JP3434359B2 - Fatigue-resistant rubber composition - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber excellent in fatigue resistance obtained by blending carbon black having a selected specific colloidal property with chloroprene rubber. Composition. [0002] Among industrial rubber products, rubber materials used for various vibration isolating materials, sealing members, hoses, belts, and the like are required to have excellent fatigue resistance against severe use 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 mainly in terms of component composition have been made. [0003] For example, Japanese Patent Application Laid-Open No. 61-290255 discloses that 100 to 100 parts by weight of chloroprene rubber is used in an amount of 1 to 20 parts by weight of a metal oxide vulcanizing agent, 5 to 30 parts by weight of silica, and reinforcing properties such as carbon black. By mixing 15 to 50 parts by weight of a filler and 2 to 10 parts by weight of bismaleimide,
Although the service life of the belt has been extended, no consideration has been given to the properties of carbon black, and the causal relationship between its colloidal properties and the fatigue resistance of the compounded rubber has not been elucidated. On the other hand, JP-A-62-57438 discloses an arithmetic mean diameter (Dn) by an electron microscope: 22 mμ ≦ D
n ≦ 38 mμ, aggregate diameter (Dst): 60 mμ ≦ Dst ≦ 1
30 mμ, standard deviation of arithmetic mean diameter distribution S (mμ): [S]
≦ 0.333 × [Dst] +45.0, aggregate strength: ΔD
BP = DBP-24M4 DBP (ml / 100g) ≦ 10 (ml / 100g
g), a carbon black having a colloidal property of N ₂ SA (m ² / g) / IA (mg / g) ≧ 1.08 is added to the rubber component by 2%.
Disclosed is a rubber composition having 0 to 100 parts by weight and having fatigue resistance and low heat generation. However, the target rubber component is a natural rubber or a diene-based synthetic rubber, and chloroprene rubber has not been studied. JP-A-64-20245 discloses a natural rubber and / or a polyisoprene rubber having excellent fatigue resistance.
A method for producing a rubber composition comprising a polybutadiene rubber and carbon black is disclosed. However,
Chloroprene rubber is not targeted for improvement, nor has the properties of the compounded carbon black been studied. Further, JP-A-1-146934 discloses an anti-vibration rubber composition containing a specific butadiene-based polymer, natural rubber and / or high cis-isoprene rubber, and carbon black. No consideration has been given to the properties. [0005] As described above, the prior arts aimed at improving rubber fatigue properties include, except for the invention of JP-A-62-57438, improvement of fatigue resistance to compound rubber from the viewpoint of colloidal properties of carbon black. I can't find the example I've tried. However, in the invention described in Japanese Patent Application Laid-Open No. 62-57438, as described above, the target rubber component is a natural rubber or a diene-based synthetic rubber, and no studies have been made on chloroprene rubber. According to the study of the present inventor, when chloroprene rubber is targeted, Japanese Patent Application Laid-Open No. 62-5743
Dst ≦ 130m specified in the invention described in JP-A-8
It has been confirmed that in μ, improvement in fatigue resistance is not effectively achieved. As described above, natural rubber or diene-based synthetic rubber and chloroprene rubber differ greatly in the design direction of carbon black characteristics for improving fatigue resistance. From such a viewpoint, the present applicant has repeatedly studied the relationship between the colloidal properties and the fatigue resistance of carbon black when chloroprene rubber is used as the target rubber component, and as a result, based on 100 parts by weight of chloroprene rubber. hand,
(1) N ₂ SA (m ² / g) ≦ 60, (2) Dst (nm) ≧ 130,
(3) It has been found that the addition of 20 to 100 parts by weight of carbon black having a selective property of ΔDst / Dst ≦ 0.95 significantly improves fatigue resistance, and is proposed in Japanese Patent Application Laid-Open No. 4-18439. did. However, when compounding carbon black with a rubber component, it is necessary to ensure a certain level of reinforcement, such as modulus and tensile strength, in addition to fatigue resistance. It has been found that when carbon black having the characteristics selected in the invention of JP-A-4-18439 is blended with chloroprene rubber, the chloroprene rubber tends to decrease in terms of reinforcement. Therefore, increase the blending amount of carbon black,
Attempts to maintain the reinforcement at a high level, on the contrary, have the problem of lowering fatigue resistance. The present inventor has conducted further studies in order to achieve a balance between reinforcing properties and fatigue resistance, which are the opposite of each other. As a result, the DBP oil absorption of the carbon black to be blended was determined by the blending with the chloroprene rubber. It has been found that by setting the amount (parts by weight) and a value not less than the value of the specific relational expression, fatigue resistance is effectively improved while maintaining reinforcement. The present invention has been developed on the basis of this finding, and its object is to improve the fatigue resistance while maintaining a high level of reinforcement by improving the invention of JP-A-4-18439. An object of the present invention is to provide a rubber composition exhibiting properties. [0011] In order to achieve the above object, a fatigue-resistant rubber composition according to the present invention comprises carbon black having the following selective properties per 100 parts by weight of chloroprene rubber. It is characterized in that it is blended in an amount of 100 parts by weight. (1) N ₂ SA (m ² / g) ≦ 60 (2) Dst (nm) ≧ 130 (3) ΔDst / Dst ≦ 0.95 (4) DBP (ml / 100g) ≧ 1.38 × A (PHR +72 where N ₂ SA is the nitrogen adsorption specific surface area, Dst is the Stokes mode diameter of the carbon black aggregate, ΔDst is the half width of the Stokes mode diameter, DBP is the DBP oil absorption, and A is the amount of carbon black (parts by weight). ). Each characteristic of the carbon black applied to the present invention is based on the following measuring method. N ₂ SA (m ² / g); ASTM D3037-88 “Standard T
est Method for Carbon Black-SurfaceArea by Nitroge
n Absorption "Based on Method B. IR by this method
The measured value of B # 6 is 76 m ² / g. Dst (nm), ΔDst (nm); JIS K622
1 (1982) 5 A carbon black sample dried according to "How to prepare a dry sample" is mixed with a 20% by volume aqueous ethanol solution containing a small amount of a surfactant to obtain a carbon black concentration of 5%.
A dispersion liquid of 0 mg / l is prepared, and this is sufficiently dispersed with an ultrasonic wave to obtain a sample. A disc centrifuge (Joyes Lobel, UK) was set to a rotation speed of 8000 rpm, and a spin solution (2% by weight glycerin aqueous solution, 25 ° C.)
After adding 0 ml, 1 ml of a buffer solution (20% by volume ethanol aqueous solution, 25 ° C.) is injected. Then, after adding 0.5 ml of carbon black dispersion at a temperature of 25 ° C. with a syringe,
The centrifugal sedimentation was started, and at the same time, the recorder was operated, and the distribution curve shown in FIG. 1 (horizontal axis: elapsed time after adding the carbon black dispersion with a syringe, vertical axis: identification of the carbon black that changed with centrifugal sedimentation) Absorbance at points). Each time T is read from this distribution curve and substituted into the following equation (Equation 1) to calculate the Stokes equivalent diameter corresponding to each time. ## EQU1 ## In Equation 1, η is the viscosity of the spin liquid (0.93
5 cp), N is the disk rotational speed (8000 rpm), r ₁ is the carbon black dispersion injection point radius (4.56cm), r ₂ is the radius to the absorbance measuring point (4.82cm), ρ _CB is carbon black density ( g / cm ³ ), ρ _l is the density of the spin solution (1.00178 g / cm ³ )
It is. The Stokes equivalent diameter of the maximum frequency in the distribution curve of Stokes equivalent diameter and absorbance obtained in this manner (FIG. 2) is defined as the Dst mode diameter (nm), and 50% of the maximum frequency.
ΔDst (nm) is the difference (half-width) between the Stokes equivalent diameters of the two large and small points at which the frequency is obtained. AS by this measurement method
TM D-24 Standard Reference Black C-3 (N234)
Dst is 80 nm and ΔDst is 60 nm. DBP (ml / 100 g); JIS K6221 (1
975) Section 6.1.2, Oil absorption method A. Among the carbon black characteristic items specified in the present invention, the range of N ₂ SA (m ² / g) ≦ 60 belongs to the soft range, and is a prerequisite for providing the compounded chloroprene rubber with fatigue resistance. Become. If the N ₂ SA exceeds 60 m ² / g, the effect of improving the fatigue resistance cannot be expected, and the heat buildup increases to cause thermal aging of the rubber. Dst (nm) ≧ 130 and ΔDst / Dst ≦
Colloidal properties of 0.95, carbon black Stokes mode diameter of aggregate is positioned high, and the distribution width for the Stokes mode diameter is characterized in that the relatively small, and particle property requirements by the N ₂ SA In addition, when the property requirements of the aggregate are simultaneously satisfied, good fatigue resistance is imparted to the compounded chloroprene rubber. The effect of improving fatigue resistance shows a remarkable improvement tendency as N ₂ SA is smaller and Dst is larger, while satisfying these characteristic requirements. The main component of the present invention, DBP (m
l / 100g) ≧ 1.38 × A (PHR) +72 The colloidal property is that when carbon black is blended with chloroprene rubber, the value of DBP is specified to be equal to or greater than the value of the relational formula according to the blending weight part, The fatigue resistance can be improved without lowering the reinforcing property. If the value of DBP is less than the value of the relational expression, it is not possible to achieve both excellent reinforcement and fatigue resistance, and in particular, the fatigue resistance significantly decreases. The carbon black having the above-mentioned characteristics can be burned at a high temperature using fuel oil and an appropriate oxidizing agent containing air or oxygen by using a wide-diameter cylindrical reactor having a drum-shaped constriction portion that gradually converges and expands. It can be manufactured by a method in which an atomized gas stream of a feedstock oil is introduced into a gas in two stages. Highly aromatic heavy oils such as creosote oil and ethylene bottom oil are used as the base oil, and the state of sufficient fine particle air flow through the atomizing injection nozzle to obtain a high degree of homogeneous mixing with the high-temperature combustion gas Introduce. The atomizing injection nozzle has, for example, a double-cylinder structure having a water-cooled mantle and an outer cylinder nozzle that can be advanced and retracted in the furnace axis direction and an extendable middle cylinder nozzle that is inserted into the outer cylinder nozzle. Separately attached to the furnace head.
The base oil is introduced in two stages through the outer cylinder nozzle and the center cylinder nozzle together with the atomizing air. The introduction position of the base oil can be changed as appropriate by the forward / backward movement of the outer cylinder nozzle and the expansion / contraction of the center axis nozzle. Using the above apparatus, the ratio of the total supply air amount to the total feedstock introduction amount and the upstream and downstream feedstock introduction amounts are adjusted by the usual method to obtain the desired N ₂ SA, Ds
A carbon black having t, ΔDst, and DBP is generated. Further, the combustion rate of the fuel oil is 170% or less, the flow rate of the combustion gas at the upstream feedstock introduction position is 60 m / sec or more, the residence time of the reaction product gas in the furnace. Is maintained at 700 milliseconds or less.
%, The combustion gas flow rate is 10 m / sec or less, and the reaction gas residence time in the furnace is from 900 to 1100 milliseconds), whereby the colloidal characteristics specified in the present invention are imparted. The carbon black having the above-mentioned selective properties is blended with chloroprene rubber according to a conventional method. The target chloroprene rubber may be either a sulfur-modified or a non-sulfur-modified type. The compounding ratio of carbon black is in the range of 20 to 100 parts by weight with respect to 100 parts by weight of the rubber component. In this case, the value of the relational expression of 1.38 × A + 72 corresponds to the compounding part A of carbon black. Carbon black having the above DBP is selectively used. Furthermore, a fatigue-resistant rubber composition of the present invention can be obtained by mixing with necessary components such as a vulcanizing agent, a vulcanization accelerator, a vulcanization aid, an antioxidant, a softener, and a plasticizer. The characteristic region of the carbon black specified in the present invention having a N ₂ SA of 60 m ² / g or less is a prerequisite for imparting fatigue resistance to the compounded chloroprene rubber. _{If 2} SA exceeds 60 m ² / g, the heat buildup increases, causing the rubber composition to thermally age and lowering the fatigue resistance. Dst
And ΔDst are characteristics relating to the size and distribution of the carbon black aggregate, and ΔDst is an index indicating the distribution of Stokes equivalent diameter of the aggregate. Stokes mode diameter of aggregate (D
st) is 130 nm or more and the ratio of the half width to Dst (ΔDst / Dst) is 0.95 or less.
Dst is relatively high, and the distribution width (ΔDs
The feature is that t) is relatively small, and when blended and kneaded with chloroprene rubber, aggregates are well separated from each other to form a very uniform dispersed structure. Since the composition of the homogeneously dispersed system has few defective portions, deterioration of fatigue resistance due to stress concentration at the defective portions can be reduced. In addition to the above-mentioned characteristic requirements, by setting the DBP of the carbon black to the compounding amount of the chloroprene rubber to a specific value or more, the fatigue resistance can be improved without lowering the reinforcing property. Can be. DBP is an index indicating the size of the three-dimensionally connected structure (structure) of carbon black particles. The larger this value is, the easier it is to share when mixing and kneading the rubber, so that the dispersion in the rubber is reduced. It will be easier. Further, the reinforcing performance of carbon black is related not only to the colloidal properties but also to the amount of the carbon black, and when the amount of the carbon black is increased, the reinforcing property is improved.
However, in fact, as the compounding amount is increased, the dispersibility in the rubber phase is reduced, and poor dispersion is caused. Therefore, improvement in reinforcing property corresponding to the compounding amount cannot be obtained, and the compounding amount is increased more than necessary. However, when the amount is increased, the number of poorly dispersed parts increases, and the fatigue resistance is significantly reduced due to stress concentration. In the present invention, the DBP value of carbon black is adjusted to a value (1.38) corresponding to the blending amount A (parts by weight) in order to improve dispersibility.
× A + 72 or more) is used to efficiently exhibit the reinforcing effect of the carbon black, and at the same time reduce the number of poorly dispersed parts to improve fatigue resistance. As described above, according to the present invention, N ₂ SA is 60 m ² / g.
Hereinafter, when Dst is 130 nm or more and ΔDst / Dst is 0.1 nm or more.
In addition to the characteristic requirement of 95 or less, DBP is 1.38 × A +
By selecting a value equal to or greater than the relational expression of 72, the various properties of these carbon blacks function comprehensively, thereby maintaining the high reinforcing properties of the compounded rubber composition and effectively improving the fatigue resistance performance. Becomes possible. EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples. Examples 1 to 4 and Comparative Examples 1 to 3 (1) Production of carbon black: A combustion chamber (inner diameter 700 mm, length 1000 mm) whose outlet on the downstream side gently converges,
It has a cylindrical structure made of refractory brick lining that is continuous with a tapered reaction zone (length: 9000 mm) that expands through a narrow-diameter portion (inner diameter 250 mm, length 200 mm), and has a tangential air supply port at the furnace head. In a reactor equipped with a wind box equipped with a quench nozzle and a quench nozzle that can be repositioned in the downstream area of the rear reaction area, feed oil atomization with a double cylinder nozzle structure from the furnace head along the furnace center axis The injection nozzle was inserted, and four combustion burners were coaxially installed around the injection nozzle. The feedstock atomization injection nozzle was adjusted so that the feedstock introduction point on the upstream side (the ejection hole of the outer cylinder nozzle) was located at the convergent portion, and the feedstock introduction point on the downstream side was located at the narrow diameter portion. The feedstock oil is a high aromatic hydrocarbon oil having a specific gravity (15 ° C) of 1.10, a benzene-insoluble content of 0.03%, a correlation coefficient (BMCI) of 140, and an initial boiling point of 103 ° C. (15 ° C)
0.903, viscosity (CST50 ° C) 16.1, residual carbon content 5.
A hydrocarbon oil having 4%, a sulfur content of 1.8% and a flash point of 96 ° C was used. Using the above-mentioned reactor, raw oil and fuel oil, production conditions such as fuel oil supply, total raw oil introduction, upstream and downstream raw oil introduction, furnace residence time, reaction additive amount, etc. Was changed, and seven types (Examples 1-4 and Comparative Examples 1-3) of carbon black were produced. Tables 1 and 2 show the conditions for forming carbon black and the characteristics of the obtained carbon black in association with each other. [Table 1] <Table note> * 1 Combustion gas flow velocity at the downstream feedstock introduction position (the same applies hereinafter). * 2 The residence time of the generated carbon black-containing gas until the water cooling point (the same applies hereinafter). [Table 2] (2) Rubber compounding: Next, the compounding amount (parts by weight) A of each carbon black shown in Tables 1 and 2 was changed and compounded into chloroprene rubber. Table 3 shows the mixing ratio of other chemicals. The compound was vulcanized at a temperature of 150 ° C. for 40 minutes to obtain a rubber composition. [Table 3] <Table Note> * 1 "Neoprene W" (manufactured by Dupont, Showa Denko) * 2 "Axel 22-S" (manufactured by Kawaguchi Chemical Co., Ltd.) * 3 "Nocrack CD" [Ouchi Shinko Chemical ( (3) Rubber Property Test Various rubber tests were performed on each of the obtained rubber compositions.
The measured results are shown in Table 4 (Example) and Table 5 (Comparative Example) together with various properties of the carbon black. Table 6 (Reference Example) shows the results for commercial carbon black varieties. In addition, the measurement of the rubber property was based on the following. Hardness test; JIS K6253 “Hardness test method for vulcanized rubber” Tensile test: JIS K6251 “Tensile test method for vulcanized rubber” Rebound resilience test; Viscosity test; JIS K6300 “Physical test method for unvulcanized rubber” Fatigue test: Measured under the following conditions at room temperature in the atmosphere using a Fatigue tester manufactured by Monsanto Co. Test piece: 2mm thick, 78mm long, 25m long narrow part
m, width 4 mm (dumbbell-shaped, according to ASTM D4482-85) Elongation: 0 to 100% Tensile cycle: 100 cycles / minute Analysis method: The number of times to break is measured 24 times per sample, and the result is obtained. Was plotted on Weibull probability paper (Japanese Standards Association), which is widely used for life analysis, to determine mean time of failure (MTTF). [Table 4] [Table 5] [Table 6] <Table Note> Reference Example 1: "Seast S" manufactured by Tokai Carbon Co., Ltd. Reference Example 2: "Seast SO" manufactured by Tokai Carbon Co., Ltd. Reference Example 3: "Seast 3" manufactured by Tokai Carbon Co., Ltd. According to the results, the rubber composition of the example satisfying the property requirements specified in the present invention has significantly improved fatigue resistance (MTTF) as compared with the rubber composition of the comparative example, and has 100% modulus and tensile strength. It turns out that the reinforcing properties such as are compatible with a good balance. Further, it is recognized that the rubber composition of the reference example is significantly inferior in fatigue resistance to the example. Example 5 and Comparative Examples 4 and 5 The same carbon black as in Example 2 was used except that the amount of chloroprene rubber was changed, and the rubber compounding and rubber properties were the same as in Example 2. The test was performed and the results are shown in Table 7. The data of Example 2 is shown again. [Table 7] [DB] prepared based on the measurement results in Tables 4 to 7.
P− (1.38 × A + 72)] and the average life count (M
FIG. 3 shows a relationship graph of (TTF). From these results, it is clear that the rubber compositions of Examples satisfying the characteristic requirements of the present invention have significantly improved fatigue resistance as compared with the rubber compositions of Comparative Examples and Reference Examples. As described above, the fatigue-resistant rubber composition provided by the present invention, which uses chloroprene rubber as a target rubber component, maintains reinforcing properties and is significantly improved by the selective properties of compounded carbon black. Provided fatigue resistance. Therefore, it is extremely useful as a rubber composition used for various industrial rubber products requiring fatigue resistance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a distribution curve showing changes in absorbance due to centrifugal sedimentation of carbon black and the elapsed time from the addition of the carbon black dispersion during the measurement of Dst. FIG. 2 is a distribution curve showing the relationship between Dst and absorbance obtained when measuring Dst. FIG. 3 shows [DBP-] in Examples, Comparative Examples and Reference Examples.
(1.38 × A + 72)] and the average lifespan (MTT)
It is a dispersion diagram showing the relationship of F).

Claims (1)

(57) [Claims] [Claim 1] With respect to 100 parts by weight of chloroprene rubber,
20 to 1 carbon black having the following selective properties
A fatigue resistant rubber composition characterized by being blended with 00 parts by weight. (1) N ₂ SA (m ² / g) ≦ 60 (2) Dst (nm) ≧ 130 (3) ΔDst / Dst ≦ 0.95 (4) DBP (ml / 100g) ≧ 1.38 × A (PHR ) +72 where N ₂ SA is the nitrogen adsorption specific surface area, Dst is the Stokes mode diameter of the carbon black aggregate, ΔDst is the half width of the Stokes mode diameter, DBP is the DBP oil absorption, and A is the blending amount of carbon black (parts by weight). ).