JP2001323107A - Rubber composition for bead filler or undertread and pneumatic tire using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for bead fillers or undertreads which is excellent in processing handleability and can compatibilize the lightweightness of a tire with the shape stability. SOLUTION: This rubber composition is prepared by compounding 100 pts.wt. diene rubber with 5-50 pts.wt. thermally expansible thermoplastic resin particles which have an expansion start temperature between the mixing temperature and the extrusion temperature and of which the expansion is complete at the vulcanization temperature or lower to be converted into hollow polymer particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rubber composition for bead filler or undertread and a pneumatic tire using the same, and more particularly, to a thermal expansion at a temperature higher than the mixing temperature of the rubber composition but lower than the extrusion temperature. Beet filler or undertread was manufactured by expanding the heat-expandable thermoplastic resin particles in the extrusion step to start,
The present invention relates to a pneumatic tire having excellent workability, light weight and shape stability.

[0002]

2. Description of the Related Art It is well known that reduction in weight of tires is desired from the viewpoint of environment and resource saving. For this reason, a summary of lightweight materials for pneumatic tires has been proposed, including those based on foaming technology. However, in the conventional method for manufacturing a lightweight tire containing a foamed material such as a foamed resin, since foaming is performed at the time of vulcanization, the shape and volume of the foamed rubber increases during vulcanization, and the shape of the member can be stably obtained. Therefore, it is practically difficult to apply such a foamed material to a member inside a tire.

As a method of stabilizing the shape of a member containing a foamed material, a method of previously blending a hollow low specific gravity material has been proposed. However, a material capable of sufficiently reducing the specific gravity has a large particle size. There is a problem that the strength of the compounded rubber in an unvulcanized state becomes extremely weak, and handling in a normal tire manufacturing process becomes difficult.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rubber composition for an undertread or a bead filler which is excellent in workability and can achieve both reduction in weight and shape stability of a tire. And

[0005]

According to the present invention, the expansion of the hollow polymer is completed in 100 parts by weight of the diene rubber, when the expansion start temperature is between the mixing temperature and the extrusion temperature and the expansion is completed at the vulcanization temperature or lower. Thermally expandable thermoplastic resin particles 5 to 50
A rubber composition for a bead filler or undertread, in which parts by weight are blended, is provided.

[0006]

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a specific heat-expandable hollow polymer is blended with a rubber for an undertread or a bead filler, and is expanded in an extrusion process, so that processing and weight reduction and shape stability can be achieved. Can be obtained.

According to the invention, preferably the average particle size is 5
Rubber composition capable of uniformly dispersing gas-filled thermoplastic resin particles of ~ 50 µm in a rubber compound and thermally expanding in an extrusion step to form a hollow polymer, which can be used as an undertread or bead filler for a pneumatic tire. You can get things. This rubber composition comprises a diene rubber material,
Heat resistance that contains a liquid or solid that generates gas by vaporization, decomposition or chemical reaction by heat, has a thermal expansion onset temperature between the mixing temperature of the rubber compound and the extrusion temperature, and withstands vulcanization of the rubber And a thermally expandable thermoplastic resin particle made of a thermoplastic resin having the following formula: The rubber composition is heated and expanded at a temperature equal to or higher than the expansion start temperature (that is, a temperature between the mixing temperature and the extrusion temperature), and then vulcanized, whereby the hollow polymer particles are uniformly dispersed in the vulcanized rubber matrix. Pneumatic tire bead filler or undertread.

[0008] Here, the "expansion start temperature" of the thermally expandable thermoplastic resin particles is measured by the following method. That is, first, 2 parts by weight of an acrylic emulsion and 1 part by weight of thermally expandable thermoplastic resin particles are mixed and dispersed,
This is applied on a glass plate to a thickness of 0.2 mm,
Next, this glass plate is left in an oven at a predetermined temperature for 1 minute, taken out and cooled, and its film thickness is measured. This operation is performed every 5 ° C. to determine a temperature at which the film thickness starts to increase, and this is defined as an expansion start temperature. In addition, as another method, there is also the following method, and almost the same expansion start temperature can be obtained by this method. That is, TMA (Thermal Mechanical Analy
ser), a certain amount of thermally expandable thermoplastic resin particles is filled in a pair of piston cylinders,
When the temperature rises at a speed of min and the expansion starts, the piston starts to move. The temperature at which the piston starts moving is defined as the expansion start temperature.

The heat-expandable thermoplastic resin particles used in the present invention contain a liquid or solid which is vaporized, decomposed or chemically reacted by heat to generate a gas in the thermoplastic resin, and has a rubber expansion start temperature of rubber compound. It is made of a thermoplastic resin having a heat resistance at a temperature between the mixing temperature of the product and the extrusion temperature and enduring vulcanization of the rubber, and the thermally expandable thermoplastic resin particles are heated to a temperature equal to or higher than the expansion start temperature. When expanded, it becomes hollow polymer particles containing gas in an outer grain made of a thermoplastic resin. The thermally expandable thermoplastic resin particles preferably have a true specific gravity of 0.1 or less and an average particle size of 30 to 150 μm, and more preferably 50 to 150 μm.

In order for the thermally expandable thermoplastic resin particles traversed in the rubber composition according to the present invention to effectively expand into hollow polymer particles, the thermally expanded thermoplastic resin particles incorporated into the rubber prior to the vulcanization of the rubber are required. By expanding the expandable thermoplastic resin particles, under high temperature and high pressure during vulcanization, the hollow polymer particles of the expanded gas-encapsulated thermoplastic resin are less crushed and larger than when expanded during vulcanization. It is possible to obtain a vulcanized rubber in which hollow polymer particles having an average particle size are uniformly dispersed. In particular, in a filler compounding system such as carbon, the thermally expandable thermoplastic resin particles can be expanded more effectively.

The volume ratio of the hollow portion of the obtained thermoplastic resin particles to the rubber is preferably 2 to 40%, more preferably 5 to 35%, particularly preferably 10 to 30%.
Most preferably, it is 10 to 25%.

Examples of such heat-expandable thermoplastic resin particles (expandable particles) include Matsumoto Microsphere F series (F-50, etc.) manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.
And Expancel manufactured by Nippon Ferrite Co., Ltd. are commercially available.

The thermoplastic resin constituting the outer grain component of the gas-filled thermoplastic resin particles has an expansion start temperature between a rubber mixing temperature and an extrusion temperature (usually 120 ° C. to 14 ° C.).
(0.degree. C.) and has heat resistance enough to withstand vulcanization of rubber. As such a thermoplastic resin, for example,
A (meth) acrylonitrile polymer and a copolymer having a high (meth) acrylonitrile content are preferably used. As the partner monomer (comonomer) in the case of the copolymer, monomers such as vinyl halide, vinylidene halide, styrene-based monomer, (meth) acrylate-based monomer, vinyl acetate, butadiene, vinylpyridine, and chloroprene are used. . In addition, the said thermoplastic resin is divinylbenzene, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, It may be made crosslinkable with a crosslinker such as allyl (meth) acrylate, triacrylformal, triallyl isocyanurate and the like. The crosslinked form is preferably not crosslinked, but may be partially crosslinked so as not to impair the properties of the thermoplastic resin.

In the present invention, the reason for using the heat-expandable thermoplastic resin particles whose expansion start temperature is between the mixing temperature and the extrusion temperature is that the rubber is appropriately expanded so as not to be broken in the processing temperature range of the rubber. It is in. If the expansion start temperature is lower than the mixing temperature, it will expand during mixing, and it will not be possible to process the rubber after mixing into a continuous sheet. If it is too high, it does not expand in the extrusion step but expands in the vulcanization step, so that the shape change of the member becomes large, and as a result, a desired shape cannot be obtained, which is not preferable.

The liquid or solid which is vaporized, decomposed or chemically reacted by heat to generate a gas includes, for example, hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane and petroleum ether. , Methyl chloride, methylene chloride, dichloroethylene,
Liquids such as chlorinated hydrocarbons such as trichloroethane, trichloroethylene, or azodicarbonamide;
Dinitrosopentamethylenetetramine, azobisisobutyronitrile, toluenesulfonylhydrazide derivative,
Solids such as aromatic succinyl hydrazide derivatives are included.

Examples of the diene rubber used for the bead filler or the rubber composition for undertread of the pneumatic tire according to the present invention include natural rubber (NR), various butadiene rubbers (BR), and various styrene-butadiene copolymers. United rubber (SBR), polyisoprene rubber (IR),
Acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), ethylene-propylene-diene copolymer rubber (EPDM), styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer And diene rubbers such as rubber. These rubbers can be used alone or as a mixture.

The thermally expandable thermoplastic resin particles contained in the bead filler and the rubber composition for undertread according to the present invention are blended in an amount of 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the diene rubber. I do. If the amount is too small, a sufficient weight reduction effect cannot be obtained, which is not preferable. On the contrary, if the amount is too large, workability and tire performance are deteriorated.

The rubber composition constituting the bead filler or undertread of the pneumatic tire according to the present invention includes:
In addition to the above essential components, further, a normal vulcanizing or crosslinking agent, a vulcanizing or crosslinking accelerator, various oils, an antioxidant,
Fillers, plasticizers, softeners, and other various additives commonly used for the rubber can be added.
As long as the amount of these additives is not contrary to the object of the present invention,
A conventional general compounding amount can be used.

According to the above-mentioned production method, a structure in which hollow polymer particles of a spherical shell-shaped thermoplastic resin having an average particle diameter of 30 to 150 μm are uniformly dispersed three-dimensionally in a matrix made of vulcanized rubber. The rubber molded product of the above can be obtained. The tire bead filler or undertread of the structure obtained in this way, when used as a tire, has a reduced weight compared to the case where a normal rubber material is provided, due to its structure and physical properties. Fuel economy and handling can be improved. Also,
Since elastic hollow polymer particles are blended, the hardness of the tire rubber does not increase and its flexibility is maintained.

[0020]

EXAMPLES The present invention will be further described with reference to the following examples, but it goes without saying that the scope of the present invention is not limited to these examples.

Comparative Examples 1 to 4 and Examples 1 to 3
Mixing for filler) Preparation of sample First step mixing The following components were mixed in a 3 liter Lab Banbury mixer for about 4 minutes and released at 160 ° C. The masterbatch obtained was subjected in common to the following second step mixture in all examples. Ingredients by weight Natural rubber (SIR20) 80 SBR (NZ Nipol 1502) 20 N334 (Carbon black manufactured by Showa Cabot) 80 Zinc oxide (Shodo Kagaku No. 1) 6 Stearic acid (Lion) 1.5 Antioxidant (Seiko Chemical) Ozonone 6C) 2 Oil (Showa Shell Sekiyu Desorex # 4) 10

Second Step Mixing The ingredients shown in Table I were mixed in a 3 liter Labo Banbury mixer for about 2 minutes and discharged at 110 ° C.

[0023]

[Table 1]

Table I Footnote Hollow polymer A: Matsumoto Yushi Pharmaceutical Co., Ltd. microsphere F20 (expansion start temperature 100 ° C.) Hollow polymer B: Matsumoto Yushi Pharmaceutical Co., Ltd. microsphere F82H (expansion start temperature 180 ° C.) Hollow polymer C: Matsumoto Yushi Pharmaceutical Co., Ltd. Microsphere F100 (expansion start temperature 130 ° C.) Blowing agent: Sankyo Kasei Cell Mic CAP (125 ° C. foaming) Sulfur: Karuizawa Refinery CZ: Ouchi Shinko Chemical Vulcanization Accelerator CZ-G RF resin (hardness correction resin): Sumitomo Durez PR-36

Comparative Examples 5 to 8 and Examples 4 to 6 (under
Mixing for tread) First Step Mixing The following components were mixed for about 4 minutes in a 3 liter Lab Banbury mixer and released at 160 ° C. The resulting masterbatch was commonly subjected to the following second step mixing in all examples. Ingredients by weight Natural rubber (SIR20) 70 BR (NZ Nipol 1220) 30 N550 (Carbon black HTC # 100 made by Nippon Carbon Co.) 50 Zinc oxide (Seido Kagaku No. 1) 4 Stearic acid (Lion) 1 Antioxidant (Seiko Chemical Ozonone 6C) 2 Oil (Showa Shell Sekiyu Desorex # 4) 15

Second Step Mixing The components shown in Table II were mixed in a 3 liter Labo Banbury mixer for about 2 minutes and released at 110 ° C.

[0027]

[Table 2]

Table II Footnote Hollow polymer A: Matsumoto Yushi Pharmaceutical Co., Ltd. microsphere F20 (expansion start temperature 100 ° C.) Hollow polymer B: Matsumoto Yushi Pharmaceutical Co., Ltd. microsphere F82H (expansion start temperature 180 ° C.) Hollow polymer C: Microsphere F100 manufactured by Matsumoto Yushi Seiyaku Co., Ltd. (expansion temperature: 130 ° C.) Blowing agent: Sankyo Kasei Cell Mic CAP (125 ° C. expanded) Sulfur: Karuizawa Smelting Co., Ltd. CZ: Ouchi Shinko Chemical Antiaging Agent Noxeller CZ -G RF resin (for hardness correction): Sumitomo Durez PR-36

[0029]Evaluation method The evaluation results shown in Tables I and II are as follows:
It is what I asked for. 1) Specific gravity The specific gravity of the rubber composition after mixing, after extrusion and after vulcanization was determined by Shimadzu.
It was measured by a fully automatic hydrometer manufactured by Seisakusho Co., Ltd.

2) Hardness after vulcanization Measured by JIS hardness meter ASKER DD2 manufactured by Kobunshi Keiki Co., Ltd.

3) Handling of mixing and extrusion The unvulcanized rubber mass after mixing with the Labo Banbury mixer is 10
It was processed into a sheet having a thickness of 7 mm using an inch lab roll (front and rear same speed). Observe the sheet edge at that time,
The superiority was determined by the presence or absence of a break of 0 mm or more.

4) Tire Shape A tire using the rubber mixed with the above lab was produced, and after vulcanization, a cross section of the tire was observed. At that time, the thickness and the position of the members were compared with each other using a normal rubber material (Comparative Example 1) as a reference to judge the superiority or the inferiority.

[0033]

As described above, according to the present invention, a specific heat-expandable hollow polymer is blended with a rubber for an undertread / bead filler and expanded in an extrusion step, whereby processing handling and weight reduction are achieved. A pneumatic tire having both shape stability can be manufactured.

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Claims (2)

[Claims] 1. A heat-expandable thermoplastic resin particle 5 having an expansion start temperature between a mixing temperature and an extrusion temperature and completes expansion below a vulcanization temperature to form a hollow polymer in 100 parts by weight of a diene rubber. A rubber composition for a bead filler or undertread, which is blended with 50 to 50 parts by weight. 2. A pneumatic tire having a bead filler or undertread containing a hollow polymer obtained by expanding the rubber composition according to claim 1 in an extrusion step.