JP2003292675A - Rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition improved in tanδ at a high temperature and in abrasion resistance. <P>SOLUTION: The rubber composition is obtained by blending a carbon black (CB) containing a natural rubber master batch produced by mixing a raw natural rubber (NR) latex and CB in an aqueous medium followed by coagulation and drying, with an additional raw rubber material having -50 to -20°C glass transition temperature (Tg) and silica, using an internal mixer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rubber composition,
More specifically, natural rubber (NR) latex and carbon black (CB) are mixed in an aqueous medium, coagulated and dried, and an additional raw material rubber having a specific high glass transition temperature (Tg) is added to the CB-containing natural rubber masterbatch. The present invention relates to a rubber composition obtained by mixing silica, which is excellent in abrasion resistance, rolling resistance and impact resilience.

[0002]

2. Description of the Related Art Conventionally, various proposals have been made for compounding carbon black with rubber by various methods to obtain a rubber composition having improved physical properties such as viscoelasticity. For example, Japanese Patent Application Laid-Open No. 9-67469 discloses a method in which carbon black is dividedly added to a terminal-modified rubber having a low Tg and a rubber having a high Tg. JP-A-9-324077 discloses the use of a wet masterbatch of carbon black and solution-polymerized SBR. JP-A-10
No. 237230 discloses a method using a wet masterbatch of carbon black and emulsion-polymerized SBR. JP-A 2000-336208 discloses that carbon black and SBR having a low viscosity and a low Tg are used for mixing.

Further, regarding preparation of an NR wet masterbatch and a rubber composition using the same, Japanese Patent Application Laid-Open Publication No. 200-2000
0 to 507892, WO99 / 16600 and the like.

[0004]

SUMMARY OF THE INVENTION In addition to the above-mentioned conventional compounding method, the present invention is a rubber compounding method using natural rubber, in which abrasion resistance and high temperature side tan δ (rolling resistance) are improved. It is to provide a rubber composition that can be suitably used for treads.

[0005]

According to the present invention, a natural rubber (NR) raw latex and carbon black (CB) are used.
C obtained by mixing and coagulating with and in an aqueous medium
B-containing natural rubber masterbatch and glass transition temperature (T
There is provided a rubber composition obtained by mixing an additional raw material rubber having g) in the range of −50 ° C. to −20 ° C. and silica in an internal mixer.

[0006]

According to the present invention, natural rubber (N
R) A latex and carbon black (CB) are mixed in an aqueous medium to obtain a masterbatch, and Tg higher than NR, in particular Tg, is added to the desired raw material rubber having a Tg of -50 ° C to -20 ° C and silica. A rubber composition is obtained. Thus, the CB-containing NR masterbatch was tan
By mixing a high Tg rubber having excellent δ temperature dependency and silica, the interaction of carbon black with a high Tg rubber matrix is reduced as compared with a rubber composition which is mechanically mixed without using a masterbatch. The rubber composition has improved tan δ (rolling resistance) and wear resistance on the high temperature side, and further has improved wear resistance as compared with the case of using a masterbatch obtained by mechanical mixing. You can get things.

The CB-containing NR masterbatch carbon black according to the present invention may be any carbon black that has been generally used for tires, but preferably has a nitrogen specific surface area (N ₂ SA). 70
m ² / g or more, preferably 80 m ² / g or more of carbon black is used as a natural rubber raw material latex (solid content conversion) 1
CB-containing NR by mechanically mixing 60 to 100 parts by weight, and more preferably 70 to 100 parts by weight of carbon black in an aqueous medium with respect to 00 parts by weight.
A masterbatch can be obtained. This CB containing NR
If necessary, a process oil, a plasticizer, an antiaging agent and the like can be added to the masterbatch. Specific methods for producing the CB-containing NR masterbatch include the methods disclosed in JP-A-48-96636, 58-152031, and JP-A-2000-507892.

According to the present invention, an additional raw material rubber is added to the CB-containing NR masterbatch in 100 parts by weight of the total rubber in the final synthetic rubber composition, preferably 10 to 60 parts by weight, more preferably 30 to 30 parts by weight. Add 60 parts by weight. If the compounding amount of the additional raw material rubber is too small, the effect of the high Tg rubber having excellent tan δ temperature dependency tends to be lost, and tan δ on the high temperature side may not be sufficiently lowered. On the other hand, if the amount is too large, the amount of NR is significantly reduced, and the destruction characteristics are deteriorated.

Examples of the additional raw rubber compounded in the CB-containing NR masterbatch according to the present invention include diene such as various styrene-butadiene copolymer rubbers, vinyl-butadiene copolymer rubbers and styrene-isoprene-butadiene copolymer rubbers. A system rubber can be used, and preferably SBR obtained by emulsion polymerization and / or solution polymerization.

According to the present invention, the CB-containing NR is added for the purpose of achieving both the reinforcing property of the additional raw material rubber and the low energy loss property.
Silica is preferably added to the masterbatch in an amount of preferably 10 to 40 parts by weight based on 100 parts by weight of total rubber. As silica, any silica that has been conventionally generally blended for rubber compositions, particularly for pneumatic tires can be blended, but wet method silica having N ₂ SA of 80 m ² / g or more is preferable. , And more preferably N ₂ SA is 120
m ² / g or more.

According to the present invention, the same or different carbon black as described above can be further compounded in the CB-containing NR masterbatch, but this compounding amount is based on 100 parts by weight of the rubber in the final rubber composition. Up to 20
It is preferably part by weight. According to the present invention, it is preferable that the total amount of fillers such as carbon black and silica is 90 parts by weight or less per 100 parts by weight of the total rubber. If this amount is too large, the rubber processability tends to deteriorate.

The rubber composition according to the present invention contains, in addition to the above-mentioned essential components, a vulcanizing agent such as sulfur, a vulcanization accelerator, a vulcanization retarder, an antiaging agent, a wax, and other generally. A general-purpose component such as an additive for rubber can be used, and the amount thereof used can be conventional.

[0013]

EXAMPLES The contents and effects of the present invention will be described more specifically below with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples.

Example 1, Standard Example and Comparative Examples 1 to 3 A rubber composition having the composition (parts by weight) shown in Table II was prepared and its physical properties were evaluated. The composition of the CB-containing NR masterbatch used in the composition of the examples is as follows.

The method for producing the masterbatch is not limited to the method described below. This master batch is Cab
Made from 70 phr filler of commercial grade N339 carbon black available from ot Corporation and standard natural rubber field latex from Maresia.

The complete compound formulation is shown in Table I below. A typical example is a commercially available tread tire for trucks, which is known to have excellent resistance to vulcanization during vulcanization.

[0017] Table I: master batch composition ──────────────────────────────── Component Parts by weight rubber 100 Carbon black 70 Antiaging Agent 6C 0.7 Aromatic Process Oil 10 ─────────────────────────────────

Details of the preparation of the masterbatch are shown below. 1. Adjustment of carbon black slurry. Carbon black is mixed with pure water in a 1 liter flask equipped with a stirrer. The pellet is fragmented by a stirrer.
A slurry with 2.5% by weight carbon black is formed.

2. Latex supply. Latex has a capacity of 1
Injected into a 1 liter flask. Anti-aging emulsion was added to the latex prior to injection. The anti-aging agent was prepared by adding potassium oleate to the anti-aging agent in a ratio of 3 to 100 and adjusting the pH to about 10 with potassium hydroxide.
It was prepared as a weight% emulsion. Further, 10 parts by weight of oil was added to 100 parts by weight of rubber by emulsifying with soap.

3. A mixture of carbon black and latex.
The carbon black slurry was transferred to a coagulation rubber reaction flask equipped with a stirrer and having a capacity of 3 liters, the latex mixture supply rate ratio to the carbon black slurry was appropriately maintained, and the latex was added into the carbon black slurry and mixed with a stirrer. . For 100 parts by weight of rubber,
70 parts by weight of the desired carbon black content was obtained.

4. dehydration. The wet crumb discharged from the coagulated rubber reaction flask is dewatered by a dewatering extruder.
In the extruder, the moist crumb is compressed and water is squeezed out of the crumb.

5. Drying and cooling. The almost dehydrated crumb is extruded and heated again. The extruder extrusion temperature was approximately 100 ° C. and the water content was approximately 0.5-1 wt%. The hot, dry crumbs cool rapidly.
The resulting dried crumb contained approximately 55.6 wt% solid rubber and approximately 38.9 wt% carbon black.

Sample Preparation Each component of the first mixing step shown in Table II was kneaded with a 1.8 liter Banbury mixer for 3 to 5 minutes, and in Comparative Example 3, S-SBR was further added in the second mixing step, 165 ± 5 ° C
It was released when it reached. Next, in the final mixing step, the vulcanization accelerator and sulfur were kneaded with an 8-inch open roll to obtain a rubber composition.

The sample composition obtained was treated with 15 × 15 ×
A target test piece was prepared by press vulcanization in a 0.2 cm mold at 160 ° C. for 20 minutes, and vulcanized physical properties were evaluated. The results are shown in Table I.

The method of testing the vulcanized physical properties of the composition obtained in each example is as follows. 1) tan δ: Measured at 20 Hz, initial elongation of 10%, dynamic strain of 2% with a rheographic solid viscoelastic device manufactured by Toyo Seiki Seisakusho (sample width 5 mm, temperature 60 ° C.). 2) Impact resilience: JIS by Ryupke impact resilience tester
It measured at 40 degreeC according to K6255. 3) Abrasion resistance: Measured with a Lambourn abrasion tester, and the abrasion loss was expressed as an index by the following method. Abrasion resistance (index) = [(weight loss of test piece of standard example) /
(Reduction in weight of each test piece)] × 100

[0026]

[Table 1]

Table II Footnote * 1: Natural rubber SIR-20 * 2: Solution polymerization SBR (Nipol NS1 manufactured by Nippon Zeon Co., Ltd.)
16) Tg = −30 ° C. * 3: Nipsil AQ made by Nippon Silica * 4: Si69 made by Dexser-Hulz * 5: Diethylene glycol * 6: HAF grade carbon black (N339): Showa Cabot * 7: Antiaging agent 6C: N -Phenyl-N '-(1,3-
Dimethylbutyl) -p-phenylenediamine * 8: Sulfur powder (5% oil treatment) * 9: Vulcanization accelerator NS: N-tert-butyl-2-benzothiazolylsulfenamide * 10: Vulcanization accelerator DPG : Diphenylguanidine * 11: 33.3% oil-extended emulsion polymerization SBR (Neon manufactured by Zeon
ipol9529) Tg = -21 ° C * 12: Solution polymerization SBR (Tufden 2000R manufactured by Asahi Kasei)
Tg = -67 ° C

Table II shows the results using natural rubber (NR) and its blends with solution polymerized SBR S-SBR ^{* 2} .

The standard example 1 is an example for all NR. In Comparative Example 1, half of NR is solution-polymerized SBR compared to Standard Example 1.
In this example, S-SBR ^{* 2} is substituted. By substituting with S-SBR ^{* 2} , tan δ at 60 ℃ rises to 40 ℃
The impact resilience of is reduced.

Comparative Example 2 is an example in which, in comparison with Comparative Example 1, 15 parts by weight of 30% of 50 parts by weight of carbon black is replaced with silica. Compared to Comparative Example 1, tan δ at 60 ° C.
Was reduced, and the impact resilience at 40 ° C. was improved. Example 1 in accordance with the present invention was further compounded with a CB containing NR masterbatch to achieve a further significant tan δ reduction of 60 ° C. and 4
An improvement in impact resilience at 0 ° C was found.

In the present invention, while CB is unevenly distributed on the NR side, silica is unevenly distributed on the SBR side, so that CB is changed to SB.
The constraint on R is reduced, and tan δ on the high temperature side and impact resilience are improved.

Comparative Example 3 is aimed at the same effect only by mechanical mixing without using the NR masterbatch in the present invention. Similar to Example 1, tan δ and impact resilience are improved, but wear resistance is deteriorated.
Shows the superiority of using NR masterbatch in. Table IV shows experimental examples for blends of NR and emulsion polymerized SBR E-SBR ^{* 11} . Comparative Examples 4, 5, 7 and Example 2 in Table III have the same relationship as Comparative Examples 1, 2, 3 and Example 1 in Table II.

By blending the CB-containing NR masterbatch, it is possible to significantly improve tan δ and impact resilience without lowering fracture characteristics such as abrasion resistance.

Further, Example 3 in Table III is an example in which carbon black was supplied from other than the NR masterbatch. It is clear that it is better than Comparative Example 6 which can be regarded as the same composition.

Table IV is the result of blending with solution polymerized SBR S-SBR ^{* 12} , where the Tg is outside the scope of the present invention. When this E-SBR ^{* 12} is used, the characteristics hardly change before and after using the NR masterbatch. In other words, there is no point in using a masterbatch.

[0036]

[Table 2]

[0037]

[Table 3]

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) C08K 5/548 C08K 5/548 C08L 9/06 C08L 9/06 21/00 21/00

Claims (6)

[Claims] 1. A CB-containing natural rubber masterbatch obtained by mixing a natural rubber (NR) raw material latex and carbon black (CB) in an aqueous medium, coagulating and drying, and a glass transition temperature (Tg) of −. A rubber composition obtained by mixing an additional raw material rubber in the range of 50 ° C to -20 ° C and silica in an internal mixer. 2. The rubber composition according to claim 1, wherein the CB-containing natural rubber masterbatch contains 60 to 100 parts by weight of CB with respect to 100 parts by weight of NR raw latex (solid content). 3. The total amount of the CB-containing natural rubber masterbatch is 10 to 60 parts by weight per 100 parts by weight of the total rubber in the final rubber composition, based on the total CB. The amount should be 30 to 70 parts by weight,
The amount of silica added is 10 per 100 parts by weight of the total rubber.
The rubber composition according to claim 1 or 2, wherein the total amount of the filler is 90 parts by weight or less. 4. The rubber composition according to claim 1, wherein the raw rubber is a styrene-butadiene copolymer rubber (SBR) obtained by a solution polymerization and / or emulsion polymerization method. 5. The rubber composition according to claim 1, further comprising a sulfur-containing silane coupling agent. 6. A pneumatic tire composed of a rubber member using the rubber composition according to claim 1.