JP5307989B2 - Rubber composition for side reinforcing rubber layer and tire having side reinforcing rubber layer using the same - Google Patents

Description

  The present invention relates to a rubber composition for a side reinforcing rubber layer and a tire having a side reinforcing rubber layer using the rubber composition.

  At present, run-flat tires with a hardened side reinforcing rubber layer disposed outside the carcass inside the side wall have been put to practical use, and even if the air pressure is lost due to puncture, etc., a certain distance Can now be run. As a result, it is not necessary to always have spare tires, and weight reduction in the entire vehicle can be expected. However, the run-flat running when the flat tire is punctured (when the air pressure is reduced) is limited in speed and distance, and further improvement in the run-flat performance is required.

As a technique to improve run-flat performance,
(1) A technique to suppress deformation by increasing the thickness of the side reinforcing rubber layer and prevent destruction due to deformation (2) Increase the amount of reinforcing filler such as carbon black, increase the hardness of the side reinforcing rubber layer, (3) A technique of increasing the vulcanization density by using a large amount of a vulcanizing agent or a vulcanization accelerator without increasing the amount of carbon black or the like, and suppressing deformation and heat generation.

  However, in the case of (1), the weight of the tire is increased, which is contrary to the original weight reduction of the run-flat tire. In the case of (2), the load on the processes such as kneading and extruding is large, and the heat generation becomes high in physical properties after vulcanization. Furthermore, in the case of (3), the elongation of the rubber becomes small and the breaking strength is lowered.

  In general, natural rubber, butadiene rubber, or the like is used as the rubber component in the rubber composition used for the side reinforcing rubber layer, and non-rubber components such as protein and lipid are included in the natural rubber. These non-rubber components, especially proteins, are said to cause molecular chain entanglement, and cause gelation. When gelation occurs, the viscosity of the rubber increases, and processing occurs. There is a disadvantage that the sexuality deteriorates. In general, in order to improve the processability of natural rubber, a method of kneading with a kneading roll machine or a closed mixer and lowering the molecular weight is used. Since it cuts at random, it causes deterioration of fuel consumption characteristics, so it is not suitable as a run-flat tire.

  Therefore, a method for removing a protein, which is one of the factors of gelation, is known, and it has been proposed to use the obtained deproteinized natural rubber as a rubber for a tire component (Patent Document). 1).

Japanese Patent No. 3294901

  The present invention provides a rubber composition for a side reinforcing rubber layer capable of improving breaking strength, low heat build-up, run flat performance and fuel efficiency, and a run flat tire having a side reinforcing rubber layer using the rubber composition. With the goal.

  The present invention relates to a rubber composition for a side reinforcing rubber layer containing a rubber component including a deproteinized natural rubber having a total nitrogen content of 0.3% by weight or less as a protein index.

  The content of the deproteinized natural rubber in the rubber component is preferably 10 to 100% by weight.

  The gel content of the deproteinized natural rubber measured as a toluene insoluble content is preferably 0.5 to 10% by weight.

  The rubber composition for a side reinforcing rubber layer preferably further contains 10 to 70 parts by weight of carbon black with respect to 100 parts by weight of the rubber component.

  The rubber composition for the side reinforcing rubber layer preferably further contains 10 to 150 parts by weight of silica with respect to 100 parts by weight of the rubber component.

  The rubber composition for a side reinforcing rubber layer preferably further contains 2 to 120 parts by weight of a lamellar natural ore with respect to 100 parts by weight of the rubber component.

  The lamellar natural ore is preferably sericite or graphite.

The rubber composition for the side reinforcing rubber layer has a rupture strength TB after vulcanization measured according to JIS K 6251 of 10 to 50 MPa, and the formula (1):
E ″ / (E *) ² ≦ 7.0 × 10 ⁻⁹ Pa ⁻¹
(Where E ″ is the loss elastic modulus after vulcanization at 70 ° C. measured under conditions of a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 1%, E * is a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 1. % Is the complex elastic modulus after vulcanization at 70 ° C. measured under the condition of%)
It is preferable to satisfy.

  The present invention also relates to a run flat tire having a side reinforcing rubber layer using the rubber composition for a side reinforcing rubber layer.

  According to the present invention, by including a specific deproteinized natural rubber, a rubber composition for a side reinforcing rubber layer that can improve breaking strength, low heat build-up, run flat performance, and low fuel consumption, and the same are used. A run flat tire having a side reinforcing rubber layer can be provided.

  The rubber composition for a side reinforcing rubber layer of the present invention contains a rubber component containing a specific deproteinized natural rubber (hereinafter sometimes referred to as DPNR).

  In the present invention, a DPNR which is contained in natural rubber (NR) in an amount of about 5 to 10% by weight, removes a protein causing gelation, and has a total nitrogen content of 0.3% by weight or less as a protein index. By blending as a part of the rubber component, breaking strength, low heat build-up, run flat performance and low fuel consumption are improved. As the treatment for deproteinizing NR, conventionally known methods described in JP-A-6-329838, JP-A-2005-47993 and the like can be employed. In addition, as a NR to be deproteinized, a conventionally used grade such as RSS # 3 or TSR20 can be used.

  In the present invention, the total nitrogen content is used as an index of the protein content of DPNR. The total nitrogen content of DPNR is 0.3% by weight or less. When the total nitrogen content exceeds 0.3% by weight, it becomes a factor causing gelation, and durability such as heat resistance and wear resistance are deteriorated. Note that the lower limit of the total nitrogen content of DPNR is preferably low, and it is desirable not to contain nitrogen if possible. However, the lower limit is usually 0.01% by weight due to limitations such as the production method.

  The weight average molecular weight of DPNR is preferably 1.4 million or more from the viewpoint of high raw rubber strength. The upper limit of the weight average molecular weight of DPNR is not particularly limited, but is usually 2.5 million from the viewpoint of excellent rubber physical properties, wear resistance, and processability.

  Further, DPNR is NR with reduced gel content, and the gel content of DPNR measured as toluene insoluble is 10% by weight or less from the viewpoint of suppressing the increase in the viscosity of unvulcanized rubber and being excellent in processability. Is preferred. The gel content of DPNR is preferably low, and it is desirable that the gel content is not contained if possible. However, the lower limit is usually 0.5% by weight due to limitations such as the production method.

  The DPNR content in the rubber component is preferably 10% by weight or more, more preferably 20% by weight or more, and still more preferably 40% by weight or more from the viewpoint of excellent rubber durability such as physical properties and heat resistance. The upper limit of the DPNR content in the rubber component is not particularly limited and may be 100% by weight, but is preferably 80% by weight or less and more preferably 70% by weight or less from the viewpoint of cost reduction.

  In the present invention, when a rubber component other than DPNR is used as the rubber component, examples of the rubber component used in combination with DPNR include NR, isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), Styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR) and the like can be mentioned, and BR is preferable from the viewpoint of excellent durability such as heat resistance.

  Examples of BR include butadiene rubber having a high cis content (BR) and BR containing a syndiotactic-1,2-polybutadiene crystal (SPB-containing BR). However, because a rubber with high hardness can be obtained. SPB-containing BR is preferred.

  Although it does not necessarily restrict | limit as SPB containing BR, VCR412, VCR617, etc. by Ube Industries, Ltd. can be used.

  The content of BR in the rubber component is preferably 20% by weight or more, more preferably 30% by weight or more from the viewpoint of excellent low heat build-up. Further, the BR content is preferably 80% by weight or less, and more preferably 60% by weight or less from the viewpoint of obtaining sufficient rubber strength.

  The rubber composition for a side reinforcing rubber layer of the present invention preferably further contains a reinforcing filler.

  Carbon black is well known as a reinforcing filler, and even if silica is used instead of carbon black, the same effect can be obtained as a rubber composition for a side reinforcing rubber layer. In addition to these, calcium carbonate, magnesium oxide, magnesium hydroxide, alumina, aluminum hydroxide, clay, talc and the like are also included. Of these, carbon black and silica are preferred because of their excellent reinforcing effect.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 30 m ² / g or more, and more preferably 35 m ² / g or more, from the viewpoint of obtaining sufficient reinforcement and durability. Also, N ₂ SA of carbon black is from the viewpoint of excellent low heat build-is preferably not more than 100 m ² / g, more preferably not more than ^{80m 2 / g, 60m 2 /} g or less is more preferred. Incidentally, N ₂ SA of carbon black is, for example, can be measured in accordance with ASTM-D3765-80.

  The dibutyl phthalate oil absorption (DBP) of carbon black is preferably 50 ml / 100 g or more, more preferably 80 ml / 100 g or more, from the viewpoint that sufficient reinforcing properties can be obtained. The DBP of carbon black is preferably 300 ml / 100 g or less, more preferably 200 ml / 100 g or less, from the viewpoint of excellent fatigue resistance such as elongation at break. In addition, DBP of carbon black can be measured according to ASTM-D3493, for example.

  The compounding amount of carbon black is preferably 10 parts by weight or more, more preferably 20 parts by weight or more, and further preferably 30 parts by weight or more with respect to 100 parts by weight of the rubber component from the viewpoint that sufficient rubber strength can be obtained. Further, the blending amount of the carbon black is preferably 100 parts by weight or less, more preferably 70 parts by weight or less, with respect to 100 parts by weight of the rubber component, from the viewpoint that the viscosity at the time of kneading is appropriately maintained and processability is excellent. More preferred are parts by weight or less.

  Silica includes those prepared by a wet method and those prepared by a dry method, but is not particularly limited.

The BET specific surface area (BET) of silica is preferably 150 m ² / g or more from the viewpoint of excellent rubber properties including tensile strength.

  The compounding amount of silica is preferably 10 parts by weight or more, more preferably 50 parts by weight or more with respect to 100 parts by weight of the rubber component, from the viewpoint of excellent reinforcing effect necessary for the rubber composition for the side reinforcing rubber layer. Further, the blending amount of silica is preferably 150 parts by weight or less, more preferably 100 parts by weight or less with respect to 100 parts by weight of the rubber component, from the viewpoint of excellent dispersibility.

  In the rubber composition for a side reinforcing rubber layer of the present invention, it is preferable to further blend a thin plate-like natural ore.

  Examples of the lamellar natural ore include mica and graphite.

  As the mica, for example, kaolinite, sericite, phlogopite, and mascobite are preferable, and among these, sericite is more preferable because it is particularly excellent in the balance between hardness and fracture strength.

  In addition, the thin plate shape in the thin plate natural ore is a concept including shapes such as a flake shape and a disk shape, and specifically, those satisfying the following average aspect ratio and average particle diameter. Further, graphite is layered graphite having a hexagonal plate-like crystal structure, and does not include carbon black or the like.

  The average aspect ratio (ratio of the average major axis to the average thickness) of the lamellar natural ore is preferably 3 or more, more preferably 5 or more, and further preferably 10 or more, from the viewpoint that sufficient rubber hardness can be obtained. The average aspect ratio of the lamellar natural ore is preferably 80 or less from the viewpoint of excellent dispersibility and sufficient fracture strength. The average aspect ratio is determined by observing the lamellar natural ore dispersed in the rubber composition with an electron microscope, measuring the major axis and minor axis of 50 arbitrary particles, and determining the average major axis a and average thickness b. , A / b. Moreover, when using mica as a thin plate-like natural ore, the average aspect ratio is preferably 10 to 20, and when graphite is used, the average aspect ratio is preferably 10 to 50.

  The average particle diameter of the lamellar natural ore is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more from the viewpoint of suppressing cost and obtaining sufficient rubber hardness. In addition, the average particle diameter of the lamellar natural ore is preferably 30 μm or less, and more preferably 20 μm or less, from the viewpoint of excellent bending fatigue resistance. In addition, an average particle diameter says the average value of the long diameter of a thin plate-like natural ore.

  The blending amount of the lamellar natural ore is preferably 2 parts by weight or more, more preferably 5 parts by weight or more, further preferably 10 parts by weight or more, and more preferably 15 parts by weight or more with respect to 100 parts by weight of the rubber component from the viewpoint of excellent physical properties. Is particularly preferred. Further, the blending amount of the lamellar natural ore is preferably 120 parts by weight or less, more preferably 80 parts by weight or less, more preferably 60 parts by weight with respect to 100 parts by weight of the rubber component from the viewpoint of excellent dispersibility and low heat build-up. The following is more preferable. In addition, when using mica as a lamellar natural ore, the compounding amount is preferably 10 to 50 parts by weight with respect to 100 parts by weight of the rubber component, and when using graphite, the compounding amount is 100 parts by weight of the rubber component. 2 to 10 parts by weight is preferred with respect to parts.

  In the present invention, when silica or lamellar natural ore is used as the reinforcing filler, it is preferable to contain a silane coupling agent. The silane coupling agent that can be suitably used in the present invention can be any silane coupling agent conventionally used in combination with silica. Specifically, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) Tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide Bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3- Riethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide Bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxy Silylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolylte Sulfides such as rasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltrisulfide Mercapto series such as ethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, vinyl series such as vinyltriethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltri Amino series such as methoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, γ Glycidoxy systems such as glycidoxypropyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, 3-nitropropyltrimethoxysilane, Nitro-based compounds such as 3-nitropropyltriethoxysilane, chloro-based compounds such as 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane and 2-chloroethyltriethoxysilane It is done. Bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, 3-mercaptopropyltrimethoxysilane and the like are preferably used because of the effect of adding a coupling agent and cost. These silane coupling agents may be used alone or in combination of two or more.

  The blending amount of the silane coupling agent is 0.1 to 20 with respect to 100 parts by weight of the total blending amount of silica and lamellar natural ore because a coupling effect can be obtained at an appropriate cost and the rubber reinforcing effect is excellent. Part by weight is preferable, and 2 to 10 parts by weight is more preferable.

  The rubber composition for a side reinforcing rubber layer of the present invention preferably further contains sulfur or a sulfur compound.

  As sulfur or a sulfur compound, insoluble sulfur is preferable because it suppresses surface precipitation of sulfur.

  The average molecular weight of insoluble sulfur is preferably 10,000 or more, more preferably 100,000 or more from the viewpoint that decomposition does not easily occur even at low temperatures and surface precipitation is difficult. The average molecular weight of insoluble sulfur is preferably 500,000 or less, more preferably 300,000 or less, from the viewpoint of excellent dispersibility in rubber.

  The compounding amount of sulfur or sulfur compound is preferably 3 parts by weight or more, more preferably 4 parts by weight or more with respect to 100 parts by weight of the rubber component, from the viewpoint that sufficient hardness is obtained, it is difficult to bend and break. Further, the amount of sulfur or sulfur compound is preferably 20 parts by weight or less, more preferably 15 parts by weight or less with respect to 100 parts by weight of the rubber component from the viewpoint that blooming is difficult and sufficient processability is obtained.

  Moreover, it is preferable to further mix a vulcanization accelerator with the rubber composition of the present invention.

  Examples of the vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N′-dicyclohexyl-2- Examples include benzothiazolylsulfenamide (DZ), mercaptobenzothiazole (MBT), dibenzothiazolyl disulfide (MBTS), and diphenylguanidine (DPG). TBBS, CBS, DZ, etc. because it is difficult, has excellent vulcanization characteristics, has excellent low heat buildup against deformation due to external force, and has great effect on improving the durability of run-flat tires. Of these, sulfenamide vulcanization accelerators are preferred.

  In addition to the rubber component, reinforcing filler, lamellar natural ore, silane coupling agent, sulfur or sulfur compound, and vulcanization accelerator, the rubber composition for the side reinforcing rubber layer of the present invention has been conventionally used in the rubber industry. For example, stearic acid, zinc oxide, anti-aging agent and the like can be appropriately blended as necessary.

  The rubber composition for a side reinforcing rubber layer of the present invention is prepared by a general method. That is, the rubber component for the side reinforcing rubber layer of the present invention is prepared by kneading the rubber component, if necessary, other compounding agents with a Banbury mixer, kneader, open roll, etc., and then vulcanizing. Can do.

  In the rubber composition for a side reinforcing rubber layer of the present invention, the rupture strength TB after vulcanization measured according to JIS K 6251 is not easily broken by the load of the vehicle during run flat running, and sufficient run flat performance is obtained. Therefore, 10 MPa or more is preferable, 12 MPa or more is more preferable, and 14 MPa or more is more preferable. The upper limit of TB is not particularly set, but is usually about 50 MPa.

Further, in the rubber composition after vulcanization according to the present invention, the loss elastic modulus (E ″) after vulcanization at 70 ° C. measured at a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 1% and a frequency of 10 Hz, initial The complex elastic modulus (E *) after vulcanization at 70 ° C. measured under the conditions of 10% strain and 1% dynamic strain is the formula (1):
E ″ / (E *) ² ≦ 7.0 × 10 ⁻⁹ Pa ⁻¹
It is preferable to satisfy.

E ″ / (E *) ² is preferably 7.0 × 10 ⁻⁹ Pa ⁻¹ or less, and is preferably 6.0 × 10 ⁻⁹ Pa ⁻¹ or less, because it is difficult to generate heat during run-flat running, can suppress thermal deterioration of rubber, and is hard to break. more preferably 10 ^-9 Pa ^-1 or less. in addition, E "/ (E *) ² of the lower limit is not set in particular, usually 1.0 × 10 about ^-9 Pa ^-1 is preferable.

  The rubber composition for a side reinforcing rubber layer of the present invention is used as a side reinforcing rubber layer among tire members because of its low heat build-up, excellent reinforcing properties and excellent run flat performance.

  Hereinafter, the side reinforcing rubber layer will be described with reference to the drawings.

  FIG. 1 is a partial cross-sectional view of a run-flat tire showing a structure having a side reinforcing rubber layer using the rubber composition for a side reinforcing rubber layer of the present invention. As shown in FIG. 1, the side reinforcing rubber layer 8 includes the tread 5, the side wall 2, the carcass 3 disposed inside the tread 5 and the side wall 2, and the outside of the carcass 3 inside the tread 5. In the run-flat tire 1 having the breaker 4 that is formed, the lining strip layer that is arranged from the bead portion 7 including the bead wire 6 and the board apex 9 to the shoulder portion on the inner side of the side wall 2 and in contact with the inner side of the carcass 3. Thus, the presence of the side reinforcing rubber layer 8 in the run-flat tire 1 can support the vehicle even when the air pressure is lost, and can provide excellent run-flat performance.

  The run flat tire of the present invention is produced by a usual method using the rubber composition for a side reinforcing rubber layer of the present invention. That is, if necessary, the rubber composition for a side reinforcing rubber layer of the present invention blended with the above-mentioned compounding agent is extruded in accordance with the shape of the side reinforcing rubber layer of the tire at an unvulcanized stage, and other tire members At the same time, an unvulcanized run-flat tire is formed by molding on a tire molding machine by a normal method. This unvulcanized run flat tire is heated and pressurized in a vulcanizer to obtain a run flat tire.

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

Hereinafter, various commercially available chemicals used in Examples and Comparative Examples will be described.
Natural rubber (NR): RSS # 3
Butadiene rubber (BR): VCR412 manufactured by Ube Industries, Ltd.
Carbon black: Diamond Black E (N ₂ SA: 41 m ² / g, DBP: 115 ml / 100 g) manufactured by Mitsubishi Chemical Corporation
Silica: Ultrasil VN3 (BET: 210 m ² / g) manufactured by Degussa
Sericite: KM-8 manufactured by Nippon Foram Co., Ltd. (aspect ratio: 15, average particle size: 17 μm)
Graphite: BF-18A manufactured by Chuetsu Graphite Co., Ltd. (aspect ratio: 40, average particle size: 18 μm)
Silane coupling agent: Si75 (bis (triethoxysilylpropyl) disulfide) manufactured by Degussa
Stearic acid: Stearic acid “Kashiwa” manufactured by Nippon Oil & Fats Co., Ltd.
Zinc oxide: Zinc oxide type 2 anti-aging agent manufactured by Mitsui Mining & Smelting Co., Ltd .: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Insoluble sulfur: Mucron OT manufactured by Shikoku Kasei Kogyo Co., Ltd.
Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Preparation Example 1: Preparation of Deproteinized Natural Rubber (DPNR) 150 ml of high ammonia type natural rubber latex (solid content 60.2%) manufactured by Softech Co., Ltd., Malaysia, 2 L of distilled water so that the rubber solid content becomes 10%. Diluted with 0.12% sodium naphthenate and adjusted to pH 9.2 by adding sodium dihydrogen phosphate. Subsequently, 2 g of deproteinase alkalase (manufactured by Novo Disc Bio Industry Co., Ltd.) was dispersed in 100 ml of distilled water and added to the diluted natural rubber latex. After adjusting the pH of the latex to 9.2 again, it was maintained at 37 ° C. for 24 hours for deproteinization treatment. The anionic surfactant polyoxyethylene lauryl ether sulfate sodium (KP4401 manufactured by Kao Co., Ltd.) is added to the latex that has been deproteinized at a rate of 1% by weight, and centrifuged at 10,000 rpm for 30 minutes. I did it. After centrifugation, the creamy rubber component separated into the upper layer was taken out and further diluted with water to obtain a deproteinized natural rubber latex having a rubber solid content of 60%.

  The deproteinized natural rubber latex was cast on a glass plate, dried at room temperature, and then dried under reduced pressure to obtain a polymer.

  The obtained polymer and a commercially available high ammonia natural rubber latex (Hytex made by Nomura Trading Co., Ltd.) were cast on a glass plate, dried at room temperature, and then dried under reduced pressure. After drying, extraction with a mixed solvent of acetone and 2-butanone (3: 1) was performed to remove impurities such as homopolymers, and deproteinized natural rubber (DPNR) was obtained.

(Nitrogen content)
The nitrogen content was measured by the Kjeldahl test method.

(Gel content)
In the present invention, the gel content in raw rubber means a value measured as a toluene insoluble matter. 70 mg of a sample obtained by cutting raw rubber into 1 mm × 1 mm was weighed, 35 ml of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, the gel was centrifuged to precipitate a gel component insoluble in toluene, and the soluble component in the supernatant was removed. Only the gel component was washed with methanol, dried, and the weight (mg) was measured. The gel content (%) was determined by the following formula.
(Gel content) = (weight after drying) / (initial sample weight) × 100

(Weight average molecular weight)
The weight average molecular weight was determined by gel permeation chromatography (solvent: tetrahydrofuran).

  The results of analysis for NR and DPNR are shown in Table 1.

Examples 1-6 and Comparative Examples 1-2
Using a 1.7 L Banbury mixer manufactured by Kobe Steel, various materials excluding sulfur and vulcanization accelerator were kneaded at 150 ° C. for 4 minutes to obtain a kneaded product. Then, on an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded for 3 minutes at 80 ° C. to obtain an unvulcanized rubber composition. Further, the obtained unvulcanized rubber composition is molded into the shape of a side reinforcing rubber layer of a tire and bonded to another tire member to form an unvulcanized run-flat tire, and the condition is kept at 150 ° C. for 25 minutes. By press vulcanization, run flat tires (size: 215 / 45ZR17) of Examples 1 to 6 and Comparative Examples 1 to 2 were obtained.

(Tensile test)
According to JIS K 6251 “Vulcanized rubber and thermoplastic rubber – Determination of tensile properties”, tensile was performed using a No. 3 dumbbell-shaped test piece cut out from the side reinforcing rubber layer (lining strip layer) of the manufactured run-flat tire. The test was conducted and the breaking strength (TB) of each formulation was measured. In addition, it shows that TB is excellent in large fracture strength.

(Viscoelasticity test)
Using a 2 mm-thick test piece cut out from the side reinforcing rubber layer (lining strip layer) of the manufactured run-flat tire, a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., frequency 10 Hz, initial strain 10%, dynamic Under the condition of 1% strain, viscoelasticity (complex elastic modulus E * and loss elastic modulus E ″) at 70 ° C. was measured, and E ″ / (E *) ² was calculated. In addition, it shows that it is excellent in low exothermic property, so that the value of E "/ (E *) ² is small.

(Run flat performance)
The run flat tire was run on the drum at an air pressure of 0 kPa at a speed of 80 km / hour, the running distance until the tire was destroyed was measured, the run flat performance index of Comparative Example 1 was set to 100, and the following calculation was performed. The mileage of each formulation was displayed as an index according to the formula. In addition, it shows that it is excellent in run-flat performance, so that a run-flat performance index is large.
(Run flat performance index) = (mileage of each formulation)
÷ (mileage of comparative example 1) x 100

(Tire weight)
The weight of the run-flat tire of each formulation was measured, and the weight difference (g) from the tire of each formulation was calculated by the following calculation formula based on the weight of the tire of Comparative Example 1 (13.5 kg). In addition, it shows that it is excellent in low-fuel-consumption property, so that a tire weight difference is small (absolute value is large).
(Tire weight difference) = (weight of each compound tire) − (weight of tire of Comparative Example 1)

  The evaluation results are shown in Table 2.

It is a fragmentary sectional view of the run flat tire which shows the structure which has the side reinforcement rubber layer using the rubber composition for side reinforcement layers of this invention.

Explanation of symbols

1 run flat tire 2 side wall 3 carcass 4 breaker 5 tread 6 bead wire 7 bead 8 side reinforcing rubber layer 9 bead apex

Claims (7)

For 100 parts by weight of a rubber component including deproteinized natural rubber having a total nitrogen content of 0.3% by weight or less as an index of protein ,
A rubber composition for a side reinforcing rubber layer, containing 2 to 10 parts by weight of graphite, which is a thin plate-like natural ore . The rubber composition for a side reinforcing rubber layer according to claim 1, wherein the content of the deproteinized natural rubber in the rubber component is 10 to 100% by weight. The rubber composition for a side reinforcing rubber layer according to claim 1 or 2, wherein the deproteinized natural rubber has a gel content of 0.5 to 10% by weight measured as a toluene insoluble matter. Furthermore, the rubber composition for side reinforcement rubber layers in any one of Claims 1-3 which contains 10-70 weight part of carbon black with respect to 100 weight part of rubber components. Furthermore, the rubber composition for a side reinforcing rubber layer according to any one of claims 1 to 4, further comprising 10 to 150 parts by weight of silica with respect to 100 parts by weight of the rubber component. The breaking strength TB after vulcanization measured according to JIS K 6251 is 10 to 50 MPa, and
Formula (1):
E ″ / (E *) ² ≦ 7.0 × 10 ⁻⁹ Pa ⁻¹
(Where E ″ is the loss elastic modulus after vulcanization at 70 ° C. measured under conditions of a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 1%, E * is a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 1. % Is the complex elastic modulus after vulcanization at 70 ° C. measured under the condition of%)
The rubber composition for a side-reinforcing rubber layer according to any one of claims 1 to 5 . The run flat tire which has a side reinforcement rubber layer using the rubber composition for side reinforcement rubber layers in any one of Claims 1-6 .

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