Provided are a rubber composition for a tread, capable of improving the fuel economy and abrasion resistance in a balanced manner while achieving a good appearance and a good cure rate; and a pneumatic tire containing the rubber composition. The present invention relates to a rubber composition for a tread, including: a solution-polymerized styrene-butadiene rubber, carbon black, silica, and polyethylene glycol, wherein a rubber component of the rubber composition contains 60 mass % or more of the solution-polymerized styrene-butadiene rubber based on 100 mass % of the rubber component, and the rubber composition includes, per 100 parts by mass of the rubber component, 10 parts by mass or less of the carbon black, 50 parts by mass or more of the silica, and 0.1 to 3.5 parts by mass of the polyethylene glycol.
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1. A pneumatic tire, comprising a tread formed from a rubber composition for a tread, comprising:
a modified solution-polymerized styrene-butadiene rubber,
a non-modified solution-polymerized styrene-butadiene rubber,
carbon black having a nitrogen adsorption specific surface area of 70 m2/g or more,
silica, and
polyethylene glycol,
the modified solution-polymerized styrene-butadiene rubber being one modified with a compound represented by the following formula (1):
##STR00002##
wherein, in formula (1), R1, R2, and R3 are the same as or different from one another, and each represents an alkyl, alkoxy, silyloxy, acetal, carboxyl or mercapto group, or a derivative thereof; R4 and R5 are the same as or different from each other, and each represents a hydrogen atom or an alkyl group; and the symbol n represents an integer; and
wherein a rubber component of the rubber composition contains 60 mass % or more of the modified solution-polymerized styrene-butadiene rubber based on 100 mass % of the rubber component, and
the rubber composition comprises, per 100 parts by mass of the rubber component, 10 parts by mass or less of the carbon black, 50 parts by mass or more of the silica, and 0.1 to 3.5 parts by mass of the polyethylene glycol.
2. The rubber composition for a tread pneumatic tire according to
3. The rubber composition for a tread pneumatic tire according to
4. The rubber composition for a tread pneumatic tire according to
5. The rubber composition for a tread pneumatic tire according to
wherein, in the rubber composition, the amount of the modified solution-polymerized styrene-butadiene rubber is 30 to 80 mass %, and the amount of the non-modified solution-polymerized styrene-butadiene rubber is 20 to 50 mass %, based on 100 mass % of the rubber component, and
the blending ratio between the modified solution-polymerized styrene-butadiene rubber and the non-modified solution-polymerized styrene-butadiene rubber is 30/70 to 90/10 30/50 to 80/20.
6. The rubber composition for a tread pneumatic tire according to
7. The rubber composition for a tread pneumatic tire according to
wherein, in the rubber composition, the proportion of the silica based on 100 mass % in total of the silica and the carbon black is 60 mass % or more, and
the combined amount of the carbon black and the silica per 100 parts by mass of the rubber component is 60 to 130 parts by mass.
8. The rubber composition for a tread pneumatic tire according to
wherein, per 100 parts by mass of the rubber component, the amount of sulfur is 0.3 to 3.0 parts by mass, the amount of vulcanization accelerator is 1 to 5 parts by mass, and the amount of oil is 5 to 30 parts by mass
wherein the rubber composition further comprises sulfur, a vulcanizing agent, and an oil; and
wherein, in the rubber composition, the amount of sulfur is 0.3 to 3.0 parts by mass, the amount of vulcanization accelerator is 1 to 5 parts by mass, and the amount of oil is 5 to 30 parts by mass, per 100 parts by mass of the rubber component.
0. 9. A pneumatic tire, comprising a tread formed from the rubber composition according to
0. 10. A pneumatic tire, comprising a tread formed from the rubber composition according to
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In terms of achieving a good cure rate and good abrasion resistance, p is preferably 80 to 100.
The polyethylene glycol preferably has a weight average molecular weight of 1000 or more, more preferably 3000 or more. The weight average molecular weight is preferably 10000 or less, and more preferably 5000 or less. The polyethylene glycol with a weight average molecular weight within the range mentioned above provides better cure rate and better abrasion resistance, thereby contributing to achieving the effects of the present invention well.
Herein, the weight average molecular weight (Mw) of polyethylene glycol can be determined by gel filtration chromatography using an LC-6A device, an RID-10A detector (both produced by Shimadzu Corporation) and an Asahipak GF-510HQ column (7.6 mm diameter×0.3 m long, produced by Showa Denko K.K.) with a water mobile phase at a flow rate of 1 mL/min and a temperature of 30° C.
The amount of polyethylene glycol per 100 parts by mass of the rubber component is 0.1 parts by mass or more, preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more. If the amount is less than 0.1 parts by mass, the effects of the invention may not be well achieved, The amount is 3.5 parts by mass or less, preferably 3 parts by mass or less, and more preferably 2.5 parts by mass or less. An amount of more than 3.5 parts by mass tends to cause too short a scorch time.
The rubber composition of the present invention preferably contains sulfur as a vulcanizing agent. The amount of sulfur per 100 parts by mass of the rubber component is preferably 0.3 to 3.0 parts by mass, more preferably 0.5 to 2.5 parts by mass, and still more preferably 1.0 to 2.0 parts by mass. An amount of less than 0.5 parts by mass tends to cause a slow cure rate and undercure and thus fail to achieve sufficient abrasion resistance and the like. Conversely, an amount of more than 3.0 parts by mass tends to cause a rapid cure rate and compound scorch and thus reduce the abrasion resistance and the like.
The rubber composition of the present invention typically contains a vulcanization accelerator. The vulcanization accelerator is not particularly limited and may be any commonly used vulcanization accelerator, including guanidine compounds, aldehyde-amine compounds, aldehyde-ammonia compounds, thiazole compounds, sulfenamide compounds, thiourea compounds, thiuram compounds, dithiocarbamate compounds, and xanthate compounds. These vulcanization accelerators may be used alone, or two or more of these may be used in combination.
From the viewpoints of dispersibility into the rubber compound and stability of the vulcanization properties, preferred among these are sulfonamide vulcanization accelerators (e.g., N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), N,N-diisopropyl-2-benzothiazolesulfenamide), and guanidine vulcanization accelerators (e.g., N,N′-diphenylguanidine (DPG), di-ortho-tolylguanidine, triphenylguanidine, orthotolyl biguanide, diphenylguanidine phthalate). More preferred are combinations of sulfenamide vulcanization accelerators with guanidine vulcanization accelerators, and particularly preferred is a combination of CBS and DPG.
The amount of vulcanization accelerator per 100 parts by mass of the rubber component is preferably 1 to 5 parts by mass, and more preferably 2 to 4 parts by mass. Since the rubber composition of the present invention contains the components mentioned above to achieve a good cure rate, the amount of vulcanization accelerator can be reduced to give a good appearance.
In addition to the above components, the rubber composition of the present invention may optionally contain compounding agents generally used for production of rubber compositions, such as various antioxidants, stearic acid, zinc oxide, waxes, oils, and vulcanizing agents.
Examples of oils include process oils, vegetable fats and oils, and mixtures of these. Examples of process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils.
If the rubber composition of the present invention contains an oil (s), the amount of oil per 100 parts by mass of the rubber component is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, whereas it is preferably 30 parts by mass or less, and more preferably 20 parts by mass or less.
The rubber composition of the present invention can be prepared by an ordinary method. Specifically, in an exemplary preparation method, the above components are kneaded in a Banbury mixer, a kneader, an open roll mill or the like, and then vulcanized.
The rubber composition of the present invention is for use in a tread of a tire.
The pneumatic tire of the present invention may be prepared using the rubber composition by an ordinary method. Specifically, an unvulcanized rubber composition containing the above components is extruded into a tread shape, and assembled with other tire components in a usual manner in a tire building machine to build an unvulcanized tire. This unvulcanized tire is heat-pressurized in a vulcanizer to form a tire.
The pneumatic tire of the present invention can be suitably used as a tire for passenger vehicles or the like.
Hereinafter, the present invention will be described in more detail with reference to examples which are not intended to limit the scope of the present invention.
The following are the list of various chemicals used in the examples and comparative examples.
SSBR (1): HPR355 (solution-polymerized SBR (terminated with an alkoxysilane by coupling; R1, R2, and R3 each represent —OCH3; R4 and R5 each represent H; n represents 3) produced by JSR Corporation, styrene content: 28 mass %, vinyl content: 56 mass %)
SSBR (2): T3830 (Tufdene 3830) (solution-polymerized SBR, styrene content: 33 mass %, vinyl content: 34 mass %, Mw: 950,000, Mn: 370,000, Mw/Mn: 2.6; containing 37.5 parts by mass of oil per 100 parts by mass of rubber solids) produced by Asahi Kasei Corp.
SSBR (3): modified SBR (solution-polymerized SBR (terminated with an alkoxysilane by coupling; R1, R2, and R3 each represent —OCH3; R4 and R5 each represent —CH2CH3; n represents 3) produced by Sumitomo Chemical Co., Ltd., styrene content: 25 mass %, vinyl content: 57 mass %)
BR: Nipol BR 1220 (cis content: 97 mass % or more) produced by ZEON CORPORATION
NR: TSR
Carbon black: Seast N220 (N2SA: 114 m2/g) produced by Mitsubishi Chemical Corporation
Silica: Ultrasil VN3 (average primary particle size: 15 nm, N2SA: 175 m2/g) produced by Evonik Degussa
Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) produced by Evonik Degussa
Aromatic oil: Process X-140 produced by JX Nippon Oil & Energy Corporation
Wax: Sunnoc N produced by Ouchi Shinko Chemical Industrial Co., Ltd.
Antioxidant: Antigone 6C (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine) produced by Sumitomo Chemical Co., Ltd.
Stearic acid: stearic acid “Tsubaki” produced by NOF Corporation
PEG: PEG #4000 (polyethylene glycol, weight average molecular weight: 4000) (HO(CH2CH2O)pH where p is about 90) produced by NOF Corporation
Zinc oxide: zinc oxide #1 produced by Mitsui Mining & Smelting Co., Ltd.
Sulfur: powdered sulfur produced by Karuizawa sulfur
Vulcanization accelerator (1): Nocceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) produced by Ouchi Shinko Chemical Industrial Co., Ltd.
Vulcanization accelerator (2): Nocceler D (N,N′-diphenylguanidine) produced by Ouchi Shinko Chemical Industrial Co., Ltd.
According to each of the formulations shown in Table 1, the chemicals, excepting the sulfur and vulcanization accelerators, were kneaded in a 1.7-L Banbury mixer produced by Kobe Steel, Ltd. To the resulting kneaded mixture were then added the sulfur and vulcanization accelerators, and the mixture was kneaded using an open roll mill to prepare an unvulcanized rubber composition. The unvulcanized rubber composition was press vulcanized in a 2-mm-thick mold at 170° C. for 15 minutes to prepare a vulcanized rubber composition (vulcanized rubber sheet).
Also, the unvulcanized rubber composition was formed into a tread shape and assembled with other tire components in a tire building machine, and the assembly was vulcanized at 170° C. for 15 minutes to prepare a test tire (tire size: 195/65R15).
The obtained unvulcanized rubber compositions, vulcanized rubber compositions, and test tires were evaluated for the following items. Table 1 shows the results.
(Mooney Viscosity, Scorch Time)
The measurement was performed using a Mooney viscosity tester “Mooney viscometer SMV-202” produced by Shimadzu Corporation in conformity with JIS K6300, “Rubber, unvulcanized—Physical testing methods”. The temperature of the tester was conditioned to 130° C. by 1-minute preheating and a small rotor was rotated at this temperature. The Mooney viscosity (ML1+4) of each unvulcanized rubber composition was measured after four-minute rotation of the small rotor. The time (scorch time (min): T5) at which the viscosity of the unvulcanized rubber composition rose by five points was also measured. Lower Mooney viscosity indicates better processability, and a shorter scorch time indicates a shorter cure time.
A scorch time of at least 15 minutes but shorter than 25 minutes is particularly good from the viewpoint of both cure time and extrusion processability. A scorch time of at least 10 minutes but shorter than 15 minutes is likely to cause compound scorch in the extrusion process, and a scorch time of shorter than 10 minutes causes compound scorch. A scorch time of 25 minutes or longer causes too long a cure time.
(Processability)
The processability was evaluated depending on the scorch time data according to the following criteria.
Good: The scorch time is at least 15 minutes but shorter than 25 minutes.
Acceptable: The scorch time is at least 10 minutes but shorter than 15 minutes, or at least 25 minutes but shorter than 30 minutes.
Poor: The scorch time is shorter than 10 minutes, or 30 minutes or longer.
(Hs)
The hardness (Hs) of each vulcanized rubber sheet was measured in conformity with JIS K6253. The measuring temperature was 23° C.
(Viscoelasticity Test)
Using a viscoelasticity spectrometer produced by Iwamoto Seisakusho Co., Ltd., the loss tangent (tan δ) and complex viscoelastic modulus (E*) at 70° C. of each vulcanized rubber sheet were determined at a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 2%. The tan δ and E* values of each rubber formulation are each expressed as an index (tan δ index or E* index) relative to that of Comparative Example 1 (=100). A higher tan δ index indicates less heat build-up and better fuel economy, and a higher E*index indicates higher E* and higher rubber hardness.
(Abrasion Resistance)
The test tires of each formulation example were mounted on a car and the car was driven 30,000 km. Then, the changes in the groove depth of the tread before and after driving were measured. The mileage at which the groove depth was reduced by 1 mm was determined and the value obtained is expressed as an index calculated from the following formula. A higher index indicates better abrasion resistance.
(Abrasion resistance index)=(the mileage at which the groove depth was reduced by 1 mm in each formulation example)/(the mileage at which the groove depth was reduced by 1 mm in Comparative Example 1)×100
(Bloom Test)
Each vulcanized rubber sheet was left in a sunny place for one month. The appearance of the resulting sheet was visually observed for evaluation according to the following criteria.
Very good: The sheet did not turn white.
Good: The sheet turned slightly white.
Poor: The sheet turned white and thus had a poor appearance.
| TABLE 1 | |||||||||||
| Com- | Com- | Com- | Com- | Com- | Com- | ||||||
| parative | parative | Exam- | Exam- | Exam- | parative | parative | parative | parative | Exam- | ||
| Example 1 | Example 2 | ple 1 | ple 2 | ple 3 | Example 3 | Example 4 | Example 5 | Example 6 | ple 4 | ||
| Chemical | SSBR (1 ) | 55 | 55 | 55 | 55 | 55 | 26 | 55 | 55 | 55 | 55 |
| Material | SSBR (2) | 48 | 48 | 48 | 48 | 48 | 37.3 | 48 | 48 | 48 | 48 |
| Composition | (net rubber | (30) | (30) | (30) | (30) | (30) | (14) | (30) | (30) | (30) | (30) |
| (parts by mass) | content) | ||||||||||
| BR | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | |
| NR | — | — | — | — | — | 45 | — | — | — | — | |
| Carbon black | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 35 | 5 | 5 | |
| Silica | 75 | 75 | 75 | 75 | 75 | 75 | 75 | 45 | 75 | 75 | |
| Silane coupling | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 3.6 | 6 | 6 | |
| agent | |||||||||||
| Aromatic oil | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | 15 | |
| Wax | 2.5 | 2.5 | 2.5 | 23 | 2.5 | 2.5 | 23 | 2.5 | 2.5 | 2.5 | |
| Antioxidant | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | |
| Stearic acid | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 23 | 2.5 | 2.5 | 2.5 | |
| PEG | — | — | 0.3 | 3 | 3 | 3 | 10 | 3 | — | 1.5 | |
| Zinc oxicide | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 2.5 | 23 | 2.5 | 2.5 | |
| Sulfur | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | 1.5 | |
| Vulcanization | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 | |
| Accelerator (1) | |||||||||||
| Vulcanization | 2 | 2.5 | 1.5 | 1.5 | 0.8 | 0.6 | 0.8 | 0.8 | 1.5 | 1.5 | |
| accelerator (2) | |||||||||||
| Total | 234.5 | 2.35 | 234.3 | 237 | 236.3 | 241.4 | 243.3 | 233.9 | 234 | 234 | |
| Evaluation | Mooney | 65 | 65 | 64 | 60 | 60 | 52 | 55 | 58 | 65 | 60 |
| viscosity | |||||||||||
| Scorch time | 32 | 22 | 22 | 16 | 18 | 5 | 6 | 7 | 40 | 18 | |
| Processability | Poor | Good | Good | Good | Good | Poor | Poor | Poor | Poor | Good | |
| Hs | 66 | 66 | 66 | 66 | 66 | 65 | 65 | 66 | 66 | 66 | |
| E* (Mpa) index | 100 | 102 | 100 | 99 | 98 | 95 | 95 | 99 | 100 | 99 | |
| tan δ index | 100 | 99 | 100 | 99 | 98 | 98 | 100 | 104 | 100 | 99 | |
| Abrasion | 100 | 99 | 103 | 107 | 106 | 100 | 105 | 104 | 100 | 108 | |
| resistance index | |||||||||||
| Bloom test | Good | Poor | Good | Good | Very good | Good | Very good | Good | Very good | Good | |
| TABLE 2 | |||
| Comparative | Example | ||
| Example 7 | 5 | ||
| Chemical Material | SSBR (3) | 55 | 55 |
| Composition | SSBR (2) | 48 (30) | 48 (30) |
| (parts by mass) | (net rubber content) | ||
| BR | 15 | 15 | |
| NR | — | — | |
| Carbon black | 5 | 5 | |
| Silica | 75 | 75 | |
| Silane coupling agent | 6 | 6 | |
| Aromatic oil | 15 | 15 | |
| Wax | 2.5 | 2.5 | |
| Antioxidant | 2.5 | 2.5 | |
| Stearic acid | 2.5 | 2.5 | |
| PEG | — | 3 | |
| Zinc oxicide | 2.5 | 2.5 | |
| Sulfur | 1.5 | 1.5 | |
| Vulcanization accelerator (1) | 2 | 2 | |
| Vulcanization accelerator (2) | 2 | 1.5 | |
| Total | 234.5 | 237 | |
| Evaluation | Mooney viscosity | 65 | 62 |
| Scorch time | 31 | 16 | |
| Processability | Poor | Good | |
| Hs | 66 | 67 | |
| E* (Mps) index | 100 | 100 | |
| tan δ index | 100 | 99 | |
| Abrasion resistance index | 100 | 106 | |
| Bloom test | Good | Good | |
Tables 1 and 2 demonstrated that adding a predetermined amount of polyethylene glycol to a rubber composition containing predetermined amounts of a solution-polymerized styrene-butadiene rubber, carbon black, and silica improves the fuel economy and abrasion resistance in a balanced manner while achieving a good appearance and a good cure rate. The formulation of Example 3, containing a less amount of vulcanization accelerators than in Example 2, achieved a good cure rate and also exhibited improved abrasion resistance and appearance.
In contrast, the formulation of Comparative Example 1 caused a longer scorch time and thus had poor processability. The formulations of Comparative Examples 3 to 5 each caused a shorter scorch time and thus had poor processability. The formulation of Comparative Example 2, containing a large amount of vulcanization accelerators, caused a poor appearance due to blooming. The formulation of Comparative Example 6, though achieving a good cure rate and a good appearance, did not show an effect of improving the abrasion resistance.
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