Method for producing rubber composition, method for producing tire, and apparatus for producing rubber composition

Abstract

To provide a method for manufacturing a rubber composition, and a method for manufacturing a tire capable of improving low heat generation property, wet road-surface braking performance, and wear resistance of the tire, and also to provide an apparatus for manufacturing such the rubber composition.SOLUTION: A method for manufacturing a rubber composition includes a step of kneading at least a rubber, a silica, and a silane coupling agent in a closed kneader 1 at a lower limit temperature or more at which a coupling reaction between the silica and the silane coupling agent proceeds. The method introduces compressed gas into a kneading chamber 4 while a ram 7 is unpressed for at least a part of time during the step. This enables efficient discharge of a volatile matter, generated in a process of the coupling reaction, out of the kneading chamber 4, thereby enabling efficient proceeding of the coupling reaction, to enable decrease of cohesive force of the silica. As a result, the method can improve low heat generation property, wet road-surface braking performance, and wear resistance of a tire.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a rubber composition, a method for producing a tire, and an apparatus for producing a rubber composition. [Background technology]

[0002] Silica, which is used as a reinforcing filler for rubber, has silanol groups and tends to aggregate through hydrogen bonding. Therefore, it is not easy to disperse silica well, especially when high silica loadings or small particle sizes are used.

[0003] It is known to use a silane coupling agent to reduce the cohesive force of silica. The silane coupling agent can react with silica during kneading, thereby preventing the silica from coagulating. In addition, the silane coupling agent can react with the double bond of rubber, for example, during vulcanization, thereby bonding silica and rubber.

[0004] Patent Document 1 describes a method for reducing the cohesive force of silica by controlling the kneading temperature to a temperature equal to or higher than the lower limit temperature at which the coupling reaction between silica and a silane coupling agent proceeds, and then kneading with the ram elevated. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-102721 Summary of the Invention [Problem to be solved by the invention]

[0006] The method described in Patent Document 1 reduces the cohesive force of silica (i.e., increases the dispersion of silica), and as a result, the low heat buildup of tires and braking performance on wet roads (hereinafter referred to as "wet road braking performance") can be improved. However, there is still room for improvement in this method.

[0007] An object of the present invention is to provide a method for producing a rubber composition that can improve the low heat buildup, wet road braking performance, and abrasion resistance of a tire, and a tire production method, and also to provide an apparatus for producing such a rubber composition. [Means for solving the problem]

[0008] In order to solve this problem, the method for producing a rubber composition of the present invention includes the steps of: The method includes a step of kneading at least rubber, silica, and a silane coupling agent in an internal kneader at a temperature equal to or higher than the lower limit temperature at which a coupling reaction of the silica and the silane coupling agent proceeds, The internal mixer includes a mixing chamber, a neck located above the mixing chamber, and a ram that can move up and down in a space within the neck. During at least a portion of the process, compressed gas is forced into the kneading chamber while the ram is not pressing. Here, "a state in which the ram is not pressing" means a state in which the ram is raised and the kneading chamber is an open system.

[0009] According to the method for producing a rubber composition of the present invention, by kneading at a temperature equal to or higher than the lower limit temperature at which the coupling reaction proceeds, the silane coupling agent can be fixed to the silica, thereby reducing the cohesive force of the silica.

[0010] Moreover, for at least a part of the time during the kneading at a temperature equal to or higher than the lower limit temperature at which the coupling reaction proceeds, By kneading with the ram not pressing (hereinafter also referred to as "non-pressing state"), volatile substances (such as water and alcohol) produced during the coupling reaction can be discharged outside the kneading chamber, allowing the coupling reaction to proceed efficiently and further reducing the cohesive force of the silica, thereby further increasing the degree of silica dispersion.

[0011] Furthermore, by feeding compressed gas into the kneading chamber without pressing, volatile substances (such as water and alcohol) can be effectively expelled from the kneading chamber, which makes it possible to more efficiently proceed with the coupling reaction and further reduce the cohesive force of silica, thereby further increasing the degree of silica dispersion.

[0012] As a result, the tire's low heat buildup, braking performance on wet roads, and wear resistance can be improved.

[0013] The internal mixer preferably has a rotor in the mixing chamber, and controls the rotation speed of the rotor by PID control so that the mixing temperature is set to the target temperature during at least a portion of the time. If the rotor were not subjected to any PID control and placed in a non-pressing state (i.e., the rotor was placed in a non-pressing state with a constant rotational speed), the kneading temperature for a certain formulation may fall below the lower limit temperature at which the coupling reaction proceeds, or, for another formulation, the kneading temperature may rise above the temperature at which gelation proceeds. In contrast, by controlling the rotor rotation speed using PID control, the kneading temperature can be stabilized, thereby preventing a decrease in the reaction rate of the coupling reaction and preventing gelation.

[0014] Preferably, the at least part of the time is 5 seconds or more. This configuration allows volatile substances (such as water and alcohol) produced during the coupling reaction to be more effectively discharged outside the mixing chamber, thereby further improving the tire's low heat buildup, braking performance on wet roads, and wear resistance.

[0015] The internal mixer further includes a hole opening on the wall surface of the mixing chamber, It is preferable that the compressed gas is fed into the kneading chamber through the holes during at least part of the time.

[0016] Preferably, the compressed gas is compressed air, since compressed air can be produced at low cost, thereby reducing costs.

[0017] The method for producing a tire of the present invention includes: a step of preparing a rubber composition by the above-described method for producing a rubber composition; and producing an unvulcanized tire using the rubber composition.

[0018] The apparatus for producing the rubber composition of the present invention comprises: an internal mixer including a kneading chamber, a neck located above the kneading chamber, a ram that can move up and down in a space within the neck, and a hole that opens in a wall surface of the kneading chamber; a compressor for generating compressed gas to be pumped into the kneading chamber through the holes.

[0019] According to the rubber composition manufacturing apparatus of the present invention, compressed gas generated by a compressor can be fed through at least one opening in the wall of the kneading chamber. For example, by feeding compressed gas into the kneading chamber without pressing, volatile substances (e.g., water and alcohol) generated during the coupling reaction can be discharged outside the kneading chamber. As a result, the coupling reaction can be efficiently promoted, and the cohesive force of silica can be reduced. In other words, the degree of silica dispersion can be increased. This can improve the low heat buildup, wet road braking performance, and wear resistance of the tire. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a conceptual diagram showing the configuration of a rubber composition manufacturing apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described.

[0022] <1. Rubber composition manufacturing equipment> First, a rubber composition manufacturing apparatus, that is, a kneading system, that can be used in this embodiment will be described.

[0023] As shown in Fig. 1, a rubber composition production apparatus 30 in this embodiment includes an internal kneader 1 and a compressor 21 that generates compressed gas to be sent to the internal kneader 1. The production apparatus 30 further includes a pipe 26 for the compressed gas that is fixed to the internal kneader 1. The production apparatus 30 may include other devices, such as an aftercooler, a tank, a main life filter, and an air dryer, between the compressor 21 and the pipe 26 in relation to the compressed gas path. Of course, the production apparatus 30 may also include pipes connecting these devices.

[0024] The compressor 21 can generate compressed gas. The compressor 21 includes a housing 25. Within the housing 25, the compressor 21 includes, for example, a motor (not shown), a compressor main body (not shown) that is driven by the motor and compresses gas (e.g., air), and a tank (not shown) that stores the compressed gas compressed by the compressor main body. In such a compressor 21, the compressed gas discharged from the compressor main body can flow into the tank via piping (not shown). Meanwhile, the compressed gas stored in the tank can exit the compressor 21 via piping (not shown). The compressor 21 may further include, for example, an aftercooler, a tank, a main life filter, and an air dryer.

[0025] Examples of compressed gases include compressed air and compressed inert gases (e.g., nitrogen gas, helium gas, neon gas, and argon gas). Of these, compressed air is preferred because it can be produced at low cost.

[0026] The compressed gas discharged from the compressor 21 is sent to the kneading chamber 4 of the internal mixer 1 via a piping 26 after passing through an aftercooler, a tank, a main life filter, an air dryer, etc. as needed. The piping 26 is provided with a pressure gauge (not shown) for measuring the pressure of the compressed gas.

[0027] The internal mixer 1 comprises a kneading chamber 4 having a casing 2 and a rotor 3, a cylindrical neck 5 located above the kneading chamber 4, an inlet 6 provided in the neck 5, a hopper door 6a capable of opening and closing the inlet 6, a ram 7 capable of moving up and down in the space within the neck 5, and a drop door 9 located on the underside of the kneading chamber 4. Examples of the internal mixer 1 include an intermeshing type internal mixer and a tangential type internal mixer.

[0028] An opening 2a is provided in the center of the top surface of the casing 2. A cylindrical neck 5 is provided above the opening 2a. An inlet 6 is provided on the side of the neck 5, through which rubber and compounding ingredients can be added. Two or more inlets 6 may be provided. The rubber and compounding ingredients added through the inlet 6 pass through the cylindrical space of the neck 5 and are then added into the casing 2 through the opening 2a of the casing 2.

[0029] The ram 7 is shaped so as to be able to close the opening 2a of the casing 2. The ram 7 can move up and down in the space of the neck 5 by means of a shaft 8 connected to the upper end of the ram 7. The ram 7 can press and apply pressure to the rubber present in the casing 2 by means of its own weight or the pressing force from the shaft 8.

[0030] The drop door 9 is closed during kneading and is opened after kneading is completed.

[0031] The rotation speed of the motor (not shown) that rotates the rotor 3 is adjusted based on a control signal from the control unit 11. The control unit 11 controls the rotation speed of the motor based on temperature information (specifically, the measured temperature Tp) inside the kneading chamber 4 sent from the temperature sensor 13. The rotation speed of the motor can be freely changed by the control unit 11. The motor can be, for example, an inverter motor.

[0032] To determine the rotation speed of the motor, a PID calculation processor provided inside the control unit 11 performs proportional (P), integral (I), and derivative (D) calculations based on the deviation between the actual temperature Tp in the kneading chamber 4 detected by the temperature sensor 13 and the target temperature Ts. Specifically, the PID calculation processor determines the rotation speed of the motor based on the sum of the control variables obtained by the proportional (P) operation, which calculates a control variable proportional to the difference (deviation e) between the actual temperature Tp and the target temperature Ts; the integral (I) operation, which calculates a control variable from the integral value obtained by integrating the deviation e along the time axis; and the derivative (D) operation, which calculates a control variable from the slope of the change in the deviation e, i.e., the derivative value. PID stands for Proportional Integral Differential.

[0033] The internal mixer 1 further has a hole that opens into the wall surface of the kneading chamber 4. In other words, the casing 2 of the internal mixer 1 has a hole that opens toward the kneading chamber 4. This hole penetrates from the outer surface to the inner surface of the casing 2. Compressed gas generated by the compressor 21 is sent into the kneading chamber 4 through this hole.

[0034] <2. Method for producing rubber composition> Next, a method for producing the rubber composition according to the present embodiment will be described.

[0035] The method for producing a rubber composition in this embodiment includes a step of preparing a rubber mixture (hereinafter referred to as "step S1") and a step of kneading at least the rubber mixture and vulcanization-related compounding ingredients to obtain a rubber composition (hereinafter referred to as "step S2").

[0036] <2.1. Step S1 (Step of Preparing Rubber Mixture)> Step S1 includes a step of kneading at least rubber, silica, and a silane coupling agent in an internal mixer 1 while controlling the kneading temperature to be below the lower limit temperature at which the coupling reaction (i.e., the reaction of silica and the silane coupling agent) proceeds (hereinafter referred to as "step K1"), a step of kneading in the internal mixer 1 while increasing the kneading temperature (hereinafter referred to as "step K2"), and a step of kneading in the internal mixer 1 while controlling the kneading temperature to be equal to or higher than the lower limit temperature at which the coupling reaction proceeds (hereinafter referred to as "step K3").

[0037] In other words, step S1 includes a step of kneading at least rubber, silica, and a silane coupling agent in an internal kneader 1 while controlling the kneading temperature so as to suppress the coupling reaction (i.e., step K1), a step of kneading in the internal kneader 1 while increasing the kneading temperature (i.e., step K2), and a step of kneading in the internal kneader 1 while controlling the kneading temperature so as to promote the coupling reaction (i.e., step K3).

[0038] Steps K1 to K3 constitute one kneading stage. The kneading stage is a cycle from the introduction of materials into the internal kneader 1 to the discharge of materials. Therefore, when transitioning from step K1 to step K2, materials such as rubber, silica, and silane coupling agent are not discharged from the internal kneader 1, and when transitioning from step K2 to step K3, materials are not discharged from the internal kneader 1 either.

[0039] <2.1.1. Step K1 (Step of Kneading While Controlling the Temperature Below the Lower Limit Temperature at Which the Coupling Reaction Proceeds)> In step K1, at least rubber, silica, and a silane coupling agent are charged into an internal mixer 1, and the components are mixed while the mixing temperature is controlled to be below the lowest temperature at which the coupling reaction proceeds. That is, in step K1, at least rubber, silica, and a silane coupling agent are charged into the internal mixer 1, and mixed while the mixing temperature is controlled to suppress the coupling reaction. Step K1 allows the silica to be effectively dispersed before the coupling reaction actively proceeds. In addition, step K1 can also reduce the amount of power consumed for producing the rubber composition. This will be explained below. If the mixing temperature were not controlled in step K1, the mixing time would be limited by the temperature rise caused by shear heating, and multiple remixings would be necessary (especially in highly silica-filled compounds). In contrast, in this embodiment, by controlling the kneading temperature in step K1, it is possible to eliminate the limitation on the kneading time due to temperature rise, thereby extending the kneading time and therefore reducing the number of re-kneadings. As a result, it is possible to reduce the amount of power consumed for producing the rubber composition. In step K1, the materials can be kneaded in a state where they are pressed down by the ram 7, i.e., in a pressed state. For at least a part of the time during step K1, kneading may be performed in a state where the ram 7 is not pressed down.

[0040] Examples of rubber include natural rubber, polyisoprene rubber, styrene butadiene rubber (SBR), polybutadiene rubber (BR), nitrile rubber, and chloroprene rubber. One or any combination of these may be selected and used. The rubber is preferably a diene rubber.

[0041] Modified rubber may be used as the rubber. Examples of modified rubber include modified SBR and modified BR. The modified rubber may have a functional group containing a heteroatom. The functional group may be introduced into the polymer chain terminal or the polymer chain, but is preferably introduced into the terminal. Examples of functional groups include amino groups, alkoxyl groups, hydroxyl groups, carboxyl groups, epoxy groups, cyano groups, and halogen groups. Among these, amino groups, alkoxyl groups, hydroxyl groups, and carboxyl groups are preferred. The modified rubber may have at least one of the exemplified functional groups. Examples of amino groups include primary amino groups, secondary amino groups, and tertiary amino groups. Examples of alkoxyl groups include methoxy groups, ethoxy groups, propoxy groups, and butoxy groups. The exemplified functional groups interact with the silanol groups (Si-OH) of silica. Here, "interaction" refers to, for example, chemical bonding or hydrogen bonding with the silanol groups of silica through a chemical reaction. The amount of modified rubber in 100% by mass of rubber used in step K1 may be 10% by mass or more, 20% by mass or more, or 30% by mass or more. The amount of modified rubber in 100% by mass of rubber used in step K1 may be 90% by mass or less, 80% by mass or less, or 70% by mass or less.

[0042] Examples of silica include wet silica and dry silica. Of these, wet silica is preferred. Examples of wet silica include precipitated silica. The specific surface area of ​​silica measured by nitrogen adsorption is, for example, 80 m 2 / g or more, and 2 / g or more, and 2 / g or more, and 2 The specific surface area of ​​silica may be, for example, 300 m 2 / g or less, and 2 / g or less, and 2 / g or less, and 2 / g or less. The specific surface area of ​​silica is measured in accordance with the multipoint nitrogen adsorption method (BET method) described in JIS K-6430.

[0043] In step K1, the amount of silica is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, even more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more, per 100 parts by mass of rubber. The amount of silica is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, even more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less, per 100 parts by mass of rubber.

[0044] Examples of silane coupling agents include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane. These can be used alone or in any combination.

[0045] In step K1, the amount of the silane coupling agent is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of silica. The upper limit of the amount of the silane coupling agent is, for example, 20 parts by mass or 15 parts by mass, relative to 100 parts by mass of silica.

[0046] In step K1, rubber, silica, and a silane coupling agent can be kneaded with carbon black, an antioxidant, stearic acid, wax, zinc oxide, oil, etc. Any one or any combination of these can be selected and used.

[0047] 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.

[0048] Examples of the antioxidant include aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, thiourea-based antioxidants, etc. The antioxidant may be used singly or in any combination selected from these.

[0049] In step K1, kneading is performed so that the kneading temperature is maintained constant. Specifically, in step K1, kneading is performed so that the measured temperature Tp is maintained at the target temperature Ts. At this time, the measured temperature Tp can be maintained within ±5°C of the target temperature Ts. The target temperature Ts may be less than 140°C, 138°C or less, 135°C or less, 132°C or less, or 130°C or less. The target temperature Ts is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 115°C or higher, and even more preferably 120°C or higher. If it is too low, it tends to take a long time to disperse the silica. The target temperature Ts can be set appropriately taking into account the formulation, particularly the type of silane coupling agent.

[0050] In step K1, the kneading is performed for, for example, 10 seconds or more, while maintaining the kneading temperature within a certain range. That is, the kneading temperature is controlled for 10 seconds or more. This is preferably 20 seconds or more, and more preferably 30 seconds or more. This may be 40 seconds or more, 60 seconds or more, or 70 seconds or more. This may be 1000 seconds or less, 800 seconds or less, 600 seconds or less, 400 seconds or less, 200 seconds or less, or 100 seconds or less.

[0051] The kneading temperature is maintained by adjusting the rotation speed of the rotor 3. Specifically, the kneading temperature is maintained by adjusting the rotation speed of the rotor 3 by PID control. Here, the rotation speed of the rotor 3 is adjusted by PID control so that the measured temperature Tp becomes the target temperature Ts. The PID control may be started from the beginning of kneading, or may be started when the measured temperature Tp reaches a predetermined temperature (for example, the target temperature Ts or a temperature slightly lower than the target temperature Ts).

[0052] <2.1.2. Step K2 (Step of Kneading While Increasing the Kneading Temperature)> In step K2, the materials are kneaded while the kneading temperature is increased. In step K2, the kneading temperature can be increased to a temperature at which the coupling reaction proceeds actively (for example, 140°C or higher). For example, the kneading temperature can be increased to the target temperature Ts of step K3 or a temperature slightly lower than the target temperature Ts. In step K2, the materials can be kneaded while being pressed down by the ram 7, i.e., in a pressed state.

[0053] <2.1.3. Step K3 (Step of kneading while controlling the temperature to be equal to or higher than the lower limit temperature at which the coupling reaction proceeds)> In step K3, the mixture is kneaded in the internal kneader 1 while the kneading temperature is controlled to be equal to or higher than the lower limit temperature at which the coupling reaction proceeds. That is, in step K3, the mixture is kneaded while controlling the kneading temperature so that the coupling reaction proceeds. According to step K3, by kneading at a temperature equal to or higher than the lower limit temperature at which the coupling reaction proceeds, the silane coupling agent can be fixed to the silica, thereby reducing the cohesive force of the silica. In addition, according to step K3, the kneading temperature is controlled, so the amount of power consumed for producing the rubber composition can be reduced. This will be explained below. If the kneading temperature were not controlled in step K3, the kneading time would be limited by the temperature increase due to shear heating, making it necessary to perform multiple re-kneadings (especially in highly filled silica compounds). In contrast, in this embodiment, by controlling the kneading temperature in step K3, the kneading time limitation due to the temperature increase can be eliminated, thereby extending the kneading time and reducing the number of re-kneadings. As a result, the amount of electricity consumed for producing the rubber composition can be reduced.

[0054] In step K3, kneading is performed so that the kneading temperature is maintained constant. Specifically, in step K3, kneading is performed so that the measured temperature Tp is maintained at the target temperature Ts. At this time, the measured temperature Tp can be maintained within ±5°C of the target temperature Ts. The target temperature Ts may be 140°C or higher, 142°C or higher, 145°C or higher, 148°C or higher, or 150°C or higher. If this is too low, the coupling reaction tends to take too long. The target temperature Ts is preferably 170°C or lower, more preferably 165°C or lower, even more preferably 160°C or lower, even more preferably 155°C or lower, and even more preferably 153°C or lower. If this is too high, gelation may occur.

[0055] In step K3, the mixture is kneaded for, for example, 20 seconds or more, while maintaining the kneading temperature within a certain range. That is, the kneading temperature is controlled for 20 seconds or more. This is preferably 40 seconds or more, more preferably 60 seconds or more, even more preferably 80 seconds or more, and even more preferably 100 seconds or more. This may be 1500 seconds or less, 1000 seconds or less, 500 seconds or less, 300 seconds or less, or 200 seconds or less.

[0056] The kneading temperature is maintained by adjusting the rotation speed of the rotor 3, as in the step K1.

[0057] During at least a portion of step K3, compressed gas is fed into the kneading chamber 4 while the ram 7 is not pressing. That is, while feeding compressed gas into the kneading chamber 4 while the ram 7 is not pressing (i.e., in a non-pressing state), kneading is performed while the kneading temperature is controlled to be equal to or higher than the lower limit temperature at which the coupling reaction proceeds. Hereinafter, the state in which the ram 7 is not pressing and compressed gas is being fed into the kneading chamber 4 may be referred to as a "volatile matter discharge state." By kneading in a volatile matter discharge state, volatile matters (e.g., water or alcohol) can be effectively discharged outside the kneading chamber 4, which allows the coupling reaction to proceed more efficiently and further reduces the cohesive force of the silica.

[0058] The state in which the ram 7 is not pressing (i.e., the non-pressing state) is a state in which the ram 7 is raised and the kneading chamber 4 is an open system. This state can be created, for example, by opening the hopper door 6a and raising the ram 7 to a level at which the gas in the kneading chamber 4 can escape to the outside of the closed-type kneader 1 through the inlet 6. This allows volatile substances (for example, water and alcohol) to be effectively discharged to the outside of the kneading chamber 4. At this time, the hopper door 6a may be, for example, fully open or half open.

[0059] The state in which the ram 7 is not pressing and compressed gas is being fed into the kneading chamber 4 (i.e., the volatile matter discharging state) may be continuous, i.e., continuous, or intermittent. An intermittent volatile matter discharging state can be created, for example, by maintaining the ram 7 in a non-pressing state while intermittently (e.g., intermittently) feeding compressed gas into the kneading chamber 4. In particular, it is preferable that the volatile matter discharging state be continuous, i.e., continuous.

[0060] The kneading in a volatile substance discharging state may be carried out throughout step K3 (i.e., it may be carried out for the entire duration of step K3), or it may be carried out for only a portion of step K3. When the kneading in a volatile substance discharging state is carried out partway through step K3, the kneading in a volatile substance discharging state may be started, for example, 10 seconds or more, 20 seconds or more, or 30 seconds or more after the start of step K3 (i.e., the start of kneading in a state in which the kneading temperature is controlled to be equal to or higher than the lower limit temperature at which the coupling reaction proceeds).

[0061] The time during which the volatile matter is discharged is preferably 5 seconds or more, more preferably 10 seconds or more, even more preferably 20 seconds or more, and even more preferably 30 seconds or more. When the time is 5 seconds or more, volatile matter (e.g., water or alcohol) produced during the coupling reaction can be more effectively discharged to the outside of the kneading chamber 4. When the volatile matter is discharged intermittently, the "time during which the volatile matter is discharged" means the total time during which the volatile matter is discharged.

[0062] The pressure of the compressed gas sent into the kneading chamber 4 in the volatile matter discharge state may be 0.2 MPa or more, 0.3 MPa or more, or 0.4 MPa or more. When the pressure is 0.2 MPa or more, volatile matters (e.g., water and alcohol) generated during the coupling reaction can be more effectively discharged outside the kneading chamber 4. Note that the "pressure of the compressed gas" may be the pressure of the compressed gas in the pipe 26. This pressure can be measured by a pressure gauge provided in the pipe 26.

[0063] The discharge rate of the compressed gas (specifically, the discharge rate of the compressed gas discharged from compressor 21) may be, for example, 300 L / min or more, or 700 L / min or more. On the other hand, the discharge rate may be, for example, 1500 L / min or less, 1000 L / min or less, or 850 L / min or less.

[0064] The temperature of the compressed gas sent into the kneading chamber 4 may be, for example, 15°C or higher, 20°C or higher, or 25°C or higher. On the other hand, the temperature of the compressed gas may be, for example, 150°C or lower, or 100°C or lower. This is because if the temperature of the compressed gas is extremely low or high, the effect of the compressed gas on the kneading temperature becomes excessively large. Note that the "temperature of the compressed gas" may be, for example, the temperature of the compressed gas leaving an air dryer. Here, the air dryer may be an air dryer built into the compressor 21, or an air dryer provided between the compressor 21 and the internal mixer 1.

[0065] As already explained, in step K3, the rotation speed of rotor 3 is controlled by PID control to set the kneading temperature to the target temperature Ts. This (specifically, controlling the rotation speed of rotor 3 by PID control) can prevent a decrease in the reaction rate of the coupling reaction and the occurrence of gelation. This will be explained. If rotor 3 were not subjected to any PID control and placed in a non-pressed state (i.e., if rotor 3 were placed in a non-pressed state at a constant rotation speed), the kneading temperature may fall below the lower limit temperature at which the coupling reaction proceeds in some formulations, or may rise above the temperature at which gelation proceeds in other formulations. In contrast, controlling the rotation speed of rotor 3 by PID control can stabilize the kneading temperature, thereby preventing a decrease in the reaction rate of the coupling reaction and the occurrence of gelation.

[0066] Thereafter, if necessary, mixing is continued up to a predetermined discharge temperature, and the drop door 9 is opened to discharge the rubber mixture.

[0067] <2.1.4.Other> If necessary, the rubber mixture can be further kneaded, i.e., re-kneaded, in order to improve the dispersibility of silica or reduce the Mooney viscosity. Re-kneading may be carried out multiple times.

[0068] A rubber mixture can be obtained by the above procedure.

[0069] <2.2. Step S2 (Step of Kneading Rubber Mixture and Vulcanization Compounding Ingredients to Obtain Rubber Composition)> In step S2, at least the 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. Kneading can be performed using a kneader. Examples of the kneader include an internal kneader and an open roll. Examples of the internal kneader include a Banbury mixer and a kneader.

[0070] In the rubber composition, the amount of silica is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, even more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more, per 100 parts by mass of rubber. The amount of silica is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, even more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less, per 100 parts by mass of rubber.

[0071] In the rubber composition, the amount of the silane coupling agent is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of silica. The upper limit of the amount of the silane coupling agent is, for example, 20 parts by mass or 15 parts by mass, per 100 parts by mass of silica.

[0072] The rubber composition may further contain carbon black, antioxidants, stearic acid, wax, zinc oxide, oil, sulfur, vulcanization accelerators, 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. The amount of vulcanization accelerator is preferably 0.1 to 5 parts by mass per 100 parts by mass of rubber.

[0073] 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.

[0074] <3. Tire manufacturing method> Next, the method for manufacturing a tire according to this embodiment will be described. Of the steps included in the method for manufacturing a tire according to this embodiment, the step of preparing the rubber composition has already been described.

[0075] The tire manufacturing method of this embodiment includes a step of producing an unvulcanized tire using a rubber composition. This step includes 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. Among these, tread rubber is preferred.

[0076] 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.

[0077] <4. 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.

[0078] In the above-described embodiment, the entire amount of silica is added in the kneading stage including steps K1 to K3. However, the above-described embodiment is not limited to this configuration. For example, the silica may be added in separate stages.

[0079] In the above-described embodiment, the rubber composition manufacturing method includes step K1. However, the above-described embodiment is not limited to this configuration. That is, the rubber composition manufacturing method does not have to include step K1. In this case, for example, at least rubber, silica, and a silane coupling agent can be charged into an internal mixer 1, mixed without temperature control, and temperature control (i.e., controlling the mixing temperature to be equal to or higher than the lower limit temperature at which the coupling reaction proceeds) can be started at a predetermined timing.

[0080] In the above embodiment, the kneading temperature is controlled by the rotation speed of the rotor 3 in step K1. However, the above embodiment is not limited to this configuration. For example, the kneading temperature may be controlled by the temperature of a heating / cooling medium flowing through a jacket (not shown) of the internal mixer 1.

[0081] In the above-described embodiment, the kneading temperature is controlled based on PID control in step K1. However, the above-described embodiment is not limited to this configuration. The kneading temperature may be controlled based on a control method other than PID control.

[0082] In the above-described embodiment, a configuration has been described in which a volatile matter discharge state (i.e., a state in which the ram 7 is not pressing and compressed gas is being sent into the kneading chamber 4) is created in step K3 (i.e., a step in which kneading is performed in the internal kneader 1 while controlling the kneading temperature to be equal to or higher than the lower limit temperature at which the coupling reaction proceeds). However, the above-described embodiment is not limited to this configuration. For example, a volatile matter discharge state may be created when kneading is performed without controlling the kneading temperature at a temperature equal to or higher than the lower limit temperature at which the coupling reaction proceeds.

[0083] In the above embodiment, the kneading temperature is controlled by the rotation speed of the rotor 3 in step K3. However, the above embodiment is not limited to this configuration. For example, the kneading temperature may be controlled by the temperature of a heating / cooling medium flowing through a jacket (not shown) of the internal mixer 1.

[0084] In the above-described embodiment, the kneading temperature is controlled based on PID control in step K3. However, the above-described embodiment is not limited to this configuration. The kneading temperature may be controlled based on a control method other than PID control.

[0085] In the above embodiment, a configuration in which the hopper door 6a is opened to create a non-pressed state has been described. However, the above embodiment is not limited to this configuration. For example, instead of opening the hopper door 6a, some hole provided in the internal mixer 1 may be opened. An example of such a hole is a hole for introducing oil into the kneading chamber 4. Since the inlet 6 opened and closed by the hopper door 6a is generally larger than the hole for introducing oil, opening the hopper door 6a leads to effective discharge of volatile matter. Therefore, opening the hopper door 6a is preferable.

[0086] In the above embodiment, a configuration has been described in which compressed gas is sent into the kneading chamber 4 through holes opened in the wall surface of the kneading chamber 4. However, the above embodiment is not limited to this configuration. For example, a pipe capable of discharging the compressed gas generated by the compressor 21 may be inserted from the inlet 6 toward the kneading chamber 4, and the compressed gas may be sent into the kneading chamber 4 from the pipe.

[0087] In the above-described embodiment, a rubber composition is obtained by kneading a rubber mixture and vulcanization-related compounding ingredients. However, the above-described embodiment is not limited to this configuration. For example, the rubber mixture may be regarded as the rubber composition. [Example]

[0088] Examples of the present invention will be described below.

[0089] <Examples 1 to 6 and Comparative Examples 1 to 5> The raw materials and chemicals used in these examples are listed below. SBR "SBR1502" manufactured by JSR Modified solution polymerized SBR "HPR350" manufactured by JSR Corporation Silica "Nipsil AQ" manufactured by Tosoh Corporation Silane coupling agent "Si75" manufactured by Degussa Stearic acid "Lunac S-20" manufactured by Kao Corporation Carbon black "N339 Seast KH" manufactured by Tokai Carbon Co., Ltd. Oil "Process NC140" manufactured by JX Nippon Oil & Gas Corporation Zinc oxide "Zinc Oxide No. 1" manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd. Sulfur "5% oil-treated sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1 "Suncerer DM-G" manufactured by Sanshin Chemical Industry Co., Ltd. Vulcanization accelerator 2 "Soccinol CZ" manufactured by Sumitomo Chemical Co., Ltd.

[0090] [Table 1]

[0091] Preparation of unvulcanized rubber in Comparative Example 1 According to Table 1, the rubber and compounding ingredients were charged into a Banbury mixer and mixed without PID control, and the mixture was discharged at 160°C (first mixing stage). In the first mixing stage, mixing was performed with a downward force applied by the ram, i.e., in a pressing state. The mixture obtained in the first mixing stage was remixed in a Banbury mixer without PID control and discharged at 160°C (second mixing stage). The mixture obtained in the second mixing stage was remixed in a Banbury mixer without PID control and discharged at 160°C (third mixing stage). The mixture obtained in the third mixing stage was mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0092] Preparation of unvulcanized rubber in Comparative Example 2 According to Table 1, the rubber and compounding ingredients were fed into a Banbury mixer and mixed with PID control (specifically, PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 180 seconds). The mixture was then discharged at 160°C (first mixing stage). In the first mixing stage, mixing was performed with a downward force applied by the ram, i.e., in a pressing state. The mixture obtained in the first mixing stage was remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The remixed mixture was then mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0093] Preparation of unvulcanized rubber in Comparative Example 3 The rubber and compounding ingredients listed in Table 1 were fed into a Banbury mixer and mixed with PID control (specifically, a first PID control with a control start temperature of 130°C, a target temperature of 130°C, and a control time of 40 seconds, and a second PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 140 seconds). The mixture was then discharged at 160°C (first mixing stage). In the first mixing stage, mixing was performed with a downward force applied by the ram, i.e., in a pressing state. The mixture obtained in the first mixing stage was remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The remixed mixture was then mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0094] Preparation of unvulcanized rubber in Comparative Example 4 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed under PID control (specifically, PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 180 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to block the Banbury mixer's inlet for 50 seconds during the 180-second control period, and the ram was elevated above the inlet. At this time, 65 seconds after the start of PID control, the hopper door was opened and the ram was elevated. The mixture obtained in the first mixing stage was remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The remixed mixture was then mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0095] Preparation of unvulcanized rubber in Example 1 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed under PID control (specifically, PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 180 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to block the Banbury mixer's inlet for 50 seconds during the 180-second control period, and the ram was elevated above the inlet. At this time, 65 seconds after the start of PID control, the hopper door was opened and the ram was elevated. Additionally, during those 50 seconds, compressed air generated by a compressor was pumped through holes in the wall of the mixing chamber. The mixture obtained in the first mixing stage was remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The remixed mixture was then mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0096] Preparation of unvulcanized rubber in Example 2 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed under PID control (specifically, PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 180 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to block the Banbury mixer's inlet, and the ram was elevated above the inlet for the middle 80 seconds of the 180-second control time. The hopper door was opened and the ram was elevated 50 seconds after the start of PID control. Additionally, compressed air generated by a compressor was pumped through holes in the wall of the mixing chamber during those 80 seconds. The mixture obtained in the first mixing stage was remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The remixed mixture was then mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0097] Preparation of unvulcanized rubber in Example 3 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed under PID control (specifically, PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 180 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door covering the Banbury mixer's inlet was opened for the middle 100 seconds of the 180-second control time, and the ram was elevated above the inlet. At this time, 40 seconds after the start of PID control, the hopper door was opened and the ram was elevated. Additionally, during those 100 seconds, compressed air generated by a compressor was pumped in through holes in the wall of the mixing chamber. The mixture obtained in the first mixing stage was then remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The mixture after re-kneading was kneaded with sulfur and a vulcanization accelerator to obtain an unvulcanized rubber (final stage).

[0098] Preparation of unvulcanized rubber in Comparative Example 5 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed with PID control (specifically, PID control consisting of a first PID control with a control start temperature of 130°C, a target temperature of 130°C, and a control time of 40 seconds, and a second PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 140 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to block the Banbury mixer's inlet for 50 seconds during the 140-second control time of the second PID control, and the ram was elevated above the inlet. At this time, 45 seconds after the start of the second PID control, the hopper door was opened and the ram was elevated. The mixture obtained in the first mixing stage was then remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The mixture after re-kneading was kneaded with sulfur and a vulcanization accelerator to obtain an unvulcanized rubber (final stage).

[0099] Preparation of unvulcanized rubber in Example 4 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed under PID control (specifically, a first PID control with a control start temperature of 130°C, a target temperature of 130°C, and a control time of 40 seconds, and a second PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 140 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to close the Banbury mixer's inlet, and the ram was elevated above the inlet for the middle 50 seconds of the 140-second control time of the second PID control. The hopper door was opened and the ram was elevated 45 seconds after the start of the second PID control. Additionally, compressed air generated by a compressor was pumped in through holes in the wall of the mixing chamber during those 50 seconds. The mixture obtained in the first kneading stage was re-kneaded in a Banbury mixer without PID control and discharged at 160°C (second kneading stage). The re-kneaded mixture was kneaded with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0100] Preparation of unvulcanized rubber in Example 5 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed under PID control (specifically, a first PID control with a control start temperature of 130°C, a target temperature of 130°C, and a control time of 40 seconds, and a second PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 140 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door covering the Banbury mixer's inlet was opened for 80 seconds during the 140-second control time of the second PID control, and the ram was elevated above the inlet. At this time, the hopper door was opened and the ram was elevated 30 seconds after the start of the second PID control. Additionally, compressed air generated by a compressor was pumped in through holes in the wall of the mixing chamber during those 80 seconds. The mixture obtained in the first kneading stage was re-kneaded in a Banbury mixer without PID control and discharged at 160°C (second kneading stage). The re-kneaded mixture was kneaded with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0101] Preparation of unvulcanized rubber in Example 6 The rubber and compounding ingredients listed in Table 1 were loaded into a Banbury mixer and mixed under PID control (specifically, a first PID control with a control start temperature of 130°C, a target temperature of 130°C, and a control time of 40 seconds, and a second PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 140 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to cover the Banbury mixer's inlet, and the ram was elevated above the inlet for the middle 100 seconds of the 140-second control time of the second PID control. The hopper door was opened and the ram was elevated 20 seconds after the start of the second PID control. Additionally, compressed air generated by a compressor was pumped in through holes in the wall of the mixing chamber during those 100 seconds. The mixture obtained in the first kneading stage was re-kneaded in a Banbury mixer without PID control and discharged at 160°C (second kneading stage). The re-kneaded mixture was kneaded with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0102] Preparation of vulcanized rubber The unvulcanized rubber was vulcanized at 150°C for 30 minutes to obtain a vulcanized rubber.

[0103] Mooney Viscosity The Mooney viscosity of the unvulcanized rubber was measured in accordance with JIS K-6300 using a rotorless Mooney measuring instrument manufactured by Toyo Seiki Seisakusho. To measure the Mooney viscosity, the unvulcanized rubber was preheated at 100°C for 1 minute, and then the rotor was rotated. The torque value 4 minutes after the rotor started to rotate was recorded in Mooney units. The Mooney viscosity of each example is shown in Table 2, with the Mooney viscosity of Comparative Example 1 set as an index of 100. The smaller the index, the lower the Mooney viscosity and the better the processability.

[0104] Abrasion resistance The wear amount was measured using a Lambourn abrasion tester in accordance with JIS K6264 under a load of 3 kg, a slip ratio of 20%, and a temperature of 23°C. The reciprocal of the wear amount in Comparative Example 1 is set as an index of 100, and the reciprocal of the wear amount in each example (the reciprocal of the wear amount) is shown in Table 2. The larger the index, the better the wear resistance.

[0105] Wet road braking performance The rebound resilience (%) was measured using a Lübke rebound resilience tester in accordance with JIS K6255 at 23°C. The reciprocal of the rebound resilience in Comparative Example 1 is set as an index of 100, and the reciprocal of each example (the reciprocal of the rebound resilience) is shown in Table 2. The larger the index, the better the braking performance on wet roads.

[0106] Fuel efficiency The tan δ of the vulcanized rubber was measured in accordance with JIS K-6394 using a viscoelasticity tester manufactured by Toyo Seiki Seisakusho, Ltd. Tan δ was measured under conditions of a frequency of 10 Hz, a dynamic strain of 1.0%, a temperature of 60°C, and a static strain (initial strain) of 10%. Table 2 shows the tan δ of each example, expressed as an index with the tan δ of Comparative Example 1 set to 100. The smaller the index, the lower the tan δ and the better the fuel economy.

[0107] [Table 2] In Table 2, the PID control performed in the first kneading stage controls the rotation speed of the rotor. "Injection of compressed air" in Table 2 means that compressed air with a discharge rate of 800 L / min and a pressure of 0.5 MPa was sent into the mixing chamber through a hole in the wall of the mixing chamber of the Banbury mixer. This pressure was measured with a pressure gauge attached to the air hose attached to the Banbury mixer. Incidentally, the temperature of the compressed air was not measured, but it is believed to have been around room temperature.

[0108] In addition, the silane coupling agent ("Si75" manufactured by Degussa) hardly reacts with silica at 130°C, but does react with silica at 150°C. Therefore, 130°C is lower than the minimum temperature at which the coupling reaction proceeds, and 150°C is higher than the minimum temperature at which the coupling reaction proceeds.

[0109] By injecting compressed air in a non-pressure state (specifically, with the ram elevated and the Banbury mixer inlet open) during kneading under PID control at a target temperature of 150°C, it was possible to improve abrasion resistance, wet road braking performance, and fuel economy compared to when compressed air was not injected (see Comparative Example 4 and Examples 1 to 3, and Comparative Example 5 and Examples 4 to 6). In addition, it was also possible to improve the Mooney viscosity.

[0110] <Examples 7 and 8 and Comparative Examples 6 and 7> The raw materials and chemicals used in these examples are listed below. NR RSS#3 SBR "SBR1502" manufactured by JSR S-SBR "Tuf1834" manufactured by Asahi Kasei Corporation Silica "Nipsil AQ" manufactured by Tosoh Corporation Silane coupling agent "Si75" manufactured by Degussa Stearic acid "Lunac S-20" manufactured by Kao Corporation Carbon black "N339 Seast KH" manufactured by Tokai Carbon Co., Ltd. Oil "Process NC140" manufactured by JX Nippon Oil & Gas Corporation Zinc oxide "Zinc Oxide No. 1" manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd. Sulfur "5% oil-treated sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator 1 "Suncerer DM-G" manufactured by Sanshin Chemical Industry Co., Ltd. Vulcanization accelerator 2 "Soccinol CZ" manufactured by Sumitomo Chemical Co., Ltd.

[0111] [Table 3]

[0112] Preparation of unvulcanized rubber in Comparative Example 6 The rubber and compounding ingredients listed in Table 3 were loaded into a Banbury mixer and mixed under PID control (specifically, PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 180 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to block the Banbury mixer's inlet for only the middle 50 seconds of the 180-second control time, and mixing was performed with the ram elevated above the inlet. At this time, 65 seconds after the start of PID control, the hopper door was opened and the ram elevated. The mixture obtained in the first mixing stage was remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The remixed mixture was then mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0113] Preparation of unvulcanized rubber in Example 7 The rubber and compounding ingredients listed in Table 3 were loaded into a Banbury mixer and mixed under PID control (specifically, PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 180 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to block the Banbury mixer's inlet for 50 seconds during the 180-second control period, and the ram was elevated above the inlet. At this time, 65 seconds after the start of PID control, the hopper door was opened and the ram was elevated. Additionally, during those 50 seconds, compressed air generated by a compressor was pumped through holes in the wall of the mixing chamber. The mixture obtained in the first mixing stage was remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The remixed mixture was then mixed with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0114] Preparation of unvulcanized rubber in Comparative Example 7 The rubber and compounding ingredients listed in Table 3 were fed into a Banbury mixer and mixed under PID control (specifically, a first PID control with a control start temperature of 130°C, a target temperature of 130°C, and a control time of 40 seconds, and a second PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 140 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to close the Banbury mixer's inlet, and the ram was elevated above the inlet for the middle 50 seconds of the 140-second control time of the second PID control. At this time, the hopper door was opened and the ram was elevated 45 seconds after the start of the second PID control. The mixture obtained in the first mixing stage was then remixed in the Banbury mixer without PID control and discharged at 160°C (second mixing stage). The mixture after re-kneading was kneaded with sulfur and a vulcanization accelerator to obtain an unvulcanized rubber (final stage).

[0115] Preparation of unvulcanized rubber in Example 8 The rubber and compounding ingredients listed in Table 3 were loaded into a Banbury mixer and mixed under PID control (specifically, a first PID control with a control start temperature of 130°C, a target temperature of 130°C, and a control time of 40 seconds, and a second PID control with a control start temperature of 150°C, a target temperature of 150°C, and a control time of 140 seconds). The mixture was then discharged at 160°C (first mixing stage). During the first mixing stage, the hopper door was opened to close the Banbury mixer's inlet, and the ram was elevated above the inlet for the middle 50 seconds of the 140-second control time of the second PID control. The hopper door was opened and the ram was elevated 45 seconds after the start of the second PID control. Additionally, compressed air generated by a compressor was pumped in through holes in the wall of the mixing chamber during those 50 seconds. The mixture obtained in the first kneading stage was re-kneaded in a Banbury mixer without PID control and discharged at 160°C (second kneading stage). The re-kneaded mixture was kneaded with sulfur and a vulcanization accelerator to obtain unvulcanized rubber (final stage).

[0116] Preparation of vulcanized rubber The unvulcanized rubber was vulcanized at 150°C for 30 minutes to obtain a vulcanized rubber.

[0117] evaluation Mooney viscosity, abrasion resistance, wet road braking performance, and fuel economy were measured using the methods described above. The Mooney viscosity of each example is shown in Table 4 as an index, with the Mooney viscosity of Comparative Example 6 set to 100. The smaller the index, the lower the Mooney viscosity and the better the processability. Regarding abrasion resistance, the reciprocal of the abrasion amount of each example is shown in Table 4 as an index, with the reciprocal of the abrasion amount of Comparative Example 1 set to 100. The larger the index, the better the abrasion resistance. Regarding wet road braking performance, the reciprocal of the rebound resilience of each example is shown in Table 4 as an index, with the reciprocal of the rebound resilience of Comparative Example 1 set to 100. The larger the index, the better the wet road braking performance. The tan δ of each example is shown in Table 4 as an index, with the tan δ of Comparative Example 6 set to 100. The smaller the index, the lower the tan δ and the better the fuel economy.

[0118] [Table 4] In Table 4, the PID control performed in the first kneading stage controls the rotor rotation speed. "Injection of compressed air" in Table 4 also means that compressed air with a discharge rate of 800 L / min and a pressure of 0.5 MPa was sent into the mixing chamber through a hole in the wall of the mixing chamber of the Banbury mixer. This pressure was also measured with a pressure gauge attached to the air hose attached to the Banbury mixer. Incidentally, although the temperature of the compressed air was not measured, it is believed to have been around room temperature.

[0119] By injecting compressed air in a non-pressure state (specifically, with the ram elevated and the Banbury mixer inlet open) during kneading under PID control at a target temperature of 150°C, it was possible to improve the abrasion resistance, wet road braking performance, and fuel economy compared to when compressed air was not injected (see Comparative Example 6 and Example 7, and Comparative Example 7 and Example 8). In addition, it was also possible to improve the Mooney viscosity. [Explanation of symbols]

[0120] 1... Internal mixer, 2... Casing, 2a... Opening, 3... Rotor, 4... Mixing chamber, 5... Neck, 6... Feeding port, 6a... Hopper door, 7... Ram, 8... Shaft, 9... Drop door, 11... Control unit, 13... Temperature sensor, 21... Compressor, 25... Housing, 26... Piping, 30... Rubber composition manufacturing apparatus

Claims

1. A method for producing a rubber composition comprising the steps of: kneading at least rubber, silica, and a silane coupling agent in an internal kneader while controlling the kneading temperature to be below the lowest temperature at which a coupling reaction between the silica and the silane coupling agent proceeds; a second step of kneading at least the rubber, the silica, and the silane coupling agent in the internal kneader at a temperature equal to or higher than the lower limit temperature at which the coupling reaction of the silica and the silane coupling agent proceeds, The internal mixer includes a mixing chamber, a neck located above the mixing chamber, and a ram that can move up and down in a space within the neck. feeding compressed gas into the kneading chamber while the ram is not pressing for at least a portion of the time during the second step; The internal mixer is provided with a rotor in the mixing chamber, In the first step, the rotation speed of the rotor is controlled by PID control so that the kneading temperature becomes a first target temperature; the first target temperature is less than 140°C; In the second step, the rotation speed of the rotor is controlled by PID control so that the kneading temperature is set to a second target temperature during at least a part of the time period; The second target temperature is 140°C or higher. A method for producing a rubber composition.

2. The method for producing a rubber composition according to claim 1 , wherein the at least a portion of the time is 5 seconds or more.

3. The internal mixer further includes a hole opening on the wall surface of the mixing chamber, Forcing the compressed gas into the kneading chamber through the holes for at least a portion of the time; A method for producing the rubber composition according to claim 1 or 2.

4. The method for producing a rubber composition according to any one of claims 1 to 3, wherein the compressed gas is compressed air.

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

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