JPH0312578B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rubber composition with excellent adhesion to iron, and more specifically, the main rubber is natural rubber (NR) and/or polyisoprene rubber (IR), and a reinforcing roast structure (Low Structure) is added to the rubber composition.
By blending large amounts of carbon black and sulfur, cobalt salt of organic acid, and less than a trace amount of sulfenamide vulcanization accelerator, it exhibits high hardness, high elongation at break, and crack growth resistance. The present invention relates to a rubber composition that exhibits excellent adhesion to steel cords, especially iron. In recent years, demands on automobile tires for safety, high-speed running performance, durability, etc. have become extremely high. For this reason, there is a growing demand for high quality in terms of destruction of tire separation and the like.
For this reason, many steel tires with highly durable steel belts are being manufactured.
Breakage of this separation often occurs from around the reinforcing layer of the belt, carcass, etc. The present inventors studied the physical properties required for the coating rubber of a steel cord for the purpose of improving the belt separation resistance of steel tires, and found that it is desirable to have the following properties. (1) High hardness, (2)
High elongation at break, (3) flex cracking resistance (low crack growth), (4) good aging properties, (5) high adhesion to steel cord (steel tire cords are usually plated with brass, etc.). However, since the belt edge is the cutting part of the steel cord, the underlying iron without plating is often exposed, so it also includes adhesion to the iron). Although it is preferable to satisfy both of these factors, it has been difficult for conventional rubber compositions to have both of these properties. The present inventors have developed a rubber composition for coating steel belts of tires, etc., in which 100 parts by weight of a rubber mainly composed of polyisoprene rubber, 60 to 100 parts by weight of roasted structured carbon black, and a cobalt salt of an organic carboxylic acid are added. 0.02~ as element content
A rubber composition (Japanese Unexamined Patent Publication No. 58-52331) has been proposed that contains 0.8 parts by weight of sulfur, a relatively large amount. This rubber composition is excellent as a belt coating rubber in that it has high breaking properties and good adhesion to steel cord, but the amount of vulcanization accelerator used is
Since the content was as high as 0.4 parts by weight or more, the adhesive force with iron was insufficient, and the result was not satisfactory from the viewpoint of preventing edge separation. The present invention was made to solve these drawbacks, and provides a rubber composition that has excellent physical properties required for steel cord coated rubber and belt edge tape, particularly excellent belt separation resistance and belt edge separation resistance. It is especially used for steel tires. The present inventors have studied the formulation of a rubber composition that is excellent in belt separation resistance and belt edge separation resistance for steel cord coating rubber for steel tires and belt edge tape, and as a result, the following facts have become clear. Since this is a rubber composition for coating steel cords, it is desirable to have a large amount of sulfur in consideration of adhesion to steel cords. This is because steel cords are usually plated with a plus plate, which reacts with sulfur and becomes adhesive. On the other hand, from the viewpoint of high hardness, it is preferable to incorporate a large amount of sulfur. In addition, from the viewpoint of high adhesion to steel cords, it is not sufficient to incorporate a large amount of sulfur; even higher adhesion can be obtained by adding a cobalt salt of an organic acid. However, when a large amount of sulfur is added, it takes time to complete vulcanization. Therefore, increasing the amount of a normal vulcanization accelerator to promote vulcanization not only causes a decrease in fracture properties and an increase in crack growth, but also
It causes poor adhesion to steel cords, especially to iron. Cobalt salts of organic acids have the effect of accelerating vulcanization and are therefore desirable not only from the standpoint of high adhesion to steel cords but also from the standpoint of accelerating vulcanization. The present inventors reduced the amount of vulcanization accelerator while maintaining the vulcanization accelerating effect of the cobalt salt of an organic acid.
When we examined the adhesion with steel cord and physical properties, we found that the amount of vulcanization accelerator used has a large effect, and it is not recommended to add the amount normally used.
It has been found that it is preferable to minimize the amount from the viewpoint of adhesion to the steel cord and physical properties. However, it has been found that even with a very small amount of vulcanization accelerator, adhesion to iron is not sufficient, and that good adhesion can be obtained by adding a specific resin, namely metacresol resin. Moreover, the combination of metacresol resin contributes to high hardness and high elongation at break. Further, the carbon black used is desirably a roast-structured one from the viewpoint of processability and breakage properties. The present invention has been made based on the above findings. That is, the present invention provides that, for 100 parts by weight of rubber containing 90 parts by weight or more of natural rubber and/or polyisoprene rubber, (1) cobalt naphthenate, cobalt rosin, or linear or branched carbon atoms having 5 to 20 carbon atoms; Cobalt salt of monocarboxylic acid with a cobalt element content of 0.1 to 0.8 parts by weight, (2) 5 to 10 parts by weight of sulfur, (3) 0.3 parts by weight or less of a sulfenamide vulcanization accelerator, (4) Metacresol resin 1 to 10 parts by weight. 10 parts by weight, and (5) Iodine adsorption amount 70-90 mg/g, DBP oil absorption amount 50
A rubber composition with excellent adhesion to iron, characterized by containing 55 to 90 parts by weight of ~80ml/100g of carbon black. The rubber used in the present invention is preferably natural rubber and/or polyisoprene rubber, but up to 10% by weight can be replaced by other rubbers, such as styrene-butadiene rubber (SBR) and polybutadiene rubber (BR). If other rubber is contained in the rubber in an amount exceeding 10% by weight, the properties of natural rubber and/or polyisoprene rubber will be lost and the rupture properties will be reduced. The cobalt salt of an organic acid 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 rosin, cobalt stearate, and cobalt oleate. The cobalt salt of the organic acid is blended with an elemental cobalt content of 0.1 to 0.8 parts by weight, preferably 0.2 to 0.5 parts by weight, per 100 parts by weight of rubber. For example, when using a cobalt salt of an organic acid containing 10% by weight of the cobalt element, rubber
1 to 8 cobalt salts of organic acids per 100 parts by weight
parts by weight, preferably 2 to 5 parts by weight. If the cobalt element content is less than 0.1 part by weight or more than 0.8 part by weight, the breaking properties and hardness will not be at the desired level, and the blending effect will be small. The amount of sulfur used in the present invention is 4 to 10 parts by weight, preferably 5 to 8 parts by weight, based on 100 parts by weight of rubber. If the amount of sulfur is less than 4 parts by weight, adhesion will not be sufficient, and if more than 10 parts by weight is added, not only will there be problems with elongation at break, but sulfur will tend to bloom on the rubber surface when unvulcanized, which will be disadvantageous in processing. . Further, the vulcanization accelerator used in the present invention is N, N
- Sulfenamide vulcanization accelerators such as dicyclhexylbenzothiazole sulfenamide (DZ) and N-oxydiethylene-2-benzothiazole sulfenamide (OBS), the amount of which is compounded per 100 parts by weight of rubber. The amount is 0.4 parts by weight or less, preferably 0.2 parts by weight or less. If it is blended in an amount exceeding that used in ordinary rubber compositions, that is, 0.4 parts by weight, it will not only be unfavorable for physical properties such as crack growth and elongation at break, but also will result in poor adhesion to iron. The metacresol resin used in the present invention is obtained by reacting metacresol with formalin or paraformaldehyde under an acid catalyst, and the metacresol unit has 3 to 6 nuclei, such as Sumikanol 610 manufactured by Sumitomo Chemical Co., Ltd. The metacresol resin is blended in an amount of 1 to 10 parts by weight, preferably 3 to 7 parts by weight, per 100 parts by weight of rubber. If the amount of metacresol resin blended is less than 1 part by weight or more than 10 parts by weight, the blending effect will be small. The carbon black used in the present invention is of a reinforcing roasted structure type, and has an iodine adsorption capacity of 70 to 90 mg/g, a DBP oil absorption capacity of 50 to 80 ml/100 g, and is S-315 and N-326 in ASTM designation. ,
This is N-327 carbon black, and carbon blacks in this range have a low modulus compared to hardness, and therefore have a high elongation at break. The amount of carbon black to be blended is 55 to 90 parts by weight, preferably 60 to 70 parts by weight, per 100 parts by weight of rubber. If the amount of carbon black is less than 55 parts by weight, the hardness will be insufficient, and if it is more than 90 parts by weight, processing will be difficult, which is not preferable. In the rubber composition of the present invention, in addition to these compounding agents, compounding agents such as zinc oxide and anti-aging agents are blended in appropriate amounts. The present invention will be specifically described below based on Examples and Comparative Examples. All formulation values in Tables 1 and 2 are parts by weight. Examples 1 to 4 and Comparative Examples 1 to 5 Rubber compositions were prepared by mixing the rubbers and compounding agents shown in Table 1 using a conventional Banbury mixer. This rubber composition was vulcanized at 160°C and the vulcanization rate was measured. The vulcanization rate was evaluated based on the time required to reach 95% of the maximum torque (T ₉₅ ) using a rheometer curve. In addition, the rubber composition was made into a sheet and heated at 160℃ for 15 minutes.
A vulcanized sheet was prepared by vulcanization, and JIS No. 3 dumbbells were punched out, and the hardness (JUS A) was measured and a tensile test was performed. The elongation at break, tensile strength, and 300% modulus of the tensile test were measured according to Section 3 of JIS-K-6301. Also in gear oven
Values after aging at 100°C for 24 hours were also measured. A flexural fatigue test was conducted using the same vulcanized sheet as used in the tensile test. The bending fatigue test is a crack growth test according to JIS-K-6301 Section 15 (bending test).
The test was repeated 100,000 times at a strain of 20 mm, and the growth length during bending was measured at room temperature and 80°C. In addition, the adhesion strength with the steel cord is determined by applying a 1 x 5 (0.25) or 3 + 9 + 15 (0.175) x 1 ^W brass-plated steel cord to a vulcanized rubber sheet obtained by vulcanizing the above rubber composition at 106°C for 20 minutes. A pull-out test was conducted in accordance with ASTM D-2229 using iron wire with a diameter of 0.94 mm, and the pull-out force and rubber coverage (%) (appearance)
It was shown in The results are shown in Table 1.

[Table] *1: Iodine adsorption amount 80mg/g, DBP oil absorption amount 100
ml/100g, *2: Iodine adsorption amount 82mg/g, DBP
Oil absorption 71ml/100g, *3: N'1.3 dimethylbutyl N-N' phenyl p-phenylenediamine (Santoflex 13), *4: Sumikanol 610 (manufactured by Sumitomo Chemical Co., Ltd.), *5: Cobalt content 10 weight %, *
6: Insoluble sulfur (80% by weight of sulfur, 20% by weight of oil), *7: NN dicyclohexyl benzothiazol sulfenamide In Table 1, Examples 1 to 3 and Comparative Example 1
-2 is a formulation in which NR is used as a rubber component and the vulcanization accelerator is varied, but as the amount of vulcanization accelerator is increased, the vulcanization rate (T ₉₅ ) becomes shorter and the hardness increases, but the tensile Both strength and elongation at break decrease, and the physical properties after aging also become disadvantageous. In addition, crack growth increases both at room temperature and at 80°C, which is disadvantageous. In addition, there is no significant difference in adhesion with steel cords with respect to adhesion with brass plating wire, but adhesion with iron wires sharply decreases as the amount of vulcanization accelerator increases. Comparative Example 3 has a formulation with reduced sulfur content, but the hardness and adhesion to the steel cord are insufficient. In Example 4 and Comparative Example 4, the effect of blending metacresol resin was evaluated. In Example 4, in which metacresol resin was blended, hardness and It can be seen that the elongation at break increases and the adhesion to iron also improves. Comparative Example 5 is a formulation using HAF type carbon black, but the elongation at break, especially after aging, is low. Examples 5 to 12 and Comparative Examples 6 to 7 Rubber compositions were prepared in the same manner as in Example 1 with the formulations shown in Table 2, vulcanized in the same manner as in Example 1, and various properties were measured. . The results are shown in Table 2.

【table】

[Table] In Table 2, Examples 5 to 7 and Comparative Example 6
~7 are IR and IR/NR blend systems. Among these, Examples 5 to 7 contain a large amount of metacresol resin, while Comparative Examples 6 to 7 do not contain metacresol resin. A comparison of the two shows that the addition of meta-cresol resin increases elongation at break, increases hardness, and improves adhesive strength to iron.
This effect is particularly noticeable when IR is used as the rubber. In Example 8, NR was used as the rubber, and in Example 9, part of the rubber was replaced with BR.
Compared to Example 5, which was a single blend, the adhesion to iron in Example 8 was slightly lower, and the physical properties at break in Example 9 were slightly lower, but within a satisfactory range. In Example 10, cobalt stearate was added in place of the cobalt naphthenate in Example 5, and although the adhesion to iron was slightly lower than in Example 5, it was within a satisfactory range. Example 11 uses a different vulcanization accelerator from Example 5, but exhibits similar properties. In addition, although Example 12 is a system in which the vulcanization accelerator was removed, it has satisfactory physical properties and adhesive properties.
It has particularly good adhesion to iron. As explained above, the rubber composition of the present invention which has natural rubber and/or polyisoprene rubber as the main rubber and which has the above-mentioned various compounding agents in specific proportions has various required properties. In particular, it is used as steel cord coated rubber and belt edge tape because of its excellent belt separation resistance.

Claims (1)

[Scope of Claims] 1. For 100 parts by weight of rubber containing 90 parts by weight or more of natural rubber and/or polyisoprene rubber, (1) cobalt naphthenate, cobalt rosin, or linear or branched carbon atoms having 5 to 20 carbon atoms; (2) 5 to 10 parts by weight of sulfur, (3) 0.3 parts by weight or less of a sulfenamide vulcanization accelerator, (4) Metacresol resin 1 to 10 parts by weight, and (5) Iodine adsorption amount 70 to 90 mg/g, DBP oil absorption amount 50
A rubber composition with excellent adhesion to iron, characterized by containing 55 to 90 parts by weight of ~80ml/100g of carbon black.