JP5456650B2 - Modified natural rubber, rubber composition for tire and pneumatic tire - Google Patents

Description

The present invention relates to a modified natural rubber and a method for producing the same, and a rubber composition for a tire and a pneumatic tire using the modified natural rubber.

Conventionally, the fuel consumption of a vehicle has been reduced by reducing tire rolling resistance and suppressing heat generation. In recent years, there has been an increasing demand for lower fuel consumption of vehicles with tires, and further studies on improving fuel efficiency are indispensable. Natural rubber, which is widely used in tires, has been considered to have higher fuel efficiency compared to styrene butadiene rubber. However, since styrene butadiene rubber has been fueled more recently, it is necessary to achieve lower fuel consumption for the entire tire. Therefore, it is necessary to reduce the fuel consumption of natural rubber.

In order to reduce the fuel consumption of natural rubber, it is conceivable to modify natural rubber. For example, Patent Document 1 discloses a method of adding a surfactant to natural rubber latex and performing a cleaning treatment. However, there is still room for improvement in improving rolling resistance.

Japanese Patent No. 3294901

The present invention solves the above problems, provides a modified natural rubber that can sufficiently reduce the phosphorus content and nitrogen content, and is excellent in fuel efficiency and heat aging resistance, and a method for producing the same. An object is to provide a rubber composition for a tire using a natural rubber and a pneumatic tire.

The present invention relates to a modified natural rubber obtained by treating agglomerated rubber obtained from a saponified natural rubber latex with an aqueous solution of an anionic surfactant and washing it. Here, the anionic surfactant is at least one selected from the group consisting of alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, alkyl benzene sulfonates, alkyl naphthalene sulfonates, and fatty acid salts. Is preferred.

The content of the anionic surfactant in 100% by mass of the aqueous solution is preferably 0.01% by mass or more. The content of the anionic surfactant in 100% by mass of the aqueous solution is more preferably 0.1% by mass or more.

The nitrogen content after 48 hours of immersion in acetone at room temperature is preferably 0.2% by mass or less. The phosphorus content of the modified natural rubber is preferably 200 ppm or less.

The present invention also includes a step 1 of saponifying natural rubber latex and a step of treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex obtained in the above step 1 with an aqueous solution of an anionic surfactant. The present invention relates to a method for producing a modified natural rubber comprising 2 and a washing step 3.

The present invention also relates to a tire rubber composition comprising a rubber component and carbon black and / or a white filler, wherein the content of the modified natural rubber is 5% by mass or more in 100% by mass of the rubber component.

The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, it is a modified natural rubber obtained by treating agglomerated rubber obtained from a saponified natural rubber latex with an aqueous solution of an anionic surfactant and washing it, so that proteins and phospholipids in the rubber are removed. It can be reduced sufficiently and fuel efficiency can be improved. In addition, according to the present invention, heat aging resistance (decrease in molecular weight during storage) can be increased to the same level as that of normal (non-modified) natural rubber, compared to conventional modified proteins. Accordingly, it is possible to provide a tire rubber composition and a pneumatic tire that are excellent in fuel efficiency and heat aging resistance.

[Modified natural rubber]
The modified natural rubber of the present invention is obtained by treating agglomerated rubber obtained from a saponified natural rubber latex with an aqueous solution of an anionic surfactant and washing it.

In the method of saponifying natural rubber latex to reduce the fuel consumption of natural rubber, proteins and phospholipids decomposed in the saponification process remain inside the rubber during solidification or remain firmly adsorbed on the rubber surface. Therefore, it cannot be sufficiently reduced by washing with water or the like. On the other hand, in the present invention, residual proteins and phospholipids can be sufficiently removed by treating and washing the agglomerated rubber saponified natural rubber latex with an aqueous solution of an anionic surfactant. Therefore, the fuel efficiency can be further improved by using the modified natural rubber of the present invention. Compared with the method of removing residual protein by treating sodium carbonate after saponification treatment, it has better heat aging resistance, can suppress the deterioration of rubber during storage, and lower fuel consumption associated with storage Can be relaxed.

Specifically, the modified natural rubber of the present invention comprises an anionic system comprising a saponification treatment of natural rubber latex and an agglomerated rubber obtained by agglomerating the saponified natural rubber latex obtained in the above step 1. It can be prepared by a production method including the step 2 of treating with an aqueous solution of a surfactant and the step 3 of washing.

(Process 1)
In step 1, natural rubber latex is saponified. Thereby, phospholipid and protein are decomposed.

Natural rubber latex is collected as sap of natural rubber trees such as Hevea, and contains rubber, water, proteins, lipids, inorganic salts, etc., and the gel content in rubber is based on the complex presence of various impurities. It is considered a thing. In the present invention, as natural rubber latex, raw latex (field latex) produced by tapping Hevea tree, or concentrated latex concentrated by centrifugal separation or creaming (refined latex, high ammonia to which ammonia is added by a conventional method) Latex, zinc oxide, TMTD, and LATZ latex stabilized with ammonia can be used.

As a method for the saponification treatment, for example, the method described in JP 2010-138359 A and JP 2010-174169 A can be suitably performed, and specifically, the following method can be used.

The saponification treatment can be carried out by adding an alkali and, if necessary, a surfactant to natural rubber latex and allowing to stand at a predetermined temperature for a certain period of time. Stirring or the like may be performed as necessary.

As the alkali used for the saponification treatment, sodium hydroxide, potassium hydroxide and the like are preferable. The surfactant is not particularly limited, and examples thereof include known nonionic surfactants such as polyoxyethylene alkyl ether sulfates, anionic surfactants, and amphoteric surfactants. A polyoxyethylene alkyl ether sulfate ester salt is preferable because it can be saponified. In the saponification treatment, the addition amount of alkali and surfactant, the temperature and time of the saponification treatment may be appropriately set.

In the saponification treatment, an anti-aging agent may be added before, during or after the saponification treatment as necessary. As an anti-aging agent, it is preferable to use a dispersion of an anti-aging agent. For example, an anti-aging agent dispersion containing an anti-aging agent, a surfactant and water (a dispersion in which an anti-aging agent is finely dispersed in water). Body). By using such a dispersion, the anti-aging agent can be absorbed (adsorbed) by the rubber particles, and good fuel economy and heat aging resistance can be obtained.

If the anti-aging agent dispersion is added before the saponification treatment, it is mixed with natural rubber latex and then saponification treatment is applied.When added during the saponification treatment, it is mixed with natural rubber latex, alkali, etc. When added after the saponification treatment, it is mixed with the saponified natural rubber latex obtained by the treatment.

In the anti-aging agent dispersion, the anti-aging agent is not particularly limited, but a phenol-based anti-aging agent is preferable because it can be easily used. Here, as the phenolic anti-aging agent, 2,2′-methylenebis- (4-methyl-6-tert-butylphenol) (Nocrack NS-6 manufactured by Ouchi Shinsei Chemical Co., Ltd.), 2,6- Di-tert-butyl-4-methylphenol (Nocrack 200 manufactured by Ouchi Shinsei Chemical Co., Ltd.), 2,2′-methylene-bis- (4-ethyl-6-tert-butylphenol) (Ap Co., Ltd.) Yoshinox 425 manufactured by I Corporation) and the like, and a compound obtained by butylating a condensate of ρ-cresol and dicyclopentadiene (Wingstay L manufactured by ELIOKEM), a reaction product of 4-methylphenol and dicyclopentadiene Also included are hindered phenolic anti-aging agents such as (Lowinox CPL manufactured by Chemtura). It is done. As the surfactant that can be used in the anti-aging agent dispersion, known anionic surfactants, nonionic surfactants, magnesium aluminum silicate hydrates, and the like can be used as appropriate.

The anti-aging agent dispersion can be produced by a known method, and can be prepared using, for example, a ball mill, a high-speed shear type stirring device, a homogenizer, or the like. The addition amount of an anti-aging agent and a surfactant can be appropriately selected.

(Process 2)
In step 2, the agglomerated rubber obtained by aggregating the saponified natural rubber latex obtained in the above step 1 is treated with an aqueous solution of an anionic surfactant. By applying this activator treatment and further washing in step 3, the protein and phospholipid decomposed by the saponification treatment can be sufficiently removed, and the remaining in the agglomerated rubber can be prevented.

Examples of the aggregation method in Step 2 include a method of adjusting the pH by adding an acid such as formic acid, acetic acid, and sulfuric acid, and adding a polymer flocculant as necessary. Thereby, not a large aggregate but a granular rubber having a diameter of about several mm to 20 mm is formed, and phospholipids and proteins are sufficiently removed by the active agent treatment and the washing step. The pH is preferably adjusted in the range of 3.0 to 5.0, more preferably 3.5 to 4.5.

Examples of polymer flocculants include cationic polymer flocculants such as methyl chloride quaternary salt polymers of dimethylaminoethyl (meth) acrylate, anionic polymer flocculants such as acrylate polymers, and acrylamide polymers. Nonionic polymer flocculants such as, and amphoteric polymer flocculants such as dimethylaminoethyl (meth) acrylate methyl chloride quaternary salt-acrylate copolymer. The addition amount of the polymer flocculant can be selected as appropriate.

Next, the obtained agglomerated rubber is subjected to an active agent treatment using an aqueous solution of an anionic surfactant. Thereby, the protein etc. strongly adhering to the agglomerated rubber can be sufficiently removed. Here, as the anionic surfactant, for example, at least one selected from the group consisting of alkyl sulfate ester salts, polyoxyethylene alkyl ether sulfate ester salts, alkyl benzene sulfonates, alkyl naphthalene sulfonates, and fatty acid salts. Can be suitably used. Examples of these salts include alkali metal salts (such as sodium salts), ammonium salts, amine salts (alkanolamine salts such as monoethanolamine, diethanolamine, and triethanolamine salts).

The alkyl sulfate ester salt is preferably a higher alkyl sulfate ester salt (higher alcohol sulfate ester salt), and is preferably an alkali metal salt such as a sodium salt. Moreover, 10-20 are preferable and, as for carbon number of the alkyl group in an alkyl sulfate ester salt, 10-16 are more preferable. Specific examples of the alkyl sulfate ester salt include sodium dodecyl sulfate, sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, triethanolamine lauryl sulfate, sodium myristyl sulfate, potassium myristyl sulfate, sodium cetyl sulfate, and potassium cetyl sulfate. It is done. Of these, sodium lauryl sulfate, ammonium lauryl sulfate, potassium lauryl sulfate and the like are preferable because they are excellent in reducing the protein amount and the like.

As a polyoxyethylene alkyl ether sulfate ester salt, the polyoxyethylene alkyl ether sulfate ester salt which has a C10-C18 alkyl group is preferable, and a sodium salt is more preferable. The carbon number is preferably 10-14. The average degree of polymerization of the oxyethylene group is preferably 1 to 10, more preferably 1 to 5. Specific examples of the polyoxyethylene alkyl ether sulfate ester salt include sodium polyoxyethylene lauryl ether sulfate, sodium polyoxyethylene myristyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate such as sodium polyoxyethylene oleyl ether sulfate, polyoxyethylene Examples thereof include ethylene alkyl ether sulfate triethanolamine. Of these, sodium polyoxyethylene lauryl ether sulfate is preferred because of its excellent effect of reducing the amount of protein and the like.

Examples of the alkylbenzene sulfonate include alkylbenzene sulfonates having 3 to 20 carbon atoms, and alkali metal salts are preferable. Specific examples of the alkylbenzene sulfonate include dodecyl benzene sulfonic acid, pentadecyl benzene sulfonic acid, decyl benzene sulfonic acid, sodium salt of cetyl benzene sulfonic acid, potassium salt, ammonium salt, triethanolamine salt, calcium salt and the like. Can be mentioned. Among these, sodium dodecylbenzenesulfonate is preferable because it is excellent in the effect of reducing the amount of protein and the like.

Examples of the alkyl naphthalene sulfonate include sodium mono, di or triisopropyl naphthalene sulfonate, potassium mono, di or triisopropyl naphthalene sulfonate, sodium octyl naphthalene sulfonate, potassium octyl naphthalene sulfonate, sodium dodecyl naphthalene sulfonate, Examples thereof include alkali metal salts of alkyl naphthalene sulfonate such as potassium dodecyl naphthalene sulfonate. Of these, sodium alkylnaphthalene sulfonate is preferred because of its excellent effect of reducing the amount of phosphorus and the like.

As the fatty acid salt, a higher fatty acid salt having 10 to 20 carbon atoms is suitable, and examples thereof include a sodium salt and a potassium salt. Specific examples of the fatty acid salt include oleic acid, stearic acid, octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, docosanoic acid, linoleic acid, 2-ethylhexanoic acid, and 2-octylundecanoic acid. And sodium salts such as mixed fatty acids derived from palm oil, palm oil, castor oil, palm kernel oil, beef tallow and the like, and potassium salts (such as castor oil potassium soap). Among these, semi-hardened beef tallow fatty acid sodium, potassium oleate, and castor oil potassium soap are preferable because they are excellent in reducing the protein amount and the like.

The aqueous solution of the anionic surfactant in step 2 can be prepared by diluting and dissolving each surfactant with water.

The content of the anionic surfactant in 100% by mass of the aqueous solution (total amount of the surfactant component) is preferably 0.01% by mass or more, more preferably 0.1% by mass or more. If it is less than 0.01% by mass, phospholipids and proteins may not be sufficiently removed. The content is preferably 20% by mass or less, more preferably 10% by mass or less. Even if it exceeds 20 mass%, there is a possibility that there will be little improvement of an effect and it becomes economically disadvantageous.

The method of treating the agglomerated rubber with the aqueous solution (activator treatment) is not particularly limited as long as the agglomerated rubber is brought into contact with the aqueous solution. For example, the method of immersing the agglomerated rubber in the aqueous solution, the aqueous solution in the agglomerated rubber The method of spraying is mentioned.

Although the said processing temperature should just be selected suitably, Preferably it is 10-50 degreeC, More preferably, it is 15-35 degreeC. Moreover, processing time is 1 minute or more normally, Preferably it is 10 minutes or more, More preferably, it is 30 minutes or more. If it is less than 1 minute, the effects of the present invention may not be obtained satisfactorily. The upper limit is not limited, but if it is too long, the production cycle becomes long and uneconomical, so it is preferably 72 hours or less.

In addition, a surfactant is added as necessary at the time of saponification in Step 1, and an anionic surfactant is added again after the solidification in Step 2, but their actions are different. The surfactant added at the time of saponification has the effect of maintaining the average particle size of 0.1 to 1 [mu] m without solidifying the rubber during the saponification progress by addition of strong alkali, that is, maintaining the stability of the latex. On the other hand, the anionic surfactant used in Step 2 has an action of removing proteins, phospholipid degradation products, residues, and the like firmly attached to the washed rubber.
Some anionic surfactants alone have a protein removal effect, but cannot maintain latex stability under strong alkali. In step 1, it is necessary to select one that can stably maintain the latex in a colloidal state even under strong alkali. On the other hand, in step 2, it is preferable to select a rubber that has already solidified and has a strong ability to peel off protein. In this regard, sodium dodecyl sulfate is particularly preferable in Step 2.

(Process 3)
In step 3, the agglomerated rubber that has been treated with the activator in step 2 is subjected to a washing treatment, whereby proteins and the like are sufficiently removed. Examples of the washing treatment include a method of diluting a rubber component with water and washing, and then centrifuging, and a method of leaving the rubber to stand and discharging the water phase and discharging the rubber component. In these methods, washing may be repeated until the desired phosphorus content and nitrogen content are achieved. After the washing treatment is completed, the modified natural rubber of the present invention is obtained by drying.

The phosphorus content of the modified natural rubber (HPNR) obtained by the above production method is preferably 200 ppm or less, more preferably 150 ppm or less. If it exceeds 200 ppm, tan δ tends to increase, and there is a possibility that the fuel efficiency cannot be improved.

The modified natural rubber preferably has a nitrogen content of 0.2 mass% or less after being immersed in acetone at room temperature (25 ° C) for 48 hours, more preferably 0.15 mass% or less. More preferably, it is 0.1 mass% or less. If it exceeds 0.2% by mass, the effect of improving fuel economy may not be sufficiently obtained. The nitrogen content means a measured value after removing the anti-aging agent in the rubber by extraction with acetone.
In addition, phosphorus content and nitrogen content can be measured by the method as described in the below-mentioned Example.

The modified natural rubber usually has a weight average molecular weight (Mw) retention rate (Mw retention rate = molecular weight after heating / molecular weight before heating × 100) after aging at 80 ° C. for 72 hours of 40% or more. The retention is preferably 50% or more, more preferably 55% or more.
In addition, a weight average molecular weight (Mw) retention rate can be measured by the method as described in the below-mentioned Example.

[Rubber composition for tire]
The rubber composition for tires of the present invention contains a rubber component and carbon black and / or a white filler, and the rubber component contains a predetermined amount of the modified natural rubber.

In the rubber composition of the present invention, the content of the modified natural rubber in 100% by mass of the rubber component is 5% by mass or more, preferably 50% by mass or more, and more preferably 100% by mass. If it is less than 5% by mass, excellent fuel efficiency may not be obtained.

As rubber components that can be used other than modified natural rubber, natural rubber (non-modified) (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), Examples include ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR).

The rubber composition of the present invention contains carbon black and / or a white filler. Thereby, the reinforcement effect is acquired.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 70 m ² / g or more, and more preferably 100 m ² / g or more. There exists a tendency for sufficient reinforcement effect not to be acquired as it is less than 70 m < ² > / g. _N 2 SA is preferably at most 200 meters ² / g of carbon black, 180 m ² / g or less is more preferable. If it exceeds 200 m ² / g, the fuel efficiency tends to decrease.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

As white filler, those commonly used in the rubber industry, for example, mica such as silica, calcium carbonate, sericite, aluminum hydroxide, magnesium oxide, magnesium hydroxide, clay, talc, alumina, titanium oxide Etc. can be used.

The content of carbon black is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. Within the above range, good fuel efficiency can be obtained.

In the rubber composition of the present invention, the total content of carbon black and white filler is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. Within the above range, low fuel consumption, wear resistance, and wet grip properties can be obtained in a well-balanced manner.

In addition to the above materials, the rubber composition of the present invention is appropriately blended with various materials generally used in the tire industry such as zinc oxide, stearic acid, various anti-aging agents, sulfur, and vulcanization accelerators. May be.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured. The rubber composition can be used for each member of a tire, and among them, it can be suitably used for a tread, a sidewall, a steel belt, a carcass and the like.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, if necessary, a rubber composition containing various materials is extruded into a shape such as a tread at an unvulcanized stage and molded by a normal method on a tire molding machine. After forming a vulcanized tire, it can be manufactured by heating and pressing in a vulcanizer.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.
The various chemicals used in the examples are described below.
Field latex: Field latex Emar E-27C (surfactant) obtained from Muhibba Co., Ltd. Emar E-27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
Wingstay L (anti-aging agent): WINGSTAY L (compound obtained by butylating the condensate of ρ-cresol and dicyclopentadiene) manufactured by ELIOKEM
Emulvin W (surfactant): Emalvin W (aromatic polyglycol ether) manufactured by BASF
Tamol NN9104 (surfactant): Tamol NN9104 manufactured by BASF (Naphthalenesulfonic acid / formaldehyde sodium salt)
Van gel B (surfactant): Van gel B (magnesium aluminum silicate hydrate) manufactured by Vanderbilt
Surfactant for cleaning: Table 1
TSR: NR (TSR)
Carbon black: Dia Black I (ISAF class) manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 114 m ² / g)
Zinc oxide: 2 types of zinc oxides manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads stearic acid anti-aging agent manufactured by NOF Corporation 6C: NOCRACK 6C (N-phenyl) manufactured by Ouchi Shinsei Chemical Co., Ltd. -N '-(1,3-dimethylbutyl) -p-phenylenediamine) (6PPD)
Insoluble sulfur: Seimi sulfur (oil content: 10%) manufactured by Nihon Kiboshi Kogyo Co., Ltd.
Vulcanization accelerator TBBS (NS): Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
(Preparation of anti-aging agent dispersion)
462.5 g of water was mixed with 12.5 g of Emulvin W, 12.5 g of Tamol NN9104, 12.5 g of Van gel B, and 500 g of Wingstay L (total of 1000 g) for 16 hours with a ball mill to prepare an anti-aging dispersion.

(Production Example 1 Preparation of solid rubbers (1) to (9))
According to Table 2, the solid content concentration (DRC) of the field latex was adjusted to 30% (w / v), and then an Emar E-27C aqueous solution diluted to 10% and an NaOH aqueous solution diluted to 40% were added. Time saponification reaction was performed to obtain a saponified natural rubber latex. Subsequently, after adding an anti-aging dispersion and stirring for 2 hours, water was further added and diluted until the rubber concentration became 15% (w / v). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, a commercially available polymer flocculant was added, and the mixture was stirred for 2 minutes for aggregation. The diameter of the aggregate (aggregated rubber) thus obtained was about 3 to 15 mm. In accordance with Table 2, after immersing the aggregate in an aqueous surfactant solution for cleaning diluted to 0.5% by mass at room temperature for 8 hours, it was taken out, washed several times with 1000 ml of water, and then dried at 90 ° C. for 4 hours. Thus, solid rubbers (1) to (9) were obtained.

(Production Example 2 Preparation of solid rubber (10))
Solid rubber (10) was obtained under the same conditions as in Production Example 1 except that it was not immersed in the cleaning surfactant aqueous solution.

(Production Example 3 Preparation of Solid Rubber (12))
Production Example, except that the saponification treatment was not performed, the anti-aging agent dispersion was not added, the polymer flocculant was not added, and the surfactant was not immersed in the cleaning surfactant aqueous solution. A solid rubber (12) was obtained under the same conditions as in 1.

(Production Example 4 Preparation of solid rubber (13))
Solid rubber (13) was obtained under the same conditions as in Production Example 1 except that a 0.5% by mass sodium chloride aqueous solution was used instead of the cleaning surfactant aqueous solution.

(Production Example 5 Preparation of solid rubber (14) to (17))
Solid rubbers (14) to (17) were obtained under the same conditions as in Production Example 1 except that the cleaning surfactants in Table 3 were used.

(Production Example 6 Preparation of solid rubber (18))
A solid rubber (18) was obtained under the same conditions as in Production Example 1 except that a 2% by mass sodium carbonate aqueous solution was used instead of the cleaning surfactant aqueous solution.

The solid rubbers (1) to (18) were evaluated as follows, and the results are shown in Tables 2 and 3.

<Measurement of phosphorus content>
The phosphorus content was determined using an ICP emission spectrometer (P-4010, manufactured by Hitachi, Ltd.).

<Measurement of nitrogen content>
(Acetone extraction (test piece preparation))
About 0.5 g of a sample obtained by chopping each solid rubber into 1 mm square was prepared. The sample was immersed in 50 g of acetone, and after 48 hours at room temperature (25 ° C.), the rubber was taken out and dried to obtain each test piece (extracted with anti-aging agent).
(Measurement)
The nitrogen content of the obtained test piece was measured by the following method.
The nitrogen content was determined by decomposing and gasifying each of the acetone-extracted test pieces obtained above using a trace nitrogen carbon measuring device “SUMIGRAPH NC95A (manufactured by Sumika Chemical Analysis Center)”. The nitrogen content was quantified by analyzing with a gas chromatograph “GC-8A (manufactured by Shimadzu Corporation)”.

<Measurement of Mooney viscosity>
About each solid rubber and TSR, it measured at 130 degreeC according to the measuring method of the Mooney viscosity based on JISK6300.
In addition, if Mooney viscosity (ML1 _{+ 4} ) is 65 or less, it can be judged that kneading is unnecessary.

<Heat aging resistance>
The weight average molecular weight of each solid rubber before and after aging was measured to determine heat aging resistance. The aging treatment was performed by chopping each rubber into 2 to 5 mm squares and storing them in an oven at 80 ° C. for 72 hours. The weight average molecular weight was measured using a gel permeation chromatograph with isoprene as a standard substance.
The heat aging resistance was expressed by molecular weight retention (molecular weight after heating / molecular weight before heating × 100) (%). It shows that heat aging resistance is excellent, so that a value is large.

From Tables 2-3, the solid rubbers (1) to (9) prepared by immersing with an aqueous cleaning solution for an anionic surfactant are compared to the solid rubber (10) prepared without immersing. In addition, the nitrogen content and phosphorus content were greatly reduced, and the Mooney viscosity was also reduced. Moreover, the weight average molecular weight (Mw) retention in the heat aging resistance test was 55-70%, and it became clear that it was equivalent to solid rubber (11).

On the other hand, in the solid rubbers (14) to (17) prepared by immersing with a cleaning aqueous solution of a nonionic surfactant, the nitrogen content and the phosphorus content are the same as those of the solid rubber (10), and the cleaning action is high. It became clear that it was not demonstrated. Moreover, even if it processed with electrolyte aqueous solution like sodium chloride, the washing | cleaning effect was not exhibited similarly (solid rubber (13)).

(Production of rubber test piece)
According to the formulation shown in Table 4, 1.7 L Banbury was used to knead chemicals other than sulfur and the vulcanization accelerator. Next, using a roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 12 minutes to obtain a vulcanized product.
The solid rubber (11) prepared from TSR was used after masticating in advance.
Each obtained vulcanizate was evaluated by the following, and the results are shown in Table 4.

(Rolling resistance)
Using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.), loss tangent (tan δ) of each compound (vulcanized product) under the conditions of temperature 70 ° C., initial strain 10%, dynamic strain 1%, frequency 10 Hz. ) Was measured, and the rolling resistance index of Comparative Example 1 was set to 100, which was calculated by the following formula. The smaller the rolling resistance index, the lower the rolling resistance, which is preferable.
(Rolling resistance index) = ((tan δ of each formulation) / (tan δ of Comparative Example 1)) × 100

From Table 4, in the examples using the produced solid rubbers (1) to (9) subjected to the immersion treatment with the anionic surfactant aqueous solution, the rolling was superior to the comparative examples using other solid rubbers. Resistance (low fuel consumption) was obtained, and it became clear that the modified natural rubber of the present invention can be suitably used for tires.
In addition, although the comparative example using solid rubber (18) was excellent in rolling resistance, there was concern about deterioration of rolling resistance due to a decrease in molecular weight when stored for a long time.

Claims (9)

A rubber component and carbon black and / or white filler,
In 100% by mass of the rubber component, the content of the modified natural rubber obtained by treating the aggregated rubber obtained from the saponified natural rubber latex with an aqueous solution of an anionic surfactant and washing is 5% by mass or more. Rubber composition for tires. 2. The anionic surfactant is at least one selected from the group consisting of an alkyl sulfate ester salt, a polyoxyethylene alkyl ether sulfate ester salt, an alkylbenzene sulfonate salt, an alkyl naphthalene sulfonate salt and a fatty acid salt. The rubber composition for tires described in 1. The tire rubber composition according to claim 1 or 2, wherein a content of the anionic surfactant in 100% by mass of the aqueous solution is 0.01% by mass or more. The tire rubber composition according to claim 1 or 2, wherein a content of the anionic surfactant in 100% by mass of the aqueous solution is 0.1% by mass or more. The tire rubber composition according to any one of claims 1 to 4, wherein the modified natural rubber has a nitrogen content of 0.2% by mass or less after being immersed in acetone at room temperature for 48 hours. The tire rubber composition according to any one of claims 1 to 5, wherein a phosphorus content of the modified natural rubber is 200 ppm or less. The weight average molecular weight (Mw) retention rate (Mw retention rate = molecular weight after heating / molecular weight before heating × 100) after aging at 80 ° C. for 72 hours of the modified natural rubber is 40% or more. The rubber composition for tires in any one of -6. Step 1 of saponifying natural rubber latex;
Treating the agglomerated rubber obtained by agglomerating the saponified natural rubber latex obtained in step 1 with an aqueous solution of an anionic surfactant;
Step 3 for cleaning ,
Step 4 of kneading the modified natural rubber produced through Steps 1 to 3 and carbon black and / or white filler;
The manufacturing method of the rubber composition for tires in any one of Claims 1-7 containing these . The pneumatic tire produced using the rubber composition in any one of Claims 1-7.