JPH11293035A - Rubber composition for tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tires which prevents changes in appearance such as browning of the tire surface, etc., caused by cross- migration of amine antioxidants, without deteriorating the ozone resistance and the oxidation resistance. SOLUTION: A rubber composition is prepared by mixing at least one rubber chosen from the group consisting of natural rubbers and diene synthetic rubbers with an amine aging inhibitor. Here, against 100 pts.wt. the above-mentioned rubber, from 0.5 to 10 pts.wt. porous carbon black is blended. A carbon black wherein the DBP oil adsorption is 300 cm<3> /100 g or larger or a ketchen black is used as the porous carbon black.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for a tire, which prevents an anti-aging agent or wax which causes brown discoloration of a tire surface from migrating to the surface, and maintains an aesthetic appearance.

[0002]

2. Description of the Related Art Tires for automobiles are used as raw rubber.
Diene rubbers such as natural rubber and butadiene rubber are used. For the purpose of preventing aging of raw rubber due to ozone and oxygen, and cracking due to hardening due to aging and running, a rubber composition in which raw rubber is compounded with an amine-based antioxidant, a paraffin-based wax, etc. has been used. I have.

[0003] However, these antioxidants and waxes easily cause a bloom phenomenon in a short period of time, and migrate to the tire surface with the passage of time, causing the tire surface to turn brown. The brown discolored tire has a remarkably bad appearance and its commercial value is low. In order to solve this problem, conventionally, a silicone coating agent (JP-A-60-38205, which is referred to as Conventional Example 1) or an alcohol solution of polyethylene glycol (JP-A-63-41203, Example 2) was applied to the tire surface, or a surfactant was incorporated into the rubber component (Japanese Patent Laid-Open No. 5-194790, which is referred to as Conventional Example 3) to prevent poor appearance. .

[0004]

The use of a coating agent has the following problems. In general, a coating material is inferior in durability of the effect because the tire surface is worn. Further, when the tire is worn, the coating agent is scattered, which adversely affects the environment, which is not preferable. In addition, it is necessary to provide a painting step in the tire manufacturing process, which is complicated.

[0005] The prior art 1 has a problem in that the bead portion is liable to slip by applying a silicon-based coating material, and the rim of the tire is liable to be removed, and the safety of the vehicle is reduced. The polyethylene glycol-based coating agent of Conventional Example 2 described above can prevent brown discoloration on the tire surface while maintaining the rim resistance, but repels the non-polar tire surface due to the polarity due to OH groups. However, it is difficult to apply it uniformly on the surface.

[0006] The above-mentioned Conventional Example 3 is also effective, but is insufficient to prevent brown discoloration of the tire due to an antioxidant or wax. On the other hand, it is conceivable to suppress the blooming phenomenon by reducing the amount of the antioxidant, but a decrease in the antioxidant content is not preferable because it leads to a decrease in weather resistance. The present invention has been made in view of such a technical background, and aims at an additive for maintaining the properties without deteriorating rubber properties such as ozone resistance and oxidation resistance. An object of the present invention is to provide a rubber composition for a tire which prevents a change in the appearance of a tire such as a bloom phenomenon caused by the above and further maintains this effect of preventing discoloration for a long time.

[0007]

Means for Solving the Problems In order to solve the above problems, the following measures have been taken. That is, in a rubber composition in which an amine-based antioxidant is mixed with at least one rubber selected from the group consisting of natural rubber and diene-based synthetic rubber, porous carbon black is added in an amount of 0.1 part by weight to 100 parts by weight of the rubber. 5 to 10 parts by weight were blended.

Examples of the diene rubber include styrene-butadiene copolymer rubber, synthetic polyisoprene rubber, butadiene rubber, and the like. These diene rubbers may be used alone or in combination, or may be used in combination with natural rubber. You may. As the amine antioxidant, for example, N-phenyl-N '-(1,3 dimethylbutyl) -p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine and the like are used. In general, the amount of the amine antioxidant is preferably 1 to 5 parts by weight based on 100 parts by weight of the rubber component.

In the present invention, a substance capable of adsorbing an amine-based anti-aging agent (hereinafter referred to as an adsorbed substance) was studied in order to prevent discoloration of the tire brown due to migration of the amine-based anti-aging agent to the surface. In the adsorption test, Bincho charcoal (two types of coarsely crushed and finely crushed) and carbon N330 were used as samples.
(A kind of carbon black generally used for tire rubber), silica VN3, and porous carbon black were used. As a result, it was found that the amount of porous carbon black adsorbed was extremely large, so that the substance was used as the adsorbed substance.

[0010] The porous carbon black, the DBP oil absorption is adopted what is 300 cm ^3/100 g or more. To clarify the porosity criterion, D is a factor correlating to the porosity of carbon black.
The BP refueling amount was specified. The DBP lubrication amount of carbon black usually used for tire rubber is approximately 10
0cm is about ³ / 100g. For example DBP oil absorption of the foregoing carbon N330 is 101 cm ^3/100 g, DBP oil absorption of the carbon N220 is 115cm ^3/100
g. The low ability of these carbon blacks to adsorb the amine-based antioxidant is apparent from the fact that the surface of the conventional tire discolors brown. Therefore, the DBP lubrication amount of ordinary carbon black is not an index of porosity.

Ketjen black is used as the porous carbon black. The Ketjen Black is known as porous carbon black and its DBP
Amount of oil is also 300cm ³ / 100g or more. Was used in the present invention, for example, DBP oil absorption is 495cm ^3/1
00 g Ketchen Black EC600JD. In addition to this, for example, DBP oil absorption is 360 cm ^3/100
g of Ketjen Black EC and the like.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. First, in order to prevent the amine-based anti-aging agent of the present invention from migrating to the surface, adsorbed substances were examined. The samples used in the adsorption test were Bincho charcoal (two types, roughly crushed and finely crushed), carbon N330, silica VN3, and Ketjenblack EC600JD as described above.

The method of the adsorption test will be described below. Anti-aging agent N- (1,3-dibutyl) -N′-phenyl-p
1 g of phenylenediamine (hereinafter abbreviated as 6c)
A methanol solution dissolved in 00 ml of methanol was prepared. 10 g of each sample was placed on a funnel with absorbent cotton, washed sufficiently with methanol, and then 5 ml of the methanol solution was uniformly poured into the sample. A further 10 ml of methanol was flowed from above, and the resulting solution was
One-fold dilution was used as a sample solution.

Next, the absorbance at 290 nm of each of the sample solutions was measured. Table 1 shows the results. The lower the measured value, the more the sample adsorbed the 6c. The absorbance of the sample solution passed through Ketjen Black EC600JD was significantly lower than those of the other samples, indicating that the Ketjen Black adsorption ability was extremely excellent.

It can be seen that carbon N330, which is usually used for tire rubber, has an adsorption ability better than Bincho charcoal or silica, but is clearly inferior to Ketjen black. Therefore, Ketjen Black has been used as a substance for adsorbing an amine antioxidant.

[0016]

[Table 1]

Next, the structure of Ketjen Black will be described. Ketjen black has a hollow shell structure in which graphite crystals are gathered thinly on the outside (in the present invention, the structure defines porosity, and hereinafter, a structure similar or similar to the structure is referred to as a porous structure) ).
It is considered that this porous structure contributes to the high adsorption capacity of Ketjen Black.

The large amount of DBP lubrication of Ketjen Black is also due to this structure.
The correlation between P refueling and porosity is explained here. Therefore, carbon black having a large DBP oil supply amount is considered to have the above-mentioned porous structure, and it can be said that the carbon black is porous. Therefore, the amine-based anti-aging agent is excellent in adsorption ability, and the transfer of the anti-aging agent to the tire surface can be effectively prevented.

Therefore, the adsorbing substance used in the present invention is not limited to Ketjen black, but may be any porous carbon black having the above-mentioned porous structure and a large DBP lubrication amount. Here, the DBP lubrication amount, which is an index of the porosity of carbon black, will be described. The DBP oil absorption amount of the carbon black to be commonly used in tire rubber is approximately 100cm ³ / 100g about. For example DBP oil absorption of the foregoing carbon N330 is 101 cm ^3/100
g, DBP lubrication amount of carbon N220 is 115 cm ³ /
100 g. The low ability of these carbon blacks to adsorb the amine-based antioxidant is apparent from the fact that the surface of the conventional tire discolors brown. 100cm ³ /
A DBP lubrication amount of about 100 g cannot be said to be porous carbon black.

Compared to these, Ketjen Black has an extremely large DBP refueling amount. For example, Ketchen black EC is 360cm ³ / 100g, said EC600JD
Is a 495cm ³ / 100g. Most preferably, the amount of DBP lubrication of the porous carbon black used for the adsorbent is about the same as that of Ketjen black. However, since the DBP refueling amount has a unique value for each carbon black, it is difficult to clearly define the same degree. In the present invention, therefore, was porous indication that DBP oil absorption is approximately 300 cm ^3/100 g or more.

Therefore, not only Ketjen Black but also the above DBP lubrication amount of 300
It was also available in cm ^3/100 g or more porous carbon black. Next, a specific example of a rubber composition will be described in detail. Using Ketjen Black EC600JD (hereinafter referred to as EC600JD) selected in the above process, five types of rubber compositions having the composition shown in Table 2 were prepared (unit is parts by weight). Carbon N550 and EC
The components other than 600 JD are all the same, and the blending amounts are all the same. The rubbers used are NR and BR, but are not limited thereto. Diene rubbers such as the aforementioned styrene-butadiene copolymer rubber and synthetic polyisoprene rubber may be used. These diene rubbers may be used alone. You may mix as mentioned above. The type of rubber to be mixed is not limited.

The antioxidant used was 6c described above, but is not limited thereto. In addition, N-tert-butyl-2-benzothiazolylsulfenamide (hereinafter abbreviated as NS) was used as the vulcanization accelerator, but is not limited thereto. In Comparative Example 1, 50 phr of carbon N550 was blended with the rubber component.
Carbon N550 is carbon black normally used for tire rubber. This example is a compounding example of a normal rubber composition for a tire, which does not contain EC600JD.

Comparative Example 2 was prepared by adding EC600J to the composition of Comparative Example 1.
D is 0.1 phr. In Comparative Example 3, 30 phr of carbon N550 and EC6
It is a blend of 00JD and 20 phr. In Example 1, 48 phr of carbon N550 and E
Example 2 prepared by blending 2 phr of C600JD, 45 phr of carbon N550 and EC6
It is a blend of 5 phr of 00JD.

The compositions were left outdoors for one week,
The degree of discoloration was evaluated. The tensile stress M300 of the respective rubber composition, the tensile strength T _B, elongation E _B, also measures the rubber physical properties of the spring hardness H _S, were evaluated together. These results are also shown in Table 2.

[0025]

[Table 2]

[0026] [Evaluation Method] the tensile stress M300, tensile strength T _B, the measurement of the elongation E _B using the AUTO GRAPH AGS-500D manufactured by Shimadzu Corporation. The test piece is a dumbbell-shaped No. 3 shape and its thickness is about 2 mm
It is. Test speed is 500mm / min, test temperature is 24
The test was performed under the conditions of ± 2 ° C. The tensile stress is 300%.
It is the value at the time of.

The spring hardness H _S is described in JI.
JIS-A hardness was measured according to SK6301. The discoloration test result is a visual result after each test piece was left outdoors for one week. The test piece was evaluated as × when the brown color of the test piece changed, 、 when the brown color did not occur, and Δ when the brown color hardly occurred. [Evaluation Results] From the results of the discoloration tests of Examples 1 and 2, it was confirmed that brown discoloration of the rubber composition can be prevented by adding Ketjen Black, ie, porous carbon black, to the rubber component.

Here, the compounding amount of the porous carbon black must be within a range that does not adversely affect the physical properties of the tire rubber. That is, it is not preferable that the measured values of the rubber composition containing Ketjen Black shown in the above specific examples are significantly different from those of Comparative Example 1 (composition example of a normal rubber composition for tires). From this viewpoint, the physical properties of the rubber composition containing EC600JD are evaluated, and the amount of Ketjen Black is also described.

When the amount of Ketjen Black (hereinafter referred to as the amount) is within the above-mentioned predetermined range of 0.5 to 10 phr (Examples 1 and 2), the physical properties in Table 2 Although there is a slight difference from each numerical value of Comparative Example 1, it is within the allowable range in the tire running property. The amount is 10
phr or more, for example, 12 ph as in Comparative Example 4.
If r, there is a discoloration prevention effect, but each physical property value is significantly different from Comparative Example 1 and is not preferable in tire running property.
It is also expensive. At 20 phr as in Comparative Example 3, this tendency becomes even more pronounced. Therefore, the amount is 1
0 phr or less is preferred.

When the blending amount is equal to or less than the above-mentioned predetermined amount, for example, if 0.1 phr of Comparative Example 2 and 0.3 phr of Comparative Example 3, each measured value is almost the same as that of Comparative Example 1, and there is almost no difference. . However, the expected effect of preventing discoloration cannot be obtained, so that it is out of the problem. From the above evaluation, the amount of Ketjen Black can be described as follows.
If it is 0.5 phr or less, the expected effect of preventing discoloration cannot be obtained. If it is 10 phr or more, the effect of preventing discoloration is remarkable, but the running property of the tire is affected and the cost is high. Therefore, the amount of Ketjen Black is 0.5 to 10
phr, and particularly preferably 1 to 5 phr.

The rubber composition for a tire of the present invention is used as a rubber composition for forming a tread portion and a sidewall portion of an automobile tire, and is particularly advantageous in a sidewall portion where brown discoloration is a problem. .

[0032]

The rubber composition for a tire of the present invention prevents the migration of the amine-based antioxidant to the surface by blending the porous carbon black. Therefore, by using the rubber composition for a tire of the present invention, it is possible to prevent blooming of an antioxidant and discoloration of brown on the tire surface without deteriorating rubber properties such as ozone resistance and oxidation resistance. Tires can be created.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 13/04 C08K 13/04 C08L 9/00 C08L 9/00 // (C08K 13/04 7:24 5:17)

Claims (3)

[Claims] 1. A rubber composition comprising at least one kind of rubber selected from the group consisting of natural rubber and diene-based synthetic rubber mixed with an amine-based anti-aging agent.
0.5 to 1 part by weight of porous carbon black
A rubber composition for a tire, wherein 0 part by weight is blended. Wherein said rubber composition for a tire according to claim 1, DBP oil absorption of the porous carbon black is characterized in that at 300 cm ^3/100 g or more. 3. The rubber composition for a tire according to claim 1, wherein the porous carbon black is Ketjen black.