JPS6116290B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition for coating steel cords, and more specifically, a rubber composition mainly composed of synthetic polyisoprene rubber (1R) has an iodine adsorption amount of 70 to 70%.
130mg/g, DBP oil absorption of 50-80ml/100g, a large amount of reinforcing low structure carbon black, a large amount of sulfur, and a sulfenamide flux accelerator and fatty acids. By simultaneously blending a cobalt salt of an organic carboxylic acid, it has high elongation at break, high strength at break, and high hardness, and has a relatively low calorific value, and has high adhesive strength when used as a steel cord coating rubber. The present invention relates to a rubber composition for coating a steel cord, which also has good processability when unvulcanized. Since automobile tires must have various functions, they are usually made by combining rubbers with various properties. Therefore, the properties of the rubber used in each part of a tire are as follows:
There are many different types, with some parts using soft rubber and others using hard rubber.
For example, rubber that is harder than other parts is often used for the steel cord covering rubber of a radial tire with a steel breaker, the edge tape or bead filler of a steel breaker, and the like. To obtain a rubber with high hardness, for example, a rubber composition containing a large amount of carbon black and a large amount of sulfur is used. If a large amount of carbon black is added, the hardness will increase, but the tensile strength and elongation at break of the vulcanized rubber will decrease, and the heat generation property of the vulcanized rubber will increase.
Disadvantages arise, such as being easier to set against dynamic deformations. Furthermore, when a large amount of sulfur is added, the physical properties at break such as the tensile strength, elongation at break, and tearing force of the vulcanized rubber are further reduced. The above-mentioned rubber containing a large amount of carbon black generates a higher amount of heat as a vulcanized rubber than normal rubber, so to improve this point, natural rubber, which is advantageous in terms of heat generation, should be used.
Alternatively, measures such as increasing the amount of vulcanization accelerator can be considered. Natural rubber is a rubber with good properties at break, but when a large amount of sulfur is added, the properties at break decrease significantly, and moreover, the properties decrease rapidly with vulcanization time.
In this system, when the amount of the galvanic accelerator is increased, the rupture properties decrease even more. In addition, there is a method to obtain high hardness rubber by adding natural resins or synthetic resins, but this method does not only reduce the physical properties at break to the extent that it makes the rubber composition hard, but also causes heat generation in the vulcanized rubber. becomes very high. Japanese Patent Application No. 166738/1987 discloses a rubber composition that has high hardness, high breakability, and good adhesion to metals, but it is still insufficient, and furthermore, since resin is used, processing is difficult. Sulfur rubber has high heat generation. It has thus been difficult to obtain a rubber composition that has high hardness and high rupture properties and suppresses set due to heat generation and dynamic deformation. The present invention provides a steel cord coating that has high hardness and high rupture properties, has relatively low heat generation, exhibits high adhesive strength when used as a steel cord coating rubber, and has good processability when unvulcanized. The object of the present invention is to provide a rubber composition for use in rubber compositions. The present inventors have researched a method of suppressing the heat generation and increase in dynamic set of vulcanized rubber of high hardness rubber compositions containing large amounts of carbon black and sulfur to obtain good fracture properties. We found the following interesting facts regarding this type of research. (1) Effect of organic acid cobalt in a system containing a large amount of sulfur. In a system containing a large amount of sulfur, if the organic acid cobalt is not included, it will take a long time to complete vulcanization, and the increase in hardness (JIS A) and modulus will be slow compared to the vulcanization time, and the hardness and modulus will not be sufficient. Increasing the vulcanization time until the tensile strength increases,
The elongation at break will drop significantly. On the other hand, systems containing organic acid cobalt accelerate vulcanization and increase hardness and modulus in a short time, so it is necessary to harden the system under vulcanization conditions that minimize the decrease in tensile strength and elongation at break. is possible. (2) Effects of synthetic polyisoprene rubber in a combination system containing a large amount of sulfur and organic acid cobalt. In high-hardness rubber compositions, natural rubber is advantageous in terms of breakage properties, heat generation properties, etc. However, in the case of containing a large amount of sulfur/organic acid cobalt, synthetic polyisoprene rubber (natural polyisoprene rubber) is used instead of natural rubber (natural polyisoprene rubber). IR) increases the elongation at break. Furthermore, adding an appropriate amount of fatty acid such as stearic acid, which is commonly used as a vulcanization accelerator in the rubber industry, increases tensile strength and tearing force. Such an effect of stearic acid is not seen in natural rubber systems. That is, the combined use of IR and fatty acid increases the fracture properties. In this case, addition of fatty acids to the natural rubber system tends to reduce tensile strength and elongation at break, and no such effect is observed. Moreover, such an effect due to the combined use of IR/fatty acid is greater in a system containing cobalt organic acid, and less effective in a system not containing cobalt organic acid. Also, systems with low sulfur content have little effect, while systems with high sulfur content are effective. In systems with low sulfur, the use of IR slightly increases the fracture properties but decreases the hardness. In such a system containing a large amount of carbon black, the combination of IR/fatty acid/large amount of sulfur/organic acid cobalt exhibits its effect. Generally, when the modulus of vulcanized rubber increases, the tensile strength, elongation at break, and tearing force tend to decrease, and the physical properties at break decrease. From this, it is advantageous for the fracture properties to increase the hardness by increasing the low elongation modulus and not increasing the high elongation modulus. Therefore, as a result, it is preferable to increase the hardness, which is considered to be an extremely low deformation modulus, but not to increase the high elongation modulus, and to ensure the physical properties at break. IR type has such characteristics compared to natural rubber type. Moreover, in a system that uses IR/fatty acid in combination, the fatty acid reduces the set against dynamic deformation, and the physical properties at break are not significantly reduced in this system compared to natural rubber systems even when the amount of vulcanization accelerator is increased. Therefore, increasing the amount of the vulcanization accelerator is advantageous in suppressing the increase in heat generation and dynamic set caused by a large amount of carbon black. As described above, by using IR/fatty acid in combination in a system containing large amounts of carbon black and sulfur, it is possible to suppress the increase in exothermic dynamic set and obtain a rubber with high hardness and high rupture properties. As a result of further research on the characteristics of this system, the present inventors found that the amount of iodine adsorbed in this system was 70 to 130 mg/
It has been found that the effect of this system is even greater by using carbon black with a DBP oil absorption of 50 to 80 ml/100 g, that is, carbon black with a low reinforcement structure (LcwStructure). When a carbon black within the above range is used in this IR/large amount of sulfur/cobalt organic acid system, the tensile strength and elongation at break are greater than other carbon blacks, and the physical properties at break are more advantageous. Moreover, normally when a large amount of carbon black is blended, the viscosity when unvulcanized increases and processability becomes disadvantageous, but when a large amount of roasted structuring carbon black is blended, the viscosity increases less than other carbon blacks. , processability is advantageous. Moreover, this system
When used on steel cord coated rubber, it has high adhesive strength, especially after overvulcanization. This means that rubber compositions used in areas that require high adhesion, such as carcass coating rubber for steel tires, and where the heat coverage history and vulcanization time may vary depending on the location during vulcanization. advantageous to In particular, tires such as truck bus tires, whose treads are refurbished after their treads have worn out, need to maintain high adhesive strength. advantageous to The present inventors arrived at the present invention from this standpoint. That is, the present invention has an iodine adsorption amount of 70 to 130 mg/g and a DBP oil absorption amount of 50 to 80 mg/g per 100 parts by weight of rubber.
Contains 60 to 100 parts by weight of carbon black, 4.5 to 10 parts by weight of sulfur, and 0.02 to 0.8 parts by weight of a chain or branched organic carboxylic acid having 5 to 20 carbon atoms as cobalt element content. The steel cord coating rubber is characterized by containing 90 parts by weight or more of synthetic polyisoprene rubber as the rubber, 0.2 to 0.8 parts by weight of a sulfenamide vulcanization accelerator as the vulcanization accelerator, and 0.5 to 4.0 parts by weight of fatty acid. This is a rubber composition for coating steel cord. The raw material rubber used in the present invention is preferably a polymer with IR alone, but it is also possible to replace 10% by weight or less with other rubbers. IR is polyisoprene rubber prepared by a solution polymerization method, such as Nipole IR-2200 (manufactured by Nippon Zeon Co., Ltd.), Claprene IR-
10 (manufactured by Kuraray). Other rubbers that can be replaced with less than 10% by weight include natural rubber, styrene-butadiene rubber (SBR), and polybutadiene rubber (BR); if these rubbers are contained in an amount exceeding 10% by weight, the IR properties will be lost. , the rupture properties deteriorate. The carbon black close structure used in the present invention is carbon black (HAF-LS,
ISAF-LS) type with iodine adsorption amount of 70~
130mg/g, DBP oil absorption in the range of 50 to 80ml/100g, and ASTM indication S-315, N-326, N-
327, N-219 carbon black. The amount of carbon black is per 100 parts by weight of raw rubber.
The amount is 60 to 100 parts by weight, and if it is less than 60 parts by weight, the hardness will not be sufficient, and if it exceeds 100 parts by weight, the tensile strength and elongation at break will be poor, and the heat generation property of the vulcanized rubber will increase. The amount of sulfur is 4.5 to 10 parts by weight per 100 parts by weight of raw rubber. If the amount of sulfur is less than 4.5 parts by weight, it is difficult to obtain rubber with high hardness, and if the amount exceeds 10 parts by weight, sulfur blooms in unvulcanized rubber and is not practical. The fatty acid is a carboxylic acid having 12 to 23 carbon atoms, such as stearic acid or palmitic acid, which is commonly used as a compounding agent for rubber compositions, and is preferably blended in an amount of 0.5 to 4.0 parts by weight, more preferably 1.0 to 23 parts by weight.
It is 3.0 parts by weight. When the amount of fatty acid blended is less than 0.5 parts by weight or more than 4.0 parts by weight, the effect of improving fracture properties, suppressing increase in heat generation and increase in dynamic set is somewhat impaired. The organic acid cobalt salt used in the present invention is a cobalt salt of a chain or branched monocarboxylic acid having 5 to 20 carbon atoms, such as cobalt naphthenate, cobalt stearate, or cobalt oleate.
The organic acid cobalt salt is preferably blended in an amount of 0.02 to 0.8 parts by weight, preferably 0.1 to 0.4 parts by weight of cobalt element per 100 parts by weight of raw rubber. Therefore, for example, a cobalt content of 10% by weight
When using cobalt naphthenate of 0.2 to 0.2 to 100 parts by weight of raw rubber,
8 parts by weight, preferably 1 to 4 parts by weight. If the cobalt element content is less than 0.02 parts by weight or more than 0.8 parts by weight, the breaking properties and hardness will not be at the desired level, and the blending effect will be poor. As the vulcanization accelerator used in the present invention, a sulfenamide vulcanization accelerator is preferably used, and the amount thereof is 0.2 to 0.8 parts by weight per 100 parts by weight of raw rubber.
Parts by weight. In the present invention, in addition to the above-mentioned compounding agents, compounding agents commonly used in the rubber industry, such as zinc oxide,
Process oil and the like are added in appropriate amounts, but addition of resins such as alkylphenol resins is not preferable because heat generation increases. The present invention will be specifically described below based on Examples and Comparative Examples. All formulations in Table 1 are parts by weight. Moreover, in fact, examples and ratios mean comparative examples. Examples 1 to 19 and Comparative Examples 1 to 43 Sulfur and the vulcanization accelerator were added to a masterbatch obtained by mixing the raw rubber shown in Table 1, sulfur, and ingredients other than the vulcanization accelerator in a normal Banbury type mixer. was added using an open roll to prepare a rubber composition. The viscosity of this rubber composition (unvulcanized rubber) was measured at ML ₁₊₄ , that is, the measurement was started after 1 minute of preheating at 100° C., and the Mooney viscosity was measured after 4 minutes. The physical properties of vulcanized rubber are determined by forming the rubber composition into a sheet,
Vulcanize at 150℃ for 30 minutes to create a vulcanized sheet, JIS3
We punched out dumbbells, measured their hardness (JISA), and conducted a tensile test. The tensile strength of the tensile test is
Elongation at break, 100% and 300% modulus are JIS−
Measured according to K-6301. The heat generation test was performed using an ATSMD-623 Gutsudori Tiflexometer, which is commonly used in the rubber industry.
It was measured by H・B・U (Heat Build Up) according to . A cylindrical sample with a diameter of 17.8 mm and a height of 25 mm obtained by vulcanization at 150℃ for 30 minutes was used as the sample.The measurement conditions were 100℃, load 25Kg, strain 4.44mm, and rotation speed 1800rpm. The amount and the compression set (permanent set) after completion were measured. Further, the adhesive strength was evaluated using a brass-plated steel cord with a 3+9+15 structure, and the steel cord was pulled out in accordance with ASTM D 2229, and evaluated based on the pulling force and rubber coverage (%) at that time. The results of these measurements are shown in Table 1.

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[Table] Comparative Examples 1 to 7 and Example 1 contain large amounts of sulfur and carbon black (HAF-LS),
Furthermore, it contains cobalt naphthenate and a vulcanization accelerator (DZ), and although the vulcanization accelerator is small, the system contains a large amount of cobalt salt, and the cobalt salt has a large vulcanization accelerating effect. The effect of blending the raw rubber and the effect of adding stearic acid in this system were evaluated. Comparisons of Comparative Examples 1, 3, 5, and 7 show that when the raw rubber is made mainly of IR, the tensile strength and modulus are slightly lower than when the raw rubber is made mainly of NR, but the elongation at break is significantly improved. In addition, Comparative Example 2 in which stearic acid was added to these formulations,
4, 6, and Example 1, H, B.U., and compression set (P.S.) are generally reduced. Furthermore, in Example 1, the tensile strength and elongation at break are also improved compared to Comparative Example 7. However, Comparative Example 2, which used NR as raw material rubber, did not have such an effect;
Even in Comparative Examples 4 and 6, in which IR and IR were blended in ratios of 50:50 and 20:80, the physical properties at break did not improve dramatically. From this, it can be seen that in this system, the vulcanized rubber of the formulation (Example 1) using IR as the raw material rubber and further adding stearic acid has high hardness and high rupture properties. Furthermore, this system has excellent adhesive strength, and no significant decrease in adhesive strength is observed even during overvulcanization. In Examples 2 to 4, 1, 3, and 4 parts by weight of stearic acid were blended into the rubber composition of Comparative Example 7, but the rubber compositions were high in hardness and high, similar to Example 1 in which 2 parts by weight of stearic acid was blended. A vulcanized rubber having fracture properties is obtained. Comparative Example 8 and Examples 5 to 8 are obtained by increasing the amount of vulcanization accelerator (DZ) in the rubber composition of Comparative Example 7 and further blending 0 to 4 parts by weight of stearic acid. Compared to Examples 1 to 3, the elongation at break was slightly lower due to the increased amount of vulcanization accelerator, but the modulus and hardness were further improved, and H.B.
U. and compression set also decrease. However, Comparative Example 8, in which no stearic acid was added, was inferior to Examples 5 to 8, in which 1 to 4 parts by weight of stearic acid was added, in terms of physical properties at break. Further, in Example 9, the carbon black of Example 6 was replaced with ISAF-LS, and this system also shows good physical properties. Comparative Examples 9 to 11 do not contain cobalt naphthenate.
Although it is an NR-based or IR-based rubber composition, the hardness is significantly reduced and the modulus is also reduced compared to Comparative Example 8 and Examples 5 to 8. This shows that even if a large amount of sulfur is blended, high hardness rubber cannot be obtained without cobalt salt. Example 10 and Comparative Examples 12 to 21 are systems using OBS as a vulcanization accelerator. Comparative Example 12 and Example 10 have high hardness and high breaking properties, but Example 10 with added stearic acid
shows higher fracture properties. Furthermore, in Comparative Example 13 in which no cobalt salt was added, the hardness decreased and the elongation at break also decreased. Comparative Examples 14 to 21 are IR-based or NR-based rubber compositions that do not contain cobalt salts, Comparative Examples 14 to 17 use HAF-LS as carbon black, while Comparative Examples 18 to 21 use HAF. ing. Comparative Examples 14 to 21 show no increase in elongation at break compared to Example 10, and particularly Comparative Examples 18 to 21 using carbon black (HAF) have extremely low elongation at break. This shows that the presence of cobalt salt is essential in order to have high hardness and high breaking properties. Comparative Examples 22 to 25 are NR or IR rubber compositions that contain a small amount of sulfur and do not contain cobalt salt, but all have low hardness and low physical properties at break, particularly modulus. Example 11 and Comparative Examples 26 to 33 are NR or IR rubber compositions using DZ as a vulcanization accelerator, and Comparative Examples 26 to 29 and Comparative Examples 32 to 33 are HAF and Comparative Example 30 as carbon black. ~31 uses ISAF. When HAF is used, the elongation at break is lower than in Example 1, and when ISAF is used, the elongation at break is high, but the Mooney viscosity becomes high. On the other hand, Example 11 is a system using ISAF-LS,
Not only is the Mooney viscosity lower, but the elongation at break is even higher. Comparative Examples 34 to 38 and Example 12 are NR-based or IR-based rubber compositions using OBS as a vulcanization accelerator, and the type of carbon black is changed. Except for Example 12, which is an IR-based rubber composition using HAF-LS as carbon black, all of the compositions had low elongation at break, so high physical properties at break could not be obtained. Also, Comparative Example 37~
38 has poor adhesion. This shows that for rubber compositions containing a large amount of sulfur and containing cobalt salt, high rupture properties can be obtained by using IR as the raw material rubber and roasted textured carbon black. Comparative Examples 39 to 41 and Examples 13 to 17 are NR or IR rubber compositions containing DZ as a vulcanization accelerator and a large amount of carbon black. Comparative example
39 to 40 contain a large amount of roasted structure carbon black, but as a raw material rubber
Since NR is used, tear strength and elongation at break are extremely low. Examples 13 and 14 are IR-based compounds containing a large amount of carbon black, and although the hardness and modulus are significantly increased, the decrease in tensile strength and elongation at break is small. Example 15 is ISAF
-LS system, but similar effects can be seen in this system as well. Although Examples 16 and 17 each used a different IR from Example 14, almost the same results as Example 14 were obtained. Comparative Example 41 uses HAF as carbon black and NR as raw rubber, but the tensile strength and elongation at break are low. Comparative Examples 42 to 43 are NR or IR rubber compositions blended with metacresol resin, which is an alkylphenol resin. Comparative Example 42 has higher modulus and hardness than rubber without metacresol resin as in Comparative Example 9, but lower tensile strength, lower elongation at break, and higher H.B.U. and compression set. Comparative Example 43 is obtained by adding stearic acid to Comparative Example 42. As in Example 14, a very large amount (90 parts by weight) of carbon black (HAF-LS) was blended, and as in Comparative Example 43, 65 parts by weight of carbon black was mixed with resin to improve hardness. Compared with those with increased hardness, the hardness is the same, but Comparative Example 43 in which resin is added is disadvantageous in that it generates more heat. Examples 18 and 19 used cobalt stearate as the cobalt salt, but almost the same results as Examples 13 and 14 using cobalt naphthenate were obtained. Among the carbon blacks of these Examples and Comparative Examples, the Mooney viscosity when uncured was the lowest when using low structure carbon black, and even if a large amount of such reinforcing carbon black was blended, the unvulcanized Mooney viscosity was the lowest. Processability is relatively easy. In terms of adhesion, among carbon blacks, low structure ie HAF-LS and ISAF-LS
The one containing the following is the highest and also has the highest pull-out force during overvulcanization. As explained above, the present invention uses synthetic polyisoprene rubber as the main raw material rubber, contains a large amount of carbon black (HAF-LS or ISAF-LS) and sulfur, and also contains a fatty acid and a cobalt salt of an organic acid carboxylic acid. In the rubber composition for covering steel cords, the vulcanized rubber has high hardness and high rupture properties, has relatively low heat generation, and exhibits high adhesive strength when used as a steel cord covering rubber, Furthermore, since it has excellent processability when unvulcanized, it is suitably used for rubber for covering steel cords of steel tires, belt edge tapes, bead fillers, etc.

Claims (1)

[Claims] 1. Iodine adsorption amount is 70 to 130 per 100 parts by weight of rubber.
mg/g, DBP oil absorption 50-80ml/100g, 60-100 parts by weight of carbon black, 4.5-10 parts by weight of sulfur,
Cobalt salt of chain or branched organic carboxylic acid with 5 to 20 carbon atoms as cobalt element content
In the steel cord coating rubber containing 0.02 to 0.8 parts by weight, 90 parts by weight or more of synthetic polyisoprene rubber as the rubber, 0.2 to 0.8 parts by weight of a sulfenamide vulcanization accelerator as the vulcanization accelerator, and 0.5 to 4.0 parts by weight of fatty acids. A rubber composition for coating a steel cord, characterized in that the rubber composition is blended with the rubber composition.