Carbon black and highly electrically resistive rubber composition

Abstract

To provide carbon black capable of achieving both high electric resistance and rebound resilience at a high level when compounding rubber, and a rubber composition obtained by compounding the same.SOLUTION: (1) Carbon black subjected to oxidation has 4-11 of the ratio Ta / Tb of the total acidity (Ta) after the oxidation to the total acidity (Tb) before the oxidation; (2) the (1) carbon black has a nitrogen adsorption specific surface area (N2SA) of 25-35 m2 / g; (3) the carbon black described in (1) or (2) is used for a high electric resistance and high rebound resilience rubber composition; and (4) a high electric resistance rubber composition is obtained by compounding any of carbon blacks (1)-(3).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a highly electrically resistive carbon black and a highly electrically resistive rubber composition containing the carbon black. [Background technology]

[0002] In recent years, automobile manufacturers have been working to improve fuel efficiency in order to reduce environmental impact. While the use of aluminum to reduce the weight of automobile structural materials has been considered an effective solution, it is also known that the use of various aluminum components can lead to new problems, such as electrolytic corrosion. To prevent electrolytic corrosion, insulation, or increasing the volume resistivity, is necessary. For example, in automotive parts such as weatherstrips and hoses, an attempt has been made to address this issue by increasing the resistivity of the carbon black filler used.

[0003] Generally, carbon black tends to have low electrical resistance due to its electrical conductivity resulting from the conjugation of π electrons. However, various methods have been attempted to inhibit this electrical conductivity and achieve high electrical resistance. For example, methods such as coating the carbon black surface with a highly electrically resistive resin (Patent Document 1) and introducing functional groups onto the carbon black surface (Patent Document 2) have been proposed. However, neither method takes into account the fact that the reactive sites are destroyed when the carbon black is compounded into rubber, resulting in a decrease in the compounded rubber's physical properties (e.g., rebound resilience). Another method (Patent Document 3) attempts to achieve both high electrical resistance and physical properties during compounding by specifying the morphology, particle hardness, etc. of the carbon black. However, due to these restrictions, high electrical resistance cannot be achieved with a wide range of carbon blacks, resulting in a lack of versatility. High electrical resistance is required for a variety of components, and technologies that can be applied to the various carbon blacks required to meet these requirements are still being investigated. For example, Patent Document 4 proposes that by setting the ratio of the total acidity of carbon black before and after oxidation treatment and the ratio of the strong acidity to the total acidity after oxidation treatment within a specific range, it is possible to achieve both high electrical resistance and high reinforcing properties (hardness) at the time of compounding rubber. Meanwhile, in the field of vibration-damping rubber and the like, components that have high electrical resistance as well as high impact resilience are required, and technology that can meet this requirement is still being investigated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-249678 [Patent Document 2] Patent No. 4464081 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-49144 [Patent Document 4] Japanese Patent Publication No. 2021-134297 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a carbon black which, when compounded with rubber, achieves both high electrical resistance and high impact resilience, and a rubber composition containing the carbon black. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above problems can be solved by the following inventions (1) to (5). (1) Carbon black that has been subjected to an oxidation treatment, characterized in that the ratio Ta / Tb of the total acidity after the oxidation treatment (Ta) to the total acidity before the oxidation treatment (Tb) is 4 to 11. (2) Carbon black according to (1), having a nitrogen adsorption specific surface area (N2SA) of 25 to 32 m 2 / g of carbon black. (3) Carbon black according to (1) or (2), characterized in that it is a carbon black for use in a rubber composition having high electrical resistance and high resilience. (4) A highly electrically resistive rubber composition containing any one of the carbon blacks (1) to (3). (5) A method for producing carbon black for a rubber composition having high electrical resistance and high resilience, characterized by subjecting carbon black to an oxidation treatment, and adjusting the ratio Ta / Tb of the total acidity (Ta) after the oxidation treatment to the total acidity (Tb) before the oxidation treatment to 4 to 11. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide carbon black which, when compounded with rubber, enables both high electrical resistivity and high impact resilience to be achieved, and a highly electrically resistive rubber composition containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will now be described in detail. To the best of the inventor's knowledge, no prior art attempt has been made to achieve both high electrical resistivity and excellent rubber properties, particularly rebound resilience, when compounded with rubber by defining a specific relationship between the total acidity and strong acidity of the carbon black surface, as in the present invention. Furthermore, the present invention presents the optimal conditions for achieving this, resulting in a carbon black with completely novel properties that exhibits remarkable effects not achievable with conventional carbon blacks. The carbon black of the present invention having such novel properties can be obtained by, for example, a general oxidation method, such as an air oxidation method in which the carbon black is brought into contact with and reacted with air in a high-temperature atmosphere, a method in which the carbon black is reacted with nitrogen oxides, ozone, or the like at room temperature, or a liquid-phase oxidation method. The oxidation method is not particularly limited, but it is important to take into account the physical properties of the original carbon black and adjust the oxidation conditions to fall within the desired range specified in the present application.

[0009] <ta tb> The total acidity represents the amount of oxygen-containing functional groups on the carbon black surface, and the surface properties defined thereby affect the electrical resistance of the carbon black and the rebound resilience of the compounded rubber, which is derived from its interaction with rubber. In the present invention, Ta / Tb, the ratio calculated from the total acidity after oxidation treatment (Ta) to the total acidity before oxidation treatment (Tb), is 4 to 11. If Ta / Tb is smaller than the specified lower limit, functional groups are not sufficiently added, resulting in a small increase in electrical resistance. On the other hand, if Ta / Tb is larger than the specified upper limit, electrical resistance increases, but the addition of functional groups is excessive, resulting in a decrease in rebound resilience. By keeping the degree of change in the total acidity after oxidation treatment (Ta) relative to the total acidity before oxidation treatment (Tb) within the above range, the rebound resilience of the compounded rubber can be appropriately improved and maintained while increasing electrical resistance. From the viewpoint of increasing the increase in electrical resistance and further suppressing a decrease in rebound resilience, Ta / Tb is preferably 5.1 to 11, and more preferably 5.5 to 9.

[0010] <n2sa> Nitrogen adsorption specific surface area (N2SA) is the specific surface area (m2) per unit weight of carbon black. 2 The carbon black of the present invention is not particularly limited as long as Ta / Tb is in the above range, but N2SA is preferably 25 to 35 m 2 If the specific surface area is less than the lower limit of the specified value, the specific surface area may be too small, and sufficient functional groups may not be imparted to the carbon black, whereas if the specific surface area is greater than the upper limit of the specified value, the specific surface area may be too large, and excessive functional groups may be imparted to the carbon black, and / or the physical properties may be adversely affected due to poor dispersion of the carbon black itself.

[0011] The carbon black of the present invention can be used as a carbon black for use in a rubber composition having high electrical resistance and high resilience, i.e., a rubber composition having high electrical resistance and high resilience. In the present invention, a rubber composition having high electrical resistance and high resilience is one having a volume resistivity of 1.0×10 7 Ωcm or more, and high resilience means that the rubber composition has a resilience modulus of 52.5% or more. Volume resistivity can be measured by the method described in JIS K6271-1:2015, and resilience modulus can be measured by the method described in JIS K6255:2013. When the carbon black of the present invention is compounded with rubber, a rubber composition having the above-described volume resistivity and resilience modulus can be prepared. In one embodiment of the carbon black of the present invention, when a rubber composition is prepared by compounding 100 parts by mass of ethylene propylene diene rubber (EPDM), 80 parts by mass of oil, and 120 parts by mass of carbon black, the volume resistivity of the rubber composition is 2.0 × 10 7 Ωcm or more, rebound resilience of 52.5% or more, and preferably volume resistivity of 5.0×10 7 It can be defined as carbon black having a viscosity of Ωcm or more and a rebound resilience of 53.0% or more.

[0012] The method for producing carbon black of the present invention is characterized by subjecting carbon black to an oxidation treatment to adjust the ratio Ta / Tb, where Ta is the total acidity after the oxidation treatment and Tb is the total acidity before the oxidation treatment, to 4 to 11. This allows for the production of carbon black for rubber compositions with high electrical resistance and high rebound resilience. Ta / Tb is preferably 5.1 to 11, and more preferably 5.5 to 9. According to the production method of the present invention, carbon black that does not achieve high levels of both electrical resistance and rebound resilience during rubber compounding can be used to produce the carbon black of the present invention, which achieves both high levels of electrical resistance and rebound resilience during rubber compounding. Furthermore, the modification method of the present invention is characterized by subjecting carbon black to an oxidation treatment to adjust the ratio Ta / Tb, where Ta is the total acidity after the oxidation treatment and Tb is the total acidity before the oxidation treatment, to 4 to 11. This allows for the modification of carbon black that does not achieve high levels of both electrical resistance and rebound resilience during rubber compounding into the carbon black for rubber compositions with high electrical resistance and high rebound resilience of the present invention, which achieves both high levels of electrical resistance and rebound resilience during rubber compounding. The oxidation treatment method is not particularly limited, and examples thereof include the air oxidation method, which is a common oxidation method in which the carbon black is brought into contact with and reacted with air in a high-temperature atmosphere, a method in which the carbon black is reacted with nitrogen oxides or ozone at room temperature, and a liquid-phase oxidation method. The carbon black used in the oxidation treatment is not particularly limited, and common carbon black can be used, but carbon black with a nitrogen adsorption specific surface area (N2SA) of 25 to 32 m2 is preferred. 2 Carbon black having a total acidity of 0.006 to 0.048 is preferred.

[0013] The high-electrical resistance rubber composition of the present invention is a rubber composition blended with the carbon black of the present invention. The rubber in the present invention is not particularly limited, but examples thereof include natural rubber, styrene-butadiene rubber, isoprene rubber, chloroprene rubber, ethylene-propylene-diene copolymer rubber, butyl rubber, halogenated butyl rubber, and acrylonitrile-butadiene rubber. These rubbers may be used alone or in any combination to form a blended rubber. The high-electrical resistance rubber composition of the present invention may also contain additives commonly used in rubber compositions, and the amount of carbon black blended can be appropriately selected depending on the rubber characteristics and the desired properties. The high-electrical resistance rubber composition of the present invention can be produced by blending and kneading rubber, the carbon black of the present invention, and, if necessary, other components such as additives, using a commonly used method. [Example]

[0014] EXAMPLES The present invention will be explained in more detail below by showing examples and comparative examples, but the present invention is not limited to these examples in any way.

[0015] Examples 1 to 7, Comparative Examples 1 to 5 <Carbon black production> Reference example (OAN: 125ml / 100g, N2SA: 30m 2 Carbon black having a total acidity of 0.07 to 0.19 after oxidation treatment was obtained in the examples. The oxidation treatment was simply carried out by a gas-phase oxidation method using ozone gas. The physicochemical properties of the obtained carbon black are shown in Table 1.

[0016] [Table 1]

[0017] The properties shown in Table 1 above were measured by the following methods. (1) OAN absorption Measurement was performed according to the method described in JIS K6217-4:2017. (2)N2SA Measurement was performed according to the method described in JIS K6217-2:2017. (3) Total acidic groups 1g of carbon black was weighed out, 50ml of 1 / 250N sodium hydroxide solution was added, and the mixture was boiled at 100°C for 2 hours in a flask fitted with a reflux condenser. 25ml of the supernatant was then titrated with 1 / 500N hydrochloric acid. A blank test was also carried out at the same time, and the total amount of acidic groups (meq / g) was calculated from the difference between the two.

[0018] Each rubber for evaluation was prepared by compounding and kneading in a conventional manner using each carbon black shown in Table 1 according to the formulation shown in Table 2. The evaluation results are shown in Table 3.

[0019] [Table 2]

[0020] [Table 3]

[0021] The properties shown in Table 3 above were measured by the following methods. (1) Rebound elasticity Measurement was performed according to the method described in JIS K6255:2013. (2) Volume resistivity Measurement was performed according to the method described in JIS K6271-1:2015.

[0022] As is clear from the evaluation results in Table 3, the rubbers made using the carbon black of the present invention have a 10% improvement over the rubbers made using the carbon blacks of the Reference Examples and Comparative Examples. 2 ~10 6 It shows high volume resistivity, maintains rebound resilience, and exhibits a certain level of improvement, demonstrating that it has achieved both high electrical resistivity and excellent rubber properties. [Industrial Applicability]

[0023] The carbon black of the present invention can be suitably used in rubber compositions that require both a high rebound resilience and an increased volume resistivity, and the highly electrically resistive rubber composition of the present invention can be suitably used in applications such as automotive weather strips and rubber hoses. < / ta>

Claims

1. Carbon black that has been subjected to an oxidation treatment, characterized in that the ratio Ta / Tb of the total acidity (Ta) after the oxidation treatment to the total acidity (Tb) before the oxidation treatment is 7.74 to 11, and the nitrogen adsorption specific surface area (N 2 SA) is 25 to 35 m 2 / g.

2. 2. The carbon black according to claim 1, which is used in a rubber composition having high electrical resistance and high resilience.

3. A highly electrically resistive rubber composition containing the carbon black according to claim 1 or 2.

4. A method for producing carbon black for use in a rubber composition having high electrical resistance and high resilience, comprising oxidizing carbon black to obtain carbon black having a ratio Ta / Tb of 7.74 to 11, where Ta is the total acidity after the oxidation treatment and Tb is the total acidity before the oxidation treatment, and N 2 SA is 25 to 35 m 2 / g.

5. A method for modifying carbon black, which comprises oxidizing carbon black having a nitrogen adsorption specific surface area (N 2 SA) of 25 to 32 m 2 / g, so that the ratio Ta / Tb of the total acidity after the oxidation treatment (Ta) to the total acidity before the oxidation treatment (Tb) is 7.74 to 11.

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