JPH02258846A - Molding of rubber product - Google Patents

Abstract

PURPOSE:To accomplish molding in high efficiency a rubber product retaining deterioration preventiveness with good appearance by working a rubber composition containing a specific rubber deterioration-preventive wax at temperatures not lower than a specified level followed by cure molding in a specific mold. CONSTITUTION:(A) A rubber composition containing >=75wt.% of normal saturated hydrocarbon and also containing rubber deteriorationpreventive wax which contains 20-45wt.% of normal saturated hydrocarbon belonging to 36-51C high- molecular weight component, is worked at >=140 deg.C followed by (B) cure molding using a mold with its surface roughness of >=3-S, thus obtaining the objective rubber product of good appearance retaining the inherent deterioration preventiveness even during high-speed and high-temperature working.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides rubber for automobile tires, etc., which does not lose its original anti-aging performance even in high-speed, high-temperature mixing with high productivity, and has improved appearance. Regarding product molding methods.

(Prior art) Conventionally, rubber compositions containing amine-based anti-aging agents and wax-based anti-aging agents have been used in rubber products such as tires to improve ozone resistance and flex fatigue performance. The wax-based anti-aging agent oozes out onto the rubber surface to form a thin film, and this thin film prevents contact between the rubber and ozone, which is particularly effective in preventing cracks under static conditions.

However, if this excessively oozes out onto the rubber surface, the rubber surface becomes white, and if it oozes partially, the rubber surface becomes mottled, which significantly impairs the appearance. Especially when the room temperature is between 30°C and 40°C under the tire storage conditions,
Deterioration in appearance due to wax oozing becomes a practical problem. If the room temperature is lower than 30℃, the amount of wax oozing out will be small (
, and there are almost no storage conditions exceeding 40°C.

Therefore, there is a need for a tire with good appearance due to the minimum amount of wax oozing out under storage conditions of 30°C to 40°C, but no technology with superior features in this respect has yet been developed. .

Additionally, in general, the characteristics of rubber compounds vary depending on various processing conditions. One of these is mixing conditions. In other words, when the mixing temperature increases, the degree of dispersion of various compounding agents changes,
Deterioration occurs due to thermal and oxidative deterioration, and depending on the compounding agent, it may disappear due to volatilization or transpiration. Therefore, in terms of performance of the mixed wire rubber composition, relatively low temperature mixing is generally good.

In particular, amine-based anti-aging agents and rubber anti-aging agents such as wax-based anti-aging agents, which are organic compound-based and have a relatively low molecular weight, are susceptible to deterioration, alteration, volatilization, and transpiration due to high-temperature mixing. For this reason, low-temperature mixing is required, especially in mixed wire rubber compositions containing rubber anti-aging agents. This is a major drawback in terms of productivity.

(Objective of the Invention) An object of the present invention is to provide a rubber product such as an automobile tire that improves productivity and has excellent appearance under product storage conditions.

(Structure of the Invention) Rubber products formed from rubber compositions containing rubber anti-aging waxes of various compositions are vulcanized and molded using molding molds with different surface roughnesses, and after being left for a certain period of time, the appearance is carefully improved. As a result of consideration,
Rubber containing a rubber anti-aging wax that has a low normal saturated hydrocarbon content (both 75% or more and a normal saturated hydrocarbon content of 20 to 45% that belongs to a high molecular weight component with a carbon number of 36 to 51) Rubber products with excellent appearance can be synergistically obtained by vulcanization molding a green tire formed from the composition using a mold with a relatively fine surface roughness of 3-8 or less. I found out that it can be done.

That is, even if a rubber composition containing a rubber anti-aging wax of the above composition with a relatively good appearance is used, when vulcanization molding is performed using a relatively rough molding mold with a surface roughness of 6-8. , the improvement in appearance is not so remarkable.

Further, even if a fine molding die having a relatively rough surface roughness of 3-8 is used, the appearance is poor if a rubber composition containing a rubber anti-aging wax other than the above-mentioned composition is used.

Only by combining a rubber composition containing a rubber anti-aging wax having the above composition with a molding die having a fine surface roughness can a rubber product with significantly superior appearance be obtained.

This is originally a mold for molding with a fine surface roughness in which a rubber composition containing a rubber anti-aging wax of the above composition that has a small amount (not excessively) oozes out onto the rubber surface in the temperature range of 30°C to 40°C. By vulcanizing and molding, the uneven whitening, particularly on a microscopic scale, is reduced, which is thought to contribute to the improvement in appearance.

Also, a rubber compound containing a rubber anti-aging wax having a normal saturated hydrocarbon content of at least 75% and a normal saturated hydrocarbon content of 20 to 45% belonging to a high molecular weight component having 36 to 51 carbon atoms. In this case, even if the mixing temperature of the Banbury mixer reaches 140°C or higher, there is almost no decrease in ozone deterioration prevention performance, and only when using the wax for preventing rubber aging of this composition, a high-speed high-temperature rubber mixing method of 160°C or higher is possible. is a useful manufacturing method. On the other hand, the normal saturated hydrocarbon content is less than 75%, or the normal saturated hydrocarbon content with 36 to 51 carbon atoms is 20%.
If a rubber anti-aging wax with a temperature lower than 100° C. is used, the ozone deterioration preventing performance will be poor, especially when mixing at a high temperature of 140° C. or higher. If the same ratio exceeds 45%, the appearance and the ability to prevent ozone deterioration at high temperatures are almost the same as in the examples, but the ability to prevent ozone deterioration at low temperatures becomes extremely poor.

(Example) EXAMPLES The present invention will be described in more detail with reference to Examples below.

Table 1 shows the NR-BR used in the tire sidewall.
The basic composition, Table 2 shows the SBR used in the tire tread.
The basic formulation is shown. Various rubber compositions obtained by optically kneading these rubber compounds in a Banbury mixer at a temperature of 150 to 190°C for 4 minutes were used for the sidewall parts and tread parts, and also for tire molding. The molds used had surface roughness of 3-S and 6-3. By combining these rubber compositions and a tire molding mold, the tire size 1 is produced.
Various tires of 85/TOSR14 were vulcanized and molded. Here, the surface roughness 3-5 indicates a surface roughness in which the maximum height of unevenness is 3 μm or less according to the roughness indication and classification according to JIS B 0601.

In addition, the tire obtained as described above was cut, multiple sheet pieces were made, each was fixed at different elongation rates, and placed in an ozone deterioration tester and left for 24 hours. Measure anti-aging performance due to ozone.

Appearance evaluation is a comprehensive evaluation of the degree of whitening of the rubber surface and the degree of non-uniformity of whitening after vulcanized tires are left at a storage temperature of 40°C for 10 days, and rubber composition number 5 is given a score of 1 to 1 with a score of 5.
Judgment was made with a score of 0. A score of 1 indicates the best appearance and a score of 10 indicates the worst appearance.

These results are shown in Table 3.

A wax having a composition within the claimed range has almost no deterioration in ozone deterioration prevention performance even when the Banbury mixing temperature is as high as 160° C. or higher, so high-speed high-temperature mixing is possible to increase productivity.

In addition, with regard to the appearance of the tire, a remarkable improvement in appearance can only be achieved by combining a rubber composition containing a wax for preventing rubber aging with the composition described in the claims and a tire molding mold with a fine surface roughness. can be seen.

On the other hand, in Comparative Example 5, even if a rubber composition containing a wax for preventing rubber aging of the above composition was used, the improvement in appearance was not so remarkable when a tire molding die with rough surface roughness was used. Moreover, Comparative Examples 6 to 16 show that even when a tire mold with a fine surface roughness is used, the appearance is poor when a rubber composition containing a rubber antiaging wax other than the above composition is used. In addition, as already mentioned above, Comparative Example 17 showed that the ability to prevent ozone deterioration at low temperatures was extremely reduced.

Table 1 NR-BR basic formulation Table 4 shows the rubber composition shown in Table 1 at 160°C, 20
This shows the wax bloom amount of the vulcanized rubber sheet.

Table 4 Since the amount of wax was small in all cases, the amount of wax bloom at 30°C and 40°C was measured as shown in Table 4.

As shown in Table 4, the rubber anti-aging waxes having the above compositions 1 to 3 were more effective at 30°C and 40°C (1 difference in hot water temperature) than the rubber antiaging waxes having the above compositions 4-6. This shows that the amount of W. sox bloom is within the required range.

Method for measuring wax bloom amount: Gomshi) (14,5anX14,5anX0.3
cm) was hung in a constant temperature dryer and taken out after 10 days.
The blooming wax was carefully scraped off with a utility knife, and its weight was measured.

In reality, the appearance of rubber becomes white due to wax blooming, which becomes a problem in most cases when the room temperature is stored for a long time at 40 degrees Celsius or below, but at 20 degrees Celsius or below.
) Osamu Uo

Claims (1)

[Claims] The content of normally saturated hydrocarbons is at least 75%, and the content of normally saturated hydrocarbons having 36-51 carbon atoms is at least 20%.
A rubber composition containing 45% rubber aging prevention wax, which is mixed at a mixing temperature of 140°C or higher, and vulcanized and molded in a mold with a surface roughness of 3-S or lower. A method for molding rubber products characterized by: