JP4679312B2 - Natural rubber, rubber composition and pneumatic tire - Google Patents

Description

  The present invention relates to natural rubber, a rubber composition, and a pneumatic tire. More specifically, the present invention relates to a natural rubber, a process for producing the same, a rubber composition thereof, and a pneumatic tire in which processability, which is a drawback thereof, is greatly improved without impairing the physical properties inherent to natural rubber.

In general, natural rubber is known as a rubber excellent in mechanical properties, low heat build-up, and abrasion resistance, but its processability is inferior to that of synthetic rubber. This is because the entanglement of polymer molecules increases through the polypeptide bond contained in the protein present in the non-rubber component of the natural rubber latex that is the raw material, the apparent molecular weight becomes very large, and the Mooney viscosity of the rubber increases. It is to bring about.
In order to improve the processability of such a natural rubber, a natural rubber that has been highly deproteinized so that the total nitrogen content is 0.1% by weight or less is described (for example, see Patent Document 1). Recently, many proposals for deproteinization technology of natural rubber have been made for special uses such as natural rubber products for medical use, and natural rubber from which non-rubber components such as protein are highly removed is known (for example, (See Patent Documents 2 to 4).

However, as in the past, when the protein is almost completely removed, the processability is improved, but the non-rubber component having an anti-aging action and a vulcanization accelerating action is almost completely removed. In the rubber composition using natural rubber, there is a problem that the elastic modulus of the rubber is lowered, the anti-aging property is inferior, and the low exothermic property is adversely affected.
Furthermore, when removing protein from the latex by centrifugation, non-rubber components other than protein are lost, which causes a problem that the physical properties of rubber are greatly reduced.
On the other hand, conventionally, as a method for improving the wear resistance of a tread rubber of a pneumatic tire, in general, by using a carbon black having a small particle diameter and a large structure, mutual interaction between the carbon black and the polymer is achieved. A technique for enhancing the action and improving the rubber reinforcement and a technique for increasing the compounding amount of carbon black are known.
However, the rubber composition of normal natural rubber containing carbon black having a fine particle size (nitrogen adsorption specific surface area (N ₂ SA) of 80 m ² / g or more) is poorly dispersed in carbon black, and therefore has a high viscosity and is processed. The physical properties such as wear resistance and low loss (low heat build-up) cannot be sufficiently obtained due to the deterioration of dispersibility.

Further, a rubber composition of a normal natural rubber containing carbon black having a low structure (DBP oil absorption is 100 ml / 100 g or less) has poor dispersion of carbon black, so that the viscosity is high and the processability is poor. With deterioration, physical properties such as wear resistance and low loss (low heat generation) cannot be obtained sufficiently.
Furthermore, silica compounding generally has poor processability, and compounding using natural rubber has a problem in that sufficient physical properties cannot be obtained due to poor processability such as silica dispersion and compound shrinkage. There is.
In any case, in a rubber composition in which fillers such as carbon black and silica are blended with conventional natural rubber, the dispersion of these fillers into the natural rubber is poor, so good wear resistance and low loss It was difficult to obtain physical properties such as (low heat generation).

JP-A-6-329838 JP-A-8-143606 Japanese Patent Laid-Open No. 11-71408 JP 2000-19001 A

  Under such circumstances, an object of the present invention is to provide a natural rubber with improved processability and a method for producing the same without deteriorating the physical properties of the natural rubber. Another object of the present invention is to provide a rubber composition using the natural rubber, particularly a tire case member, a tire tread member, and a pneumatic tire.

As a result of diligent research, the present inventor has found that natural rubber obtained by partially decomposing a protein contained in a non-rubber component of natural rubber latex within a certain range is effective in solving the above problems. Completed the invention.
That is, the present invention
1. Natural rubber obtained by deproteinizing natural rubber latex, and adjusted to have a total nitrogen content of 0.12 to 0.30% by weight,
2. 2. The natural rubber according to 1 above, wherein the natural rubber is obtained by coagulating the natural rubber latex after the deproteinization treatment without centrifuging the non-rubber component and drying the natural rubber latex;
3. The natural rubber according to claim 1 or 2, wherein the Mooney viscosity (ML _{1 + 4} ) and stress relaxation time (T ₈₀ ) of the rubber satisfy the following formulas I and II.
40 ≦ ML _{1 + 4} ≦ 100 ……… I
T ₈₀ <0.0035exp (ML _{1 + 4} /8.2)+20 ...... II
[Where ML _{1 + 4} is the Mooney viscosity measured value at 100 ° C., T ₈₀ is the time (seconds) required to stop the rotor rotation immediately after ML _{1 + 4} measurement and the ML _{1 + 4} value is reduced by 80%. ). ]
4). A rubber composition comprising the natural rubber according to any one of 1 to 3 and a filler,
5. 20 parts by weight of carbon black having a nitrogen adsorption specific surface area of 80 m ² / g or more or a DBP oil absorption of 110 ml / 100 g or less is included as a filler per 100 parts by weight of the rubber component containing the natural rubber. The rubber composition as described in 4 above,
6). 5. The rubber composition as described in 4 above, comprising 20 to 80 parts by weight of silica as a filler per 100 parts by weight of the rubber component containing the natural rubber.
7). The rubber composition as described in any one of 4 to 6 above, wherein the natural rubber is contained in the total rubber component by 5% by weight or more,
8). In the deproteinization treatment step of the natural rubber latex, after the partial deproteinization treatment so that the total nitrogen content in the solid component is in the range of 0.12 to 0.30% by weight, , A method for producing natural rubber, characterized in that the non-rubber component is solidified without being separated and dried.
9. A rubber composition for a tire case member comprising the natural rubber according to any one of 1 to 3,
10. The rubber composition for a tire case member according to 9, wherein the tire case member is a tire internal member,
11. A tire case member using the rubber composition according to 9 or 10,
12 The tire case member according to 11 above, wherein the rubber composition is used as a belt or carcass coating rubber.
13. A rubber composition for a tire tread, comprising a rubber component containing the natural rubber according to any one of 1 to 3 and a filler,
14 The rubber composition for a tire tread according to the above 13, wherein the filler is at least one selected from carbon black or silica,
15. A tire tread comprising the rubber composition according to any one of 7, 13, and 14,
16. 16. A pneumatic tire, wherein the rubber composition according to 5 or 6 is used as a constituent member of a tire; A pneumatic tire comprising the tire case member and / or the tire tread according to 11, 12, or 15,
Is to provide.

  ADVANTAGE OF THE INVENTION According to this invention, the natural rubber with improved processability and its manufacturing method can be provided, without reducing the physical property which natural rubber has originally. Moreover, the rubber composition using this natural rubber, especially a tire case member, a tire tread member, and a pneumatic tire can be provided.

The natural rubber in the present invention is obtained by adjusting the total nitrogen content to 0.12 to 0.30% by weight by deproteinization treatment of natural rubber latex. The natural rubber latex used as a raw material is not particularly limited, and a field latex, a commercially available latex, or the like can be used.
In the present invention, the natural rubber latex can be deproteinized by a known method. For example, a decomposition treatment method using an enzyme, a method of repeatedly washing with a surfactant, a method of using an enzyme and a surfactant in combination, a transesterification method using sodium methoxide, sodium hydroxide, potassium hydroxide, etc. There is a saponification method using
Here, as the enzyme, in addition to protease, peptidase, cellulase, pectinase, lipase, esterase, amylase and the like can be used alone or in combination. The enzyme activity of these enzymes is suitably in the range of 0.1 to 50 APU / g.

The added amount of these proteolytic enzymes is 0.005 to 0.5 parts by weight, preferably 0.01 to 0.2 parts by weight, based on 100 parts by weight of the solid component in the natural rubber latex. Is appropriate. When the amount of the protease is less than the above range, the protein degradation reaction may be insufficient, which is not preferable. On the other hand, if a proteolytic enzyme is added beyond the above range, deproteinization proceeds too much, and the desired processability and physical properties cannot be balanced.
In the present invention, when performing the proteolytic treatment, a surfactant may be added together with the proteolytic enzyme. As the surfactant, an anionic, cationic, nonionic, amphoteric surfactant and the like can be added.

In the present invention, it is necessary to adjust the total nitrogen content in the latex solid content to be 0.12 to 0.30% by weight by the above deproteinization technique.
This nitrogen is derived from the nitrogen of the polypeptide bond. Quantification of polypeptide binding can be performed by measuring absorbance at 3280 cm ⁻¹ due to polypeptide binding of protein by infrared spectroscopy. Here, a total nitrogen content of 0.12% by weight means that approximately 80% of the polypeptide bonds are degraded. Also, a total nitrogen content of 0.30% by weight means that the polypeptide bonds are degraded by almost 20%.
In the present invention, if the total nitrogen content is less than 0.12% by weight, the improvement effect of mechanical properties (particularly tensile properties) and low exothermic properties cannot be obtained, and the aging resistance properties may be deteriorated. . Only when the total nitrogen content is in a specific range of 0.12% by weight or more, the effect of improving the tensile properties and low heat build-up of the rubber composition can be obtained. This is considered to be because the viscosity of the rubber is moderately reduced due to the decomposition of the peptide bond, the dispersibility of the atomized carbon black or the like in the rubber is improved, and the interaction between the filler and the rubber is increased.
On the other hand, when it exceeds 0.30% by weight, workability is inferior. From such a viewpoint, the total nitrogen content is preferably 0.12 to 0.30% by weight, particularly preferably 0.18 to 0.25% by weight. The polypeptide degradation rate is preferably 20 to 80%, particularly preferably 30 to 70%.
The natural rubber latex deproteinized as described above is preferably coagulated without separating non-rubber components. When the non-rubber component is separated, the aging resistance may be inferior.

That is, in the method for producing natural rubber according to the present invention, in the deproteinization treatment step of the natural rubber latex, the partial deproteinization is performed so that the total nitrogen content in the solid component is in the range of 0.12 to 0.30% by weight. After the treatment, the obtained natural rubber latex is preferably coagulated without separation of non-rubber components and dried.
The rubber component obtained by coagulating the treated latex is washed and then dried using a normal dryer such as a vacuum dryer, an air dryer, a drum dryer or the like, whereby the natural rubber in the present invention can be obtained.

Further, from the viewpoint of rubber processability, it is possible to shorten the relaxation time of input. However, the natural rubber according to the present invention is partially deproteinized so that branch points are selectively cut and stress is reduced. The relaxation time is reduced, and excellent processability (shrinkability and shape stability) is obtained.
In the present invention, the stress relaxation time of natural rubber is defined by the relationship with the ML _{1 + 4} value at the time of Mooney viscosity measurement, and preferably satisfies both the following formulas I and II.
40 ≦ ML _{1 + 4} ≦ 100 ……… I
T ₈₀ <0.0035exp (ML _{1 + 4} /8.2)+20 ...... II
[However, ML _{1 + 4} is the Mooney viscosity measurement value at 100 ° C., T ₈₀ is the time (seconds) required to stop the rotor rotation immediately after ML _{1 + 4} measurement and to reduce the ML _{1 + 4} value by 80%. It is. ]
Furthermore, the constant viscosity effect can be improved by including the hydrazide compound in the natural rubber in the present invention.

Next, the rubber composition in the present invention preferably contains at least 5% by weight of the specific natural rubber in the rubber component. If this amount is less than 5% by weight, a rubber composition having desired physical properties may not be obtained. The preferred content of this natural rubber is 10% by weight or more.
Examples of the rubber component used in combination with the specific natural rubber include normal natural rubber and diene synthetic rubber. Examples of the diene synthetic rubber include styrene-butadiene copolymer (SBR), polybutadiene (BR), Examples thereof include polyisoprene (IR), butyl rubber (IIR), ethylene-propylene copolymer, and mixtures thereof.

The rubber composition in the present invention preferably contains the natural rubber and a filler. Although it does not specifically limit as a filler, The thing normally used for rubber industries, such as carbon black, a silica, an alumina, aluminum hydroxide, clay, a calcium carbonate, can be used.
When the rubber composition in the present invention contains carbon black, the nitrogen adsorption specific surface area (N ₂ AS) is 80 m ² / g or more or the DBP oil absorption amount (n -What blended 20-100 weight part of carbon black whose dibutyl phthalate oil absorption) is 110 ml / 100g or less is preferable. More preferable carbon black has a nitrogen adsorption specific surface area of 100 m ² / g or more, or a DBP oil absorption of 90 ml / 100 g or less.

That is, when natural rubber that has been partially deproteinized in the present invention is used, carbon black having a fine particle diameter with a nitrogen adsorption specific surface area of 80 m ² / g or more, or DBP oil absorption is 100 ml / 100.
Even when blended with carbon black with a low structure of g or less, the dispersion of carbon black is improved compared to the case of using conventional natural rubber, so the wear resistance and low loss (low heat build-up) of the rubber composition are improved. ) And the like can be greatly improved.
Here, there is no restriction | limiting in particular as carbon black, Arbitrary things can be selected and used from what was conventionally used as a reinforcing filler of rubber | gum. Examples of the carbon black include FEF, SRF, HAF, ISAF, and SAF. From the viewpoint of wear resistance, HAF, ISAF, and SAF are preferable.

Moreover, the rubber composition in this invention has a preferable thing which mix | blended 20-80 weight part with respect to 100 weight part of rubber components in the case of a silica mixing | blending. That is, when silica is blended with the partially deproteinized natural rubber, the silica dispersion and the shrinkage of the blend are greatly improved compared to the case of using conventional natural rubber. Physical properties such as exotherm can be remarkably improved.
The silica is not particularly limited, but wet silica, dry silica, and colloidal silica are preferable. Such fillers can be used alone or in admixture of two or more.

  In the rubber composition of the present invention, various chemicals usually used in the rubber industry, for example, vulcanizing agents, vulcanization accelerators, process oils, anti-aging agents, as long as the object of the present invention is not impaired. A scorch inhibitor, zinc white, stearic acid and the like can be contained.

The rubber composition in the present invention is particularly suitably used as tire rubber, and can be applied to all tire members such as tread rubber (including cap rubber and base rubber), side rubber, ply rubber, and bead filler rubber.
Especially as a tire member, it is used suitably for a tire case member and a tire tread. Here, the tire case member includes all rubber members except for the tread rubber, but the tire inner member is particularly preferable, for example, belt coating rubber, carcass ply coating rubber, squeegee rubber between plies, and between tread and belt. A cushion rubber, a bead filler, etc. are mentioned.

In the natural rubber of the present invention, due to appropriate decomposition of protein peptide bonds, the entanglement of natural rubber molecules is reduced and the rubber is easy to relieve stress. As a result, the rubber composition has excellent crack growth resistance. Become a thing. In addition, the adhesion is improved because the protein which is an inhibition factor of adhesion is removed. Furthermore, as a result of a moderate decrease in the rubber viscosity, the dispersibility of the fine filler in the rubber is improved, and the mechanical properties and low heat build-up are also improved. Abrasion resistance and the like are improved by significantly improving the dispersibility of the filler.
For this reason, when the rubber composition according to the present invention is applied to a tire case member, for example, a coating rubber of a belt or a carcass ply rubber, the cord separation property, rubber / cord adhesion property, rubber mechanical property of the tire after running Properties (such as retention of elongation at break) can be significantly improved.
Moreover, when the rubber composition in the present invention is applied to a tire tread, the wear resistance, low heat generation property, tear resistance and the like of the tread rubber can be remarkably improved.
The natural rubber and the rubber composition thereof in the present invention can be used for applications such as anti-vibration rubber, belts, hoses and other industrial products in addition to tires.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
In the following examples and comparative examples, measurement of the total nitrogen content in natural rubber, Mooney viscosity, stress relaxation time, and various physical properties of vulcanized rubber were measured as follows.
(1) Measurement of total nitrogen content The total nitrogen content was measured by the Kjeldahl method and determined as a ratio (% by weight) to the total amount.
(2) Mooney viscosity and stress relaxation time of natural rubber Mooney viscosity [ML _{1 +} 4/100 ° C.] was measured at 100 ° C. according to JIS K6300-1994.
The stress relaxation time (T ₈₀ ) was measured as the time (seconds) required to stop the rotor rotation immediately after the ML _{1 + 4} measurement and reduce the ML _{1 + 4} value by 80%.
(3) Mooney Viscosity of Conbound (Rubber Composition) The Mooney viscosity [ML _{1 +} 4/130 ° C.] was measured at 130 ° C. according to JIS K6300-1994. The smaller this value, the better the workability.

(4) Physical properties of vulcanized rubber composition (a) Tensile strength The strength (Tb) at the time of cutting was measured according to JISK6301-1995.
(B) tan δ (dynamic loss)
Using a viscoelasticity measuring apparatus (Rheometrics), tan δ (50 ° C.) was measured at a temperature of 50 ° C., a strain of 5%, and a frequency of 15 Hz. The smaller tan δ (50 ° C.), the lower the heat generation.
(C) Heat aging resistance (index)
The tensile strength after heat aging at 100 ° C. for 72 hours was divided by the tensile strength before heat aging and expressed as a percentage. The larger this value, the better the heat aging resistance.
(D) Abrasion resistance (index)
The amount of wear at a slip rate of 60% at room temperature was measured using a Lambourn type wear tester and displayed as an index. A larger index is better.

Example 1, Reference Examples 1 to 3 and Comparative Examples 1 to 5
<Production method of natural rubber>
Production Example 1
(1) Peptide bond decomposition process of natural rubber latex Anionic surfactant [“Demol” manufactured by Kao Co., Ltd., surfactant concentration is 2.5 wt%] 24.7 ml, protease (Novozymes “Alcalase”) 2.5L, type DX ") 0.06 g was added and mixed to prepare a solution.
Next, 1000 g of natural rubber latex having a solid content of 20% by weight was kept constant at 40 ° C. in a water bath, the solution was added dropwise while stirring, and stirring was continued at the same temperature for 5 hours. Got.
(2) Coagulation / Drying Step The rubber obtained by acid coagulation is passed through a drum dryer set at 130 ° C. five times, and then dried in a vacuum dryer at 40 ° C. for 8 hours to produce natural rubber (a ) Was manufactured.

Production examples 2 and 3
In Production Example 1, instead of protease, Production Example 2 uses peptidase (“Debitrase” manufactured by Soho Tsusho) and Production Example 3 uses sodium hydroxide to obtain natural rubber latex (B) and (C). Then, natural rubber (b), (c) was manufactured by acid coagulation and drying.

Production Example 4
In Production Example 1, the amount of protease added and the stirring time with natural rubber latex were changed to the conditions shown in Table 1 to obtain natural rubber latex (D), which was then coagulated and dried to produce natural rubber (d). did.

Production Example 5
Natural rubber latex (E) was obtained in the same manner as in Production Example 1 except that the protease was changed to 0.04 g. Subsequently, after centrifuging at a rotational speed of 7500 rpm using a latex separator SLP-3000 (manufactured by Saito Centrifuge Co., Ltd.), natural rubber (e) was produced through a coagulation / drying process.

Production Example 6
In Production Example 1, the amount of protease added and the stirring time with natural rubber latex were changed to the conditions shown in Table 1 to obtain natural rubber latex (F), which was then coagulated and dried to produce natural rubber (f). did.

Production Example 7
In Production Example 1, natural rubber (g) was obtained by directly coagulating and drying without going through the peptide bond decomposing step.
About the natural rubber (a)-(g) obtained by the said manufacture examples 1-7, the total nitrogen content in rubber | gum, Mooney viscosity (ML1 _{+ 4} , 100 degreeC), and stress relaxation time were measured. The results are shown in Table 1.

  Using the various prototype natural rubbers shown in Table 1 obtained in Production Examples 1 to 7, kneading was carried out by a conventional method according to the formulation shown in Table 2, and rubber compositions were prepared.

*0 カーボンブラックＮ３３９：東海カーボン（株）製「シーストＫＨ」(商標)、Ｎ₂ＳＡ；９２、ＤＢＰ吸油量；１２０
*1 老化防止剤６Ｃ：Ｎ−フェニル−Ｎ−１，３―ジメチルブチル−
ｐ−フェニレンジアミン
*2 加硫促進剤ＤＺ：Ｎ，Ｎ−ジシクロヘキシル−２−ベンゾチアゾリルスルフェンアミド

* 0 Carbon Black N339: “Seast KH” (trademark) manufactured by Tokai Carbon Co., Ltd., N ₂ SA; 92, DBP oil absorption amount: 120
* 1 Anti-aging agent 6C: N-phenyl-N-1,3-dimethylbutyl
p-Phenylenediamine
* 2 Vulcanization accelerator DZ: N, N-dicyclohexyl-2-benzothiazolylsulfenamide

The rubber composition was measured for its Mooney viscosity (ML _{1 + 4} , 130 ° C.) and vulcanized at 145 ° C. for 33 minutes to measure the physical properties of the vulcanized rubber. The results are shown in Table 3.

In the above, the natural rubbers of Example 1 and Reference Examples 1 to 3 have a total nitrogen content after deproteinization of 0.12 to 0.30% by weight, which is within the scope of the present invention. Compared to ˜5, it can be seen that the vulcanized rubber composition is excellent in both tensile strength and low exothermic property (tan δ). Particularly in Example 1 and Reference Examples 1 and 2 using rubber that was not centrifuged after deproteinization , in addition, the heat aging resistance was remarkably excellent.
Comparative Example 1 used a high deproteinized natural rubber (d) having a total nitrogen content of 0.015% by weight, and Comparative Example 2 was a natural rubber (f) having a total nitrogen content of 0.36% by weight. ), Comparative Example 3 uses natural rubber (g) without deproteinization, Comparative Example 4 increases the degree of mastication of natural rubber (g) and decreases Mooney viscosity, Comparative Example 5 uses a blend of natural rubber (g) and synthetic polyisoprene (trade name “IR2200”; manufactured by JSR Corporation), but none of the effects of the present invention are obtained.

Reference Examples 4 to 6 and Comparative Examples 6 to 11
Using various types of experimental natural rubbers a, d, and g shown in Table 4 obtained in Production Examples 1, 4, and 7, kneading was carried out by a conventional method according to the formulation shown in Table 5 to prepare a rubber composition. .

*3 カーボンブラックＮ３２６：東海カーボン（株）製 「シースト３００」(商標)、Ｎ₂ＳＡ；７５、ＤＢＰ吸油量；８４
*4 カーボンブラックＮ１１０：東海カーボン（株）製 「シースト９」（商標）、Ｎ₂ＳＡ；１３０、ＤＢＰ吸油量；１１３
*5 シリカ：日本シリカ工業（株）製「ニプシルＡＱ」
*6 シランカップリング剤：デグッサ社製「Ｓｉ６９」
*7 加硫促進剤ＤＰＧ：ジフェニルグアニジン
*8 加硫促進剤ＤＭ：ジベンゾチアジルジサルファイド
*9 加硫促進剤ＮＳ：Ｎ−ｔ−ブチル−２−ベンゾチアゾリルスルフェンアミド

* 3 Carbon black N326: “Seast 300” (trademark), N ₂ SA; 75, DBP oil absorption: 84, manufactured by Tokai Carbon Co., Ltd.
* 4 Carbon Black N110: “Seast 9” (trademark) manufactured by Tokai Carbon Co., Ltd., N ₂ SA; 130, DBP oil absorption: 113
* 5 Silica: “Nipsil AQ” manufactured by Nippon Silica Industry Co., Ltd.
* 6 Silane coupling agent: “Si69” manufactured by Degussa
* 7 Vulcanization accelerator DPG: Diphenylguanidine
* 8 Vulcanization accelerator DM: Dibenzothiazyl disulfide
* 9 Vulcanization accelerator NS: Nt-butyl-2-benzothiazolylsulfenamide

The rubber composition was measured for its Mooney viscosity (ML _{1 + 4} , 130 ° C.) and vulcanized at 145 ° C. for 33 minutes to measure the physical properties of the vulcanized rubber. The results are shown in Table 6.

As a result, it can be seen that Reference Examples 4 to 6 in the present invention are remarkably superior in both low heat buildup and wear resistance as compared with the respective comparative examples.

Reference Examples 7 to 9 and Comparative Examples 12 and 13
A tire was manufactured using a prototype natural rubber as a tire case member, and a tire performance test was performed.
<Tire performance test>
For the test tire having a tire size of 185 / 70R14, the durability of the tire was evaluated as follows.
Twenty tires of the above-mentioned size were prepared, and after running 80,000 km in the field, the tires were collected, and the tires after running were evaluated. In addition, each evaluation was calculated | required as an average value of 20 tires.
(A) Belt end separation resistance Cut samples including a belt layer were prepared from two locations on the circumference of the collected tire, and the crack lengths (the cereal side and the anti-cereal side) of the belt end were measured. The evaluation results are shown as an index with the value of Comparative Example 13 as 100. The larger the value, the better the belt end separation resistance.
(B) Rubber / steel cord adhesion (after running)
A sample including the belt layer is taken out from the collected tire, the steel cord in the belt layer is pulled at a speed of 50 mm / min by a peel test, and the adhesion state of the rubber adhered to the exposed steel cord surface is visually evaluated. Judgment was made according to the following criteria.
Rank A: Rubber adhesion rate 80% to 100% Rank B: Rubber adhesion rate 60% to 80% (c) Rubber rupture elongation retention rate Belt coated rubber according to JIS K 6251 from the tire before running and the collected tire A sample was cut out to a thickness of 0.5 mm to prepare a dumbbell-shaped test piece. This was subjected to a tensile test based on JIS K 6301, and the elongation retention at the time of cutting was calculated by the following equation. It shows that the durability with respect to heat aging property is excellent, so that a numerical value is large.
Elongation retention at break (%) = [(Elongation when cutting belt-coated rubber after running) / (Elongation when cutting belt-coated rubber before running)] × 100

<Production method of natural rubber>
Production Example 8
(1) Peptide bond decomposition process of natural rubber latex Anionic surfactant [“Demol” manufactured by Kao Corporation, surfactant concentration is 2.5 wt%] 24.7 ml of water, 136 g of water, protease (“Alcalase” manufactured by Novozymes) 2.5L, type DX ") 0.06 g was added and mixed to prepare a solution.
Next, 1000 g of natural rubber latex having a solid content of 20% by weight was kept at a constant temperature of 40 ° C. in a water bath, the solution was added dropwise with stirring, and stirring was continued at the same temperature for 5 hours. Got.
(2) Coagulation / Drying Step The rubber obtained by acid coagulation is passed through a drum dryer set at 130 ° C. five times, and then dried in a vacuum dryer at 40 ° C. for 8 hours to produce natural rubber (h ) Was manufactured.

Production Example 9
In Production Example 8, a natural rubber latex (I) was obtained by using peptidase (“Debitrase” manufactured by Kokusho Tsusho) instead of protease, and then coagulated and dried to produce natural rubber (i).

Production Example 10
In Production Example 8, the amount of protease added and the stirring time with natural rubber latex were changed to the conditions shown in Table 7 to obtain natural rubber latex (J), which was then coagulated and dried to produce natural rubber (j). Manufactured.

Production Example 11
In the same manner as in Production Example 8, natural rubber latex (H ′) obtained in the peptide bond decomposition step of natural rubber latex was obtained. Furthermore, after centrifuging at a rotational speed of 7500 rpm using a latex separator SLP-3000 (Saito Centrifuge Co., Ltd.), natural rubber (k) was produced through a coagulation / drying process.

Production Example 12
In Production Example 8, natural rubber (L) was obtained by directly coagulating and drying without going through the peptide bond decomposition step.
About each latex immediately before coagulation of the said manufacture examples 8-12, the total nitrogen content in a solid component and the Mooney viscosity (ML1 _{+ 4} , 100 degreeC) of obtained natural rubber (h)-(L) were measured. The results are shown in Table 7.

  Using each type of natural rubber h to L shown in Table 7 obtained in Production Examples 8 to 12, the rubber composition was prepared by kneading by a conventional method according to the formulation shown in Table 8.

*10 カーボンブラック：東海カーボン（株）製、「シースト３」（商標）、Ｎ₂ＳＡ；７９、ＤＢＰ吸油量；１０２

* 10 Carbon black: “Seast 3” (trademark), manufactured by Tokai Carbon Co., Ltd., N ₂ SA; 79, DBP oil absorption: 102

  Using each of the above rubber compositions as a coating rubber for a steel cord carcass ply, a tire having a tire size of 185 / 70R14 was prototyped and subjected to a tire performance test by the above-described method. Rubber / steel cord adhesion and rubber break elongation retention were evaluated. The results are shown in Table 9.

In the above, the tires of Reference Examples 7 to 9 in the present invention have a total nitrogen content after deproteinization in the range of 0.12 to 0.30% by weight of the present invention, and Comparative Examples 12 and 13 Compared to the above, it can be seen that the belt end separation resistance of the tire after running is excellent. In particular, in the tires of Reference Examples 7 and 8 using rubber that was not centrifuged after deproteinization , the rubber / steel cord adhesion and the rubber breaking elongation retention ratio were remarkably excellent.
The rubber used in the tire of Comparative Example 12 is a highly deproteinized natural rubber (j) having a total nitrogen content of 0.055% by weight, and the rubber of Comparative Example 13 is a natural rubber without deproteinization treatment. (L) is used, but none of the effects of the present invention is obtained.

Reference Examples 10-12 and Comparative Examples 14, 15
A tire was manufactured using a prototype natural rubber as a tire tread, and a tire performance test was performed.
<Tire performance test>
Using various types of rubber for the tread, tires for heavy loads having a tire size of 11R22.5 were manufactured and evaluated for wear resistance, low heat buildup and tear resistance as follows.
(D) Abrasion resistance After traveling 50000 km on a general road with a real vehicle, the travel distance per 1 mm of wear was calculated from the remaining groove in the tread portion, and the value of the tire of Comparative Example 15 was displayed as an index. The higher the index, the better the wear resistance.
(E) Low exothermic property The tire produced above was run on a drum at 80 km / h, the rolling resistance was measured, and the value of the tire of Comparative Example 15 was indicated as 100 and indicated as an index. The larger the index, the better the low heat buildup.
(F) Tear resistance In the tire prepared as described above and subjected to the wear resistance test, the crack generated at the bottom of the block groove was visually observed and evaluated according to the following evaluation criteria.
(Double-circle): The crack was not recognized visually.
○: Although minute cracks were observed, no progress of cracks was observed.
X: It was recognized that the crack progressed and the crack connected.
Using the prototype natural rubbers h to L shown in Table 7 obtained in Production Examples 8 to 12, the rubber composition was prepared by kneading by a conventional method according to the formulation shown in Table 10.

*11 カーボンブラックＩＳＡＦ: Ｎ₂ＳＡ；１１５、ＤＢＰ吸油量；１１４

* 11 Carbon black ISAF: N ₂ SA; 115, DBP oil absorption: 114

  Using each rubber composition obtained above as a tread rubber, a tire of 11R22.5 was prototyped and a tire performance test was conducted by the above-described method to evaluate the wear resistance, low heat buildup and tear resistance. The results are shown in Table 11.

In the above, the tires of Reference Examples 10 to 12 in the present invention have a total nitrogen content after deproteinization in the range of 0.12 to 0.30% by weight of the present invention, and Comparative Examples 14 and 15 It can be seen that both wear resistance and low heat build-up are remarkably superior. In particular, the tires of Reference Examples 10 and 11 using rubber that has not been centrifuged after deproteinization are further excellent in tear resistance.
The rubber used in the tire of Comparative Example 14 is a highly deproteinized natural rubber (j) having a total nitrogen content of 0.055% by weight, and the rubber of Comparative Example 15 is a natural rubber without deproteinization treatment ( L) is used, but the effect of the present invention is not obtained in any case.

  According to the present invention, a natural rubber with improved processability can be obtained without deteriorating the physical properties of the natural rubber. Further, the rubber composition has improved low heat buildup and wear resistance and can be applied to various rubber industrial products, but is particularly suitable for pneumatic tires as tire case members, tire tread members and the like.

Claims (17)

Obtained natural rubber latex was deproteinized with Ke emissions reduction method, the total nitrogen content contains a filler and a natural rubber which is adjusted to a 0.18 to 0.25 wt% A rubber composition.   The rubber composition according to claim 1, wherein the natural rubber is obtained by coagulating the natural rubber latex after the deproteinization treatment without centrifuging the non-rubber component and drying the natural rubber latex. The rubber composition according to claim 1 or 2, wherein the Mooney viscosity (ML _{1 + 4} ) and stress relaxation time (T ₈₀ ) of natural rubber satisfy the following formula I and formula II.
40 ≦ ML _{1 + 4} ≦ 100 ……… I
T ₈₀ <0.0035exp (ML _{1 + 4} /8.2)+20 ...... II
[However, ML _{1 + 4} is the Mooney viscosity measurement value at 100 ° C., T ₈₀ is the time (seconds) required to stop the rotor rotation immediately after ML _{1 + 4} measurement and to reduce the ML _{1 + 4} value by 80%. It is. ] 20 parts by weight of carbon black having a nitrogen adsorption specific surface area of 80 m ² / g or more or a DBP oil absorption of 110 ml / 100 g or less is included as a filler per 100 parts by weight of the rubber component containing the natural rubber. The rubber composition according to any one of claims 1 to 3.   The rubber composition according to any one of claims 1 to 3, comprising 20 to 80 parts by weight of silica as a filler per 100 parts by weight of a rubber component containing the natural rubber.   The rubber composition according to any one of claims 1 to 5, wherein the natural rubber is contained in the total rubber component in an amount of 5% by weight or more.   A rubber composition for a tire case member, comprising the rubber composition according to any one of claims 1 to 3.   The rubber composition for a tire case member according to claim 7, wherein the tire case member is a tire internal member.   A tire case member using the rubber composition according to claim 7 or 8.   The tire case member according to claim 9, wherein the rubber composition is used as a belt or carcass coating rubber.   A rubber composition for a tire tread, comprising a rubber component containing the natural rubber according to any one of claims 1 to 3 and a filler.   The rubber composition for a tire tread according to claim 11, wherein the filler is at least one selected from carbon black or silica.   A tire tread comprising the rubber composition according to any one of claims 6, 11 and 12.   A pneumatic tire, wherein the rubber composition according to claim 4 is used as a constituent member of a tire.   A pneumatic tire, wherein the rubber composition according to claim 5 is used as a constituent member of a tire.   A pneumatic tire comprising the tire case member according to claim 9.   A pneumatic tire comprising the tire tread according to claim 13.