JPH072863B2 - Rubber composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rubber composition having improved fatigue resistance, and more specifically, to a chloroprene rubber containing carbon black having a uniform colloidal property. And a rubber composition having fatigue resistance.

[Conventional technology]

Out of the industrial rubber products, rubber materials used for various antivibration materials, seal members, hoses, belts, etc. are required to have excellent fatigue resistance against harsh usage environments. Therefore, attempts to improve the fatigue resistance of this type of rubber product have been actively made in the past, and many proposals for improvement have been made mainly in terms of the component composition.

For example, JP-A-60-108444 discloses that fatigue resistance by a wet carbon masterbatch method in which an organic suspension containing carbon black from which grit has been removed by passing through a sieve and rubber latex or rubber cement is mixed and coagulated is set. A rubber composition is disclosed. However, compounding carbon black with fine grit removed limits the degree of improvement in fatigue resistance, and in the case of chloroprene rubber, the carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 60.
If it exceeds m ² / g, the fatigue resistance will be extremely reduced even if the fine grit is removed. In the invention of JP-A-61-290255, 100 parts by weight of chloroprene rubber is used and 1 part of metal oxide vulcanizing agent is added.
.About.20 parts by weight, silica 5 to 30 parts by weight, reinforcing fillers such as carbon black 15 to 50 parts by weight, and bismaleimide 2 to 10 parts by weight are combined to extend the life of the rubber V-belt. However, since no consideration is given to the characteristics of carbon black, the causal relationship between its colloidal properties and the fatigue resistance of compounded rubber is not clear. On the other hand, in Japanese Patent Laid-Open No. 62-57438, the arithmetic mean diameter (Dn) by an electron microscope: 22 mμ ≦ Dn ≦ 38 mμ, the aggregate diameter (st): 60 mμ ≦ st ≦ 130 mμ, the standard deviation of the arithmetic mean diameter distribution S (mμ): [S] ≦ 0.333 × [st] +45.0, Aggregate strength: ΔDBP = DBP-24M4DBP (ml / 100g) ≦ 10 ml / 100
Fatigue resistance and heat resistance rubber with carbon black having colloidal characteristics of g, N ₂ SA (m ² / g) / IA (mg / g) ≧ 1.08 mixed in 20 to 100 parts by weight with respect to the rubber component. The composition is shown. However, the rubber component used in the invention is natural rubber or diene synthetic rubber, and chloroprene rubber has not been studied. The anti-vibration rubber composition described in JP-A-64-9250 is a vulcanizable rubber 10
A mixture of 0 part by weight of polyamide fine short fibers of 5 to 100 parts by weight, a reinforced rubber composition, carbon black and a vulcanizable rubber in a specific range of ratios for the purpose of improving fracture strength and fatigue properties. However, the characteristics of the blended carbon black have not been examined. JP-A-64-20245 discloses a method for producing a rubber composition comprising natural rubber and / or polyisoprene rubber, polybutadiene rubber, and carbon black having excellent fatigue resistance. However, chloroprene rubber has not been targeted for improvement, and the characteristics of blended carbon black have not been examined. Further, the invention of JP-A 1-146934 is directed to an anti-vibration rubber composition containing a specific butanediene polymer, natural rubber and / or high cis-isoprene rubber and carbon black. Therefore, it is characterized by the polymer composition and no consideration is given to the properties of the blended carbon black.

[Problems to be Solved by the Invention]

Thus, in the prior art aimed at improving the rubber fatigue property, except for the invention of Japanese Patent Laid-Open No. 62-57438, examples in which the fatigue property of a compounded rubber is improved from the colloidal characteristics of carbon black are I can't find it.

Further, as described above, the invention of JP-A-62-57438 has a target rubber component of natural rubber or diene-based synthetic rubber, and has not been studied for chloroprene rubber. According to the study by the present inventor, when chloroprene rubber is targeted, st ≦ 13 specified in the invention of JP-A-62-57438.
It has been confirmed that the improvement of fatigue resistance is not effectively achieved at 0 mμ. Therefore, the natural rubber or diene-based synthetic rubber and the chloroprene rubber differ greatly in the design direction of the carbon black characteristics for improving fatigue resistance.

An object of the present invention is to provide a rubber composition having excellent fatigue resistance, which contains chloroprene rubber as a target rubber component and carbon black having optimal colloidal properties in this case.

[Means for Solving the Problems]

The rubber composition according to the present invention for achieving the above object is characterized in that 20 to 100 parts by weight of carbon black having the following selective characteristics is blended with 100 parts by weight of chloroprene rubber. There is.

(1) N ₂ SA (m ² / g) ≤ 60 (2) st (nm) ≥ 130 (3) ΔDst / st ≤ 0.95 where N ₂ SA is the nitrogen adsorption specific surface area and st is the Stokes of the carbon black aggregate. The mode diameter, ΔDst, refers to the full width at half maximum of the Stokes mode diameter.

Each characteristic of carbon black applied to the present invention is based on the following measuring methods.

(1) N ₂ SA ASTM D3037-86 “Standard Test Method for Carbon Bla
ck-Surface Area by Nit-rogen Adsorption "Method B. The N ₂ SA value of IRB # 5 measured by this method is 80.3 m ² /
It becomes g.

(2) st, ΔDst JISK6221 (1982) 5 “Dry sample preparation” based on the dry carbon black sample containing a small amount of surfactant
A 20 vol% ethanol aqueous solution is mixed to prepare a dispersion having a carbon black concentration of 100 mg / l, which is sufficiently dispersed by ultrasonic waves to obtain a sample. A disk centrifuge (Joyes Lobel, UK) was set at a rotation speed of 6000 rpm, and a spin liquid (2 wt% glycerin aqueous solution at a temperature of 25 ° C) was applied to 1
After adding 5 ml, 1 ml buffer solution (20 vol at 25 ° C
% Ethanol aqueous solution). Next, 0.5 ml of the carbon black dispersion liquid at a temperature of 25 ° C. is added with a syringe, and then centrifugal sedimentation is started. At the same time, a recorder is operated to optically create a distribution curve of aggregate Stokes equivalent diameter. The Stokes mode diameter with the maximum frequency in the obtained distribution curve is st
(Nm) and a frequency of 50% of the maximum frequency is obtained.
The difference between the points (half width) is ΔDst (nm). ASTM D24 "Standard Reference Black C-3 (N
−234) ”has a st of 80 nm and a ΔDst of 60 nm.

Of the carbon black characteristic items specified in the present invention, N ₂
The range of SA (m ² / g) ≤ 60 belongs to the soft system region and is a prerequisite for providing the compounded chloroprene rubber with fatigue resistance. If N ₂ SA exceeds 60 m ² / g, the effect of improving fatigue resistance cannot be expected, and the heat buildup increases, causing heat aging of the rubber.

The colloidal properties of st (nm) ≧ 130 and ΔDst / st ≦ 0.95 are characterized in that the Stokes mode diameter of the carbon black aggregate is located at a high position and the distribution width with respect to the Stokes mode diameter is relatively small. When this colloidal property requirement is satisfied at the same time as the particle requirement by the low N ₂ SA, good fatigue resistance is imparted to the compounded chloroprene rubber.

This fatigue resistance improving effect shows a remarkable improvement tendency as N ₂ SA is smaller and st is larger, while satisfying the above-mentioned carbon black characteristic requirements.

The carbon black having the above-mentioned characteristics is used in a high-temperature combustion gas obtained by using a wide-diameter cylindrical reactor having a drum-shaped throttle portion that gradually converges and expands, and is mixed with fuel oil and an appropriate oxidizing agent containing air or oxygen. It can be produced by a method of introducing an atomized air stream of the raw material oil into two stages.

Heavy aromatic heavy oils such as creosote oil and ethylene bottom oil are used as feedstock, and sufficient fine particle airflow is achieved through the atomizing injection nozzle to obtain a highly homogeneous mixture with high temperature combustion gas. Introduced in. The atomization injection nozzle has, for example, a double cylinder structure having an outer cylinder nozzle that has a water-cooled mantle and is capable of advancing and retracting in the furnace axial direction, and an expandable center cylinder nozzle that is inserted into the outer cylinder nozzle. Separately, it is attached to the furnace head. The feedstock oil is introduced in two stages with the atomizing air through the outer cylinder nozzle and the middle cylinder nozzle, but the position of the feedstock oil can be changed appropriately by advancing and retracting the outer cylinder nozzle and expanding and contracting the middle cylinder nozzle. .

Using the above-mentioned device, the ratio of the pre-supply air amount and the total amount of the raw fuel oil and the amount of the reaction additive are adjusted by a conventional method to produce carbon black having a desired N ₂ SA. Conventional combustion of coarse carbon black, such as a combustion rate of 170% or less, a flow rate of combustion gas at the upstream feedstock introduction position of 60 m / sec or more, and a residence time of reaction product gas in the furnace of 700 ms or less. Colloidal specified in the present invention by setting conditions different from the conditions (fuel oil burning rate 200% or more, combustion gas flow rate 10 m / sec. Or less, reaction product gas residence time in the furnace 900 to 1100 milliseconds) Characteristic is given.

The carbon black having the above-mentioned selective properties is compounded in the chloroprene rubber according to a conventional method. The target chloroprene rubber may be either sulfur-modified or non-sulfur-modified. The blending ratio of carbon black is in the range of 20 to 100 parts by weight with respect to 100 parts by weight of the chloroprene rubber component, and a vulcanizing agent, a vulcanization accelerator, an antioxidant, a vulcanization aid,
The rubber composition of the present invention is obtained by kneading together with necessary components such as a softening agent and a plasticizer.

[Action]

The rubber composition according to the present invention has N ₂ SA having a low surface area of 60 m ² / g or less, a st of 130 nm or more, and a ΔD st / st ratio of 0.95.
Carbon black having the following colloidal properties is blended, and the selective characteristics of the carbon black effectively function to impart excellent fatigue resistance to chloroprene rubber.

In particular, the Stokes mode diameter (st) of the aggregate is relatively high, and this Stokes mode diameter (st)
In the colloidal characteristic range of carbon black having a relatively small distribution width (ΔDst), the aggregates are well separated from each other when kneaded with chloroprene rubber to form a very uniform dispersion structure. The compounded structure of the uniform dispersion system not only has few defects, but also serves to equalize the load on the rubber polymer molecular chains during fatigue. A rubber composition having effectively improved fatigue resistance is obtained through such an action.

〔Example〕

 Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 4 (1) Manufacture of carbon black A combustion chamber (inner diameter 700 mm, in which the downstream outlet part converges gently)
It has a cylindrical structure made of refractory brick lining continuous to a tapered reaction zone (length 9000 mm) that expands and expands (length 1000 mm) through a narrow diameter part with an inner diameter of 250 mm and length of 200 mm, and is tangential to the furnace head. In a reactor equipped with a wind box equipped with a directional air supply port and a quench nozzle that can be relocated in the downstream region of the rear reaction chamber, a double cylinder nozzle structure from the furnace head to the center axis of the furnace A raw oil atomization injection nozzle was inserted, and four combustion burners were coaxially installed around the nozzle. The feedstock atomization injection nozzle was adjusted such that the feedstock oil introduction point on the upstream side (the ejection hole of the outer cylinder nozzle) was located at the convergent portion and the feedstock oil introduction point on the downstream side was located at the narrow diameter portion.

Carbon black satisfying the characteristic requirements of the present invention was produced using the above-mentioned reaction furnace.

Specific gravity (15/4 ℃) 0.903, viscosity (CST 50 ℃) 1 for fuel oil
6.1, residual coal content 5.4%, sulfur content 1.8%, flash point 96 ℃ hydrocarbon oil is used, as feedstock, specific gravity (15/4 ℃) 2.10, benzene insoluble matter 0.03%, correlation coefficient (BMCI) 140, initial boiling point 1
A highly aromatic hydrocarbon oil at 03 ° C was used.

Table 1 shows the generation conditions applied to Table 1, and Table 2 shows the characteristics of the obtained carbon black. In addition, Comparative Examples 1 to 4 in Table 2
Shows a conventional quality carbon black which is out of the specific range of the present invention.

(2) Rubber compounding Next, each carbon black in Table 2 was compounded in the chloroprene rubber in the compounding ratio shown in Table 3, and the compounding was vulcanized at a temperature of 145 ° C for 35 minutes to obtain a rubber composition.

(3) Fatigue test A rubber fatigue test is performed on each of the obtained rubber compositions,
The results are shown in Table 4.

The fatigue test was carried out in advance in a dumbbell shape (length 78 mm,
Using a Monsanto Fatigue tester for a vulcanization specimen with a thickness of 2 mm, a narrow portion length of 25 mm, and a width of 4 mm), the elongation rate is 0 to 100%, the tension cycle is 100 cycles / minute, and the conditions are ambient room temperature. The sample is repeatedly stretched and the number of times to break is measured 24 times per sample, and the results are plotted on the Weibull probability paper (Japan Standards Association), which is widely used for life analysis. : mean time o
f failure) times were calculated.

From the results of Table 4, each rubber composition according to the example shows a high degree of fatigue resistance, but the rubber composition of the comparative example which does not satisfy any of the requirements of the carbon black characteristics of the present invention is significantly larger than that of the example. It is recognized that the fatigue resistance is poor.

〔The invention's effect〕

As described above, the rubber composition provided by the present invention has a significantly improved fatigue compared with the compounded carbon black having the selective characteristics of the compounded carbon black, in particular, the uniform colloidal property, and the carbon black of the conventional type having the equivalent particle diameter when compounded. It has resistance.

Therefore, it is useful as a rubber composition used in various industrial rubber products that require fatigue resistance.

Claims (1)

[Claims] 1. A rubber composition comprising 100 parts by weight of chloroprene rubber and 20 to 100 parts by weight of carbon black having the following selective properties. (1) N ₂ SA (m ² / g) ≤ 60 (2) st (nm) ≥ 130 (3) ΔDst / st ≤ 0.95 where N ₂ SA is the nitrogen adsorption specific surface area and st is the Stokes of the carbon black aggregate. The mode diameter, ΔDst, refers to the full width at half maximum of the Stokes mode diameter.