JP2012158716A - Unvulcanized diene-based rubber coagulation, method for producing the same, unvulcanized rubber composition and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an unvulcanized diene-based rubber coagulation having a reduced content of an ammonium salt, a method for producing the same, vulcanized rubber of an unvulcanized rubber composition containing the unvulcanized diene-based rubber coagulation and to significantly improve adhesiveness, heat build-up and reinforcing properties of pneumatic tires.SOLUTION: The method for producing an unvulcanized diene-based rubber coagulation includes a step for coagulating a diene-based rubber latex by adding fine foams to the diene-based rubber latex comprising a natural rubber latex as a main component and removing the ammonia contained in the diene-based rubber latex.

Description

  The present invention relates to an unvulcanized diene rubber coagulated product and a method for producing the same, and more specifically to an unvulcanized diene rubber coagulated product in which almost no ammonium salt remains and a method for producing the same. Furthermore, the present invention relates to an unvulcanized rubber composition containing the unvulcanized diene rubber coagulated product, and a pneumatic tire using the unvulcanized 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, a coagulant made of a strong acid such as formic acid or sulfuric acid or a salt such as aluminum chloride is used, and finally a dehydration and drying is performed through a coagulation step of coagulating the natural rubber latex. In such a coagulation step, the natural rubber latex is generally coagulated in the natural rubber latex by neutralizing ammonia acting as a latex stabilizer with the coagulant and precipitating it as an ammonium salt. Since the obtained natural rubber coagulated product contains precipitated ammonium salt, it is necessary to remove the ammonium salt by repeatedly washing the natural rubber coagulated product. If such washing is insufficient, it has been a problem that it adversely affects the adhesiveness, heat build-up and reinforcing properties of vulcanized rubber made from natural rubber coagulum. On the other hand, it is preferable to perform sufficient washing in consideration of the physical properties of the vulcanized rubber. However, since much time and labor are consumed, the productivity is deteriorated. Moreover, since the waste liquid after washing contains a strong acid, there has been a concern about adverse environmental effects during disposal.

  The following Patent Document 2 describes a method for producing a conductive foam by adding a gas that does not coagulate the latex composition to a latex composition containing a conductive filler and mechanically stirring them. Has been. However, the production methods described in these patent documents cannot produce an unvulcanized diene rubber coagulated material that can be a raw material for an unvulcanized rubber composition.

  Patent Document 3 below describes a method for coagulating a natural rubber latex containing a filler without using a coagulant such as an acid by utilizing a shearing force generated by a mechanically generated high-speed flow. Further, it is described that atmospheric gas may be introduced as a high-speed auxiliary fluid. However, in the method described in this patent document, since the high-speed flow containing the auxiliary fluid does not circulate, the recovery rate of the unvulcanized diene-based rubber coagulum is poor, and furthermore, the degree of dispersion of the filler is not uniform. The dispersibility of the filler in the unvulcanized rubber composition containing the unvulcanized diene rubber coagulated product is deteriorated, and the reinforcing property of the final vulcanized rubber is deteriorated.

JP 2004-99625 A JP 2004-202989 A JP 2000-507892 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an unvulcanized diene rubber coagulated product in which almost no ammonium salt remains and a method for producing the same, and the unvulcanized diene rubber coagulated product. It is to significantly improve the adhesiveness, heat build-up, and reinforcing property of the vulcanized rubber and the pneumatic tire of the unvulcanized rubber composition containing the.

  The above object can be achieved by the present invention as described below. That is, the method for producing an unvulcanized diene rubber coagulated product according to the present invention adds fine bubbles to a diene rubber latex containing natural rubber latex as a main component, and removes ammonia contained in the diene rubber latex. By doing this, the method has a step of coagulating the diene rubber latex.

  According to the production method described above, the shock wave caused by the collapse (cavitation phenomenon) of fine bubbles added to the diene rubber latex and the concentration of the gas due to the high filling of the fine bubbles into the diene rubber latex result in the diene rubber latex. The contact area with ammonia present as a stabilizer increases, and ammonia is volatilized and removed. As a result, ammonia that acts as a latex stabilizer can be removed without using a coagulant made of a strong acid such as formic acid or sulfuric acid, or a salt such as aluminum chloride, so that the diene rubber latex can be coagulated. it can. As a result, it is possible to produce an unvulcanized diene rubber coagulated product in which almost no ammonium salt remains, which has been a problem in the conventional method using a coagulant. In addition, according to the said manufacturing method, since an ammonium salt hardly generate | occur | produces in the process of coagulating a diene rubber latex, it was required in the method of using the conventional coagulant | flocculant. A cleaning process is also unnecessary.

  In the above production method, the average bubble diameter of the fine bubbles is 100 μm or less, the average number of the fine bubbles is 50,000 / ml or more, and the fine bubbles mainly include air or carbon dioxide. It is preferable that it is a fine bubble which consists of the gas used as a component. According to such a configuration, an unvulcanized diene rubber coagulated product can be produced more reliably and easily.

  In the unvulcanized diene rubber coagulated product produced by any one of the above production methods, almost no ammonium salt remains. Therefore, the unvulcanized rubber composition containing such an unvulcanized diene rubber coagulated product is useful as a raw material for a pneumatic tire, particularly a steel topping rubber, which requires adhesion, heat generation and reinforcement. .

  The method for producing an unvulcanized diene rubber coagulum according to the present invention comprises adding fine bubbles to a diene rubber latex containing natural rubber latex as a main component, and removing ammonia contained in the diene rubber latex. And a step of coagulating the diene rubber latex (coagulation step).

  Specifically, diene rubber latex containing 50% by mass or more of natural rubber in solid content (rubber component) ratio is used as the diene rubber latex containing natural rubber latex as a main component. In order to maintain rubber physical properties derived from natural rubber, it is preferable to contain 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more. In addition, although solid content (rubber component) density | concentration contained in diene type rubber latex is not specifically limited, About 1-60 mass% is illustrated.

  Natural rubber latex 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 diene rubber latex that may be contained in addition to the natural rubber latex include polyisoprene rubber latex, polybutadiene rubber latex, polystyrene butadiene rubber latex, and the like. As these diene rubber latexes, commercially available products can also be suitably used. Specifically, for example, IR100K (manufactured by Sumitomo Seika Co., Ltd.) as polyisoprene rubber latex, SR-113 (Japan A & L Co., Ltd.) as polybutadiene rubber latex. SR-117 (manufactured by Nippon A & L Co., Ltd.) and the like as polystyrene butadiene rubber latex.

  Examples of the gas constituting the fine bubbles include air, carbon dioxide, nitrogen, argon, oxygen, and helium. These may be used alone or in admixture of two or more. Among these, the use of air or carbon dioxide is preferable because an unvulcanized diene rubber coagulated product can be produced more reliably and easily.

  As a method for adding fine bubbles to the diene rubber latex, a method known to those skilled in the art can be used. For example, mechanical stirring is used to generate (add) fine bubbles by generating vortices in the diene rubber latex, or the swirling center of the swirling flow generated by sending water in the circumferential direction is set to negative pressure. This is a swirling liquid flow type that self-sucks air and tears the gas phase, and a static mixer type that guides gas-liquid 2 flow spirally with a guide vane and crushes by mushroom-like protrusions fixed inside the pipe Ejector type that makes gas and liquid coexist in turbulent flow and separates the gas as bubbles so that the gas is sheared. Large gas bubbles are generated by shock waves purified by abrupt changes in liquid flow velocity by flowing gas and liquid at the same time. Venturi type to be crushed, pressurized dissolution type that is generated by dissolving gas once in pressurized water and abruptly reducing pressure, pore type method that sends compressed air into liquid through fine holes, rotor Rotating type that self-sucks and generates gas by rotating at high speed in the stator of the periphery, ultrasonic type that is generated when water molecules are separated by exciting bubbles and cavities are generated, mixing nitrogen and water vapor There are a method of adding fine bubbles by a vapor compression method in which water vapor is condensed by blowing steam with a nozzle and a nitrogen bubble that does not condense is generated, and an electrolysis method in which fine bubbles of oxygen and hydrogen are generated by electrolysis of water. Can be mentioned.

  As a method for adding fine bubbles to the diene rubber latex, a commercially available fine bubble generator can be suitably used. Specifically, for example, microbubble generator MBG20ND07Z-1HH000 manufactured by Nikuni, Pilot Plant series 9000 manufactured by Roots, YJ-07 manufactured by By Clean, Type 1,3 manufactured by Auratech Etc. In the present invention, it is preferable to produce a circulation system plant including these devices and generate (add) fine bubbles by these devices while circulating a diene rubber latex at about 40 L / min, for example.

  Add to diene rubber latex to ensure coagulation of diene rubber latex and improve adhesion, heat generation and reinforcement of vulcanized rubber of the unvulcanized diene rubber coagulated product. The average bubble diameter of the fine bubbles is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less. In addition, the smaller the average cell diameter of the fine bubbles, the more reliably the diene rubber latex can be coagulated, and the adhesion, heat generation and reinforcement of the vulcanized rubber of the obtained unvulcanized diene rubber coagulated product are improved. Therefore, the lower limit of the average bubble diameter of the fine bubbles is not particularly limited.

  Furthermore, in order to coagulate the diene rubber latex reliably and to improve the adhesion, heat build-up, and reinforcement of the vulcanized rubber of the obtained unvulcanized diene rubber coagulum, The average number of fine bubbles added to is preferably 50000 / ml or more, more preferably 70000 / ml or more, and still more preferably 100000 / ml or more. As the average number of fine bubbles increases, the diene rubber latex can be solidified more reliably, and the adhesiveness, heat build-up, and reinforcement of the vulcanized rubber of the obtained unvulcanized diene rubber coagulated product are improved. Therefore, the upper limit of the average number of fine bubbles is not particularly limited.

  As a method of calculating the average bubble diameter and the average number of fine bubbles, for example, a photographic image of fine bubbles is taken at a predetermined magnification (for example, 10 to 1000 times), and the average bubbles of the fine bubbles per fixed area are obtained by this image processing. There is a method of calculating the diameter (or calculating the average number converted from the number per fixed area).

  In order to solidify the diene rubber latex reliably, more than 25 L of fine bubbles (volume at 27 ° C. and 1 atm) are used for 1 L of diene rubber latex containing 60% by mass of solid content (rubber component). It is preferable to do. As the amount of fine bubbles used increases, the diene rubber latex can be solidified more reliably, and the adhesiveness, heat build-up, and reinforcement of the vulcanized rubber of the obtained unvulcanized diene rubber coagulated product are improved. For this reason, the upper limit of the amount of fine bubbles used is not particularly limited.

  In the production method according to the present invention, the diene rubber latex may be mixed as necessary while adding fine bubbles to the diene rubber latex. The mixing method is not particularly limited, and those equipped with a propeller type stirring blade that mainly gives thrust can be used, and crushing blades that mainly give shearing force, such as a chopper composed of blade type blades. It is also possible to use one provided with 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 temperature-controlled at 10 to 100 ° C. during mixing.

  After the coagulation step, an unvulcanized diene rubber coagulum is produced by dehydrating and drying the unvulcanized diene rubber coagulum as necessary. Examples of the dehydration method include a method of separating a diene rubber latex coagulum and moisture from a latex solution containing a diene rubber latex coagulum by a known method using a mesh or centrifugal separation. Examples of the drying method include a method in which the diene rubber latex coagulum is heated while mechanically stirring as necessary. The heating temperature at the time of drying is preferably a temperature at which the moisture content can be sufficiently reduced while maintaining the diene rubber latex coagulated product in an unvulcanized state, specifically 100 to 150 ° C. The moisture content of the unvulcanized diene rubber coagulated product after drying is preferably 1.5% or less.

  In the unvulcanized diene rubber coagulated product according to the present invention, almost no ammonium salt remains. Specifically, the ammonium salt in the unvulcanized diene rubber coagulated product is reduced to 0.4% by mass or less, preferably 0.2% by mass or less, and more preferably 0.1% by mass or less. Therefore, the unvulcanized rubber composition containing such an unvulcanized diene rubber coagulated product is useful as a raw material for a pneumatic tire, particularly a steel topping rubber, which requires adhesion, heat generation and reinforcement. .

  The unvulcanized rubber composition according to the present invention includes carbon black, a sulfur vulcanizing agent, a vulcanization accelerator, silica, a silane coupling agent, an oxidation agent, if necessary, in addition to the unvulcanized diene rubber coagulated product. Contains compounding agents commonly used in the rubber industry such as zinc, stearic acid, vulcanization accelerators, vulcanization retarders, organic peroxides, anti-aging agents, softeners such as wax and oil, and processing aids. May be.

  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.

  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 unvulcanized 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.

  In addition to the unvulcanized diene rubber coagulated product, the unvulcanized rubber composition according to the present invention includes carbon black, a sulfur vulcanizing agent, a vulcanization accelerator, silica, a silane coupling agent, Zinc oxide, stearic acid, vulcanization accelerators, vulcanization retarders, organic peroxides, anti-aging agents, softeners such as waxes and oils, processing aids, etc., ordinary Banbury mixers, kneaders, rolls, etc. It can be obtained by kneading using a kneader used in the rubber industry.

  In addition, the blending method of each of the above components is not particularly limited, and a blending component other than a vulcanizing component such as a sulfur vulcanizing agent and a vulcanization accelerator is previously kneaded to obtain a master batch, and the remaining components are added. Any of a method of further kneading, a method of adding and kneading each component in an arbitrary order, a method of adding all components simultaneously and kneading may be used.

  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) Natural Rubber Latex Natural Rubber Concentrated Latex; manufactured by Regex Corporation (DRC (Dry Rubber Content) = 60%)
Natural rubber field latex; manufactured by Golden Hope (DRC = 30.5%)
b) Carbon black “N326”; “Seast 300” (manufactured by Tokai Carbon Co., Ltd.)
c) Gas composing fine bubbles Air gas (air)
Carbon dioxide gas (manufactured by Taiyo Nippon Sanso)
d) Anti-aging agent 6PPD (manufactured by Monsanto)
e) Zinc oxide No. 3 zinc white (Mitsui Metals)
f) Resorcin “Sumikanol 620” (manufactured by Sumitomo Chemical Co., Ltd.)
g) Melamine derivative “CYRETS 963L”
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) Coagulant
Formic acid (primary 85% diluted to 10% by mass solution and adjusted to pH 1.2), “Nacalai Tesque”

Examples 1-9
While stirring natural rubber latex with a portable mixer manufactured by Satake (A510-0.2AI: 0.2 kw, 50 L tank), fine bubbles are generated (added) while being circulated through the Nikoni microbubble generator MGB20ND07Z-1HH000. This allowed the natural rubber latex to coagulate (coagulation step). In Examples 1 to 7 and Example 9, atmospheric gas (air) was used as the gas constituting the fine bubbles, and in Example 8, carbon dioxide gas was used as the gas constituting the fine bubbles. The amount of fine bubbles in Table 1 means fine bubbles (L) added per liter of latex.

  While the latex solution containing the diene rubber latex coagulated product obtained in the coagulation step is heated to 130 ° C., using a screw press V-01 type manufactured by Suehiro EPM, until the water content becomes 1.5% or less By dehydrating and drying, unvulcanized diene rubber coagulated products according to Examples 1 to 9 were produced.

  The resulting unvulcanized diene rubber coagulated product, carbon black and various additives are dry-mixed using a Banbury mixer at the compounding ratios shown in Table 1 to obtain an unvulcanized rubber composition. Manufactured.

Comparative Example 1
An unvulcanized diene rubber coagulated product is produced in the same manner as in Examples 1 to 9, except that formic acid is added as a coagulant to coagulate the diene rubber latex instead of adding fine bubbles. did. In addition, the addition amount of formic acid (10 mass% solution) was made into the ratio of 3 mass% with respect to the solid content (rubber component) amount of natural rubber latex.

(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 1 is set to 100, and the lower the numerical value, the lower the exothermic property and the better. The results are shown in Table 1.

(Reinforcing properties of vulcanized rubber (elongation at break))
In accordance with JIS K6251, the reinforcing properties of the vulcanized rubber produced were evaluated by elongation at break. Evaluation is shown by index evaluation when the comparative example 1 is set to 100, and the higher the numerical value, the higher the reinforcement and the better. The results are shown in Table 1.

(Adhesiveness of vulcanized rubber)
The unvulcanized rubber composition was molded into two sheets, and steel cords plated with brass were arranged side by side at 12/25 mm intervals, and vulcanized and bonded while sandwiched between the other sheets ( Vulcanization at 150 ° C. for 30 minutes). Next, the two rubber sheets sandwiched with the steel cord were wet heat aged at 105 ° C.-100% RH for 96 hours, and then the two rubber sheets were peeled off to visually check the rubber coverage (%) on the steel cord. Evaluated. Evaluation means that the higher the coverage, the better the adhesion. The results are shown in Table 1.

  From the result of Table 1, compared with the vulcanized rubber of the unvulcanized rubber composition containing the unvulcanized diene rubber coagulum of Comparative Example 1, the unvulcanized diene rubber coagulum of Examples 1-9. It can be seen that the vulcanized rubber of the unvulcanized rubber composition contained improves the heat generation property, the reinforcing property and the reinforcing property. In particular, it can be seen that the adhesiveness after wet heat deterioration is dramatically improved as compared with Comparative Example 1.

Claims (8)

  It has a step of coagulating the diene rubber latex by adding fine bubbles to the diene rubber latex containing natural rubber latex as a main component and removing ammonia contained in the diene rubber latex. A method for producing an unvulcanized diene rubber coagulated product.   The method for producing an unvulcanized diene rubber coagulated product according to claim 1, wherein an average cell diameter of the fine bubbles is 100 μm or less.   The method for producing an unvulcanized diene rubber coagulum according to claim 1 or 2, wherein the average number of the fine bubbles is 50,000 / ml or more.   The method for producing an unvulcanized diene rubber coagulum according to any one of claims 1 to 3, wherein the fine bubbles are fine bubbles made of a gas mainly composed of air or carbon dioxide.   An unvulcanized diene rubber coagulated product produced by the production method according to claim 1.   An unvulcanized rubber composition containing the unvulcanized diene rubber coagulated product according to claim 5.   A pneumatic tire using the unvulcanized rubber composition according to claim 6.   The pneumatic tire according to claim 7, wherein the unvulcanized rubber composition according to claim 6 is used for a topping rubber for steel.