JPH10226736A - Rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition which can give a vulcanizate having well balanced tan δ without detriment to abrasion resistance and is desirable for use as a rubber composition for tire treads. SOLUTION: This composition is prepared by kneading a carbon-black- containing rubber composition obtained by the coagulation, dehydration and drying of a rubber latex mixture containing 50-90 pts.wt (in terms of the solid matter) latex of at least one stock rubber A having an average glass transition temperature TgA of -120 deg.C to -15 deg.C, 40-100 pts.wt. carbon black and at most 70 pts.wt. softener, a stock rubber B in an amount to give a total rubber content of 100 pts.wt. and a softener in an amount to give a total softener content of 80 pts.wt. or below with a sealed mixer. The ratio FA/FB should be 1.2 to 3.0 (wherein FA is the concentration of carbon black based on the rubber polymer in the rubber latex mixture, and FB is the concentration of carbon black based on the rubber polymer after kneading with the mixer).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon black-containing rubber composition, and more particularly to a carbon black-containing rubber composition suitable for use in a cap tread of a pneumatic tire.

[0002]

2. Description of the Related Art It has been proposed to improve the balance of tan δ of tire tread rubber in order to reduce the fuel consumption of automobiles. Proposed.

For example, Japanese Unexamined Patent Publication (Kokai) No. 59-159839 discloses a rubber composition obtained by dry-mixing SBR and BR having different styrene contents, and Japanese Unexamined Patent Publication (Kokai) No. 2-129241 discloses a solution in which a terminal-modified / coupling rubber is prepared as a solution. A method for producing a rubber composition in which a rubber composition is mixed with carbon black and then a diene rubber is compounded. On the other hand, JP-A-58-
Japanese Patent No. 152031 discloses a master batch composed of SBR and BR.
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes producing a rubber composition by dividing and mixing a high molecular weight rubber and a low molecular weight rubber. Furthermore, JP-A-8-269243 discloses a high glass transition point S.
Low glass transition point SB containing BR and carbon black in advance
Blending with R masterbatch is disclosed.

[0004]

However, the above-mentioned techniques such as the split mixing method of the blending components and the use of the terminal-modified rubber have problems such as that the effect is weak in a high blending system of oil and carbon black. There is still a need for improvement. Further, in the case of the split mixing, the carbon black concentration increases at the time of the first mixing, which is expected to cause deterioration in workability such as scorch (scorch) at the time of mixing. There is a problem that the amount is limited. In addition, since a desired effect cannot be obtained by using a commonly used master batch, it is essential to devise a master batch.

Accordingly, an object of the present invention is to provide a rubber composition which can be suitably used for a tire tread excellent in tan δ balance of a vulcanized rubber while maintaining abrasion resistance.

[0006]

According to the present invention, 50 to 90 parts by weight of a latex of at least one kind of raw rubber A having an average glass transition temperature TgA of -120 ° C to -15 ° C (in terms of solid content), carbon A carbon black-containing rubber composition obtained by coagulating, dewatering, and drying a rubber latex mixture containing 40 to 100 parts by weight of black and 70 parts by weight or less of a softening agent, and a raw rubber B having a total rubber amount of 100 parts by weight And a softening agent having a total softening agent amount of 80 parts by weight or less is kneaded with an internal mixer, the carbon black concentration F _A with respect to the rubber polymer in the rubber latex mixture, and the rubber kneaded with the internal mixer. rubber composition is provided the ratio F _a / F _B of carbon black concentration F _B to the polymer is 1.2 to 3.0.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the structure, operation and effect of the present invention will be described in detail. The present inventors have determined that the t
found that anδ is almost independent of the rubber-adsorbed phase near fillers such as carbon black, and was found to be solely due to the matrix phase.Improving the tanδ balance by isolating the carbon black surface from the matrix phase as much as possible Was successful.

Further, the inventors of the present invention preferentially disperse carbon black to the high Tg and low Tg raw rubbers and distribute the carbon black unevenly to the low Tg raw rubbers to obtain a tan of 60 ° C. with respect to 0 ° C.
It has been found that the temperature gradient of δ is good and that the tan δ balance can be improved by using this.

Therefore, in the present invention, from the viewpoint of the interaction between the carbon black and the rubber, tan δ is controlled by preventing the rubber matrix phase far from the carbon inside the compound from being restricted by the carbon. It is a thing. Specifically, the average glass transition temperature T
gA is -120 ° C to -15 ° C, preferably -120 ° C to
A master batch composed of the latex of the raw material rubber of Group A at −20 ° C. and carbon black, the raw rubber B having an average glass transition temperature TgB of TgA + 10 ° C. or higher, and a softener and other rubber additives are mixed by an internal mixer. By doing so, a desired rubber composition can be obtained.

The carbon black used in the present invention is preferably used for a tire tread.
Nitrogen adsorption specific surface area (N ₂ SA) (ASTM D 303
7 is 50 to 200 m ² / g, more preferably 80 to 160 m ² / g, and dibutyl phthalate (DBP) oil absorption (measured according to JIS K 6221) is preferably 60 to 140 ml / g. Use 100 g, more preferably 100-130 ml / 100 g. The carbon black may be an organic or inorganic surface treatment for increasing the bonding with rubber or a material obtained by attaching a small amount of metal oxide such as silica to the surface. The compounding amount of carbon black compounded in the rubber composition of the present invention, that is, the carbon-containing rubber composition, is such that the final rubber polymer amount
40 to 100 parts by weight, preferably 5 to 100 parts by weight
0 to 100 parts by weight. If the compounding amount of the carbon black is too small, the reinforcing property decreases, and desired physical properties cannot be obtained. Conversely, if the compounding amount is too large, it becomes difficult to produce a carbon black master batch, which is not preferable.

The carbon masterbatch according to the present invention is most preferably a wet masterbatch in which a raw rubber latex and carbon black are mixed in an aqueous system. In a dry masterbatch mixed with an internal mixer (that is, a split mixing method), when rubber and carbon black are mixed in a mixer, the rubber molecules undergo mechanical shearing, and molecular cutting proceeds. The balance of the reinforcing properties is lost, and the abrasion resistance and the like are inferior to those of the wet master batch.

The rubber polymer contained in the carbon black masterbatch according to the present invention, ie, the rubber mixture containing carbon black, is not particularly limited as long as it satisfies the above glass transition temperature TgA. It is a system polymer. Such conjugated diene polymers include butadiene, isoprene, pentadiene,
One or more polymers or copolymers of conjugated dienes such as chloroprene, at least one conjugated diene and at least one monomer copolymerizable therewith, for example, styrene, vinyltoluene, α-methylstyrene Aromatic vinyl compounds such as, acrylonitrile, unsaturated nitrile compounds such as methacrylonitrile, acrylic acid, methacrylic acid,
Examples thereof include copolymers with unsaturated carboxylic acids such as maleic acid and maleic anhydride, and esters of unsaturated carboxylic acids such as methyl acrylate, ethyl acrylate, butyl acrylate, and methoxyethyl acrylate. A particularly preferred polymer is a block copolymer having a polymer block mainly composed of a conjugated diene and a polymer block mainly composed of an aromatic vinyl compound. The boundaries between each block of the block copolymer may be clear or unclear. The proportion of each block is from 0 to 100% by weight of a conjugated diene.
0 to 100% by weight of aromatic vinyl diene, preferably 20 to 80% by weight of conjugated diene, 20 to 8% of aromatic vinyl diene
0% by weight.

The amount of the rubber polymer varies depending on the kind of the raw material rubber to be added, each content in the polymer, the molecular weight of the polymer, etc., but generally 50% of the rubber polymer content of 100 parts by weight. To 90 parts by weight, preferably 50 to 70 parts by weight
Parts by weight. If the amount of the rubber polymer is too small, it is difficult to produce a carbon master batch,
Conversely, if it is too large, the desired effect cannot be obtained, which is not preferable.

The method of compounding the carbon black-containing latex containing the raw material rubber A is not particularly limited. Generally, a mixture obtained by uniformly dispersing carbon black and a softening agent in rubber latex is mixed and stirred, and then coagulated according to a conventional method. ,
Dehydration and drying may be performed. As the softening agent used here, aromatic process oil, paraffin oil, etc.
Generally, 70 parts by weight or less, preferably 0 to 55 parts by weight, of those used for rubber compounding is added.

On the other hand, the raw material rubber B is not particularly limited as long as it satisfies the above glass transition temperature, but is preferably a diene-based raw rubber (polybutadiene, styrene-butadiene copolymer, styrene-
Isoprene-butadiene copolymer, polyisoprene and natural rubber).

The compounding amount of these raw rubbers B is 100 parts by weight as a whole rubber, that is, 50 to 10 parts by weight. If necessary, together with an additional softener and other general rubber additives, The desired rubber composition can be obtained by kneading with the carbon black-containing rubber composition in a closed mixer such as a Banbury mixer.

According to the present invention, the raw rubber A has an average weight average molecular weight Mw (A) of 100,000 to 1.2 million, and the raw rubber B has an average weight average molecular weight Mw (B) of 200,000 or more. And 0.1 ≦ Mw (A) / Mw (B) ≦ 6.0
It is preferable that the following relationship is satisfied.

According to the present invention, there is also provided a carbon black concentration F _A for the rubber polymer in the rubber latex mixture.
If, in an internal mixer the ratio F _A / F _B of carbon black concentration F _B to rubber polymer after kneading 1.2
It is preferably 3.0.

According to the present invention, when the tan δ (0 ° C.) of the rubber composition used for the cap tread is 0.4 or more, the t
It is preferable that an δ (60 ° C.) is 0.1 or more.

[0020]

EXAMPLES Hereinafter, the contents and effects of the present invention will be described more specifically with reference to standard examples, examples and comparative examples, but it is needless to say that the scope of the present invention is not limited to these examples. . Standard Examples 1 to 10, Examples 1 to 10, and Comparative Examples 1 to 10 Rubber compositions of various formulations shown in Tables I to V were prepared and their physical properties were evaluated.

The components used in the formulations of the standard examples, examples and comparative examples are as follows.

Masterbatch 1-3 Raw material rubber latex: Styrene butadiene / copolymer rubber latex having 25% styrene content, 16% vinyl content, glass transition temperature -51 ° C, and weight average molecular weight of 620,000 Carbon black: N ₂ SA (M ² / g) is 112, D
ISAF-grade carbon black having a BP oil absorption (ml / 100 g) of 112 Softener: Aromatic process oil ─────── Raw rubber latex carbon black Softener (parts by weight) (parts by weight) (parts by weight) ──────────────────────── ─────────── Master batch 1 50 75 50 Master batch 2 50 60 35 Master batch 3 50 50 25 ───────────────────── ──────────────

Masterbatch 4-5 Raw material rubber latex: Styrene butadiene / copolymer rubber latex having a styrene content of 25%, a vinyl content of 16%, a glass transition temperature of -51 ° C. and a weight average molecular weight of 620,000 Carbon black: N ₂ SA (M ² / g) is 92, DB
HAF-grade carbon black with P oil absorption (ml / 100g) of 117 Softener: Aromatic process oil ─────── Raw rubber latex carbon black Softener (parts by weight) (parts by weight) (parts by weight) ──────────────────────── ─────────── Master batch 4 70 85 50 Master batch 5 70 65 30 ─────────────────────────── ────────

Master batch 6 to 7 Raw rubber latex: polyisoprene rubber latex having a glass transition temperature of -63 ° C and a weight average molecular weight of 1.2 million and c having a glass transition temperature of -106 ° C and a weight average molecular weight of 650,000
is-polybutadiene rubber latex carbon black: N ₂ SA (m ² / g) is 84, DB
HAF-grade carbon black with a P oil absorption (ml / 100 g) of 130 Softener: Aromatic process oil ─────── Raw rubber latex carbon black Softener (parts by weight) (parts by weight) (parts by weight) ──────────────────────── ─────────── Master batch 6 50 50 10 Master batch 7 Isoprene: 50 50 10 Butadiene: 20 ────────────────────── ─────────────

Masterbatch 8 Raw rubber latex: styrene butadiene / copolymer rubber latex having a styrene content of 36%, a vinyl content of 16%, a glass transition temperature of -36 ° C. and a weight average molecular weight of 820,000 carbon black: N ₂ SA (m ² / g) is 153, D
HAF-grade carbon black having a BP oil absorption (ml / 100 g) of 127 Softener: Aromatic process oil ─────── Raw rubber latex carbon black Softener (parts by weight) (parts by weight) (parts by weight) ──────────────────────── ─────────── Master batch 8 60 95 52 ───────────────────────────────── ── (Note: The amount of raw rubber latex is the amount in terms of solid content)

Masterbatch 9 Raw rubber latex: Styrene butadiene / copolymer rubber latex having a styrene content of 25%, a vinyl content of 16%, a glass transition temperature of -51 ° C. and a weight average molecular weight of 620,000 carbon black: N ₂ SA (m ² / g) is 112, D
ISAF-grade carbon black having a BP oil absorption (ml / 100 g) of 112 Softener: Aromatic process oil ─────── Raw rubber latex carbon black Softener (parts by weight) (parts by weight) (parts by weight) ──────────────────────── ─────────── Master batch 9 100 60 34 ───────────────────────────────── ──

Other ingredients SBR1: Styrene content 36%, vinyl content 16
50.0 phr oil-extended emulsion-polymerized styrene-butadiene copolymer rubber having a glass transition temperature of -36 ° C and a weight average molecular weight of 720,000 SBR2: styrene content 25%, vinyl content 16
%, 37.5 phr oil-extended emulsion-polymerized styrene-butadiene copolymer rubber having a glass transition temperature of -51 ° C and a weight average molecular weight of 620,000 SBR3: styrene content 35%, vinyl content 14
50.0 phr oil-extended emulsion-polymerized styrene-butadiene copolymer rubber having a glass transition temperature of -36 ° C and a weight average molecular weight of 820,000 SBR4: styrene content 48%, vinyl content 13
20.0 phr oil-extended emulsion-polymerized styrene-butadiene copolymer rubber having a glass transition temperature of -21 ° C and a weight average molecular weight of 1.28 million

IR: isoprene copolymer rubber having a glass transition temperature of -63 ° C. and a weight average molecular weight of 870,000 cis-BR: cis-type butadiene copolymer rubber having a glass transition temperature of -106 ° C. and a weight average molecular weight of 650,000

Carbon black 1: N ₂ SA (m ² /
g) is 112, DBP oil absorption (ml / 100g) is 112
Carbon black 2: N ₂ SA (m ² / g) of 92, D
HAF-grade carbon black having a BP oil absorption (ml / 100 g) of 117 Carbon black 3: N ₂ SA (m ² / g) of 84, D
HAF-grade carbon black having a BP oil absorption (ml / 100 g) of 130 carbon black 4: N ₂ SA (m ² / g) of 153
SAF grade carbon black with DBP oil absorption (ml / 100g) of 127

SBR5: Solution-polymerized styrene-butadiene copolymer rubber having a styrene content of 21%, a vinyl content of 67%, a glass transition temperature of -30 ° C. and a weight average molecular weight of 360,000 SBR6: a styrene content of 40% and a vinyl content of 35
%, Glass transition temperature -26 ° C, weight average molecular weight 900,000 37.5 phr oil-extended solution polymerized styrene-butadiene copolymer rubber

Zinc oxide: Zinc flower No. 3 Stearic acid: Industrial stearic acid Antioxidant 6C: N-phenyl-N '-(1,3-dimethylbutyl) -p-phenylenediamine Softener: Aromatic process oil Wax : Industrial paraffin wax Powder sulfur: Powder sulfur treated with 5% oil Vulcanization accelerator NS: N-tert-butyl-2-benzothiazolylsulfenamide Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazyl Sulfenamide Vulcanization accelerator DPG: diphenylguanidine

Sample Preparation As a first step, each component shown in Table I was kneaded in a 1.8 liter closed mixer for 3 to 5 minutes and released when the temperature reached 165 ± 5 ° C. Next, as a final step, a vulcanization accelerator and sulfur were kneaded with an 8-inch open roll to obtain a rubber composition. In the case of two-step mixing as a comparative example, the first step is performed by kneading for 3 to 4 minutes with a 1.8-liter closed mixer,
Release when 150 ± 5 ° C. is reached, then in a second step 3-5 with a 1.8 liter closed mixer with the remaining ingredients.
The mixture was kneaded for one minute and released when the temperature reached 165 ± 5 ° C. Then, as a final step, a vulcanization accelerator and sulfur were kneaded with an 8-inch open roll to obtain a rubber composition. In the case of one-step mixing, the components other than the vulcanization accelerator and sulfur are kneaded in a 1.8-liter closed mixer for 3 to 4 minutes, and released when the temperature reaches 165 ± 5 ° C. The agent and sulfur were kneaded with an 8-inch open roll to obtain a rubber composition.

The sample composition was press-vulcanized in a mold of 15 × 15 × 0.2 cm at 160 ° C. for 20 minutes to prepare a target test piece, and the vulcanization properties were evaluated.

The method for testing the vulcanizate properties of the composition obtained in each example is as follows. 1) 300% deformation stress, breaking strength: JIS K 625
1 (measured in accordance with No. 3 dumbbell type) 2) tan δ: Measured with a rheograph solid manufactured by Toyo Seiki Seisakusho at 20 Hz, initial elongation 10%, dynamic strain 2% (sample width 5 mm, temperature 0 ° C.) 3) Abrasion resistance: Measured with a Lambourn-type abrasion tester, and the loss on abrasion is indicated by an index according to the following method.

Abrasion resistance (index) = [(weight loss in reference test piece) / (weight loss in each test piece)] × 100 However, the reference test pieces are shown in Tables I to II as standard examples 1 and 2, respectively. In Table III, the results were calculated as Standard Example 6, in Table IV, Standard Example 8, and in Table V, as Standard Example 9.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

As described above, according to the present invention, the use of a master batch can improve the burn during mixing and further improve the balance of tan δ. It is possible to achieve the same or better improvement effect of split mixing for any carbon concentration without considering the burn during mixing due to the increase in carbon concentration in conventional split mixing. It is also available for systems.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 20, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

The rubber polymer contained in the carbon black masterbatch according to the present invention, ie, the rubber mixture containing carbon black, is not particularly limited as long as it satisfies the above glass transition temperature TgA. It is a system polymer. Such conjugated diene polymers include butadiene, isoprene, pentadiene,
One or more polymers or copolymers of conjugated dienes such as chloroprene, at least one conjugated diene and at least one monomer copolymerizable therewith, for example, styrene, vinyltoluene, α-methylstyrene Aromatic vinyl compounds such as, acrylonitrile, unsaturated nitrile compounds such as methacrylonitrile, acrylic acid, methacrylic acid,
Examples thereof include copolymers with unsaturated carboxylic acids such as maleic acid and maleic anhydride, and esters of unsaturated carboxylic acids such as methyl acrylate, ethyl acrylate, butyl acrylate, and methoxyethyl acrylate.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09C 3/10 C09C 3/10

Claims (7)

[Claims] 1. An average glass transition temperature TgA of -120 ° C.
Coagulation, dehydration and drying of a rubber latex mixture containing 50 to 90 parts by weight of a latex of raw rubber A at 50 to -15 ° C (in terms of solid content), 40 to 100 parts by weight of carbon black and 70 parts by weight or less of a softening agent The rubber composition containing carbon black obtained by
Raw rubber B in an amount of 00 parts by weight and a total softener amount of 8
0 parts by weight or less of a softening agent is kneaded in a closed mixer, and the carbon black concentration F _A for the rubber polymer in the rubber latex mixture and the carbon black concentration F for the rubber polymer after kneading in the closed mixer.
The ratio F _A / F _B is a rubber composition which is 1.2 to 3.0 with _B. 2. The average glass transition temperature TgB of raw rubber B
2. The rubber composition according to claim 1, wherein TgA + 10 (° C.) ≦ TgB. 3. The average weight average molecular weight Mw of the raw rubber A
(A) is 100,000 to 1.2 million, the average weight average molecular weight Mw (B) of the raw rubber B is 200,000 or more, and 0.1 ≦ Mw (A) / Mw (B) ≦ 6.0. The rubber composition according to claim 1 or 2, wherein 4. The nitrogen specific surface area of carbon black (N ₂
The rubber composition according to any one of claims 1 to 3, wherein SA) is 50 to 200 m ² / g, and dibutyl phthalate (DBP) oil absorption is 60 to 140 ml / 100 g. 5. A styrene-butadiene copolymer rubber (SB) obtained by raw material rubber B obtained by solution polymerization and / or emulsion polymerization.
The rubber composition according to any one of claims 1 to 4, which is R). 6. A pneumatic tire comprising a cap tread portion using the rubber composition according to claim 1. Description: 7. The pneumatic tire according to claim 6, wherein the rubber composition has a tan δ (0 ° C.) of 0.4 or more and a tan δ (60 ° C.) of 0.1 or more.