JP2010248327A - Method for preparing rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a rubber composition, by which the rubber composition having a low water content can efficiently be prepared in a short time without giving a large load to a kneader. <P>SOLUTION: This method for preparing the rubber composition, comprising mixing a rubber latex with a slurry prepared by dispersing a filler in water, coagulating a rubber-filler mixture from the mixture liquid, dehydrating the coagulated mixture with a dehydration device, introducing the obtained coagulation product into a screw extruder 8, extruding the coagulation product to thermally dry, and then kneading the rubber composition containing the dried coagulation product 17 as a component with a kneader to prepare the rubber composition, is characterized by connecting a gear pump 15 to the tip of the screw extruder 8, rotating the screw 10 of the extruder 8 to press and feed the coagulation product to the gear pump 15, and driving the gear pump 15 to directly feed the heated coagulation product 17 discharged from the gear pump 15 into the kneader 16. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for preparing a rubber composition using a wet masterbatch prepared from a rubber latex and a slurry in which a filler such as carbon black is dispersed.

  Conventionally, as a method for producing rubber having excellent dispersibility and processability, as shown in Patent Document 1, natural rubber latex and a filler slurry such as carbon black are mixed, and a natural rubber and a filler are mixed with a coagulant. There is known a method using a so-called wet masterbatch in which a mixture is solidified, and the obtained solidified product is separated from water, further dehydrated and then dried. The wet masterbatch obtained by this method is superior in dispersibility of carbon black to the rubber component compared to a dry masterbatch obtained by kneading natural rubber and filler using a kneading roll, and rubber after vulcanization. It has the advantage of excellent properties (strength, wear resistance, etc.).

  By the way, the coagulated product still contains a lot of moisture even after the dehydration treatment. If there is a lot of moisture in the coagulated product, then when kneading the rubber composition containing other chemicals into the coagulated product (wet masterbatch) using a Banbury mixer etc., the moisture will ooze out to the surface of the rubber composition. Further, there was a risk that slipping occurred between the rubber composition and the rotor of the mixer, and kneadability was lowered. Moreover, when there is much water | moisture content in a solidified material, when the rubber composition was vulcanized | cured, the possibility that a space | gap might arise because the water | moisture content in a rubber composition evaporated.

  As a method for solving the above problem, as shown in Patent Document 2, the coagulated product is introduced into a screw extruder, and the screw is rotated to extrude the coagulated product, whereby the moisture in the coagulated product is evaporated by heating and dried. The method is known. The solidified product after drying is molded into a bale and stored, and is supplied to the kneader while remaining in a bale during kneading.

Patent Registration No. 2633913 JP 2006-348237 A

  However, the wet masterbatch is hard and poor in flexibility as compared with the unvulcanized rubber alone at room temperature because the filler is uniformly dispersed in the rubber. Therefore, kneading a wet masterbatch stored at room temperature has a problem that a large load is applied to the kneader and power consumption is increased, and the kneading time is prolonged and productivity is lowered.

  Therefore, in view of the above problems, an object of the present invention is to provide a method for preparing a rubber composition that has a low moisture content, can be efficiently prepared in a short time without imposing a large load on the kneader.

  In order to solve the above-mentioned problems, the present inventor has intensively studied. As a result, when a gear pump is connected to the tip of the screw extruder and the screw is rotated in a state in which the discharge of the solidified product from the screw extruder is restricted, the solidified product is obtained. It is possible to easily heat up to the temperature at which the water is evaporated and the moisture evaporates, and further, the coagulated material discharged from the gear pump is supplied to the kneader in a heated state, thereby greatly reducing the load on the kneader. In addition, it has been found that the kneading time can be shortened and the present invention has been completed.

  That is, in the present invention, a mixture of rubber latex and a slurry in which a filler is dispersed in water is coagulated, and the mixture of rubber and filler is solidified and dehydrated by a dehydrator, and the resulting coagulated product is screwed. A method for preparing a rubber composition in which a rubber composition comprising a dried coagulated product as a constituent component is kneaded with a kneader, introduced into an extruder and extruded, and at the tip of the screw extruder By connecting a gear pump and rotating the screw of the extruder, the gear pump is driven while pressurizing the coagulated product toward the gear pump, and the heated coagulated product discharged from the gear pump is directly supplied to the kneader. And

  According to the said structure, if the screw of a screw extruder is rotated and a solidified material is conveyed toward a gear pump, conveyance of a solidified material will be dammed by a gear pump, and the pressure of the solidified material near a gear pump will become high.

  When the screw is rotated while pressure is applied to the solidified material in this way, the amount of heat generated by the friction, shearing, and expansion of the rubber between the inner surface of the barrel and the outer surface of the screw increases, and the temperature of the solidified material is suitable for moisture evaporation. The temperature can be increased to 110 ° C. to 150 ° C., and the solidified product can be dried.

  In addition, although the solidified substance is in a hard state near room temperature, it becomes softer as the temperature increases, and exhibits fluidity when the temperature is raised to a temperature suitable for moisture evaporation. Therefore, it becomes possible to smoothly extrude the solidified product from the extruder while being appropriately plasticized. Furthermore, if the coagulated product discharged from the gear pump is supplied to the kneading machine as the main component of the rubber composition in a heated state, the load on the kneading machine can be greatly reduced because the coagulated product has flexibility. Thus, the kneading time can be shortened.

  It should be noted that the temperature of the solidified product in the vicinity of the gear pump changes according to the pressure applied to the solidified product, and the pressure applied to the solidified product changes depending on the number of rotations of the screw. Therefore, the temperature of the solidified product can be easily controlled by adjusting the number of rotations of the screw. As a result, even if the pressure of the coagulum fluctuates by driving the gear pump, the pressure of the coagulum, that is, the temperature of the coagulum can be maintained constant by adjusting the number of rotations of the screw.

  Further, by using a gear pump, after supplying a predetermined amount of the solidified product to the kneader, the discharge of the solidified product can be stopped by once stopping the gear pump. That is, it becomes possible to supply the coagulum intermittently. In this case, the solidified substance in the extruder can be maintained at a constant pressure by adjusting the rotation of the screw while the discharge of the solidified substance is stopped. As a result, the coagulated product discharged from the gear pump can be directly supplied to the kneader.

  Furthermore, the gear pump used in the present invention is excellent in quantitativeness. Therefore, by measuring the number of rotations of the gear pump, it is possible to calculate the amount of coagulum supplied to the kneader, and therefore, it is possible to save the trouble of weighing the coagulum separately.

  In order to dehydrate the coagulated product obtained by coagulating the mixture of rubber and filler from a mixture of rubber latex and slurry in which the filler is dispersed in water, a method such as centrifugation, screw press, or filter press is used. Can be adopted. Among them, in the screw press method, the temperature of the screw of the screw press machine can be controlled, and the solidified product can be efficiently dehydrated while being softened by heating.

  In this way, when the solidified product is discharged from the dehydrator in a heated state, if the heated solidified product is introduced directly into the screw extruder, the load on the screw extruder is reduced. The solidified product can be smoothly extruded from the extruder.

  It is desirable that the coagulated product discharged from the gear pump evaporates the water remaining inside as much as possible. Therefore, in the present invention, a die is connected to the discharge port of the gear pump, and a solidified product having a predetermined cross-sectional shape is extruded from the opening (discharge port) of the die. Specifically, the opening shape of the die is preferably formed into a slit shape, that is, a shape having an opening length longer than the opening width. Thereby, the shape of the solidified substance pushed out from the discharge port becomes a shape with a small thickness and a wide surface area such as a ribbon shape or a sheet shape.

  Therefore, the coagulated product extruded from the slit-shaped opening can smoothly evaporate the water remaining inside, and can quickly cool the coagulated product in a high temperature state. The specific opening shape of the die may be a wave shape or a zigzag shape in addition to a linear slit shape. Furthermore, it is also possible to form a combination of slits such as a T-shape, an H-shape, a + -shape, and the like. It is also possible to make the opening shape of the discharge port into an annular slit and extrude the solidified product into a cylindrical shape and then cut it into a sheet shape.

  The temperature of the solidified product is preferably 110 ° C. to 150 ° C. when discharged from the discharge port. Within this range, the solidified product can be sufficiently dried, and thermal degradation of the solidified product can be prevented. Moreover, it is preferable that the temperature of the solidified material supplied to a kneading machine shall be 40 to 150 degreeC. If the temperature is lower than this range, the solidified product may not be sufficiently flexible. If the temperature is higher than the above range, it becomes difficult to control the temperature in combination with shear heat generation during kneading, and vulcanization proceeds. There is.

  The water content of the coagulated product extruded from the extruder is preferably 1.5% by weight or less, and more preferably 1.0% by weight or less. If too much heat is applied to the coagulated product, the rubber may be thermally deteriorated. If the moisture content is 1% by weight or less, the effect on the kneadability and the properties of the vulcanized rubber is not so different. Therefore, considering these, the water content may be about 0.5% by weight or more. By setting the moisture content within the above range, the rubber composition can be favorably kneaded in the next kneading step.

  In the present invention, it is preferable that the water content of the coagulum to be charged into the extruder is 5% by weight or less. If the water content exceeds 5% by weight, the water may not be sufficiently evaporated in the extruder.

  The wet masterbatch obtained by the above production method has a low water content and is excellent in kneadability because it is appropriately plasticized. In addition, the rubber composition using the wet masterbatch according to the present invention has a low water content, excellent kneadability, and the rubber molecular chains are not cut excessively, so that the rubber properties after vulcanization are good. Can be maintained.

  As described above, the rubber composition using the wet masterbatch obtained according to the present invention is excellent in breaking strength and wear resistance, and therefore includes rubber compositions for tires such as tire dread rubber and sidewall rubber. It can be suitably used for various rubber compositions.

  In the present invention, from a mixture of rubber latex and a slurry in which a filler is dispersed in water, the mixture of rubber and filler is coagulated and dehydrated by a dehydrator, and the resulting coagulated product is fed to a screw extruder. A method for preparing a rubber composition in which a rubber composition containing a dried coagulated product as a constituent component is kneaded with a kneading machine by introducing and extruding, and a gear pump is connected to the tip of the screw extruder. By rotating the screw of the extruder, the gear pump is driven while the coagulum is pressurized toward the gear pump, and the heated coagulum discharged from the gear pump is supplied directly to the kneader, so that the water content is The rubber composition can be prepared efficiently in a short period of time without applying a large load on the kneader.

Process drawing which shows the preparation method of the rubber composition which concerns on this invention Cross section of extruder and kneader used in the above preparation method The graph which shows the time-dependent change of the electric power at the time of kneading | mixing in Example 2, and temperature. The graph which shows the time-dependent change of the electric power and temperature at the time of kneading | mixing in the comparative example 1

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing a method for preparing a rubber composition according to the present invention. First, the rubber latex preparation step 1 and the filler slurry adjustment step 2 are performed to prepare a rubber latex and a filler slurry.

  As rubber latex, it is also possible to use synthetic rubber latex in addition to natural rubber latex. The concentration of the rubber latex is preferably adjusted so that the solid content is 10 wt% to 40 wt% with a dispersion medium such as water.

  As the filler, in addition to carbon black and silica, talc, clay, other inorganic fillers, and the like can be used. When carbon black is used as the filler, various grades that are usually used as rubber fillers can be used. Specific examples include SAF, ISAF, HAF, FEF and the like, and these can be used alone or in admixture of two or more. As for the slurry density | concentration of a filler, solid content is 1 to 20 weight%, and it is more preferable that it is 3 to 15 weight%.

  The prepared rubber latex and carbon black slurry are subjected to dispersion treatment as necessary. The dispersion treatment can be performed using a high shear (rotor / stator) mixer, a homogenizer, a colloid mill, or the like. These devices can make particles finer by increasing the number of rotations or extending the processing time.

  Next, in the mixing / coagulation step 3, the rubber latex and the filler slurry are mixed with an appropriate stirring device, and then the rubber and the filler are used using a coagulant such as an acid such as formic acid or a metal salt such as aluminum sulfate. Solidify the mixture. In this case, if a stirring device that can give a strong impact to the mixed solution such as a high shear (rotor / stator) mixer or a homogenizer used in the dispersion processing device is used, the mixture is solidified without using a coagulant. be able to. Of course, a coagulant may be used at this time.

  In the solid-liquid separation step 4, the solidified product obtained as described above is alternately subjected to solid-liquid separation and washing to wash off the coagulant, and finally dehydrated in a state where moisture and impurities are removed. (Dehydration step 5). In the dehydration treatment, the water content of the coagulated product is required to be 5% by weight or less, and specifically, a method such as centrifugation, screw press, filter press or the like can be adopted. After dehydration, the solidified product is subjected to a drying / plasticizing step 6.

  FIG. 2 is a cross-sectional view of a screw extruder and a kneader used in the drying / plasticizing step 6. The screw extruder 8 includes a barrel 9 and a screw 10 installed inside the barrel 9, and a charging port 11 into which a solidified material after dehydration processing is charged is formed on the outer periphery of the rear portion of the barrel 9. A hopper 14 is provided at the insertion port 11. It is also possible to project a mixing pin on the inner peripheral surface of the barrel in order to enhance the plasticizing effect of the solidified product.

  A gear pump 15 is connected to the tip of the screw extruder 8 (tip of the barrel 9). The die 12 is attached to the discharge port 15 a of the gear pump 15, and the solidified material is discharged from the opening (discharge port) 13. Note that the opening of the die 12 is formed in a slit shape.

  In the present embodiment, a single screw extruder is used as the screw extruder, but a multi-screw extruder can also be used. However, it is preferable to use a single screw extruder from the viewpoint of suppressing excessive rubber molecular chain breakage caused by rotation of a plurality of screws.

  In the extruder 8 configured as described above, when the solidified product after the dehydration process is supplied to the extruder 8, the solidified product is sent to the front end side of the barrel 9 by the rotation of the screw 10. On the other hand, since the gear pump 15 is connected to the tip of the barrel 9, the rotation of the screw 10 is performed when the gear pump 15 is stopped or when the solidified material conveying speed of the gear pump is lower than the solidified material conveying speed of the screw 10. Along with this, the coagulum is gradually accumulated on the upstream side of the gear pump 15, and the pressure and temperature of the coagulum increase. A temperature sensor for detecting the temperature of the solidified product is installed at the barrel tip, and the rotational speed of the screw 10 is adjusted so that the temperature of the solidified product falls within the range of 110 ° C to 150 ° C. That is, when the temperature of the solidified product is increased, the rotational speed of the screw 10 is decreased, and when the temperature of the solidified product is decreased, the rotational speed of the screw 10 is increased.

  The solidified product maintained at a temperature suitable for the evaporation of moisture by the above-described operation is discharged in a ribbon-shaped state from the discharge port 13 by driving the gear pump 15. By forming the solidified product into a shape having a small thickness and a large surface area in this way, water remaining in the solidified product can be smoothly evaporated.

  Furthermore, it becomes possible to quickly reduce the temperature of the solidified product, and it is possible to suppress a decrease in rubber properties. The water content of the coagulated product after the drying / plasticizing step 6 is preferably 1.5% by weight or less. If it exceeds 1.5% by weight, in the next kneading step, slippage occurs between the rotor 16a of the kneader 16 and the rubber composition, resulting in longer kneading time, and the remaining water evaporates during vulcanization. As a result, voids may occur in the rubber product after vulcanization.

  By passing through the above process, the dried solidified substance, ie, the wet masterbatch 17, can be manufactured. The wet master batch 17 formed into a strip shape is directly supplied to the kneader 16 as it is. The temperature of the wet master batch 17 supplied to the kneader 16 is set to 40 ° C to 150 ° C. After weighing the wet master batch 17, by mixing and kneading other chemicals (kneading step 7), it is possible to efficiently prepare a rubber composition in a short time without imposing a large load on the kneader. .

  Since a kneading machine such as a Banbury mixer is a batch type, once a predetermined amount of wet masterbatch 17 is supplied to the kneader, the supply of the wet masterbatch 17 must be stopped for a while. In the embodiment, the supply of the wet master batch 17 can be controlled by stopping the gear pump 15.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, unless this invention exceeds the summary, it is not limited to these Examples.

[Production of wet masterbatch]
In this example, a wet master batch 17 was prepared using the apparatus described in the above embodiment, and a rubber composition was prepared using the wet master batch 17. Specifically, natural rubber latex was used as the rubber latex in the rubber latex preparation step 1, and the concentration was adjusted to 25% by weight of the rubber component. Furthermore, carbon black (SAF manufactured by Tokai Carbon Co., Ltd.) was used as a filler in the filler slurry preparation step 2, and this was dispersed in water with a high shear mixer to prepare a slurry having a solid content of 5% by weight.

  Thereafter, in the mixing / coagulation step 3, the rubber latex and the carbon black slurry were uniformly mixed using a high-speed mixer so that the rubber solid content: carbon black (weight ratio) = 100: 50. Then, while stirring the mixed solution, formic acid was added as a coagulant to adjust the pH to about 3 to 4 to produce a coagulum. The obtained solidified product was subjected to a dehydration process using a screw press (screw temperature: 100 ° C.) in a dehydration process 5 after a solid-liquid separation process 4. The water content of the solidified product after the dehydration treatment was 5% by weight.

  The obtained solidified product was directly supplied to a cold feed single screw extruder (barrel diameter 60 mm, barrel length L / barrel diameter D = 10) while being heated, and as shown in Table 1, the tip of the barrel The pressure applied to the solidified product in the part was changed variously to perform drying / plasticization treatment (Examples 1 and 2 and Comparative Example 1). In either case, the temperature control of the barrel and screw was set to 95 ° C. In Examples 1 and 2, the ribbon-shaped wet master batch 17 discharged from the gear pump 15 was supplied to the kneader as it was. On the other hand, in Comparative Example 1, the ribbon-shaped wet master batch 17 was formed into a bale and stored at room temperature, and then supplied to a kneader.

  The water content of the ribbon-like solidified product (wet masterbatch 17) obtained by drying and plasticizing was measured. The measurement results are shown in Table 1. In addition, MX-50 (105 degreeC measurement) by A & D company was used as a measuring instrument, and the average value and standard deviation of 3 samples sampled every 5 minutes were measured.

[Preparation of rubber composition]
A rubber composition was prepared using the wet master batch 17. The composition of the rubber composition is 1 part by weight of stearic acid (manufactured by Nippon Oil & Fats), 1 part by weight of an anti-aging agent (manufactured by Monsanto 6PPD), 150 parts by weight of wet masterbatch solids (of which 100 parts by weight of rubber component), zinc Contains 3 parts by weight of Hana (Mitsui Kinzoku No. 1), 1 part by weight of wax (manufactured by Nippon Seiwa), 2 parts by weight of sulfur (manufactured by Tsurumi Chemical Co., Ltd.) and 1 part by weight of accelerator (CBS made by Sanshin Chemical) did.

  The total amount of the rubber composition was 1.5 kg, and the kneading machine 16 was kneaded using a B-type Banbury mixer manufactured by Kobe Steel. In addition, the wet masterbatch of the same numerical value as the average moisture content described in Table 1 was used for the kneader.

  The kneading conditions were as follows. First, the wet masterbatch was put into a kneader, the ram was lowered and kneaded for 2 minutes, then the ram was raised once, and other components were put into the kneader to restart kneading. After 4 minutes from the start of kneading, the ram was raised to scrape off the rubber composition adhering to the periphery of the ram, and the ram was lowered again to continue the kneading. And kneading | mixing was complete | finished when the temperature of the rubber composition became 135 degreeC.

[Evaluation results]
The time-dependent changes in power and temperature during kneading in Example 2 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively. In the figure, the solid line indicates power and the broken line indicates temperature. In both Example 2 and Comparative Example 1, the temperature of the wet masterbatch 17 when discharged from the gear pump was 105 ° C., and the water content was the same as 2% by weight.

  However, in Example 2, the wet master batch 17 was fed to the kneader in a heated state of 60 ° C., whereas in the comparative example 1, a bale-shaped molded product stored at 30 ° C. was used. Supply to kneading machine. As a result, the time required for Example 2 to reach 135 ° C. was shorter than that of Comparative Example 1, and the total kneading time of Example 2 was 1 minute and 20 seconds shorter than that of Comparative Example 1.

  Moreover, the maximum power value A during the kneading was 9.4 kW in Example 2, whereas in Comparative Example 1, the wet masterbatch 17 at room temperature was very hard and thus increased to 11 kW. In Example 1, it can be seen that a considerable load is applied to the kneader. Furthermore, the total amount of power during kneading (power amount [kWh] = power [kW] × time [h]) was 512 kWh in Example 2, but 688 kWh in Comparative Example 1, which is It became clear that it can save power consumption considerably.

  Moreover, about Example 1, since the discharge temperature of the wet masterbatch 17 was high temperature of 125 degreeC 20 degreeC higher than Example 2, the average moisture content became a low value of the half of Example 2. Furthermore, in Example 1, since it supplied to the kneader at 80 ° C., which is 20 ° C. higher than that in Example 2, the kneading time in Example 1 is 20 seconds shorter than in Example 2, and the total amount of power during kneading is reduced. Became 485 kWh. In addition, the standard deviation of the moisture content was significantly smaller in Example 1 than in Example 2 and Comparative Example 1. Accordingly, the moisture content of the wet masterbatch can be accurately calculated in Example 1 with fewer sampling times than in Example 2 and Comparative Example 1, and the time for calculating the solid content of the wet masterbatch is shortened. It becomes possible to do.

  In both Examples 1 and 2, after supplying a predetermined amount of wet masterbatch to the kneader, the gear pump is temporarily stopped and the rotation speed of the screw 10 is adjusted to keep the solidified temperature at the tip of the barrel constant. I tried to keep it. After the first kneading in the kneading machine is completed and the rubber composition in the kneading machine is discharged, the gear pump is driven again to supply the wet master batch to the kneading machine, and the second kneading is performed under the same conditions as the first time. Carried out. As a result, the kneading time and the characteristics of the vulcanized rubber were the same for the first time and the second time. Thereby, it became clear that a wet masterbatch can be intermittently supplied directly to a kneader using a gear pump.

DESCRIPTION OF SYMBOLS 1 Rubber latex preparation process 2 Filler slurry preparation process 3 Mixing / coagulation process 4 Solid-liquid separation process 5 Dehydration process 6 Drying / plasticization process 7 Kneading process 8 Screw extruder 9 Barrel 10 Screw 11 Input port 12 Die 13 Discharge port 14 Hopper 15 Gear pump 16 Kneading machine 17 Wet masterbatch

Claims (9)

From a mixture of rubber latex and slurry in which filler is dispersed in water, the rubber and filler mixture is coagulated and dehydrated by a dehydrator, and the resulting coagulum is introduced into a screw extruder and pressed. A method of preparing a rubber composition in which a rubber composition comprising a coagulated product after drying as a constituent component is kneaded with a kneader, wherein a gear pump is connected to the tip of the screw extruder, and the extruder Preparation of a rubber composition characterized in that the coagulum is supplied to the gear pump while the coagulum is pressurized by rotating the screw of the screw, and the heated coagulum discharged from the gear pump is directly supplied to the kneader by driving the gear pump. Method. A method for preparing a rubber composition, wherein the amount of coagulum supplied to the kneader is calculated by measuring the number of rotations of the gear pump. The method for preparing a rubber composition according to claim 1 or 2, wherein the coagulated product is discharged from the dehydrator in a heated state, and the coagulated product in the heated state is directly introduced into a screw extruder. The method for preparing a rubber composition according to any one of claims 1 to 3, wherein a die is connected to a discharge port of the gear pump. The method for preparing a rubber composition according to any one of claims 1 to 4, wherein the temperature of the solidified product supplied to the kneader is 40 ° C to 150 ° C. The method for preparing a rubber composition according to any one of claims 1 to 5, wherein the water content of the coagulated product extruded from the extruder is 1.5% by weight or less. The method for preparing a rubber composition according to any one of claims 1 to 6, wherein the temperature of the solidified product extruded from the gear pump is 110 ° C to 150 ° C. The method for preparing a rubber composition according to any one of claims 1 to 7, wherein the water content of the coagulated product charged into the extruder is 5% by weight or less. A rubber composition produced by the method according to claim 1.

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