MASTERBATCH MANUFACTURING METHOD AND TIRE MANUFACTURING METHOD

Abstract

To provide a method for producing a master batch which serves as a raw material for a vulcanized rubber excellent in low heat build-up properties and breaking strength.SOLUTION: The method for producing a master batch according to the present invention includes the steps of: dispersing carbon black in a dispersion medium in the presence of a surfactant having an aromatic ring to prepare a carbon black slurry; mixing at least the carbon black slurry and a rubber latex to prepare a mixed liquid; and coagulating the mixed liquid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a masterbatch and a method for producing a tire. [Background technology]

[0002] In rubber products such as pneumatic tires, improving the dispersibility of carbon black can improve the physical properties of vulcanized rubber, such as low heat buildup. The dispersibility of carbon black can be improved by preparing rubber products using a masterbatch in which carbon black is dispersed. The masterbatch can be prepared, for example, by mixing rubber latex and carbon black slurry and coagulating the mixture.

[0003] Patent Document 1 describes that a surfactant can be added to the carbon black slurry during the preparation of the masterbatch in order to improve the dispersion of the carbon black. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-175980 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not state that a surfactant was actually added to the carbon black slurry, and therefore does not substantiate that the addition of a surfactant improves the dispersibility of carbon black, nor does it substantiate that the addition of a surfactant improves the physical properties of vulcanized rubber.

[0006] An object of the present invention is to provide a method for producing a masterbatch, which is a raw material for vulcanized rubber that has excellent low heat buildup and breaking strength. In addition, an object of the present invention is to provide a method for producing a tire using the masterbatch produced by the method. Here, "breaking strength" is synonymous with tensile strength. Specifically, "breaking strength" refers to the maximum tensile force recorded when a vulcanized rubber (e.g., a test piece cut from the vulcanized rubber) is pulled until it breaks, divided by the cross-sectional area of ​​the vulcanized rubber before testing. [Means for solving the problem]

[0007] One of the means for solving this problem is the method for producing a masterbatch of the present invention, which comprises the steps of: a step of dispersing carbon black in a dispersion medium in the presence of a surfactant having an aromatic ring to prepare a carbon black slurry; a step of mixing at least the carbon black slurry and rubber latex to prepare a mixed liquid; and solidifying the mixture. Here, the term "dispersion medium" refers to a liquid containing water. The dispersion medium may be, for example, pure water, tap water, or water containing an organic solvent or chemicals.

[0008] In the method for producing a masterbatch of the present invention, carbon black is dispersed in a dispersion medium in the presence of a surfactant when preparing a carbon black slurry, and therefore, the carbon black can be highly dispersed.

[0009] Furthermore, because the surfactant has an aromatic ring, it is possible to disperse carbon black to a higher degree. This is thought to be because the aromatic ring of the surfactant interacts with the surface functional groups of the carbon black, thereby allowing the surfactant to be effectively adsorbed to the carbon black.

[0010] By mixing such carbon black slurry with rubber latex and coagulating the mixture, it is possible to produce a coagulum, i.e., crumb, in which the carbon black is highly dispersed. This means that the variation in the amount of carbon black per crumb (hereinafter sometimes referred to as "incorporation amount") can be reduced. As a result, the low heat buildup and breaking strength of the vulcanized rubber can be improved. In addition, it is also possible to shorten the time required to disperse the carbon black to a certain level (hereinafter sometimes referred to as "carbon black slurry processing time").

[0011] The surfactant preferably has a plurality of aromatic rings in the molecule.

[0012] This configuration can further improve the low heat buildup and breaking strength of the vulcanized rubber, which is believed to be because the surfactant has multiple aromatic rings, allowing the surfactant to be more effectively adsorbed onto the carbon black.

[0013] The surfactant is preferably a sodium salt of a β-naphthalenesulfonic acid formalin condensate.

[0014] This configuration can further improve the low heat buildup and breaking strength of the vulcanized rubber. This is thought to be because the sodium salt of β-naphthalenesulfonic acid formalin condensate has multiple naphthalene rings, which allows it to be more effectively adsorbed to carbon black.

[0015] The tire manufacturing method of the present invention includes: a step of preparing a masterbatch using the above-described manufacturing method; preparing a rubber composition using the masterbatch; and producing an unvulcanized tire using the rubber composition. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described.

[0017] <1. Masterbatch manufacturing method> The method for producing a masterbatch according to this embodiment includes the steps of preparing a carbon black slurry (hereinafter, sometimes referred to as "step A"); mixing at least the carbon black slurry and rubber latex to prepare a mixed liquid (hereinafter, sometimes referred to as "step B"); and solidifying the mixed liquid (hereinafter, sometimes referred to as "step C"). Because the method for producing a masterbatch according to this embodiment includes these steps, it is possible to produce a coagulum, i.e., crumbs, in which the carbon black is highly dispersed. This means that the variation in the amount of carbon black per crumb (i.e., the amount of carbon black incorporated) can be reduced. As a result, the low heat buildup and breaking strength of the vulcanized rubber can be improved. In addition, it is also possible to shorten the time required to disperse the carbon black to a certain level (i.e., the carbon black slurry processing time). The method for producing a masterbatch according to this embodiment can further include the step of dehydrating the coagulum (hereinafter, sometimes referred to as "step D").

[0018] <1.1. Step A (Step of Preparing Carbon Black Slurry)> In step A, carbon black slurry is prepared by dispersing carbon black in a dispersion medium in the presence of a surfactant having an aromatic ring. Carbon black is hydrophobic, but since the carbon black is dispersed in the dispersion medium in the presence of a surfactant, the carbon black can be highly dispersed.

[0019] Carbon black slurry can be prepared by adding a surfactant and carbon black to a dispersion medium and stirring the mixture. Alternatively, carbon black may be added to the dispersion medium after the surfactant has been added or dispersed, followed by stirring. Carbon black slurry can also be prepared by adding a surfactant to the dispersion medium after the carbon black has been added or dispersed, followed by stirring. A dispersing machine, such as a high-shear mixer, homomixer, ball mill, bead mill, high-pressure homogenizer, ultrasonic homogenizer, or colloid mill, can be used for stirring.

[0020] The surfactant has an aromatic ring. Specifically, the surfactant has an aromatic ring in its molecule. Because the surfactant has an aromatic ring, carbon black can be dispersed to a higher degree. This is thought to be because the aromatic ring of the surfactant interacts with the surface functional groups of the carbon black, thereby allowing the surfactant to effectively adsorb to the carbon black. Examples of aromatic rings include a benzene ring, a naphthalene ring, and an anthracene ring. Of these, a naphthalene ring and an anthracene ring are preferred, with a naphthalene ring being more preferred. When the surfactant has a condensed ring such as a naphthalene ring or an anthracene ring in its molecule, the low heat buildup and breaking strength of the vulcanized rubber can be further improved. This is thought to be because the surfactant has a condensed ring, allowing the surfactant to more effectively adsorb to the carbon black.

[0021] It is preferable that the surfactant has multiple aromatic rings in the molecule. Here, when the aromatic ring is a fused ring such as a naphthalene ring or anthracene ring, the fused ring is counted as one. Therefore, for example, if a surfactant has only one naphthalene ring in the molecule, the surfactant is considered to have one aromatic ring in the molecule. In other words, the surfactant is not considered to have multiple aromatic rings in the molecule. By having multiple aromatic rings in the molecule, the surfactant can further improve the low heat buildup and breaking strength of the vulcanized rubber. This is thought to be because the surfactant has multiple aromatic rings, which allows it to more effectively adsorb to carbon black.

[0022] As long as the surfactant has an aromatic ring, the type of surfactant is not particularly limited. The surfactant can be classified into, for example, anionic surfactants (i.e., anionic surfactants), cationic surfactants (i.e., cationic surfactants), zwitterionic surfactants, and nonionic surfactants. Among these, anionic surfactants are preferred.

[0023] In particular, the surfactant is preferably β-naphthalenesulfonic acid formalin condensate sodium salt. By using β-naphthalenesulfonic acid formalin condensate sodium salt as the surfactant, the low heat buildup and breaking strength of the vulcanized rubber can be further improved. This is thought to be because β-naphthalenesulfonic acid formalin condensate sodium salt has multiple naphthalene rings, which allows it to adsorb more effectively to carbon black. An example of β-naphthalenesulfonic acid formalin condensate sodium salt is commercially available from Kao Corporation under the name "Demol NL."

[0024] The amount of the surfactant is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the dispersion medium, and preferably 5 parts by mass or less, more preferably 2 parts by mass or less, per 100 parts by mass of the dispersion medium.

[0025] The dispersion medium is a liquid containing water. The dispersion medium may be, for example, pure water, tap water, or water containing an organic solvent or chemicals. The dispersion medium may also contain particles.

[0026] Examples of carbon black that can be used include furnace blacks such as SAF, ISAF, HAF, FEF, and GPF, as well as conductive carbon blacks such as acetylene black and ketjen black. The carbon black may be granulated carbon black, which is granulated in consideration of its handling properties, or ungranulated carbon black. One or more of these may be used.

[0027] The amount of carbon black in the carbon black slurry is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, based on 100% by mass of the carbon black slurry. The amount of carbon black in the carbon black slurry is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the carbon black slurry.

[0028] The carbon black slurry may contain a surfactant, a dispersing medium, and carbon black. In the carbon black slurry, the carbon black may be dispersed in the dispersing medium.

[0029] For carbon black slurries, the D90 of the carbon black, i.e., the particle size (volume basis) corresponding to 90% of the cumulative particle size distribution, can be used as an index of the dispersibility of the carbon black. The smaller the D90, the more highly dispersed the carbon black is. The D90 is preferably 6.0 μm or less, more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. The D90 may be, for example, 0.5 μm or more, or 1.0 μm or more. The D90 is a value measured by the method described in the Examples below.

[0030] <1.2. Step B (Step of Preparing Mixture)> In step B, at least the carbon black slurry and the rubber latex are mixed to prepare a mixed liquid. For this mixing, a dispersing machine such as a high-shear mixer, a homomixer, a ball mill, a bead mill, a high-pressure homogenizer, an ultrasonic homogenizer, or a colloid mill can be used.

[0031] The rubber latex is preferably a diene-based rubber latex. The diene-based rubber latex is a rubber latex containing diene-based rubber particles (hereinafter sometimes simply referred to as "rubber particles"). In the diene-based rubber latex, the diene-based rubber particles may be dispersed in a colloidal state in a dispersion medium. Specifically, in the diene-based rubber latex, the diene-based rubber particles may be dispersed in a colloidal state in water. The diene-based rubber latex may contain an organic solvent. Thus, the dispersion medium may be, for example, water containing an organic solvent. The diene-based rubber may have an unsaturated hydrocarbon bond, preferably a carbon-carbon double bond, in the main chain.

[0032] Examples of diene rubber latex include natural rubber latex and synthetic rubber latex, with natural rubber latex being preferred.

[0033] Examples of natural rubber latex include concentrated natural rubber latex and field latex. In natural rubber latex, rubber particles can be dispersed in a colloidal state in a dispersion medium. Specifically, in natural rubber latex, rubber particles can be dispersed in a colloidal state in water. Natural rubber latex may contain an organic solvent. Thus, the dispersion medium may be, for example, water containing an organic solvent.

[0034] The dry rubber content of the rubber latex is preferably 10% by mass or more, more preferably 20% by mass or more. The upper limit of the dry rubber content in the rubber latex is, for example, 60% by mass or 50% by mass.

[0035] The carbon black slurry and rubber latex may be mixed so that the amount of carbon black is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the dry rubber content of the natural rubber latex. This mixing may be performed so that the amount of carbon black is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less, per 100 parts by mass of the dry rubber content of the natural rubber latex.

[0036] <1.3. Step C (Step of solidifying the mixed liquid)>

[0037] In step C, the mixed liquid is coagulated. That is, the rubber particles and carbon black in the mixed liquid are coagulated. To coagulate the mixed liquid, a coagulant may be added to the mixed liquid. The coagulant is, for example, an acid. Examples of acids include formic acid and sulfuric acid. The coagulant may be added while stirring the mixed liquid, while heating the mixed liquid, or by any combination of these (i.e., stirring and heating). Of course, the mixed liquid may be coagulated without using a coagulant.

[0038] After coagulation, the coagulated material is separated from the waste liquid as needed. The coagulated material may be in the form of small pieces. These small pieces are sometimes called crumbs. A filter, for example, can be used to separate the coagulated material from the waste liquid.

[0039] <1.4. Step D (Step of Dehydrating the Coagulated Material)> In step D, the coagulated material is dehydrated. For example, an extruder, an oven, a vacuum dryer, or an air dryer can be used to dehydrate the coagulated material. Among these, an extruder is preferred. By using an extruder, the coagulated material can be dehydrated by an action such as squeezing, and the dehydrated coagulated material can be plasticized while being dried. An example of an extruder is a single-screw extruder.

[0040] <1.5. Other processes> The extruded coagulum, i.e., the dehydrated coagulum, is cut as needed and compression-molded into any desired shape (for example, a bale shape) as needed. For cutting, for example, a pelletizer can be used.

[0041] The masterbatch thus obtained can be in the form of a bale, but the masterbatch is not limited to a bale shape and may be in the form of, for example, a pellet, a rod, or a sheet.

[0042] The masterbatch includes a rubber component. The rubber component may include natural rubber. The amount of natural rubber in 100% by mass of the rubber component in the masterbatch may be, for example, 80% by mass or more, 90% by mass or more, or even 100% by mass.

[0043] The masterbatch may contain carbon black. The amount of carbon black is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. The amount of carbon black is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less, per 100 parts by mass of the rubber component.

[0044] <2. Tire manufacturing method> The tire manufacturing method of the present embodiment includes the steps of preparing a masterbatch by the above-described method, preparing a rubber composition using the masterbatch, and preparing an unvulcanized tire using the rubber composition.

[0045] <2.1. Step of preparing rubber composition using masterbatch> This process (specifically, the process of preparing a rubber composition using the masterbatch) can include kneading at least the masterbatch and compounding ingredients to prepare a rubber mixture, and kneading at least the rubber mixture and vulcanization-based compounding ingredients to obtain a rubber composition.

[0046] In this process, at least the masterbatch and compounding ingredients are kneaded to prepare a rubber mixture. Examples of compounding ingredients include fillers, zinc oxide, stearic acid, wax, antioxidants, silane coupling agents, and vulcanization-related compounding ingredients. The compounding ingredients can be selected from these ingredients alone or in any combination. However, it is preferable not to add vulcanization-related compounding ingredients at this stage. Examples of fillers include carbon black, silica, clay, talc, calcium carbonate, magnesium carbonate, and aluminum hydroxide. The fillers can be selected from these ingredients alone or in any combination. When carbon black is added at this stage, the properties of the carbon black may be the same as or different from those of the carbon black used in the carbon black slurry. For example, the grade of carbon black added at this stage may be the same as or different from the grade of carbon black used in the carbon black slurry, as specified by ASTM (American Society for Testing and Materials). Examples of antioxidants include aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, and thiourea-based antioxidants. One or any combination of these antioxidants can be selected and used. Other rubbers may be kneaded together with the masterbatch and compounding ingredients. Examples of such rubbers include natural rubber, polyisoprene rubber, styrene-butadiene rubber, nitrile rubber, and chloroprene rubber. One or any combination of these rubbers can be selected and used. Kneading can be performed using a kneader. Examples of kneaders include internal kneaders and open roll mixers. Examples of internal kneaders include Banbury mixers and kneaders.

[0047] In this process, at least a rubber mixture and vulcanization-related compounding agents are kneaded to obtain a rubber composition. Examples of vulcanization-related compounding agents include vulcanizing agents such as sulfur and organic peroxides, vulcanization accelerators, vulcanization accelerator aids, and vulcanization retarders. The vulcanization-related compounding agents can be selected from these, or any combination thereof. Examples of sulfur include powdered sulfur, precipitated sulfur, insoluble sulfur, and highly dispersible sulfur. Examples of sulfur can be selected from these, or any combination thereof. Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators. The vulcanization accelerators can be selected from these, or any combination thereof. Kneading can be performed using a kneader. Examples of kneaders include internal kneaders and open roll kneaders. Examples of internal kneaders include Banbury mixers and kneaders.

[0048] The rubber composition includes a rubber component derived from the masterbatch. The amount of the rubber component derived from the masterbatch can be, for example, 20% by mass or more, 40% by mass or more, 60% by mass or more, 80% by mass or more, or even 100% by mass, relative to 100% by mass of the rubber in the rubber composition.

[0049] The rubber composition contains carbon black. The amount of carbon black is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of rubber in the rubber composition. The amount of carbon black is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less, per 100 parts by mass of rubber in the rubber composition.

[0050] The rubber composition may further contain zinc oxide, stearic acid, wax, antioxidant, silica, silane coupling agent, sulfur, vulcanization accelerator, surfactant, etc. The rubber composition may contain one or any combination of these. The amount of sulfur is preferably 0.5 to 5 parts by mass in terms of sulfur content per 100 parts by mass of rubber in the rubber composition. The amount of vulcanization accelerator is preferably 0.1 to 5 parts by mass per 100 parts by mass of rubber in the rubber composition.

[0051] The rubber composition can be used to manufacture tires. Specifically, it can be used to manufacture tire components that constitute tires. For example, the rubber composition can be used to manufacture tread rubber, sidewall rubber, chafer rubber, bead filler rubber, etc. The rubber composition can be used to manufacture one or any combination of these tire components.

[0052] <2.2. Step of producing an unvulcanized tire using the rubber composition> The tire manufacturing method of this embodiment includes a step of producing an unvulcanized tire using a rubber composition. This step may include producing tire components including the rubber composition and producing an unvulcanized tire including the tire components. Examples of tire components include tread rubber, sidewall rubber, chafers, and bead fillers. Among these, tread rubber is preferred.

[0053] <2.3. Other processes> The tire manufacturing method of the present embodiment may further include a step of vulcanizing and molding the unvulcanized tire. The tire obtained by the method of the present embodiment may be a pneumatic tire.

[0054] <3. Various modifications can be made to the above-described embodiment> The above-described embodiment can be modified in various ways. For example, the above-described embodiment can be modified by selecting one or more of the following modifications.

[0055] In the above-described embodiment, a configuration in which water is used as a dispersion medium to prepare a carbon black slurry has been described in detail. However, the above-described embodiment is not limited to this configuration. For example, a dilute rubber latex may be used instead of water. For example, a carbon black slurry can be prepared by adding a surfactant and carbon black to a dilute rubber latex and stirring the mixture. Alternatively, the carbon black may be added to the dilute rubber latex after the surfactant has been added or dispersed, followed by stirring the mixture. The carbon black slurry may also be prepared by adding a surfactant to the dilute rubber latex after the carbon black has been added or dispersed, followed by stirring the mixture. In the dilute rubber latex, rubber particles may be dispersed in a colloidal state in water. The water may be, for example, water containing an organic solvent. The dry rubber content of the dilute rubber latex is preferably 0.1% by mass or more, more preferably 0.3% by mass or more. The upper limit of the dry rubber content is preferably 5% by mass, more preferably 2% by mass. The dilute rubber latex can be prepared, for example, by diluting natural rubber latex with water. Synthetic rubber latex may be used in place of natural rubber latex.

[0056] In the above-described embodiment, a configuration in which a masterbatch and compounding ingredients are mixed to prepare a rubber mixture has been described. However, the above-described embodiment is not limited to this configuration. For example, the rubber mixture may be regarded as a masterbatch.

[0057] In the above-described embodiment, the tire is a pneumatic tire. However, the above-described embodiment is not limited to this configuration. [Example]

[0058] Examples of the present invention will be described below.

[0059] The raw materials and chemicals used in the examples are listed below. Surfactant A "Demol NL" manufactured by Kao Corporation Anionic surfactants β-Naphthalenesulfonic acid formalin condensate sodium salt Surfactant B "Emulgen A060" manufactured by Kao Corporation Nonionic surfactants Natural rubber latex "NR Field Latex" manufactured by Golden Hope Solid natural rubber "NR Field Latex" manufactured by Golden Hope Dry solid rubber Carbon black "Diablack A" manufactured by Mitsubishi Chemical Corporation Zinc oxide "Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid "Stearic acid" manufactured by NOF Corporation Wax "OZOACE0355" manufactured by Nippon Seiro Co., Ltd. Anti-aging agent A "Santoflex 6PPD" manufactured by Flexis Anti-aging agent B "Nocrac 224" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur "Oil Treatment 150 Mesh Powdered Sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator "Suncerer NS-G" manufactured by Sanshin Chemical Industry Co., Ltd.

[0060] Preparation of Masterbatch in Comparative Example 1 Carbon black was added to solid natural rubber and then kneaded to obtain a masterbatch.

[0061] Preparation of Masterbatch in Comparative Example 2 Carbon black and a surfactant were added to solid natural rubber and then kneaded to obtain a masterbatch.

[0062] Preparation of Masterbatch in Comparative Example 3 30 parts by mass of carbon black was added to 100 parts by mass of water and stirred at room temperature using a PRIMIX Robomix to prepare a carbon black slurry. Natural rubber latex was added to the carbon black slurry according to the formulation shown in Table 1, and the mixture was stirred at 90°C using a Kawata Super Mixer SMV-20 mixer to obtain a mixed solution. Formic acid was added as a coagulant to the mixed solution until the pH reached 4, yielding a coagulated product. The coagulated product was dehydrated using a Suehiro EPM V-02 screw press (squeezer-type single-screw extruder / dehydrator) and discharged at 120°C. A masterbatch was thus obtained.

[0063] Preparation of Masterbatches in Example 1 and Comparative Example 4 30 parts by weight of carbon black and 1 part by weight of surfactant were added to 100 parts by weight of water and stirred at room temperature using a PRIMIX Robomix to prepare a carbon black slurry. Natural rubber latex was added to the carbon black slurry according to the formulation shown in Table 1, and the mixture was stirred at 90°C using a Kawata Super Mixer SMV-20 mixer to obtain a mixed solution. Formic acid was added as a coagulant to the mixed solution until the pH reached 4, yielding a coagulated product. The coagulated product was dehydrated using a Suehiro EPM V-02 screw press (squeezer-type single-screw extruder / dehydrator) and discharged at 120°C. A masterbatch was thus obtained.

[0064] Preparation of unvulcanized rubber in each example The compounding ingredients except for sulfur and vulcanization accelerator were added to the masterbatch according to Table 1 and kneaded in a Banbury mixer (i.e., non-pro kneading) to obtain a rubber mixture. The rubber mixture, sulfur, and vulcanization accelerator were kneaded in a Banbury mixer (i.e., pro kneading) to obtain unvulcanized rubber.

[0065] Preparation of vulcanized rubber The unvulcanized rubber was vulcanized at 150°C for 30 minutes to obtain a vulcanized rubber.

[0066] tanδ The tan δ of the vulcanized rubber was measured in accordance with JIS K-6394 2007. Specifically, it was measured using a viscoelasticity tester manufactured by Toyo Seiki Seisakusho, under conditions of a temperature of 60°C, a frequency of 10 Hz, a static strain of 10%, and a dynamic strain of 1%. Table 1 shows the tan δ of each example, with the tan δ of Comparative Example 1 set as an index of 100. A smaller index indicates lower heat buildup and better tire fuel economy performance.

[0067] Tensile strength (i.e. breaking strength) The tensile strength of the vulcanized rubber was measured in accordance with JIS K-6251 2017. Specifically, dumbbell-shaped test pieces of dumbbell size 3 were cut out from the vulcanized rubber, and the tensile force of the dumbbell-shaped test pieces was measured using a tensile tester to determine the tensile strength (i.e., the maximum tensile force recorded when the test piece was pulled until it broke, divided by the cross-sectional area of ​​the test piece before the test). The tensile strength of each example is shown in Table 1, with the tensile strength of Comparative Example 1 set as an index of 100. A larger index indicates a higher tensile strength.

[0068] Carbon black slurry particle size distribution (D90) Water was added to the carbon black slurries prepared in Comparative Examples 3 and 4 and Example 1 to prepare diluted solutions containing 0.005% by mass of carbon black. The D90 of these diluted solutions was determined using an image analysis particle size distribution analyzer (Jasco International Inc., "IF-3200" with analysis software "PIA-Pro Image Analysis Software ver. 2016" under measurement conditions: cell thickness 50 μm, sample concentration 0.005% by weight, cumulative particle number analyzed 15,000 to 30,000 particles). That is, the particle size (volume basis) corresponding to 90% of the cumulative particle size distribution was determined. The D90 values, expressed in μm, are shown in Table 1.

[0069] [Table 1]

[0070] The vulcanized rubbers of Example 1 and Comparative Example 4, in which the carbon black slurries were prepared with the addition of a surfactant, had smaller tan δ and greater tensile strength than the vulcanized rubber of Comparative Example 3, in which the carbon black slurries were prepared without the addition of a surfactant. This is thought to be because the dispersion of the carbon black was improved by the surfactant, as the D90 of the carbon black slurries of Example 1 and Comparative Example 4 was smaller than the D90 of Comparative Example 3.

[0071] The vulcanized rubber of Example 1, in which the carbon black slurry was prepared using surfactant A, had a smaller tan δ and a greater tensile strength than the vulcanized rubber of Comparative Example 4, in which the carbon black slurry was prepared using surfactant B. This is thought to be because the D90 of the carbon black slurry of Example 1 was smaller than that of Comparative Example 4, and surfactant A enabled the carbon black to be dispersed to a higher degree.

Claims

1. a step of dispersing carbon black in a dispersion medium in the presence of a surfactant having an aromatic ring to prepare a carbon black slurry; a step of mixing at least the carbon black slurry and rubber latex to prepare a mixed liquid; and solidifying the mixture, In the carbon black slurry, the particle size (volume basis) of the carbon black corresponding to 90% of the cumulative particle size distribution is 1.0 μm or more and 4.0 μm or less. Masterbatch manufacturing method.

2. The method for producing a masterbatch according to claim 1 , wherein the surfactant has a plurality of the aromatic rings in the molecule.

3. The method for producing a masterbatch according to claim 1 or 2, wherein the surfactant is a sodium salt of a β-naphthalenesulfonic acid formalin condensate.

4. a step of producing a masterbatch by the method for producing a masterbatch according to any one of claims 1 to 3; preparing a rubber composition using the masterbatch; and producing an unvulcanized tire using the rubber composition. Tire manufacturing method.

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