JPS61111343A - Improved rubber composition - Google Patents

Abstract

PURPOSE:To provide a rubber compsn. excellent in age resistance, color-fastness, appearance, etc., by incorporating a natural rubber and/or synthetic rubber with an antioxidant complex in which an antioxidant is included within a cyclodextrin. CONSTITUTION:3-1mol of an antioxidant [e.g., N-(1,3-dimethylbutyl)-N'-phenyl-p- phenylenediamine] to be included, dissolved in a small amt. of a proper solvent (e.g., acetone), is added to a satd. soln. of 1mol of cyclodextrin in water to yield an antioxidant complex in which the antioxidant is included within the cyclodextrin. 100pts.wt. natural rubber and/or synthetic rubber (e.g., synthetic polyisoprene rubber), 1-20pts.wt. said complex, and, if necessary, a reinforcing agent such as carbon black, a softening agent such as aroma oil, a vulcanizer, a vulcanizing accelerator, etc., are incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention is a rubber composition, in particular, a rubber composition containing an anti-aging agent complex in which an anti-aging agent is encapsulated by cyclodextrin. The present invention relates to a rubber composition that has improved aging resistance and discoloration resistance at the same time and has an excellent appearance even after aging.

(Background Art) In recent years, with the improvement of the road paving ratio and the use of radial tires, the lifespan of tires has been rapidly increasing, and more and more cases are being used for long periods of time.

Tires generally use diene rubber, so anti-aging agents are added to prevent aging caused by ozone and oxygen, but since anti-aging agents are gradually consumed while the tire is running, the amount of anti-aging agents is limited. As mentioned above, it is blended in a relatively large amount because it is necessary to improve tire life and prevent deterioration and cracking at the end of tire running.

On the other hand, recently consumer demands for tires have diversified, and traditionally it was important for tires to be durable and long-lasting.
However, as automobiles become more sophisticated and sophisticated, there is a growing demand for high-performance tires, 9 luxury tires, and fashionable tires.

Against this background, the above-mentioned anti-aging agents, especially amine-based anti-aging agents, tend to bloom in a short period of time, causing the surface of the tire to turn brown and seriously polluting the exterior while the tire is in stock at a tire store or while the tire is being driven. It has recently become a big problem because it has the disadvantage of causing problems.

In other words, as tire life increases, large amounts of anti-aging agents are added to prevent deterioration, cracks, etc. at the end of tire use, and as a result, the appearance of the tire tends to worsen.
It has been extremely difficult to achieve both so-called sustainability and appearance, in which tires exhibit aging resistance such as weather resistance over a long period of time.

(Objective of the present invention) As a result of intensive studies aimed at solving these drawbacks, the present inventors found that when an anti-aging agent is included in cyclodextrin, which is known as a functional carbohydrate,
The clathrated anti-aging agent gradually dissolves into the rubber, so when it is stored at a tire store or displayed at a store.

Because only the amount of plume necessary for weather resistance is produced, the appearance does not turn brown significantly, and even at the end of the tire run, a sufficient amount of anti-aging agent remains, so the appearance and aging resistance are maintained. In particular, the present invention was achieved by discovering that it is possible to achieve both sustainability of aging resistance.

Furthermore, in order to balance the anti-aging effect at the initial stage of use and the anti-aging effect at the end of use after aging, the conventional exposed, unclathrated anti-aging agent and the above-mentioned clathrated anti-aging agent complex are used together. This is what I propose.

(Structure of the present invention) The structure of the present invention is such that the anti-aging agent is added to 100 parts by weight of rubber made of natural rubber and/or synthetic rubber using cyclodextrin at a molar ratio of 1/3 to 1/1.
An improved rubber composition comprising 1 to 20 parts by weight of an antiaging complex clathrated in a proportion of 1 to 20 parts by weight, and further adding an antiaging agent to 100 parts by weight of rubber made of natural rubber and/or synthetic rubber.・0.1 to 2.0 parts by weight, and 0.5 to 15 parts by weight of an antiaging agent complex in which the antiaging agent is clathrated with cyclodextrin at a molar ratio of 1/3 to 1/1; The present invention relates to an improved rubber composition. In the case of the above combination, it is preferable that the total amount of the unclathrated anti-aging agent and the anti-aging agent in the clathrated composite is 0.5 to 4 parts by weight.

The synthetic rubber used in the present invention includes synthetic polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, butyl rubber, halogenated butyl rubber, and the like.

The anti-aging agent complex used in the present invention is a complex of 6 to 12 glucose molecules obtained by treating starch with a cyclodextrin-producing enzyme produced by microorganisms of the genus Bacillus (BmaIl1ua).
-Cyclodextrin is a non-reducing maltooligosaccharide linked in a cyclic form by 1,4-glucoside bonds. Preferably α-cyclohexadextrin, β-cycloahebutadextrin (Fig. 1) and γ-cyclooctadextrin are preferred. Particularly preferred is one in which an anti-aging agent is included in β-cyclooctadextrin.

Here, the anti-aging agent refers to N-(1,3-dimethylbutyl)-N'-phenyl-P-phenylenediamine, N-7
Enyl-N'-isopropyl-P-7enylenediamine, N,N'-diphenyl-P-phenylenediamine,
N,N'-di-2-naphthyl-P-phenylenediamine, phenyl-l-naphthylamine, alkylated diphenylamine, N-(3-methacryloyloxy-2-hydroxypropyl)-N'-phenyl-P-phenylenediamine, mixture Diaryl-P-phenylenediamine, poly-(2,2,4-trimethyl-1,2-dihydroquinoline, 6-nitoxy-2,2,4-trimethyl-
1,2-dihydroquinoline, reaction product of diphenylamine and a7ton, 2.6-di-tert-butyl-4-methylphenol, 2.6-di-tert-butyl-4-ethylphenol, 2.2°-methylenebis( 4-ethyl-6-tert-butylphenol), styrenated phenol, 2.2°-methylenebis(4-methyl-6-t
art-butylphenol), 4,4'-thiobis(6
-tert-butyl-3-methylphenol), 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, etc., and these may be used alone or in combination of two or more.

By the way, β-cyclooctadextrin especially contains N-
The anti-aging agent complex containing (1,3-dimethylbutyl)-No-phenyl-P-phenylenediamine and N-phenyl-N'-isopropyl-P-phenylenediamine is used in tire sidewalls and shoulder parts. It has been found that the present invention has significant effects when used as a rubber composition.

In this specification, inclusion refers to wrapping an anti-aging agent in a cylindrical molecular cavity of a cyclodextrin, and the anti-aging agent complex is defined as a molar ratio of the above-mentioned cyclodextrin and anti-aging agent. The ratio of 1/3 to 1/1 is 1/3 to 1/1, and the blending amount y is 1 to 20 parts by weight per 100 parts by weight of rubber. If the ratio of cyclodextrin to anti-aging agent is less than 1/3, the amount of anti-aging agent dissolved into the rubber is too small, and the effective concentration of the anti-aging agent in the rubber against rubber deterioration is reduced. If it exceeds 1/1, inclusion becomes difficult, which is not preferable.

In addition, if the amount of the composite is less than 100 parts by weight, the anti-aging effect will not be sufficiently exhibited, and if it exceeds 20 parts by weight, not only will the weight-increasing effect be lost, but especially if an amine-based anti-aging agent is used, the aging effect will bloom. Since the amount of inhibitor becomes too large, the appearance will be impaired, which is not preferable.

In the present invention, the anti-aging agent complex in which the above-mentioned various anti-aging agents are encapsulated in cyclodextrin may be used in combination with the above-mentioned various anti-aging agents that are not encapsulated in cyclodextrin. Therefore, rubber products that are used under harsh conditions must have a sufficient amount of anti-aging agent from the initial stage of use. case,
``More than necessary anti-aging agent blooms on the surface, which impairs the appearance, but it is consumed by rain and car washing, and at the end of the tire's life, there is almost no anti-aging agent in the rubber, and the end-stage This causes cracking, but if the clathrated anti-aging agent complex and non-clathrated anti-aging agent are used together, the effect of the anti-aging agent can be maintained from the initial stage of use to the final stage of tire use. It is. At this time, the amount of the unclathrated anti-aging agent is 0.1 to 2.0 parts by weight. If it is less than 0.1 part by weight, there is no effect, and if it exceeds 2.0 parts by weight, the appearance will be impaired, so it is not preferable. The amount is 0.5 to 15 parts by weight. If it is less than 0.5 parts by weight, there is no point in using the antioxidant complex, and if it exceeds 15 parts by weight, it will no longer have a weight increasing effect, which is undesirable.Furthermore, the unclathrated antioxidant and the clathrated antioxidant It is preferable that the weight ratio is in the range of 1/3 to 1/1 in order to effectively maintain the anti-aging effect from the initial stage of use to the final stage of use.

In addition to the anti-aging agent complex and the anti-aging agent, reinforcing agents such as carbon black, softening agents such as aroma oil and spindle oil, vulcanization accelerators, stearic acid, zinc white, etc. may also be used as necessary. Rubber compounding agents such as vulcanization accelerators and vulcanizing agents may be added within the usual range.

The rubber composition of the present invention having the above-mentioned structure is suitably used for tire sidewalls, treads, belts, carcass, etc., but it can also be used for rubber products other than tires, such as conveyor belts, hoses, anti-vibration rubber. It can also be applied to industrial products such as The anti-aging agent complex used in the present invention is prepared by dissolving the anti-aging agent to be included in a small amount of a suitable solvent (acetone, ethanol, etc.) and adding it to a saturated aqueous solution of cyclodextrin. It is obtained by stirring until precipitation of .

The present invention will be explained in detail below using test examples, examples, and comparative examples.

Test Example 1 500 g of β-cyclodextrin (Nippon Shokuhin Kako Co., Ltd. Seldex-N) was added to 3 portions of water and heated to 75 to 80° C. with stirring to dissolve. On the other hand, as a clathrate anti-aging agent, N-(1,3-dimethylbutyl)-N'
-7Enyl-P-phenylenediamine (105g) was dissolved in ethanol, and β-
Gradually add to the cyclodextrin solution. Heating was stopped, stirring was continued for about 3 hours until the oily part on the surface of the solution disappeared, and then the solution was cooled to room temperature. The generated clathrates were collected by centrifugation and dried at 70-80°C to obtain anti-aging agent complex I.

Test Example 2 An anti-aging agent complex (2) was obtained in the same manner as in Test Example 1, except that 99 g of N-isopropyl-N'-phenyl-P-phenylenediamine was used as the anti-aging agent.

Test Example 3 6-nitoxy 1,2-dihy! as an anti-aging agent!
F D-2,2,4-,ulf)I,*/+)y□□5
An anti-aging agent composite m was obtained in the same manner as in Test Example 1 except that g was used.

Examples 1-5. Comparative Examples 1 to 4 Various rubber compositions having the formulation contents shown in Table 1 were prepared by conventional methods, and after vulcanization, the amount of dynamic ozone crack generation, degree of discoloration,
The residual rate of antioxidant after heat treatment and the amount of dynamic ozone cracks generated after heat treatment were evaluated. The results are shown in Table 1.

The evaluation method is as follows.

[Dynamic ozone crack generation amount]

A test piece was prepared by vulcanizing the unvulcanized rubber composition at 145°C for 30 minutes, and the ozone concentration was set to 5 in an ozone weather meter.
The amount of cracks generated after 15 hours was visually evaluated under the conditions of 0 PPhm, temperature of 40° C., and dynamic elongation rate of 30%. It was expressed as an index, with 0 representing the state with no cracks occurring before ozone deterioration and 10.0 representing the state of the rubber composition without aging protection after ozone deterioration. The smaller the value, the better.

[Degree of discoloration]

Vulcanized rubber that evaluated the amount of dynamic ozone crack generation □ Using a test piece, a color difference meter CR-100 manufactured by Minolta Camera ■ was used to measure a line, b zero, saturation c heat sla line a line ten f I asked for laziness. The larger the value, the greater the degree of discoloration and the more contaminated it is.

[Residual rate of anti-aging agent after heat treatment]

A test piece was prepared by vulcanizing the unvulcanized rubber composition at 145°C for 30 minutes, and after heat treatment in a gear oven at 100°C for 168 hours, the remaining antiaging agent was extracted with 77 tons.
Quantification was done by thin layer chromatography. The residual rate was determined by the following formula by determining the amount of anti-aging agent extracted from the test piece before heat treatment using A7T.

[Dynamic ozone crack generation amount after heat treatment] An unvulcanized rubber composition was vulcanized at 145°C for 30 minutes to prepare a test piece.
After being left in a gear open state at 00° C. for 168 hours, the amount of dynamic ozone cracks generated was evaluated in the same manner as described above.

However, the ozone deterioration time was 5 hours.

The anti-aging agent χ awards for Tables 1), 21 and 3 were 3 and 3 respectively.
, 2 and ll members.

As is clear from Table 1, the rubber composition of the present invention containing the anti-aging agent complex has improved staining resistance and a good amount of dynamic ozone crack generation after heat treatment, so it has good durability. It has been improved.

Example 6, Comparative Examples 5 to 6 Rubber compositions having the formulations shown in Table 2 were prepared by a conventional method, and these unvulcanized rubber compositions were tested for tire size 1000.
The truck and bus tires used as the sidewalls of the R20 tires were driven on an actual vehicle for 80,000 hours, and then the degree of cracking in the sidewalls was visually observed. Further, the residual rate of the anti-aging agent at that time was evaluated by the method described above, and the results are shown in Table 2.

Table 2 As is clear from Table 2, the tire of Example 6, in which the rubber composition of the present invention was used in the tire sidewall, had a large amount of anti-aging agent remaining even in the later stages of running, so the degree of crack occurrence was good. It is.

(Effects of the Invention) According to the present invention, a rubber composition with excellent aging resistance and appearance can be obtained by blending an antiaging agent complex in which an antiaging agent is encapsulated with cyclodextrin.

Claims (2)

[Claims] (1) Rubber 100 made of natural rubber and/or synthetic rubber
An improved rubber composition comprising 1 to 20 parts by weight of an anti-aging agent complex in which the anti-aging agent is aged with cyclodextrin at a molar ratio of 1/3 to 1/1. . (2) Rubber 100 made of natural rubber and/or synthetic rubber
For each part by weight, the anti-aging agent is 0.1 to 2.0 parts by weight, and the anti-aging agent is mixed with cyclodextrin in a molar ratio of 1/1.
3 to 1/1 ratio of aged anti-aging complex to 0.5
An improved rubber composition containing ~15 parts by weight.