability cannot be ensured. If it is less than 5 μm, the foaming rate tends to be small and it becomes difficult to obtain a sufficient lightening effect.

Here, it is preferable that the tread surface portion is a portion of 5 to 10 mm in the center direction from the tire surface, and the inside of the tread is a portion of 1 to 7.5 mm in the tire center direction from the lowermost portion of the surface portion. If the thickness of the surface portion is less than 5 mm, the internal fine bubbles appear early due to wear caused by running, and there is a tendency that a sufficient braking distance cannot be obtained. Moreover, when the thickness of the tread surface portion exceeds 10 mm and / or the thickness of the inner layer is less than 1 mm, sufficient steering stability tends to be unable to be ensured when traveling. And when the internal thickness is 10 mm or more, the surface layer thickness cannot be secured, and there is a tendency that a sufficient lightening effect cannot be obtained.

In order to obtain the desired average cell diameter of the tread surface portion, the torque of the vulcanization rate curve at 160 ° C. (according to JIS K 6300 “Testing method for unvulcanized rubber”) in the rubber composition forming the foam rubber layer When the difference (MH−ML) between the minimum value (ML) and the maximum value (MH) is set to ME, the time (scorch time) t10 (minute) to reach ML + 0.1ME is 2.5 to 3.5. Minute is preferable, and 2.8 to 3.2 minutes is more preferable. When t10 is 2.5 minutes or more, the foaming reaction is started before the vulcanization starts and the viscosity increases, and the bubbles on the surface portion can be enlarged. When t10 is less than 2.5 minutes, vulcanization occurs earlier than foaming, and thus there is a tendency that bubbles having a large particle diameter cannot be obtained on the surface portion. Moreover, productivity can be ensured by making t10 into 3.5 minutes or less, and when it exceeds 3.5 minutes, there exists a tendency for productivity to fall.

The scorch time t10 can be controlled by, for example, the amount of 1,3-diphenylguanidine (Noxeller D) that is a vulcanization accelerator. In order to adjust the scorch time t10 to 2.5 to 3.5 minutes, for example, 1,3-diphenylguanidine (Noxeller D) is preferably 0.1 to 1.0 part by mass with respect to 100 parts by mass of the rubber component. More preferably, 0.2 to 0.8 parts by mass may be blended.

Furthermore, in order to obtain a desired average cell diameter inside the tread, in the vulcanization step of the rubber composition for a tire, the vulcanization pressure is preferably 1.4 to 5.0 MPa, and preferably 1.5 to 3.0 MPa. Is more preferable. By setting the vulcanization pressure to 1.4 MPa or more, it is possible to suppress bubble growth inside, and since the internal heat is slower than the surface portion, the vulcanization reaction precedes foaming and is fine. Bubbles can be generated. When the vulcanization pressure is less than 1.4 MPa, the effect of suppressing the bubble growth is not sufficient, and bubbles having a large particle diameter are generated inside, and a desired cell structure cannot be obtained. However, when the vulcanization pressure exceeds 5.0 MPa, the pressure applied to the mold increases, and the mold cannot withstand the pressure, and there is a tendency that a safety problem is likely to occur.
Although a vulcanization temperature is not specifically limited, 140-180 degreeC is preferable and 150-170 degreeC is more preferable.

The foamed rubber layer is preferably produced using a pyrolytic foaming agent. Thermally decomposable foaming agents are less likely to produce residues that affect the physical properties of the rubber composition after vulcanization, as compared to foaming agents such as micro-cellular using inert gas. .

The pyrolytic foaming agent is not particularly limited, and examples thereof include azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, 4,4′-oxobisbenzenesulfonylhydrazide, sodium hydrogen carbonate and the like. In particular, azodicarbonamide, 4,4'-oxobisbenzenesulfonyl hydrazide, and sodium hydrogen carbonate tend to make it difficult to produce a residue that affects the physical properties of the rubber composition after vulcanization. These foaming agents can be used alone or in combination.

Although the compounding quantity of a thermal decomposition type foaming agent is not specifically limited, 3-8 mass parts is preferable with respect to 100 mass parts of rubber components, and 4-7 mass parts is more preferable. If it exceeds 8 parts by mass, the expansion ratio exceeds 50%, and if it is less than 3 parts by mass, the expansion ratio tends to be less than 10%.

The following formula that combines the surface and the inside of the foam rubber:
Foaming rate = (density of solid phase in vulcanized rubber / density of vulcanized rubber−1) × 100%
Is preferably 10 to 50%, more preferably 20 to 40%. When the foaming rate is 10 to 50%, it is possible to achieve both weight reduction and steering stability, wear resistance, and durability. On the other hand, when the foaming ratio is less than 10%, the effect of reducing the weight is reduced, and when it exceeds 50%, steering stability, wear resistance, and durability tend to be lowered.

The rubber component contained in the rubber composition used in the present invention is not particularly limited. For example, natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), styrene isoprene butadiene. Examples include diene rubbers such as rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). These may be used alone or in combination of two or more. Among these, SBR and BR are preferable because the effect of improving crack growth resistance is high, and the combined use of SBR and BR is more preferable.

SBR and BR are not particularly limited, and those common in the tire industry can be used.

The content of SBR in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 45% by mass or more, and further preferably 55% by mass or more. Further, the SBR content may be 100% by mass, but is preferably 90% by mass or less. If it is in the said range, the effect of this invention will be acquired favorably.

The content of BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 15% by mass or more. The BR content is preferably 70% by mass or less, more preferably 55% by mass or less, and still more preferably 45% by mass or less. If it is in the said range, the effect of this invention will be acquired favorably.

The total content of SBR and BR in 100% by mass of the rubber component is preferably 60% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. If it is in the said range, the effect of this invention will be acquired favorably.

In addition to the rubber component, the rubber composition used in the present invention can be appropriately blended with additives generally used in the production of rubber compositions. Known additives can be used, such as sulfur vulcanizing agents; thiazole vulcanization accelerators, thiuram vulcanization accelerators, sulfenamide vulcanization accelerators, guanidine vulcanization accelerators. Vulcanization accelerators such as stearic acid and zinc oxide; organic peroxides; fillers such as carbon black, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica; Examples thereof include processing aids such as oils and lubricants; anti-aging agents; and coupling agents.

The shape of the foam is not particularly limited. Since the average cell diameter inside the tread of the foam rubber layer is smaller than the tread surface part, it can be applied to summer tires that require steering stability, and due to the water absorption effect of foaming, It can be run on some snowy roads.

The pneumatic tire of the present invention is produced by a usual method using a rubber composition. That is, if necessary, a rubber composition in which various additives are blended with a rubber component is extruded in accordance with the shape of the tire tread at an unvulcanized stage. The tire is molded by a normal method on a tire molding machine, and the tread member is bonded together with other tire members to form an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to be foamed to produce the pneumatic tire of the present invention.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
SBR: Nipol 1502 manufactured by Nippon Zeon Co., Ltd. (styrene amount: 23.5% by mass) 80 parts by mass BR: Hisys BR150B manufactured by Ube Industries, Ltd. 20 parts by mass Carbon black: Show black manufactured by Cabot Japan Co., Ltd. N220 (nitrogen adsorption specific surface area (N ₂ SA): 125 m ² / g) 20 parts by mass Silica: Ultrasil VN3 (nitrogen adsorption specific surface area (N ₂ SA): 175 m ² / g) manufactured by Degussa Co. 80 parts by mass Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa, Inc. 5 parts by mass anti-aging agent: NOCRACK 6C (N-1,3-dimethyl, manufactured by Ouchi Shinsei Chemical Co., Ltd.) Butyl-N′-phenyl-p-phenylenediamine) 3 parts by mass Stearic acid: 5 parts by mass of stearic acid manufactured by NOF Corporation Il: Mineral oil PW-380 manufactured by Idemitsu Kosan Co., Ltd. 10 parts by mass Zinc oxide: Zinc flower No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. 2 parts by weight Wax: Sunnock wax manufactured by Ouchi Shinsei Chemical Co., Ltd. 2 parts by mass sulfur: powdered sulfur produced by Tsurumi Chemical Industry Co., Ltd. 2 parts by mass vulcanization accelerator 1: Noxeller D (1,3-diphenylguanidine) produced by Ouchi Shinsei Chemical Industry Co., Ltd. 0.1-1. 5 parts by mass vulcanization accelerator 2: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd. 2 parts by mass blowing agent: Neocerbon manufactured by Eiwa Kasei Kogyo Co., Ltd. N # 1000SW (4,4′-oxobisbenzenesulfonylhydrazide, average particle size 14 μm) 5 parts by mass

(Examples 1-12 and Comparative Examples 1-2)
According to the blending amount of diphenylguanidine shown in Tables 1 and 2, materials other than sulfur and a vulcanization accelerator were kneaded for 3 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 5 minutes at 50 ° C. using an open roll to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was formed into a tread shape at the vulcanization pressure shown in Tables 1 and 2, and bonded to other tire members, and vulcanized at 170 ° C. for 15 minutes, whereby each example. And the tire (tire size 195 / 65R15) of the comparative example was produced. The following evaluation was performed using the obtained tire. The evaluation results are shown in Tables 1 and 2.

<Average cell diameter>
From the obtained tire, a tread block was cut out and sliced in the thickness direction, and bubbles were observed with a scanning electron microscope (Scanning Electron Microscope: SEM / XL 30 ESEM manufactured by Philippe). The diameter of the observed bubble is taken as the bubble diameter, and for all the bubbles in the range of 1 mm × 1 mm, the equivalent circle diameter is calculated, and the arithmetic average value of all the equivalent circle diameters is calculated. The average bubble diameter was measured for each.

<Steering stability>
The resulting tire is assembled on a 15 x 6 JJ aluminum wheel rim, filled with internal pressure 210 kPa (same front and rear), mounted on four wheels of a 2000cc domestic FF vehicle, and driver 1 in the test course I drove with a passenger car and made a sensory evaluation. Example 1 was evaluated with an index of 100. The larger the value, the better.

<Wet braking performance>
The resulting tire is assembled on a 15 x 6 JJ aluminum wheel rim, filled with internal pressure 210 kPa (same front and rear), mounted on four wheels of a 2000cc domestic FF vehicle, and driver 1 in the test course By name, the braking distance from an initial speed of 100 km / h was measured on a wet asphalt road surface. And it evaluated by the index | exponent which sets the wet grip performance index | exponent of Example 1 to 100. FIG. In the evaluation, the wet braking performance (wet grip performance) of each formulation was displayed as an index according to the following formula. Larger values indicate better wet braking performance.
(Wet braking performance index) = (Brake distance of Example 1) / (Brake distance of each formulation) × 100

<Abrasion resistance>
After the tire was assembled on a 15x6 JJ aluminum wheel rim and filled with an internal pressure of 210 kPa (same front and rear), mounted on a four-wheeled vehicle with a 2000cc domestic FF car and running on a general road The remaining groove after 6 months was measured, and it was written as an index by a 100-point method with Example 1 as 100. The larger the value, the better.

<Weight>
The test tire was measured on a weighing scale fixed in a horizontal state. It shows with an index when Example 1 is set to 100. The larger the value, the better the weight and the better.
Weight index = weight of Example 1 / weight of each Example or Comparative Example × 100%

In the tires of Examples 1 to 12, compared with the tires of Comparative Examples 1 and 2, the steering stability and wet braking performance can be exhibited at a higher level. Particularly, in the tires of Examples 1 to 7, the wear resistance and the weight can be exhibited at a high level.

Claims (8)

A pneumatic tire using a foamed rubber layer in a tread portion, wherein an average cell diameter inside the tread of the foamed rubber layer is smaller than a tread surface portion.
(However, it is a pneumatic tire having an annularly formed tread portion and a pair of sidewall portions and bead portions connected to both sides of the tread portion, wherein the tread portion has a plurality of block rows on the tread portion. In a pneumatic tire having a tread pattern including and having a two-layer structure in which a cap rubber layer and a base rubber layer are laminated from the outside in the tire radial direction, the block has an inclination with respect to the tire axial direction. In the both sides of the shoulder portion, there are a plurality of sipes extending in the tire width direction substantially parallel to each other between adjacent blocks in the circumferential direction, the cap rubber layer is cylindrical closed cells containing alumina, and the base rubber layer is spherical Each of which contains closed cells, and the Shore A hardness of the base rubber layer is larger than the Shore A hardness of the cap rubber layer. Except for the pneumatic tire.) 2. The pneumatic tire according to claim 1, wherein the foamed rubber layer has an average cell diameter of 40 to 100 μm at a tread surface portion and 5 to 40 μm inside. The pneumatic tire according to claim 1 or 2, wherein the tread surface portion is 5 to 10 mm in a central direction from the tire surface, and the inside of the tread is 1 to 7.5 mm in a central direction from the lowermost portion of the surface portion. The pneumatic tire according to any one of claims 1 to 3, wherein a vulcanization pressure in the vulcanization step is 1.4 to 5.0 MPa. The difference between the minimum value (ML) and the maximum value (MH) of the torque of the vulcanization rate curve at 160 ° C. (according to JIS K 6300 “Testing method for unvulcanized rubber”) of the rubber composition used for the foam rubber layer The pneumatic tire according to any one of claims 1 to 4, wherein a time t10 (min) for reaching ML + 0.1ME is 2.5 minutes or more when (MH-ML) is ME. . The pneumatic tire according to claim 1, wherein the foamed rubber is manufactured using a pyrolytic foaming agent. The foaming agent is azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, 4,4′-oxobisbenzenesulfonyl hydrazide, or sodium hydrogen carbonate, according to claim 6. Pneumatic tire. The following formula summarizing the surface portion and the inside of the foamed rubber layer:
Foaming rate = (density of solid phase in vulcanized rubber / density of vulcanized rubber−1) × 100%
The pneumatic tire according to any one of claims 1 to 7, wherein the foaming ratio calculated by the formula (1) is 10 to 50%.