JP5426605B2 - Highly purified natural rubber and method for producing the same - Google Patents

Description

The present invention relates to a highly purified natural rubber, a production method thereof, a tire rubber composition using the highly purified natural rubber, and a pneumatic tire using the rubber composition.

Conventionally, vehicle fuel efficiency has been reduced by reducing the rolling resistance of tires and suppressing heat generation, but in recent years, there has been an increasing demand for fuel efficiency reduction for tires, and further studies are indispensable. . Natural rubber, which is widely used for tires, generally has higher fuel efficiency compared to styrene butadiene rubber. However, as styrene butadiene rubber has been fueled recently, it is natural to achieve further fuel efficiency. It is essential to promote fuel efficiency reduction of rubber.

Regarding reduction in fuel consumption of natural rubber, for example, Patent Document 1 proposes natural rubber obtained by saponifying natural rubber latex and removing phospholipids and proteins. As a result, the fuel efficiency can be improved, but it is not yet sufficient, and further reduction of tan δ is desired. In addition, tires and raw material natural rubber are required not only to have low fuel consumption but also performance such as heat aging resistance.

JP 2010-138359 A

The present invention solves the above-mentioned problems and provides a highly purified natural rubber having improved fuel economy and heat aging resistance, a method for producing the same, a tire rubber composition using the highly purified natural rubber, and a pneumatic tire. The purpose is to do.

The present invention relates to a highly purified natural rubber obtained by agglomerating and washing a modified natural rubber latex prepared by subjecting natural rubber latex to a saponification treatment and a proteolysis treatment.

In the highly purified natural rubber, the saponification treatment and the proteolysis treatment are preferably performed in the order of saponification treatment and proteolysis treatment. Here, it is preferable that the proteolytic treatment is performed after adjusting the latex after the saponification treatment to pH 11 or less.

In the highly purified natural rubber, the saponification treatment and the protein degradation treatment may be performed in the order of the protein degradation treatment and the saponification treatment.

In the highly purified natural rubber, the saponification treatment is preferably performed with a strong alkaline compound, and the proteolysis treatment is preferably performed with a proteolytic enzyme.

The present invention includes a step (1) for preparing a modified natural rubber latex by subjecting a natural rubber latex to a saponification treatment and a proteolytic treatment, and a step (2) for aggregating the modified natural rubber latex to obtain an agglomerated rubber. And a method for producing the highly purified natural rubber, comprising the step (3) of washing the agglomerated rubber.

In the proteolytic treatment in the above production method, 0.001 to 10 parts by mass of the proteolytic enzyme is preferably added to 100 parts by mass of the rubber solid content in the natural rubber latex.

The present invention relates to a tire rubber composition comprising a rubber component and carbon black and / or a white filler, wherein the content of the highly purified 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 having a tire member produced using the rubber composition.

According to the present invention, natural rubber latex is subjected to both saponification treatment and proteolytic treatment to prepare a modified natural rubber latex, and then the agglomerated rubber prepared by agglomerating the latex is washed. Since it is a highly purified natural rubber obtained, proteins and phospholipids in the rubber can be sufficiently reduced, and fuel efficiency can be improved. In addition, the highly purified natural rubber has a heat aging resistance equivalent to that of a normal natural rubber (non-modified) because a decrease in molecular weight during storage is suppressed. Accordingly, it is possible to provide a tire rubber composition and a pneumatic tire that are excellent in fuel efficiency and heat aging resistance.

[Purified natural rubber]
The highly purified natural rubber of the present invention is obtained by agglomerating and washing a modified natural rubber latex prepared by subjecting natural rubber latex to saponification treatment and proteolysis treatment.

In the method of saponifying natural rubber latex to reduce the fuel consumption of natural rubber, proteins and phospholipids decomposed by saponification are confined inside the rubber during solidification of the rubber, or remain firmly adsorbed on the rubber surface. Therefore, these components cannot be sufficiently reduced by washing with water. In this regard, by immersing the rubber particles after acid coagulation of the latex in an alkaline aqueous solution such as sodium carbonate, the residual nitrogen amount can be reduced to 0.15% or less to reduce rolling resistance, and further acid treatment. Thus, the deterioration of heat aging resistance due to alkali treatment can be suppressed, and excellent heat aging resistance can also be obtained. However, the high-purity rubber prepared through a series of treatments with alkali, acid, alkali, and acid has a drawback in that a large amount of chemicals is used and a lot of time is required for each treatment.

On the other hand, the highly purified natural rubber of the present invention is prepared by washing rubber particles agglomerated with acid after subjecting natural rubber latex to both saponification treatment and proteolysis treatment. The saponification treatment decomposes and removes phospholipids and proteins, and further proteolysis treatment further decomposes proteins that could not be sufficiently removed or decomposed only by the saponification treatment, and the rubber particle surface. The remaining protein is also decomposed and removed. Specifically, by adding acid to the latex after saponification treatment and adjusting the pH at which the proteolytic enzyme works to decompose the protein on the rubber surface and dissolve it in the aqueous phase, the amount of residual nitrogen is greatly reduced. it can. As for phosphorus, saponification treatment decomposes phospholipids on the rubber surface, and the degradation action is not affected even when a proteolytic enzyme is used in combination with saponification, so that the amount of phosphorus can be sufficiently reduced. Therefore, in the present invention, proteins and phospholipids are sufficiently removed, and excellent fuel efficiency is obtained.

A method of increasing the amount of alkali during saponification is also conceivable, but this method cannot improve the protein removal effect. In addition, the phospholipid removal (degradation) effect is insufficient only with proteolytic enzymes. Furthermore, as described above, the amount of nitrogen can also be reduced by performing alkali treatment after acid coagulation, but it is a newly discovered finding that the same reduction effect is exhibited in both saponification treatment and proteolysis treatment, In the present invention, the combined use has an effect exceeding the prediction of those skilled in the art.

Moreover, since the highly purified natural rubber of the present invention can be prepared by washing after acid coagulation, it is usually in a slightly acidic atmosphere. Therefore, the molecular weight change at the time of rubber aging is similar to that of TSR (block-like natural rubber), and it has sufficient heat aging resistance. Therefore, excellent low fuel consumption and heat aging resistance can be obtained without specially performing alkali treatment after acid coagulation and further acid treatment thereafter, and thus the production process can be simplified. Furthermore, when the alkali treatment is performed, there is a concern about early vulcanization (scorch) and rubber burning, but since the rubber of the present invention has a vulcanization rate similar to that of TSR, there is no such concern.

The highly purified natural rubber of the present invention includes, for example, a step (1) of preparing a modified natural rubber latex by subjecting a natural rubber latex to a saponification treatment and a proteolytic treatment, and agglomerating the modified natural rubber latex. It can be prepared by a production method including a step (2) for obtaining agglomerated rubber and a step (3) for washing the agglomerated rubber.

(Process 1)
In step (1), natural rubber latex is subjected to both saponification treatment and proteolysis treatment. Thereby, phospholipid and protein are fully 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 a natural rubber latex, raw latex (field latex) produced by tapping Hevea tree, concentrated latex (purified latex, high ammonia latex to which ammonia is added by a conventional method) concentrated by centrifugation or creaming method , Zinc oxide, TMTD and ammonia stabilized LATZ latex, etc.) can be used.

(1) Saponification treatment As a saponification treatment method, for example, the method described in JP2010-138359A and JP2010-174169A can be suitably performed. Can be implemented.

The saponification treatment can be performed 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 may be performed as necessary.

The alkali used for the saponification treatment is preferably a strong alkaline compound such as sodium hydroxide or potassium hydroxide. The surfactant is not particularly limited, and includes known nonionic surfactants, anionic surfactants, and amphoteric surfactants. Polyoxyethylene is used because it can be saponified well without solidifying the rubber. Alkyl ether sulfate salts are preferred.

In the saponification treatment, the amount of alkali added may be appropriately set, but is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber solid content in the natural rubber latex. The addition amount of the surfactant is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the rubber solid content of the natural rubber latex. The temperature and time of the saponification treatment may be set as appropriate, and is usually about 20 to 70 ° C. and about 1 to 72 hours.

(2) Proteolytic treatment The proteolytic treatment of natural rubber latex can be performed, for example, by a treatment using a proteolytic enzyme. The proteolytic enzyme is not particularly limited, and conventionally known proteolytic enzymes can be used. Among them, alkaline protease and the like are preferable. The origin of the proteolytic enzyme may be any of those derived from bacteria, those derived from filamentous fungi, those derived from yeast, etc., but those derived from bacteria, particularly those belonging to the genus Bacillus. In addition, enzymes such as lipase, esterase, amylase, laccase and cellulase may be used in combination.

The amount of proteolytic enzyme used varies depending on the activity of the enzyme and is not particularly limited. In general, the amount of proteolytic enzyme added is 100 parts by mass of rubber solid content in natural rubber latex. It is preferable to adjust to 0.001-10 mass parts, and it is more preferable to adjust to 0.01-3 mass parts. Within the above range, the protein in the latex can be sufficiently decomposed while maintaining its activity, and there is a tendency to exhibit an effect commensurate with the amount used.

The protein degradation treatment for natural rubber latex is performed by adding a proteolytic enzyme to natural rubber latex and adding a predetermined amount of surfactant as necessary, and then for several tens of minutes to about one week, preferably 3 hours to 3 days. Aged to a certain extent. The aging treatment may be performed while stirring the latex, or may be performed in a standing state. Moreover, you may adjust temperature as needed. In order to make enzyme activity sufficient, it is preferably adjusted to 5 to 80 ° C, more preferably 5 to 70 ° C.

The saponification treatment and the protein degradation treatment can be performed in any order. For example, the protein degradation treatment may be performed after the saponification treatment, or the saponification treatment may be performed after the protein degradation treatment. It is also possible to perform both processes simultaneously. In the method of saponification after proteolytic treatment, that is, the method in which the rubber in the latex state is stabilized with a surfactant, then the protein on the rubber particle surface is degraded with a proteolytic enzyme, and then saponified. At the stage where the rubber is solidified, the rubber is greatly hardened, which may make cleaning difficult. On the other hand, a method of performing proteolytic treatment after saponification treatment, that is, a method of adding a proteolytic enzyme after saponification is more preferable because washing becomes easy.

As a method of subjecting the proteolytic treatment after the saponification treatment, it is preferable that the proteolytic treatment is performed after adjusting the latex after the saponification treatment to pH 11 or less from the viewpoint of detergency. Specifically, an acid is added to a saponified latex having a pH of 13 or more, and the pH is lowered to 11 or less. By degrading the protein remaining on the rubber particle surface in a state where the enzyme works, it can be dissolved in the aqueous phase. it can. Therefore, phosphorus and nitrogen can be sufficiently reduced in the cleaning process. In this case, it is necessary to add an acid before adding a proteolytic enzyme, but even if no proteolytic enzyme is added, an acid must be added at the time of coagulation. Absent.

The latex after the saponification treatment is adjusted to pH 11 or less, but is preferably adjusted to 10.5 or less. The lower limit of the pH is preferably 8 or more, more preferably 9 or more. The pH can be adjusted with a known acidic compound, and can be implemented by adding diluted formic acid, acetic acid, sulfuric acid or the like.

In the saponification treatment or proteolysis treatment, an anti-aging agent may be added before, during or after these treatments 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.

In addition, when adding an anti-aging agent dispersion | distribution before these processes, both processes are performed after mixing with natural rubber latex. Moreover, when adding during a saponification process, it mixes with an alkali etc., and when adding during a proteolytic process, it mixes with a proteolytic enzyme etc. When added after these treatments, it is mixed with the modified natural rubber latex obtained by performing both treatments.

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 antioxidant, 2,2′-methylenebis- (4-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-4-methylphenol, 2,2′- Methylene-bis- (4-ethyl-6-tert-butylphenol) and the like, a compound obtained by butylating a condensate of ρ-cresol and dicyclopentadiene, and a reaction product of 4-methylphenol and dicyclopentadiene And hindered phenolic anti-aging agents such as 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.

Although the addition amount of the antioxidant can be appropriately selected, the lower limit is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, with respect to 100 parts by mass of the rubber solid content in the natural rubber latex. The upper limit is preferably 5 parts by mass or less, more preferably 2 parts by mass or less. Moreover, although the addition amount of surfactant can be selected suitably, it is 1-20 mass parts preferably with respect to 100 mass parts of anti-aging agents.

(Process 2)
In step (2), the modified natural rubber latex prepared by performing both treatments in step (1) is agglomerated to obtain an agglomerated rubber.

Examples of the aggregation method in the step (2) include a method of adjusting pH by adding an acid such as formic acid, acetic acid and sulfuric acid, and adding a polymer flocculant as necessary. Thereby, a granular rubber having a diameter of about 3 to 20 mm, preferably 3 to 10 mm, is formed instead of a large aggregate. The pH is preferably adjusted in the range of 3.0 to 4.8, more preferably 3.5 to 4.5. Thereby, the surface area of the rubber particles is greatly increased, and residual impurities can be washed away in the aqueous phase.

Examples of polymer flocculants include cationic polymer flocculants such as methyl chloride quaternary salt polymer of dimethylaminoethyl (meth) acrylate, anionic polymer flocculants such as acrylate polymer, and acrylamide polymer. 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.

(Process 3)
In step (3), the agglomerated rubber produced in step (2) is washed. Examples of the washing method include a method of diluting a rubber component with water and washing and then centrifuging, and a method of allowing the rubber component to float by standing and discharging only the aqueous phase and taking out the rubber component. Although the former centrifugal separation is an effective cleaning method, there are problems such as limitation of continuous operation time and cost increase due to cleaning. Therefore, the latter method in which only the aqueous phase is discharged by floating the rubber is more preferable. Specifically, water is added to the rubber and stirred for 1 to 5 minutes. After the stirring, when the rubber floats, the operation of draining the water from the bottom is repeated 1 to several times, so that impurities in the aqueous phase are 1 to several times. It becomes possible to make it a thousandth. By drying after completion of the washing treatment, a highly purified natural rubber having a sufficiently reduced phosphorus content and nitrogen content can be obtained.

The phosphorus content of the highly purified natural rubber 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. Phosphorus can be reduced to 200 ppm or less by saponification treatment, but this reduction effect is not affected even when a proteolytic enzyme is used in combination, and no change is observed.

The nitrogen content in the highly purified natural rubber is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, and further preferably 0.1% by mass or less from the viewpoint of low fuel consumption. Although the saponification treatment alone can reduce the nitrogen amount only to about 0.25% by mass, it can be further reduced to about 0.08 to 0.15% by mass by using a proteolytic treatment in combination. In addition, when rubber | gum contains an anti-aging agent, the said nitrogen content is a value after being immersed in acetone at room temperature (25 degreeC) for 48 hours, and the value after removing the anti-aging agent in rubber | gum by acetone extraction. It is.

Although the rolling resistance can be sufficiently reduced by the above nitrogen amount, if it is necessary to further reduce, the nitrogen amount can be reduced by further treating the rubber with alkali after washing or before washing. However, there is a problem that the number of steps increases and the heat aging resistance deteriorates, and the deterioration of the heat aging resistance can be improved by the acid treatment, but it further increases one step.
In addition, phosphorus content and nitrogen content 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 highly purified natural rubber. When the viscoelasticity of a kneaded vulcanizate containing rubber, carbon black, etc. with reduced phosphorus content and nitrogen content is measured, there is a relationship between the nitrogen content and tan δ, but there is a relationship, the more the nitrogen content decreases. tan δ is lowered. Therefore, a rubber having a low rolling resistance can be produced by using a highly purified natural rubber having a small amount of nitrogen.

In the rubber composition of the present invention, the content of highly purified 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 80% by mass. If it is less than 5% by mass, excellent fuel efficiency may not be obtained.

Rubber components that can be used in addition to highly purified natural rubber include natural rubber (non-modified) (NR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and styrene isoprene butadiene rubber (SIBR). ), Ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and the like.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 70 m ² / g or more, and more preferably 80 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 of carbon black is preferably 180 m ² / g or less, and more preferably 150 m ² / g or less. If it exceeds 180 m ² / g, the fuel efficiency tends to decrease.
In addition, the nitrogen adsorption specific surface area of carbon black is a value measured according to JIS K 6217-2: 2001.

As white fillers, those generally 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, good fuel efficiency can be obtained.

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, a rubber composition containing various materials as necessary is extruded into a shape such as a tread at an unvulcanized stage and molded by a normal method on a tire molding machine to form an unvulcanized tire. After production, it can be produced 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.
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 LANXESS
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
Field latex: Field latex Emar E-27C (surfactant) obtained from Muhibbah Lateks, Inc. Emar E-27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.
Alkaline protease: Alkaline protease KP3939 (proteolytic enzyme) manufactured by Kao Corporation
Acid: 94% formic acid (general industrial grade, diluted and used as 2% aqueous formic acid solution)
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: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples 1-6 and Comparative Examples 1-3>
(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 by a ball mill to prepare an antioxidant dispersion.

Example 1
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of 10% Emar E-27C aqueous solution and 60 g of 25% NaOH aqueous solution were added to 1000 g of the latex and saponified for 24 hours at room temperature. Reaction was performed to obtain a saponified natural rubber latex. Thereafter, formic acid was slowly added, and when the pH reached about 10, 0.3 g of alkaline protease was dissolved in several ml of water, added, stirred for 5 minutes, and allowed to stand at room temperature overnight. A modified natural rubber latex was obtained (the amount is as shown in Table 1).
Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, a cationic 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 10 mm. After removing water from the resulting aggregate as much as possible, adding 1000 ml of water and stirring for 2 minutes, repeating the operation of removing water as much as possible, and then drying at 90 ° C. for 4 hours to solid rubber (high purity natural rubber) )

(Example 2)
A solid rubber was produced in the same manner as in Example 1 except that the amount of alkaline protease added was changed to 0.03 g.

(Example 3)
A solid rubber was produced in the same manner as in Example 1 except that the amount of alkaline protease added was changed to 0.003 g.

Example 4
A solid rubber was produced in the same manner as in Example 1 except that the amount of alkaline protease added was changed to 3 g.

(Example 5)
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of a 10% Emar E-27C aqueous solution was added to 1000 g of the latex, and stirred well for 30 minutes. Next, 0.3 g of alkaline protease was dissolved in about several ml of water, added, stirred for 5 minutes, and allowed to stand overnight at room temperature. Thereafter, 60 g of 25% NaOH aqueous solution was added, and saponification reaction was performed at room temperature for 24 hours to obtain a modified natural rubber latex.
Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, a cationic polymer flocculant was added, and the mixture was stirred for 2 minutes for aggregation. The diameter of the obtained aggregate (aggregated rubber) was about 10 to 20 mm. To the resulting aggregate, 1000 ml of water was added and stirred for 2 minutes, and water was removed as much as possible. The operation was repeated three times, followed by drying at 90 ° C. for 4 hours to obtain a solid rubber.

(Example 6)
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of 10% Emar E-27C aqueous solution and 60 g of 25% NaOH aqueous solution were added to 1000 g of the latex and saponified for 24 hours at room temperature. Reaction was performed to obtain a saponified natural rubber latex. Thereafter, formic acid was slowly added, and when the pH reached about 10, 0.3 g of alkaline protease was dissolved in several ml of water, added, stirred for 5 minutes, and allowed to stand at room temperature overnight. A modified natural rubber latex was obtained.
Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, a cationic 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 10 mm. The obtained agglomerate was taken out, immersed in 1000 ml of a 5% by mass aqueous sodium carbonate solution, allowed to stand overnight, and then the rubber was taken out. To this, 1000 ml of water was added and stirred for 2 minutes to remove water as much as possible. Next, this rubber was immersed in a 2% by weight aqueous formic acid solution and allowed to stand overnight, then the rubber was taken out and the same water washing operation was repeated three times, followed by drying at 90 ° C. for 4 hours to obtain a solid rubber.

(Comparative Example 1)
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of 10% Emar E-27C aqueous solution and 60 g of 25% NaOH aqueous solution were added to 1000 g of the latex and saponified for 24 hours at room temperature. Reaction was performed to obtain a saponified natural rubber latex.
Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, a cationic 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. To the resulting aggregate, 1000 ml of water was added and stirred for 2 minutes, and water was removed as much as possible. The operation was repeated three times, followed by drying at 90 ° C. for 4 hours to obtain a solid rubber.

(Comparative Example 2)
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of 10% Emar E-27C aqueous solution and 60 g of 25% NaOH aqueous solution were added to 1000 g of the latex and saponified for 24 hours at room temperature. Reaction was performed to obtain a saponified natural rubber latex.
Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, a cationic 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. The obtained agglomerates were taken out and immersed in 1000 ml of a 2% by weight aqueous sodium carbonate solution at room temperature for 4 hours, and then the rubber was taken out. To this, 1000 ml of water was added and stirred for 2 minutes to remove the water as much as possible. The operation was repeated three times and then dried at 90 ° C. for 4 hours to obtain a solid rubber.

(Comparative Example 3)
After adjusting the solid content concentration (DRC) of the field latex to 30% (w / v), 25 g of 10% Emar E-27C aqueous solution and 60 g of 25% NaOH aqueous solution were added to 1000 g of the latex and saponified for 24 hours at room temperature. Reaction was performed to obtain a saponified natural rubber latex.
Next, 6 g of the anti-aging dispersion was added and stirred for 2 hours, and then further diluted with water to a rubber concentration of 15% (w / v). Thereafter, formic acid was added with slow stirring to adjust the pH to 4.0, a cationic 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. The obtained agglomerates were taken out and immersed in 1000 ml of a 2% by weight aqueous sodium carbonate solution at room temperature for 4 hours, and then the rubber was taken out. To this, 1000 ml of water was added and stirred for 2 minutes to remove water as much as possible. Next, the rubber was immersed in a 2% by weight aqueous formic acid solution for 6 hours, then the rubber was taken out, and the same water washing operation was repeated 3 times, followed by drying at 90 ° C. for 4 hours to obtain a solid rubber.

The solid rubber obtained above was evaluated as follows, and the results are shown in Table 1. A TSR is also shown as a reference example.

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

<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 as molecular weight retention (molecular weight after aging / molecular weight before aging × 100) (%). It shows that heat aging resistance is excellent, so that a value is large.

From Table 1, in Examples 1-4 and 6 in which proteolytic treatment was performed after saponification, the amount of nitrogen and phosphorus were sufficiently reduced, heat aging resistance was good, and saponification treatment, alkali treatment, and acid treatment were performed. The same performance as in Comparative Example 3 was obtained. In particular, in Example 6, although the total number of processing steps was large, these characteristics were very excellent. Moreover, although the characteristic was excellent also in Example 5 which performed saponification after the proteolysis process, the tendency for a residual nitrogen amount to be a little larger than Example 1 was seen.

In Comparative Example 1 in which proteolytic treatment, alkali treatment, and acid treatment were not performed, the amount of nitrogen was large. Moreover, in the comparative example 2 which has not performed the protein degradation process and the acid process, heat aging resistance was inferior.

<Examples 7 to 12 and Comparative Examples 4 to 6>
(Production of rubber test piece)
According to the formulation shown in Table 2, chemicals other than sulfur and a vulcanization accelerator were kneaded using 1.7 L Banbury. 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 obtained unvulcanized rubber composition and vulcanized product were evaluated as follows, and the results are shown in Table 2.

<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 6 was set to 100, and the following calculation formula was used. 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 6) × 100

<T95: Optimal vulcanization time>
The vulcanization curve was measured at 150 ° C. with a curast meter 7 manufactured by JSR Trading. According to a conventional method, the time required to reach 95% of the difference between the maximum torque and the minimum torque (minimum torque + (maximum torque−minimum torque) × 0.95) was determined as T95 (optimum vulcanization time (minutes)). The smaller the T95, the faster the vulcanization rate (the closer to normal natural rubber, the easier to handle. The faster the vulcanization, the greater the subsequent reversion).

From Table 2, in Examples 7-12 using the solid rubber of Examples 1-6, the favorable fuel-consumption property was acquired and the tendency for performance to be excellent, so that there were few amounts of nitrogen was seen. Further, the fuel efficiency was better than that of Comparative Example 6 using the solid rubber of Comparative Example 3 having a small amount of nitrogen and phosphorus. Furthermore, in the examples, T95 was close to TSR, and the vulcanization time was also good.

Claims (11)

A highly purified natural rubber obtained by agglomerating and washing a modified natural rubber latex prepared by subjecting natural rubber latex to saponification treatment and proteolysis treatment ,
The saponification treatment is a strongly alkaline compound, and the proteolytic treatment is performed by a proteolytic enzyme,
The highly purified natural rubber, wherein the amount of the strongly alkaline compound added in the saponification treatment is 0.1 to 5 parts by mass with respect to 100 parts by mass of the rubber solid content in the natural rubber latex . The highly purified natural rubber according to claim 1, wherein the saponification treatment and the protein degradation treatment are performed in the order of saponification treatment and protein degradation treatment. The highly purified natural rubber according to claim 2, wherein the latex after the saponification treatment is adjusted to pH 11 or less and then subjected to a proteolytic treatment. The highly purified natural rubber according to claim 1, wherein the saponification treatment and the proteolysis treatment are performed in the order of proteolysis treatment and saponification treatment. The high-purity natural rubber according to any one of claims 1 to 4, wherein the aggregation is performed by adding acid to adjust pH to form a granular rubber having a diameter of 3 to 20 mm . The highly purified natural rubber according to any one of claims 1 to 5, wherein the washing floats the rubber and discharges only the aqueous phase. The highly purified natural rubber according to any one of claims 1 to 5, which has a phosphorus content of 200 ppm or less and a nitrogen content of 0.2 mass% or less. A step (1) for preparing a modified natural rubber latex by subjecting the natural rubber latex to a saponification treatment and a proteolytic treatment, a step (2) for agglomerating the modified natural rubber latex to obtain an agglomerated rubber, and the agglomeration. look including a step (3) to wash the rubber,
The saponification treatment is a strongly alkaline compound, and the proteolytic treatment is performed by a proteolytic enzyme,
The additive amount of the strong alkali compound saponification of the rubber solid content of 100 parts by weight of the natural rubber latex, according to any one of claims 1 to 7, which is 0.1 to 5 parts by weight A method for producing highly purified natural rubber. The method for producing highly purified natural rubber according to claim 8 , wherein in the proteolytic treatment, 0.001 to 10 parts by mass of a proteolytic enzyme is added to 100 parts by mass of the rubber solid content in the natural rubber latex. A rubber component and carbon black and / or white filler,
The rubber component in 100% by mass, claim 1-7 tire rubber composition content is 5 mass% or more highly purified natural rubber according to any one of. The pneumatic tire which has the member for tires produced using the rubber composition of Claim 10 .