JP2012158667A - 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 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 (I) for producing a diene-based rubber latex coagulation by using carbon dioxide as a coagulant and coagulating a diene-based rubber latex comprising a natural rubber latex as a main component and a step (II) for producing an unvulcanized diene-based rubber coagulation by dehydrating and drying the diene-based rubber latex coagulation to remove an ammonium salt contained in the diene-based rubber latex coagulation.

Description

  The present invention relates to an unvulcanized diene rubber coagulated product and a method for producing the same, and more particularly to an unvulcanized diene rubber coagulated product having a reduced ammonium salt content 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.

  In the following Patent Documents 2 and 3, a process of adding a conductive substance and a vulcanizing agent to natural rubber latex, mixing air by mechanical stirring and foaming, and the obtained natural rubber foam (foam rubber) ) Under high vacuum, a process for freezing foam rubber, and a process for injecting carbon dioxide into the frozen foam rubber and solidifying into open cells is described. Yes. Moreover, in the following patent document 4, the manufacturing method which uses a carbon dioxide as a coagulation component of the spray latex foam for buildings is described.

JP 2004-99625 A Japanese Patent No. 400020 JP 2004-144927 A Special table 2010-514899

  However, none of the production methods described in the above-mentioned patent documents can produce an unvulcanized natural rubber coagulum that can be a raw material for an unvulcanized rubber composition. In addition, in the manufacturing method described in the above-mentioned patent document, it is not possible to reduce ammonium salt in foam rubber or spray latex foam for buildings, so the adhesiveness, heat build-up, and reinforcement of vulcanized rubber deteriorate. There is a concern to do.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an unvulcanized diene rubber coagulated product having a reduced ammonium salt content and a method for producing the same, and the unvulcanized diene system. An object of the present invention is to greatly improve the adhesiveness, heat build-up, and reinforcement of vulcanized rubber and pneumatic tires of an unvulcanized rubber composition containing a rubber coagulum.

  The above object can be achieved by the present invention as described below. That is, the method for producing an unvulcanized diene rubber coagulum according to the present invention uses a carbon dioxide as a coagulant to coagulate a diene rubber latex having a natural rubber latex as a main component, thereby producing a diene rubber latex. Step (I) for producing a coagulated product, and dehydrating and drying the diene rubber latex coagulated product to remove ammonium salts contained in the diene rubber latex coagulated product, thereby unvulcanized diene rubber. And a step (II) of producing a coagulated product.

  According to the above production method, when coagulating a diene rubber latex containing natural rubber latex as a main component using carbon dioxide as a coagulant (step (I)), ammonia acting as a stabilizer for natural rubber latex and By reaction with carbon dioxide, ammonium salts such as ammonium hydrogencarbonate are produced as by-products in the diene rubber latex coagulum. However, the ammonium salt contained in the diene rubber latex coagulum is decomposed and volatilized by heating at the time of dehydration and drying in step (II). Salt can be removed. As a result, according to the production method according to the present invention, an unvulcanized diene rubber coagulated product having a reduced ammonium salt content can be produced.

  In the production method, it is preferable to use carbon dioxide gas, carbon dioxide-containing water, or dry ice as the coagulant. By using these coagulants, an unvulcanized diene rubber coagulated product having a reduced ammonium salt content can be produced reliably and simply.

  The unvulcanized diene rubber coagulated product produced by any one of the above production methods has reduced ammonium salt. 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 coagulated product according to the present invention uses a carbon dioxide as a coagulant to coagulate a diene rubber latex containing natural rubber latex as a main component, thereby producing a diene rubber latex coagulated product. The process (I) for producing an unvulcanized diene rubber coagulum is performed by removing the ammonium salt contained in the diene rubber latex coagulum by dehydrating and drying the diene rubber latex coagulum. Step (II).

  In the step (I), a diene rubber latex containing a natural rubber latex as a main component is used as a raw material. Specifically, a diene rubber latex containing 50% by mass or more of natural rubber in a solid content (rubber component) ratio is used. 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.

Further, in step (I), carbon dioxide is used as a coagulant. Examples of carbon dioxide that is particularly easily available and that can be easily handled include carbon dioxide gas, water containing carbon dioxide, or dry ice. In order to solidify the diene rubber latex with certainty, the carbon dioxide gas is 25 L (27 ° C., volume at 1 atm) with respect to 1 L of the diene rubber latex containing 60% by mass of the solid content (rubber component). In the case of carbon dioxide-containing water, it is preferable to use a gas volume (CO ₂ GV) of 2.0 or more of ₂ L or more, and dry ice of 50 g or more. There are no particular limitations on the upper limit of the amounts of carbon dioxide gas, carbon dioxide-containing water, and dry ice. In the present invention, the “gas volume (CO ₂ GV)” means how many times the amount of carbon dioxide gas generated when carbon dioxide gas is completely extracted from a certain amount of target water. Indicates whether it corresponds. For example, 2.8 gas volume means that 2.8 L of carbon dioxide gas is contained in 1 L of water.

  The method of adding carbon dioxide as a coagulant to the diene rubber latex containing natural rubber latex as the main component and coagulating while mixing is not particularly limited, and a propeller type stirring blade that mainly gives thrust In addition, it is also possible to use a chopper having a crushing blade that mainly gives a shearing force, such as a chopper composed of a blade type blade. 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 mixer may be temperature-controlled at 10 to 100 ° C. during mixing.

  In step (II), the ammonium solution contained in the diene rubber latex coagulum is removed by dehydrating and drying the latex solution containing the diene rubber latex coagulum obtained in step (I). Produces vulcanized diene rubber coagulum. 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. Heating during drying decomposes and volatilizes ammonium salts such as ammonium hydrogen carbonate (decomposition temperature 58 ° C.) contained in the diene rubber latex coagulum. Thereby, the unvulcanized diene rubber coagulated product according to the present invention can be produced. The moisture content of the unvulcanized diene rubber coagulated product after drying is preferably 1.5% or less.

  The unvulcanized diene rubber coagulated product according to the present invention is reduced in ammonium salt. 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 Carbon black “N234”; “Seast 7HM” (manufactured by Tokai Carbon Co., Ltd.)
Carbon black “N326”; “Seast 300” (manufactured by Tokai Carbon Co., Ltd.)
c) Coagulant
Carbon dioxide gas (manufactured by Taiyo Nippon Sanso)
Carbon dioxide-containing water Carbon dioxide gas (manufactured by Taiyo Nippon Sanso Co., Ltd.) at 0 ° C. to 1 atm is dissolved in 2.0 to 4.5 gas volumes in a pressure vessel (196 kPa pressure tank). 5L (0 ℃ -101.3kPa) of carbon dioxide gas is generated, manufactured by Nippon Liquid Acid Co., Ltd.)
Formic acid (primary 85% diluted to 10% by mass solution and adjusted to pH 1.2), “Nacalai Tesque”
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.)

Examples 1-7
Table 1 shows carbon dioxide as a coagulant for 100 parts by mass of solid content (rubber component) of natural rubber latex in a state where natural rubber latex is stirred (11300 rpm) using a household mixer SM-L56 manufactured by SANYO. A diene rubber latex coagulum was produced by adding at the stated ratio and continuing stirring for 3 minutes after completion of the addition (step (I)).

  While the latex solution containing the diene rubber latex coagulum obtained in the step (I) is heated to 130 ° C., the moisture content is 1.5% or less using a screw press V-01 type manufactured by Suehiro EPM. The unvulcanized diene rubber coagulated product according to Examples 1 to 7 was manufactured by dehydrating and drying until it became (Step (II)).

  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 was produced by the same method as in Examples 1 to 7, except that formic acid was used in place of carbon dioxide as the coagulant. The amount of formic acid (10% by mass solution) added was 3% by mass with respect to the solid content (rubber component) of the natural rubber latex (adjusted so that the pH of the natural rubber latex was about 4). .

(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 higher 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 1-7. 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 (6)

A step (I) of producing a diene rubber latex coagulated product by coagulating a diene rubber latex containing natural rubber latex as a main component using carbon dioxide as a coagulant;
Dehydrating and drying the diene rubber latex coagulum to remove ammonium salts contained in the diene rubber latex coagulum and producing an unvulcanized diene rubber coagulum (II); A method for producing an unvulcanized diene rubber coagulated product, comprising:   The method for producing a coagulated unvulcanized diene rubber according to claim 1, wherein carbon dioxide gas, carbon dioxide-containing water, or dry ice is used as the coagulant.   An unvulcanized diene rubber coagulated product produced by the production method according to claim 1 or 2.   An unvulcanized rubber composition containing the unvulcanized diene rubber coagulated product according to claim 3.   A pneumatic tire using the unvulcanized rubber composition according to claim 4.   The pneumatic tire according to claim 5, wherein the unvulcanized rubber composition according to claim 4 is used as a topping rubber for steel.