Carbon black for use in rubber compositions for tires

Abstract

To provide a rubber composition which enables manufacture of a vulcanized rubber which is excellent in abrasion resistance and breaking strength, and is excellent in workability, and a tread and a tire which is excellent in abrasion resistance and breaking strength.SOLUTION: There is provided a carbon black used for a rubber composition for a tire in which an oil absorption amount is 120-143 mL / 100 g, an oil absorption amount by a compressive sample is 105-122 mL / 100 g, a difference in the oil absorption amount between the oil absorption amount and the compressive sample is 11-33 mL / 100 g, a specific surface area of cetyltrimethylammonium bromide is 130-153 m2 / g, a hydrogen generation amount is 2,300-3,500 ppm, and a ratio (ΔD50 / Dst) of a half-value width ΔD50 of a peak including a most frequent size Dst of aggregate distribution obtained by a centrifugal sedimentation method to the Dst is 0.75 to 0.88.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to carbon black for use in rubber compositions for tires. [Background technology]

[0002] In recent years, in response to social demands for energy and resource conservation, tires with low rolling resistance are required to reduce automobile fuel consumption. In response to such demands, a known method for reducing the rolling resistance of tires is to use a rubber composition with reduced hysteresis loss, i.e., low heat buildup, in tire components, particularly tread rubber, by reducing the amount of carbon black used or using low-grade carbon black. However, simply reducing the amount of carbon black used can reduce the abrasion resistance of the vulcanized rubber. While tire rolling resistance can be improved by increasing the proportion of polybutadiene rubber in the rubber component or by increasing the elasticity of the vulcanized rubber, this leaves room for further consideration in terms of the tear resistance of the tire. Various studies have been conducted to address these issues.

[0003] For example, a rubber composition that can reduce rolling resistance while improving abrasion resistance and wet performance when applied to tire components such as treads has been disclosed, which comprises (A) a rubber component; (B) carbon black for rubber compounding, obtained by using a reactor having a combustion gas generation zone, a reaction zone, and a reaction termination zone connected in series, generating high-temperature combustion gas in the combustion gas generation zone, and then spraying raw materials into the reaction zone to quench the reaction gas flow containing the carbon black and terminate the reaction; (C) an organosilicon compound that has, in its molecule, a cyclic structure containing a nitrogen atom and a silicon atom and one or more sulfur atoms, and has a site where one or more groups with little steric hindrance are bonded to the silicon atom; and (D) an inorganic filler, wherein the carbon black for rubber compounding satisfies a certain relationship (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-87173 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the invention disclosed in Patent Document 1 achieved a certain degree of success in improving the mechanical properties of vulcanized rubber, the processability of the vulcanized rubber tends to decrease, and further improvement is an ongoing challenge. In view of the above circumstances, an object of the present invention is to provide a carbon black suitable for a rubber composition for tires, which can produce tires that achieve higher levels of abrasion resistance, breaking strength, and processability. [Means for solving the problem]

[0006] A carbon black for use in a rubber composition for tires, the carbon black having an oil absorption of 120 to 143 mL / 100 g, an oil absorption of 105 to 122 mL / 100 g as measured by a compressed sample, a difference between the oil absorption and the oil absorption of 11 to 33 mL / 100 g as measured by a compressed sample, and a cetyltrimethylammonium bromide specific surface area of ​​130 to 153 m 2 / g, the amount of hydrogen generated is 2300 to 3500 ppm, and the ratio (ΔD50 / Dst) of the mode diameter Dst of the aggregate distribution obtained by centrifugal sedimentation to the half-value width ΔD50 of the peak including the Dst is 0.75 to 0.88. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide carbon black suitable for a rubber composition for a tire, which can give a tire that combines high levels of abrasion resistance, breaking strength, and processability. [Brief explanation of the drawings]

[0008] [Figure 1]FIG. 1 is a partial vertical sectional front view illustrating an example of a carbon black production furnace for producing carbon black. DETAILED DESCRIPTION OF THE INVENTION

[0009] The carbon black of the present invention has the following properties (1) to (6). (1) The oil absorption capacity is 120 to 143 mL / 100 g. (2) The oil absorption of the compressed sample is 105 to 122 mL / 100 g. (3) The difference between the oil absorption amount and the oil absorption amount by the compressed sample is 11 to 33 mL / 100 g. (4) Cetyltrimethylammonium bromide specific surface area is 130-153m 2 / g. (5) The amount of hydrogen generated is 2300 to 3500 ppm. (6) The ratio (ΔD50 / Dst) of the mode diameter Dst of the aggregate distribution obtained by centrifugal sedimentation to the half-value width ΔD50 of the peak containing Dst is 0.75 to 0.88.

[0010] Carbon black having the properties (1) to (6) may be referred to as "carbon black of the present invention." "Oil absorption" is sometimes abbreviated as "OAN." "Oil absorption by compressed specimen" is sometimes abbreviated as "COAN." The difference between the oil absorption amount and the oil absorption amount by the compressed sample is sometimes referred to as "ΔOAN." "Cetyltrimethylammonium bromide specific surface area" is sometimes referred to as "CTAB specific surface area" or simply abbreviated as "CTAB."

[0011] The carbon black of the present invention, which satisfies the above requirements (1) to (6) simultaneously, can provide a rubber composition for tires that can improve breaking strength without impairing abrasion resistance and suppress deterioration of processability. Although the reason for this is unclear, it is thought that the effects of the present invention can be achieved by improving abrasion resistance through high hydrogenation, high ΔOAN, and uniform aggregate distribution, and by selecting OAN and CTAB in a balanced manner. The carbon black of the present invention and the rubber composition containing the carbon black will be described in detail below.

[0012] [Rubber component] The rubber component generally used in tires includes at least one diene rubber selected from the group consisting of natural rubber (NR) and synthetic diene rubber. Specific examples of synthetic diene rubbers include synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), butadiene-isoprene copolymer rubber (BIR), styrene-isoprene copolymer rubber (SIR), and styrene-butadiene-isoprene copolymer rubber (SBIR). The diene rubber is preferably natural rubber, synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), or isobutylene-isoprene rubber, and more preferably natural rubber or butadiene rubber. The diene rubber may be used alone or in a blend of two or more.

[0013] The rubber component may contain either natural rubber or synthetic diene rubber, or both, but from the viewpoint of further improving abrasion resistance and strength at break, the rubber component preferably contains at least natural rubber. From the same viewpoint, the proportion of natural rubber in the rubber component is preferably 50% by mass or more, more preferably 55% by mass or more.

[0014] [Carbon black] The carbon black of the present invention is not particularly limited as long as it has the above-mentioned properties (1) to (6), and one type may be used alone, or two or more types may be mixed and used.

[0015] (1) OAN The carbon black of the present invention has an OAN of 120 to 143 mL / 100 g. OAN is the volume (mL) of paraffin oil or other liquid absorbed per 100g of carbon black, and is an index of the degree of development of the aggregate structure made up of primary particles of carbon black. If the OAN is less than 120 mL / 100 g, the aggregate structure will not develop sufficiently and the rubber reinforcement will not be obtained, and if it exceeds 143 mL / 100 g, the aggregate structure will develop excessively, the dispersibility of the carbon black will deteriorate, and the effect of improving physical properties will not be obtained. From this viewpoint, the OAN of carbon black is 120 to 143 mL / 100 g, preferably 125 to 141 mL / 100 g, and more preferably 127 to 140 mL / 100 g. The OAN is measured by the method described in ASTM D2414-21 (JIS K6217-4:2017).

[0016] (2) COAN The carbon black of the present invention has a COAN of 105 to 122 mL / 100 g. The COAN is the OAN measured after applying a pressure of 24,000 psi four times. The COAN is measured according to the method described in ASTM D3493-21 ​​(JIS K6217-4:2017).

[0017] This COAN is an index used to evaluate the skeletal structure of carbon black, which is primarily composed of a primary structure, and is used to determine the OAN based on the true, non-destructive structural form (primary structure), excluding the OAN due to the deformable or destructive structural form (secondary structure) caused by so-called van der Waals forces.

[0018] If the COAN is less than 105 mL / 100 g, the rubber trapping force is not increased and the abrasion resistance of the tire is impaired, whereas if the COAN is more than 122 mL / 100 g, the viscosity of the rubber composition increases and the processability decreases. From this viewpoint, the COAN is 105 to 122 mL / 100 g, preferably 107 to 120 mL / 100 g, and more preferably 107 to 118 mL / 100 g.

[0019] (3)ΔOAN The carbon black of the present invention has a difference (ΔOAN) between the OAN and the COAN of 11 to 33 mL / 100 g. ΔOAN is an index of the surface activity of carbon black. If ΔOAN is less than 11 mL / 100 g, the surface activity is low, resulting in less interaction between the rubber component and the carbon black, resulting in reduced abrasion resistance of the vulcanized rubber. If ΔOAN is more than 33 mL / 100 g, the surface activity is too high, resulting in excessive interaction with the rubber component, causing the vulcanized rubber to lose its softness and reduce processability. From this viewpoint, the ΔOAN is 11 to 33 mL / 100 g, preferably 15 to 30 mL / 100 g, and more preferably 17 to 29 mL / 100 g.

[0020] (4)CTAB specific surface area The carbon black of the present invention has a CTAB specific surface area of ​​130 to 153 m 2 / g. The CTAB specific surface area of ​​carbon black is 130m 2 If the viscosity is less than 153 m / g, the vulcanized rubber will not be excellent in abrasion resistance and breaking strength. 2 If the CTAB specific surface area exceeds 132 m / g, the rubber composition will not have good processability. 2 / g or more, and 134m 2 From the viewpoint of further improving the processability of the rubber composition, the CTAB specific surface area of ​​the carbon black is preferably 150 m / g or more. 2 / g or less, and 148m 2It is more preferable that the saturation coefficient is 1 / g or less. The CTAB specific surface area of ​​carbon black can be measured by a method in accordance with JIS K6217-3:2001.

[0021] (5) Amount of hydrogen generated The carbon black of the present invention generates hydrogen in an amount of 2300 to 3500 ppm. If the amount of hydrogen generated is less than 2300 ppm, the surface activity is low and the interaction between the rubber component and carbon black is reduced, resulting in a decrease in the abrasion resistance of the vulcanized rubber.If the amount of hydrogen generated is more than 3500 ppm, the surface activity is too high and excessive interaction with the rubber component occurs, causing the vulcanized rubber to lose its softness and reduce processability. From this viewpoint, the amount of hydrogen generated is preferably 2400 to 3400 ppm by mass, more preferably 2450 to 3200 ppm by mass, and even more preferably 2500 to 3000 ppm by mass.

[0022] In the present invention, the amount of hydrogen generated means the amount of hydrogen gas generated (ppm by mass) when carbon black is heated in an inert gas atmosphere at 2000°C for 15 minutes using a high-sensitivity hydrogen analyzer (EMGA621W manufactured by Horiba, Ltd., using a TCD detector). More specifically, the amount of hydrogen generated can be measured based on the following steps (i) to (iii). (i) Dry the carbon black in a thermostatic oven at 125°C for 1 hour and then cool it to room temperature (23°C) in a desiccator. (ii) Accurately weigh out approximately 20 mg of the carbon black obtained in (i) and place it in a tin tubular sample container, which is then crimped and sealed. (iii) Using a hydrogen analyzer, measure the amount of hydrogen gas generated when the sample container is heated to 2000°C for 15 minutes under an argon stream.

[0023] (6) ΔD50 / Dst The carbon black of the present invention has a ratio (ΔD50 / Dst) of the mode diameter Dst of the aggregate distribution obtained by centrifugal sedimentation to the half-value width ΔD50 of the peak including Dst of 0.75 to 0.88. Dst refers to the aggregate diameter giving the most frequent aggregate distribution obtained using centrifugal sedimentation according to the method described in JIS K6217-6:2019. ΔD50 (nm) is the width of the distribution when the frequency is half the height of the maximum point on the aggregate distribution curve obtained by centrifugal sedimentation.

[0024] If ΔD50 / Dst exceeds 0.88, the breaking strength may not be maintained, and if ΔD50 / Dst is less than 0.75, the dispersibility of carbon black in the vulcanized rubber composition deteriorates, impairing the processability of the rubber composition. From the viewpoint of further reducing the rolling resistance of the tire, ΔD50 / Dst is preferably from 0.77 to 0.87, more preferably from 0.78 to 0.86, and even more preferably from 0.79 to 0.85.

[0025] The carbon black of the present invention is not particularly limited as long as it can be produced by any method that can produce carbon black having the above properties (1) to (6), but it is preferable to follow the production method described below. The interior of a carbon black production furnace has a structure in which a combustion zone, a reaction zone, and a reaction termination zone are connected together, and the entire structure is covered with a refractory material. The carbon black production furnace includes, as a combustion zone, a combustible fluid introduction chamber, an oxygen-containing gas introduction cylinder that uses a flow straightening vane to straighten the oxygen-containing gas introduced from the outer periphery of the furnace head through an oxygen-containing gas introduction pipe and introduces the gas into the combustible fluid introduction chamber, and a fuel oil sprayer introduction pipe that is installed on the central axis of the oxygen-containing gas introduction cylinder and introduces a hydrocarbon fuel into the combustible fluid introduction chamber. In the combustion zone, high-temperature combustion gas is generated by combustion of the hydrocarbon fuel.

[0026] The carbon black production furnace comprises, as a reaction zone, a converging chamber with a gradually converging cylindrical shape, a feedstock oil introduction chamber downstream of the converging chamber that includes, for example, four feedstock oil spray ports, and a reaction chamber downstream of the feedstock oil introduction chamber. The feedstock oil spray ports introduce feedstock hydrocarbons by spraying into the high-temperature combustion gas flow from the combustion zone. In the reaction zone, the feedstock hydrocarbons are introduced by spraying into the high-temperature combustion gas flow, and are converted into carbon black by incomplete combustion or a pyrolysis reaction.

[0027] FIG. 1 is a partial longitudinal sectional front view of an example of a carbon black production furnace for producing the carbon black for rubber compounding, showing a reaction chamber 10 into which high-temperature gas containing the carbon black raw material (raw material hydrocarbon) is introduced, and a reaction continuation and cooling chamber 11. As shown in FIG. 1, the carbon black production furnace 1 is equipped with the reaction continuation and cooling chamber 11 having a multi-stage quench medium introduction means 12 as a reaction termination zone. The multi-stage quench medium introduction means 12 sprays a quench medium such as water onto the high-temperature combustion gas flow from the reaction zone. In the reaction termination zone, the high-temperature combustion gas flow is quenched by the quench medium to terminate the reaction. The carbon black production furnace 1 may further include a device for introducing a gas into the reaction zone or the reaction termination zone. Here, the "gas" may be air, a mixture of oxygen and hydrocarbons, or a combustion gas produced by a combustion reaction of these, etc.

[0028] The combustion zone is the region where a high-temperature gas stream is generated by the reaction of fuel and air, and its downstream end refers to the point where the feedstock oil is introduced into the reactor (the most upstream point if it is introduced at multiple points), for example, the upstream side of the point where the feedstock oil is introduced (the left side in Figure 1). The reaction zone refers to the region from the point where the feed hydrocarbon is introduced (the most upstream in the case of multiple locations) to the point where the multistage quench medium introduction means 12 in the reaction continuation and cooling chamber 11 is activated (where a quench medium such as water is introduced) (these means are freely inserted and removed within the reaction continuation and cooling chamber 11, and their locations are selected depending on the type and characteristics of the product). That is, for example, if feed oil is introduced through the third feed oil spray port and water is introduced through the multistage quench medium introduction means 12, the region between these two points constitutes the reaction zone. The reaction terminating zone refers to the region below (to the right in FIG. 1 ) the point where the quench water injection spray means is activated. In FIG. 1, the term "reaction continuation and cooling chamber 11" is used because the region from the introduction of raw materials to the activation of the means for injecting and spraying quenching water for terminating the reaction is the reaction zone, and the region thereafter is the reaction terminating zone, and the position where the quenching water is introduced may be moved depending on the required carbon black performance.

[0029] The vulcanized rubber obtained from the rubber composition containing the carbon black of the present invention exhibits high levels of abrasion resistance, breaking strength, and processability, which are usually contradictory properties, and can therefore be used in a variety of rubber products, such as tires, vibration-proof rubber, seismic isolation rubber, belts such as conveyor belts, rubber crawlers, and various hoses. [Example]

[0030] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0031] [Method for producing carbon black] Using a carbon black production furnace as shown in Figure 1, each carbon black was produced under the conditions shown in Table 2. Heavy oil A with a specific gravity of 0.8622 (15°C / 4°C) was used as fuel, and heavy oil with the properties shown in Table 1 was used as feedstock.

[0032] [Table 1]

[0033] [Table 2]

[0034] Here, the OAN and COAN are controlled by adjusting the amount of KOH. The ΔOAN is controlled by adjusting the amount of quench water. The CTAB is controlled by adjusting the amount of raw material introduced and the amount of air introduced. The amount of hydrogen generated is controlled by adjusting the reaction time. In addition, ΔD50 / Dst is controlled by adjusting the amount of air introduced. However, the above manufacturing conditions are merely examples, and as long as the desired values ​​can be obtained, manufacturing can be carried out under other manufacturing conditions, or the desired values ​​can be achieved by adjusting other manufacturing conditions.

[0035] The physical properties of the carbon black obtained under the above production conditions are shown in Table 3.

[0036] [Table 3]

[0037] The properties of each carbon black were determined by the following methods.

[0038] (1) OAN The OAN was measured according to the method described in ASTM D2414-21 (JIS K6217-4:2017). (2) COAN The COAN was measured according to the method described in ASTM D3493-21 ​​(JIS K6217-4:2017).

[0039] (3)ΔOAN ΔOAN was calculated as the difference between the OAN and COAN.

[0040] (4)CTAB specific surface area CTAB specific surface area (m 2 / g) was measured by a method in accordance with JIS K 6217-3:2001.

[0041] (5) Amount of hydrogen generated The carbon black was dried in a thermostatic oven at 125°C for 1 hour and then cooled to room temperature (23°C) in a desiccator. Approximately 20 mg of the resulting carbon black was precisely weighed and placed in a tin tube-shaped sample container, which was then sealed with a crimp. Using a high-sensitivity hydrogen analyzer, the amount of hydrogen gas generated was measured when the sample container was heated to 2000°C for 15 minutes under an argon stream.

[0042] (6) Aggregate distribution by centrifugal sedimentation (ΔD50 / Dst) Dst and ΔD50 (nm) were measured according to the method described in JIS K6217-6:2019. From these measurement results, ΔD50 / Dst was calculated.

[0043] <Preparation of Rubber Composition> To evaluate the performance of each carbon black, rubber compositions were prepared according to conventional methods using the components shown in Table 4. Details of each component in Table 4 are as follows. RSS#1: Ribbed Smoked Sheet No. 1 MBTS: 2,2'-dibenzothiazyl disulfide IPPD: N-isopropyl-N-phenyl-p-phenylenediamine

[0044] [Table 4]

[0045] <Rubber manufacturing and evaluation> The rubber compositions were evaluated for processability. Furthermore, the rubber compositions were vulcanized to prepare vulcanized rubber test pieces, and the abrasion resistance and breaking strength were evaluated. The results are shown in Table 5.

[0046] 1. Abrasion resistance Using the test pieces, a DIN abrasion test was carried out in accordance with JIS K6264-2:2005. The abrasion loss (mm 3 ) was measured. The reciprocal of each wear amount is shown as an index, assuming that the reciprocal of the wear amount in Comparative Example 1 is 100. A larger index value indicates better wear resistance.

[0047] 2. Breaking strength The tensile strength at break (TB) of the vulcanized rubber was measured based on JIS K 6251:2017 as the maximum tensile force required to stretch the vulcanized rubber at room temperature (25°C) and break it. The breaking strength of the vulcanized rubber of Comparative Example 1 was set to 100, and the breaking strengths of the Examples and Comparative Examples other than Comparative Example 1 were expressed as an index. The higher the index, the greater the breaking strength of the vulcanized rubber. The acceptable range is 99 or more, and preferably 102 or more.

[0048] 3. Processability The viscosity of the rubber compositions of the Examples and Comparative Examples was measured at 130°C in accordance with JIS K 6300-1:2013 (Mooney viscosity), and the viscosity of each rubber composition was expressed as an index, with the viscosity of the rubber composition of Comparative Example 1 being set at 100. The larger the index value, the better the processability of the rubber composition. The acceptable range is 101 or more.

[0049] [Table 5]

[0050] As is clear from Table 5, the vulcanized rubbers using the carbon blacks of the Examples achieved high levels of abrasion resistance, breaking strength, and processability. Furthermore, the vulcanized rubbers using the carbon blacks of the Comparative Examples did not achieve high breaking strength and processability, despite having the same level of abrasion resistance as the vulcanized rubbers of the Examples, and therefore did not achieve a high level of both. Therefore, if the rubber compositions of the Examples are used in the manufacture of treads and tires, treads and tires with excellent abrasion resistance and breaking strength can be manufactured. [Industrial Applicability]

[0051] By using a rubber composition containing the carbon black of the present invention, it is possible to obtain vulcanized rubber that is excellent in abrasion resistance and breaking strength without impairing the processability of the rubber composition. Therefore, the carbon black of the present invention is suitable for use in rubber compositions used in the production of tire cases, tread members, etc. for various tires for passenger cars, light passenger cars, light trucks, and heavy loads {for trucks and buses, and off-the-road tires (for mining vehicles, construction vehicles, small trucks, etc.)}. [Explanation of symbols]

[0052] 1. Carbon black manufacturing furnace 10 Reaction chamber 11 Reaction continuation and cooling chamber 12 Multistage quench medium introduction means

Claims

【Request Item 1】 The oil absorption is 125 to 143 mL / 100 g, the oil absorption by a compressed sample is 107 to 120 mL / 100 g, the difference between the oil absorption and the oil absorption by a compressed sample is 17 to 29 mL / 100 g, and the cetyltrimethylammonium bromide specific surface area is 132 to 150 m ２ / g, the amount of hydrogen generated is 2500 to 3000 ppm, and the ratio (ΔD50 / Dst) of the mode diameter Dst of the aggregate distribution obtained by centrifugal sedimentation to the half-value width ΔD50 of the peak including the mode diameter Dst is 0.79 to 0.88.

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