JP2014234469A - Rubber composition and tire prepared using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition which provides a tire having improved reduced rolling resistance and wear resistance at high levels by combining a specific rubber component with a specific carbon black, and a tire prepared using the same.SOLUTION: According to a rubber composition of the present invention, a natural rubber to be used is one obtained by hydrolysis of phospholipid, for example, hydrolysis by enzyme treatment of lipase and/or phospholipase, and obtained by blending oxidized carbon black with the rubber composition. There is also provided a tire prepared using the rubber composition.

Description

  The present invention relates to a rubber composition and a tire using the same, and more specifically, a rubber composition having improved low heat buildup and wear resistance by blending a hydrolyzed natural rubber and oxidized carbon black. And a tire using the same.

  In recent years, there has been an increasing demand for lower fuel consumption of automobiles in response to the global movement of regulations on carbon dioxide emissions due to increasing interest in environmental issues, and there is a need to meet the above requirements. . For this reason, a rubber composition and a tire in which a specific rubber component and a specific carbon black are combined, and those that further improve the low heat build-up due to reduction in wear resistance and rolling resistance are desired.

  The rubber composition usually contains carbon black for rubber. Carbon black improves the performance of the compounded rubber composition by its physicochemical characteristics, that is, the unit particle diameter, the surface area per unit mass (specific surface area), the degree of particle connection (structure), and the surface properties. It has a big impact. For this reason, carbon black having different characteristics is selectively used depending on required rubber performance, environment in which it is used, and the like. In particular, rubber compositions used for tires are excellent in wear resistance (wear resistance) due to contact with the road by rotating at a high speed, and at the same time, repeated deformation of the rubber composition caused by contact with the road surface. It is an important factor to reduce the hysteresis loss characteristic due to (low heat generation property). However, wear resistance and low heat build-up are mutually contradictory characteristics. In order to solve this problem, carbon black having various characteristics has been proposed.

Natural rubber is also frequently used in many fields such as industrial equipment such as tires, rubber belts, rubber rolls, priders, and fenders, and sporting goods such as tennis balls, basketball, soccer balls, and volleyball. It is also frequently used in the bio field. Further, in tires, it is used as a material for all components constituting rubber tires such as treads, sidewalls, ply coating rubbers, and bead fillers.
In recent years, natural rubber latex has been chemically or enzymatically treated to decompose or remove components other than rubber components contained in natural rubber, thereby improving the properties of natural rubber (reducing exothermic properties of natural rubber, etc.). Has been proposed.

  For example, it has been proposed to chemically reduce the total nitrogen amount in natural rubber (see Patent Document 1) and to repeat saponification and washing in order to reduce the amount of phosphorus in natural rubber (Patent Document 2). Patent Document 3 and Patent Document 4).

  To further improve wear resistance and low heat build-up in recent years, further improve wear resistance and low heat build-up by combining natural rubber and reinforcing filler, especially specific carbon black, whose characteristics are not reduced. There is a need for rubber compositions and tires that can be used.

JP-A-6-329838 JP 2010-174169 A JP 2010-138360 A JP 2010-138359 A

  The present invention provides a rubber composition that gives a tire having a high level of reduction in rolling resistance and wear resistance by combining a specific rubber component and a specific carbon black, and a tire using the rubber composition. For the purpose.

The present invention uses natural rubber as a rubber component, further hydrolyzes the phospholipid bonded to the end of the natural rubber molecule, and is reactive with the hydroxyl group generated at the end of the hydrolyzed portion of the phospholipid. By giving affinity and binding properties to oxidized carbon black, and without damaging the quality of natural rubber such as aging resistance, the natural rubber is made reactive and used together with oxidized carbon black. The goal has been achieved.
That is, the rubber composition of the present invention is characterized by blending oxidized carbon black with natural rubber obtained by hydrolyzing phospholipids of natural rubber molecules.

Natural rubber obtained by hydrolyzing phospholipid is expected to have affinity with oxidized carbon black, and binding properties such as acid-base reaction and hydrogen bonding. From the viewpoint of not impairing the original properties of natural rubber, an enzyme-treated phospholipid is preferable because it exhibits affinity and binding properties with oxidized carbon black and does not impair the properties of natural rubber.
In the natural rubber phospholipid hydrolysis treatment, phospholipid ester bonds in the natural rubber raw latex are released to separate fatty acids such as oleic acid and palmitic acid. The ester decomposition treatment of the phospholipid in the latex can be a chemical treatment, but an enzyme treatment of lipase and / or phospholipase is preferable.

In the hydrolysis of phospholipids in natural rubber, it is preferable that phospholipids in natural rubber are degraded by 50% or more, more preferably 70% or more, and even more preferably 85% or more. This is because the hydrous silicic acid having a specific structure exhibits sufficient affinity and binding to natural rubber. The undegraded phospholipid of the natural rubber is preferably 0.66 wt% or less, more preferably 0.4 wt% or less, and further preferably 0.3 wt% or less.
In the hydrolysis treatment of natural rubber, it is preferable to use a natural rubber latex that is adjusted to pH 7 or more within 1 hour after collection.
The degradation amount (%) of phospholipid is determined by setting an index of reactivity (indicating an increase in fatty acid in a latex solution of fatty acid generated by ester decomposition from phospholipid as an index).
In addition, the enzyme treatment is preferably performed at an optimum pH and an optimum temperature. In the present invention, the pH is preferably 5 or more and 11 or less, and is preferably 70 ° C. or less. If necessary, it is preferable to treat with a surfactant in addition to the enzyme treatment.

The oxidized carbon black used in the present invention can be oxidized using conventional techniques such as oxidation with ozone, dichromate, or oxidizing acid. In the present invention, carbon black treated with an oxidizing agent of nitrogen is particularly preferable.
Oxidized carbon black has hydroxyl groups such as OH, CHO, and CO, aldehyde groups, and ketone groups (quinone groups) on carbon black. Nitrogen oxidizing agents include acids such as nitric acid and nitrous acid, and nitrogen oxides such as nitrogen dioxide, dinitrogen tetroxide and nitrogen pentoxide.

In such a rubber composition of the present invention, it is preferable to contain 10% by mass or more of natural rubber with respect to the total amount of the rubber component, and 10 to 10 parts by mass of oxidized carbon black with respect to 100 parts by mass of the rubber component. It is preferable to contain in the ratio of 250 mass parts.
Furthermore, this invention also provides the tire which uses a rubber composition.

  According to the rubber composition according to the present invention, the ester bond in the phospholipid of natural rubber is hydrolyzed to generate a hydroxyl group at the end, and in particular, it is selectively hydrolyzed by enzymatic treatment, so that the natural rubber has The stable characteristics are not impaired, and the generation of this hydroxyl group improves the affinity with oxidized carbon black, and results in binding properties such as acid-base reaction and hydrogen bonding. As a result, the rubber composition of the present invention The tire obtained by using is excellent in oxidation aging resistance and abrasion resistance, and rolling resistance is improved.

It is the figure which showed the decomposition reaction of the phospholipid in the natural rubber latex decomposed | disassembled by a phospholipase process. It is a graph of the reactivity parameter | index which shows the increase amount of the fatty acid in the latex produced by enzymatic decomposition with respect to the enzyme amount shown in FIG. FIG. 2 is a chart of FT-IR showing a decrease in ester bond and an increase in fatty acid in latex caused by the enzymatic degradation of FIG. 1.

  The rubber composition of the present invention contains natural rubber obtained by hydrolyzing phospholipids of natural rubber molecules and oxidized carbon black.

<Natural rubber>
The natural rubber used in the present invention is obtained by hydrolyzing a phospholipid bonded to the natural rubber, and the hydrolysis is for treating a latex of the natural rubber.
As shown in FIG. 1, the natural rubber molecule contains phospholipid. Phospholipids produce free fatty acids such as oleic acid and palmitic acid by ester decomposition.
As shown in FIG. 2, in the hydrolysis, the amount of fatty acid generated by the decomposition is set as an index of phospholipid decomposition reactivity.
As shown in FIG. 3, the amount of fatty acid in the latex solution generated by enzyme degradation is determined by measuring the peak amount of [—COOH] in the vicinity of 1710 [cm ⁻¹ ] using an FT-IR measuring device (manufactured by Varian). .

The index of reactivity is set by measuring the amount of initial fatty acid in the raw latex solution used in advance, and setting this value as the phospholipid decomposition rate of 0%. The latex solution contains 100 mass of latex as the solid content of natural rubber. Phospholipase is added at a ratio of 0.1, 0.2, 0.5, 1.0, and 5.0 parts by mass, respectively. As shown in FIG. 3, the amount of change in the fatty acid peak in the latex solution after the reaction was measured, and as shown in FIG. 2, the maximum amount of fatty acid was determined from the change in the amount of fatty acid in the reference curve. The decomposition rate of phospholipid is 100%. In the estimation of the maximum value, a value at an infinite enzyme addition amount is estimated based on the reference curve characteristic.
Therefore, the degradation rate (%) of phospholipid in the natural rubber as a raw material = {(measured fatty acid amount) − (initial fatty acid amount)} / {(maximum fatty acid amount set as an index) − (initial fatty acid amount)} × 100. The amount of undegraded phospholipid (based on the amount of fatty acid) (wt%) in the raw latex (100 g) is (maximum fatty acid amount g) − (initial fatty acid amount g), and after the predetermined reaction treatment The amount (wt%) of undegraded phospholipid in the latex is (maximum fatty acid amount g) − (measured fatty acid amount g).
Here, 2000 LEN / g (Novozyme standard unit) phospholipase (manufactured by Novozyme) was used as the enzyme used in the index setting. The reaction conditions were such that a latex solution having a latex solid content concentration of 20 wt% was used, the pH was set to 8, and the reaction was performed at room temperature (25 ° C.) for 16 hours.

The natural rubber latex used as a raw material means a field latex obtained from a natural rubber tree, and either a commercially available ammonia-treated latex or a fresh field latex can be used as the latex.
In the present invention, the latex is preferably adjusted to pH 7 or more within 1 hour after collection. When such a latex is used, it is easy to uniformly disperse the added enzyme in the latex solution.

Examples of the enzyme that degrades phospholipids of natural rubber include lipase and / or phospholipase used as a measurement index as described above.
The lipase and phospholipase are not particularly limited, and any of those derived from bacteria, those derived from filamentous fungi, and those derived from yeast may be used. Moreover, lipase and phospholipase are international unit 100 (U / g) or more, preferably 1000 (U / g) or more, more preferably 10,000 (U / g) or more, and further preferably 100,000 (U / g) or more. That is good. Examples of such lipases and phospholipases include commercially available NS44151 (a product manufactured by Novozyme), lipase M “Amano” 10 (a product manufactured by Amano Enzyme Co., Ltd.), lipase OF (a product manufactured by Meika Inc.), phospholipase A1. (Product of Sankyo Co., Ltd.).
In addition, in the use of the above-described indicator enzyme, it is preferable to use an enzyme having a purity of 2000 LEN / g (Novozyme standard unit) or higher phospholipase (manufactured by Novozyme) or higher.
The amount of lipase and / or phospholipase added during such enzyme treatment is in the range of 0.01 to 10 parts by weight, particularly 0.1 to 5 parts by weight, based on 100 parts by weight of the solid component in the natural rubber latex. It is preferable. When the addition amount is in the above range, a decomposition rate of 50% or more of the phospholipid in the natural rubber can be achieved.

The natural rubber used in the present invention may be further subjected to an enzyme treatment with a protease in addition to lipase and / or phospholipase.
Like the lipase and phospholipase, the protease is not particularly limited, and may be any of bacteria, filamentous fungi, or yeast. Further, the titer of the protease is preferably 100 (U / g) or more, preferably 1000 (U / g) or more, more preferably 10,000 (U / g) or more, and further preferably 100,000 (U / g). That is good. Examples of such proteases include commercially available Alcalase 2.5L-type DX (manufactured by Novozymes), pro leather FG-F (manufactured by Amano Enzymes) and the like.
In the present invention, in addition to the above-mentioned enzymes, peptidase, cellulase, pectinase, esterase, amylase and the like can be used in combination.

In addition, when such an enzyme is added, other additives such as phosphates such as potassium phosphate, potassium phosphate and sodium phosphate, and acetates such as potassium acetate and sodium acetate as pH adjusters. Furthermore, acids such as sulfuric acid, acetic acid, hydrochloric acid, nitric acid, citric acid and succinic acid or salts thereof, or ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like can be used.
In the present invention, the enzyme treatment is preferably performed at an optimum pH, but considering the dispersibility in latex, pH 5 to 11 is preferable, and pH 7 to 10 is particularly preferable.

In the present invention, the enzyme treatment is performed at a temperature of 70 ° C. or less, preferably at a temperature of 60 ° C. or less, more preferably at 50 ° C. or less.
When the enzyme treatment temperature exceeds 70 ° C., the stability of the natural rubber latex decreases, and the latex coagulates during the enzyme treatment. After coagulation, the degradation effect by the enzyme decreases. For this reason, it becomes difficult to produce natural rubber having excellent processability.
When the enzyme treatment temperature exceeds 70 ° C., the stability of the natural rubber latex decreases, and the latex coagulates during the enzyme treatment. After coagulation, the degradation effect by the enzyme decreases. For this reason, it becomes difficult to produce natural rubber having excellent processability.

  In the present invention, the enzyme treatment time is 12 hours or longer, more preferably 16 hours or longer and 48 hours or shorter. With such a reaction time, the phospholipid in the latex is sufficiently decomposed. Phospholipid degradation is 50% or more, more preferably 70% or more, and still more preferably 80% or more. For this reason, if it is the said preferable processing time, reaction can fully be achieved.

The natural rubber used in the present invention is preferably treated together with the enzyme treatment and a surfactant. As the surfactant, nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants and the like can be used. In particular, nonionic surfactants and anionic surfactants can be used. It is preferable to use an agent or the like.
As the nonionic surfactant, for example, polyoxyalkylene ether, polyoxyalkylene ester, polyhydric alcohol fatty acid ester, sugar fatty acid ester, and alkyl polyglycoside are suitable.
As the anionic surfactant, for example, carboxylic acid type, sulfonic acid type, sulfuric acid ester type, and phosphoric acid ester type are suitable.
Examples of the carboxylic acid surfactant include fatty acid salts, polyvalent carboxylates, rosinates, dimer salts, polymer acid salts, tall oil fatty acid salts, and the like. Examples of the sulfonic acid surfactant include alkylbenzene sulfonate, alkyl sulfonate, alkyl naphthalene sulfonate, naphthalene sulfonate, and diphenyl ether sulfonate. Examples of sulfate surfactants include alkyl sulfates, polyoxyalkylene alkyl sulfates, polyoxyalkylene alkyl phenyl ether sulfates, tristyrenated phenol sulfates, polyoxyalkylene distyrenated phenol sulfates. Etc. Examples of phosphate ester surfactants include alkyl phosphate ester salts and polyoxyalkylene phosphate ester salts.

  The natural rubber latex treated with the enzyme as described above coagulates without completely separating non-rubber components. When the non-rubber component is separated, the aging resistance is poor. The rubber component obtained by coagulating the treated latex is washed and then dried using a normal dryer such as a vacuum dryer, air dryer, drum dryer or the like, whereby the natural rubber used in the present invention can be obtained. .

<Oxidized carbon black>
The oxidized carbon black used in the present invention can be oxidized using conventional techniques such as oxidation with ozone, dichromate, or oxidizing acid.
Oxidized carbon black has hydroxyl groups such as OH, CHO, and CO, aldehyde groups, and ketone groups (quinone groups) on carbon black. The amount of these functional groups is preferably in the range of 0.5 to 7 wt%, particularly preferably in the range of 1.2 to 5 wt% per 100 g of carbon black. If the functional group amount of the oxidized carbon black is within the above range, the affinity and binding property with the rubber component can be sufficiently provided.
In the present invention, carbon black treated with an oxidizing agent of nitrogen is particularly preferable. Nitrogen oxidizing agents include acids such as nitric acid and nitrous acid, and nitrogen oxides such as nitrogen dioxide, dinitrogen tetroxide and nitrogen pentoxide.
These manufacturing methods are disclosed in US Pat. Nos. 3,914,148; 4,075,140; and 4,075,157. For example, carbon black is dispersed in nitric acid solution having a concentration of 0.05 to 1% by mass in a ratio of 2: 1 to 1: 2, pelletized by a pellet mill at a temperature of about 100 ° C., and dried at a temperature of about 200 to 300 ° C. It is shown that it is manufactured.

Examples of the carbon black used for the oxidized carbon black include any carbon black that is generally available and is commercially produced.
In particular, carbon black has a dibutyl phthalate absorption (DBP) of 95 to 220 mL / 100 g, a compressed DBP absorption (24M4DBP) of 90 to 200 mL / 100 g, and a cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of 70 to 200 m2 / g. Are preferred.
The dibutyl phthalate absorption amount (DBP) and the compressed DBP absorption amount (24M4DBP) are measured by the method described in ASTM D2414-88 (JIS K6217-4: 2001) and are absorbed per 100 g of carbon black. DBP) in mL. The cetyltrimethylammonium bromide adsorption specific surface area (CTAB) is measured by the method described in JIS K6217-3: 2001, and is expressed as a specific surface area m ² / g per unit mass of carbon black.

  For example, useful carbon blacks include furnace black, channel black, and lamp black. More specifically, examples of carbon black include super abrasion furnace (SAF) black, high abrasion furnace (HAF) black, high speed extrusion furnace (FEF) black, fine particle furnace (FF) black, quasi super Abrasion resistant furnace (ISAF) black, semi-reinforcing furnace (SRF) black, intermediate workability channel black, hard workability channel black and conductive channel black. Other carbon blacks that can be used include acetylene black. Typical carbon blacks used are N110, N121, N220, N231, N242, N293, N299, N326, N330, N332, N339, N343, N347, N351, N358, N375, N472, N539, N472, N539 , N550, N660, N683, N754, and N765.

<Rubber composition>
The rubber composition of the present invention preferably contains 10% by mass or more, particularly 30% by mass or more of the above natural rubber with respect to the total amount of the rubber component. By including the natural rubber, the effect of oxidized carbon black is sufficiently enhanced.
As the rubber component, polybutadiene rubber, styrene-butadiene copolymer rubber, synthetic isoprene rubber, ethylene-propylene-diene rubber, chloroprene rubber, and the like can be included in addition to the natural rubber.

Moreover, it is preferable to contain oxidized carbon black in the ratio of 10-250 mass parts with respect to 100 mass parts of rubber components.
In such a range, the rubber composition containing oxidized carbon black has desired physical properties such as wear resistance and low rolling resistance. Furthermore, the content of oxidized carbon black is preferably 20 to 150 parts by mass, and more preferably 30 to 120 parts by mass with respect to 100 parts by mass of the rubber component.
In addition to the rubber component and oxidized carbon black, the rubber composition of the present invention includes other components such as carbon black other than oxidized carbon black, inorganic fillers, vulcanizing agents, vulcanization accelerators, zinc oxide, stearic acid, A compounding agent usually used in the rubber industry such as an anti-aging agent can be appropriately selected and blended within a range not impairing the object of the present invention. As these compounding agents, commercially available products can be suitably used. The rubber composition is prepared by blending a rubber component, oxidized carbon black, and various appropriately selected compounding agents, kneading using a Banbury mixer, roll, internal mixer, intensive mixer, etc. It can be prepared by extrusion or the like.

<Tire>
The tire of the present invention is characterized in that the rubber composition is applied to any of tire members. Here, in the tire of the present invention, it is particularly preferable to use the rubber composition of the present invention for a tread. The tire using the rubber composition for a tread has excellent wear resistance and low rolling resistance and low fuel consumption. Excellent in properties. In addition, as gas with which the tire of the present invention is filled, normal or air with a changed oxygen partial pressure, or an inert gas such as nitrogen is exemplified. When the rubber composition of the present invention is used for a tread, for example, it is extruded on a tread member, and is pasted and molded by a usual method on a tire molding machine to form a raw tire. The green tire is heated and pressed in a vulcanizer to obtain a tire.

The present invention will be described below based on examples, but the configuration of the present invention is not limited to the following examples.
<Production example of hydrolyzed natural rubber>
(Production example a)
(1) Enzymatic treatment process of natural rubber latex Water added to natural rubber latex (within 1 hour after collection) treated with clone species GT-1 and NH ₃ 0.4 wt% to a solid content concentration of 15 wt% To the prepared latex solution 1000 g, phospholipase (2000 LEN / g Novozyme) was added to each 100 parts by mass of latex solids in a proportion of 5.0 parts by mass, stirred, and dispersed. It was allowed to stand for 16 hours. The latex solution was adjusted to pH 8 and reacted at room temperature (25 ° C.).
(2) Coagulation / Drying Step Next, formic acid was added to the obtained latex to adjust the pH to 4.7 and coagulate. This solid was crushed 5 times with a scraper through a shredder, and then dried with a hot air dryer at 110 ° C. for 210 minutes to obtain natural rubber.
The degradation rate of phospholipids was 87%, and the amount of undegraded phospholipids of natural rubber was 0.12%.

[Carbon blacks A to C used]
(Carbon black A)
Carbon black A (control) used ASTM code N330.
(Carbon black B)
Carbon black A is oxidized in an ozone atmosphere at room temperature for 2 hours.
(Carbon black C)
Carbon black A is oxidized in an ozone atmosphere at room temperature for 3 hours.

The performance of each carbon black is shown in Table 1 below.
In addition, the measurement of the amount of functional groups (> C = O, -OH) is based on the following method.
[> Method for measuring C = O functional group concentration]
1) Preparation of oximed carbon black
Two Erlenmeyer flasks containing about 1.5 g of carbon black are prepared. One flask is prepared by dissolving 1 g of hydroxylamine hydrochloride in 20 ml of pyridine, and 20 ml of pyridine is added to the other flask. A condenser tube with a sphere is attached to the top of the Erlenmeyer flask, and a calcium chloride tube and a deoxygenator are connected to the condenser tube. The entire apparatus is replaced while flowing nitrogen gas to create a nitrogen atmosphere.
The flask is placed in an oil bath maintained at 100 ° C. and reacted at this temperature for 16 hours. After completion of the reaction, 50 ml of 3N hydrochloric acid is added while cooling the reaction product to neutralize excess hydroxylamine. The contents are suction filtered to separate the oximed carbon black and washed with about 300 ml of distilled water. This is No. Transfer onto 5B filter paper and wash with 300 ml distilled water.
The washed oximed carbon black is placed in a drier kept at 105 ° C. and dried to a constant weight to prepare oximed carbon black (the same operation is performed with a blank).
2) Determination of nitrogen content <Preparation of sample for determination>
About 0.2 g of oximed carbon black and control carbon black are weighed accurately and placed in a semi-micro Kjeldahl decomposition bottle. Add 2.5 g of calcium sulfate and 0.02 g of mercuric oxide to each, and finally add 4 ml of concentrated sulfuric acid.
A decomposition bottle is attached to a semi-micro Kjeldahl decomposition device, and tap water is poured into an exhaust gas suction aspirator and heated. The strength of the flame is initially weakened so that the contents of the decomposition bottle do not boil. When the generation of white smoke in the decomposition bottle decreases, the intensity is gradually increased, and the fire is increased to the point of boiling. Ignition is continued for an additional hour after the contents of the decomposition bottle are completely clear. Turn off the fire, let it cool to room temperature, remove the bottle from the cracker, and add about 10 ml of distilled water in small portions. The contents are then placed in a sample flask of a semi-micro Kjeldahl nitrogen distillation apparatus.
<Quantification of nitrogen content>
A sample flask is attached to a distillation apparatus, and a beaker containing 5 ml of 2% boric acid solution is connected to the outlet of a condenser tube with a bulb of the distillation apparatus. 25 ml of a sodium hydroxide / sodium thiosulfate (50% / 5%) solution is injected from the alkali inlet of the distillation apparatus, and the inlet and the steam port are closed, and distillation is performed for 9 minutes.
A 2% boric acid solution in which ammonia is dissolved is titrated with 1/100 N hydrochloric acid. Using an ammonium sulfate solution with a known amount of nitrogen, the above procedure was performed to create a calibration curve, and the milliequivalent of nitrogen was determined from the titration amount of the sample and the calibration curve. The milliequivalent of> C = O functional group per gram of carbon black (Meq / g) is calculated by the following equation.

[Measurement method of -OH functional group concentration]
1) Preparation of acetylated carbon black 20 ml of pyridine and 10 ml of acetic anhydride are placed in an Erlenmeyer flask containing about 2 g of carbon black, and a calcium chloride tube is connected to the upper part of a condenser tube with a bulb, and a deoxygenator is connected to this tube. . The apparatus is replaced with flowing nitrogen gas to create a nitrogen atmosphere.
The flask is placed in an oil bath maintained at 120 ° C. and reacted at this temperature for 15 hours. After completion of the reaction, while cooling the reaction product, 100 ml of distilled water is added to decompose excess acetic anhydride, and then acetylated carbon black is separated by suction filtration and washed with about 300 ml of distilled water.
The washed acetylated carbon black is placed in a drier maintained at 105 ° C. and dried to a constant weight to prepare acetylated carbon black.
2) Determination of acetic acid
About 1 g of acetylated carbon black is precisely weighed and placed in a beaker, and a solution obtained by adding 2 g of barium hydroxide to 20 ml of warm distilled water is added thereto. The vessel is placed in a 100 ° C. water bath and hydrolyzed for 5 hours. The contents are allowed to cool and filtered with suction using a membrane filter. The beaker and filter are washed with a small amount of distilled water, and the combined filtrate and washing solution are allowed to flow down to a column of cation exchange resin Amberlite IR120 (manufactured by Organo Corporation) activated with hydrochloric acid to release acetic acid. Wash the column without acetic acidity.
This effluent is titrated with 1/500 N sodium hydroxide solution using a mixed indicator of methyl red and bromocresol green.
Prior to this titration, a calibration curve is prepared in advance using a 1/500 standard acetic acid standard solution, and the amount of acetic acid is determined from the titration value using this calibration curve.
The milliequivalent (meq / g) of —OH functional group per gram of carbon black is calculated by the following formula.

(Examples 1-4 and Comparative Examples 1-6)
In Examples 1 to 4, the phospholipid enzyme-decomposed natural rubber production example a having 1.0 parts by mass of the enzyme added was used, and the carbon blacks A, B and C in Table 1 were used to make a Banbury mixer. Thus, 10 rubber compositions were prepared according to the formulation of the rubber composition shown in Table 2 below. In Comparative Examples 1 to 6, natural rubber (usually the amount of enzyme added in Production Example a is 0, the degradation rate of phospholipid is 0%, the amount of undegraded phospholipid of natural rubber is 0.91 wt%) is used. The rubber composition was adjusted.

Next, 10 types of tires for trucks of tire size 11R22.5 using these 10 types of rubber compositions as treads were produced, and rolling resistance and wear resistance were evaluated. These results are shown in Table 3.
The tire wear resistance and rolling resistance were evaluated according to the following methods.
(1) Wear resistance evaluation method The test tire is mounted on a vehicle, the remaining amount of the groove is measured when the vehicle runs 40,000 km, and the index is displayed with the reciprocal of the remaining amount of the tire of Comparative Example 1 being 100. did. The larger this value, the better the wear resistance.
Wear resistance index = (remaining groove of the test tire) × 100) / (remaining groove of the tire of Comparative Example 1)
(2) Evaluation method of rolling resistance The running resistance when the drum was rotated freely on the drum was measured. Based on the rolling resistance value thus obtained, a rolling resistance index was determined according to the following formula. The higher the value, the better the rolling resistance.
Rolling resistance index = (Rolling resistance value of test tire × 100) / (Rolling resistance value of tire of Comparative Example 1)

  As is clear from the results of Table 3 above, Examples 1 to 4 that are within the scope of the present invention have characteristics such as wear resistance and reduced rolling resistance, as compared with Comparative Examples 1 to 6 that are outside the scope of the present invention. It was found to be excellent.

  The rubber composition and tire according to the present invention have a combination of a natural rubber that exhibits reactivity and improved oxidative aging characteristics and a reactive oxidized carbon black, such as reduced wear resistance and rolling resistance. It has excellent characteristics and has high industrial applicability.

Claims (7)

  A rubber composition comprising a natural rubber obtained by hydrolyzing a phospholipid of a natural rubber molecule and oxidized carbon black.   The rubber composition according to claim 1, wherein the oxidized carbon black is contained in a range of 15 to 250 parts by mass with respect to 100 parts by mass of the rubber component.   The rubber composition according to claim 1 or 2, wherein 50% or more of the phospholipid in the natural rubber is decomposed. The rubber composition according to any one of claims 1 to 3, wherein the amount of undegraded phospholipid in the natural rubber is 0.66% by weight or less.
(The amount of undegraded phospholipid is the weight percentage of the amount of fatty acid produced by treating natural rubber to be measured with an excess enzyme and decomposing it)   The rubber composition according to any one of claims 1 to 4, wherein the hydrolysis of the phospholipid is an enzyme treatment.   The rubber composition according to any one of claims 1 to 5, comprising 10% by mass or more of natural rubber based on the total amount of the rubber component.   A tire using the rubber composition according to any one of claims 1 to 6.

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