JP2006168447A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire capable of effectively suppressing air leakage without degrading rolling resistance. <P>SOLUTION: In the pneumatic radial tire, a carcass layer 4 is provided on a pair of bead parts 3, 3, and the carcass layer 4 is returned from the inside to the outside of the tire around a bead core 5. An air leakage suppressing layer 10, in which an air permeation factor is 3 ×10<SP>-12</SP>to 4 × 10<SP>-10</SP>cc cm/cm2 sec cmHg, is arranged in a region which is the outside of a folded portion 4b in a tire width direction of the carcass layer 4 and at least corresponding to a folded portion 4b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic radial tire suitable for a passenger car, and more particularly to a pneumatic radial tire that can effectively suppress air leakage without deteriorating rolling resistance.

  Conventionally, in a pneumatic radial tire for a passenger car equipped with a carcass layer, in order to suppress air leakage, the inner liner layer disposed on the innermost surface of the tire is thickened, or a material with low air permeability is used for the inner liner layer. Things have been done. However, when the inner liner layer is thickened, the tire weight is increased and the rolling resistance is deteriorated accordingly.

  On the other hand, when a material with low air permeability is used for the inner liner layer, air leakage can be suppressed without increasing the tire weight (see, for example, Patent Document 1). However, in a pneumatic radial tire having a structure in which the carcass layer is folded from the inside to the outside of the tire around the bead core, when the air that has passed through the inner liner layer reaches the carcass layer, the air passes through the folded portion of the carcass layer. Propagated rapidly to the edge of the layer. This is because the air permeability of the carcass cord, which is generally a twisted cord, is much higher than that of the surrounding rubber composition.

  Therefore, in order to effectively suppress air leakage, it is effective to dispose a material with low air permeability in the sidewall region that greatly contributes to air leakage (see, for example, Patent Document 2). However, when butyl rubber having a loss factor higher than that of a diene rubber generally used in the sidewall region is disposed in the entire sidewall region where bending deformation is large, there is a problem that the rolling resistance is significantly deteriorated.

In addition, a method (for example, see Patent Document 3) in which a material having a low air permeability is arranged between the chafer or the like of the bead portion and the carcass layer has been proposed. It is difficult to effectively suppress propagation to the outer surface of the tire through the folded portion of the carcass layer.
JP-A-11-123907 JP 2000-190713 A Japanese Patent Laid-Open No. 62-139705

  An object of the present invention is to provide a pneumatic radial tire that can effectively suppress air leakage without deteriorating rolling resistance.

In order to achieve the above object, the pneumatic radial tire of the present invention is a pneumatic radial tire in which a carcass layer is mounted between a pair of bead portions, and the carcass layer is folded around the bead core from the inside of the tire to the outside. Air having an air permeability coefficient of 3 × 10 ⁻¹² to 4 × 10 ⁻¹⁰ cc · cm / cm ² · sec · cmHg at the outer side in the tire width direction of the folded portion of the carcass layer and corresponding to at least the folded portion A leak suppression layer is arranged.

  In the present invention, since the air leakage suppression layer is disposed at an area outside the folded portion of the carcass layer in the tire width direction and corresponding to at least the folded portion, the air propagated to the folded portion of the carcass layer leaks to the outer surface of the tire. Can be effectively suppressed. In addition, since the air leakage suppression layer may be selectively disposed in a region corresponding to the folded portion of the carcass layer, even if the loss coefficient of the material constituting the air leakage suppression layer is high, the rolling resistance is deteriorated. It can be minimized.

  In the present invention, the thickness of the air leakage suppression layer is preferably 0.2 to 1.5 mm. Moreover, it is preferable that the distance from the upper end of an air leak suppression layer to the edge part of a carcass layer shall be 10 mm or less. As a result, it is possible to obtain a good air leakage suppression effect while more reliably avoiding deterioration of rolling resistance.

  As a constituent material of the air leakage suppression layer, at least one selected from butyl rubber, halogenated butyl rubber, hydrogenated nitrile rubber, and epoxidized natural rubber can be used. Alternatively, a thermoplastic elastomer composition obtained by kneading a thermoplastic resin component and an elastomer component may be used as a constituent material of the air leakage suppression layer.

  Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows a pneumatic radial tire for passenger cars according to an embodiment of the present invention. In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion. A carcass layer 4 is mounted between the pair of bead portions 3 and 3. The carcass layer 4 is composed of a plurality of organic fiber cords oriented in the tire radial direction. As the organic fiber cord, nylon cord, polyester cord, or the like can be used. The carcass layer 4 is folded from the tire inner side to the outer side so as to wrap the bead core 5 and the bead filler 6 embedded in the bead part 3. That is, the carcass layer 4 forms a main body portion 4a and a folded portion 4b with the bead core 5 as a boundary. A chafer 7 made of an organic fiber fabric is embedded in the bead portion 3 so as to cover the bead toe.

  On the other hand, on the outer peripheral side of the carcass layer 4 in the tread portion 1, a plurality of belt layers 8 are embedded over the entire circumference of the tire. These belt layers 8 include a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between the layers. A belt cover layer 9 formed by winding an organic fiber cord substantially at 0 ° with respect to the tire circumferential direction is provided around the edge portion of the belt layer 8.

  In the pneumatic radial tire, the air leakage suppression layer 10 is disposed in a region corresponding to the folded portion 4b at least outside the folded portion 4b of the carcass layer 4 in the tire width direction. That is, in FIG. 1, the air leakage suppression layer 10 is disposed at least in the range from the end position A of the carcass layer 4 to the lowest point B of folding. The air leakage suppression layer 10 is located outside the chafer 7 in the tire width direction. The end position A of the carcass layer 4 is set in a range of 20 to 75% of the tire cross-section height from the bead heel side.

  By disposing the air leakage suppression layer 10 in the range as described above, it is possible to effectively suppress the air filled in the tire from leaking to the outer surface of the tire through the folded portion 4b of the carcass layer 4. it can. In addition, since the air leakage suppression layer 10 may be selectively disposed in a region corresponding to the folded portion 4b of the carcass layer 4, even if the loss coefficient of the material constituting the air leakage suppression layer 10 is high, the air leakage suppression layer 10 rolls. The deterioration of resistance can be minimized.

The air permeability coefficient of the air leakage suppression layer 10 is in the range of 3 × 10 ⁻¹² to 4 × 10 ⁻¹⁰ cc · cm / cm ² · sec · cmHg, more preferably 3 × 10 ^{−12 to} 1.5 × 10. It is set in the range of ^-10 cc · cm / cm ² · sec · cmHg. This air permeability coefficient is measured using air as a gas by a measuring method according to JIS K7126 “Method for testing gas permeability of plastic films and sheets (Method A)”. If this air permeability coefficient exceeds 4 × 10 ⁻¹⁰ cc · cm / cm ² · sec · cmHg, the effect of suppressing air leakage becomes insufficient. Further, it is technically difficult to make the air permeability coefficient less than 3 × 10 ⁻¹² cc · cm / cm ² · sec · cmHg with the tire constituent material.

  The thickness of the air leakage suppression layer 10 is set in the range of 0.2 to 1.5 mm, more preferably in the range of 0.5 to 1.0 mm. If the thickness of the air leakage suppression layer 10 is less than 0.2 mm, the air leakage suppression effect becomes insufficient, and conversely if it exceeds 1.5 mm, the rolling resistance is deteriorated.

  The air leakage suppression layer 10 needs to be selectively disposed at least in a region corresponding to the folded portion 4b of the carcass layer 4, that is, a region serving as an air leakage path, in order to avoid deterioration of rolling resistance. Further, the distance D from the upper end of the air leakage suppression layer 10 to the end of the carcass layer 4 is preferably 10 mm or less. Even if the distance D exceeds 10 mm, no further air leakage suppression effect can be expected, and only rolling resistance is deteriorated.

  As a constituent material of the air leakage suppression layer 10, at least one selected from butyl rubber (IIR), halogenated butyl rubber (X-IIR), hydrogenated nitrile rubber (H-NBR), and epoxidized natural rubber should be used. Can do. The rubber is suitable as a tire constituent material and has a low air permeability.

When using halogenated butyl rubber, in order to realize vulcanization adhesion (co-vulcanization) between halogenated butyl rubber and diene rubber, which has been impossible in the past, grafting to halogenated butyl rubber, and at the time of vulcanization It is desirable to add a compound that generates a thiol group (—SH) that reacts with the diene rubber by heat into the rubber compound. As such a compound for vulcanization adhesion, for example, it is desirable to use a compound represented by the following chemical formula (1) or (2).

  When halogenated butyl rubber is used as a constituent material of the air leakage suppression layer 10 and the compound for vulcanization adhesion is blended in the rubber compound, the adhesion between the air leakage suppression layer 10 and the peripheral rubber is improved. Can do. Therefore, the tie rubber usually used for adhesion of the inner liner layer can be omitted, and deterioration of rolling resistance due to the tie rubber can be avoided.

  Moreover, as a constituent material of the air leakage suppression layer 10, a thermoplastic elastomer composition obtained by kneading a thermoplastic resin component and an elastomer component can also be used.

  As the thermoplastic resin component of the thermoplastic elastomer composition used in the present invention, any thermoplastic resin having a Young's modulus of more than 500 MPa, preferably 500 to 3000 MPa can be used, and the blending amount of the resin and elastomer It is 10 weight% or more with respect to the total weight of the polymer component to contain, Preferably it is 20 to 85 weight%.

  As such a thermoplastic resin, for example, polyamide resin [for example, nylon 6 (N6), nylon 66 (N66), nylon 46 (N46), nylon 11 (N11), nylon 12 (N12), nylon 610 (N610 ), Nylon 612 (N612), nylon 6/66 copolymer (N6 / 66), nylon 6/66/610 copolymer (N6 / 66/610), nylon MXD6, nylon 6T, nylon 6 / 6T Polymer, nylon 66 / PP copolymer, nylon 66 / PPS copolymer], polyester resin [for example, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), polybutylene terephthalate / tetramethylene Glycol copolymer, PET / PEI Polymer, polyarylate (PAR), polybutylene naphthalate (PBN), liquid crystal polyester, aromatic polyester such as polyoxyalkylene diimide diacid / polybutylene terephthalate copolymer], polynitrile resin [for example, polyacrylonitrile (PAN) , Polymethacrylonitrile, acrylonitrile / styrene copolymer (AS), methacrylonitrile / styrene copolymer, methacrylonitrile / styrene / butadiene copolymer], poly (meth) acrylate resin [for example, polymethyl methacrylate (PMMA), polyethyl methacrylate, ethylene ethyl acrylate copolymer (EEA), ethylene acrylic acid copolymer (EAA), ethylene methyl acrylate resin (EMA)], polyvinyl resin [for example, vinyl acetate (E A), polyvinyl alcohol (PVA), vinyl alcohol / ethylene copolymer (EVOH), polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), vinyl chloride / vinylidene chloride copolymer, vinylidene chloride / methyl acrylate copolymer Coalesced], cellulose resins [eg cellulose acetate, cellulose acetate butyrate], fluorine resins [eg polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorofluoroethylene (PCTFE), tetrafluoroethylene / ethylene copolymer Coalesced (ETFE)], imide resins [for example, aromatic polyimide (PI)] and the like.

  As an elastomer component of the thermoplastic elastomer composition used in the present invention, any elastomer having a Young's modulus of 500 MPa or less or a reinforcing agent, a filler, a crosslinking agent for improving the dispersibility and heat resistance of the elastomer, An elastomer composition to which a necessary amount of a compounding agent such as a softening agent, an anti-aging agent, or a processing aid is added can be used, and the amount is 10% by weight or more based on the total weight of the polymer components including the resin and the elastomer, preferably 10 to 80% by weight.

  Examples of such elastomers include diene rubbers and hydrogenated products thereof [for example, NR, IR, epoxidized natural rubber, SBR, BR (high cis BR and low cis BR), NBR, hydrogenated NBR, hydrogenated SBR. ], Olefin rubber [e.g. ethylene propylene rubber (EPDM, EPM), maleic acid modified ethylene propylene rubber (M-EPM)], butyl rubber (IIR), isobutylene and aromatic vinyl or diene monomer copolymer, acrylic rubber ( ACM), ionomer, halogen-containing rubber [for example, brominated product of Br-IIR, Cl-IIR, isobutylene paramethylstyrene copolymer (Br-IPMS), chloroprene rubber (CR), hydrin rubber (CHC, CHR), chlorosulfonated Polyethylene (CSM), chlorinated polyethylene (C ), Maleic acid-modified chlorinated polyethylene (M-CM)], silicone rubber (eg, methyl vinyl silicone rubber, dimethyl silicone rubber, methyl phenyl vinyl silicone rubber), sulfur-containing rubber (eg, polysulfide rubber), fluoro rubber (eg, vinylidene fluoride) Rubber, fluorine-containing vinyl ether rubber, tetrafluoroethylene-propylene rubber, fluorine-containing silicon rubber, fluorine-containing phosphazene rubber), thermoplastic elastomer (eg styrene elastomer, olefin elastomer, polyester elastomer, urethane elastomer) , Polyamide-based elastomer).

  The composition ratio of the thermoplastic resin component and the elastomer component may be appropriately determined depending on the balance of the thickness and flexibility of the film, but the preferred range is 10/90 to 90/10, more preferably 20/80 to 85/15. It is.

  In the thermoplastic elastomer composition according to the present invention, other polymers and compounding agents such as a compatibilizing agent can be mixed as a third component in addition to the above essential components. The purpose of mixing other polymers is to improve the compatibility between the thermoplastic resin component and the elastomer component, to improve the film molding processability of the material, to improve heat resistance, to reduce costs, etc. Examples of the material used for this include polyethylene, polypropylene, polystyrene, ABS, SBS, and polycarbonate.

The thermoplastic elastomer composition is prepared by melt-kneading a thermoplastic resin and an elastomer (unvulcanized material in the case of rubber) in advance using a twin-screw kneading extruder or the like, and adding an elastomer component in the thermoplastic resin forming a continuous phase. It is obtained by dispersing. When the elastomer component is vulcanized, a vulcanizing agent may be added under kneading to dynamically vulcanize the elastomer. Further, various compounding agents (excluding the vulcanizing agent) to the thermoplastic resin or the elastomer component may be added during the kneading, but are preferably mixed in advance before kneading. The kneading machine used for kneading the thermoplastic resin and the elastomer is not particularly limited, and examples thereof include a screw extruder, a kneader, a Banbury mixer, and a biaxial kneading extruder. Among these, it is preferable to use a twin-screw kneading extruder for kneading the resin component and the rubber component and for dynamic vulcanization of the rubber component. Further, two or more types of kneaders may be used and kneaded sequentially. As conditions for melt-kneading, the temperature may be higher than the temperature at which the thermoplastic resin melts. The shear rate during kneading is preferably 2500 to 7500 sec ⁻¹ . The entire kneading time is from 30 seconds to 10 minutes, and when a vulcanizing agent is added, the vulcanization time after addition is preferably from 15 seconds to 5 minutes. The thermoplastic elastomer composition produced by the above method is formed into a film by molding with a resin extruder or calender molding. The method for forming a film may be a method of forming a film of a normal thermoplastic resin or thermoplastic elastomer.

  The thin film of the thermoplastic elastomer composition thus obtained has a structure in which the elastomer is dispersed as a discontinuous phase in a thermoplastic resin matrix. By adopting the dispersion structure in such a state, it is possible to set the Young's modulus in the range of 50 to 500 MPa and to impart appropriate rigidity as a reinforcing layer of the tire.

  The thermoplastic elastomer composition can be molded into a sheet or a film and embedded alone in the tire, but an adhesive layer may be laminated in order to enhance the adhesion to the adjacent rubber. Specific examples of the adhesive polymer constituting the adhesive layer include ultrahigh molecular weight polyethylene (UHMWPE), ethylene ethyl acrylate copolymer (EEA), ethylene methyl acrylate resin (EMA) having a molecular weight of 1 million or more, preferably 3 million or more. ), Acrylate copolymers such as ethylene acrylic acid copolymer (EAA) and their maleic anhydride adducts, polypropylene (PP) and its maleic acid modification, ethylene propylene copolymer and its maleic acid modification, Polybutadiene resin and its modified maleic anhydride, styrene-butadiene-styrene copolymer (SBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), fluorine thermoplastic resin, polyester thermoplastic resin, etc. Can be mentioned. These can be extruded into a sheet form or a film form by a conventional method, for example, using a resin extruder. The thickness of the adhesive layer is not particularly limited, but it is preferable that the thickness is small for weight reduction of the tire, and 5 μm to 150 μm is preferable.

  In a pneumatic radial tire for a passenger car with a tire size of 185 / 65R14, a carcass layer is mounted between a pair of bead portions, and the carcass layer is folded around the bead core from the inside of the tire to the outside. The tires of different conventional examples, comparative examples 1 and 2 and examples 1 to 3 were produced.

In the conventional example, an air leakage suppression layer is not added to the bead portion (see FIG. 2). In Comparative Example 1, an air leakage suppression layer is disposed between the bead filler and the main body portion of the carcass layer (see FIG. 3). In Comparative Example 2, an air leakage suppression layer is disposed between the bead filler and the folded portion of the carcass layer (see FIG. 4). In Examples 1 to 3, an air leakage suppression layer is arranged in a region corresponding to the folded portion outside the folded portion of the carcass layer in the tire width direction (see FIG. 1). Table 1 shows the thickness (mm) and air permeability coefficient (cc · cm / cm ² · sec · cmHg) of the air leakage suppression layer.

  These test tires were evaluated for air leakage and rolling resistance by the following test methods, and the results are shown in Table 1.

Air leak:
Each test tire was assembled on a wheel having a rim size of 14 × 5 · 1/2 J, and left for 3 months under an initial pressure of 200 kPa, a room temperature of 21 ° C. and no load. The internal pressure was measured every 4 days, and the measurement value Pt, the initial pressure P0, and the elapsed days t were returned to Pt / P0 = exp (−αt) to obtain the α value. Using the obtained α value, t = 30 (day) was substituted, and the pressure decrease rate β (% / month) per month was obtained from the following equation (1). The evaluation results are shown as an index with the conventional example being 100. A smaller index value means less air leakage.
β = [1-exp (−αt)] × 100 (1)

Rolling resistance:
Each test tire was assembled on a wheel with a rim size of 14 × 5 · 1/2 J, and was run using an indoor drum tester under the conditions of an air pressure of 200 kPa, a load of 4 kN, and a speed of 80 km / h, and the rolling resistance at that time was measured. The evaluation results are shown as an index with the conventional example being 100. It means that rolling resistance is so small that this index value is small.

  As can be seen from Table 1, in the tires of Examples 1 to 3, air leakage could be effectively suppressed as compared with the conventional example without deteriorating rolling resistance. On the other hand, in the tires of Comparative Examples 1 and 2, the same level of air leakage as in the conventional example occurred. That is, in Comparative Examples 1 and 2, when the air filled in the tire reaches the carcass layer, the air is propagated to the outer surface of the tire through the folded portion of the carcass layer. However, in the tires of Examples 1 to 3, since the air leakage suppression layer is provided outside the folded portion of the carcass layer, such air propagation can be blocked.

1 is a meridian half sectional view showing a pneumatic radial tire for a passenger car according to an embodiment of the present invention. It is a meridian half sectional view showing a pneumatic radial tire for passenger cars of a conventional example. 2 is a meridian half cross-sectional view showing a pneumatic radial tire for passenger cars of Comparative Example 1. FIG. 6 is a meridian half sectional view showing a pneumatic radial tire for a passenger car of Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 4a Main body part 4b Folding part 5 Bead core 6 Bead filler 7 Chafer 8 Belt layer 9 Belt cover layer 10 Air leak suppression layer

Claims (5)

In a pneumatic radial tire in which a carcass layer is mounted between a pair of bead portions, and the carcass layer is folded back from the inside of the tire around the bead core, the folded portion of the carcass layer is at least on the outer side in the tire width direction. A pneumatic radial tire in which an air leakage suppression layer having an air permeability coefficient of 3 × 10 ⁻¹² to 4 × 10 ⁻¹⁰ cc · cm / cm ² · sec · cmHg is arranged in a region corresponding to the portion. The pneumatic radial tire according to claim 1, wherein the thickness of the air leakage suppression layer is 0.2 to 1.5 mm. The pneumatic radial tire according to claim 1 or 2, wherein a distance from an upper end of the air leakage suppression layer to an end of the carcass layer is 10 mm or less. The pneumatic radial tire according to any one of claims 1 to 3, wherein the air leakage suppression layer is composed of at least one selected from butyl rubber, halogenated butyl rubber, hydrogenated nitrile rubber, and epoxidized natural rubber. The pneumatic radial tire according to any one of claims 1 to 3, wherein the air leakage suppression layer is composed of a thermoplastic elastomer composition obtained by kneading a thermoplastic resin component and an elastomer component.

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