JP2007169385A - Tire rubber composition and tire having sidewall using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire rubber composition capable of reducing rolling resistance and improving tear strength and flex-crack growth resistance, and to provide a tire having a sidewall using the same. <P>SOLUTION: The tire rubber composition comprises a hydrogenated product of a natural polyisoprenoid. There is also provided a tire having a sidewall using the composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire and a tire having a sidewall 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, Carbon black having excellent reinforcement and strength has been used. However, it is known that a double bond portion of a highly unsaturated rubber such as BR has a property of depolymerization by reacting with ozone, and causes cracking on the rubber surface when left standing or running.

  Therefore, in order to suppress this, there is a known method of increasing the crack resistance improving agent such as an anti-aging agent, but this causes a bloom, and the tire surface changes to a brown color, thereby deteriorating the appearance of the tire. There is.

  In order to solve this problem, it is known that ethylene propylene diene rubber (EPDM) or the like can be blended to improve weather resistance and crack resistance. A brominated styrene isobutylene copolymer (BIMS) is also expected to have the same effect. However, these rubbers are excellent in durability but have a problem in crack growth resistance.

In recent years, in particular, there has been a demand for lower fuel consumption of automobiles, and tires are also required to reduce rolling resistance. In addition, environmental issues have become more important, regulations on reducing CO ₂ emissions have been tightened, oil resources are limited, and supply is decreasing year by year, so oil prices are expected to rise in the future. However, there are limits to the use of formulations containing petroleum resources such as carbon black.

  Therefore, for example, an attempt has been made to reduce the rolling resistance of the entire tire by using a white filler such as silica or calcium carbonate instead of a part of carbon black, but the rubber strength cannot be improved. There's a problem.

  Patent Document 1 discloses a rubber composition for a sidewall in which rolling resistance is reduced without decreasing discoloration resistance and ozone resistance by blending predetermined amounts of carbon black and calcium carbonate. Still, it contains a large amount of carbon black, and there is still room for improvement in rolling resistance. Further, as in the present invention, no consideration is given to the problem that the bending fatigue resistance such as the bending crack growth resistance and the tearing strength, etc., which are generated when the carbon black is reduced and the white filler is increased, are reduced. In this case, it has been difficult to improve fuel efficiency. Furthermore, Patent Document 1 contains 50% by weight of BR in the rubber component, which is not environmentally friendly.

JP 2003-113270 A

  An object of the present invention is to provide a rubber composition for a tire capable of reducing rolling resistance and improving tear strength and bending crack growth resistance, and a tire having a sidewall using the rubber composition.

  The present invention relates to a rubber composition for tires containing a hydrogenated natural polyisoprenoid.

  The tire rubber composition contains a diene rubber, and the content of the hydrogenated product of natural polyisoprenoid in the hydrogenated product of the diene rubber and natural polyisoprenoid is 3 to 40% by weight. The content of the rubber is preferably 60 to 97% by weight.

  The hydrogenated product of natural polyisoprenoid is obtained by pressurizing hydrogen in the presence of a metal catalyst in an organic solvent, and the hydrogenation rate is preferably 10 to 100%.

  The tire rubber composition is preferably composed of a continuous phase and one or more discontinuous phases, and the continuous phase and one or more discontinuous phases preferably have a sea-island structure.

  The present invention also relates to a tire having a sidewall using the tire rubber composition.

  According to the present invention, a rubber composition for a tire that can reduce rolling resistance and improve tear strength and resistance to flex crack growth by containing a hydrogenated natural polyisoprenoid, and a side using the same A tire having a wall can be provided.

  The rubber composition for tires of the present invention contains a natural polyisoprenoid hydrogenated product.

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). Is a naturally occurring polymer having a (co) polymerized structure, for example, natural rubber (NR), terpene, Hevea seed rubber, Indian rubber, eucommia, or Lactarius mushroom-derived isoprene units Polymer etc. are raised.

  The hydrogenated product of natural polyisoprenoid refers to a compound obtained by causing a hydrogenation reaction of natural polyisoprenoid, such as hydrogenated natural rubber (H-NR), hydrogenated terpene, Hevea seed rubber tree, Indian rubber tree , Hydrogenated products of isoprene unit polymers derived from Eucommia or Lactarius genus mushrooms. Among them, it can be applied to rubber compositions for tires and sidewalls using them, polyisoprenoids other than natural rubber are not industrially used, and the three-dimensional structure is not regular compared to natural rubber, and polymerization H-NR is preferable because the degree is small and it is economically impossible to calculate a large amount.

  Examples of the hydrogenation reaction include a general method such as pressurizing hydrogen in the presence of a metal catalyst in an organic solvent.

  The hydrogenation rate of the hydrogenated product of natural polyisoprenoid is preferably 10% or more, and more preferably 50% or more. When the hydrogenation rate of the natural polyisoprenoid hydrogenation is less than 10%, there is no significant difference in physical properties as compared with normal NR, and further, the effect of improving ozone resistance and flex resistance tends not to be obtained. There is. Further, the hydrogenation rate of the hydrogenated product of natural polyisoprenoid is preferably 100% or less, and particularly 95% or less is more preferable because it can increase the elastic force to lower the hardness and exhibit properties as rubber. 90% or less is more preferable.

  The rubber composition preferably further contains a diene rubber.

  Examples of the diene rubber include NR, epoxidized natural rubber (ENR), styrene butadiene rubber (SBR), butadiene rubber (BR), and other rubbers other than hydrogenated products of point salt polyisoprenoids. Since it is a resource and is environmentally friendly, NR, ENR and their modified products are preferred, and NR is more preferred.

  The content of the hydrogenated natural polyisoprenoid and the hydrogenated natural polyisoprenoid in the diene rubber is preferably 3% by weight or more, more preferably 5% by weight or more, still more preferably 10% by weight or more, and 20% by weight. The above is particularly preferable. When the content of the hydrogenated natural polyisoprenoid is less than 3% by weight, there is a tendency that sufficient ozone resistance and flex resistance are not exhibited as compared with NR alone. Further, the content of the hydrogenated product of natural polyisoprenoid is preferably 40% by weight or less, and more preferably 30% by weight or less. When the content of the hydrogenated natural polyisoprenoid exceeds 40% by weight, the hardness of the rubber tends to increase.

  The rubber composition for tires of the present invention improves heat resistance, chemical resistance and ozone resistance, and further improves durability against repeated fatigue, and therefore comprises a continuous phase and one or more discontinuous phases. The continuous phase and the one or more discontinuous phases preferably exhibit a sea-island structure. The sea-island structure is a structure in which the continuous phase is the sea and the discontinuous phase is the island, and the H-NR (island) is dispersed in the NR phase (sea). When fracture nuclei occur, it is preferable that the continuous phase is a diene rubber and the discontinuous phase is a hydrogenated natural polyisoprenoid because the H-NR (island) layer delays the propagation of the fracture.

  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.

  When calcium carbonate is used as the filler, it is preferable to perform a surface treatment such as a fatty acid treatment because the reinforcing property can be improved by using it together with a hydrogenated product of natural polyisoprenoid.

  The content of the filler is preferably 5 parts by weight or more, and more preferably 30 parts by weight or more with respect to 100 parts by weight of the rubber component. If the filler content is less than 5 parts by weight, sufficient reinforcing properties tend not to be obtained. Moreover, 150 weight part or less is preferable and, as for content of a filler, 80 weight part or less is more preferable. When the content of the filler exceeds 150 parts by weight, the hardness is excessively increased and there is a tendency to have a practical problem.

  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 (2-triethoxysilylpropyl) tetrasulfide, and 3-mercaptopropyl. Examples include triethoxysilane and 2-mercaptoethyltrimethoxysilane. These silane coupling agents may be used alone or in combination of two or more.

  When silica and a silane coupling agent are blended, the content of the silane coupling agent is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more with respect to 100 parts by weight of silica, and 1 part by weight or more. Is more preferable. When the content of the silane coupling agent is less than 0.1 parts by weight, the silica does not sufficiently react with silica and the reinforcing property tends not to be improved.

  In addition to natural polyisoprenoid hydrogenated products, diene rubbers, fillers and silane coupling agents, the rubber composition for tires of the present invention includes compounding agents conventionally used in the tire industry, such as stearic acid, oxidation Zinc, various anti-aging agents, softening agents such as wax, vulcanizing agents such as sulfur, various vulcanization accelerators and the like can be blended.

  The rubber composition for tires of the present invention has a rubber composition for sidewalls because it can improve ozone resistance and flex crack growth resistance compared to conventional sidewalls containing BR as a rubber component. It is preferable to use a product.

  The tire of the present invention is produced by a usual method using the tire rubber composition of the present invention. That is, if necessary, the rubber composition for tires of the present invention blended with the above compounding agent is extruded in accordance with the shape of each member of the tire at an unvulcanized stage, and is processed on a tire molding machine by a normal method. An unvulcanized tire is formed by molding with. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain the tire of the present invention.

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

The chemicals used in the examples and comparative examples are summarized below.
Natural rubber (NR): RSS # 3
Hydrogenated natural rubber (H-NR): produced by the following production method (hydrogenation rate: 50%)
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd.
Silica: Ultrazil VN3 manufactured by Degussa (BET specific surface area: 175 m ² / g)
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
Stearic acid: Stearic acid “paulownia” manufactured by NOF Corporation
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: NOCRACK 6C (N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical )
Wax: Ozoace 0355 manufactured by Nippon Seiki Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Co., Ltd.

(Production of hydrogenated product of natural polyisoprenoid (H-NR))
Malaysian solid natural rubber (SMR-CV60, weight average molecular weight (Mw): 1.3 million) was dissolved in toluene to prepare a 2 wt% toluene solution. In a fully hydrogen-substituted autoclave, 1 kg of the toluene solution and 50 g of metal catalyst RhCl (PPH ₃ ) ₃ (chlorotris (triphenylphosphine) rhodium) are added to a heat-resistant container, and hydrogen gas is injected (pressure: 8 MPa). The temperature in the autoclay part was adjusted to 70 to 80 ° C., and a hydrogenation reaction was performed with stirring for 96 hours. Thereafter, methanol was gradually added 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.

Examples 1-4 and Comparative Examples 1-5
In accordance with the formulation of Table 1, using a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd., chemicals other than sulfur and a vulcanization accelerator were filled to a filling rate of 58%, and 140 rpm at 140 rpm. A kneaded product was obtained by kneading until reaching 0C.

  Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained 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 160 ° C. for 20 minutes, and a vulcanization of about 2 mm × 130 mm × 130 mm was obtained. A rubber slab sheet (for viscoelasticity test) and a vulcanized rubber sample (for demach flex crack growth test) were prepared.

(Viscoelasticity test)
Using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho, the loss tangent (tan δ) of the vulcanized rubber slab sheet was measured under conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. The rolling resistance index of Comparative Example 1 was set to 100, and the rolling resistance was indicated by an index according to 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 K 6252 “Vulcanized Rubber and Thermoplastic Rubber-Determination of Tear Strength”, tear strength (N / mm) is obtained by using an angle-shaped test piece without a cut formed from a vulcanized rubber composition. The tear strength index of Comparative Example 1 was taken as 100, and the tear strength was expressed as an index by 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)
In accordance with JIS K 6260 “Demach Bending Crack Growth Test Method for Vulcanized Rubber and Thermoplastic Rubber” 1 million bending tests on vulcanized rubber sample under conditions of temperature 23 ° C. and relative humidity 55% The subsequent crack length or the number of bends until it grew to a 1 mm crack was measured. Then, based on the obtained crack length and the number of bends, the number of bends until the crack grew 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 percentage with respect to the length of the original rubber composition sample.

  The test results are shown in Table 1.

(Evaluation of polymer dispersion)
Morphology of the vulcanized rubber samples of Examples 1 to 4 and Comparative Example 1 was observed with a transmission electron microscope (TEM).

  The evaluation results of polymer dispersion are shown in FIG.

  In Examples 1 to 4 to which H-NR is added, the rolling resistance can be reduced, and the tear strength and the bending crack growth resistance can be improved. In particular, in Example 4 in which the blending ratio of NR and H-NR is 97/3 to 40/60, as shown in FIG. 1 (b), NR2 is contained in NR2, and these are the island phases. As can be seen from the formation of, the H-NR phase can be uniformly dispersed in the NR phase, the rolling resistance can be reduced, and the tear strength and flex crack growth resistance can be improved.

(A) is a transmission electron micrograph of the vulcanized rubber sample obtained in Comparative Example 1, (b) is a transmission electron micrograph of the vulcanized rubber sample obtained in Example 4, (C) is a transmission electron micrograph of the vulcanized rubber sample obtained in Example 3, (d) is a transmission electron micrograph of the vulcanized rubber sample obtained in Example 2, (E) is a transmission electron micrograph of the vulcanized rubber sample obtained in Example 1.

Explanation of symbols

1 H-NR
2 NR

Claims (6)

A tire rubber composition containing a hydrogenated product of natural polyisoprenoid. Contains diene rubber,
The content of the hydrogenated natural polyisoprenoid and the hydrogenated natural polyisoprenoid in the diene rubber is 3 to 40% by weight, and the content of the diene rubber is 60 to 97% by weight. The rubber composition for tires according to 1. The tire rubber composition according to claim 2, wherein the diene rubber is natural rubber. A natural polyisoprenoid hydrogenation product is obtained by pressurizing hydrogen in an organic solvent in the presence of a metal catalyst,
The rubber composition for tires according to claim 1, 2 or 3, wherein the hydrogenation rate of the hydrogenated product of natural polyisoprenoid is 10 to 100%. Consisting of a continuous phase and one or more discontinuous phases,
The tire rubber composition according to claim 1, 2, 3 or 4, wherein the continuous phase and one or more discontinuous phases have a sea-island structure. A tire having a sidewall using the tire rubber composition according to claim 1, 2, 3, 4 or 5.