JPS6257438A - Ruber composition - Google Patents

Abstract

PURPOSE:A composition, obtained by incorporating a specific carbon black with natural and diene based synthetic rubber and having remarkably improved dispersibility of the carbon black and further markedly improved fatigue failure resistance and low thermogenic properties at the same time. CONSTITUTION:A rubber composition obtained by incorporating a rubber compo nent selected from natural rubber and diene based syntheitc rubber with 20-100 pts.wt. carbon black having the following characteristics; 22mmu<=Dn<=38mmu, 60mmu<=Dst<=130mmu, [S]<=0.333<=[Dn]+0.0800, [DELTAD50]<=0.333X[Dst]+45.0, <=10 ml/100gDELTADBP=-24M4DBP (ml/100g), and >=1.08 ratio N2SA (m<2>/g)/IA(mg/g) [Dn is the arithmetic means diameter measured under an electron microscope; Dst is the aggregate diameter mode value; S(mmu) is the standard deviation of the above-mentioned arithmetic mean diameter distribution; DELTAD50(mmu) is the half width of aggregate distribution; DELTADBP is the aggregate strength; N2 SA(m<2>/g) is the nitrogen adsorption specific surface area; IA (mg/g) is the iodine absorption].

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to industrial products such as conveyor belts that require fatigue resistance and heat resistance, rubber products such as tires, and especially frame materials for large tires. The invention relates to rubber compositions suitable for making.

(Prior Art) In recent years, there has been a desire to improve the durability of rubber products such as those mentioned above, and in particular, tires for trucks and buses (TBR) have been improved.
The lifespan of large tires such as these has been improved, and in this era, there is a strong demand for retread durability for frame materials, and it has become important to improve the durability of pelt-coated rubber, ply-coated rubber, etc. Under these current conditions, after a long period of use, the tire becomes unusable because the cracks generated at the ends of the belt grow and propagate deep between the belts, causing separation between the belts.

In this case, the growth of cracks is promoted by a rise in temperature due to heat generated by the rubber as the tire runs. Therefore, it is essential to reduce the crack growth rate by suppressing the heat generation of belt coating rubber to improve tire durability.

Currently, as mentioned above, in order to reduce the length of cracks that occur at the end of the tire belt at the end of tire running, and to extend the fracture life of the frame material, that is, to improve fatigue fracture resistance, the carbon For black, it is recommended to (a) reduce the structure and incorporate a large amount of one with a small particle size, and at present, carbon black such as N-326 is preferably used.

In addition, in order to prevent the tire temperature from rising due to the heat generated by running large tires, thermally deteriorating the rubber, and shortening the tire life, in other words, as a method to promote low heat generation, the carbon black used ( b) It is recommended to use carbon black with a high structure and large particle size (currently, carbon black such as N-550 is preferably used) in a reduced amount.

(Problems to be Solved by the Invention) However, the methods (a) and (b) above are contradictory in terms of tire performance, and cannot simultaneously satisfy fatigue fracture resistance and heat generation resistance. In some cases, the solution was thought to be impossible.

This time, the present inventor reexamined carbon black from a different perspective from the conventional way of thinking about carbon black. In other words, the particle size and aggregate size of carbon black are generally measured indirectly using the adsorption method, but the adsorption method does not adequately express the particle size and its distribution as well as the aggregate size and its distribution. We can only look at it in terms of average values. For example, the particle size is calculated from the amount of nitrogen or iodine adsorbed on the carbon surface.

The present inventors have introduced a highly accurate concept of the above-mentioned side diameters and their distribution without using adsorption methods, and in particular through direct morphological measurements using electron microscopy and centrifugal sedimentation methods, and have determined the particle diameter and aggregates of carbon black. We focused on the fact that diameters and their distribution have a significant influence on the physical properties of compounded rubber. Here, measurements using an electron microscope are performed on the particle size,
The arithmetic mean particle diameter (Dn) was determined by the following procedure. First, a carbon black sample was dispersed in chloroform using an ultrasonic cleaning method (dispersion conditions include, for example, a frequency of 28K).
After ultrasonic cleaning at Z for 30 minutes, the dispersed sample was fixed on a carbon support membrane, and the sample was directly examined under an electron microscope at a magnification of 20.000x and a total magnification of 80.000-100.
．． From the electron micrograph taken at 1,000 times magnification, 1.
The diameter of 000 carbon black particles was measured, and the average particle diameter (Dn) was determined by an arithmetic average from a histogram of 3 mμ divisions. Then, the standard deviation value at that time is S
And so.

In addition, the measurement using the centrifugation method was performed using the following method regarding aggregate distribution. In other words, the carbon black aggregate distribution is
Measurements were made using a disk centrifage manufactured by Joyce Leble. First, carbon black was accurately weighed, added to a 20% ethanol aqueous solution to make the carbon black concentration 0.01% by weight, and then dispersed using ultrasonic waves (for example, for 10 minutes) to prepare a sample solution. Set the rotation speed of the disk centrifage to 6. Set to OOORPM, inject the sample solution (0.25 ml to 1.00 ml!) into 30 ml of spin solution (2% glycerin aqueous solution) using a syringe, start centrifugal sedimentation all at once, and collect aggregates by photoelectric precipitation. A distribution curve was created.

The half width Δ[)50 and the mode p, t (mode value) are the first
Obtained from the figure. In addition, the broken line part in the drawing is the same length,
The half width is the solid line portion shown in the figure.

When carbon black is kneaded in a Banbury mixer, etc., the aggregates are partially destroyed by the force (energy) applied from the outside, and in order to maintain the form before kneading, the strength of the aggregates must be increased. It is necessary to keep

Regarding the aggregate strength, the oil absorption amount of DBP (dibutyl phthalate) of the carbon black before kneading is measured according to the method of JIS K6221, and the carbon black before kneading is also measured according to the method of ASTM D-3037.
．． DBP after repeated compression 4 times with 0OOPSI
The value after subtracting the oil absorption amount (ΔDBP) is ΔDBP = DBP
−24λ (represented by 4DBP, the smaller the value, the harder it is to break, and it can be used as a measure of aggregate strength. In the present invention, ΔDBP is referred to as aggregate strength. This ΔDBP value is the value of aggregate strength during kneading. prevent destruction,
In order to improve reinforcing properties and maintain a high level of low heat build-up, it is better to make it as small as possible.

In addition, in order to increase the degree of carbon black dispersion in the compounded rubber, it is necessary to apply sufficient shear force to the carbon black aggregates, and if the aggregate strength (ΔDBP) is low, the aggregates may be subjected to less stress during kneading. Carbon black tends to be broken by force, and carbon black is not subjected to sufficient shearing force, resulting in a decrease in its degree of dispersion. Therefore, it was confirmed that a smaller ΔDBP, that is, a higher aggregate strength, is advantageous for improving fatigue resistance and heat generation resistance.

Furthermore, the specific surface and product N2SA (rn2/g
) and the ratio of both IA adsorbing iodine (mg/g) (N, SA/I
A) is usually used as a surrogate measure for the surface activity of carbon black, and the higher this ratio, the stronger the reinforcing layer of carbon black and polymer (rubber content) produced during kneading.
That is, the amount of gelation of the polymer and carbon black increases. It also improves the reinforcing properties of compounded rubber, and is an important factor in improving fatigue resistance and heat generation resistance. Here, the nitrogen adsorption specific surface area N2SA is a value measured according to ASTM D-3037, and the iodine adsorption amount IA is a value measured according to JISK-6221.

In this way, by making the carbon black particles uniform in size within a certain range and making the aggregate diameter uniform, the carbon black as a whole can be made highly homogeneous and have a high degree of activity with the polymer. When carbon black is kneaded into a polymer, the carbon black is better separated from each other and uniformly dispersed in the rubber, resulting in a homogeneous compounded rubber. In this way, the energy loss between the carbon blacks is extremely small, and the heat generation property is significantly improved. Regarding the fatigue properties of compounded rubber, due to the uniform state of carbon dispersion, the load on the polymer molecular chains within the compounded rubber is evenly shared, the number of defect points in the compounded rubber is reduced, and the aggregate strength is high. It was discovered that the fatigue fracture phenomenon was significantly improved, and the present invention was achieved.

Therefore, the rubber composition of the present invention is prepared under the following conditions for at least one rubber component selected from the group consisting of natural rubber and diene-based synthetic rubber: (a) Arithmetic mean diameter (Dn) as measured by an electron microscope: 22 m
p≦D, (, 38 mμ (b) Aggregate diameter (mode value) (Dnt): 60
m t-t≦D-t<130m p (c) Standard deviation of the arithmetic mean particle size distribution of (a) above S (mμ): [S″) mO, 333x CD, ] +0.080
0 (d) Half width of aggregate distribution ΔD50 (mμ): [ΔD
50) <0.333 x [D, t) +45.
0 (E) Aggregate strength ΔDBP = DBP −24M4D
BP (mj2/100g) is 10m! ! /100g
Below (to) N2N2SA (/g)/IA (mg/g)
Carbon black that satisfies the ratio of 1.08 or more is 20
It is characterized by containing ~100 parts by weight.

The rubber composition of the present invention requires the use of carbon black that satisfies the above conditions (a) to (f), and the arithmetic mean particle diameter (Dn) of the carbon black as measured by an electronic microscope is When it is smaller than 22 mμ, the fatigue fracture resistance improves, but the heat generation property of the compounded rubber increases and the heat generation durability of the tire decreases.On the other hand, when it becomes larger than 38mμ, the heat generation property of the compounded rubber becomes small, which is good. However, this is not preferable because the fatigue fracture resistance is lowered. As the particle size distribution becomes smaller, the fatigue resistance can be significantly improved if the particle size is the same, and the deterioration of heat generation can be minimized.In the present invention, the standard deviation S ( m
μ) to 0.333 X (Dn:] +o, o50o
The following shall apply.

Regarding the aggregate diameter Dst (mμ), if the particle size is smaller than 60 mμ, the rubber properties will be similar to those when the particle size is too small, and the fatigue resistance will improve, but the heat generation property of the compounded rubber will increase, which is not desirable. If this is the case, the heat build-up will be reduced, which is good, but the fatigue fracture resistance will be lowered, which is not preferable. For the aggregate distribution, the half-width of the distribution ΔI
) 50 is 0.333 xD, t+450 or less, the fatigue resistance is significantly improved, and at the same time, the decrease in heat resistance is suppressed to a small extent, which is advantageous.

The strength ΔDBP of the aggregate is set to 10 mβ/100 g or less in order to prevent the aggregate from breaking during kneading, improve reinforcing properties, and maintain a high degree of low heat build-up.

In addition, the ratio (N2SA/IA
) is larger than 7100 g, the surface activity of carbon black is not satisfied, and in order to increase the surface activity and improve the reinforcing properties of the compounded rubber, it is necessary to set it to 10 m1/100 g or more.

The carbon black used in the present invention that satisfies these conditions is manufactured using a dedicated hard carbon black furnace using the ordinary rubber furnace method. , disperse into uniform oil droplets.

(b) Avoid prolonged exposure to excessively high temperatures to avoid recycling of carbon black aggregates suspended in the combustion products. This narrows the distribution size of the aggregates and removes large aggregates.

(c) Increase the linear velocity in the reaction zone and change the quenching position by water to control the reaction time of carbon particles flowing in the furnace.

(d) A hard carbon furnace will be used as the reactor.

In the rubber composition of the present invention, carbon black that satisfies the conditions (a) to (f) above is added at 20% of the rubber content.
~100 parts by weight is added, because if it is less than 20 parts by weight, the heat generation property will be improved but the fatigue fracture resistance will be poor, while if it exceeds 100 parts by weight, it will not be possible to process.

The rubber composition of the present invention also includes compounding agents commonly used in the rubber industry, such as fillers, softeners, vulcanizing agents, vulcanization accelerators,
Anti-aging agents and the like may be blended within the usual range of blending amounts as appropriate and necessary.

(Example) The invention is illustrated by the following examples.

Example 14 rubber compositions were prepared using the ingredients shown in Table 1 below in the mixing ratios, but with the carbon black species shown in Table 2, and used as belt coating rubber. Tire size TBR10.0O-R -2014PRR2
20, belt ea 4 steel cord layers, carcass structure 1 steel cord layer One tire was prototyped and subjected to a drum test, and the test results are shown in Table 2 along with the evaluation characteristics of carbon black.

Table 1 Ingredients Amount (parts by weight) Natural rubber
100 carbon black
50 stearic acid 2
Cobalt naphthyphosphate 4 Anti-aging agent (S
ANTOFIE X13) 2 Zinc white
6 Vulcanization accelerator (Ixela OZ
) 1 sulfur 4
．． 5 Evaluation method A. Nitrogen adsorption specific surface area (N2SA, m2/g) is AS
Measured in accordance with TM D-3037.

B. Iodine adsorption specific surface area (IA, mg/g) is JIS
Measured in accordance with K-6221.

C. DBP oil absorption (ml/100g) is JIS K-6
Measured in accordance with 221.

-, 24M4DBP ll oil amount (m A/100g)
AsTM D-3037i: Measured in accordance with AsTM D-3037i.

E. Crack growth A vulcanized rubber sheet with a thickness of 2 marks is punched out using a JIS No. 1 blade die, and the dumbbell-shaped test piece is initially cut (scratched) with a width of 0.3+nm in the maximum strain area (center). Insert with a razor blade. This is repeatedly elongated at strains of 30%, 40%, 50%, and 60%, and the lifespan until breakage at each strain is measured in an atmosphere at 70°C.

At the same time, the energy applied to the sample at each strain was calculated using the following equation, and the rupture life at the same energy was compared.

The crack growth values in Table 2 are based on input energy T = 5
The fracture life (number of times) at 0g/++on, the larger the value, the better.

However, ε: strain, σ: stress, π: pi.

0 rebound resilience was measured at room temperature using a Dunlop trypsometer. The larger the impact resilience value is, the more the rubber composition is suitable for the purpose of improving low heat generation property, that is, heat generation resistance.

Drum test conditions After filling the test tire with an internal pressure of 6.50 kg-f/c [[t], a step load test is carried out at a constant test speed of 60 km/flr.

Load Running time 1st step 1659 kg 8 hours 2nd step 2014.5 kg 8 hours 3rd step 2370 kg 8 hours Add a load of 355.5 kg every 8 hours.

The test results are displayed as (number of final steps) x (running time at the final step).

This test method is commonly used to test belt-coated rubber tires, and it runs on a drum in a highly thermally stimulated state, making it possible to simulate the durability in real life.

(Effect of the invention) As explained above, the rubber composition of the present invention has the above-mentioned (
A product that contains a specific amount of carbon black that satisfies the conditions of a) to (f), and the carbon black is highly homogenized with the particle size and aggregate size within a narrow fixed range, has high aggregate strength, and is a polymer. By having a high degree of activity with , the dispersibility is significantly improved, and as is clear from Table 2, it is possible to achieve the effect of achieving both fatigue fracture resistance and low heat build-up. This makes it extremely useful for forming frame materials for various industrial rubber products and tires, especially large tires, which require fatigue fracture resistance and low heat generation performance.

[Brief explanation of drawings]

FIG. 1 is a carbon black aggregate distribution curve diagram. Procedures Amendment Written November 5, 1985 Michibe Uga, Commissioner of the Patent Office1, Indication of the case Patent Application No. 194726 of 19852, Name of the invention Rubber composition3, Person making the amendment Related Patent applicant (527) Brideston Co., Ltd. 4, Agent 5, Subject of amendment Drawing 6 in the “Detailed Description of the Invention” section of the specification, Contents of the amendment (as attached) Page 5 of the L specification tube “Distributed” in line 5 is “distributed”
In line 14 of the same page, "centrifugal advancement method" is corrected to "centrifugal sedimentation method." 2. Corrected "carbon black" in line 9 of page 6 to "carbon black aggregate" and changed "carbon black aggregate" to "carbon black aggregate" in line 11 of page 6.
"The aggregate is partially destroyed" should be corrected to "although it is partially destroyed." 8. Corrected "adsorption amount" in line 16 of page 7 to "adsorption amount" and changed "mixing at high level" to "mixing at high level" in line 18 of the same page.
Correct. 4. Correct "pressed" in line 8 of page 10 to "press". 5. On page 11, lines 5 to 6, "larger than 10m1/100g" was corrected to "l" smaller than 1.08", and on line 8 of the same page, "more than 1omz/xoog" was changed to rl, os that's all"
and add the following between lines 9 and 10 of the same page. ``In the rubber composition of the present invention, 20 to 100 parts by weight of carbon black satisfying the above conditions (a) A-(f) is added to the rubber content, but the reason for this is that it is less than 20 parts by weight. If the amount exceeds 100 parts by weight, the rubber composition of the present invention may contain compounding agents commonly used in the rubber industry, such as fillers. Agents, softeners, vulcanizing agents, vulcanization accelerators, anti-aging agents, etc. can be blended as appropriate and within the range of usual blending amounts. ” 6. Remove # from lines 4 to 13 on page 12, and from lines 17 to 1 on page 12.
In line 8, ``However, the type of carbon black'' should be corrected to ``Also, the type of carbon black.'' 7, page 18, line 1 (7) “TBRlo, 0O-R
-20J is corrected to l" TBR10,00R20J. 8. Correct "0) to (f) above" in line 8 of page 18 to "(b) to (b) described on page 9," In line 11 of the same page, "required" is corrected to "required".・9. Correct Figure 1 as shown in the attached correction diagram.

Claims (1)

[Claims] 1. For at least one rubber component selected from the group consisting of natural rubber and diene-based synthetic rubber, the following conditions (a) Arithmetic mean diameter (D_n) as measured by an electron microscope: 22 m
μ≦D_n≦38mμ (b) Aggregate diameter (mode value) (D_s_t): 60mμ≦D_s_t≦130mμ (
c) Standard deviation S (mμ) of the above arithmetic mean particle size distribution: [S]≦0.333×[D_n]+0.0800 (d)
Half width of aggregate distribution ΔD_5_0 (mμ): [ΔD_5
＿0〕≦0.333×[D_s_t]+45.0(e)
Aggregate strength ΔDBP=DBP-24M4DBP (ml/
100g) is 10ml/100g or less.
A rubber composition characterized in that it contains 100 parts by weight.