JPS634582B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition, and more specifically, it contains an organic acid cobalt and a relatively large amount of sulfur, and further contains a meta-cresol resin and polymethoxymethylmelamine, and has no additives in adhesion to a steel cord. Post-vulcanization adhesion due to moisture absorption during curing (hereinafter referred to as unvulcanized water-resistant adhesion), adhesion due to moisture absorption after vulcanization (hereinafter referred to as post-vulcanization water-resistant adhesion), and hot water moisture absorption after vulcanization. The present invention relates to a rubber composition that has good adhesion (hereinafter referred to as post-vulcanization hot water resistant adhesion) even during high-temperature vulcanization and also has good physical properties at break. BACKGROUND OF THE INVENTION Conventionally, as demands for automobile tires have become more sophisticated, steel tires have come into widespread use. Steel tires are advantageous in terms of vehicle maneuverability, stability, and tire wear resistance, but
Steel cords are used as reinforcing materials, and the adhesion between the steel cords and rubber has a significant impact on the quality of the product, so in order to obtain this good adhesion, various technologies have been developed to date. It extends to Tires are exposed to various environments from the manufacturing process to when they are actually used by users in the market and throughout their lifespan, so they must maintain strong adhesion under all conditions.
In other words, when manufacturing tires, it is necessary to have sufficient adhesion during vulcanization (hereinafter referred to as initial adhesion), and furthermore, if unvulcanized rubber is left in an environment where it tends to absorb moisture, unvulcanized rubber will deteriorate. absorbs moisture, reducing the adhesion of the rubber after vulcanization, but it is necessary to maintain good adhesion even under such conditions. On the other hand, even if sufficient adhesion is obtained during vulcanization, moisture in the air may penetrate through the rubber layer during use of the tire and reach the surface of the steel cord, reducing adhesive strength. In addition, if the tire's tread surface receives a puncture wound or cut while driving, water will infiltrate from this area, and when the tire becomes hot while driving, the infiltrated water and heat will cause the steel cords to bond along the gaps. In some cases, deterioration progresses. As described above, there are various types of poor adhesion between steel cord and rubber in tires, but in order for a tire to withstand use, these adhesion properties, namely initial adhesion, unvulcanized water resistant adhesion, and post vulcanized water resistant Adhesion and hot water resistance after vulcanization must all be good, and although techniques to satisfy each of these individually are known in the prior art, it is difficult to satisfy them all at the same time. It was hot. Especially since steel tires have come to be used in large quantities, there has been a growing trend towards increased production of steel tires, but the factors that influence tire productivity are:
This is a vulcanization process, and the shorter this process, the higher the productivity, but in order to achieve this, vulcanization must be performed at a high temperature for a short period of time. However, in rubber compositions containing cobalt salts of organic acids, which have traditionally been used because of their good adhesion to steel cords, the higher the vulcanization temperature, the lower the above-mentioned unvulcanized water-resistant adhesion and post-vulcanized water-resistant adhesion. There was a tendency for both the adhesiveness and hot water resistance after vulcanization to decrease significantly. Further, since the steel cord coating rubber of a steel tire covers a very hard steel cord, it is preferable to use hard (high hardness, high modulus) rubber. In order to obtain such hard rubber, a rubber composition containing a large amount of sulfur and a large amount of carbon black is often used, but such rubber compositions have high hardness and modulus after vulcanization, but
The drawback was that the tensile strength and elongation at break were reduced. The present invention has good initial adhesion to steel cord, unvulcanized water resistant adhesion, post vulcanized water resistant adhesion, and post vulcanized hot water resistant adhesion, and these adhesion properties are also good during high temperature vulcanization. The present invention also aims to provide a rubber composition with high hardness and excellent properties at break, which is particularly useful as a rubber for covering steel cords in steel tires. As a result of researching the adhesion between steel cords and rubber and the physical properties of coated rubber, the present inventor has developed a rubber composition containing a large amount of organic acid cobalt-based sulfur, which is commonly used. When added in combination with methoxymethyl melamine, all types of adhesive properties are improved, and these adhesive properties remain good even during high-temperature vulcanization, and the hardness is significantly increased without decreasing physical properties at break such as elongation at break. The present invention has been achieved by discovering that this can be increased. That is, the rubber composition of the present invention contains, based on 100 parts by weight of raw rubber, (1) 0.1 to 0.5 parts by weight of organic acid cobalt salt as cobalt element content, (2) 1 to 10 parts by weight of metacresol resin, (3) 0.5 to 10 parts by weight of polymethoxymethylmelamine and (4) 3 to 10 parts by weight of sulfur, the rubber composition satisfies the above object. As mentioned above, rubber compositions containing organic acid cobalt salts, which are commonly used as steel cord coating rubber, are vulcanized at high temperatures, especially at temperatures exceeding 170°C, resulting in unvulcanized water resistant adhesion and post vulcanized water resistant adhesive properties. Both adhesion and hot water resistance after vulcanization are reduced. On the other hand, when each of the meta-cresol resin and polymethoxymethyl melamine is added alone, these adhesive properties are improved, but when both are used in combination, a synergistic effect is exhibited and an even higher level is reached. In this case, in order to improve the adhesion using the metacresol resin alone, a large amount must be added, which is disadvantageous because the heat generation property of the vulcanized rubber increases. On the other hand, if a large amount of polymethoxymethylmelamine is used alone to improve adhesion, there will be disadvantages such as delayed vulcanization and deterioration of the physical properties at break of the vulcanized rubber. On the other hand, when both are used in combination, adhesion can be improved with a small amount of each. Moreover, this effect is greater not only in low-temperature vulcanization but also in high-temperature vulcanization. In this case, not all alkylphenol resins commonly used in the rubber industry for tackifiers and the like are effective, but among alkylphenol resins, only metacresol resin is effective. Additionally, as the hardness and modulus of vulcanized rubber increases, the elongation at break tends to decrease.
Although the breaking strength is low, metacresol resin increases hardness and elongation at break. On the other hand, polymethoxymethylmelamine increases hardness but decreases elongation at break. Therefore, when both are used in combination, the hardness can be further increased and the decrease in elongation at break due to the addition of polymethoxymethylmelamine can be prevented by the meta-cresol resin, so the hardness can be increased without reducing the physical properties at break. Regarding this physical property, it is not effective for all alkylphenol resins that are commonly used in the rubber industry for tackifiers, etc., but is a unique phenomenon observed only in meta-cresol resins. The metacresol resin used in the present invention is obtained by reacting metacresol with formalin or paraformaldehyde under an acid catalyst, and is a novolak type resin with 2 to 6 nuclei in the metacresol unit, and has a softening point of 80 to 120 ° C. For example, Sumikanol 610 manufactured by Sumitomo Chemical Co., Ltd. Polymethoxymethylmelamine is a melamine derivative of a formalin donor such as hexamethoxymethylmelamine, such as Cyrez manufactured by American Cyanamid.
It is 963. Polymethylolmelamine is also effective. Further, the metacresol resin used in the present invention is used in an amount of 1 to 10 parts by weight, preferably 2 to 6 parts by weight, based on 100 parts by weight of the raw material rubber. If the amount is less than 1 part by weight, the effect will be small, and if it is added in an amount exceeding 10 parts by weight, the heat generation property of the vulcanized rubber will increase, which is not preferable. On the other hand, polymethoxymethylmelamine is used in an amount of 0.5 to 10 parts by weight, preferably 1 to 6 parts by weight, per 100 parts by weight of raw rubber. If the amount is less than 0.5 parts by weight, the effect will be small, and if the amount is more than 10 parts by weight, there will be disadvantages such as a large decrease in elongation at break and a delay in vulcanization. The raw rubber used in this invention is natural rubber (NR)
Alternatively, polyisoprene rubber (IR) is preferred, but it is also possible to replace 50 parts by weight or less of NR or IR with polybutadiene rubber (BR) or styrene-butadiene rubber (SBR). The organic acid cobalt used in the present invention is preferably cobalt such as a linear or branched monocarboxylic acid having 5 to 20 carbon atoms, such as cobalt naphthenate, cobalt stearate, cobalt octylate, and cobalt oleate. It's salt. The organic acid cobalt used here has a Co element content of 0.1 to 0.6 parts by weight per 100 parts by weight of rubber.
It is preferable to use 0.2 to 0.4 parts by weight. Therefore, for example, when cobalt naphthenate with a Co content of 10% is used, 1 to 6 parts by weight, preferably 2 parts by weight of cobalt naphthenate per 100 parts by weight of rubber.
~4 parts by weight is preferable. If the Co content is less than 0.1 part by weight based on 100 parts by weight of rubber, the blending effect will be small, and if it exceeds 0.6 part by weight, the blending effect will be small. Further, the amount of sulfur is 3 to 10 parts by weight. If the amount is less than 3 parts by weight, the effect of the addition will be small, and if it is added in an amount exceeding 10 parts by weight, sulfur will bloom on the surface of the unvulcanized rubber, causing a problem in processing. The present invention will be specifically explained below using Examples and Comparative Examples. The preparation of the rubber composition and the adhesion test were performed according to the following method, and the physical properties at break were measured by punching out a JIS No. 3 dumbbell in accordance with JIS-K-6301.
Hardness was measured according to JIS A. In the table, all formulations are in parts by weight. Preparation of Rubber Composition According to the formulation in the table, sulfur, vulcanization accelerator, compounding ingredients other than polymate xymethyl melamine, and raw rubber were mixed in a Banbury type mixer, and the remaining compounding ingredients were added to a masterbatch using an open roll. Adhesion test <Initial adhesion> Brass-plated steel cords (3+9+15 structure) arranged in parallel at 12.5 mm intervals were coated with a rubber composition on both sides to make the embedded width 25 mm, and the fabric was heated at 160°C for 20 minutes at 170°C. After vulcanization for 15 minutes, the wire was pulled out as a test sample in accordance with ASTM-D2229 and evaluated based on the pulling force (index) and rubber coverage (%). <Unvulcanized water-resistant adhesion> The water-resistant adhesion due to moisture absorption during unvulcanization is determined by leaving the above fabric uncured in an atmosphere of 30°C and 86% relative humidity for two weeks, then testing at 160°C for 20 minutes at 170°C. ×15
A test sample was prepared by vulcanization for 1 minute, and the wire was pulled out and evaluated in the same manner as the initial adhesion. <Water-resistant adhesion after vulcanization> Adhesion deterioration caused by moisture permeating through the rubber after vulcanization and reaching the steel cord can be confirmed by leaving the sample for drawing after vulcanization at 70℃ x 96% RH for two weeks. A pullout evaluation was performed. <Hot water resistant adhesion after vulcanization> Adhesive deterioration caused by moisture entering from external injury can be measured by cutting the lower end wire of the cut sample at 70°C.
It was immersed in warm water and left for two weeks, then pulled out and evaluated. Evaluations of these adhesive properties and physical properties are also shown in the table.

【table】

【table】

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【table】

[Table] Examples 1 to 6 and Comparative Examples 1 to 9 A system in which 100 parts by weight of natural rubber was blended with 3 parts by weight of cobalt naphthenate and 7 parts by weight of sulfur.
Comparative Examples 2 to 5 were obtained by adding meta-cresol resin to this type of rubber composition. 160 from this result
When vulcanized at ℃ for 20 minutes, the hardness (JIA A) increases along with the meta-cresol resin, the elongation at break increases, and the tensile strength slightly decreases. On the other hand, comparative example 6~
9, hexamethoxymethylmelamine (hereinafter referred to as
(abbreviated as HMM), but HMM
The hardness increases with the amount of carbon, but tends to decrease with the elongation at break and tensile strength. On the other hand, the adhesion of Comparative Examples 2 to 9 is based on the initial adhesion.
Adhesion was good for both 160°C x 20 minutes and 170°C x 15 minutes, but the pull-out force was slightly lower at 170°C x 15 minutes.
As is clear from Comparative Examples 2 to 5, as the amount of meta-cresol resin increases, the water-resistant adhesive properties of all of them improve. Furthermore, in Comparative Examples 6 to 9, as the amount of HMM increases, the adhesiveness, especially the hot water resistant adhesiveness after vulcanization, is improved. Examples 1 to 6 are systems in which metacresol resin and HMM are used in combination, and as the amounts of both increase, both hardness and 100% modulus increase, and in systems containing a large amount of metacresol resin, there is almost no decrease in elongation at break. On the other hand, the adhesion is determined by metacresol resin and
As the amount of HMM increases, water-resistant adhesion, especially water-resistant adhesion after vulcanization, and hot water-resistant adhesion after vulcanization reach a high level. For example, Comparative Example 5 and Examples 2, 3, and 5 show the effect of adding HMM when compounding 6 parts by weight of metacresol resin, but as the amount of HMM increases, especially at 170°C
Both pullout force and rubber coverage increase after 15 minutes of vulcanization. This effect is greater than that of Comparative Example 3 and Examples 1 and 4 in which 2 parts by weight of the metacresol resin was blended. From this, metacresol resin and HMM
There is a mutual effect between the two. Examples 7 to 10 and Comparative Examples 10 to 12 A system in which 2.5 parts by weight of cobalt stearate and 6 parts by weight of sulfur were added to raw rubber consisting of 70 parts by weight of natural rubber and 30 parts by weight of isoprene rubber.
In this system as well, the mutual effect of blending metacresol resin and HMM was observed. Example 11 and Comparative Examples 13 to 18 A system in which 3 parts by weight of cobalt naphthenate and 4 parts by weight of sulfur were added to 100 parts by weight of natural rubber.
In this system as well, the mutual effect of blending metacresol resin and HMM is observed (Example 11).
However, as shown in Comparative Examples 15 and 16, products containing t-butylphenol/formaldehyde resin, which is a general alkylphenol resin, instead of metacresol resin, or those containing HMM in addition to this, are water resistant after vulcanization. Adhesion and hot water resistance after vulcanization are poor. Comparative Examples 17 and 18 are examples in which hexamethylenetetramine, a general formalin donor, is used in place of HMM, but the unvulcanized water-resistant adhesion and post-vulcanized water-resistant adhesion are extremely poor. As explained above, the rubber composition of the present invention has improved hardness without reducing physical properties at break by adding metacresol resin and polymethoxymethylmelamine to a rubber composition system containing organic acid cobalt and a relatively large amount of sulfur. In addition, each adhesive property, namely initial adhesion, unvulcanized water resistant adhesion, post vulcanized water resistant adhesion, and post vulcanized hot water resistant adhesion, is good, and these adhesion properties are particularly good even during high temperature vulcanization. Since it is a rubber composition that does not cause damage, it is preferably used as a steel cord coating rubber.

[Brief explanation of the drawing]

Figure 1 is a graph showing the influence (rubber coverage) of metacresol resin and hexamethoxymethylmelamine HMM on water-resistant adhesion after vulcanization at 170°C x 15 minutes, and Figure 2 is a graph showing the influence (rubber coverage) of 15 minutes at 170°C. Meta-cresol resin and hexamethoxymethyl melamine affect hot water-resistant adhesion after vulcanization
It is a graph showing the influence of HMM (rubber coverage).

Claims (1)

[Claims] 1. For 100 parts by weight of raw rubber, (1) 0.1 to 0.6 parts by weight of organic acid cobalt salt as cobalt element content, (2) 1 to 10 parts by weight of metacresol resin, (3) A rubber composition having good adhesion to metal materials after vulcanization, characterized by containing 0.5 to 10 parts by weight of polymethoxymethylmelamine and (4) 3 to 10 parts by weight of sulfur.