JPS5852331A - Rubber composition - Google Patents

Abstract

PURPOSE:To provide a rubber composition with high hardness, high break strength, low heat value, and good fabrication in an unvulcanized form, by incorporating a stock rubber which contains a synthetic polyisoprene rubber with carbon black and a Co salt of an organic carboxylic acid. CONSTITUTION:100pts.wt. stock rubber containing at least 90wt% synthetic polyisoprene rubber is incorporated with 60-100pts.wt. carbon black of iodine adsorption 70-130mg/g and DBP adsorption 50-80ml/100g, 4.5-10pts.wt.sulfur, and 0.02-0.8pts.wt. calculated as the content of Co element, Co salt of straight or branched 5-20C organic carboxylic acid. Said stock rubber is pref. a homopolymer of polyisoprene, and at most 10wt% of the rubber may be replaced by other rubbers. The alternatives include natural rubber, styrene-butadiene rubber, polybutadiene rubber, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rubber composition, and more particularly to a synthetic rubber composition. I.J.
A rubber composition containing inozolene rubber (IR) as the main rubber has an iodine adsorption amount of 70 to 130 ■/gXDBP oil absorption amount of 50
~B □ ml! / 100. li' carbon bra,
In other words, the reinforcing property is low
By blending a large amount of carpin black (structure), a large amount of sulfur, and a cobalt salt of organic carginic acid at the same time, it has high hardness 1, high rupture physical properties, and has a relatively high calorific value. The present invention relates to a rubber composition that has a low adhesive strength, exhibits high adhesive strength when used as a steel cord coating rubber, and has good processability when unvulcanized.

Since automobile tires must have various functions, they are usually made by combining rubbers with different properties. Therefore, in tires, the properties of the rubber used in each part vary widely, with soft rubber used in some parts and hard rubber used in other parts.

For example, rubber that is harder than other parts is often used for the steel cord coating rubber of a radial tire with a steel breaker, the edzotede of a steel breaker, or a bead filler.

In order to obtain a rubber with high hardness, for example, a rubber composition containing a large amount of carpin black and a large amount of sulfur is used. When a large amount of carpin black is added, the hardness increases, but the tensile strength and elongation at break of the vulcanized rubber decrease, the heat generation property of the vulcanized rubber increases, and it becomes easier to set against dynamic deformation. disadvantages arise. 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 carbine black generates a higher amount of heat in the vulcanized rubber than normal rubber, so in order to improve this point, it is necessary to use natural rubber, which is advantageous in terms of heat generation, and accelerate vulcanization. Possible measures include increasing the amount of the agent. Natural rubber has good properties at break, but if a large amount of sulfur is added, the properties at break tend to deteriorate significantly, and the strength decreases rapidly with vulcanization time. In this system, when the amount of vulcanization accelerator is increased, the physical properties at break decrease even more.

In addition, there is a method of obtaining high hardness rubber by adding natural resins or synthetic resins, but even with this method, the harder the rubber composition, the lower the physical properties at break, and the heat generation of the vulcanized rubber is extremely high. It becomes expensive.

Japanese Patent Application No. 55-166738 discloses a rubber composition that has high hardness, high breaking properties, and good adhesion to metals, but this is still insufficient and a resin is used. Vulcanized rubber generates a high amount of heat.

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 rubber composition 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 purpose is to

The present inventors have researched a method for suppressing the heat generation and increase in dynamic set of vulcanized rubber of high hardness rubber compositions containing large amounts of carbine black and sulfur, and found that the compounding agents to be added and We found the following interesting facts regarding this type of research.

(1) Effect of organic acid co-glut 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 with respect to the vulcanization time, and the hardness and mono- If the vulcanization time is prolonged until the lath has risen sufficiently, the tensile strength and elongation at break will drop significantly. On the other hand, in systems containing organic acid salts, vulcanization is faster, hardness and modulus cannot be increased in a short time, and vulcanization conditions with less decrease in tensile strength and elongation at break are required. It is possible to make it hard.

(2) Effects of synthetic polyisozolene 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 polyisogrene (natural rubber) is used instead of natural rubber (natural polyisogrene rubber). IR) increases the elongation at break. Furthermore, adding an appropriate amount of a 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, even if fatty acids are added to the natural rubber system, the tensile strength and elongation at break tend to decrease, 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 content, the use of IR slightly increases the fracture properties but decreases the hardness. In such a system containing a large amount of carbine black, the combination of (1) R/fatty acid/large amount of sulfur/cobalt organic acid 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. For this reason, it is advantageous for the fracture properties if an increase in hardness increases the low elongation modulus but not 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 to ensure the physical properties at break without increasing the high elongation modulus. The IR type has such characteristics compared to the natural rubber type. Furthermore, in a system using IR/fatty acid in combination, the fatty acid reduces the set resistance against dynamic deformation, and this system also exhibits less deterioration in physical properties at break even when the amount of vulcanization accelerator is increased compared to a natural rubber system. 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 car blank.

As described above, by using R/fatty acid in combination with a system containing large amounts of carbon brane, phosphor, and sulfur, it is possible to suppress an increase in exothermic dynamic set and obtain a rubber with high hardness and high rupture properties.

As a result of further research into the characteristics of this system, the present inventors found that the iodine adsorption amount used in this system was 70 to 13 pq/jj.

Carbon black with a DBP oil absorption of 50 to 80 m1/100 g, that is, a low structure (LowSt) with reinforcing properties.
It has been found that the effect of this system is even greater by using carbon black with a carbon black of RTR'Cture.

If 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 will be greater than other carbine blanks, and the physical properties at break will be more advantageous. Moreover, when a large amount of carbon black is blended, the viscosity of the unmyelinated state increases and processability becomes disadvantageous, but when a large amount of carbon black is blended, the viscosity of low-structure carbine plaque increases compared to other carbon blacks. Since the amount is smaller, processability is advantageous. Furthermore, this system has high adhesive strength when used for steel cord coated rubber, especially after overvulcanization. This is advantageous for rubber compositions used in areas that require high adhesion, such as carcass coating rubber for steel tires, and where the thermal history and degree of vulcanization may vary depending on location during vulcanization. be. In particular, tires such as truck and gas tires, whose treads are refurbished after their treads have worn out, need to maintain high adhesion, so the rubber composition for such tires is It is very advantageous as a product.

The present inventors arrived at the present invention from this standpoint.

In other words, the present invention is based on 90% by weight or more of synthetic material. 100 parts by weight of the raw material comb containing lysoglen comb has an iodine adsorption amount of 70 to 130 mq/9 and a DBP oil absorption amount of 50 to 80 m
l/100 g of Kerr G7 black 60-100 parts by weight, sulfur 4.5-10 parts by weight, and carbon number 5-20.
This is a rubber composition characterized in that a cobalt salt of a chain or branched organic caldic acid is blended with a cobalt element content of 0.02 to 08 parts by weight.

The raw material rubber used in the present invention is preferably a polymer made of IR alone, but it is also possible to replace 10% by weight or less with other rubbers. IR is a polyisoprene rubber prepared by a solution polymerization method, such as Nipol IR-2200 (manufactured by Nippon Zeon Co., Ltd.) and Kuraprene IR-10 (manufactured by Kuraray Co., Ltd.). Other rubbers to be replaced at 10% by weight or less include natural rubber and styrene-butanoene rubber (SBR)1. T?
If these combs are contained in an amount exceeding 10% by weight, the IH properties will be lost and the rupture properties will be reduced. 1 The carbon black used in the present invention is of the carbon black (HAF-LS, rsAF-LS) type, and has an iodine adsorption capacity of 70 to 130/l, a DBP oil absorption range of 50 to 80 m1/l00g, and has an ASTM
Display S-315, N-326, N-327, N-21
9 carbon bra. The amount of carbon black blended is 60 to 100 parts by weight per 100 parts by weight of the raw rubber. 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 vulcanization will be poor. Rubber becomes more heat generating.

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 a rubber with high hardness, and if the amount exceeds 10 parts by weight, sulfur bloom in the unvulcanized rubber is severe and it is not practical.

The fatty acids are those with 12 to 2 carbon atoms, such as stearic acid and P-lumitic acid, which are commonly used as compounding agents in rubber compositions.
It is preferably blended in an amount of 0.5 to 4 parts by weight, and more preferably in an amount of 1 to 3 parts by weight. If the content of fatty acid is less than 0.5 parts by weight or more than 4 parts by weight, the effects of improving the properties at break and suppressing the increase in heat generation and dynamic set are somewhat impaired.

The organic acid cobalt salt used in the present invention is a co/J rut salt of a chain or branched monocardic acid having 5 to 2 carbon atoms, such as cobalt naphthenate, cobalt stearate, or oleate.

The organic acid cobalt salt is preferably used 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, when using cobalt naphthenate with a cobalt content of 10% by weight, the amount of cobalt naphthenate is 0.2 to 8 parts by weight, preferably 1 to 4 parts by weight, based on 100 parts by weight of the raw material. . Cobalt element content is 0.0
If the amount is less than 2 parts by weight or exceeds 0.8 parts by weight, the physical properties of
The hardness is not at the desired level and the blending effect is low.

In the present invention, in addition to the above-mentioned compounding agents, compounding agents normally used in the rubber industry, such as zinc oxide, process oil, vulcanization accelerator, etc., are added in appropriate amounts, but resins such as alkylphenol resins are not added. This is not preferable because it increases heat generation.

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 22 and Comparative Examples 1 to 40 Sulfur and vulcanization were added to a master patch obtained by mixing the raw rubber shown in Table 1 and compounding ingredients other than sulfur and vulcanization accelerator in a normal Banbury type mixer. A rubber composition was prepared by adding an accelerator using an open roll. The viscosity of this rubber composition (unvulcanized rubber) is ML, +4, that is, 100°C
Measurement was started after one molecule was heated, and the Mooney viscosity was measured after 4 minutes.

The physical properties of the vulcanized rubber were determined by forming the rubber composition into a sheet and heating it at 150°C.
A vulcanized sheet was prepared by vulcanization for 30 minutes, and JIS No. 3 dumbbells were punched out, and the hardness (JIS A) was measured and a tensile test was performed. Tensile strength of tensile test, elongation at break, ・1
00chi and 300% modulus are JIS-630
Measured according to 1.

The heat generation test was performed using a Gutdrich flexmeter commonly used in the rubber industry, and measured H, B, U (Heat Build Up) according to ATSM D-623. A cylindrical sample with a diameter of 17.8 mm and a height of 25 mm obtained by vulcanization of 150"C for 130 minutes was used as the sample, and the measurement conditions were 100"C1, load of 25 kg, and strain of 4.4.
4 mm and a rotational speed of 180 rpm, the calorific value after 25 minutes and the compression set (sormanent 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 according to AS'TM 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.

1st: Nipol lR2200 (manufactured by Nippon Zeon Co., Ltd.), 2nd
: Fragileno IR-10 (manufactured by Kuraray Co., Ltd.), No. 3: Manufactured by Japan Synthetic Rubber Co., Ltd., No. 4: ASTM indication N-220, iodine adsorption amount 121 m9/9, DBP oil absorption amount 114 ml/
] 009g*5: ASTM indication N-230, iodine adsorption amount 82mq/g, DBP oil absorption amount 102m171
009, *6: ASTM indication N-226, iodine adsorption amount 82 m9/El, DBP oil absorption amount 7. ; L: r
ug/100g.

*7: ASTM indication N-247, iodine adsorption amount 9
0mg/9, DBP oil absorption ii 24ml/100g,
*8: ASTMtt N-219, iodine adsorption amount]] 8m97g, DBP oil absorption amount 78m17100
g, 9th: cobalt content 10% by weight, 10th: oil extendable insoluble sulfur (net 80% by weight), *]l: N, N socyclohexyl benzothiazyl sulfenamide, 1st
2: N, N-okinoethylene benzothiazyl sulfenamide.

Comparative Examples 1 to 6 and Examples 1 to 2 contain a large amount of sulfur and carbon black (HAF-LS), and further contain naphthenic acid col and a vulcanization accelerator (DZ), with a small amount of vulcanization accelerator. This 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.

Comparison of Comparative Example 1.3.5 and Example 1 shows that the composition mainly composed of IR as the raw material comb has slightly lower tensile strength and mono-strength than the composition mainly composed of NR, but the elongation at break is significantly lower. improves. Furthermore, in Comparative Examples 2.4.6 and Example 2 in which stearic acid was added to these formulations, H, B, U, and compression set (p, s) were generally reduced. Furthermore, in Example 2, the tensile strength and elongation at break are also improved.

However, Comparative Example 2 in which NR was used as the raw material rubber did not have such an effect, and the ratio of NR and IR was 50:50 and 20:8.
Even in Comparative Examples 4 and 6, which were blended at a ratio of 0, the physical properties at break did not improve dramatically. From this,
It can be seen that in this system, the vulcanized rubber containing IR as the raw material rubber and the addition of 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 3 to 5, 1.3.4 parts by weight of stearic acid was blended into the rubber composition of Example 1, but the rubber compositions had high hardness and high hardness, similar to Example 2 in which 2 parts by weight of stearic acid was blended. A vulcanized rubber having fracture properties is obtained.

Examples 6 to 10 are vulcanization accelerators (
DZ) and 0 to 4 parts by weight of stearic acid were added, but compared to Examples 1 to 4, the elongation at break was slightly lower due to the increased amount of vulcanization accelerator; is further improved, and H, B, U, and compression set are also reduced. Further, in Example 11, the carbon black of Example 8 was replaced with l5A-LS, but
This system also shows good physical properties.

Comparative Examples 7 to 9 are NR-based or TR-based rubber compositions that do not contain cobalt naphthenate, but compared to Examples 6 to 10, the hardness is significantly reduced and the monocularity is also reduced. This shows that even if a large amount of sulfur is blended, high hardness rubber cannot be obtained without cobalt salt.

Examples 12 to 13 and Comparative Examples 10 to 18 are systems using OBS as a vulcanization accelerator.

Examples 12 and 13 have high hardness and high breaking properties, but
In Comparative Example 10 in which no cobalt salt was added, the hardness decreased and the elongation at break also decreased.

Comparative Examples 11 to 18 are IR or NR rubber compositions containing no cobalt salt, Comparative Examples 11 to 14 use HAF-LS as carbon black, while Comparative Examples 15 to 18) I am using it.

Comparative Example 11y18 showed no increase in elongation at break compared to Examples 12 to 13, especially carbon black (HAF).
Comparative Examples 15 to 18 using the following have extremely low elongation at break. This shows that the presence of cobalt salt is essential for a pot with high hardness and high breaking properties.

Comparative Examples 19 to 22 are NR4 or IR rubber compositions that have a small amount of sulfur and do not contain cobalt salt, but
Both have low hardness and low fracture properties, especially monoyelasticity.

Example 14 and Comparative Examples 23 to 30 are NR or IR rubber compositions using DZ as a vulcanization accelerator, and Comparative Examples 23 to 26 and Comparative Examples 29 to 30 are carbon bras and HAF as a rubber. Examples 27-28 use ISAF. ) (When AP is used, the elongation at break is the same as in Example 1.
-2, and when 15AF is used, the elongation at break is high, but the Mooney viscosity is high. In contrast, Example 1
4 is a system using 15F-LS, which not only has a lower Mooney viscosity but also has an even higher elongation at break.

Comparative Examples 31 to 35 and Example 15 are NR-based or IR-based rubber compositions using OBS as a vulcanization accelerator, and the type of cardan black is changed.

Except for Example 15, which is an IR rubber composition using HAF-LS as the carton black, all of the rubber compositions had low elongation at break, so high physical properties at break could not be obtained. Also, Comparative Examples 34-3
5 has poor adhesiveness. This shows that in a comb composition containing a large amount of sulfur and cobalt salt, high breaking properties can be obtained by using IR as the raw material rubber and low structure carpin black. .

Comparative Examples 36 to 38 and Examples 16 to 20 used DZ as a vulcanization accelerator and contained a large amount of carpin black. Comparative example 36
Although 37 contains a large amount of carbon black, the tear strength is low because NR is used as the raw material rubber.
Elongation at break is extremely low. Examples 16-17 are further car? It contains a large amount of Numbura and Ri, and has extremely hardness and
Although the modulus has increased, the decrease in tensile strength and elongation at break is small. Example 18 is the 15AF-LS system, but
A similar effect can be seen in this system as well. Example 19
-20 used different IR from Example 17, but almost the same results as Example 17 were obtained. Comparative example 38
is HAF as carpin black and NR as raw rubber.
is used, but its tensile strength and elongation at break are low.

Comparative Examples 39 to 40 are NR or IR rubber compositions containing metacresol resin, which is an alkylphenol resin. Comparative Example 39 is mono-laminous and has higher hardness but lower tensile strength and elongation at break (higher H, B, U, and compression set) than rubber without meta-cresol resin as in Comparative Example 7. .

Comparative Example 40 is obtained by adding stearic acid to Comparative Example 39. As in Example 17, carbon black (HAF
-LS) in a very large amount (90 parts by weight) is compared with one in which the hardness is increased by adding resin to 65 parts by weight of carbon black as in Comparative Example 40, the hardness is the same. However, Comparative Example 40 in which resin was added is disadvantageous in that heat generation increases.

Almost the same results as in Examples 16 to I7 were obtained.

Regarding the Carpin Black odor in these Examples and Comparative Examples, the Mooney viscosity when unvulcanized was the lowest in those using loin-structured Carpin Black; However, it is relatively easy to process when unvulcanized.

In terms of adhesion, among carbon blacks, those containing low traction, ie, HAF-LS and 15AF-LS, have the highest adhesive strength, and also have the highest pull-out force during overvulcanization.

As explained above, the present invention uses synthetic polyisolune rubber as the main raw material comb, contains a large amount of carbon brane, silica (HAF-LS or 15AF-LS), and sulfur, and also contains cobalt salt of organic carbic acid. In the comb composition, the vulcanized rubber has high hardness and high rupture properties, has relatively low heat build-up, exhibits high adhesive strength when used as a steel cord coating rubber, and Since it has excellent processability during vulcanization, it is suitably used for steel cord coating rubber for steel tires, belt gills, bead fillers, etc.

Patent applicant: Yokohama Rubber Co., Ltd.

Claims (1)

[Claims] 1. 70 to 130 rn of iodine adsorbed to 100 parts by weight of raw rubber containing 90% by weight or more of synthetic I-lisoprene rubber.
9/g, DBP oil absorption 50-80 m//100# carpin black 60-100 parts by weight, sulfur 4.5-1
1. A rubber composition characterized in that a cobalt salt of a chain or branched organic caldic acid having 5 to 20 carbon atoms is blended in an amount of 0.02 to 0.8 parts by weight as a cobalt element content.