JPH0116851B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a radial tire for passenger cars, and more specifically, a rubber composition that prevents discoloration and deterioration of the appearance of the tire sidewall due to blooming of anti-aging agents and wax is disposed in the sidewall. Regarding radial tires for passenger cars. [Prior art] In consideration of bending fatigue resistance, natural rubber (abbreviated as NR), polybutadiene rubber (abbreviated as BR), and styrene-butadiene rubber (abbreviated as SBR) are used as sidewall rubber for radial tires for passenger cars. Compositions consisting of blends of By the way, NR, BR and SBR also have extremely poor ozone resistance and weather resistance by themselves. Therefore, in order to improve ozone resistance and weather resistance, rubber compositions for sidewalls contain amine-based anti-aging agents (for example, phenyl-1,3-dimethylbutyl-p-
Phenyl diamine, phenyl-isopropyl-
It is essential to blend p-phenylenediamine-based anti-aging agents such as p-phenylenediamine and diphenyl-p-phenylenediamine with paraffin wax. These anti-aging agents and waxes bloom on the surface of the sidewall rubber and form a film covering the rubber surface, preventing sunlight and ozone from attacking the polymer molecules of the rubber and preventing the rubber from deteriorating. However, the amine anti-aging agent itself is colored, and becomes further colored when oxidized in the air. For this reason, the rubber surface changes color due to the anti-aging agent and its oxides present on the rubber surface, significantly deteriorating the appearance. This condition becomes more severe as time passes after manufacturing. Furthermore, when waxes bloom, they form a white film that sticks to the tire surface like white dirt, deteriorating its appearance. As a result, the commercial value of tires that have been stored for long periods of time or tires that have been left on display shelves for long periods of time is significantly reduced. Furthermore, even if the vehicle is mounted on the vehicle and driven, this condition of deterioration in appearance is not improved, and in some cases, consumers complain about the poor appearance. On the other hand, radial tires have become the mainstream of tires, and their lifespans are significantly increasing, and there is a growing desire for radial tires that do not deteriorate over a longer period of time. By the way, as mentioned above, a rubber composition containing diene rubber as a polymer component is used in the sidewall portion of a radial tire for a passenger car, and blooming of the anti-aging agent and discoloration inevitably occur. In order to improve the appearance, a rubber for sidewalls that does not contain amine anti-aging agents and waxes, which are the causative substances, is required. Further, the following functions (1) to (3) are required for the sidewall rubber of a radial tire for a passenger car. (1) Excellent bending fatigue resistance. (2) It has excellent weather resistance and ozone resistance, and this property lasts for a long time. (3) It must have sufficient adhesion to carcass cord rubber and cap tread rubber. Therefore, the present inventors conducted studies to develop a rubber that does not use amine anti-aging agents or waxes that cause deterioration in appearance, and has the properties (1) to (3) above. Ethylene propylene rubber (EPDM, EPM) is known as an example of a polymer that has sufficient weather resistance even without the addition of an amine anti-aging agent or wax. However, these EPDM and EPM have low affinity with diene polymers, and rubbers mainly composed of EPDM and EPM have extremely poor adhesion with rubbers mainly composed of diene polymers, resulting in tire sidewall rubber. It cannot be used as Further, halogenated butyl rubber is a polymer with excellent bending fatigue resistance, and also has better ozone resistance than diene rubber. However, like EPDM, its adhesion to diene rubber compositions is significantly inferior. [Object of the Invention] The present invention provides a rubber composition for use in passenger cars that prevents deterioration of the appearance of the sidewall portion and has a well-balanced flex fatigue resistance, weather resistance, ozone resistance, and adhesion properties in the sidewall portion. The purpose is to provide radial tires. [Structure of the Invention] The radial tire for a passenger car of the present invention that achieves the above object comprises 30 to 80 parts by weight of brominated butyl rubber, 10 to 30 parts by weight of ethylene propylene diene terpolymer rubber having an iodine value of 20 to 30, and natural rubber, or polyptadiene rubber, styrene-butadiene rubber,
For 100 parts by weight of a rubber component consisting of 10 to 50 parts by weight of a diene rubber consisting of a blend of at least one rubber selected from polyisoprene rubber and natural rubber, a softening point of 80 to 120°C and a fixed carbon of 25 ~50%,
In addition to blending 5 to 25 parts by weight of a petroleum resin with an aromatic index of 0.68 or more and 0.1 to 0.8 parts by weight of a thiazole vulcanization accelerator, a rubber composition containing no amine anti-aging agent was placed in the sidewall part. This is a characteristic feature. In the present invention, the rubber composition disposed in the sidewall portion contains 5 to 25 parts by weight of a petroleum resin and 0.1 to 0.8 parts by weight of a thiazole vulcanization accelerator to 100 parts by weight of the rubber component. Contains no aging agents. As a result, it is possible to completely prevent discoloration of the rubber surface and deterioration of appearance due to discoloration and oxidation of amine-based antiaging agents, which have been considered problems in the past, for a long period of time. The rubber component consists of brominated butyl rubber, EPDM and diene rubber. The brominated butyl rubber is not particularly limited, but preferably has an isoprene content of 1.0 to 3.0 mol% and a bromine bond content of 1.0 to 3.0% by weight from the viewpoint of ozone resistance and adhesion with diene rubber. The amount thereof in 100 parts by weight of the rubber component is 30 to 80 parts by weight, preferably 50 to 75 parts by weight. If the amount of brominated butyl rubber exceeds 80 parts by weight, processability and
In particular, roll bagging during mixing and deterioration and shrinkage of the skin during extrusion become significant. Moreover, if it is less than 30 parts by weight, the ozone resistance and flex fatigue resistance of the obtained rubber composition will decrease. In addition, EPDM is blended to impart ozone resistance to the resulting rubber composition, and its type is not particularly limited, but when rubber with an iodine value of 20 to 30 is mixed with diene rubber, covulcanization It has good properties and is preferred. When the iodine value is less than 20, the amount of double bonds is small,
Co-vulcanization deteriorates. Moreover, when it exceeds 30, the number of double bonds increases too much and ozone resistance decreases. The blending amount of EPDM is preferably 10 to 30 parts by weight,
If the amount is less than 10 parts by weight, the resulting rubber composition will not have sufficient ozone resistance, and if it exceeds 30 parts by weight, the adhesion to diene rubber compositions such as carcass rubber will be extremely poor. 10 to 50 parts by weight of diene rubber is blended,
NR, BR, polyisoprene rubber (IR),
Examples include SBR, and NR is preferable due to its adhesiveness with carcass rubber, etc., but if the adhesiveness during molding allows, NR and BR, NR and IR, NR and SBR, etc.
A blend of NR, SBR, and BR, or a blend of NR, BR, and IR may also be used. In other words, in diene rubber, NR is always
is used as a blend component to prevent a decrease in tackiness (tackiness) during unvulcanization and improve adhesion to carcass rubber and the like. If the blending amount of the diene rubber is less than 10 parts by weight, the adhesion to the diene rubber will decrease, and the mixing and extrusion processability will decrease. Moreover, if it exceeds 50 parts by weight, ozone resistance and bending fatigue resistance will be extremely deteriorated. Next, the petroleum resin used in the present invention is:
A fraction rich in aromatic components extracted from a petroleum fraction (average molecular weight 200 to 800) with furfural, phenol, or other appropriate solvent is mixed with an oxygen-containing gas or a gas containing oxygen and ozone at a temperature of 200 to 380°C. A resin material obtained by contact reaction with a softening point of 80 to 120.
℃, fixed carbon 25 to 50%, aromatic index 0.68 or more, and petroleum resins in this range are vulcanized after vulcanization of a rubber component containing halogenated butyl rubber to a rubber composition containing other diene rubber. Improves adhesion. The softening point corresponds to the hardness of the vulcanized rubber; if the softening point is less than 80°C, the vulcanized rubber will be too soft and its durability will deteriorate, and if it exceeds 120°C, it will become too hard and lose its flexibility. It becomes easier to crack. Furthermore, if the fixed carbon content exceeds 50%, the softening point will be too high, and if it is less than 25%, it will become sticky. Furthermore, if the aromatic index is less than 0.68, the affinity with diene rubber will deteriorate and the rubber-rubber adhesion will decrease. The amount of petroleum resin added in the present invention is the rubber component.
The amount is 5 to 25 parts by weight per 100 parts by weight, and if it is less than 5 parts by weight, the adhesion to rubber compositions containing other diene rubbers such as carcass rubber will be poor and interfacial peeling will occur. Moreover, if the amount exceeds 25 parts by weight, the vulcanizate of the rubber composition, especially the tensile strength, will decrease. Examples of the thiazole-based vulcanization accelerator used in the present invention include dibenzothiazyl disulfide, 2-mercaptobenzothiazole, etc. Dibenzothiazyl disulfide is preferable, and the blending amount thereof is as follows: The amount is 0.1 to 0.8 parts by weight, preferably 0.1 to 0.5 parts by weight, based on 100 parts by weight of the rubber component. If the amount of the thiazole-based vulcanization accelerator exceeds 0.8 parts by weight, the flex fatigue resistance of the rubber composition will decrease and the scorch time will be extremely accelerated, which is not preferable. Moreover, if it is less than 0.1 part by weight, the degree of vulcanization of the diene rubber will be insufficient, and the vulcanized physical properties, especially the tensile strength, will decrease. Further, in the present invention, as long as the thiazole-based vulcanization accelerator is used, other vulcanization accelerators can also be used in combination. Furthermore, in the present invention, in addition to the above-mentioned petroleum resin and vulcanization accelerator, fillers, softeners, vulcanizing agents, vulcanization aids, vulcanization retarders, etc., which are usually used as compounding agents for rubber, may be appropriately used. Can be blended. [Effects of the Invention] As described above, according to the present invention, since no amine-based anti-aging agent is blended, the discoloration and deterioration of the appearance of the rubber surface caused by the coloring and oxidation of the amine-based anti-aging agent can be prevented for a long time. A specific amount of a specific petroleum resin and By blending a specific amount of a thiazole-based vulcanization accelerator, in addition to eliminating the above-mentioned conventional drawbacks caused by the blending of amine-based anti-aging agents and waxes in the sidewall portion of radial tires for passenger cars, the sidewall It improves the bending fatigue resistance, weather resistance, and ozone resistance required for rubber parts, and can maintain excellent adhesion with carcass coat rubber and captread rubber. Note that the method for measuring physical properties in the present invention will be described below. a Ozone test (evaluation of ozone resistance and discoloration) in accordance with JIS K6301. After 48 hours at an ozone concentration of 100 pphm, a temperature of 40°C, and an elongation of 40%, the sample was observed and the degree of discoloration was checked. b Bending test (evaluation of bending fatigue resistance) Based on JIS K6301. However, the sample width is 50
mm, the stroke is 57 mm, and after vulcanization it is 25 mm as it is.
The amount of crack growth (mm) after being bent 100,000 times at ℃ was measured. On the other hand, after the sample was vulcanized, it was heat aged in a gear oven at 100°C for 48 hours and then measured. The former is indicated as unaged in the table described below, and the latter is indicated as aged. Examples of the present invention will be described below. [Example] 1. Ozone test and bending test Ozone test and bending test were conducted on various rubber compositions. All amounts of ingredients are in parts by weight.
The vulcanization conditions were all 160°C x 15 minutes. Table 1 shows the above test results for each component polymer alone or in a blend system. These results show that EPDM has excellent ozone resistance, that as the amount of chlorinated butyl rubber increases, the bending fatigue resistance improves, and that in formulation No. 6, which does not contain EPDM, chlorinated butyl rubber has a weight of 80%. It is understandable that ozone cracks are generated even though some parts are included. Table 2 shows the ozone test and bending test results for the compositions of the present invention and comparative examples. Comparative Example 1 shows a sidewall rubber containing a currently used amine anti-aging agent as a control. As is clear from Table 2, in the radial tire for passenger cars of the present invention, the sidewall portion does not discolor at all, and by using brominated butyl rubber instead of chlorinated butyl rubber, the crack resistance is significantly improved. The ozone resistance is also improved. 2 Tire test Tire shown in Figure 1 (tire size 195/
Comparative example 2 in Table 2 on the sidewall part of 60R14)
A tire in which the rubber composition of Example 1 was disposed was produced. The following two indoor drum tests were conducted on these tires. B. Female cut growth test, which is one of the indexes of bending fatigue resistance: Female cuts with a length of 4 mm x depth of 1 mm were placed at four locations around the tire circumference of the sidewall rubber in Figure 2, which shows the side surface of the tire, and the growth test was performed as shown in Table 3. The vehicle was run under the conditions shown in Figure 2, and the female cutlet growth rate (%) was determined from the female cutlet growth values before and after the run. (b) Running test under ozone atmosphere, which is one of the indicators of ozone resistance and degree of discoloration: After running under the conditions shown in Table 3 in an ozone atmosphere of 100 pphm, the appearance of the sidewall portion of the tire was observed. The results are shown in Table 4. The growth rate of female cutlets from Example 6 to Example 1 is 25
%, and that of Comparative Example 1 was 125%, confirming that the bending fatigue resistance of the tire was also at a sufficient level in Example 1. Furthermore, it is clear that there is no particular problem in the adhesion between the sidewall rubber and the carcass rubber or captread rubber. Further, in Examples 6 to 1, ozone cracks were not generated at all, and it was confirmed that the ozone resistance was at a sufficient level. In addition, the appearance of Example 1 was completely unchanged from before the test, despite the severe discoloration of Comparative Example 1.
It is clear that there is no discoloration.

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【table】 [Brief explanation of drawings]

FIG. 1 is an explanatory view of a meridian half cross section of a tire showing an example and a comparative example of a radial tire for a passenger car according to the present invention, and FIG. 2 is an explanatory side view of the tire.

Claims (1)

[Claims] 1 30 to 80 parts by weight of brominated butyl rubber, iodine number 20
~30 parts by weight of ethylene propylene diene terpolymer rubber, and natural rubber, or a blend of natural rubber with at least one rubber selected from polyptadiene rubber, styrene butadiene rubber, and polyisoprene rubber. of diene rubber consisting of
5 to 25 parts by weight of a petroleum resin with a softening point of 80 to 120°C, 25 to 50% fixed carbon, an aromatic index of 0.68 or more, and a thiazole vulcanization accelerator, per 100 parts by weight of a rubber component consisting of 10 to 50 parts by weight. A radial tire for a passenger car, characterized in that a rubber composition containing 0.1 to 0.8 parts by weight and not containing an amine anti-aging agent is disposed in a sidewall portion.