JP2008174015A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire with improved appearance showing blackness having good-looking gloss by heightening the blackness degree of the outer surface of the pneumatic tire. <P>SOLUTION: At least a part of the outer surface of the pneumatic tire 1 is provided with a rubber member 10 composed of rubber composition containing 10-80 pts.wt of carbon black having a nitrogen adsorbing specific surface area (N<SB>2</SB>SA) of 125 m<SP>2</SP>/g or more out of 100 pts.wt of a rubber component. In the rubber member 10, the brightness L* value is 20 or less, and the surface roughness Ra is 0.1-0.7 μm. The rubber member 10 could be a display part 12 on an outer surface of a side wall part 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pneumatic tire that improves the appearance quality of the tire, and more particularly to a pneumatic tire that improves the blackness of a rubber composition and provides a clear black color on the outer surface of the tire by imparting gloss. Is.

  Usually, a pneumatic tire is formed of black rubber mixed with carbon black as a reinforcing agent. However, oil such as wax added to rubber to prevent deterioration due to ozone, oxygen or heat in the atmosphere and additives such as amine-based anti-aging agent migrate to the tire outer surface over time and bloom, The outer surface of the tire may change from black to white or brown, or may appear dull and lose its luster, which may impair the appearance. Such a tendency is particularly prominent in the sidewall portion that is easily visible from the outside. In particular, in recent years, demands for improving tire appearance performance have increased due to the differentiation of user preferences and the trend toward higher grades.

  Conventionally, in order to solve such problems, attempts have been made to reduce the amount of bloom by reducing the amount of wax, an antioxidant, and the like. For example, in the following Patent Document 1, a specific ethylene-propylene-diene copolymer (EPDM) excellent in ozone resistance, a halogenated butyl rubber, and a specific carbon black are blended to reduce the amount of the antioxidant. Although a rubber composition that can reduce discoloration due to aging of the side wall rubber while improving ozone resistance is disclosed, this document does not mention improving blackness for the purpose of preventing discoloration due to bloom.

  Further, in Patent Document 2, the surface roughness of the sidewall molding surface is molded with a tire mold of less than 0.381 microns, so that the 60 ° glossiness of the sidewall has a surface glossiness greater than 10. A tire that forms a highly reflective surface on the sidewall by forming a dense and smooth skin-like surface layer that delays the diffusion of chemicals such as antioxidants from inside the rubber is described. The relationship between the surface roughness of the tire and the blackness of the outer surface of the tire is not shown. Further, in order to increase the blackness, it is necessary to increase the glossiness. However, if the glossiness is excessively increased, there may be a problem that a scratch pattern due to rubbing or the like is conspicuous.

Further, in Patent Document 3, the surface roughness (RaT) of a vulcanized tire is in a range of 1.5 to 20 μm when measured with a stylus type surface roughness meter, and the glossiness of the tire surface is determined. It is described that the appearance is improved, and the fine surface roughness does not correspond to the improvement of the glossiness.
JP-A-5-32827 JP 2004-17964 A JP 2000-142026 A

  In recent years, there has been an increasing demand for higher grades and higher quality by users, and there is a demand for pneumatic tires to improve appearance in pursuit of good-looking blackness.

  Then, an object of this invention is to provide the pneumatic tire which raised the blackness of the outer surface of a pneumatic tire, and improved the external appearance which shows the blackness which has the glossiness with a good appearance.

  The present inventors have conducted extensive research in view of such a situation, and while improving the blackness with a specific carbon black composition, the outer surface of the tire is given a certain range of surface roughness and glossiness is improved. It has been found that balancing the blackness and the glossiness by adjusting it closely leads to an improvement in appearance.

That is, the present invention provides 10 to 80 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 125 m ² / g or more with respect to 100 parts by weight of the rubber component on at least a part of the outer surface of the tire. A pneumatic tire comprising a rubber member having a lightness L ^* value of 20 or less and a surface roughness Ra of 0.1 to 0.7 μm, comprising a rubber composition.

  In the present invention, it is effective for improving the appearance that the rubber member is arranged on at least a part of the outer surface of the sidewall portion, and the display forming portion for characters, figures, patterns, etc. on the sidewall portion is effective. It is good.

  According to the present invention, the blackness of the surface of a pneumatic tire can be improved and the blackness can be enhanced. Particularly, when applied to a sidewall portion that is easy to be visually recognized from the outside, the appearance of black is clearly visible without impairing the tire performance. It is possible to provide a pneumatic tire that exhibits excellent black gloss and excellent appearance.

  Embodiments of the present invention will be described below.

The pneumatic tire of the present invention comprises a rubber composition containing 10 to 80 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 125 m ² / g or more with respect to 100 parts by weight of a rubber component. A rubber member having an L ^* value of 20 or less and a surface roughness Ra of 0.1 to 0.7 μm is disposed on the outer surface of the tire.

Here, the lightness L ^* value is a value that serves as an index of blackness when the outer surface of the tire is measured with a colorimetric colorimeter in accordance with the provisions of JIS Z8722. If the L ^* value exceeds 20, the tire will appear grayish, or it will appear whitish depending on the viewing angle and the reflection of light, resulting in insufficient blackness, and the blackness cannot be satisfied and the appearance is not improved.

The L ^* value largely depends on the formulation of the rubber composition. In the present invention, an L ^* value of 20 or less is secured by containing a specific amount of specific carbon black.

That is, in the present invention, the rubber composition constituting the rubber member is 10 to 80 carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 125 m ² / g or more with respect to 100 parts by weight of the rubber component. Part by weight is included, whereby the L ^* value can be 20 or less. N ₂ SA is measured in accordance with ASTM D3037.

The carbon black is a reinforcing agent for the rubber composition and also serves as a black pigment for coloring the rubber composition black. As the carbon black for obtaining an L ^* value of 20 or less, it is preferable to use a carbon black having a fine particle and a low structure, that is, a carbon black having an N ₂ SA of 125 m ² / g or more is suitable. Specifically, carbon black having N ₂ SA of SAF grade or higher can be mentioned.

The upper limit of N ₂ SA of carbon black is not particularly limited. However, if N ₂ SA becomes too large, processing due to deterioration in rubber properties such as heat generation, rubber hardness, bending fatigue resistance, rolling resistance, and poor dispersibility. The upper limit of N ₂ SA is preferably about 200 m ² / g because of the possibility of deteriorating the properties.

The compounding amount of the carbon black is 10 to 80 parts by weight, preferably 20 to 60 parts by weight, and more preferably less than 50 parts by weight with respect to 100 parts by weight of the rubber component. If the amount of carbon black is less than 10 parts by weight, it is difficult to obtain an L ^* value of 20 or less, and if it exceeds 80 parts by weight, the particles are small, so the dispersibility deteriorates and the processability decreases.

  Further, in combination with the above-mentioned SAF grade or higher carbon black, ISAF, HAF, FEF, GPF grade carbon black conventionally used in tire rubber compositions may be used according to the required characteristics of the rubber composition. Good. As a result, the processability can be improved by making up for a decrease in dispersibility of the fine carbon black, and rubber properties such as bending fatigue resistance and rolling resistance when the rubber composition is used for a sidewall can be improved. .

  Further, as the rubber component, diene rubber is preferable, and natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and styrene butadiene rubber (SBR), which are generally used in tire rubber compositions. Diene-based synthetic rubbers such as these can be used, and at least one selected from these, or a blend of two or more can be used. In the case of sidewall rubber, NR, IR, and BR are preferable because rubber properties such as strength and bending fatigue resistance are improved.

  In addition, from the viewpoint of improving weather resistance such as ozone resistance, heat resistance, etc., ethylene-propylene-diene copolymer (EPDM) and halogenated butyl rubber (BIIR, CIIR) are used in a small amount together with the diene rubber. Also good.

  In the rubber composition, fillers other than carbon black, such as silica, are included in the range not departing from the object of the present invention, and vulcanization of anti-aging agents, waxes, zinc white, stearic acid, oils, resins, sulfur, etc. Various known compounding agents generally used in tire rubber compositions such as vulcanizing agents and vulcanization accelerators can be blended, and various compounding agents are blended into the raw rubber, and a kneader such as a Banbury mixer is used. It can be prepared according to a conventional method.

While examining the improvement in blackness of the rubber composition, the present inventors have noticed that the appearance is not improved so much even though the tire satisfies the lightness L ^* value as a blackness index within a range of 20 or less. It was. Therefore, after further diligent investigation, the blackness, that is, the absolute value of the L ^* value alone cannot satisfy the apparent blackness, and the tire outer surface has a fineness (the size of the surface unevenness, It has been found that the blackness and glossiness are balanced by adding depth), and the satisfaction of the apparent blackness is remarkably improved.

  That is, the rubber member has a surface roughness Ra in the range of 0.1 to 0.7 μm, and is to increase the glossiness of the outer surface of the tire.

  The surface roughness Ra is an arithmetic average roughness of the degree of unevenness of the surface measured on the outer surface of the tire with a stylus type surface roughness meter in accordance with the provisions of JIS B0601.

If the surface roughness Ra is less than 0.1 μm, light is reflected on the rubber member on the tire surface and the tire tends to appear whitish. Also, when oil or mud adheres to the tire surface, rubbing, etc. Small scratches are also noticeable. On the other hand, when the surface roughness Ra is larger than 0.7 μm, the balance with the blackness is lost, and even if the L ^* value is 20 or less, the black looks dull and lacks the glossiness and the appearance is deteriorated. To do.

  The surface roughness Ra of the tire outer surface can be formed by a tire vulcanization mold having a molding surface having a surface roughness substantially equal to the roughness of the tire surface. That is, the surface roughness of the mold is transferred to the outer surface of the tire by vulcanization molding with substantially the same surface roughness.

  The surface roughness of the mold forming surface can be adjusted using a known method such as a shot blast method, a metal plating method, or a mirror polishing method.

  FIG. 1 is a half sectional view of a pneumatic tire 1 according to an embodiment of the present invention. FIG. 2 shows a partial perspective view of the pneumatic tire 1. The pneumatic tire 1 includes a tread portion 2, a sidewall portion 3 that extends outward in the tire radial direction from both ends, and a bead portion 4 that continues to the outer end of the sidewall portion 3 and is fixed to a rim flange. In this example, a radial structure carcass 6 in which the ply end is folded back and locked to the bead core 5, a belt layer 7 disposed on the outer periphery of the tread portion of the carcass 6, and a belt reinforcing layer wound around the outer periphery of the belt layer 7 A passenger car radial tire having 8 is illustrated.

  The pneumatic tire 1 is provided with a rubber member on the outer surface, and the rubber member may be all or a part of the outer surface of the tire, and the sidewall portion 3 that is easily visible from the outside improves the appearance. This is effective. Of course, the rubber member may cover the surface of the tire with a film-like body of a rubber composition having a thickness of about 0.2 to 2 mm.

  Further, the rubber member can be a part of the sidewall portion 3, for example, a brand name, tire size, design pattern, etc., in which the rubber member 10 is formed in an uneven shape on the outer surface of the sidewall as shown in FIG. The display unit 12 may be a character, a figure, a pattern, or the like, and the appearance of the display unit 12 is conspicuous in the sidewall unit 3, and the design and identification can be improved. Moreover, the display part 12 may be formed in the same plane without providing unevenness on the sidewall surface.

  In the case of a tire in which the sidewall portion 3 has two or more multilayered sidewalls composed of an inner layer and an outer layer, a rubber member may be applied to the outer layer constituting the sidewall surface.

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

  In this embodiment, the rubber member is applied to the entire sidewall portion of the pneumatic tire.

  According to the compounding recipe (parts by weight) shown in Table 1, rubber compounds A to C for side walls were prepared by kneading by a conventional method using a Banbury mixer with a capacity of 200 liters. The rubber components and compounding agents used are as follows.

[Rubber ingredients, compounding agents]
・ Natural rubber (NR): Made in Thailand RSS # 3
-Butadiene rubber (BR): Ube Industries, Ltd. BR150B
Carbon black (CB) FEF: Tokai Carbon Co., Ltd. Seest SO (N ₂ SA = 42 m ² / g)
Carbon black (CB) SAF: Tokai Carbon Co., Ltd. Seast 9 (N ₂ SA = 142 m ² / g)
Aroma oil: Japan Energy Co., Ltd. X-140
Paraffin wax: Nippon Seiwa Co., Ltd. Ozoace-0355
Anti-aging agent 6C: Nouchi 6C, Ouchi Shinsei Chemical Co., Ltd.
・ Stearic acid: Kao Corporation Lunac S-20
・ Zinc oxide: Mitsui Kinzoku Mining Co., Ltd. Zinc Hua 1 ・ Sulfur: Hosoi Chemical Industry Co., Ltd. 5% oil-treated powder sulfur ・ Vulcanization accelerator NS: Ouchi Shinsei Chemical Co., Ltd. Noxeller NS-P

A radial tire having a size of 195 / 65R15 88S in which the obtained rubber composition was applied to the sidewall portion was prototyped. For the prototype tire, the surface roughness of the molding surface of the side wall molding die made of an aluminum alloy is adjusted to Ra = 0.07 to 2.6 μm by a known shot blasting method, chrome plating method, and mirror polishing method. A tire was vulcanized and molded under the same vulcanization conditions using the resulting rubber composition in combination with each rubber composition shown in Table 2. The lightness L ^* value of the sidewall portion of the prototype tire, the surface roughness Ra, and the appearance appearance evaluation by the panel were measured by the following methods. The results are shown in Table 2.

[Brightness L ^* value]
Using the color difference meter “ZE2000” manufactured by Nippon Denshoku Industries Co., Ltd., the side wall of the prototype tire is measured in accordance with the method of JIS Z8722, and L ^* values at five locations in the tire circumferential direction are measured. The average value was obtained.

[Surface roughness]
Using the stylus type surface roughness tester “E-35A” manufactured by Tokyo Seimitsu Co., Ltd., the side wall of the prototype tire is measured according to the method of JIS B0601, and Ra is measured at five locations in the tire circumferential direction. The average value was obtained.

[Appearance evaluation]
In accordance with the provisions of JIS Z8723, the blackness of appearance was observed by five panelists, and the average value of the five persons was regarded as the appearance evaluation. The results are shown in Table 2, with “◎” indicating excellent, “◯” indicating good, “Δ” indicating slightly inferior, and “×” indicating inferior.

From Table 1, it is necessary to apply SAF grade carbon black to the rubber composition in order to make the L ^* value 20 or less. The smaller the Ra, the lower the L ^* value even in the same blend, and the synergistic effect of both. It can be seen that the appearance improves. Even if the L ^* value satisfies 20 or less, if Ra is less than 0.1, the rubber member appears whitish and the appearance evaluation is lowered (Comparative Example 5).

  The pneumatic tire of the present invention is suitable not only for general-purpose automobile tires such as passenger car tires, light truck tires, truck bus tires, but also for competition and game tires.

It is a half sectional view of the pneumatic tire of an embodiment. It is a fragmentary perspective view of a pneumatic tire same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pneumatic tire 3 ... Side wall part 10 ... Rubber member 12 ... Display part

Claims (2)

On at least part of the outer surface of the tire,
The lightness L ^* value is 20 or less, comprising a rubber composition containing 10 to 80 parts by weight of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 125 m ² / g or more with respect to 100 parts by weight of the rubber component. And a rubber member having a surface roughness Ra of 0.1 to 0.7 μm. The pneumatic tire according to claim 1, wherein the rubber member is at least a part of an outer surface of the sidewall portion.

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