JP2012158666A - Rubber composition and production method therefor, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition with an exothermic property and improved fatigue resistance and to manufacture a pneumatic tire.SOLUTION: The rubber composition is obtained by dry mixing of a natural rubber wet master batch prepared by mixing a natural rubber latex and a carbon black-containing slurry solution in a liquid phase and drying the same, and a dry rubber including as the main component a natural rubber and/or a polyisoprene rubber. It is preferable that the total amount of the rubber component in the natural rubber wet master batch A and the total amount of the rubber component in the dry rubber B satisfy A:B=90:10 to 70:30.

Description

  The present invention relates to a rubber composition and a method for producing the same, and more specifically, to a rubber composition excellent in heat generation and fatigue resistance, particularly useful for a pneumatic tire and a method for producing the same. . Furthermore, the present invention relates to a pneumatic tire using the rubber composition.

  Conventionally, in the rubber industry, it is known to use a natural rubber wet masterbatch in order to improve the processability and dispersibility of fillers when producing rubber compositions containing fillers such as carbon black. (For example, Patent Document 1 below). This is because the filler and the dispersion solvent are mixed in advance at a certain ratio, and the slurry solution containing filler in which the filler is dispersed in the dispersion solvent by mechanical force and the natural rubber latex 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 natural rubber wet masterbatch, compared to using a rubber dry masterbatch obtained by dry-mixing the filler and rubber, the dispersibility of the filler is superior and rubber properties such as processability and reinforcement are improved. An excellent rubber composition 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 manufactured.

  In Patent Document 2 below, for the purpose of achieving both the light weight of a tire and the durability of a belt, (i) a slurry solution is obtained by dispersing water in a water using a high shear mixer in the absence of a surfactant. And (ii) mixing the slurry solution with at least one of natural rubber latex and synthetic isoprene rubber latex, a rubber masterbatch produced by a method comprising a belt layer coating rubber The point used as is described. However, as a result of intensive studies by the inventor, it has been found that such a rubber composition has room for further improvement in terms of heat generation and fatigue resistance.

  In Patent Document 3 below, natural rubber (NR) raw material latex and carbon black (CB) are mixed, coagulated and dried in an aqueous medium for the purpose of improving wear resistance and high temperature side tan δ. Use of a rubber composition obtained by mixing a natural rubber masterbatch containing CB, an additional raw rubber having a glass transition temperature (Tg) in the range of −50 ° C. to −20 ° C., and silica in a closed mixer. And styrene-butadiene copolymer rubber is exemplified as such additional raw material rubber. Further, in Patent Document 4 below, for the purpose of improving the balance of tan δ and abrasion resistance of the vulcanized rubber, 50 to 90 parts by weight of latex of the raw material rubber A (in terms of solid content), carbon black 40 Carbon black-containing rubber composition obtained by coagulating, dehydrating and drying a rubber latex mixture containing ˜100 parts by weight and a softening agent of 70 parts by weight or less, raw rubber B having a Tg lower than raw rubber A by 10 ° C. or more, and the total The point of using a rubber composition obtained by kneading a softener in an amount of 80 parts by weight or less with a hermetic mixer is described, and styrene-butadiene copolymer rubber is exemplified as such an additional raw material rubber. Yes. However, as a result of intensive studies by the present inventor, the methods described in these documents have a large difference in Tg between the natural rubber wet masterbatch and the additional raw rubber, and therefore there is room for further improvement in terms of heat generation and fatigue resistance. Turned out to be.

JP 2000-507892 A JP 2010-163055 A JP 2003-292675 A JP-A-10-237230

  The present invention has been made in view of the above circumstances, and an object thereof is to produce a rubber composition having improved heat generation and fatigue resistance, a method for producing the same, and a pneumatic tire.

As a result of intensive studies to solve the above problems, the present inventors have found the following points.
(1) In addition to the natural rubber wet masterbatch, a rubber composition obtained by adding dry rubber greatly different from the Tg of the rubber component (natural rubber) in the natural rubber wet masterbatch and dry-mixing them will generate heat. There is a tendency to deteriorate the performance and fatigue resistance.
(2) In addition to natural rubber wet masterbatch, dry rubber close to the Tg of the rubber component (natural rubber) in the natural rubber wet masterbatch, specifically, dry rubber mainly composed of natural rubber and / or polyisoprene rubber In addition, in the rubber composition obtained by dry-mixing these, exothermic property and fatigue resistance are remarkably improved.

  The present invention has been made as a result of the above-described studies, and achieves the above-described object with the following configuration.

  That is, the rubber composition according to the present invention comprises a natural rubber wet masterbatch obtained by mixing a natural rubber latex and a carbon black-containing slurry solution in a liquid phase and drying, and natural rubber and / or polyisoprene rubber as main components. It is obtained by dry mixing with dry rubber.

  In the rubber composition, exothermic property and fatigue resistance are remarkably improved. The cause of this is not clear, but probably because the Tg of the rubber component (natural rubber) in the natural rubber wet masterbatch and the Tg of the dry rubber are close to each other, they are sufficiently compatible with each other during dry mixing. It is estimated that the resistance and fatigue resistance are remarkably improved.

  In the present invention, “dry mixing” means mixing at least two mixed components such as natural rubber wet masterbatch and dry rubber in a state where the water content of the entire mixed component is 5% or less. To do. Specific examples of the dry mixing method include a method of mixing using a kneader such as a Banbury mixer, an open roll, or a kneader.

  In the rubber composition, when A is the total amount of rubber components in the natural rubber wet masterbatch and B is the total amount of rubber components in the dry rubber, A: B = 90: 10 to 70:30. preferable. Such a configuration is preferable because the heat buildup and fatigue resistance of the rubber composition are further improved.

  In the rubber composition, when the total amount of the rubber components in the rubber composition is 100 parts by mass, the carbon composition may be obtained by dry-mixing in a state where 0 to 5 parts by mass of carbon black is further added. preferable. Such a configuration is preferable because the heat buildup and fatigue resistance of the rubber composition are improved in a well-balanced manner.

  As described above, since the rubber composition according to the present invention is excellent in heat generation and fatigue resistance, the pneumatic tire obtained by using such a rubber composition, in particular, the rubber composition according to the present invention is used as a tread rubber and / or Or the pneumatic tire used for the belt topping rubber is excellent in heat generation and fatigue resistance.

  The method for producing a rubber composition according to the present invention comprises a step (I) of producing a natural rubber wet masterbatch by mixing a natural rubber latex and a carbon black-containing slurry solution in a liquid phase and drying, and the natural rubber. It has a step (II) of dry-mixing a wet masterbatch and a dry rubber containing natural rubber and / or polyisoprene rubber as a main component. According to this production method, it is possible to produce a rubber composition with significantly improved heat generation and fatigue resistance. In order to produce a rubber composition having further improved heat generation and fatigue resistance, in the step (II), the total amount of rubber components in the natural rubber wet masterbatch is A, and the total amount of rubber components in the dry rubber. Is B: 90:10 to 70:30, and when the total amount of the rubber components in the rubber composition is 100 parts by mass, 0 to 5 parts by mass of carbon black is further added. It is preferable to contain.

  The rubber composition according to the present invention includes a natural rubber wet masterbatch obtained by mixing a natural rubber latex and a carbon black-containing slurry solution in a liquid phase and drying, and a dry rubber mainly composed of natural rubber and / or polyisoprene rubber. And obtained by dry mixing.

  The carbon black-containing slurry solution can be produced by mixing carbon black and a dispersion solvent. As a method of mixing carbon black and a dispersion solvent, a general dispersion machine such as a high shear mixer, a high shear mixer, a homomixer, a ball mill, a bead mill, a high pressure homogenizer, an ultrasonic homogenizer, or a colloid mill is used. The method of making it disperse | distribute is mentioned.

  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.

  In the present invention, when a carbon black-containing slurry solution containing a surfactant is used as a raw material, it is possible to finally produce a rubber composition with better carbon black dispersibility. 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, instead of the surfactant or in addition to the surfactant, an alcohol such as ethanol may be added to the carbon black-containing slurry solution. Also in this case, a carbon black-containing slurry solution having excellent carbon black dispersibility can be obtained. 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.

  Although the carbon black density | concentration in a carbon black containing slurry solution is not specifically limited, It is preferable that it is 1-20 mass%, and it is more preferable that it is 3-15 mass%.

  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.

  In addition to the natural rubber latex solution, a synthetic rubber latex solution may be used in combination as a raw material for the natural rubber wet masterbatch. Examples of the synthetic rubber latex solution include those produced by emulsion polymerization of styrene-butadiene rubber, butadiene rubber, nitrile rubber, and chloroprene rubber. However, in order to maintain rubber physical properties such as durability derived from natural rubber, the content of natural rubber is preferably 80% by mass or more in the rubber component (dry mass) of the natural rubber wet masterbatch. 90% by mass or more, more preferably 100% by mass.

  The dry rubber that is dry-mixed with the natural rubber wet masterbatch is composed mainly of natural rubber and / or polyisoprene rubber. Specifically, in the rubber component of the dry rubber, the total amount of natural rubber and polyisoprene rubber is preferably 50% by mass or more, more preferably 80% by mass or more, and substantially natural rubber and / or It is particularly preferable that the rubber is composed only of polyisoprene rubber.

  When the natural rubber wet masterbatch and dry rubber are dry-mixed, these ratios are as follows: A: B = when the total amount of rubber components in the natural rubber wet masterbatch is A and the total amount of rubber components in the dry rubber is B. It is preferably 90:10 to 70:30.

  When the total amount of the rubber components in the rubber composition was 100 parts by mass, it was obtained by dry-mixing in addition to natural rubber wet masterbatch and dry rubber and further adding 0 to 5 parts by mass of carbon black. The rubber composition is preferable because the heat buildup and fatigue resistance of the rubber composition are improved in a well-balanced manner. However, if the content of carbon black is too large, there is a concern that the exothermic property and fatigue resistance of the rubber composition will deteriorate, so the content is preferably 5 parts by mass or less.

  Since the rubber composition according to the present invention is excellent in heat generation and fatigue resistance, it can be suitably used for pneumatic tires that are required to improve heat generation and fatigue resistance. In particular, since tread rubber and / or belt topping rubber is required to improve heat generation and fatigue resistance, the rubber composition according to the present invention is used for tread rubber and / or belt topping rubber. It can be particularly suitably used as a rubber composition.

  Below, the manufacturing method of the rubber composition which concerns on this invention is demonstrated. The method for producing a rubber composition according to the present invention comprises a step (I) of producing a natural rubber wet masterbatch by mixing a natural rubber latex and a carbon black-containing slurry solution in a liquid phase and drying, and the natural rubber. A step (II) of dry-mixing a wet masterbatch and a dry rubber mainly composed of natural rubber and / or polyisoprene rubber;

Step (I)
In the step (I), the method of mixing the natural rubber latex and the carbon black-containing slurry solution in the liquid phase is not particularly limited, and a method equipped with a propeller type stirring blade that mainly gives thrust can be used. In addition, it is also possible to use a chopper having a crushing blade that mainly gives a shearing force, such as a chopper made up of blade type blades. Moreover, the method of mixing using common dispersers, such as 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, is also mentioned. If necessary, the entire mixing system such as a disperser may be heated during mixing.

  A natural rubber wet masterbatch is manufactured by mixing the natural rubber latex and the carbon black-containing slurry solution in a liquid phase, coagulating as necessary, and then drying. The coagulation / drying method may be a coagulation / drying method in which a coagulant is contained in a carbon black-containing natural rubber latex solution and dried after coagulation, or a dry / solidification method in which the carbon black-containing natural rubber latex solution is dried without coagulation. .

  As a coagulant used in the coagulation drying method, an acid such as formic acid and sulfuric acid usually used for coagulation of a rubber latex solution, and a salt such as sodium chloride can be used.

  As a method for drying the carbon black-containing natural rubber latex solution, various drying devices such as an oven, a vacuum dryer, and an air dryer can be used.

  In the present invention, a coagulant is added to a carbon black-containing natural rubber latex solution obtained by mixing a slurry solution containing carbon black and a natural rubber latex solution in a liquid phase, and then the obtained coagulant is added. The aggregate may be collected and dried. As the flocculant, those known as flocculants in natural rubber latex solutions can be used without limitation, and specific examples include cationic flocculants.

Step (II)
In the step (II), the natural rubber wet masterbatch and the dry rubber are dry-mixed while being heated to 40 to 160 ° C. as necessary. In this step (II), when the total amount of rubber components in the natural rubber wet masterbatch is A and the total amount of rubber components in the dry rubber is B, it is preferable that A: B = 90: 10 to 70:30. When the total amount of rubber components in the rubber composition is 100 parts by mass, it is preferable to further contain 0 to 5 parts by mass of carbon black.

  When mixing natural rubber wet masterbatch and dry rubber in process (II), sulfur vulcanizing agent, vulcanization accelerator, silica, silane coupling agent, zinc oxide, stearic acid, vulcanization as required Additives usually used in the rubber industry such as accelerator aids, vulcanization retarders, organic peroxides, anti-aging agents, softeners such as wax and oil, and processing aids may be blended.

  Sulfur as the sulfur-based vulcanizing agent may be normal sulfur for rubber, and for example, powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur and the like can be used. The sulfur content in the rubber composition according to the present invention is preferably 0.3 to 6.5 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 6.5 parts by mass, both heat resistance and durability will be improved. Getting worse. In order to secure the rubber strength of the vulcanized rubber and improve the heat resistance and durability, the sulfur content should be 1.5 to 5.5 parts by mass with respect to 100 parts by mass of the rubber component. Is more preferably 2 to 4.5 parts by mass.

  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.

  As an anti-aging agent, an aromatic amine-based anti-aging agent, an amine-ketone anti-aging agent, a monophenol anti-aging agent, a bisphenol anti-aging agent, a polyphenol 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 anti-aging agent is more preferably 1 to 5 parts by mass and further preferably 2 to 4.5 parts by mass with respect to 100 parts by mass of the rubber component.

  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 “N234”; “Seast 7HM” (manufactured by Tokai Carbon Co., Ltd.)
Carbon black “N326”; “Seast 300” (manufactured by Tokai Carbon Co., Ltd.)
b) Dispersion solvent Water c) Natural rubber latex solution Natural rubber concentrated latex; 25% concentration solution obtained by diluting Reticex (DRC (Dry Rubber Content) = 60%) with distilled water Natural rubber field latex; Golden Hope ( DRC = 30.5%) in 25% strength solution diluted with distilled water d) Coagulant Formic acid (primary 85%, 10% solution diluted to pH 1.2), “manufactured by Nacalai Tesque”
e) Dry rubber (A) Polyisoprene rubber “IR2200” (manufactured by JSR)
(B) Polyisoprene rubber “SIR-20” (Indonesia)
(C) Natural rubber “RSS # 3” (Thailand)
f) Zinc oxide No. 3 zinc white (Mitsui Metals)
g) Anti-aging agent 6PPD (manufactured by Monsanto)
h) Sulfur "Critex OT-20" (manufactured by Akzo)
i) Vulcanization accelerator N, N-dicyclohexylbenzothiazole-2-sulfenamide “Noxeller DZ” (manufactured by Ouchi Shinsei Chemical Co., Ltd.)
j) Resorcin “SUMIKANOL 620” (manufactured by Sumitomo Chemical Co., Ltd.)
k) Melamine derivative “Cylettes 963L”

Examples 1-9, Comparative Examples 1-3
Carbon black was added to distilled water so as to have the number of parts shown in Table 1. (The number of parts of carbon black in Table 1 is the number of parts by weight relative to 100 parts by weight of the solid content (rubber content) in natural rubber latex) Then, carbon black was dispersed using PRIMIX's Robomix (conditions of the Robomix: 9000 rpm, 30 minutes) to produce a slurry solution containing carbon black (carbon black concentration: 5% by mass). The obtained carbon black-containing slurry solution and natural rubber latex were mixed at a compounding ratio shown in Table 1 using a household mixer SM-L56 type manufactured by SANYO (mixer conditions 11300 rpm, 30 minutes), A carbon black-containing natural rubber latex solution was prepared. To this, formic acid as a coagulant is added until the pH of the carbon black-containing natural rubber latex solution becomes 4, and the coagulum is dried to a moisture content of 1.5% or less with a screw press V-01 type manufactured by Suehiro EPM. By doing so, the natural rubber wet masterbatch (NR / CB-WMB1-9) was manufactured (process (I)).

  The obtained natural rubber wet masterbatch and dry rubber, together with carbon black and various additives shown in Table 2, are dry-mixed using a Banbury mixer, according to Examples 1 to 9 and Comparative Examples 1 to 3. A rubber composition was produced (step (II)).

(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.

(Exothermic property of vulcanized rubber)
According to JIS K6265, the exothermic property of the vulcanized rubber produced was evaluated by loss tangent tan δ. Tan δ was measured using a rheometer E4000 manufactured by UBM under the conditions of 50 Hz, 80 ° C., and dynamic strain of 2%, and the measured value was used as an index. Evaluation is shown by index evaluation when Comparative Example 2 is set to 100 for Examples 1 to 6 and Comparative Examples 1 and 2, and the smaller the numerical value, the lower the exotherm and the better. Moreover, about Examples 7-9 and Comparative Example 3, it shows by index evaluation when Comparative Example 3 is set to 100, and it means that exothermic property is so low that a numerical value is small and it is favorable.

(Fatigue resistance of vulcanized rubber)
The fatigue resistance of the manufactured vulcanized rubber was evaluated according to JIS K6260. Evaluation is shown by index evaluation when Comparative Example 2 is set to 100 for Examples 1 to 6 and Comparative Examples 1 to 2, and Comparative Example 3 is set to 100 for Examples 7 to 9 and Comparative Example 3. It is shown by the index evaluation of time, and the larger the value, the better the fatigue resistance.

  From the results of Table 2, a rubber composition obtained by dry-mixing a natural rubber wet masterbatch and dry rubber to a vulcanized rubber of the rubber composition of Comparative Example 2 using only the natural rubber wet masterbatch (Examples 1 to 6). It can be seen that the exothermic property and fatigue resistance of the vulcanized rubber are improved. On the other hand, the vulcanized rubber of the rubber composition (Comparative Example 1) obtained by simply dry-mixing dry rubber and carbon black with the vulcanized rubber of the rubber composition of Comparative Example 2 is exothermic and fatigue resistant. It turns out that gets worse.

  Similarly, the addition of a rubber composition (Examples 7 to 9) obtained by dry-mixing a natural rubber wet masterbatch and dry rubber to the vulcanized rubber of the rubber composition of Comparative Example 3 using only the natural rubber wet masterbatch. It can be seen that vulcanized rubber improves heat generation and fatigue resistance.

Claims (8)

  A natural rubber wet masterbatch obtained by mixing a natural rubber latex and a carbon black-containing slurry solution in a liquid phase and drying, and a dry rubber mainly composed of natural rubber and / or polyisoprene rubber was obtained by dry mixing. A rubber composition characterized by being a thing.   The rubber composition according to claim 1, wherein A: B = 90: 10 to 70:30, where A is the total amount of rubber components in the natural rubber wet masterbatch and B is the total amount of rubber components in the dry rubber. object.   3. The rubber composition according to claim 1 or 2, wherein the total amount of rubber components in the rubber composition is 100 parts by mass, and is obtained by dry mixing in a state where 0 to 5 parts by mass of carbon black is further added. Rubber composition.   A pneumatic tire using the rubber composition according to claim 1.   The pneumatic tire according to claim 4, wherein the rubber composition according to any one of claims 1 to 3 is used for a tread rubber and / or a belt topping rubber. A process (I) of producing a natural rubber wet masterbatch by mixing a natural rubber latex and a carbon black-containing slurry solution in a liquid phase and drying;
A method for producing a rubber composition comprising the step (II) of dry-mixing the natural rubber wet masterbatch and a dry rubber containing natural rubber and / or polyisoprene rubber as a main component.   In the step (II), when the total amount of rubber components in the natural rubber wet masterbatch is A and the total amount of rubber components in the dry rubber is B, A: B = 90: 10 to 70:30 Item 7. A method for producing a rubber composition according to Item 6.   The method for producing a rubber composition according to claim 6 or 7, further comprising 0 to 5 parts by mass of carbon black when the total amount of rubber components in the rubber composition is 100 parts by mass in the step (II). .