MASTERBATCH MANUFACTURING METHOD AND TIRE MANUFACTURING METHOD

Abstract

To provide a method for producing a masterbatch capable of efficiently reducing the moisture content of a coagulated product.SOLUTION: There is provided a method for producing a masterbatch which comprises a step of mixing at least a filler slurry and a natural rubber latex to prepare a mixed solution and a step of adding a coagulant into the mixed solution so that the pH is 5.0 or more and less than 8.0. Since a coagulant is added into the mixed solution so that the pH is 5.0 or more, the moisture content of a coagulated product can be efficiently reduced. The surface properties of a coagulated product become a state having adhesiveness suitable for pressing or kneading (for example, a state having suitable adhesiveness capable of reducing or suppressing a slip which may occur during pressing or kneading by an extruder) by adding a coagulant into the mixed solution so that the pH is 5.0 or more, as a result, it is believed that a coagulated product can be efficiently pressed and kneaded.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] When manufacturing rubber products such as tires, wet masterbatches are sometimes used to improve the dispersibility of fillers (e.g., carbon black) and improve processability (see, for example, Patent Documents 1 to 3). Wet masterbatches can be manufactured, for example, by mixing natural rubber latex with fillers, co-coagulating the rubber particles and fillers in the natural rubber latex, and then squeezing, drying, and plasticizing the coagulated product. For squeezing, drying, and plasticizing, the coagulated product can be put into an extruder, for example.

[0003] It is known that coagulants are used to coagulate the rubber particles and fillers in natural rubber latex. In natural rubber latex, such as concentrated natural rubber latex, the pH is adjusted to a high level, for example, around pH 9 to 10, to suppress spontaneous coagulation. Therefore, the pH is lowered by using a coagulant, which removes the negative charge of the rubber particles (i.e., removes the electrical repulsion between the rubber particles), allowing the rubber particles to aggregate.

[0004] When a coagulant is used, it is common to add it until the pH reaches about 4 (see, for example, Patent Document 2). This is because the isoelectric point of the rubber particles in natural rubber latex (strictly speaking, the isoelectric point of the protein that covers the rubber particles) is pH 4.5. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-328135 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-222765 [Patent Document 3] Special table number 2000-507892 Summary of the Invention [Problem to be solved by the invention]

[0006] Meanwhile, it is desirable to establish a method for efficiently reducing the water content of the coagulated product in the process of producing a wet masterbatch, because efficient reduction of the water content of the coagulated product leads to reduction in the energy and time required to dry the coagulated product.

[0007] An object of the present invention is to provide a method for producing a masterbatch that can efficiently reduce the water content of the coagulated product. [Means for solving the problem]

[0008] The method for producing a masterbatch of the present invention, which is a means for solving this problem, comprises the steps of: mixing at least a filler slurry and natural rubber latex to prepare a mixed liquid; and adding a coagulant to the mixture so that the pH is 5.0 or higher but lower than 8.0.

[0009] The method for producing a masterbatch of the present invention involves the steps of mixing a filler slurry and natural rubber latex and then adding a coagulant to the mixture, and therefore the filler can be dispersed to a higher degree than when the filler is added to natural rubber and kneaded in a Banbury mixer (i.e., when dry kneading is performed).

[0010] Furthermore, because the coagulant is added to the mixed solution so that the pH is 5.0 or higher, the water content of the coagulated material can be reduced efficiently. This is thought to be because, by adding the coagulant to the mixed solution so that the pH is 5.0 or higher, the surface properties of the coagulated material become a state of appropriate stickiness for squeezing and kneading (for example, a state of appropriate stickiness that can reduce or suppress slippage that can occur during squeezing and kneading in an extruder), and as a result, the coagulated material can be effectively squeezed and kneaded.

[0011] Furthermore, since the coagulant is added to the mixed liquid so that the pH is less than 8.0, the coagulated material can be prevented from becoming excessively sticky. As a result, for example, when the coagulated material is put into an extruder, the inlet of the extruder can be prevented from being clogged with the coagulated material.

[0012] The method for producing a tire 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

[0013] Hereinafter, an embodiment of the present invention will be described.

[0014] <1. Masterbatch manufacturing method> The method for producing a masterbatch of this embodiment includes at least a step of mixing a filler slurry and natural rubber latex to prepare a mixed liquid (hereinafter, sometimes referred to as "step A"), and a step of adding a coagulant to the mixed liquid (hereinafter, sometimes referred to as "step B"). Because the method for producing a masterbatch of this embodiment includes steps A and B, the filler can be dispersed to a higher degree than when the filler is added to natural rubber and kneaded in a Banbury mixer (i.e., when dry kneading is performed). The method for producing a masterbatch of this embodiment can further include a step of dehydrating the coagulated product (hereinafter, sometimes referred to as "step C").

[0015] <1.1. Step A (Step of Preparing Mixture)> In step A, at least a filler slurry and natural rubber latex are mixed to prepare a mixed liquid.

[0016] Step A can include a step of adding one of the filler slurry and the natural rubber latex to the other (hereinafter sometimes referred to as "Step A1"), and a step of stirring this while heating (hereinafter sometimes referred to as "Step A2").

[0017] <1.1.1. Step A1 (Step of Adding Either Filler Slurry or Natural Rubber Latex to the Other)> In step A1, one of the filler slurry and the natural rubber latex is added to the other. That is, the filler slurry and the natural rubber latex are mixed. In the method of adding the other to either the filler slurry or the natural rubber latex, one can be added to the other while stirring the other. For example, the natural rubber latex can be added to the filler slurry while stirring the filler slurry. Conversely, the filler slurry can be added to the natural rubber latex while stirring the natural rubber latex. In the method of adding the other to either the filler slurry or the natural rubber latex, one stream (e.g., the natural rubber latex stream) can be merged with the other stream (e.g., the filler slurry stream). Incidentally, to add one to the other, the other stream can be caused to collide with the other at a speed of less than 370 m / s, for example, 360 m / s or less. Of course, they can also be caused to collide at a speed of 370 m / s or more. Furthermore, stirring can be performed after adding the other to the other.

[0018] The filler slurry can contain a filler and water. The filler slurry can be obtained by adding a filler to water and stirring. For stirring, a dispersing machine such as a high-shear mixer, homomixer, ball mill, bead mill, high-pressure homogenizer, ultrasonic homogenizer, colloid mill, etc. can be used. The filler slurry may contain other additives, such as an organic solvent and a surfactant, as necessary.

[0019] Examples of fillers include carbon black, silica, clay, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide, zeolite, and mica. One or any combination of these may be selected and used. It is preferable to use at least carbon black as the filler.

[0020] 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.

[0021] When the filler slurry contains carbon black, the amount of carbon black in the filler slurry 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 filler in the filler slurry.

[0022] In the following description, a filler slurry containing carbon black may be referred to as a carbon black slurry. The carbon black slurry may contain a filler other than carbon black in addition to carbon black.

[0023] Examples of natural rubber latex include concentrated natural rubber latex and field latex. These can be diluted before use as needed. 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.

[0024] The dry rubber content of the natural 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 natural rubber latex is, for example, 60% by mass or 50% by mass.

[0025] It is preferable to combine the filler slurry and natural rubber latex so that the amount of filler per 100 parts by mass of the dry rubber content of the natural rubber latex is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more.It is preferable to combine the two so that the amount of filler per 100 parts by mass of the dry rubber content of the natural rubber latex is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less.

[0026] <1.1.2. Step A2 (Step of stirring while heating)> In step A2, the liquid prepared in step A1, i.e., a liquid prepared by adding one of the filler slurry and natural rubber latex to the other, is heated and stirred. This allows the filler slurry and natural rubber latex to be mixed, i.e., blended, and promotes co-coagulation of the rubber particles and filler. To heat and stir this liquid, a mixing vessel equipped with agitating blades is preferably used. Of these, a mixing vessel having a mechanism in which the agitating blades rotate inside a cylindrical container is preferred. Examples of mixing vessels equipped with agitating blades include the "Super Mixer" manufactured by Kawata Corporation, the "Super Mixer" manufactured by Shin-ei Machinery Works, the "Universal Mixer" manufactured by Tsukishima Machine Sales, and the "Henschel Mixer" manufactured by Nippon Coke and Engineering Co., Ltd.

[0027] In step A2, the amount of heat imparted to the mixed solution by heating, specifically, the amount of heat per unit time and unit mass, is preferably 25 J or more. When the amount is 25 J or more, the co-coagulation can be promoted to a certain extent by the thermal energy. On the other hand, this amount of heat is preferably 250 J or less. When the amount is 250 J or less, excessive co-coagulation can be suppressed. As a result, deterioration of the dispersibility of the filler, which may be caused by excessive co-coagulation, can be avoided. In order to set this amount of heat to 25 J or more and 250 J or less, for example, the heating temperature is preferably 70°C to 180°C and the stirring time while heating is preferably 5 to 60 minutes, and more preferably the heating temperature is 80°C to 160°C and the stirring time while heating is 10 to 45 minutes.

[0028] The peripheral speed of the stirring blade is preferably less than 10 m / s. When the peripheral speed is less than 10 m / s, excessive co-coagulation can be suppressed. As a result, deterioration of the dispersibility of the filler, which may be caused by excessive co-coagulation, can be avoided.

[0029] <1.2. Step B (Step of adding coagulant to the mixed liquid)> In step B, a coagulant is added to the mixture to adjust the pH to 5.0 or higher but less than 8.0. Adding the coagulant to adjust the pH to 5.0 or higher effectively reduces the water content of the coagulated material. This is thought to be because adding the coagulant to adjust the pH to 5.0 or higher gives the coagulated material a surface with a suitable stickiness for squeezing and kneading (e.g., a suitable stickiness that reduces or inhibits slippage during squeezing and kneading in an extruder), thereby enabling effective squeezing and kneading of the coagulated material. Adding the coagulant to adjust the pH to less than 8.0 prevents the coagulated material from becoming excessively sticky, which, for example, prevents the extruder inlet from clogging with the coagulated material when the coagulated material is fed into the extruder.

[0030] In step B, the coagulant is preferably added to the mixed solution so that the pH is 5.1 or higher. In step B, the coagulant is preferably added to the mixed solution so that the pH is less than 7.8, more preferably less than 7.6, and even more preferably less than 7.4.

[0031] The coagulant is not particularly limited as long as it can lower the pH of the mixed solution. Examples of the coagulant include acids. Examples of acids include formic acid and sulfuric acid. The coagulant may be added while stirring the mixed solution, while heating the mixed solution, or by any combination of these (i.e., stirring and heating).

[0032] 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.

[0033] <1.3. Step C (Step of Dehydrating the Coagulated Material)> In step C, the coagulated material is dehydrated. In step C, it is preferable to compress the coagulated material and then plasticize it while drying it.

[0034] To dehydrate the coagulated material, for example, an extruder, an oven, a vacuum dryer, or an air dryer can be used. Among these, an extruder is preferred. By using an extruder, the coagulated material can be compressed and then kneaded. That is, the coagulated material can be compressed and then plasticized while drying. An example of an extruder is a single-screw extruder.

[0035] The loss on heating after dehydration is preferably 1.5% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.8% by mass or less. The loss on heating is measured and calculated by the method described in the Examples.

[0036] <1.4. Other processes> The dehydrated coagulum is cut as needed and compression molded into any desired shape as needed. For cutting the coagulum, for example, a pelletizer can be used.

[0037] 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 sheet.

[0038] The masterbatch includes a rubber component containing natural rubber. In the masterbatch, the amount of natural rubber in 100% by mass of the rubber component can be, for example, 80% by mass or more, 90% by mass or more, or even 100% by mass.

[0039] The masterbatch may contain a filler. The amount of the filler is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the rubber component. The amount of the filler is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of the rubber component.

[0040] In the masterbatch, the amount of carbon black in 100% by mass of the filler 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.

[0041] <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.

[0042] <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.

[0043] In this process (specifically, the process of preparing a rubber composition using a masterbatch), 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. Examples of fillers can be selected from these ingredients alone or in any combination. 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. The antioxidants can be selected from these ingredients alone or in any combination. 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 may be selected and used. Kneading can be performed using a kneading machine. Examples of kneading machines include internal kneaders and open rolls. Examples of internal kneading machines include Banbury mixers and kneaders.

[0044] In this process (specifically, the process of preparing a rubber composition using a masterbatch), at least a rubber mixture and vulcanization-related compounding agents are kneaded to obtain a rubber composition. Examples of the 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, either individually or in any combination. Examples of sulfur include powdered sulfur, precipitated sulfur, insoluble sulfur, and highly dispersible sulfur. Examples of sulfur can be selected from these, either individually or in any combination. 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, either individually or in any combination. The kneading can be performed using a kneader. Examples of the kneader include an internal kneader and an open roll. Examples of the internal mixer include a Banbury mixer and a kneader.

[0045] In this way, this step (specifically, the step of producing a rubber composition using the masterbatch) can include at least non-productive mixing and productive mixing.

[0046] 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 component in the rubber composition.

[0047] The rubber composition may contain a filler. The amount of the filler is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the rubber component in the rubber composition. The amount of the filler is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, even more preferably 70 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of the rubber component in the rubber composition.

[0048] In the rubber composition, the amount of carbon black in 100% by mass of the filler 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.

[0049] The rubber composition may further contain zinc oxide, stearic acid, wax, antioxidant, silica, silane coupling agent, sulfur, vulcanization accelerator, 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 the rubber component in the rubber composition. The amount of vulcanization accelerator is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component in the rubber composition.

[0050] 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.

[0051] <2.2. Step of producing an unvulcanized tire using the rubber composition> The tire manufacturing method of the present embodiment includes a step of producing an unvulcanized tire using the 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, chafer rubber, and bead filler rubber.

[0052] <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.

[0053] <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.

[0054] In the above-described embodiment, a configuration in which water is used to prepare the filler slurry has been described. However, the above-described embodiment is not limited to this configuration. For example, dilute rubber latex may be used instead of water. Specifically, the filler slurry may be prepared by adding a filler to dilute rubber latex and stirring the mixture. In dilute rubber latex, rubber particles may be dispersed in water in a colloidal state. 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 instead of natural rubber latex.

[0055] In the above-described embodiment, step A2 is described as a step of stirring a liquid prepared by adding one of the filler slurry and the natural rubber latex to the other while heating. However, the above-described embodiment is not limited to this. For example, step A2 may be a step of stirring the liquid (i.e., the liquid prepared by adding the other of the filler slurry and the natural rubber latex) without heating it.

[0056] In the above-described embodiment, the tire is a pneumatic tire. However, the above-described embodiment is not limited to this configuration. [Example]

[0057] Examples of the present invention will be described below. Note that, hereinafter, the masterbatch may be referred to as "MB."

[0058] The raw materials and chemicals used in the examples are listed below. Concentrated natural rubber latex (dry rubber content = 31.2% Mw = 232,000) manufactured by Golden Hope Carbon black "Seast 9" manufactured by Tokai Carbon Co., Ltd.

[0059] Preparation of master batches for each example Water was added to concentrated natural rubber latex manufactured by Golden Hope Rubber Industries to prepare a diluted natural rubber latex with a dry rubber content of 0.5% by mass and a natural rubber latex with a dry rubber content of 25% by mass. Carbon black was added to this diluted natural rubber latex, and the mixture was stirred at 3,600 rpm for 30 minutes using a Silverson "Flashblend" mixer to prepare a carbon black slurry (hereinafter, this step may be referred to as "step (I)"). Natural rubber latex with a dry rubber content of 25% by mass was added to this carbon black slurry according to Table 1 (i.e., natural rubber latex was added to the carbon black slurry so as to obtain the formulation in Table 1), and the mixture was stirred under heating using a Kawata mixer (Supermixer SMV-20) under the conditions shown in Table 1 (hereinafter, this step may be referred to as "step (II)"). Next, while stirring the mixture, a coagulant, specifically a 10% by mass aqueous solution of formic acid (pH 1.2), was added to the mixture until the pH reached the value shown in Table 1 (hereinafter, this step may be referred to as "step (III)"). The coagulated material thus formed was separated from the coagulated liquid (i.e., waste liquid). The coagulated material was dehydrated at 200°C using a squeezer-type single-screw extruder (Suehiro EPM Co., Ltd., V-02 screw press). That is, the coagulated material was squeezed using the squeezer-type single-screw extruder, and then plasticized while drying at 200°C. A masterbatch was obtained using this procedure.

[0060] Heating loss As an index of the efficiency of reducing the moisture content, the loss on heating of the coagulated product after dehydration, i.e., the loss on heating of the masterbatch, was evaluated. Specifically, the loss on heating of the masterbatch was measured in accordance with JIS K6238-2 using an A&D heat-drying moisture meter MX-50. In other words, the volatile content was measured in accordance with JIS K6238-2. The smaller the loss on heating, the lower the moisture content of the coagulated product after dehydration, i.e., the lower the moisture content of the masterbatch. Heating weight loss = {(mass of MB before heating - mass of MB after heating) / mass of MB before heating} x 100

[0061] Inlet clogging The squeezer type single screw extruder dehydrator was operated for 20 minutes, and it was recorded whether clogging of the inlet occurred or not.

[0062] [Table 1] Table 1 will be explained in more detail below. The "heating temperature in step (II)" is the heating temperature, that is, the temperature at the end of stirring in step (II). The "amount of heat in step (II)" is the amount of heat per unit time and unit mass imparted to the mixed solution by heating in step (II). This amount of heat was calculated using the following formula. Amount of heat = (Temperature at the end of stirring [K] - Temperature at the start of stirring [K]) x Specific heat [J / kg K] / Stirring time [sec] In addition, "-" in the loss on heating column indicates that the measurement was not performed.

[0063] In Comparative Example 1, in which coagulant was added until the pH reached 4.2, the loss on heating was 2.5%. On the other hand, in Example 1, in which coagulant was added until the pH reached 5.2, the loss on heating was only 0.4%. In Example 2, in which coagulant was added until the pH reached 6.9, the loss on heating was also only 0.4%. In Comparative Example 2, in which coagulant was added until the pH reached 8.5, clogging of the inlet occurred. This is thought to be because the coagulated product produced in Comparative Example 2 was more viscous than the other examples (i.e., Comparative Example 1, Example 1, and Example 2).

[0064] In Examples 3 and 4, in which the coagulant was added until the pH reached 5.1 or 7.2, the loss on heating was smaller than in Comparative Example 3, in which the coagulant was added until the pH reached 4.0. In Comparative Example 4, in which the coagulant was added until the pH reached 8.6, clogging of the inlet occurred. This is thought to be because the coagulated product produced in Comparative Example 4 was more viscous than in the other examples (i.e., Comparative Example 3, Example 3, and Example 4).

[0065] In Examples 5 and 6, in which the coagulant was added until the pH reached 5.4 or 7.2, the loss on heating was smaller than in Comparative Example 5, in which the coagulant was added until the pH reached 4.3. In Comparative Example 6, in which the coagulant was added until the pH reached 8.5, clogging of the inlet occurred. This is thought to be because the coagulated product produced in Comparative Example 6 was more viscous than in the other examples (i.e., Comparative Example 5, Example 5, and Example 6).

Claims

1. mixing at least a filler slurry and natural rubber latex to prepare a mixed liquid; adding a coagulant to the mixture so that the pH is 7.2 or more and less than 8.0; In the step of adding the coagulant to the mixed solution, the mixed solution contains a filler, and the filler consists solely of carbon black. Masterbatch manufacturing method.

2. a step of preparing a masterbatch by the method for producing a masterbatch according to claim 1; preparing a rubber composition using the masterbatch; and producing an unvulcanized tire using the rubber composition. Tire manufacturing method.

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