JP5383004B2 - Rubber composition for sidewall - Google Patents

Description

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

  Conventionally, tire damage has been caused by rusting of the reinforcing steel cord inside the tire due to the influence of air and moisture penetrating from the inner surface of the tire, or by hardening due to crosslinking when the rubber adhered to the cord is oxidized and deteriorated It is a well-known technique in the tire industry that the phenomenon that occurs is greatly improved by using an inner liner based on butyl rubber inside the tire.

  However, in recent years, especially as the life of tires progresses, deterioration due to the effects of air and moisture penetrating from the outside of the tire is becoming a situation that cannot be ignored. In particular, studless tires that have been removed for many years in the summer and tires for large trucks and buses that have become longer-life are susceptible to the effects of air and moisture that permeate from the outside.

  In order to solve these problems, it is effective to increase the thickness of the sidewall, but the normal diene rubber is 5-7 times easier to pass air and oxygen than the butyl inner rubber, so it is quite gauge There is a problem that the effect cannot be expected unless the thickness is increased, and the cost and the structural design are quite difficult.

  As another means, a means using a butyl rubber that can be co-crosslinked with a diene rubber as a side wall has been proposed. However, if the degree of co-crosslinking is insufficient, a problem that the rubber for the side wall is separated is proposed. There is a risk of occurrence, and there is a problem that a considerably high manufacturing technique is required and the cost is high, which is not industrially useful.

  Furthermore, a method of adding a material having a high gas barrier property such as a flake filler such as silica, resin powder, clay, etc. (see, for example, Patent Document 1) can be considered. There is a high possibility that it will become a base point, and the inorganic powder has a characteristic of easily adhering moisture, so that there is a problem that the moisture content of the rubber composition itself is increased.

  From the above, it is not easy to improve the permeation resistance of air and moisture of the rubber in the sidewall portion on an industrial basis.

JP 2004-345470 A

  An object of this invention is to provide the rubber composition for sidewalls which reduces the amount of air permeation | transmission and the destructive characteristic of a rubber composition does not fall.

In the present invention, 3 to 15 parts by weight of a thermal expansion microcapsule having an average particle diameter of 10 to 95 μm and having an independent outer shell part made of a thermoplastic resin with respect to 100 parts by weight of a rubber component, The present invention relates to a rubber composition for a sidewall containing 40 to 60 parts by weight of carbon black of ˜85 m ² / g.

The density of the rubber composition is preferably less than 1 g / cm ³ .

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

  The present invention contains a thermal expansion microcapsule whose outer shell portion is a thermoplastic resin in the rubber component, and thus has flexibility, and the liquid-containing thermoplastic resin before thermal expansion has a small particle size. Therefore, there is little destruction of the thermally expanded microcapsule in the rubber composition kneading step or the vulcanization step.

  In addition, since the outer shell part of the thermal expansion microcapsule in the rubber component is a thermoplastic resin, it is difficult for air or moisture to pass through. Since it has to detour and a movement distance becomes long, as a result, the air permeation-proof performance in a side wall part improves.

  Furthermore, since the inside of the thermally expanded microcapsule is hollow, the density of the rubber composition can be reduced.

  The rubber composition for a side wall of the present invention contains thermally expanded microcapsules whose independent outer shell portions are thermoplastic resins.

  The rubber composition of the present invention includes, as rubber components, natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR) diene rubber, acrylonitrile-butadiene rubber (NBR), Epoxidized natural rubber, epichlorohydrin rubber, chloroprene rubber and the like can be included.

  The thermally expanded microcapsule whose outer shell portion is a thermoplastic resin is a spherical hollow particle having a void inside. As used herein, the term “spherical” refers to the shape of a rounded particle that does not have an acute angle part, and includes an elliptical shape or a part of the shape that is distorted. Independent means that the thermally expanded microcapsules are separated from each other without sticking to each other.

  As the thermoplastic resin in the outer shell portion of the thermally expanded microcapsule, for example, a polymer of (meth) acrylonitrile or a copolymer having a high (meth) acrylonitrile content is preferably used. As the other monomer (comonomer) in the copolymer, monomers such as vinyl halide, vinylidene halide, styrene monomer, (meth) acrylate monomer, vinyl acetate, butadiene, vinyl pyridine, chloroprene are used. In addition, as the thermoplastic resin, divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, Examples include allyl (meth) acrylate, triacryl formal, and triallyl isocyanurate. The crosslinked form is preferably uncrosslinked, but may be partially crosslinked to such an extent that the properties as a thermoplastic resin are not impaired.

  The thermal expansion microcapsule of the present invention can be produced, for example, from thermoplastic resin particles enclosing a commercially available liquid. Examples of the thermoplastic resin particles encapsulating the liquid that is a raw material of the thermal expansion microcapsule include “EXPANSEL 091DU-80” or “EXPANSEL 092DU-120” manufactured by EXPANCEL, Sweden, or Matsumoto Yushi It is available as “Matsumoto Microsphere F-85”, “Matsumoto Microsphere F-100” or “Matsumoto Microsphere F-80VS” manufactured by Pharmaceutical Co., Ltd.

  As a method for producing a thermally expandable microcapsule, for example, thermally expandable thermoplastic resin particles encapsulating a liquid that is vaporized by heat to generate a gas are heated at a temperature equal to or higher than the expansion start temperature, and as a result, A gas-encapsulated thermoplastic resin microcapsule in which the inside of the outer shell made of the thermoplastic resin is encapsulated with gas is obtained.

  The temperature for heating and expanding the thermally expandable thermoplastic resin particles encapsulating the liquid is preferably 130 ° C. or higher, more preferably 140 ° C. or higher, from the viewpoint of good non-expandability in the extrusion process. Further, the temperature for heating and expanding is preferably 190 ° C. or lower, more preferably 180 ° C. or lower, from the viewpoint that the stability of the expansion characteristics is good.

  The average particle diameter of the thermoplastic resin particles before thermal expansion is preferably 5 μm or more and more preferably 10 μm or more from the viewpoint of good dispersibility in rubber. In addition, the average particle diameter of the thermoplastic resin particles before thermal expansion is preferably 50 μm or less, and more preferably 40 μm or less, from the viewpoint of less breakage due to mixing.

  Examples of the liquid that is vaporized by heat to generate a gas include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, and petroleum ether, methyl chloride, methylene chloride, dichloroethylene, trichloroethane, And liquids such as chlorinated hydrocarbons such as trichloroethylene.

  In order to obtain the effects of the present invention, the average particle size of the thermally expanded microcapsule is 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more from the viewpoint of good air permeation resistance. The average particle diameter of the thermally expanded microcapsules is 95 μm or less from the viewpoint that the distance between the thermally expanded microcapsules can be kept sufficiently and the rubber component is not broken under the influence of distortion caused by running of the tire.

  The content of the thermally expanded microcapsule is 3 parts by weight or more from the viewpoint of good air permeation resistance with respect to 100 parts by weight of the rubber component, and preferably 5 parts by weight or more from the viewpoint of cost reduction. The content of the thermally expanded microcapsule is 15 parts by weight or less, preferably 10 parts by weight or less, from the viewpoint of good crack growth resistance with respect to 100 parts by weight of the rubber component.

The density of the thermally expanded microcapsule is preferably 0.02 g / cm ³ or more from the viewpoint of good crack growth resistance. The density of the thermally expanded microcapsule is preferably 0.05 g / cm ³ or less from the viewpoint of reducing the density of the rubber composition.

  The content of carbon black blended in the rubber composition is 40 parts by weight with respect to 100 parts by weight of the rubber component from the viewpoint of good air permeation resistance, crack growth resistance, and damage resistance (tensile strength). Thus, 43 parts by weight or more is preferable from the viewpoint of good crack growth resistance and damage resistance, and 45 parts by weight or more is more preferable from the viewpoint of good damage resistance. Further, the content of carbon black blended in the rubber composition is 60 parts by weight or less with respect to 100 parts by weight of the rubber component from the viewpoint of excellent low heat buildup and excellent crack growth resistance. From the viewpoint of good crack growth resistance and low heat buildup, 57 parts by weight or less is preferable, and from the viewpoint of good crack growth resistance, 55 parts by weight or less is more preferable.

The nitrogen adsorption specific surface area of carbon black is 45 m ² / g or more from the viewpoint of good crack growth resistance and trauma resistance, and preferably 50 m ² / g or more from the viewpoint of good trauma resistance. . Further, the nitrogen adsorption specific surface area of carbon black is 85 m ² / g or less from the viewpoint of improving low heat buildup and air permeation resistance, and 80 m ² / g or less from the viewpoint of good air permeation resistance. Is preferred. The nitrogen adsorption specific surface area of carbon black can be measured in accordance with the method for obtaining the specific surface area of the nitrogen adsorption method of JIS K 6217-2.

  The rubber composition for a sidewall of the present invention generally includes a tire such as a reinforcing agent such as silica, a softening agent such as aroma oil, a vulcanizing agent such as stearic acid, zinc oxide, and sulfur, and a vulcanization accelerator. The additive used in industry can be mix | blended suitably.

  When the thermally expandable microcapsule that is a thermoplastic resin in the outer shell portion is contained in the rubber component, the density of the entire rubber composition can be relatively lowered because the density of the thermally expanded microcapsule is small.

  The thermal expansion microcapsule, which is a thermoplastic resin for the outer shell, is generally a material with a higher cost than rubber. However, since it is a very low density material, depending on the rubber used, the thermal expansion microcapsule However, it may be cheaper in volume cost comparison. In such a case, by including the thermally expanded microcapsules, it becomes possible to impart characteristics such as weight reduction and cost reduction in addition to the improvement of rubber performance.

The density of the rubber composition is preferably 0.96 g / cm ³ or more, more preferably 0.97 g / cm ³ or more from the viewpoint of good crack growth resistance and reinforcement. The density of the rubber composition is preferably less than 1 g / cm ³ from the viewpoint that it is possible to reduce the weight of, more preferably 0.99 g / cm ³ or less, more preferably 0.98 g / cm ³ or less.

  The thermal expansion microcapsule in the present invention is flexible because the outer shell portion is a thermoplastic resin, and the liquid encapsulated thermoplastic resin before thermal expansion has a small particle size, so that the rubber kneading step The thermal expansion microcapsules are less broken at.

  Furthermore, the thermoplastic resin in the outer shell portion of the thermally expanded microcapsule is generally difficult to pass air or moisture. For this reason, the air and moisture that try to escape through the rubber component must bypass the periphery of the sphere of the thermally expandable microcapsule, resulting in a long movement distance. As a result, the air permeation resistance is improved.

  A normal rubber composition for a sidewall includes a first step of kneading a chemical other than a vulcanizing agent and a vulcanization accelerator, and a vulcanizing agent and a vulcanization accelerator in a kneaded product obtained by the first step. In general, it is produced using two kneading steps consisting of a second step of further adding kneading. In addition, the thermal expansion microcapsule in the rubber composition for a side wall of the present invention includes the first step of kneading and the second step of kneading by further adding a vulcanizing agent and a vulcanization accelerator to the kneaded product. Either of the steps may be blended. However, when the thermally expanded microcapsules are blended in the first step, the rubber is used when the thermally expanded microcapsules are produced by thermally expanding the thermoplastic resin containing the liquid. If a thermoplastic resin containing a liquid is added during the kneading step, the volume of the rubber composition increases and cannot be removed from the mixer, or cannot be extruded to a predetermined size in the subsequent step. The kneading temperature must be set to a temperature at which the liquid thermoplastic resin containing the liquid does not vaporize and expand.

  Therefore, it is preferable that a thermoplastic resin containing a liquid is blended in the second step and thermally expanded when heated and pressurized in a vulcanizer to form thermally expanded microcapsules.

  The tire of the present invention is produced by a usual method using the rubber composition for a sidewall as a sidewall of the tire. That is, the rubber composition is extruded into the shape of a tire sidewall at an unvulcanized stage, and bonded together by a normal method on a tire molding machine to form an unvulcanized tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a pneumatic tire.

Next, various chemicals used in Examples and Comparative Examples will be described in detail.
Natural rubber (NR): RSS # 3
Polybutadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd.
Carbon black (CB HAF): Diamond black HA manufactured by Mitsubishi Chemical Corporation (nitrogen adsorption specific surface area: 74 m ² / g)
Carbon black (CB FEF): N550 (nitrogen adsorption specific surface area: 40 m ² / g) manufactured by Cabot Japan
Thermal expansion microcapsule 1: liquid-encapsulated thermoplastic resin particles (Matsumoto Microsphere F-80VS (average particle diameter after expansion: 20 to 40 μm)) manufactured by Matsumoto Yushi Seiyaku Co., Ltd.
Thermal expansion microcapsule 2: Liquid-encapsulated thermoplastic resin particles (Matsumoto Microsphere F-82 (average particle diameter after expansion: 100 to 160 μm)) manufactured by Matsumoto Yushi Seiyaku Co., Ltd.
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Stearic acid adhesive resin manufactured by Nippon Oil & Fats Co., Ltd .: Marcaretz T-100A manufactured by Maruzen Petrochemical Co., Ltd.
Anti-aging agent 6C: 6PPD manufactured by Flexis Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiki Co., Ltd.
Powdered sulfur: 5% oil-treated sulfur vulcanization accelerator manufactured by Nippon Dry Sulfur Industry Co., Ltd. NS: Noxeller NS (N-tert-butyl-2-benzothiazylsulfenamide manufactured by Ouchi Shinsei Chemical Co., Ltd.) )

Examples 1-3 and Comparative Examples 1-8
In accordance with the formulation shown in Table 1, liquid encapsulated thermoplastic resin particles, raw materials for thermal expansion microcapsules, chemicals other than sulfur and a vulcanization accelerator were added under a condition of a discharge temperature of 160 ° C. using a Banbury mixer. Kneaded for 5 minutes to obtain a kneaded product. Next, liquid-encapsulated thermoplastic resin particles, sulfur and a vulcanization accelerator are added to the obtained kneaded product, and kneaded for 2 minutes at a discharge temperature of 100 ° C. using a Banbury mixer. A rubber composition was obtained. Furthermore, the obtained unvulcanized rubber composition was press vulcanized for 30 minutes under the condition of 150 ° C. to obtain vulcanized rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 8.

(Tensile strength)
A sample was produced from the produced rubber composition using a No. 3 dumbbell according to JIS-K6251 and a tensile test was performed. The higher the modulus (TB) at break, the higher the rubber strength.

(Demach flex crack growth test)
In accordance with JIS K6260 “Testing method for demature bending cracking of vulcanized rubber and thermoplastic rubber”, cracks after 5,000,000 tests were performed on samples of vulcanized rubber composition under conditions of a temperature of 23 ° C. and a relative humidity of 55%. Those having a length or growth of 5 mm or more were evaluated as x, and those having a growth of less than 5 mm were marked as ◯.

(Rubber density)
0.5 g of a rubber composition was cut out from a vulcanized rubber composition sheet having a thickness of 2 mm and measured with a hydrometer. If the rubber density was less than 1 g / cm ³ , it was judged that the weight was reduced.

(Air permeability)
The air permeability was measured at a temperature of 40 ° C. using an air permeability measuring device (GTR TESTER M-C1) manufactured by Toyo Seiki Seisakusho, in accordance with ASTM P-1434-75M method. The air permeability was indexed by the measurement. Indexing was performed by multiplying the value obtained by dividing the numerical value of Comparative Example 1 by the number of other levels by 100. As Comparative Example 1 is 100, the larger the value, the better. In addition, it is 110% or more that it is judged that the air permeation resistance is improved.

  Each evaluation result is shown in Table 1.

Claims (3)

3 to 15 parts by weight of a thermal expansion microcapsule having an average particle diameter of 10 to 40 μm and an independent outer shell part made of a thermoplastic resin, and a nitrogen adsorption specific surface area of 45 to 85 m ² / G rubber carbon composition containing 43 to 57 parts by weight of carbon black,
A rubber composition for a sidewall, wherein the thermoplastic resin is a (meth) acrylonitrile polymer or a copolymer having a high (meth) acrylonitrile content . The rubber composition for a side wall according to claim 1, wherein the density of the rubber composition is less than 1 g / cm ³ . A tire having a sidewall comprising the rubber composition for a sidewall according to claim 1.