JPS63258940A - Rubber composition - Google Patents

Abstract

PURPOSE:To provide a rubber composition of high hardness, outstanding in physical properties in terms of rupture, particularly suitable as a steel cord covering rubber, comprising a feedstock rubber consisting mainly of synthetic polyisoprene rubber, cobalt salt of rosin, carbon black and sulfur. CONSTITUTION:The objective composition can be obtained by incorporating (A) 100pts.wt. of a feedstock rubber containing >=80wt.% of synthetic isoprene rubber with (B) 0.02-0.8 (pref. 0.05-0.4)pt.wt. (on a basis of cobalt element content) of a cobalt salt of rosin containing 1-10wt.% of cobalt with a softening point of 60-110 deg.C (C) 60-100pts.wt. of carbon black with an iodine absorption of 70-130mg/g and dibutyl phthalate oil absorption of 50-80ml/100g, and (D) 4.5-10pts.wt. of sulfur, and furthermore, if needed, (E) zinc oxide, process oil, curing accelerator, etc. the process is as follows: a master batch prepared by blending the component A with ingredients other than the component D and curing accelerator is incorporated with the component D and said curing accelerator using an open roll.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rubber composition, and more specifically, it has high hardness and high breaking properties, and also exhibits high adhesive strength when used as a steel cord coated rubber. The present invention also relates to a rubber composition that has good processability when unvulcanized.

[Prior Art] In recent years, the requirements and quality of automobile tires in terms of safety, high-speed running performance, durability, etc. have become increasingly high. 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 various 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.

Furthermore, the steel cord covering rubber needs to be hard and maintain high adhesion to 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, unless this force is high, not only will the belt edge separation resistance of steel tires be insufficient, but also high adhesion will be required for tires such as truck and bus tires whose treads are refurbished after their treads have worn out. If they do not retain their strength, rehabilitation will be difficult.

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. When it becomes sulfur, there is a problem in that the adhesion between the rubber and the steel cord decreases.

[Problems to be Solved by the Invention] The present invention has been made to solve these drawbacks of the prior art. The purpose of the present invention is to provide a rubber composition that exhibits high adhesive strength even when overvulcanized and has good processability when unvulcanized, and is particularly useful for coating rubber on steel cords 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 cords 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 relative to the vulcanization time, and the hardness and modulus will not be sufficient. If the vulcanization time is prolonged until the strength increases, the tensile strength and elongation at break will decrease significantly. On the other hand, systems containing organic acid cobalt accelerate vulcanization and increase hardness and modulus in a short period of vulcanization, so it is possible to increase hardness 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, the addition of the cobalt salt of rosin causes the rubber composition to have 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 a combination system containing a 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, among which carbon black with iodine adsorption of 70 to 1301115 F/g, dibutyl phthalate) ( DBP) Loin structure with oil absorption of 50-80rdl 100g (Low 5structure)
carbon black, such as carbon black I 5A
F-LS and carbon black HAF-LS have the highest adhesion to the steel cord, and also have high elongation at break. In addition, normally when a large amount of carbon black is blended, the viscosity when uncured increases and processability becomes disadvantageous, but carbon black in the above range shows less increase in viscosity when blended in a large amount than other carbon blacks. Therefore, processability is advantageous (
The iodine adsorption amount was measured according to JISK8221, and the DBP oil absorption amount was measured according to JISK5021).

As described above, a rubber composition containing a large amount of carbon black and sulfur in a specific range and containing cobalt salt of rosin has high hardness and high breaking physical properties, and has excellent adhesion to steel cord and is unvulcanized. 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, in the present invention, the cobalt salt of rosin has a cobalt element content of 0.02 to 0 with respect to 100 parts by weight of raw rubber containing 80% by weight or more of synthetic polyisoprene rubber.
．． 8 parts by weight and an iodine adsorption amount of 70 to 130 rItg/g
and dibutyl phthalate oil absorption 50-80m/100
This is a rubber composition characterized by containing 60 to 100 parts by weight of carbon black (g) and 4.5 to 10 parts by weight of sulfur. It provides high adhesive strength from to over-vulcanization, so it is suitable for materials such as tires where the degree of vulcanization varies depending on location.

The raw material rubber used in the present invention is polyisoprene rubber (IR
), which accounts for 20% by weight of the raw material rubber.
The following are natural rubber (NR), styrene butadiene rubber (
It is also possible to replace it with a diene polymer such as SBR) or polybutadiene rubber (BR). If polyisoprene rubber is less than 80% by weight in the raw rubber, the adhesive force with the steel cord (hereinafter simply referred to as adhesive force) 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 of this rosin has a cobalt content of 1 to 10
% is effective, and the softening point is 60-110°C. Rosin here refers to a natural resin collectively known as wood rosin, gum rosin, tall rosin, etc., and contains the resin acid abietic acid (Abetic Ac1d) as the main component (about 50%) and dihydroabietic acid (D).
It is a mixture containing acids such as hydroabletlc Ac1d), neoabietic acid (Neoabletlc Ac1d), isopimaric acid (Isopimaric Ac1d), and palustrlc acid (PalustrlcAcld), and has a softening point of 60 to 100°C and an acid value of 120.
~200. The cobalt salt of rosin has a cobalt element content of 0.02 to 100 parts by weight of raw rubber.
It is contained in an amount of 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, and if it exceeds 0.8 parts by weight, the adhesive strength, especially the adhesive strength during overvulcanization, will decrease.

The carbon black used in the present invention is carbon black HAF-LS, 15AF-LS type, and has an iodine adsorption amount of 70 to 130ffi5F/g, D B
P oil absorption is in the range of 50 to 80Id/100g, A
S-315, N-328, N-327, N in STM display
-219 carbon black. The content of carbon black is 60 to 100 parts by weight per 100 parts by weight of raw rubber.
Parts by weight. If the carbon black content is less than 60 parts by weight, a high hardness rubber cannot be obtained, and if it exceeds 100 parts by weight, processing problems are large and it is not practical.

In addition, the amount of sulfur is 4.5 to 1 per 100 parts by weight of raw rubber.
If the amount of sulfur is less than 4.5 parts by weight, high hardness rubber will be difficult to obtain, and if the amount exceeds 10 parts by weight, processing problems such as sulfur bloom in unvulcanized rubber may occur, making it difficult to put into practical use. Not on point.

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 IB Sulfur and A rubber composition was prepared by adding the vulcanization accelerator with an oven roll. Note that the cobalt salt of rosin, that is, rosin cobalt, was created by a double decomposition method. In other words, in the formulations of cobalt naphthenate, cobalt stearate, and cobalt rosin in the table, the content in parentheses indicates the cobalt element content.

Mooney viscosity (ML,
, 4) was measured in accordance with JIS K6800 after one molecule was heated at 100° C., and the viscosity was evaluated after 4 minutes. Also,
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 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, 10
0% and 300% modulus were measured in accordance with JIS K8301.

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 2.

Groups 1 to 2 are IR rubber compositions containing 65 parts by weight of carbon black and a large amount of sulfur.

(1) The l group is an IR rubber composition containing different types of carbon black or cobalt salts of organic acids. In this system, a comparative example containing rosin cobalt (cobalt element content 5% by weight) is used. 3 and Example 1
The scorch time 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, in Comparative Example 3 using HAF as carbon black, H
Compared to Example 1 using AF-LS, the coach time was shorter and the elongation at break and adhesive strength were inferior. From this, IR
It can be seen that among rubber compositions using rosin cobalt and carbon black HAF-LS in combination, the rubber composition has a long scorch time and is excellent in physical properties at break and adhesive strength, especially adhesive strength during overvulcanization.

(2) Group (2) is an IR rubber composition in which the type of carbon black was further changed, and the type and amount of cobalt salt of an organic acid were also changed. Comparative Examples 4 and 5 are systems in which carbon black ISAF and cobalt naphthenate or cobalt rosin are blended, but all have short scorch times and low elongations at break as compared to IR systems. Moreover, the adhesive strength during overvulcanization and overvulcanization is also inferior to those of Examples 2 to 4 described below. Example 2 is carbon black I 5AF-
Although it is a combination of LS and rosin cobalt, it has a long scorch time and has excellent breaking properties and adhesive strength. Comparative Example 6 is a combination of carbon black HAF-H3 and rosin, but the elongation at break is extremely poor and the adhesive strength is also quite poor.

Examples 3 and 4 used carbon black HAF-LS and rosin cobalt (cobalt element content ff11G weight %) different from the rosin cobalt used in Examples 1 and 2, but in this case, Almost the same favorable results as in Example 2 can also be obtained. Comparative example 7 is carbon black H
Although this is a system using AF-LS and cobalt stearate, it is inferior to Examples 2 to 4 in tensile strength, elongation at break, and adhesive strength.

This shows that the IR rubber composition using carbon black HAF-LS and rosin cobalt can lengthen the scorch time and provide favorable breaking properties and adhesive strength. .

■～■ Group is I containing a large amount of carbon black.
These are an R-based rubber composition, an NR-based rubber composition (Comparative Example 10), or a blend-based rubber composition of NR and IH (Comparative Example 11).

Comparative Examples 8 to 9 in the (3) ■ group are IR rubber compositions containing a large amount of carbon black HAF or HAF-LS and further containing cobalt naphthenate. Although the modulus increases, the scorch time is short and the elongation at break and adhesive strength are significantly inferior.

(4)■ Group contains a large amount of carbon black HAF-LS, and also contains rosin cobalt (cobalt content 5
%), or a blend of these rubber compositions.

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, but the hardness and modulus decreased somewhat as the amount of carbon black was reduced.
The scorch time is longer, the tensile strength and elongation at break are also increased, and the adhesion strength is 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. Comparative Example 10 using NR as a raw material rubber had a shorter scorch time, lower tensile strength and elongation at break, and lower rubber coverage during overvulcanization than Example 5 using IR as a raw material rubber. Inferior. On the other hand, Comparative Example 11 using a blend of NR and IR as the raw material rubber is similar to Example 5.
The tensile strength and elongation at break are lower than that of 200%, and the rubber coverage during overvulcanization and overvulcanization is also inferior.

(5) Group (2) is an IR rubber composition containing a large amount of rosin cobalt (cobalt element content: 5% by weight) and different types of carbon black. carbon black I
Comparative Example 12 containing SAF had a short scorch time;
Poor adhesive strength during overvulcanization.

In addition, Comparative Example 13 and Comparative Example 1 in which carbon black HAF-HS and carbon black HAF were blended, respectively.
In No. 4, the tensile strength and elongation at break were extremely low, and the adhesive strength was also poor. On the other hand, carbon black I 5AF-L
Example 9 in which S was blended had a long scorch time, and favorable breaking properties and adhesive strength were obtained. This shows that in an IR rubber composition containing a large amount of rosin cobalt and carbon black, favorable results can be obtained only when the carbon black of the loin structure is used.

(e) Vl group is carbon black HAF-LS
This is an IR rubber composition containing a large amount of rosin cobalt, with different types and amounts of rosin cobalt. Examples 10 to 12 were blended with varying amounts of rosin cobalt with a cobalt element content of 10% by weight, and Examples 13 to 14 were blended with varying amounts of rosin cobalt with a cobalt element content of 3% by weight. However, both have a long scorch time and provide favorable breaking properties and adhesive strength.

(7)■Group is IR and polybutadiene rubber (BR)
A large amount of carbon black HA is added to the rubber composition used in combination with
F-LS and rosin cobalt (cobalt content 5% by weight)
It is a combination of. In Example 15, BR was added to the raw rubber.
This is a rubber composition containing 200% of the rubber composition by weight, 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, that is, Comparative Example 16, includes Examples 3-
Although this is a rubber composition in which the amount of rosin cobalt in the rubber composition No. 4 is further increased, the adhesive strength is inferior. From this, it is preferable that the amount of rosin cobalt added is 0.8 mff1 part or less as the cobalt element content per 100 parts by weight of raw rubber.

[Effects of the Invention] As explained above, the iodine adsorption amount is 70 to 130 mg/g in a system mainly composed of synthetic polyisoprene rubber.

The rubber composition of the present invention contains a large amount of carbon black and sulfur having a DBP oil absorption of 150 to 80 td/100 g, and further contains a specific amount of rosin cobalt salt. Moreover, when used as steel cord coating rubber, overvulcanization,
It exhibits high adhesion when overvulcanized 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, the cobalt salt of rosin has a cobalt element content of 0.02 to 0.8 parts by weight and an iodine adsorption amount of 70 to 130 mg/ A rubber composition comprising 60 to 100 parts by weight of carbon black having a dibutyl phthalate oil absorption of 50 to 80 ml/100 g, and 4.5 to 10 parts by weight of sulfur.