JP6378065B2 - Rubber wet masterbatch and rubber composition containing rubber wet masterbatch - Google Patents

Description

  The present invention relates to a rubber wet masterbatch containing at least a filler, a dispersion solvent, and a particulate crumb obtained using a rubber latex solution as raw materials, and a rubber composition containing the rubber wet masterbatch. In particular, the present invention relates to a rubber wet masterbatch that can be a raw material for a vulcanized rubber having excellent tear resistance and fatigue resistance, and a rubber composition containing the rubber wet masterbatch.

  Conventionally, in the rubber industry, it has been known to use a rubber wet masterbatch in order to improve the processing performance and the dispersibility of a filler when producing a rubber composition containing a filler such as carbon black. Yes. This is because the filler and the dispersion solvent are mixed in advance at a certain ratio, and the filler-containing slurry solution in which the filler is dispersed in the dispersion solvent by mechanical force and the rubber latex solution are mixed in the liquid phase. Thereafter, the solidified product obtained by adding a coagulant such as an acid is recovered and dried. When using a rubber wet masterbatch, compared to using a rubber dry masterbatch obtained by mixing the filler and rubber in a solid phase, the dispersibility of the filler is superior, and rubber properties such as processing performance and reinforcement performance A rubber composition having excellent resistance is obtained. By using such a rubber composition as a raw material, for example, a rubber product such as a pneumatic tire with reduced rolling resistance and excellent fatigue resistance can be produced.

  In the rubber wet masterbatch manufacturing method described above, when water is removed from the filler-containing rubber coagulated product obtained after the coagulation step, the rubber wet masterbatch contains particulate crumb in which the filler is uniformly dispersed in the rubber component. Is obtained. The rubber wet masterbatch containing the obtained particulate crumb is compressed and / or heated to be processed into, for example, a plate-like bale for storage / transport, etc., or to improve moldability. . The veil of the rubber wet masterbatch is then kneaded with various compounding agents and processed into the desired rubber composition, but when the crumbs of the rubber wet masterbatch processed into veil are firmly adhered, When mixing compounding agents, etc., there was a risk of causing poor dispersion.

  The following Patent Document 1 describes a technique for manufacturing a rubber wet masterbatch including a substantially cylindrical crumb having a maximum length of 40 to 60 mm and a width and thickness of 5 to 10 mm using a pelletizer. Has been.

US2008-0110771

  However, as a result of intensive studies by the present inventors, when a rubber composition is produced using a rubber wet masterbatch containing a substantially columnar crumb obtained by the technique described in Patent Document 1, a substantially columnar crumb is obtained. Even when processed into a veil, or simply deposited and stored, the contact area on the cylinder side of the crumb is increased and kneaded with various compounding agents due to strong adhesion. In some cases it was found to cause poor dispersion.

  The present invention has been made in view of the above circumstances, and its purpose is to suppress the adhesion of crumb in rubber wet masterbatch when dispersing various compounding agents, and to enhance the dispersibility of various compounding agents, An object of the present invention is to provide a rubber wet masterbatch capable of improving the tear resistance and fatigue resistance of the final vulcanized rubber, and a rubber composition containing the rubber wet masterbatch.

  The above object can be achieved by the present invention as described below. That is, the present invention is a rubber wet masterbatch containing at least a filler, a dispersion solvent, and a particulate crumb obtained from a rubber latex solution, the crumb having a maximum length A and a minimum length B. The ratio (A / B) is 1 ≦ A / B ≦ 5, and the maximum length A is 39 mm or less.

  When the maximum length of a crumb is A and the minimum length is B, a cuboid or columnar crumb with an A / B exceeding 5 is a contact area between adjacent crumbs during storage or when processed into a bale. Becomes larger and its adhesion grows. Therefore, when mixing with various compounding agents, poor dispersion tends to occur. On the other hand, the rubber wet masterbatch according to the present invention has a ratio (A / B) between the maximum length A and the minimum length B of the crumb of 1 or more and 5 or less, so when being stored or processed into a bale The contact area between adjacent crumbs is reduced, and the adhesion is also reduced. Therefore, when mixing with various compounding agents, poor dispersion hardly occurs.

  Furthermore, since the maximum length A of the particulate crumb is set to 39 mm or less, when kneading various compounding agents and crumb, a shearing force acts uniformly on the crumb. For this reason, various compounding agents can be suitably dispersed in a rubber wet masterbatch containing crumb. On the other hand, when the maximum length A of the crumb is larger than 39 mm, the shearing force acting on the crumb may become uneven, and as a result, poor dispersion of various compounding agents is likely to occur.

  In the rubber wet masterbatch, it is preferable that the crumb has a substantially spherical shape or a substantially elliptical shape. In this case, due to the fact that the contact between adjacent crumbs approaches point contact and the contact area becomes smaller, the dispersion failure can be more effectively suppressed when finally mixed with various compounding agents.

  In the rubber wet masterbatch, the crumb preferably has a filler content of 65 parts by mass or less when the total amount of rubber components is 100 parts by mass. When the total amount of the rubber component is 100 parts by mass, when the filler content exceeds 65 parts by mass, the adhesion between adjacent crumbs becomes small, and therefore, poor dispersion occurs when mixed with various compounding agents. It tends to be difficult. On the other hand, in the present invention, the filler content is small (when the total amount of the rubber component is 100 parts by mass, the filler content is 65 parts by mass or less), and the adhesion between adjacent crumbs is increased. Even in this case, due to the devised crumb size and shape, poor dispersion can be suppressed even if various compounding agents are mixed.

  In the rubber wet masterbatch, when the density of the rubber wet masterbatch calculated from the mass ratio of the rubber component and the filler is Da and the bulk density of the rubber wet masterbatch calculated from the mass per unit volume is Db Db / Da ≦ 0.79 is preferable. When Db / Da exceeds 0.79, the contact area between adjacent crumbs increases during storage or in a rubber wet masterbatch processed into a bale, so the contact area also increases, and various compounding agents are mixed. When this occurs, poor dispersion tends to occur. On the other hand, if Db / Da ≦ 0.79, the degree of adhesion between adjacent crumbs can be effectively reduced in a rubber wet masterbatch. it can.

  The present invention relates to a rubber composition containing the rubber wet masterbatch. Vulcanized rubber obtained by vulcanizing such a rubber wet masterbatch and a rubber composition is excellent in tear resistance and fatigue resistance.

  The rubber wet masterbatch according to the present invention includes at least a filler, a dispersion solvent, and particulate crumbs obtained using a rubber latex solution as a raw material. Such a particulate crumb is manufactured through at least a solidification step and a heating step. Each step will be described below.

(Coagulation process)
In the coagulation step, a slurry solution containing a filler and a dispersion solvent and a rubber latex solution are mixed and coagulated to produce a filler-containing rubber coagulum. In particular, in the coagulation step, when the filler is dispersed in the dispersion solvent, a step of producing a slurry solution containing the filler to which the rubber latex particles are adhered by adding at least a part of the rubber latex solution (I ), The slurry solution, and the remaining rubber latex solution to produce a filler-containing rubber latex solution to which rubber latex particles are adhered, and a filler-containing rubber latex to which rubber latex particles are adhered. It is preferable to have a step (III) of coagulating the solution to produce a filler-containing rubber coagulated product.

  In the present invention, the filler means an inorganic filler usually used in the rubber industry, such as carbon black, silica, clay, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide. Among the inorganic fillers, carbon black can be particularly preferably used in the present invention.

  As carbon black, for example, conductive carbon black such as acetylene black and ketjen black can be used in addition to carbon black used in ordinary rubber industry such as SAF, ISAF, HAF, FEF, and GPF. The carbon black may be a granulated carbon black or a non-granulated carbon black granulated in the normal rubber industry in consideration of its handleability.

  As the dispersion solvent, it is particularly preferable to use water, but for example, water containing an organic solvent may be used.

  Natural rubber latex solution and synthetic rubber latex solution can be used as the rubber latex solution.

  The natural rubber latex solution is a natural product produced by the metabolic action of plants, and a natural rubber / water system is particularly preferred in which the dispersion solvent is water. The number average molecular weight of the natural rubber in the natural rubber latex used in the present invention is preferably 2 million or more, and more preferably 2.5 million or more. Examples of the synthetic rubber latex solution include those produced by emulsion polymerization of styrene-butadiene rubber, butadiene rubber, nitrile rubber, and chloroprene rubber.

  Hereinafter, an example of a preferable coagulation step will be described based on an example in which a natural rubber latex solution is used as the filler and carbon black and a rubber latex solution. In this case, it is possible to produce a rubber wet masterbatch in which the degree of dispersion of carbon black is very high and the low heat generation performance, durability performance and rubber strength are further improved when vulcanized rubber is used. Natural rubber latex can be used without distinction, such as concentrated latex and fresh latex called field latex.

(1) Step (I)
In step (I), when carbon black is dispersed in a dispersion solvent, a slurry solution containing carbon black to which natural rubber latex particles are adhered is produced by adding at least a part of the natural rubber latex solution. The natural rubber latex solution may be mixed with a dispersion solvent in advance, and then carbon black may be added and dispersed. Alternatively, carbon black may be added to the dispersion solvent, and then carbon black may be dispersed in the dispersion solvent while adding the natural rubber latex solution at a predetermined addition rate, or carbon black may be added to the dispersion solvent. Then, carbon black may be dispersed in a dispersion solvent while adding a certain amount of natural rubber latex solution in several times. By dispersing carbon black in the dispersion solvent in the presence of the natural rubber latex solution, a slurry solution containing carbon black with natural rubber latex particles attached thereto can be produced. The amount of the natural rubber latex solution added in the step (I) is 0.075 to 12% by mass with respect to the total amount of the natural rubber latex solution used (the total amount added in the step (I) and the step (II)). Illustrated.

  In the step (I), the amount of solid content (rubber) of the natural rubber latex solution to be added is preferably 0.25 to 15% by mass ratio with respect to carbon black, and preferably 0.5 to 6%. preferable. Moreover, it is preferable that the solid content (rubber) density | concentration in the natural rubber latex solution to add is 0.2-5 mass%, and it is more preferable that it is 0.25-1.5 mass%. In these cases, it is possible to produce a rubber wet masterbatch in which the degree of dispersion of carbon black is increased while reliably attaching the natural rubber latex particles to the carbon black.

  In the step (I), as a method of mixing carbon black and a dispersion solvent in the presence of a natural rubber latex solution, a high shear mixer, a high shear mixer, a homomixer, a ball mill, a bead mill, a high pressure homogenizer, an ultrasonic homogenizer, a colloid mill, etc. And a method of dispersing carbon black using a general disperser.

  The "high shear mixer" is a mixer having a rotor and a stator, and the rotor rotates with a precise clearance between a rotor capable of high-speed rotation and a fixed stator. Means a mixer with a high shearing action. In order to produce such a high shearing action, it is preferable that the clearance between the rotor and the stator is 0.8 mm or less and the circumferential speed of the rotor is 5 m / s or more. A commercial item can be used for such a high shear mixer, for example, “High Shear Mixer” manufactured by SILVERSON.

  In the present invention, carbon black and a dispersion solvent are mixed in the presence of a natural rubber latex solution to produce a slurry solution containing carbon black to which natural rubber latex particles are adhered, in order to improve the dispersibility of the carbon black. An activator may be added. As the surfactant, known surfactants in the rubber industry can be used, and examples thereof include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. It is done. Further, alcohol such as ethanol may be used instead of or in addition to the surfactant. However, when a surfactant is used, there is a concern that the rubber properties of the final vulcanized rubber will be lowered. Therefore, the amount of the surfactant to be blended is 100 mass of solid content (rubber) of the natural rubber latex solution. The amount is preferably 2 parts by mass or less, more preferably 1 part by mass or less, and substantially no surfactant is used. Moreover, you may add an anti-aging agent in order to suppress deterioration of solid content (rubber) of a natural rubber latex solution in process (I) and process (II). As the anti-aging agent, anti-aging agents known in the rubber industry can be used, and examples thereof include amine-based, phenol-based, organic phosphite-based, and thioether-based agents.

  The carbon black to which the natural rubber latex particles are adhered in the slurry solution produced in the step (I) has a 90% volume particle size (μm) (“D90”) of preferably 31 μm or more, and more than 35 μm. It is more preferable. In this case, the dispersibility of the carbon black in the slurry solution is excellent and the reaggregation of the carbon black can be prevented, so that the storage stability of the slurry solution is excellent, and the low heat generation performance of the final vulcanized rubber, Excellent durability and rubber strength. In the present invention, D90 of the carbon black to which the natural rubber latex particles are attached means a value measured in addition to the carbon black and including the attached natural rubber latex particles.

(2) Step (II)
In step (II), the slurry solution and the remaining natural rubber latex solution are mixed to produce a carbon black-containing rubber latex solution to which the natural rubber latex particles are adhered. The method of mixing the slurry solution and the remaining natural rubber latex solution in a liquid phase is not particularly limited, and the slurry solution and the remaining natural rubber latex solution are mixed with a high shear mixer, a high shear mixer, a homomixer, and a ball mill. And a mixing method using a general disperser such as a bead mill, a high-pressure homogenizer, an ultrasonic homogenizer, and a colloid mill. If necessary, the entire mixing system such as a disperser may be heated during mixing.

  The remaining natural rubber latex solution preferably has a higher solid content (rubber) concentration than the natural rubber latex solution added in step (I), considering the drying time and labor in the next step (III). Specifically, the solid content (rubber) concentration is preferably 10 to 60% by mass, and more preferably 20 to 30% by mass.

(3) Step (III)
In the step (III), the carbon black-containing rubber latex solution to which the natural rubber latex particles are adhered is coagulated to produce a filler-containing rubber coagulated product. Examples of the coagulation method include a method in which a coagulant is contained in a carbon black-containing rubber latex solution to which natural rubber latex particles are adhered and coagulated.

  As the coagulant used in the coagulation step, acids such as formic acid and sulfuric acid usually used for coagulation of rubber latex solutions, and salts such as sodium chloride can be used.

  In the filler-containing rubber coagulated product obtained after the step (III), the ratio of the rubber component to the filler is 100 parts by weight of rubber (solid) so that the amount of filler in the crumb is finally within a desired range It is preferable to contain 65 parts by mass or less of the filler with respect to (min). In this case, finally, a rubber wet masterbatch with excellent dispersibility of various compounding agents while improving the balance of the degree of dispersion of the filler and the low heat generation performance and durability when used as a vulcanized rubber. Can be manufactured.

(Heating process)
In the heating step, the filler-containing rubber coagulum is dehydrated, dried and plasticized in one step by heating to 180 to 200 ° C., for example, using a single screw extruder. The filler-containing rubber coagulum discharged from the single screw extruder becomes a crumb with a low water content. For example, depending on the speed at which the crumb is discharged from the single screw extruder and the cutter installed at the discharge port of the single screw extruder The maximum length A and the minimum length B of the crumb are optimized by adjusting the cutting speed of the crumb and further the charging speed of the filler-containing rubber coagulum to be fed into the single screw extruder. A crumb set at (A / B) can be manufactured. Specifically, for example, if the speed at which the crumb is discharged from the single-screw extruder is faster than the cutting speed of the crumb by the cutter installed at the discharge port of the single-screw extruder, When the crumb cutting speed by the cutter installed at the discharge port of the single screw extruder is adjusted so that the crumb (length A is long) is obtained and the extrusion length is substantially the same as the discharge port of the single screw extruder, A / B is close to 1, and a substantially spherical or ellipsoidal crumb is obtained.

  In the present invention, it is preferable to set the maximum length A of the particulate crumb to 39 mm or less in order to suppress dispersion failure when various compounding agents are mixed in the rubber wet masterbatch. Although this adjustment method is not particularly limited, for example, it can be adjusted by optimizing the charging speed of the filler-containing rubber coagulum charged into the single screw extruder during the heating process. When this charging speed is increased, the filler-containing rubber coagulum is densely filled in the single-screw extruder, so that the particle size of the crumb discharged from the discharge port increases.

  A rubber wet masterbatch obtained by blending the obtained crumbs with various compounding agents as required is compressed and / or heated and processed into, for example, a plate-like veil. Here, when the density of the rubber wet masterbatch calculated from the mass ratio of the rubber component and the filler is Da, and the bulk density of the rubber wet masterbatch calculated from the mass per unit volume is Db, Db / Da ≦ Processing into a bale of 0.79 is preferable because the degree of adhesion between adjacent crumbs can be reduced and the degree of dispersion of various compounding agents can be increased.

  The rubber wet masterbatch according to the present invention includes a kneading step and a vulcanizing compounding agent kneading step following the heating step, and mixing various compounding agents with the rubber wet masterbatch to produce a rubber composition. Can do.

(Kneading process)
Compound other than vulcanizing compound such as stearic acid, zinc white, anti-aging agent, silica, silane coupling agent, softener such as wax and oil, processing aid, etc. in rubber wet masterbatch obtained after heating process A process in which an agent is added and kneaded using a mixing and dispersing machine. In the kneading process, these compounding ingredients are mixed with the rubber component to increase the strength of the rubber product after vulcanization, to improve the rubber kneading performance, resulting from radicals generated by the breaking of rubber molecular chains The effect of preventing deterioration of the rubber is obtained. In the kneading step, a meshing Banbury mixer, a tangential Banbury mixer, a kneader, or the like can be used, and it is particularly preferable to use a meshing Banbury mixer.

  As an anti-aging agent, an aromatic amine-based anti-aging agent, an amine-ketone-based anti-aging agent, a monophenol-based anti-aging agent, a bisphenol-based anti-aging agent, a polyphenol-based anti-aging agent, dithiocarbamic acid, which are usually used for rubber Anti-aging agents such as a salt-based anti-aging agent and a thiourea-based anti-aging agent may be used alone or in an appropriate mixture. The content of the antioxidant is more preferably 0.3 to 3.0 parts by mass, and 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the rubber component (solid content) of the rubber wet masterbatch. More preferably, it is a part.

(Vulcanization system compounding process)
A vulcanizing compounding agent such as a vulcanizing agent such as sulfur or a vulcanization accelerator is added to the rubber composition obtained after the kneading step, and the whole is kneaded. When the rubber composition obtained after the vulcanizing compounding agent kneading step is heated to a predetermined temperature or more, the vulcanizing agent in the rubber composition reacts with the rubber molecules, forms a bridge structure between the rubber molecules, and the molecules A three-dimensional network is formed to give rubber elasticity.

  Sulfur should just be normal sulfur for rubber | gum, For example, powder sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur etc. can be used. The content of sulfur in the rubber composition according to the present invention is preferably 0.3 to 6 parts by mass with respect to 100 parts by mass of the rubber component. If the sulfur content is less than 0.3 parts by mass, the crosslinking density of the vulcanized rubber will be insufficient and the rubber strength will be reduced. If it exceeds 6 parts by mass, both heat resistance and durability will be deteriorated. . In order to ensure good rubber strength of the vulcanized rubber and to further improve heat resistance and durability, the sulfur content is 2.0 to 4.5 parts by mass with respect to 100 parts by mass of the rubber component. Is more preferable.

  As the vulcanization accelerator, sulfenamide vulcanization accelerator, thiuram vulcanization accelerator, thiazole vulcanization accelerator, thiourea vulcanization accelerator, guanidine vulcanization, which are usually used for rubber vulcanization. Vulcanization accelerators such as accelerators and dithiocarbamate vulcanization accelerators may be used alone or in admixture as appropriate. As for content of a vulcanization accelerator, it is more preferable that it is 1-5 mass parts with respect to 100 mass parts of rubber components, and it is further more preferable that it is 1.5-4 mass parts.

  Hereinafter, the present invention will be described in more detail with reference to examples. The raw materials used and the equipment used are as follows.

(Raw materials used)
a) Carbon black
Carbon black “N330”; “Seast 3” (manufactured by Tokai Carbon Co., Ltd.)
Carbon black “N110”; “Seast 9” (manufactured by Tokai Carbon Co., Ltd.)
Carbon black “N550”; “Seast SO” (manufactured by Tokai Carbon Co., Ltd.)
b) Dispersion solvent Water c) Rubber latex solution Natural rubber concentrated latex solution; made by Golden Hope ((DRC (Dry Rubber Content)) = 31.2% and water adjusted to 25% by mass at room temperature d) Coagulant formic acid (primary 85%, 10% solution diluted to pH 1.2), (manufactured by Nacalai Tesque)
e) Zinc Hana No. 3 Zinc Hana (Mitsui Metals)
f) Stearic acid “Lunac S-20” (manufactured by Kao Corporation)
g) Wax “OZOACE0355” (manufactured by Nippon Seiwa Co., Ltd.)
h) Antiaging agent Antiaging agent (A) Aromatic amine type: N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine “6PPD” (manufactured by Monsanto), melting point 44 ° C.
Anti-aging agent (B) 2,2,4-trimethyl-1,2-dihydroquinoline polymer “RD” (manufactured by Ouchi Shinsei Chemical Co., Ltd.), melting point 80-100 ° C.
i) Sulfur “5% oil-filled fine powder sulfur” (manufactured by Tsurumi Chemical Co., Ltd.)
j) Vulcanization accelerator Vulcanization accelerator (A) N-cyclohexyl-2-benzothiazolesulfenamide "Sunseller CM" (manufactured by Sanshin Chemical Industry Co., Ltd.)
Vulcanization accelerator (B) 1,3-diphenylguanidine “Noxeller D” (Ouchi Shinsei Chemical Co., Ltd.)

(Evaluation)
The evaluation was performed on rubber obtained by heating and vulcanizing each rubber composition at 150 ° C. for 30 minutes using a predetermined mold.

(Clam size)
A screening test was performed in accordance with JIS Z-8815-1994, and the particle size distribution of the particle group was measured. Next, the percentage of openings on the sieve obtained by adding the percentage on the sieve for each sieve opening in order from the maximum opening was calculated to be 90% and 100%. The opening at which the percentage on the integrated sieve is 90% is referred to as the maximum length A, and the opening at which the percentage on the integrated sieve is 100% is referred to as the minimum length B. Such particle sizes are shown in Tables 1-2.

(Tear resistance of vulcanized rubber)
A sample in which a crescent shape defined by JIS K6252 was punched out and a notch of 0.50 ± 0.08 mm was put in the center of the indentation was tested with a tensile tester of Shimadzu Corporation at a tensile speed of 500 mm / min. Evaluation is indexed with Comparative Example 1 as 100 for Examples 1-3 and Comparative Examples 2-5, Indexed with Comparative Example 6 as 100 for Example 4, and Comparative Example 7 as 100 for Example 5. Indexing was performed, and Examples 6 to 8 were indexed with Comparative Example 8 as 100, Example 9 was indexed with Comparative Example 9 as 100, and Example 10 was indexed with Comparative Example 10 as 100. The larger the value, the better the tear resistance.

(Fatigue resistance of vulcanized rubber)
It measured according to JIS K6260. Evaluation is indexed with Comparative Example 1 as 100 for Examples 1-3 and Comparative Examples 2-5, Indexed with Comparative Example 6 as 100 for Example 4, and Comparative Example 7 as 100 for Example 5. Indexing was performed, and Examples 6 to 8 were indexed with Comparative Example 8 as 100, Example 9 was indexed with Comparative Example 9 as 100, and Example 10 was indexed with Comparative Example 10 as 100. Higher values mean higher fatigue resistance and better results.

Example 1
50 parts by mass of carbon black is added to a diluted natural rubber latex solution adjusted to 0.5% by mass (the solid content (rubber amount) of the latex solution is 1 part by mass with respect to carbon black), and this is added to PRIMIX A carbon black-containing slurry solution to which the natural rubber latex particles were adhered was produced by dispersing carbon black using Robomix (conditions of the Robomix: 9000 rpm, 30 minutes) (Step (I)).

  Next, water is added to the remaining natural rubber concentrated latex solution (solid content (rubber) concentration of 25 mass%) to the carbon black-containing slurry solution to which the natural rubber latex particles produced in the step (I) are attached. And the natural rubber latex solution used in step (I) is added so that the solid content (rubber) amount is 100 parts by mass, and then a household mixer SM-L56 manufactured by SANYO Co., Ltd. is used. Mixing was performed using a mold (conditions of the mixer: 11300 rpm, 30 minutes) to produce a carbon black-containing natural rubber latex solution to which the natural rubber latex particles were adhered (step (II)).

(Coagulation process)
A carbon black-containing natural rubber coagulated product is added to the carbon black-containing natural rubber latex solution to which the natural rubber latex particles produced in the step (II) are attached, until a pH of 4 is obtained by adding a 10% by weight aqueous solution of formic acid as a coagulant. Produced (step (III)).

(Heating process)
Using a squeezer type single screw extruder [Suehiro EPM, part number V-02, barrel diameter 90 mm, (barrel length) / (barrel diameter) (L / D) = 8.6], heating temperature With the temperature set to 200 ° C. (heating temperature of heating screw 200 ° C.), the carbon black-containing natural rubber coagulum obtained in step (III) is charged into a single screw extruder (feeding speed 200 g / min) and kneaded. However, dehydration, drying, and plasticization were performed in one step. When the crumb dried in the single screw extruder is discharged from the discharge port, it is cut by a cutter rotating coaxially with the screw axis (cutting speed (15 times / min)), and the maximum length of the crumb A = 20 mm, minimum A substantially spherical crumb having a length B = 20 mm and A / B = 1 was produced. The obtained crumb was press-molded into a plate-like veil (bale width 40 mm, bale length 60 mm, bale thickness 10 mm) to produce a natural rubber wet masterbatch made of crumb processed into a bale. In Tables 1 and 2, Da means the density of the rubber wet masterbatch calculated from the mass ratio of the rubber component and carbon black, and Db means the bulk density of the rubber wet masterbatch calculated from the mass per unit volume. The Db of the natural rubber wet masterbatch processed into a bale can be calculated by (mass of bale) / ((bale width) × (bale length) × (bale height)).

(Kneading process and vulcanizing compound compounding process)
For the natural rubber wet masterbatch made of crumb processed into a veil, using a B-type Banbury mixer (manufactured by Kobe Steel), blending various additives listed in Table 1 and Table 2 into a rubber composition, The physical properties of the vulcanized rubber were measured. The results are shown in Tables 1 and 2.

Comparative Examples 1, 6, 7, 8, 9, 10
A rubber composition and a vulcanized rubber were produced in the same manner as in Example 1 except that a dry masterbatch was used instead of the rubber wet masterbatch.

Examples 2-10, Comparative Examples 2-5
A rubber composition and a vulcanized rubber were produced in the same manner as in Example 1 except that the crumb shape, A, B, A / B, Da, Db, and Da / Db were changed.

  From the results of Tables 1 and 2, it can be seen that the vulcanized rubbers of the rubber wet masterbatch-containing rubber compositions according to Examples 1 to 10 are excellent in tear resistance and fatigue resistance.

Claims (4)

A rubber wet masterbatch containing at least a filler, a dispersion solvent, and a particulate crumb obtained from a rubber latex solution,
The crumb has a ratio (A / B) between its maximum length A and minimum length B,
1 ≦ A / B ≦ 5
, And the and the maximum length A is Ri der less 39 mm,
When the density of the rubber wet masterbatch calculated from the mass ratio of the rubber component and the filler is Da, and the bulk density of the rubber wet masterbatch calculated from the mass per unit volume is Db, Db / Da ≦ 0. A rubber wet masterbatch, which is 79 .   The rubber wet masterbatch according to claim 1, wherein the shape of the crumb is substantially spherical or elliptical.   The rubber wet masterbatch according to claim 1 or 2, wherein the crumb has a content of the filler of 65 parts by mass or less when the total amount of rubber components is 100 parts by mass. The rubber composition containing the rubber wet masterbatch in any one of Claims 1-3 .