JPH0238607B2 - TAIYANOBERUTOSOHOKYOYOSUCHIIRUKOODONOHIFUKUGOMUSOSEIBUTSU - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a rubber composition, and more specifically, the present invention relates to a rubber composition that has high hardness and high breaking properties, and also exhibits high adhesive strength when used as a steel cord coating rubber for reinforcing the belt layer of a tire. The present invention relates to a rubber composition that also has good processability when unvulcanized. [Prior Art] In recent years, the quality requirements for automobile tires such as safety, high-speed running performance, and durability have become higher and higher. In order to meet such high demands, steel tires with steel cords in the reinforcing layer have rapidly become popular. In general, automobile tires must have a variety of functions, so they are usually made by combining rubbers with different properties. Therefore, the properties of the rubber used in each part of a tire vary widely, with soft rubber used in some parts and hard rubber used in other parts. Rubber that is harder than other parts is often used for the steel cord covering rubber of steel tires and the edge tape and bead filler of steel breakers. Generally, such hard rubbers have low physical properties at break such as tensile strength and elongation at break. In addition, steel cord coated rubber is hard rubber,
It is also necessary to maintain high adhesive strength with the steel cord. The adhesion force referred to here is, for example, the pull-out force when pulling out a steel cord embedded in rubber. The physical properties of the rubber coating must also be strong. In addition, if such force is not high, not only will the belt edge separation resistance of steel tires be insufficient, but also the belt edge separation will be high in tires such as truck and bus tires, which have their treads refurbished after they have worn out. Rehabilitation will be difficult if adhesive strength is not maintained. Conventionally, cobalt salts of organic acids such as cobalt naphthenate and cobalt stearate have been used in steel cord coating rubber to increase the adhesive strength between the rubber and the steel cord. There was a problem that when it became sulfur, the adhesive strength between the rubber and steel cord decreased. [Problems to be Solved by the Invention] The present invention has been made to solve these drawbacks of the prior art.
The purpose of this invention is to provide a rubber composition that exhibits high adhesive strength from proper vulcanization to overvulcanization, and has good processability when unvulcanized, and is particularly used as a steel cord coating rubber for steel tires. [Means for Solving the Problems] The present inventors have researched a method for obtaining high breaking properties and good adhesion to steel cord after vulcanization in a high hardness rubber composition containing large amounts of carbon black and sulfur. As a result, we discovered the following interesting facts regarding raw rubber, compounding agents, their types, and properties. (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. Organic acid cobalt generally has the above-mentioned effect, but natural resin rosin in particular has the effect of increasing the elongation at break, so this cobalt salt still has the characteristic of high elongation at break, and moreover, rosin It also has the characteristic that it lengthens the scorch time. Therefore, by adding the cobalt salt of rosin, the above composition has a longer unvulcanized scorch, a faster vulcanization rate, and a higher elongation at break. Furthermore, among the various organic acid cobalt salts, rosin cobalt salt has the highest adhesive strength. (2) Effect of carbon black in combination system with large amount of sulfur/organic acid cobalt. In order to obtain high hardness rubber in a system containing a large amount of sulfur, it is necessary to use reinforcing carbon black such as carbon black ISAF or HAF, but among these, carbon black with iodine adsorption of 70 to 130 mg/g and dibutyl phthalate (DBP) oil absorption are required. Low Structure carbon black with a volume of 50-80ml/100g, such as carbon black ISAF-LS,
Carbon black HAF-LS has the highest adhesion to steel cord, and also has the highest elongation at break. Additionally, if a large amount of carbon black is added, the viscosity of the unvulcanized product will increase and processability will be disadvantageous.
Carbon black in the above range has an advantage in processability because the increase in viscosity when blended in large amounts is smaller than other carbon blacks (Iodine adsorption amount is JIS K
6221, and DBP oil absorption is JIS K 5021.
). As described above, the rubber composition containing a large amount of carbon black and sulfur in a specific range and containing rosin cobalt salt has high hardness, high breaking properties, and is an unvulcanized rubber composition with excellent adhesion to steel cord. However, such effects are limited to compositions whose main rubber is polyisoprene rubber as the raw material rubber. The present inventors obtained this knowledge and arrived at the present invention. That is, the present invention uses synthetic polyisoprene rubber.
For 100 parts by weight of raw rubber containing 80% by weight or more,
Cobalt salt in rosin as cobalt element content
0.02-0.8 parts by weight and iodine adsorption amount 70-130mg/g
And dibutyl phthalate oil absorption 50-80ml/100g
A coating rubber composition for a steel cord for reinforcing a belt layer of a tire, characterized in that it contains 60 to 100 parts by weight of carbon black and 4.5 to 10 parts by weight of sulfur. Since the composition provides high adhesive strength from normal vulcanization to overvulcanization, it is suitable for products such as tires where the degree of vulcanization varies depending on location. The raw material rubber used in the present invention is mainly polyisoprene rubber (IR), and 20% by weight or less of the raw material rubber is natural rubber (NR), styrene-butadiene rubber (SBR), polybutadiene rubber (BR), etc. It is also possible to replace it with a diene polymer. Polyisoprene rubber is the raw material rubber
If it is less than 80% by weight, the adhesive strength with the steel cord (hereinafter simply referred to as adhesive strength) will be poor, and the vulcanized physical properties such as tensile strength and elongation at break will decrease. The cobalt salt of rosin contained in the rubber composition of the present invention is a cobalt salt of the carboxylic acid of rosin, and after converting the rosin into a sodium salt with, for example, sodium hydroxide, it undergoes metathesis through a desalination reaction with cobalt chloride. Obtained by reaction.
The cobalt salt in this rosin has a cobalt content of 1
~10% is effective and the softening point is 60~110℃
It is. Also, the term rosin here refers to natural resins collectively known as udrosin, gum rosin, tall rosin, etc., and the resin acid abietic acid (Abetic acid).
A mixture containing Acid as the main component (approximately 50%) and other acids such as Dehydroabietic Acid, Neoabietic Acid, Isopimaric Acid, and Palustric Acid. can be,
It has a softening point of 60-100°C and an acid value of 120-200.
Cobalt salt in rosin is added to 100 parts by weight of raw rubber.
The cobalt element content is 0.02 to 0.8 parts by weight, preferably 0.05 to 0.4 parts by weight. If the cobalt element content is less than 0.02 parts by weight, the effect will be small;
If it exceeds 0.8 parts by weight, the adhesive strength, especially the adhesive strength during overvulcanization, decreases. The carbon black used in the present invention is of the carbon black HAF-LS, ISAF-LS type, with an iodine adsorption amount of 70 to 130 mg/g and a DBP oil absorption amount of 50.
~80ml/100g, S- according to ASTM
315, N-326, N-327, N-219 carbon black. The content of carbon black is 60 to 100 parts by weight per 100 parts by weight of raw rubber. If the carbon black content is less than 60 parts by weight, high hardness rubber cannot be obtained, and if it exceeds 100 parts by weight, processing problems will occur and it is not practical. In addition, the amount of sulfur is 4.5 to 10 per 100 parts by weight of raw rubber.
If the amount of sulfur is less than 4.5 parts by weight, it will be difficult to obtain a high hardness rubber, and if the amount exceeds 10 parts by weight, processing problems such as sulfur bloom in unvulcanized rubber will occur, making it impractical. In the present invention, in addition to these compounding agents, compounding agents commonly used in the rubber industry, such as zinc oxide, process oil, vulcanization accelerator, etc., are added in appropriate amounts. [Examples] 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 15 and Comparative Examples 1 to 16 Sulfur and vulcanization were added to a masterbatch obtained by mixing raw rubber, sulfur, and compounding ingredients other than the vulcanization accelerator in an ordinary Banbury type mixer according to the formulation shown in Table 1. A rubber composition was prepared by adding the sulfur accelerator in an open roll. Note that the cobalt salt of rosin, that is, rosin cobalt, was created by a double decomposition method. In addition, in the formulations of cobalt naphthenate, cobalt stearate, and cobalt rosin in the table, the content inside the box indicates the cobalt element content. The Mooney viscosity (ML ₁₊₄ ) of this rubber composition (unvulcanized rubber) is 1 at 100°C in accordance with JIS K 6300.
Measurement was started after 4 minutes of preheating, and the viscosity was evaluated after 4 minutes. Further, the scorch time was evaluated as the time required for the torque to increase by 5 points from the minimum torque of Mooney viscosity at 125°C. The physical properties of vulcanized rubber are determined by forming the rubber composition into a sheet,
Create a vulcanized sheet by vulcanizing at 150℃ for 30 minutes, and JIS
A No. 3 dumbbell was punched out, and its hardness (JIS A) was measured and a tensile test was conducted. Tensile strength of tensile test,
Elongation at break, 100% and 300% modulus are JIS K
Measured in accordance with 6301. In addition, 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 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 2.

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[Table] - Group is an IR rubber composition containing 65 parts by weight of carbon black and a large amount of sulfur. (1) Group consists of IR rubber compositions containing different types of carbon black or cobalt salts of organic acids. The scorch time of Example 1 was longer than that of Comparative Examples 1 and 2 in which cobalt naphthenate was blended. Furthermore, a comparison between Comparative Example 1 and Comparative Example 3 or Comparative Example 2 and Example 1 using the same carbon black shows that the elongation at break and the adhesive strength are improved. However, as carbon black
Comparative Example 3 using HAF had a shorter scorch time than Example 1 using HAF-LS, and was inferior in elongation at break and adhesive strength. From this, it can be seen that among IR-based rubber compositions, rubber compositions that use a combination of rosin cobalt and carbon black HAF-LS have a long scorch time and have excellent physical properties at break and adhesive strength, especially adhesive strength during overvulcanization. I understand. Group (2) is an IR rubber composition with a different type of carbon black and a different type and amount of cobalt salt of an organic acid.
Comparative Examples 4 and 5 are systems in which carbon black ISAF is blended with cobalt naphthenate or cobalt rosin, but both have short scorch times and low elongation at break as compared to IR systems. Furthermore, the adhesive strength during proper vulcanization and overvulcanization is also inferior to those of Examples 2 to 4 described below. Example 2, which is a combination of carbon black ISAF-LS and rosin cobalt, has a long scorch time and has excellent properties at break and adhesive strength. Comparative Example 6 is a combination of carbon black HAF-HS and rosin, but the elongation at break is extremely poor and the adhesive strength is also quite poor. Examples 3 and 4 are carbon black HAF-LS and rosin cobalt different from the rosin cobalt used in Examples 1 and 2 (cobalt element content 10% by weight).
However, in this case as well, almost the same favorable results as in Example 2 can be obtained. Comparative Example 7 is a system using carbon black HAF-LS and cobalt stearate, but it is inferior to Examples 2 to 4 in tensile strength, elongation at break, and adhesive strength. Therefore, IR using carbon black HAF-LS or ISAF-LS and rosin cobalt
It can be seen that the rubber composition increases the scorch time and provides favorable breaking properties and adhesive strength. The ~ group includes an IR rubber composition containing a large amount of carbon black, an NR rubber composition (Comparative Example 10), or a blend rubber composition of NR and IR (Comparative Example 11). (3) Comparative Examples 8 to 9, which are a group, contain a large amount of carbon black HAF or HAF-LS,
Furthermore, although the IR rubber composition contains cobalt naphthenate, the hardness and modulus increase by incorporating a large amount of carbon black, but the scorch time is short and the elongation at break and adhesive strength are significantly inferior. Group (4) is a rubber composition that contains a large amount of carbon black HAF-LS and further contains rosin cobalt (cobalt content 5%), such as IR type or NR type, or a blend of these. Example 5 has a longer scorch time and higher tensile strength and elongation at break than Comparative Examples 8 and 9 in which cobalt naphthenate was blended. Moreover, adhesive strength is also improved. In Examples 6 and 7, the amount of carbon black HAF-LS was reduced compared to Example 5. Although the hardness and modulus decreased somewhat due to the reduced amount of carbon black, the scorch time became longer and the tensile strength increased. Strength and elongation at break are also increased, and adhesion remains at the same level. In Example 8, the amount of rosin cobalt was reduced compared to Example 5, but the tensile strength and elongation at break were slightly lower, and the adhesive strength during overvulcanization was also slightly lower. In addition, Comparative Example 10 using NR as a raw material rubber is Example 5 using IR as a raw material rubber
The scorch time is shorter, the tensile strength and elongation at break are lower, and the rubber coverage during overvulcanization is also inferior. On the other hand, Comparative Example 11, which used a blend of NR and IR as the raw rubber, had lower tensile strength and elongation at break than Example 5, and was also inferior in rubber coverage during proper vulcanization and overvulcanization. Group (5) is an IR rubber composition containing a large amount of rosin cobalt (cobalt element content: 5% by weight) and different types of carbon black.
Comparative Example 12, which contained carbon black ISAF, had a short scorch time and poor adhesive strength during overvulcanization. Also, comparative examples containing Carbon Black HAF-HS and Carbon Black HAF.
In No. 13 and Comparative Example 14, the tensile strength and elongation at break were extremely low, and the adhesive strength was also poor. On the other hand, Example 9, in which carbon black ISAF-LS was blended, had a long scorch time and had favorable breaking properties and adhesive strength. From this, it can be seen that in an IR rubber composition containing a large amount of rosin cobalt and carbon black, favorable results can be obtained only with a blend using roasted structuring carbon black. Group (6) is an IR rubber composition containing a large amount of Carbon Black HAF-LS with different types and amounts of rosin cobalt. Example
In Examples 10 to 12, rosin cobalt with a cobalt element content of 10% by weight was blended in varying amounts, and in Examples 13 to 14, rosin cobalt with a cobalt element content of 3% by weight was blended in varying amounts. ,
Both have a long scorch time and provide favorable breaking properties and adhesive strength. Group (7) is a rubber composition that combines IR and polybutadiene rubber (BR) with a large amount of carbon black HAF-LS and rosin cobalt (cobalt content 5% by weight). Example 15 is a rubber composition containing 20% by weight of BR in the raw rubber, but the scorch time is long and the physical properties at break are also favorable. In terms of adhesive strength, although the pull-out force is slightly inferior, the rubber coverage is high and is at a desirable level overall. Comparative Example 15 is a rubber composition containing 30% by weight of BR in the raw rubber, but is inferior to Example 15 in physical properties at break and adhesive strength.
From this, in order to obtain the desired effect, it is necessary that the raw rubber contains 80% by weight or more of IR. (8) Group, Comparative Example 16, is Example 3
This is a rubber composition in which the amount of rosin cobalt in the rubber compositions 1 to 4 is further increased, but the adhesive strength is inferior.
From this, the amount of rosin cobalt added is preferably 0.8 parts by weight or less as the cobalt element content per 100 parts by weight of raw rubber. [Effects of the invention] As explained above, in a system mainly composed of synthetic polyisoprene rubber, the iodine adsorption amount is 70 to 130 mg/g,
The rubber composition of the present invention contains a large amount of carbon black and sulfur having a DBP oil absorption of 50 to 80 ml/100 g, and further contains a specific amount of rosin cobalt salt. Moreover, when used as a steel cord coating rubber for reinforcing the belt layer of a tire, it exhibits high adhesion in both properly vulcanized and overvulcanized cases, and is also advantageous against scorch when unvulcanized.

Claims (1)

[Claims] 1. For 100 parts by weight of raw material rubber containing 80% by weight or more of synthetic polyisoprene rubber, 0.02 to 0.8 parts by weight of rosin cobalt salt as cobalt element content, 70 to 130 mg/g of iodine adsorption, and oil absorption of dibutyl phthalate. 60 to 100 parts by weight of carbon black in an amount of 50 to 80 ml/100 g, and 4.5 to 10 parts of sulfur.
A rubber composition for coating a steel cord for reinforcing a belt layer of a tire, comprising parts by weight of a steel cord for reinforcing a belt layer of a tire.