JPH0480057B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a tire in which so-called white rubber is disposed in the sidewall portion, and more particularly to a pneumatic tire in which yellowing (discoloration) of the white rubber is eliminated. [Prior Art] In recent years, as the trend toward decorative automobiles has progressed, there has been an increasing demand for the use of so-called black rubber in the sidewall portions of tires as well as for the provision of colored decorations. Conventionally, there are white tires that have white letters (so-called white letters) or white lines (so-called white ribbons) formed on the sidewall. These white tires have a great commercial value due to their white appearance, and for this reason, maintaining whiteness (resistance to yellowing) is an important performance requirement. Note that, due to its functions, the white rubber of the sidewall portion of a white tire is required to have bending fatigue resistance, ozone resistance, and crack resistance at the junction with the black side rubber. Therefore, white rubber is ethylene propylene diene terpolymer rubber (EPDM) or halogenated butyl rubber (X-IIR, where X means halogen).
We use a polymer with excellent crack resistance and ozone resistance, such as diene rubber, and add white fillers such as clay, calcium carbonate, zinc white, titanium white, silica, magnesium carbonate, etc. It contains sulfur, an organic vulcanizing agent, and a vulcanization accelerator as a vulcanizing agent. It is known that the white rubber on the sidewalls turns yellow when exposed to sunlight while the tire is being stored, transported, or used. For this reason, protective paint, which is mainly made of soft plastic and contains pigment, is applied to the sidewalls, and if necessary, paper tape is used to wrap the paint over the sidewalls.
This protective paint protects against contaminants (e.g., amines, anti-aging agent)
It also has the role of preventing adhesion and migration to the sidewall portion. Furthermore, when using a tire, it is necessary to remove the protective paint in order to re-appear the white rubber on the sidewall, so the protective paint is required to be easily removable before the tire is used. Ru. Therefore, a paint made by dissolving a water-soluble polymer in water and containing a pigment and a surfactant as a pigment dispersant has conventionally been used as a protective paint. In this case, the water-soluble polymer is
For example, polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyacrylamide, etc. However, applying or removing such a protective paint is troublesome, and the use of a protective paint is expensive. [Object of the Invention] An object of the present invention is to provide a pneumatic tire that does not yellow even when the white rubber disposed in the sidewall portion is exposed. Preventing yellowing of the white rubber in the sidewall has been a concern of tire manufacturers for some time, but the mechanism of yellowing was not understood and there was currently no specific anti-yellowing solution. Therefore, as a result of intensive research including analysis of the factors that cause yellowing, the present inventors found that the yellowing of white rubber is greatly influenced by the amount of free sulfur in the rubber. It was discovered that yellowing progresses dramatically when the limit is exceeded, and the present invention was developed based on this finding. [Structure of the Invention] That is, the pneumatic tire of the present invention comprises 100 parts by weight of rubber containing 15 to 60 parts by weight of halogenated butyl rubber, 15 to 30 parts by weight of ethylene propylene diene terpolymer rubber, and 70 to 10 parts by weight of diene rubber. A rubber composition with a free sulfur content of 0.05% or less, which contains 10 to 60 parts by weight of clay and 10 to 30 parts by weight of titanium dioxide as a white filler, and also uses sulfenamide-based and guanidine-based vulcanization accelerators. This is made by placing objects on the sidewall. Hereinafter, the configuration of the present invention will be explained in detail with reference to the drawings. FIG. 1 is an explanatory cross-sectional view showing a sidewall portion of a pneumatic tire of the present invention. In FIG. 1, A is a sidewall portion, inside of which a carcass layer 1 is folded and rolled up around a bead filler 2 and a bead wire 3 from the inside of the tire to the outside of the tire. White rubber 4 is arranged on the sidewall part A,
Black side walls 5, 5' are arranged at both ends of this white rubber 4. In the present invention, a rubber composition consisting of the following (1) to (3) is used as the white rubber 4. (1) 15 to 60 parts by weight of X-IIR as a rubber component,
EPDM 15~30 parts by weight and diene rubber 70~
Contains 10 parts by weight (100 parts as total rubber amount)
parts by weight). X-IIR is not particularly limited, but it is preferable to use a rubber containing 1.0 to 2.0 mol% of isoprene and 1.0 to 2.0% by weight of bound halogen. EPDM is also not particularly limited, but those with an iodine value of 20 to 30 are preferred because they exhibit good co-vulcanization when mixed with diene rubber. Note that the grade of X-IIR and EPDM is not particularly limited, as the vulcanization system used may be changed depending on the difference in vulcanizability. Examples of the diene rubber include natural rubber (NR), isoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), and polybutadiene rubber (BR). The amount of X-IIR to be blended is 15 to 60 parts by weight, preferably 20 to 40 parts by weight. If the amount exceeds 60 parts by weight, the vulcanization rate of the system will become extremely slow, and the amount of vulcanization accelerator used to compensate for this will increase, resulting in a rapid increase in the degree of vulcanization of the diene rubber, which will reduce the durability of the entire rubber composition. The crack resistance will be reduced. Since EPDM is blended to play the role of imparting ozone resistance to the resulting rubber composition, 15 to 30 parts by weight is sufficient. If it exceeds 30 parts by weight, the vulcanization rate will decrease. The amount of X-IIR and EPDM must be at least 15 parts by weight, since if the amount is less than 15 parts by weight, the resulting rubber composition will have poor ozone resistance. Note that X-IIR and EPDM have a slower vulcanization rate than diene rubber. Therefore, if the amount of these compounds is increased in order to maintain ozone resistance, the vulcanization rate of the resulting rubber composition will be slowed down.
The amount of free sulfur under the same vulcanization conditions will increase. Therefore, it is preferable to keep the blending amounts of X-IIR and EPDM as low as possible within the above range, taking into account the amount of diene rubber. (2) 10 to 60 parts by weight of clay and 10 to 30 parts by weight of titanium dioxide as white fillers per 100 parts by weight of total rubber.
Contains parts by weight. If the clay content is less than 10 parts by weight, it will be too small, and if it exceeds 60 parts by weight, the amount of titanium dioxide (titanium white) must be increased to achieve whiteness, resulting in a high content. , the crack resistance deteriorates. Titanium dioxide is blended to play the role of imparting whiteness to the resulting rubber composition.
10 to 30 parts by weight is sufficient. If it exceeds 30 parts by weight, crack resistance will decrease. In addition to these white fillers, powder additives commonly used for rubber, such as zinc white, calcium carbonate, silica, and magnesium carbonate, may be blended. (3) Free sulfur content shall be 0.05% or less. The amount of free sulfur in the resulting rubber composition is 0.05
%, the yellowing of the rubber composition becomes extremely severe, which is unsuitable. Note that the amount of free sulfur varies depending not only on the vulcanization rate of the rubber composition but also on the vulcanization conditions. By changing the tire vulcanization conditions, the amount of free sulfur can vary. In order to reduce the amount of free sulfur, it is possible to increase the vulcanization conditions to a higher temperature or for a longer time, or to increase the vulcanization conditions to a higher temperature and a longer time. However, all of these changes the vulcanization conditions for other parts of the tire.
As the process progresses toward overvulcanization, the physical properties of other parts deteriorate, resulting in a decrease in tire performance. Moreover, the energy required for vulcanization increases, the vulcanization time becomes longer, and there are disadvantages such as a decrease in productivity. Therefore, the amount of free sulfur
In order to keep the content below 0.05%, it is preferable to keep the vulcanization rate at an appropriate level. For this purpose, the amount of free sulfur in the rubber sheet obtained by press-vulcanizing the rubber composition at 160°C for 15 minutes must be 0.05%.
(The degree of vulcanization of the white rubber in the tire is in good agreement with the degree of vulcanization during press vulcanization at 160°C for 15 minutes in Examples and Comparative Examples of the present invention described below). (4) As vulcanization accelerators, sulfenamide-based and guanidine-based products should be used together. When a thiazole type is used in combination with a guanidine type, the amount of the thiazole type used becomes large, so it is not preferable. [Effects of the Invention] As explained above, according to the present invention, the above (1) to
In the rubber composition consisting of (4), since sulfenamide-based and guanidine-based vulcanization accelerators were used together, post-vulcanization progressed even after vulcanization was completed, and as a result,
The amount of bound sulfur increases, the amount of free sulfur in the compounded rubber decreases, and yellowing of the sidewall portion can be effectively prevented. EXAMPLES The effects of the present invention will be specifically explained below with reference to Examples and Comparative Examples. Examples and Comparative Examples The following tests were conducted on various rubber compositions. The amounts of the ingredients are all parts by weight. Vulcanization conditions were 160°C x 15 minutes. Ozone test (ozone resistance): According to JIS K 6301. Ozone concentration 50pphm, temperature 40℃, elongation 40%, 48 hours. Bending test (cracking resistance): According to JIS K 6301. Stroke 40mm, room temperature,
Amount of crack growth (mm) after flexing 100,000 times. Brightness change test: Conventionally, the only way to judge the discoloration of colored rubber was by visual inspection, and it was difficult to express the degree of discoloration numerically. Therefore, the present inventors decided to use the L ^* a ^* b ^* color system recommended by the Commission Internationale de l'Eclairage (CIE) as a method for numerically expressing the degree of color change. This L ^* a ^*
The b ^* color system consists of the L ^* axis, a ^* axis, and b ^* axis, which represent lightness, green ← → red, blue ← → yellow, and chromaticity L ^*
It is expressed by three numbers: a ^* b ^* . L ^* a ^*
b ^* Using the color system, it is possible to numerically determine how much the color after discoloration has changed from the original color. Therefore, the chromaticity, which was conventionally determined visually, has become
It is expressed in a numerical value called L ^* a ^* b ^* color system, and the brightness (whiteness) is determined by its size. The test method is as follows. The test piece was irradiated with ultraviolet rays, and the samples before and after irradiation were measured using a Minolta camera colorimeter.
The L ^* value (lightness) of the L ^* a ^* b ^* color system was measured, and the amount of change in the L ^* value was defined as the change in lightness. The larger the L ^* value, the brighter it is, and the degree of discoloration can be determined by how much the L ^* value decreases due to ultraviolet irradiation. For ultraviolet rays, use Toshiba health line lamp FL40S 2
It was generated from a fluorescent lamp. 20cm from the tube
The samples were placed in a separate location and exposed to ultraviolet light for 7 days. Amount of free sulfur: According to the method of ASTM D297 (1984) Section 28 for a 2 mm sheet press-cured at 160°C for 15 minutes. (1) Table 1 below shows the results of examining the discoloration properties of various rubber compositions (Nos. 1 to 5). As a result, NR,
Rubber composition containing EPDM and C-IIR (No.
It can be seen that samples 1 to 3) are less likely to change color.

[Table] (2) The results of examining the relationship between the amount of free sulfur and discoloration are shown in Table 2 below and Figure 2. From Table 2 and FIG. 2, it can be seen that as the amount of free sulfur increases, the change in brightness also increases, and when the amount of free sulfur exceeds 0.05%, the change in brightness also increases. No.
Rubber composition No. 9 shows that even if the amounts of the rubber component and white filler are within the range of the present invention, the absolute value of the change in brightness becomes large when the amount of free sulfur is outside the range. Further, it can be seen that when the value of the brightness change is up to -2, there is almost no decrease in whiteness due to discoloration.

[Table] (3) The results of the change in brightness, amount of free sulfur, ozone test, and bending test are shown in Table 3 below. From this Table 3, a large amount of free sulfur causes discoloration (No. 12, 13), a small amount of EPDM and C-IIR causes poor ozone resistance (No. 15), and a large amount of clay causes poor crack resistance. (No. 20). Further, it can be seen that Nos. 14 and 16 to 19 are all excellent in discoloration (change in brightness), ozone resistance, and crack resistance.

【table】

[Table] (4) The rubber compositions No. 12 (comparative example) and No. 17 (example) in Table 3 were vulcanized to form the sidewall of the tire (tire size P195/75 R14) shown in Figure 1. White rubber 4 was placed in part A, and a female cut growth drum test in an indoor drum test, which is one of the indicators of tire crack resistance, was conducted. In this test, as shown in Figure 3 showing the side surface of the tire, female cuts with a length of 4 mm and a depth of 1 mm were made at four locations on the circumference of the white rubber 4 tire, and the air pressure was 1.8 Kg/cm ² , the load was 630 Kg, and the speed was 80 Km/hr. , Female cutlet growth rate (%) based on the female cutlet growth value before and after driving under the condition of a mileage of 5000 km.
I started by asking for. The results are shown in Table 4 below. As can be seen from Table 4, the female cut growth rate of No. 17 was 10% and that of No. 12 was 12%, confirming that the crack resistance of No. 17 was at a sufficient level. Furthermore, the amount of free sulfur was measured for each white rubber 4, and a discoloration test was conducted. The results showed that the amount of free sulfur in No. 17 was as low as 0.02%, and the degree of discoloration was also at a sufficient level.
It was found that No. 12 had a high free sulfur content of 0.19% and had severe discoloration.

【table】 [Brief explanation of the drawing]

Fig. 1 is a cross-sectional explanatory diagram showing the sidewall portion of the pneumatic tire of the present invention, Fig. 2 is a diagram showing the relationship between the amount of free sulfur and changes in brightness, and Fig. 3 is a side view of the tire showing the state of female cut in the sidewall portion. It is a diagram. 1...Carcass layer, 2...Bead filler, 3
...Bead wire, 4...White rubber, 5,
5'... Black side wall, 6... Female cut.

Claims (1)

[Claims] 1 Clay 10 as a white filler is added to 100 parts by weight of rubber containing 15 to 60 parts by weight of halogenated butyl rubber, 15 to 30 parts by weight of ethylene propylene diene terpolymer rubber, and 70 to 10 parts by weight of diene rubber.
Air made by disposing a rubber composition containing ~60 parts by weight and 10 to 30 parts by weight of titanium dioxide and a sulfenamide-based and guanidine-based vulcanization accelerator and having a free sulfur content of 0.05% or less in the sidewall part. Included tires.