JP2011052146A - Rubber composition for tire and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tires with the rolling resistance reduced, and the tear strength and bend and crack development resistance improved, capable of restraining physical property change after vulcanization while providing good initial physical properties, and a tire produced using the composition. <P>SOLUTION: The rubber composition for tires includes a hydrogenated product of a natural polyisoprenoid, sulfur, a vulcanization accelerator, and an organic peroxide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a rubber composition for a tire and a tire using the same.

Conventional rubber compositions for tire sidewalls include natural rubber (NR) excellent in tensile strength and tear strength (crack resistance), butadiene rubber (BR) excellent in flex crack growth resistance, and carbon black (reinforcing agent). However, it is known that a double bond portion of a highly unsaturated rubber such as BR causes cracks on the rubber surface. To solve this problem, it has been proposed to blend ethylene propylene diene rubber (EPDM) and improve weather resistance and crack resistance, but it is excellent in rubber durability but inferior in flex crack growth resistance. End up.

On the other hand, especially in recent years, there has been a demand for lower fuel consumption of automobiles, and tires are also required to reduce rolling resistance. Furthermore, environmental issues have become more important, and the use of petroleum resources such as carbon black tends to be limited. For this reason, attempts have been made to reduce rolling resistance by replacing carbon black with white fillers such as silica and calcium carbonate, but when carbon black is reduced and white filler is increased, resistance to flex crack growth, etc. There is a problem that the bending fatigue resistance and tear strength of the steel are reduced.

Patent Document 1 proposes to reduce rolling resistance and improve tear strength and resistance to flex crack growth by using a hydrogenated natural rubber or the like, but these performances still have room for improvement. . In addition, hydrogenated natural rubber generally has a tendency to have poor crosslinking efficiency due to the sulfur vulcanization system, so that it is difficult to increase the crosslinking density. In contrast to this problem, even if the amount of sulfur and vulcanization accelerator is increased to increase the crosslinking density, the property is likely to cause a change in physical properties due to unreacted sulfur after vulcanization due to the large amount of the compound. Will be newly generated. Thus, when hydrogenated natural rubber is used, it is contradictory to improve the initial physical properties by increasing the crosslinking density and to suppress the physical property changes after vulcanization, and it is difficult to achieve both.

JP 2007-169385 A

The present invention solves the above problems, reduces rolling resistance, improves tear strength and flex crack growth resistance, and suppresses changes in physical properties after vulcanization while having good initial physical properties. An object of the present invention is to provide a rubber composition for tires and a tire produced using the composition.

The present invention relates to a rubber composition for tires containing a hydrogenated natural polyisoprenoid, sulfur, a vulcanization accelerator, and an organic peroxide.
In the rubber composition, the hydrogenation rate of the hydrogenated product of the natural polyisoprenoid is preferably 10 to 100 mol%.
In the rubber composition, the content of hydrogenated natural polyisoprenoid in 100% by mass of the rubber component is preferably 20% by mass or more.
The rubber composition is preferably one in which the organic peroxide is blended in such an amount that the active oxygen is 1.0 to 3.2% by mass of the total sulfur content.
The rubber composition preferably contains 10 to 100 parts by mass of silica with respect to 100 parts by mass of the rubber component.
The present invention also relates to a pneumatic tire having a sidewall produced using the rubber composition.

According to the present invention, there is provided a rubber composition for a tire in which a sulfur vulcanization system (sulfur, vulcanization accelerator) and an organic peroxide vulcanization system (organic peroxide) are blended with a hydrogenated natural polyisoprenoid. Therefore, the rolling resistance can be reduced, and the tear strength and the flex crack growth resistance can be improved. It is also possible to suppress changes in physical properties after vulcanization while having good initial physical properties. Therefore, the use of the rubber composition can provide a pneumatic tire with improved performance in a well-balanced manner.

The rubber composition for tires of the present invention contains a hydrogenated natural polyisoprenoid, sulfur, a vulcanization accelerator, and an organic peroxide. By adding sulfur, a vulcanization accelerator and an organic peroxide to a hydrogenated natural polyisoprenoid as a rubber component, that is, by using a sulfur vulcanization system and an organic peroxide vulcanization system in combination, NR and BR The occurrence of cracks in the blend using this blend rubber can be improved, and both tear strength (crack resistance) and flex crack growth resistance can be achieved. Further, the rolling resistance can be reduced while suppressing the deterioration of the performance. Therefore, rolling resistance, tear strength, and bending crack growth resistance can be improved in a well-balanced manner.

Furthermore, when a sulfur vulcanization system is applied to hydrogenated natural polyisoprenoids such as hydrogenated natural rubber, it is difficult to achieve both improvement of initial physical properties and suppression of physical property changes after vulcanization. In addition, the combined use of the organic peroxide vulcanization system can increase the crosslinking density without increasing the amount of sulfur and vulcanization accelerator, and can also suppress changes in physical properties due to unreacted sulfur. Therefore, by increasing the crosslinking density, the initial physical properties can be improved, and at the same time, changes in physical properties after vulcanization can be suppressed.

The rubber composition of the present invention contains a hydrogenated natural polyisoprenoid as a rubber component. Natural polyisoprenoid is a general term for polymers composed of isoprene units (C ₅ H ₈ ) produced by positive synthesis of certain plants and mushrooms collected from trees of Hevea brasiliensis species (Hevea gum), Of the polymers having a structure in which isoprenoids are (co) polymerized, they are naturally produced. For example, natural rubber (NR), terpene, Hevea seed rubber, Indian rubber, Eucommia, or isoprene unit polymer derived from Lactarius genus mushrooms can be used.

The hydrogenated product of natural polyisoprenoid refers to a compound obtained by causing a hydrogenation reaction to natural polyisoprenoid. For example, hydrogenated natural rubber (H-NR), hydrogenated terpene, Hevea seed rubber tree, Indian rubber tree , Hydrogenated product of isoprene unit polymer derived from Eucommia or Lactarius genus mushroom. Among these, H-NR is preferable because it can be suitably applied to a tire rubber composition and a sidewall using the rubber composition.

As the hydrogenation reaction, for example, a conventionally known method such as a method of pressurizing hydrogen in the presence of a metal catalyst in an organic solvent or a method using hydrazine can be used (Japanese Patent Laid-Open No. 59-161415, etc.). .

The hydrogenation rate of the hydrogenated product of natural polyisoprenoid is preferably 10 mol% or more, and more preferably 50 mol% or more. If it is less than 10 mol%, there is no significant difference in physical properties as compared with normal NR, and there is a tendency that the effect of improving ozone resistance and flex resistance cannot be obtained. Further, the hydrogenation rate of the hydrogenated product of natural polyisoprenoid is preferably 100 mol% or less, and in particular, it can reduce the hardness by increasing the elastic force and exhibit properties as a rubber. More preferred is 90 mol% or less.

The content of hydrogenated natural polyisoprenoid in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more. If it is less than 20% by mass, the effect of improving the resistance to flex crack growth tends to be small.

The rubber composition preferably further contains another diene rubber as a rubber component.
Other diene rubbers include, for example, NR, epoxidized natural rubber (ENR), styrene butadiene rubber (SBR), butadiene rubber (BR), etc., but these are non-petroleum resources and are environmentally friendly. , ENR and their modified products are preferred, and NR is more preferred. Further, by further blending these rubber components with the hydrogenated natural polyisoprenoid, both tear strength and resistance to flex crack growth can be achieved.

In the present invention, a sulfur vulcanization system using sulfur and a vulcanization accelerator and an organic peroxide vulcanization system using an organic peroxide are used in combination.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

The amount of sulfur is preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.5 part by mass, it tends to be difficult to obtain a sufficient crosslinking density. Moreover, this compounding quantity becomes like this. Preferably it is 4.0 mass parts or less, More preferably, it is 3.0 mass parts or less, More preferably, it is 2.5 mass parts or less. If it exceeds 4.0 parts by mass, it tends to be too hard.

The vulcanization accelerator is not particularly limited, and examples thereof include guanidine vulcanization accelerators such as diphenylguanidine, diortotriguanidine, triphenylguanidine, orthotolylbiguanide, and diphenylguanidine phthalate; N-tert-butyl-2-benzo Thiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), N, N-diisopropyl-2 -Sulfenamide vulcanization accelerators such as benzothiazole sulfenamide; thiazole vulcanization accelerators such as MBT (2-mercaptobenzothiazole) and MBTS (dibenzothiazyl disulfide); TMTD (tetramethylthiuram disulfide), Tetra Thiuram vulcanization accelerators such as tilthiuram disulfide and tetramethylthiuram monosulfide; Thiourea vulcanization accelerators such as thiacarbamide and diethylthiourea; Dithiocarbamate vulcanization such as zinc ethylphenyldithiocarbamate and zinc butylphenyldithiocarbamate Accelerators: Aldehyde-amine or aldehyde-ammonia vulcanization accelerators such as acetaldehyde-aniline reactant, hexamethylenetetramine (HMT); imidazoline vulcanization accelerators; xanthate vulcanization accelerators, and the like. Of these, sulfenamide-based vulcanization accelerators are preferred from the standpoint of suppressing the change in physical properties after vulcanization while maintaining the initial balance of rolling resistance, tear strength, flex crack growth resistance, and initial properties. Is particularly preferred.

The blending amount of the vulcanization accelerator is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and further preferably 0.8 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 0.3 part by mass, it tends to be difficult to obtain a sufficient vulcanization rate. Moreover, this compounding quantity becomes like this. Preferably it is 3.0 mass parts or less, More preferably, it is 2.0 mass parts or less, More preferably, it is 1.5 mass parts or less. When it exceeds 3.0 parts by mass, it tends to be too hard or the vulcanization speed becomes too fast.

As the organic peroxide, for example, one that easily generates a peroxy radical in the presence of heat or a redox system can be used. 1,1-bis (t-butylperoxy) -3,5,5 -Trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, α, α'-bis (t-butylperoxide Oxy) -p-diisopropylbenzene, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexyne-3 , Benzoyl peroxide, t-butylperoxybenzene, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxy Maleic acid, t-butyl peroxy isopropyl carbonate, etc. are mentioned. Among them, dicumyl peroxide, 2,5-dimethyl-2 is preferable because it can suppress changes in physical properties after vulcanization while having rolling resistance, tear strength, flex crack growth resistance performance balance, and initial physical properties. , 5-bis (t-butylperoxy) hexane is preferred.

The compounding amount of the organic peroxide is preferably such an amount that the active oxygen is 1.0 to 3.2% by mass of the total sulfur content. Here, the total sulfur content refers to the content of sulfur contained in the rubber composition. In addition to sulfur used in the sulfur vulcanization system, sulfur content is added when a sulfur-containing compound is used as a vulcanization accelerator. The amount of sulfur in the sulfur accelerator is also added. Active oxygen refers to free radicals generated from the organic peroxide. If the active oxygen is less than 1.0% by mass of the total sulfur content, it tends to be difficult to obtain a sufficient crosslinking density. If it exceeds 3.2 mass%, the flex crack growth resistance tends to deteriorate.

The tire rubber composition of the present invention preferably further contains a filler.
Examples of the filler include carbon black, silica, calcium carbonate, aluminum hydroxide, clay, mica, alumina, talc, and the like. These fillers are not particularly limited, and two or more kinds can be used alone. May be used in combination. Among these, one or more fillers selected from the group consisting of silica, calcium carbonate, and aluminum hydroxide are preferable, and silica is more preferable because of low cost and improved reinforcing properties and low fuel consumption.

While rolling resistance can be reduced by increasing the amount of silica and decreasing the amount of carbon black, there is a tendency for bending crack growth resistance and tear strength to decrease, but when silica is added together with the above-described components of the present invention, tear strength is increased. And rolling resistance can be reduced, suppressing the fall of a bending crack growth resistance. The silica is not particularly limited, and examples thereof include those prepared by a wet method or a dry method.

The BET specific surface area (BET) of the silica is preferably 100 m ² / g or more, and more preferably 150 m ² / g or more. If it is less than 100 m ² / g, the tear strength tends to decrease. Further, BET of silica is preferably 250 meters ² / g or less, more preferably ^{220m 2 / g, 200m 2 /} g or less is more preferable. When it exceeds 250 m ² / g, the workability tends to deteriorate. Here, the BET specific surface area of silica is a value measured by the BET method according to ASTM D3037-81.

The content of silica is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 10 parts by mass, the tear strength tends to decrease. The silica content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, and still more preferably 50 parts by mass or less. When it exceeds 100 parts by mass, the workability tends to deteriorate.

When silica is blended as a filler, it is preferable to use a silane coupling agent in combination.
Examples of the silane coupling agent include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-triethoxy). Silylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane and the like. Of these, bis (3-triethoxysilylpropyl) disulfide and bis (3-triethoxysilylpropyl) tetrasulfide are preferable from the viewpoint of the balance between processability and rolling resistance. These silane coupling agents may be used alone or in combination of two or more.

When the silica and the silane coupling agent are blended, the content of the silane coupling agent is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more with respect to 100 parts by mass of silica, and 1 part by mass or more. Is more preferable. If it is less than 0.1 parts by mass, it does not sufficiently react with silica and the reinforcing property tends not to be improved. On the other hand, the content of the silane coupling agent is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. When it exceeds 20 parts by mass, not only the effect of improving the reinforcing property with respect to the added amount is reduced, but also the workability tends to deteriorate.

In addition to the above components, the rubber composition for tires of the present invention contains a compounding agent conventionally used in the tire industry, for example, stearic acid, zinc oxide, various anti-aging agents, a softening agent such as wax, and the like. Can do.

As a method for producing the rubber composition for a tire of the present invention, a known method can be used, for example, the above components are kneaded using a rubber kneader such as an open roll, a Banbury mixer, a closed kneader, Thereafter, it can be produced by a vulcanization method or the like. The rubber composition can be particularly suitably used for a sidewall because it has excellent performance.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, the rubber composition containing the above components is extruded in accordance with the shape of a tire member such as a sidewall at an unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. By doing so, an unvulcanized tire is formed. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The use of the pneumatic tire of the present invention is not particularly limited, but it can be suitably used particularly for passenger cars, trucks and buses.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

Production Example 1 Production of hydrogenated natural rubber (H-NR) (H-NR A)
Malaysian solid natural rubber (SMR-CV60, weight average molecular weight (Mw): 1.3 million) was dissolved in toluene to prepare a 2 mass% toluene solution. In an autoclave sufficiently purged with hydrogen, 1 kg of the toluene solution and 50 g of metal catalyst RhCl (PPH ₃ ) ₃ (chlorotris (triphenylphosphine) rhodium) were added to a heat-resistant container, and hydrogen gas was injected (pressure: 8 MPa). The temperature in the autoclave was adjusted to 70 to 80 ° C., and a hydrogenation reaction was performed with stirring for 96 hours. Then, methanol was added little by little to the toluene solution after the reaction while stirring until the solid rubber was completely precipitated. The obtained solid rubber was vacuum-dried at 60 ° C. for 24 hours to obtain H-NR A.

Production Example 2
(H-NR B)
H-NR B was obtained by the same operation as H-NR A, except that the reaction time was changed to 65 hours.

Production Example 3
(H-NR C)
H-NR C was obtained in the same manner as H-NR A except that the reaction time was changed to 10 hours.

(Measurement method of hydrogenation rate)
The obtained dry rubber was dissolved in deuterium chloroform, and the following calculation formula was used by nuclear magnetic resonance (NMR) spectroscopic analysis from the ratio of the integrated value h (ppm) of the carbon-carbon double bond part and the aliphatic part. The hydrogenation rate was calculated.
(Hydrogenation rate H%) = h (0.87) / (h (0.875) + 3 × h (5.14) + 3 × h (2.69)) × 100
The hydrogenation rates of the prepared hydrogenated natural rubbers (H-NR A, H-NR B, H-NR C) are shown in Table 1.

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
(material)
Natural rubber: SMR-CV60
H-NR A: produced in Production Example 1 H-NR B: produced in Production Example 2 H-NR C: produced in Production Example 3 Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 210 m ² / g)
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Stearic acid: Zinc stearate manufactured by NOF Corporation: Zinc oxide No. 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N-1,3-dimethyl, manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) Butyl-N′-phenyl-p-phenylenediamine)
Wax: Ozoace 0355 manufactured by Nippon Seiki Co., Ltd.
Sulfur: Powder sulfur manufactured by Tsurumi Chemical Co., Ltd. (sulfur content: 100% by mass)
Vulcanization accelerator: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide, sulfur content: 24.2% by mass) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Organic peroxide a: Park Mill D manufactured by NOF Corporation (dicumyl peroxide, amount of active oxygen: 5.92% by mass)
Organic peroxide b: Perhexa 25B-40 manufactured by NOF Corporation (2,5-dimethyl-2,5-di (t-butylperoxy) hexane, active oxygen content: 4.41% by mass)

Examples 1-5 and Comparative Examples 1-3
<Creation of evaluation sample>
In accordance with the formulation of Table 2, using a 250 cc lab plast mill manufactured by Toyo Seiki Seisakusho, chemicals other than sulfur, vulcanization accelerator and organic peroxide were filled so that the filling rate would be 58%. A kneaded product was obtained by kneading at 80 rpm until reaching 140 ° C.
Next, using an open roll, sulfur, a vulcanization accelerator, and an organic peroxide were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition. Further, the obtained unvulcanized rubber composition was molded into a predetermined size, and a vulcanized rubber composition was obtained by press vulcanization at 180 ° C. for 20 minutes, and an evaluation sample (vulcanized rubber slab sheet , Vulcanized rubber samples) were prepared.
The following evaluation was performed using the obtained sample for evaluation. The test results are shown in Table 2.

(Rolling resistance index)
Loss tangent of sample for evaluation (vulcanized rubber slab sheet) under conditions of temperature 70 ° C, initial strain 10%, dynamic strain 2%, frequency 10Hz, using viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd. (Tan δ) was measured, and the rolling resistance index of Comparative Example 1 was set to 100, and calculated by the following formula. The larger the rolling resistance index, the lower the rolling resistance, which is preferable.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Tear test)
In accordance with JIS K6252 “vulcanized rubber and thermoplastic rubber—How to determine tear strength”, tear strength (N / mm) using a not-cut angle-shaped test piece molded from a vulcanized rubber composition Was measured. The tear strength index of Comparative Example 1 was assumed to be 100, and the tear strength was expressed as an index according to the following formula. The larger the tear strength index, the higher the tear strength, which is preferable.
(Tear Strength Index) = (Tear Strength of Each Formulation) / (Tear Strength of Comparative Example 1) × 100

(Demach flex crack growth test)
According to JIS K6260 “Demach bending cracking test method for vulcanized rubber and thermoplastic rubber” 1 million times for the sample for evaluation (vulcanized rubber sample) under the conditions of a temperature of 23 ° C. and a relative humidity of 55%. The length of the crack after the bending test or the number of bending until the crack grew to 1 mm was measured. And based on the obtained crack length and the number of times of bending, the number of times of bending at which a crack grows to a length of 1 mm in the vulcanized rubber sample was expressed logarithmically. A larger value indicates that cracks are less likely to grow and that the resistance to flex crack growth is superior. Here, 70% and 110% indicate the elongation ratio with respect to the length of the original vulcanized rubber sample.

(Crosslink density)
In accordance with JIS K6258 “Immersion test of vulcanized rubber”, the volume change rate before and after being immersed in toluene at room temperature for 72 hours was measured. The volume change rate of Comparative Example 1 was taken as 100, and indexed by the following calculation formula. A larger index indicates a higher crosslink density.
(Volume change rate index) = (Volume change rate of Comparative Example 1) / (Volume change rate of each formulation)

(Changes in physical properties after vulcanization)
According to JIS K6257 “Heat aging test of vulcanized rubber”, the elongation at break before and after accelerated curing at 80 ° C. for 72 hours was measured. The break elongation retention rate of Comparative Example 1 was taken as 100, and the index was expressed by the following formula. The larger the index, the smaller the change.
(Break elongation retention index) = (Break elongation retention of each formulation) / (Break elongation retention of Comparative Example 1)

In an example in which sulfur vulcanization system and organic peroxide vulcanization system are used in combination with hydrogenated natural rubber, the rolling resistance performance (fuel consumption performance), tear strength (crack resistance) and flex crack growth resistance are well balanced. there were. Moreover, since the crosslinking density was high, the initial physical properties were excellent, and at the same time, the physical properties after vulcanization could be suppressed.

On the other hand, in Comparative Examples 1 and 3 using natural rubber, the rolling resistance performance and tear strength were greatly inferior and the flex crack growth resistance was also inferior. Moreover, about these performances, although the comparative example 2 which does not mix | blend the organic peroxide showed some improvement, it was greatly inferior compared with the Example. Furthermore, in Comparative Example 2, since hydrogenated natural rubber was used, the crosslinking density was low.

Claims (6)

A rubber composition for tires containing a hydrogenated natural polyisoprenoid, sulfur, a vulcanization accelerator, and an organic peroxide. The tire rubber composition according to claim 1, wherein the hydrogenation rate of the hydrogenated product of natural polyisoprenoid is 10 to 100 mol%. The rubber composition for tires according to claim 1 or 2, wherein the content of hydrogenated natural polyisoprenoid in 100% by mass of the rubber component is 20% by mass or more. The tire rubber composition according to any one of claims 1 to 3, wherein the organic peroxide is blended in such an amount that the active oxygen is 1.0 to 3.2 mass% of the total sulfur content. The rubber composition for tires according to any one of claims 1 to 4, comprising 10 to 100 parts by mass of silica with respect to 100 parts by mass of the rubber component. The pneumatic tire which has a side wall produced using the rubber composition in any one of Claims 1-5.