JPS6127703A - Radial tire improved in its durability on bad load - Google Patents

Abstract

PURPOSE:To increase carbon reinforcement effect as well as make a cross bridge form effective and thereby improve durability of a tire on a bad road by compounding specific carbon black while properly compounding a vulcanizer and a vulcanizing accelerator. CONSTITUTION:Blend rubber comprising 50-90wt.pts. of natural rubber and 50- 10wt.pts. of polyisoprene rubber is employed as a base for a tread rubber composition. 40-60wt.pts. of carbon black of a specific physical property is compounded for 100wt.pts. of such blend rubber. Here, the carbon black of the specific physical property is highly reinforcing carbon black having: a nitrided surface area of 115-150m<2>/g, the amount of absorption of dibutylphthalate of 105- 150m<2>/g, and the degree of coloration more than 110%. In addition, 1.0-1.5wt. pts. of sulfer are compounded for 100wt.pts. of the blend rubber, while 2.2wt.pts. or more of the total compounding amount of a vulcanizing accelerator and the sulfur are employed for 100wt.pts. of the blend rubber.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to a radial tire with improved rough road durability.
In more detail, the characteristics required of dump trucks, which mainly operate on unpaved roads and rough roads, are pneumatic tires for trucks and buses with treads that have improved overall rough road durability such as wear, cut chipping, and heat generation. Regarding large steel radial tires.

[Prior art]

Among large radial tires, the quality requirements for dump trucks, which are subjected to the most severe usage conditions, are not limited to wear resistance and tread separation resistance (heat generation properties).
This is overall rough road durability including cut chipping resistance.

In other words, the tire characteristics that are of great interest to dump truck users are:
The objective is to withstand a certain degree of overload and high speed, and to complete its lifespan with as little damage to the tread surface as possible, regardless of whether it is on paved roads, unpaved roads, or rough roads.

However, it is difficult to achieve both wear resistance, which is a characteristic required for paved roads, and cut chipping resistance, which is a characteristic required by rough roads or non-paved roads. It was difficult for the keyboard to satisfy the complex and diversifying market demands.

As one of the solutions to this problem,
As shown in Japanese Patent Publication No. 42482, there is a study to optimize carbon black properties, that is, carbon reinforcement mechanism, and on the other hand, as shown in Japanese Patent Publication No. 54-4383, zinc white/stearic acid , and vulcanization accelerator/
There is a response from sulfur suitability, that is, from the crosslinked form.

However, in recent years, as the use of radial tires for large tires has increased, the scope of use of radial tires for trucks and buses is also expanding, and not only durability on rough roads but also high speed, fuel efficiency, etc. As performance is required, it is no longer possible to meet this situation simply by optimizing and optimizing carbon reinforcement and crosslinking forms.

Furthermore, as in Japanese Patent Application No. 58-235182, a method has been proposed in which a rubber composition having a specific function is placed in a two-layer or three-layer tread structure. There is a strong desire to pursue the ultimate performance by

By the way, in terms of rough road durability, cut and chipping resistance is particularly important for large RAJ and AL tires.

The present inventors elucidated the cut chipping phenomenon as follows from a large number of actual vehicle driving tests.

In other words, the cut chipping phenomenon occurs intensively when tires run on unpaved roads littered with quarry stones and gravel, and is repeatedly subjected to braking and cornering at moderate speeds on such roads. This phenomenon occurs when the surface of the tread rubber is removed.

Looking at this phenomenon from the perspective of physical properties of tread rubber,
This can be correlated with the physical property change phenomenon in which the network chain density determined from the degree of rubber swelling increases abnormally due to heat and stress fatigue caused by tire running, and the elongation at break decreases.

Moreover, such physical property changes are quite similar when running under the same conditions, so in order to complete the life under any running conditions, it is necessary to maintain the rubber elasticity even at the end of running. It is necessary to set the network chain density to a low value, that is, to set the rubber swelling degree to a high value to ensure elongation at break, and it is thought that this is the only way to suppress the occurrence of cut chipping.

On the other hand, when looking at the performance of large radial tires from the perspective of wear characteristics, the deformation of the entire tread becomes large unless there is a certain degree of tread rigidity. This will lead to a decrease in wear resistance, so it is necessary to ensure appropriate rigidity.

In this way, in order to establish a tread rubber composition that improves the overall rough road durability of large radial tires for heavy loads, it is necessary to have a certain level of tread stiffness as the initial tread rubber physical properties and to have as high an initial level as possible. A tread rubber composition having a degree of swelling is required, and the following methods can be considered for this purpose.

B. As a method to ensure tread rigidity and improve wear resistance, the type and amount of carbon black should be selected to provide an effective reinforcing effect.

That is, the modulus of the tread rubber is optimized and tread rigidity is ensured by optimizing the balance of the particle size and stracture of carbon black, as well as the quantitative balance of each carbon black.

B. As a method of improving the cut-depping property by setting the initial rubber swelling degree to a high level, the composition is formulated in an effective cross-linked form.

Namely, sulfur, vulcanization accelerator, which determines the network chain density of rubber,
Furthermore, we aim to optimize the amount of stearic acid, and in particular, optimize the vulcanization accelerator/sulfur ratio and their total blending amount in order to suppress the occurrence of anisotropy associated with running fatigue.

[Purpose of the invention]

The purpose of the present invention is to enhance the carbon reinforcing effect by blending a specific carbon black, and on the other hand, to improve the durability on rough roads by activating the crosslinking form by appropriately blending a vulcanizing agent and a vulcanization aid. The objective is to provide an improved radial tire.

[Structure of the invention]

The present invention, which achieves the above object, has a nitrogen specific surface area of 115 to 100 parts by weight of a blend rubber consisting of 50 to 90 parts by weight of natural rubber and 50 to 10 parts by weight of polyisoprene rubber.
150 Id/g, dibutyl phthalate absorption 10
5-130ml/100g, 40-60 parts by weight of carbon black with a tinting power of 110% or more, fatty acid 0.5-2 with an iodine value of 5% or less and a stearic acid content of 50% or more.
．． 5 parts by weight, and 1.0 to 1.5 parts by weight of sulfur, the weight ratio of the metal oxide or metal salt to the fatty acid is 2.5 or more, and the sulfur and the vulcanization accelerator. The invention is characterized by using a tread rubber composition in which the total amount of the tread rubber composition is 2.2 parts by weight or more.

In the present invention, a blended rubber consisting of 50 to 90 parts by weight of natural rubber and 50 to 10 parts by weight of polyisoprene rubber serves as the base of the tread rubber composition.

The polyisoprene rubber used here has a cis-1,4-bond content of 70% or more and an average molecular weight of 600,000 to 1,200,000.

If the cis-1,4-bond is less than 70%, rubber formation =
This is not preferable because the force becomes too high and the tread separation resistance decreases.

Furthermore, if the average molecular weight is less than 600,000, it will cause high heat generation and a decrease in breaking strength properties, while if it is less than 1,200,000, it will become hard in terms of processability such as mixing and extrusion, which is not preferable.

This is not desirable.

In the present invention, 40 to 6 parts of carbon black having specific physical properties are added to 100 parts by weight of such blended rubber.
0 parts by weight, preferably 45 to 55 parts by weight.

If the amount of carbon black is less than 40 parts by weight,
The wear resistance and cut resistance of the obtained radial tire are poor, and if it exceeds 60 parts by weight, the chipping resistance and heat generation properties are undesirable.

Carbon black having specific physical properties used in the present invention refers to nitrogen specific surface area (hereinafter abbreviated as N2S^) force (1
15 to 150 rrr/g, and the dibutyl phthalate absorption amount (hereinafter abbreviated as DBP) is 105 to 130 m
g/100g, and is a highly reinforcing carbon black with a tinting strength of 110% or more.

Carbon black plays an important role in the reinforcing effect, and although it is expected that wear resistance will be improved by increasing N25A, that is, decreasing the particle size, or increasing DBP, that is, increasing the struture, It is known to reduce cut chipping properties.

Therefore, in the above-mentioned Japanese Patent Publication No. 54-42482, a method is adopted in which the particle size is set as small as possible and the strafture is set to a low value, but the effect of improving the wear resistance of the particle size and the strafture is studied in detail. As a result, the effect of strafture appears stronger.

If the DBP is less than 105ml/100g, no matter how high the N25A is set, it will not be possible to satisfy the ultimate performance regarding wear resistance.
If it exceeds 130 mg/100 g, the chipping resistance will be significantly reduced, which is not preferable.

Also, the particle size is 115 n? /g
If the wear resistance is less than 150%/g, the wear resistance decreases.
Exceeding this will cause problems in terms of heat generation characteristics and workability.

Furthermore, if the tinting power of carbon black is less than 0%, tear resistance decreases, causing a decrease in cut chipping resistance.

However, considering the cut resistance, chipping resistance, and heat generation properties mentioned above, and with the aim of improving wear resistance backed by reinforcing effects, it is not enough to satisfy the ultimate performance of radial tires. I can't.

Therefore, in the present invention, in order to satisfy the ultimate performance, sulfur,
The amounts and ratios of vulcanizing agents such as vulcanization accelerators and vulcanizing aids such as zinc white and stearic acid were investigated.

By blending these individual ingredients in predetermined amounts, it is possible to satisfy the ultimate performance in terms of overall rough road durability such as wear resistance, cut chipping resistance, heat generation property, etc. not only on good roads but also on rough roads. It's arrived.

That is, in the present invention, 0.5 to 2.5 parts by weight of fatty acids having an iodine value of 5% or less and a stearic acid content of 50% or more are blended with respect to 100 parts by weight of the blended rubber.

Generally, as the content of fatty acids such as stearic acid is reduced, the tensile properties are significantly reduced, and the temperature dependence of tan δ becomes smaller, increasing tan δ at high temperatures, which increases the heat generation of the tread rubber itself. It is known to have a negative effect on tire durability, such as by significantly increasing the

However, on the other hand, it is possible to significantly increase the rubber swelling degree and set the initial network chain density to a low value.
Effective for chipping resistance.

That is, if the amount of fatty acid blended is less than 0.5 parts by weight, ta
n δ becomes too high, which is unfavorable in terms of heat generation characteristics. Moreover, if it exceeds 2.5 parts by weight, it is not effective for controlling the rubber swelling degree.

In addition, if the iodine value exceeds 5%, the vulcanization rate will be significantly delayed and heat generation will increase, resulting in a decrease in tread separation resistance.If the stearic acid content is less than 50%, metal salts such as zinc stearate will The blooming speed increases, causing problems in the molding process.

As the fatty acid, stearic acid, oleic acid, lauric acid, palmitic acid, etc. are used, and stearic acid is preferably used.

In the present invention, in such a range where the amount of fatty acids blended is small, it is important to set the amount of metal oxides such as zinc white or metal salts such as zinc stearate. The ratio of fatty acid/metallic salt is 2.5 or more, and dynamic fatigue properties such as heat generation properties can be improved while maintaining a high degree of rubber swelling.

In addition to zinc white, magnesium oxide is used as a metal oxide, and as a metal salt, in addition to zinc stearate,
Magnesium stearate and the like are used. 4 Furthermore, in the present invention, 1.0 to 1.5 parts by weight of sulfur is blended with respect to 100 parts by weight of the blended rubber, and the total blended amount of the vulcanization accelerator and sulfur is 10 parts by weight of the blended rubber.
The amount should be 2.2 parts by weight or more compared to 0 parts by weight.

By blending sulfur in this range, it is possible to maintain high tensile properties and maintain a low network chain density of the rubber even in the range where the amount of fatty acid blended is small as described above. It is also effective in suppressing the occurrence of anisotropy that accompanies running characteristics, and can achieve both wear resistance and cut chipping resistance, which were conventionally considered to be contradictory properties.

The method for measuring the physical properties of each component constituting the composition of the present invention will be shown below.

Nitrogen specific surface area - This is also applicable to the ASTM D 3037B method, and is measured by determining the amount of nitrogen gas required to form a monomolecular layer.

Dibutyl phthalate absorption amount--J I S x-62
In 21, the amount of dibutyl phthalate absorbed (ml) per 100 g of dry carbon was calculated, and the larger the value, the higher the strutness of the carbon.

Optical reflective needle (Welch 5cientifi'c Co., Ltd.)
, ), and shows the ratio to standard black IRB #3, which is generally influenced by the particle size and the distribution of stractures.

Iodine value: Determined by titration evaluation of N/10 sodium thiosulfate solution based on JIS K-3341.

Stearic acid content - Determined by gas chromatography.

〔Effect of the invention〕

As described above, the radial tire of the present invention has a nitrogen specific surface area of 115 to 150 n? with respect to 100 parts by weight of a blend rubber consisting of 50 to 90 parts by weight of natural rubber and 50 to 10 parts by weight of polyisoprene rubber. /g, dibutyl phthalate absorption 105-130ml /100g, coloring power 110%
40 to 60 M parts of carbon black, iodine value 5
% or less and stearic acid content 5'O% or more fatty acids 0
．． 5 to 2.5 parts by weight, and 1.0 to 1.5 parts by weight of sulfur, and the weight ratio of the metal oxide or metal salt to the fatty acid is 2.5 or more, and the sulfur and the vulcanized By using a tread rubber composition in which the total amount including the accelerator is 2.2 parts by weight or more, it is possible to obtain a radial tire with improved wear resistance, cut chipping resistance, and durability on rough roads such as heat generation. I can do it.

Such a radial tire is suitable as a radial tire for buses, trucks, and especially dump trucks.

Examples of the present invention will be described below.

〔Example〕

Examples 1 to 6 50 parts by weight of CB-3 carbon black and 10 parts by weight of white carbon were blended with 100 parts by weight of blended rubber of natural rubber and polyisoprene rubber, and zinc white, stearic acid, and vulcanization were added. A rubber composition containing an appropriate amount of an accelerator and sulfur is used as the cap tread, and the carcass and belt are made of a steel cord layer.
R20,14PR, lug-type steel radial tires were manufactured and evaluated and tested for wear resistance, cut chipping resistance, and durability. The results are shown in Table 1 below, and the properties of the carbon black are shown in Table 2.

Comparative Examples 1 to 16 50 parts by weight of each type of carbon black was blended with 100 parts by weight of natural rubber, and 10 parts by weight of white carbon was added.
parts by weight, 3 parts by weight of zinc white, 3 parts by weight of stearic acid, 1 part by weight of anti-aging agent, 1.0 part by weight of vulcanization accelerator, and 1 part by weight of sulfur.
．． Example 1 using a rubber composition containing 0 parts by weight
Tires were manufactured in the same manner as above, and evaluation tests were conducted.

The results are shown in Table 1) The properties of carbon black are also shown in Table 2.

The method for measuring the physical property values in Table 1 is as follows.

300% modulus, EL (elongation at break), Hs (
Hardness) was measured according to the JIS K2SO3 method.

Tan δ was measured using a dynamic viscoelasticity measuring machine at a frequency of 20 Hz.
, a dynamic strain of 10%±2%, and a temperature of 100° C., and expressed as an index with Comparative Examples 1 and 8 set as 100. The larger the value, the better the heat generation characteristics and the better the tread separation resistance.

The wear index value is an index value when Comparative Examples 1 and 8 are taken as 100, and the wear amount was measured using a Lambourn abrasion tester under two conditions with a slip ratio of 25% and 35%.

The degree of rubber swelling (Vc) is 48 when a piece of rubber is placed in a benzene solvent.
It shows the degree of volumetric swelling after being immersed for a period of time, and the larger the value, the lower the network chain density and the better the cut chipping resistance.

Durability is measured by increasing the load at the time steps shown in Table 3 below, driving at a constant speed of 55 km/HR, and determining at which time step failure occurs.
An indoor durability test was conducted under the conditions of No. 119, and Comparative Example 1 and Comparative Example 8 were set as 100 and expressed as an index. The better the durability, the larger the value.

Table 3 wear resistance is average speed 55km/HR1 load 120%,
Users on good roads with a paved rate of approximately 99% and an average speed of 301f/
An actual vehicle test was conducted using a user on a rough road with an HR1 load of 140% and an unpaved rate of 20% or more, and the distance traveled until the residual hot water reached 3.2 + n/m was calculated using an index with Comparative Example 1 and Comparative Example 8 as 100. Indicated.

The larger the value, the better the wear resistance and the longer the tire life.

Regarding cut resistance and chipping resistance, we conducted an appearance check on the rough road users mentioned above, and found that cut resistance is measured by the number of external injuries that enter the tread surface, while chipping resistance is measured by the degree of occurrence of peeling phenomena on the tread surface. The ratio was calculated using Comparative Example 1 and Comparative Example 8 as 100.

The larger the value, the better the cut resistance and chipping resistance.

As is clear from Table 1, the wear and cutting performance of CB-1's low structure carbon significantly decreased due to the lack of tread rigidity, while the chipping performance of CB-4's high structure carbon decreased significantly. .

In addition, the small particle size carbon of CB-2 was particularly poor in durability, and tread separation occurred in all of the tires on good roads in actual vehicle tests.

On the other hand, CB-
Nos. 3, 5, and 6 provide a good balance of abrasion resistance, cut resistance, chipping resistance, and even durability, but do not reach the point where the ultimate performance is satisfied.

Therefore, when we conducted a variable experiment using CB-3 carbon black, vulcanizing agent, and vulcanizing aid, we found that the first
As shown in Table 1, Comparative Examples 9 to 11, in systems containing a large amount of fatty acids, increasing the amount of vulcanizing agent does work effectively against tread separation, but it significantly reduces chipping performance.

However, as in Comparative Example 14, if the metal salt is reduced too much, the exothermic properties will deteriorate.

In addition, when using a system with less fatty acids and reducing the amount of vulcanizing agent as in Comparative Example 13, although chipping performance is good, tread separation is induced and wear and cutting performance are significantly reduced due to lack of tread rigidity. I don't like it because I let it happen.

In this way, by optimizing the carbon black, the vulcanizing agent, and the vulcanizing aid as in Examples 1 to 6, it is possible to obtain the ultimate performance regarding overall rough road durability.

(Hereafter, margin)

Claims (1)

[Claims] 50 to 90 parts by weight of natural rubber and 50 to 90 parts by weight of polyisoprene rubber
100 parts by weight of blended rubber consisting of 10 parts by weight, nitrogen specific surface area 115 to 150 m^2/g, dibutyl phthalate absorption amount 105 to 130 ml/100 g, 40 to 60 parts by weight of carbon black with a tinting power of 110% or more, and iodine. 0.5 to 2.5 parts by weight of fatty acids with a value of 5% or less and a stearic acid content of 50% or more, and 1.0 to 1.5 parts of sulfur.
parts by weight, the weight ratio of the metal oxide or metal salt to the fatty acid is 2.5 or more, and the total amount of the sulfur and the vulcanization accelerator is 2.2 parts by weight or more. A radial tire with improved durability on rough roads, characterized by using a tread rubber composition.