JP5937443B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for tires and a pneumatic tire using the same.

Conventionally, the rubber composition for tires has been used as a filler with carbon black, which can easily interact with the rubber component and has an excellent reinforcing effect. However, in recent years, from the viewpoint of low fuel consumption and environmental protection. White fillers such as silica are used in place of carbon black.

However, white fillers such as silica have a lower affinity with natural rubber, butadiene rubber, styrene butadiene rubber, etc., which are widely used for tires, compared to carbon black, and wear resistance and mechanical strength (tensile strength and fracture) Often inferior in terms of elongation.

As a method for solving this problem, it has been proposed to use a silane coupling agent having reactivity with a white filler such as a rubber component or silica, but the reaction with the white filler should be sufficiently advanced. However, the unreacted white filler may remain poorly dispersed and the desired performance may not be exhibited. Furthermore, in order to prevent this, if a large amount of silane coupling agent is blended, due to the residual silane coupling agent, rubber burn during processing, wear resistance of vulcanized rubber and mechanical strength may be reduced. is there.

Patent Document 1 discloses a tire rubber composition containing a basic aqueous solution having a pH of 8 to 12 and silica for the purpose of enhancing the compatibility between silica and rubber, but the interaction between rubber and silica is disclosed. Cannot be sufficiently obtained, and the improvement effect such as low fuel consumption is not satisfactory. Therefore, it is desired to provide a silica-containing rubber that can improve fuel economy, wear resistance, and processability in a well-balanced manner.

JP 2000-219779 A

An object of the present invention is to solve the above problems and provide a rubber composition for a tire that improves fuel economy, wear resistance, and processability in a well-balanced manner, and a pneumatic tire using the same.

The present invention relates to a tire rubber composition containing a rubber component containing a modified natural rubber having a phosphorus content of 200 ppm or less, a white filler, and a cyclized rubber.
It is preferable that 10 to 200 parts by mass of the white filler and 0.1 to 40 parts by mass of the cyclized rubber are included with respect to 100 parts by mass of the rubber component.

The cyclization rate of the cyclized rubber is preferably 0.1 to 40%.
The cyclized rubber is preferably at least one selected from the group consisting of cyclized natural rubber, cyclized isoprene rubber, and cyclized butadiene rubber.

The white filler is preferably silica.
The nitrogen content of the modified natural rubber is preferably 0.3% by mass or less.
The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, since it is a rubber composition for a tire containing a rubber component containing a modified natural rubber having a phosphorus content of 200 ppm or less, a white filler, and a cyclized rubber, fuel efficiency and wear resistance are reduced. And processability can be improved in a well-balanced manner.

The tire rubber composition of the present invention includes a rubber component containing a modified natural rubber having a phosphorus content of 200 ppm or less, a white filler, and a cyclized rubber.

Rubber compounded with white fillers such as silica generally has low dispersibility of the filler and it is difficult to obtain the desired performance, but in the present invention, silica compounded with modified natural rubber with a low amount of phosphorus as the rubber component By further adding cyclized rubber to the rubber, the interaction between silica and the rubber component such as modified natural rubber can be enhanced. Accordingly, the dispersibility of the white filler is improved, and both low fuel consumption and wear resistance can be achieved, and good processability can be obtained, and the balance of these performances can be improved synergistically.

Furthermore, by using a cyclized rubber having a predetermined cyclization rate, the dispersibility of a white filler such as silica is dramatically improved, and the performance balance can be remarkably improved.

In the present invention, a modified natural rubber having a small amount of phosphorus is used as the rubber component. Thereby, the performance balance of low fuel consumption, abrasion resistance, and workability can be remarkably improved.

Natural rubber (modified natural rubber) from which phospholipids contained in natural rubber (NR) have been reduced and removed (modified natural rubber, preferably from which protein and gel content have also been removed) has the property of not generating heat. Compared with the use of, further reduction in fuel consumption can be achieved. In addition, the unvulcanized rubber composition containing the modified natural rubber is excellent in processability and can be sufficiently kneaded without any special mastication process. Further, it is possible to suppress a decrease in breaking strength and the like, and it is possible to effectively improve fuel efficiency and wear resistance.

The modified natural rubber (HPNR) has a phosphorus content of 200 ppm or less. If it exceeds 200 ppm, the gel amount will increase during storage, and the tan δ of the vulcanized rubber will increase and the fuel efficiency will deteriorate, or the Mooney viscosity of the unvulcanized rubber will increase and the processability will tend to deteriorate. There is a possibility that low fuel consumption, wear resistance, and workability cannot be improved in a well-balanced manner. The phosphorus content is preferably 150 ppm or less, and more preferably 100 ppm or less. Here, the phosphorus content can be measured by a conventional method such as ICP emission analysis. Phosphorus is derived from phospholipids (phosphorus compounds).

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. If it exceeds 0.3% by mass, the Mooney viscosity will increase during storage and the processability tends to deteriorate, and there is a possibility that the fuel economy, wear resistance and processability cannot be improved in a well-balanced manner. The nitrogen content can be measured by a conventional method such as Kjeldahl method. Nitrogen is derived from protein.

The gel content in the modified natural rubber is preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 7% by mass or less. If it exceeds 20% by mass, the Mooney viscosity tends to increase and the processability tends to deteriorate, and the fuel economy, wear resistance, and processability may not be improved in a well-balanced manner. The gel content means a value measured as an insoluble content with respect to toluene, which is a nonpolar solvent, and may be simply referred to as “gel content” below. The measuring method of gel content rate is as follows. First, a natural rubber sample is soaked in dehydrated toluene, light-shielded in the dark and left for 1 week, and then the toluene solution is centrifuged at 1.3 × 10 ⁵ rpm for 30 minutes to obtain an insoluble gel content and a toluene soluble content. Isolate. Methanol is added to the insoluble gel and solidified, and then dried, and the gel content is determined from the ratio between the mass of the gel and the original mass of the sample.

The modified natural rubber is preferably substantially free of phospholipids. “Substantially free of phospholipid” represents a state in which a natural rubber sample is extracted with chloroform and a peak due to phospholipid does not exist at −3 ppm to 1 ppm in ³¹ P-NMR measurement of the extract. The peak of phosphorus present at -3 ppm to 1 ppm is a peak derived from the phosphate structure of phosphorus in the phospholipid.

As a method for producing the modified natural rubber, for example, the production method described in JP 2010-138359 A, that is, the step (A) of obtaining a saponified natural rubber latex by saponifying the natural rubber latex, and the obtained Examples of the method include a step (B) of washing the saponified natural rubber latex until the phosphorus content in the rubber is 200 ppm or less. Specifically, first, a natural rubber latex is saponified with an alkali to prepare a saponified natural rubber latex, and then the agglomerated rubber obtained by agglomerating the saponified natural rubber latex contains phosphorus to the rubber content. A modified natural rubber (saponified natural rubber) can be produced by a method of repeatedly washing with water until the rate becomes 200 ppm or less and drying.

According to the above production method, the phosphorus compound separated by saponification is washed away, so that the phosphorus content of the natural rubber can be suppressed. Moreover, since the protein in natural rubber is decomposed by the saponification treatment, the nitrogen content of the natural rubber can be suppressed.

The content of the modified natural rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 20% by mass or more, and further preferably 40% by mass or more. If it is less than 5% by mass, the workability, fuel efficiency and wear resistance may not be improved in a well-balanced manner. The content of the modified natural rubber is preferably 95% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less. If it exceeds 95% by mass, sufficient processability, fuel efficiency and wear resistance may not be obtained.

Other rubber components include natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), butadiene isoprene rubber and other diene rubbers, chlorine Examples include butyl rubbers such as butyl rubber, and those obtained by condensing or modifying these rubbers can also be used. Especially, it is preferable to use BR as another rubber component from a viewpoint of the said performance balance. These rubber components may be used alone or in combination of two or more.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd. Commonly used in the tire industry such as BR containing syndiotactic polybutadiene crystals can be used.

When the rubber composition of the present invention contains BR, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more. . If it is less than 5% by mass, the wear resistance tends to decrease. The BR content is preferably 80% by mass or less, more preferably 60% by mass or less. When it exceeds 80 mass%, there exists a tendency for workability and low fuel consumption to fall.

In the present invention, from the viewpoint of the performance balance, the total content of the modified natural rubber and BR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 90% by mass or more, and further preferably 100% by mass. %.

It does not specifically limit as a white filler, A well-known thing can be used in the tire field | area, For example, a silica, a calcium carbonate, aluminum hydroxide etc. are mentioned. Among these, silica is preferable because the effects of the present invention can be sufficiently obtained.

Examples of the silica include, but are not limited to, dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and wet process silica is preferable because it has many silanol groups.

Nitrogen adsorption specific surface area of the silica _(N 2 SA) of preferably at least ^{40 m} 2 / g, more preferably at least ^{50m 2 / g, 100m 2 /} g or more, and particularly preferably equal to or greater than 150m ² / g. If it is less than 40 m < ² > / g, there exists a tendency for the fracture strength after vulcanization to fall. The _N 2 SA of the silica is preferably not more than 500 meters ² / g, more preferably at most 300m ² / g. When it exceeds 500 m ² / g, there is a tendency that low heat build-up and rubber processability are lowered.
The nitrogen adsorption specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

10 mass parts or more are preferable with respect to 100 mass parts of rubber components, as for content of a white filler, 20 mass parts or more are more preferable, and 30 mass parts or more are further more preferable. If it is less than 10 parts by mass, the low heat build-up may be insufficient. The content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and still more preferably 100 parts by mass or less. When it exceeds 200 parts by mass, it becomes difficult to disperse the filler into the rubber, and the processability of the rubber tends to deteriorate.

In the present invention, a reinforcing filler other than the white filler may be blended, but the content of the white filler in 100% by mass of the reinforcing filler is preferably 20% by mass or more, and 50 More preferably, it is more preferably 70% by mass or more. If it is less than 20% by mass, the low heat build-up tends to be insufficient.

The rubber composition of the present invention may contain a silane coupling agent.
The silane coupling agent is not particularly limited, and conventionally known silane coupling agents can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (3-tri Methoxysilylpropyl) sulfide type such as tetrasulfide; mercapto type such as 3-mercaptopropyltrimethoxysilane; vinyl type such as vinyltriethoxysilane; amino type such as 3-aminopropyltriethoxysilane; γ-glycidoxypropyl Examples thereof include glycidoxy type such as triethoxysilane; nitro type such as 3-nitropropyltrimethoxysilane; chloro type such as 3-chloropropyltrimethoxysilane.

The content of the silane coupling agent is preferably 0 to 20 parts by mass with respect to 100 parts by mass of the rubber component. If it exceeds 20 parts by mass, the effect of dispersing the filler cannot be obtained for an increase in cost, and further, the reinforcing property and wear resistance may be lowered, and unreacted silane coupling agent remains. As a result, there is a risk that the rubber will be burned during processing and the breaking performance of the rubber after vulcanization may be reduced. The lower limit is more preferably 1 part by mass or more, further preferably 3 parts by mass or more, and the upper limit is more preferably 15 parts by mass or less, and still more preferably 10 parts by mass or less.

The rubber composition of the present invention preferably contains carbon black as the other reinforcing filler. Thereby, the outstanding reinforcement property is obtained, abrasion resistance improves, and the said performance balance can be improved notably. Carbon black is not particularly limited, and examples thereof include SAF, ISAF, HAF, FF, and GPF.

Carbon black having an average particle size of 31 nm or less and / or a DBP oil absorption of 100 ml / 100 g or more is preferable. By blending such carbon black, necessary reinforcing properties are imparted to ensure wear resistance, and the effects of the present invention are remarkably obtained.

If the average particle size of the carbon black exceeds 31 nm, the wear resistance may be deteriorated. The average particle diameter is more preferably 25 nm or less, and further preferably 23 nm or less. The average particle size is preferably 15 nm or more, and more preferably 19 nm or more. If it is less than 15 nm, the viscosity of the blended rubber is significantly increased, and the processability may be deteriorated. In the present invention, the average particle diameter is a number average particle diameter and is measured by a transmission electron microscope.

When the DBP oil absorption amount (dibutyl phthalate oil absorption amount) of carbon black is less than 100 ml / 100 g, the reinforcing property is low, and it may be difficult to ensure wear resistance. The DBP oil absorption is more preferably 105 ml / 100 g or more, and even more preferably 110 ml / 100 g or more. The DBP oil absorption is preferably 160 ml / 100 g or less, and more preferably 150 ml / 100 g or less. If it exceeds 160 ml / 100 g, it is difficult to produce carbon black itself. The DBP oil absorption of carbon black is measured according to JIS K6217-4: 2001.

The content of carbon black is preferably 1 part by mass or more and more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1 part by mass, the reinforcing property is secured and the desired wear resistance may not be obtained. The content is preferably 50 parts by mass or less, more preferably 20 parts by mass or less, and still more preferably 10 parts by mass or less. If it exceeds 50 parts by mass, the fuel efficiency tends to deteriorate.

As the cyclized rubber, compounds having various chemical structures have been proposed, but the cyclized rubber in the present invention is not limited to any of them, and any compound can be used.
In the present invention, the cyclized rubber is not a rubber component, but an additive having an action of improving the compatibility of the white filler such as silica and the rubber component and improving the dispersibility of the white filler such as silica ( White filler dispersion improver).

The cyclization rate of the cyclized rubber is preferably 0.1% or more, more preferably 1% or more, and further preferably 3% or more. If it is less than 0.1%, sufficient interaction with the white filler cannot be obtained, and the fuel efficiency may be deteriorated. The cyclization rate is preferably 40% or less, more preferably 35% or less, and still more preferably 30% or less. If it exceeds 40%, the cyclized rubber may gel or adhere to the kneader.

The cyclization rate is the ratio of double bonds reacted by the cyclization reaction to the number of double bonds of the raw rubber component (conjugated diene polymer) before the cyclization reaction. For example, by measuring the peak areas of protons derived from double bonds before and after the cyclization reaction of the conjugated diene polymer used as a raw material by ¹ H-NMR analysis, the cyclization reaction when the pre-cyclization reaction is 100 The ratio of the double bond remaining in the subsequent cyclized product is obtained, and can be measured as a value (%) represented by the calculation formula = (100−the ratio of the double bond remaining in the cyclized product).

The number average molecular weight (Mn) of the cyclized rubber is preferably 1,000 to 1,000,000, more preferably 5,000 to 500,000, and 10,000 to 300,000. More preferably. If it is less than 1,000, the wear resistance and fuel efficiency may be deteriorated, and if it exceeds 1,000,000, the viscosity increases and the workability may be deteriorated.

The molecular weight distribution of the cyclized rubber, that is, the weight average molecular weight / number average molecular weight (Mw / Mn) is preferably 4 or less.
In addition, Mw / Mn is a standard polystyrene conversion value measured by GPC.

The glass transition temperature (Tg) of the cyclized rubber is not particularly limited and is usually −100 to 100 ° C., but preferably −90 to 80 ° C., more preferably −90 to 40 from the viewpoint of the effect of the present invention. ° C, more preferably -90 to 20 ° C, particularly preferably -90 to 5 ° C.

The gel amount of the cyclized rubber is preferably 10% by mass or less, more preferably 5% by mass or less from the viewpoint of the effect of the present invention, and a gel having substantially no gel is more preferable.

As the cyclized rubber, a conjugated diene polymer cyclized product can be preferably used. The conjugated diene polymer cyclized product is prepared by (co) polymerizing a conjugated diene monomer or a conjugated diene monomer and another monomer copolymerizable with the conjugated diene monomer by a known method. And the like obtained by cyclizing the conjugated diene polymer.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-methyl- Examples include 1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, and the like. These monomers may be used alone or in combination of two or more.

Examples of other monomers copolymerizable with the conjugated diene monomer include styrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, and p-tert. -Butylstyrene, α-methylstyrene, α-methyl-p-methylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, p-bromostyrene, 2-methyl-1,4-dichlorostyrene, Aromatic vinyl monomers such as 2,4-dibromostyrene and vinylnaphthalene; Chain olefin monomers such as ethylene, propylene and 1-butene; Cyclic olefin monomers such as cyclopentene and 2-norbornene; 1,5 -Hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadiene, 5-ethylidene-2-no Non-conjugated diene monomers such as rubornene; (meth) acrylic acid esters such as methyl (meth) acrylate and ethyl (meth) acrylate; (meth) acrylonitrile, (meth) acrylamide and the like. These monomers may be used alone or in combination of two or more.

The content of the conjugated diene monomer unit in the conjugated diene polymer may be appropriately selected within a range not impairing the effects of the present invention, but is preferably 40 mol% or more, more preferably 60 mol% or more, and even more preferably. Is 80 mol% or more.

As the cyclized rubber, the conjugated diene polymer cyclized product described above can be used. Among them, cyclized natural rubber, cyclized isoprene rubber, cyclized butadiene rubber and the like are particularly preferable from the viewpoint of the effect of the present invention.

As described above, the conjugated diene polymer cyclized product can be prepared by cyclizing the conjugated diene polymer, but this cyclization reaction can be carried out by a known method, for example, after the (co) polymerization reaction, one-pot reaction as it is. And a method of cyclization by adding a cyclization catalyst in (5), (co) polymerization, a method of re-creating a solution from a dried conjugated diene polymer, and the like.

Here, in the cyclization reaction, for example, a known cyclization catalyst is allowed to act directly on raw rubber or on a rubber solution, and a part of chain molecules in the rubber molecule is cyclized to reduce double bonds. Thereby obtaining a cyclized rubber. Examples of the cyclization catalyst include organic sulfonic acids such as sulfuric acid and p-toluenesulfonic acid, and chlorosulfonic acid.

The content of the cyclized rubber is preferably 0.1 parts by mass or more, more preferably 2 parts by mass or more, and further preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 40 mass parts or less, More preferably, it is 30 mass parts or less. If it is less than 0.1 part by mass, the effect of dispersing the white filler is not sufficient, and if it exceeds 40 parts by mass, the physical properties of the rubber may be lowered.

In addition to the above components, the rubber composition of the present invention includes oils, waxes, anti-aging agents, additives such as stearic acid and zinc oxide, vulcanizing agents such as sulfur, vulcanization accelerators, vulcanization acceleration aids, etc. May be appropriately blended.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading each of the above components with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing. The rubber composition can be used for each member of a tire, and the arrangement thereof is not limited.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, the rubber composition containing the above components is extruded in accordance with the shape of the tread, sidewall, etc. at the unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. Thus, an unvulcanized tire is formed. The pneumatic tire of the present invention can be manufactured by heating and pressurizing the unvulcanized tire in a vulcanizer. The pneumatic tire is suitable for passenger car tires, heavy duty tires, studless tires, and the like.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

(Production Example 1)
A pressure-resistant reactor equipped with a stirrer substituted with nitrogen was charged with 1400 g of dehydrated toluene and 18 mmol of n-butyllithium, and the internal temperature was maintained at 60 ° C. 487 g of isoprene was continuously added to the reactor over 15 minutes, and the internal temperature was controlled not to exceed 75 ° C. Thereafter, the mixture was reacted at 70 ° C. for 10.5 hours, and then 1.4 mmol of methanol was added as a polymerization terminator to terminate the polymerization reaction.
After stopping the polymerization reaction, the temperature was raised to 80 ° C., 4.24 g of p-toluenesulfonic acid was added, and the cyclization reaction was performed for 1 hour while maintaining the temperature at 80 ° C. Subsequently, an aqueous solution in which 1.70 g of sodium carbonate was dissolved in 5.1 g of water was added to stop the cyclization reaction, and the reaction solution was filtered to remove the catalyst residue. After adding 0.4 g of an anti-aging agent (Irganox 1010: manufactured by Ciba Specialty Chemicals) to this solution, toluene was distilled off and dried under reduced pressure to obtain a cyclized rubber 1.

(Production Example 2)
In a pressure vessel equipped with a stirrer substituted with nitrogen, 300 g of liquid polyisoprene (Kuraray LIR-30: Mn = 28,000) and 700 g of toluene were charged. The mixture was heated to 80 ° C. to completely dissolve polyisoprene, and then 2 g of p-toluenesulfonic acid was added to carry out a cyclization reaction while maintaining the internal temperature at 80 ° C. After reacting for 1 hour, a 25% aqueous solution of sodium carbonate containing 0.8 g of sodium carbonate was added to stop the reaction, stirred at 80 ° C. for 30 minutes, and then filtered to remove the catalyst residue. After adding 0.3 g of an anti-aging agent (Irganox 1010: manufactured by Ciba Specialty Chemicals) to this solution, toluene was distilled off and dried under reduced pressure to obtain a cyclized rubber 2.

(Production Example 3)
A cyclized rubber 3 was obtained in the same manner as in Production Example 2, except that liquid polybutadiene (manufactured by Sartomer, Rycon 150, Mn = 5,200) was used instead of liquid polyisoprene.

(Production Example 4)
Instead of liquid polyisoprene, polybutadiene (Ube Industries, UBEPOL 150L, Mn = 250,000) was used, and the cyclized rubber 4 was prepared in the same manner as in Production Example 2 except that the cyclization reaction time was changed to 3 hours. Obtained.

The physical properties of the obtained cyclized rubber were measured by the following methods, and the results are shown in Table 1.

(Cyclization rate of cyclized rubber)
The cyclization rate of the cyclized rubber was determined by the peak area ratio of protons in the polymer before and after the cyclization reaction by ¹ H-NMR measurement using an AV400 NMR apparatus manufactured by BRUKER, data analysis software TOP SPIN2.1. . In addition, the detailed cyclization rate calculation method is as having described in the following literature.
Y. Tanaka and H.M. Sato, J .; Polym. Sci: Poly. Chem. Ed. , 17, 3027 (1979)

(Number average molecular weight (Mn) and weight average molecular weight (Mw) of cyclized rubber)
The calibration curve obtained from the molecular weight distribution curve obtained by performing gel permeation (permeation) chromatography of cyclized rubber (GPC, manufactured by Tosoh Corporation) using polystyrene as a standard substance and tetrahydrofuran as a solvent at a temperature of 40 ° C. Mn and Mw were calculated.

(Glass transition temperature Tg of cyclized rubber)
The glass transition temperature of the cyclized rubber was measured using a differential scanning calorimeter (manufactured by Seiko Denshi Kogyo Co., Ltd .: SSC5200) under the conditions of a starting temperature of −100 ° C. and a heating rate of 10 ° C./min.

(Gel amount of cyclized rubber)
After 0.2 g of a sample cut to 2 mm square was immersed in 100 ml of toluene for 48 hours, the ratio of the dry weight of the gel remaining on the 80-mesh wire net was shown as a percentage.

Hereinafter, various chemicals used in Production Example 5 will be described together.
Natural rubber latex: Field latex surfactant obtained from Muhibah Lateks, Inc .: Emal-E27C (polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production Example 5 Production of Saponified Natural Rubber)
After adjusting solid content concentration (DRC) of natural rubber latex to 30% (w / v), 25 g of 10% Emal-E27C aqueous solution and 50 g of 40% NaOH aqueous solution are added to 1000 g of natural rubber latex (wet state), A saponification reaction was carried out at room temperature for 48 hours to obtain a saponified natural rubber latex. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 for aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 90 ° C. for 4 hours to obtain a solid rubber (HPNR).

The solid content (HPNR) and NR (RSS # 3) obtained in Production Example 5 were measured for nitrogen content, phosphorus content, and gel content by the methods described below. The results are shown in Table 2.

(Measurement of nitrogen content)
The nitrogen content was measured using CHN CORDER MT-5 (manufactured by Yanaco Analytical Co., Ltd.). For the measurement, first, a calibration curve for determining the nitrogen content was prepared using antipyrine as a standard substance. Next, about 10 mg of the sample was weighed, and an average value was obtained from the measurement results of three times to obtain the nitrogen content of the sample.

(Measurement of phosphorus content)
The phosphorus content of the sample was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation). In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and uses a measurement peak of P atom in an 80% aqueous phosphoric acid solution as a reference point (0 ppm), and raw rubber with chloroform. More extracted components were purified, dissolved in CDCl ₃ and measured.

(Measurement of gel content)
A raw rubber sample 70.00 mg cut to 1 mm × 1 mm was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, centrifugation was performed to precipitate a gel component insoluble in toluene, the soluble component of the supernatant was removed, and only the gel component was solidified with methanol, and then dried and the mass was measured. The gel content (mass%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

As shown in Table 2, the saponification natural rubber (HPNR) had a reduced nitrogen content, phosphorus content, and gel content as compared to RSS # 3. Further, in ³¹ P-NMR measurement, HPNR showed no peak due to phospholipid at -3 ppm to 1 ppm.

The chemicals used in the examples and comparative examples are summarized below.
NR: RSS # 3
HPNR: Modified natural rubber obtained in Production Example 5: UBEPOL BR150B manufactured by Ube Industries, Ltd.
Cyclized rubber 1-4: Production Examples 1-4
Silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Carbon black: Dia Black I manufactured by Mitsubishi Chemical Corporation (ISAF carbon, average particle size 23 nm, DBP oil absorption 114 ml / 100 g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Oil: Process X-140 (aromatic process oil) manufactured by Japan Energy Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Stearic acid: Stearic acid “paulownia” manufactured by NOF Corporation
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylene) manufactured by Ouchi Shinsei Chemical Diamine)
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
In accordance with the formulation of Table 3, using a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd., chemicals other than sulfur and a vulcanization accelerator were filled to a filling rate of 58%, and 140 rpm at 140 rpm. A kneaded product was obtained by kneading until reaching 0C. Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded to obtain an unvulcanized rubber composition.
Further, the obtained unvulcanized rubber composition was molded into a predetermined size, and a vulcanized rubber composition was obtained by press vulcanization at 150 ° C. for 20 minutes, and a vulcanization of about 2 mm × 130 mm × 130 mm was obtained. A rubber slab sheet was prepared.

The following evaluation was performed about the obtained unvulcanized rubber composition and vulcanized rubber slab sheet. The results are shown in Table 3.

(Processability)
Based on JIS K6300-1, Mooney viscosity (ML _{1 + 4} ) was measured at 130 ° C., and Comparative Example 1 was taken as 100, and the workability index was calculated from the following formula. The larger the index, the better the processability when unvulcanized.
(Processability index) = (Mooney viscosity of Comparative Example 1) / (Mooney viscosity of each formulation) × 100

(Viscoelasticity test)
Using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho, the loss tangent (tan δ) of the vulcanized rubber slab sheet was measured under conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. The rolling resistance index of Comparative Example 1 was set to 100, and the index was displayed by the following formula. The larger the rolling resistance index, the lower the rolling resistance, which is preferable.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Abrasion resistance)
Using a Lambourne abrasion tester manufactured by Iwamoto Seisakusho, the amount of wear was measured at a surface rotation speed of 50 m / min, an additional load of 3.0 kg, a sandfall of 15 g / min and a slip rate of 20%. The inverse of was taken. And the reciprocal number of the wear amount of the comparative example 1 was set to 100, and the reciprocal number of the wear amount of the other composition was expressed as an index. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.

Compared with the comparative example which does not use HPNR and cyclized rubber, in Examples 1-4 which added cyclized rubber to the silica compounded rubber which used HPNR as a rubber component, workability, low fuel consumption, and wear resistance are improved. It was clarified that the performance balance can be improved synergistically at the same time. Further, even in Examples 5 to 6 in which the addition amount of the cyclized rubber was increased, the fuel economy and wear resistance could be remarkably improved while maintaining the workability indexes “99” and “98” which are practically no problem. It was.

Claims (6)

Seen containing a rubber component phosphorus content comprises the following modified natural rubber 200 ppm, and the white filler, a cyclized rubber,
A tire rubber composition in which a cyclization rate of the cyclized rubber is 0.1 to 40% . The tire rubber composition according to claim 1, comprising 10 to 200 parts by mass of the white filler and 0.1 to 40 parts by mass of the cyclized rubber with respect to 100 parts by mass of the rubber component. The tire rubber composition according to claim 1 or 2, wherein the cyclized rubber is at least one selected from the group consisting of cyclized natural rubber, cyclized isoprene rubber, and cyclized butadiene rubber. The tire rubber composition according to any one of claims 1 to 3 , wherein the white filler is silica. The tire rubber composition according to any one of claims 1 to 4 , wherein the nitrogen content of the modified natural rubber is 0.3 mass% or less. The pneumatic tire produced using the rubber composition in any one of Claims 1-5 .