JP2011218982A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire with belt reinforcing layers, for improving maneuvering stability and high-speed durability while reducing weight.SOLUTION: For the belt reinforcing layers 7, 8, polyester (PET) cords in a single twisted structure are used, each of which has (1) a nominal fineness (D) of 1,000-2,000 dtex, and (2) a twist factor (K) of 700-2,000, as represented by the following expression (I), and is subjected to (3) dip treatment (adhesive coating treatment) using, at least, at least one of blocked isocyanate water solution and epoxy compound dispersion, and resorcinol-formaldehyde-latex (RFL) mixture: K=T×(D/1.38)(I), where T is the number of twists per 10 cm (twist count/10 cm), D is the nominal fineness of the whole cord (decitex (dtex)), and 1.38 is the specific gravity of the polyester.

Description

  The present invention relates to a pneumatic radial tire using a single twisted polyester cord with improved heat-resistant adhesion as a reinforcing material for a belt reinforcing layer (band layer, cap ply). In particular, the present invention relates to a pneumatic radial tire that is excellent in handling stability and durability in high-speed driving and can achieve weight reduction.

  In pneumatic radial tires, for the purpose of improving high-speed durability, rolling resistance, and road noise, a belt reinforcing layer in which reinforcing cords are arranged in the tire circumferential direction is arranged on the outer peripheral side of the belt layer. Yes. This belt reinforcing layer is provided in order to prevent the belt layer made of a steel cord or the like from being lifted particularly during high-speed traveling. In particular, the belt reinforcing layer is disposed so as to cover at least both ends in the width direction of the belt layer in order to prevent lifting at both ends in the width direction (near the shoulder portion) of the belt layer.

  Conventionally, an organic fiber cord having a double twist structure is mainly used for the belt reinforcing layer. In other words, after twisting a bundle of organic fiber strands (filaments) such as nylon and polyester (PET, etc.), a plurality of “yarns” obtained in this way are bundled and twisted by further twisting. A combined cord is mainly used (for example, Patent Document 1).

  Such a twisted fiber cord has the opposite twisting directions of the lower twist and the upper twist, so that the shape retention is good but the twisting process is large and the production cost is high. In addition, the cord weight is increased due to the increased diameter of the cord, and the ply thickness is increased due to the complicated cross-sectional shape.

  Therefore, for example, in Patent Document 2 below, an organic fiber cord having a single twist structure is used as a reinforcing material for the belt reinforcing layer (band layer), and the elongation at a predetermined load, “residual tension”, the number of cords to be driven, and the like It has been proposed that various conditions be in a specific range. According to specific examples (Examples 1 and 2 in Table 1), it was a cord obtained by applying a twist of 16 to 20 per 10 cm to a bundle of filaments (filaments) of 1600 to 2100 dtx of nylon 66. Are used in accordance with various conditions. And by adopting such an organic fiber cord, it is said that "high speed steering stability, high speed durability, and noise performance can be improved while achieving low cost and light weight".

According to claim 1, paragraph 0020, etc. of Patent Document 2, for an organic fiber cord having a single twist structure, “twist coefficient T (= N · D ^{1 / 2} ) needs to be reduced to 150-750 "to a smaller range than before. And when the twist coefficient T is large, “the effect of improving the tightening force is not sufficiently achieved”, the twist coefficient T is “preferably in the range of 200 to 600”.

  However, the configuration of Patent Document 2 is not necessarily sufficient to improve the high-speed durability of the tire while maintaining steering stability. Therefore, fiber cords such as a twisted structure are still generally used for belt reinforcement layers.

  On the other hand, Patent Document 3 uses an organic fiber cord made of polyketone, which is “shoulder belt reinforcing layer 4 having a Young's modulus of 8 GPa or more”, and the belt reinforcing layer in the center portion has a general Young's modulus smaller than this. It has been proposed to use organic fiber cords. In paragraph 0057 of Patent Document 3, it is described that the organic fiber may have a single twist structure. However, there is no description about what conditions need to be adopted in the case of a single twist structure.

  On the other hand, when polyester fibers such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are used for the belt reinforcement layer, they are superior in terms of elastic modulus and dimensional stability, so they are higher than when nylon cords are used. Rigidity can be realized, which is advantageous in handling stability. However, when a polyester fiber cord is used, the durability of the tire tends to be low. For this reason, nylon cords are still mainly used as cords for belt reinforcement layers. As a cause of the low durability, it is mentioned that the durability of adhesion between the polyester cord and the rubber is insufficient. For this reason, various studies have been conducted on the composition and conditions of the resin liquid when the polyester cord is immersed in the reactive resin liquid (dip treatment).

  For example, in the following Patent Document 4, an oxazoline compound is used as a treatment liquid for an inner layer (undercoat layer) together with an epoxy compound and latex, and resorcin-formaldehyde-latex (RFL) is used as a treatment liquid for an outer layer (overcoat layer). It has been proposed. However, the durability of the tire when continuously running at high speed (tire high-speed durability) is not always sufficient only by devising the treatment liquid for imparting adhesiveness and adhesion durability.

JP 2005-022455 A JP 2002-154304 A JP 2007-196754 A JP 2009-203594 A

  The present invention has been made in view of the above-described problems of the prior art, and by improving the configuration of the fiber cord of polyester used for the belt reinforcing layer, it is possible to stabilize operation while achieving low cost and light weight. An object of the present invention is to provide a pneumatic radial tire with improved durability and high-speed durability.

  In view of the above-mentioned problems, the present inventor accidentally found out the twist coefficient, fineness, heat shrinkage stress, dry heat shrinkage rate, etc. in the fiber cords of polyethylene terephthalate (PET) and other polyesters. It has been found that a very excellent effect can be obtained by employing specific conditions, and the present invention has been completed.

That is, the pneumatic radial tire according to the present invention covers the belt layer provided in the tread portion and at least both ends of the belt layer (corresponding to both ends in the width direction of the tread) outside the belt layer in the radial direction. In a pneumatic radial tire using a fiber cord having a polyester single twist structure for the belt reinforcement layer, (1) nominal fineness (D) is 1000 to 2000 dtex Yes, (2) The twist coefficient (K) represented by the following formula (I) is 700 to 2000, (3) At least one of the blocked isocyanate aqueous solution and the epoxy compound dispersion, and resorcin-formaldehyde-latex The (RFL) mixed solution is used at least using a dip treatment (adhesive coating treatment).
K = T · (D / 1.38) ^1/2 …… (I);
Here, T is the number of twists per 10 cm (times / 10 cm), D is the nominal fineness of the entire cord (decitex), and 1.38 is the specific gravity of the polyester.

  Preferably, when the fiber cord is subjected to a peeling test from a rubber layer after being rubberized with a rubber material for a belt reinforcing layer and vulcanized at 140 ° C. for 40 minutes, The coverage ratio is 90% or more, and when a peel test from the rubber layer is performed after overvulcanization at 170 ° C. for 120 minutes, the rubber adhesion rate is 80% or more. The fiber cord preferably has a twist number (T) of more than 21 and 50 or less.

  According to the present invention, in particular, when a polyester cord having a single twist structure is used for the belt reinforcing layer, a polyester cord having a relatively large twist coefficient (K) is used, and a specific nominal fineness (D) and heat shrinkage characteristics are used. By using the one having the above, it is possible to improve steering stability and high-speed durability while achieving low cost and light weight.

It is the half section view which cut the pneumatic radial tire of an embodiment in the direction of an axis.

  FIG. 1 is a schematic half sectional view of a pneumatic radial tire (hereinafter referred to as a radial tire) T for a passenger car according to an embodiment of the present invention.

  The radial tire T includes a pair of bead portions 1 and sidewall portions 2 and a tread portion 3 connected to both sidewall portions 2, and a two-ply radial that reinforces between bead cores 4 and 4 embedded in the bead portion 1. The carcass 5 is folded around the bead core 4 from the inner side to the outer side of the carcass 5, wound up along the bead filler 9, and locked by the side wall portion 2. A belt 6 formed of two cord crossing layers provided on the outer periphery of the crown portion of the radial carcass 5 and belt reinforcing layers 7 and 8 formed of polyester cord wound along the outer periphery of the belt 6 are provided.

  The organic fiber cords of the belt reinforcement layers 7 and 8 are heat-shrinked during tire vulcanization to tighten the belt 2 in the circumferential direction, thereby increasing the rigidity in the tire circumferential direction and the belt restraining force, and due to centrifugal force during high-speed running Suppression of belt rise, diameter growth, and distortion at the belt end can be suppressed, and durability and steering stability can be improved at high speed.

  The carcass 5 is made of organic fiber cords such as polyester, nylon and rayon, and the belt 2 is made of steel such as 1 × 4, 1 × 5, 2 + 2, 2 + 1 structure with a filament diameter of about 0.20 to 0.30 mm. Rigid organic fiber cords such as cords or aramid cords are used. The number of laminated carcass, belt, and belt reinforcing layer can be appropriately increased or decreased depending on the tire size and application.

  In the illustrated example, the belt reinforcing layers 7 and 8 are formed on the outer periphery of the belt 6, the inner belt reinforcing layer 7 is the entire width (A + B) of the belt 6, and the folded outer belt reinforcing layer 8 is the both ends of the belt 6. Covers B. The belt reinforcing layers 7 and 8 are wound in a spiral shape by winding a predetermined nylon cord described below at an angle of approximately 0 ° with respect to the tire circumferential direction, thereby tightening the belt 6 in the circumferential direction, and in the tire circumferential direction and the radial direction. Obtains a tagging effect that increases rigidity and belt restraint force, suppresses belt rise and diameter growth due to centrifugal force during high-speed driving, and distortion at the belt end, improving high-speed durability and steering stability Yes. The belt reinforcing layers 7 and 8 are, for example, a ribbon-like belt-shaped member that is formed by aligning organic fiber cords and covered with rubber, and is wound in a spiral shape while abutting the side end portions for each circumference of the molding drum when molding a tire. Is done. Alternatively, the single cord that has been subjected to the adhesion treatment may be wound in a spiral shape while being shifted in the tire width direction.

  The polyester cords used for the belt reinforcement layers 7 and 8 are made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or other polyester fibers having a specific gravity of around 1.38. It may consist of: The nominal fineness (D) of the polyester cord, that is, the apparent fineness (weight / unit length) of the whole cord is 1000 to 2000 dtex, preferably 1050 to 1700 dtex. If the nominal fineness (D) of the polyester cord is lower than this range, the strength (N) of the cord will be reduced. Therefore, in order to ensure the strength of the belt reinforcement layers 7 and 8, the number of cords to be driven and reinforcement It is necessary to increase the number of layers. For example, it is necessary to increase the number of cords to be driven until failure such as separation is likely to occur. Therefore, it is disadvantageous for adhesiveness and heat generation, and durability is lowered. On the other hand, when the nominal fineness (D) of the polyester cord exceeds the above range, the cord diameter becomes large, so that the thickness of the belt reinforcing layers 7 and 8 becomes large. For this reason, weight reduction of a tire cannot be achieved and, as a result, it is also disadvantageous for fuel consumption.

  The polyester cord used for the belt reinforcing layers 7 and 8 has a twist coefficient (K) represented by the above formula (I) of 700 to 2000, preferably 800 to 2000, more preferably 800 to 1700, and still more preferably 800 to 1300. It is. By setting the twist coefficient within this range, the belt 6 is appropriately tightened by heat shrinkage during vulcanization molding, and the above-mentioned tire circumferential direction rigidity and belt restraint are improved, and high speed durability and steering stability are achieved. Can be secured.

  When the twist coefficient (K) of the polyester cord is lower than the above range, the fatigue resistance is lowered, and the cord breaks or tread separation easily occurs due to buckling fatigue. Further, if the twist coefficient exceeds the above range, the rigidity when the composite with rubber is reduced, the steering stability at the time of tire mounting is lowered.

  The polyester cord used for the belt reinforcing layers 7 and 8 is at least one that has been subjected to a dipping process (adhesive coating process) using the following adhesive resin solution. That is, (1) at least one of blocked isocyanate aqueous solution and epoxy compound dispersion and (2) resorcin-formaldehyde-latex (RFL) mixed solution are used simultaneously or sequentially to dip in one or more stages. The processed one is used. Preferably, the dip treatment with the first treatment liquid containing the above (1) and the dip treatment with the second treatment liquid containing the above (2) are preferably performed sequentially, and it is particularly preferable to perform in this order.

  According to the first preferred embodiment for the dip treatment, a treatment solution containing (A) a carrier and (B) a blocked isocyanate aqueous solution is used as the first treatment solution, and (B) A solution containing a dispersion of a blocked isocyanate solution, (C) an epoxy compound, and (D) a resorcin-formaldehyde-latex (RFL) mixture is used. According to the second preferred embodiment of the dip treatment, a compound containing (E) an oxazoline group, (C) an epoxy compound, and (F) a rubber latex is used as the first treatment liquid. (D) A solution containing a resorcin-formaldehyde-latex (RFL) mixed solution is used. Note that after the dip treatment with the second treatment liquid, the dip treatment with the first treatment liquid may be performed again. By such dipping treatment, heat resistant adhesiveness can be imparted to the polyester cord.

  The treatment liquid containing the carrier (A) is obtained by dissolving, dispersing or emulsifying the carrier in water, and contains a solvent other than the carrier, an auxiliary agent such as a dispersion, an emulsifier or a stabilizer, a spinning oil, and the like. It may be. The carrier is a substance that penetrates and diffuses into the polyester fiber, increases the swelling of the polyester fiber, and changes the internal structure of the fiber so that the adhesive molecules can easily enter. The dispersion and the RFL solution are firmly bonded to the polyester fiber to improve heat resistant adhesion. Preferable examples of the carrier include phenol derivatives such as p-chlorophenol and o-phenylphenol, halogenated benzenes such as monochlorobenzene and trichlorobenzene, and a reaction product of resorcin, p-chlorophenol and formaldehyde. . A particularly preferred example is a reaction product of resorcin, p-chlorophenol and formaldehyde.

  (B) The blocked isocyanate-containing aqueous solution is not particularly limited as the isocyanate component contained, but tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate polyisocyanate is preferable, and diphenylmethane diisocyanate polyisocyanate mixture is heat resistant. Excellent in performance and preferable.

  (C) Although an epoxy compound is not specifically limited, Preferably the crosslink density of resin becomes high and the outstanding heat resistant adhesiveness is obtained by using polyfunctional epoxy more than bifunctional. Preferable examples of the epoxy compound include polyglycidyl ether compounds of aliphatic polyhydric alcohols such as glycerol / polyglycidyl ether, diglycerol / polyglycidyl ether, polyglycerol / polyglycidyl ether, and sorbitol / polyglycidyl ether.

  (D) The RFL mixed solution is an initial condensate obtained by reacting resorcin and formalin in the presence of an acid or alkali catalyst, styrene butadiene latex, carboxy-modified styrene butadiene latex, styrene butadiene vinyl pyridine latex, carboxy modified styrene butadiene vinyl pyridine latex, One or two or more mixed aqueous solutions such as natural rubber and polybutadiene latex are used. Preferably, by using a styrene butadiene vinyl pyridine latex or a carboxy-modified styrene butadiene vinyl pyridine latex, excellent heat resistant adhesiveness can be obtained. Any known technique may be applied to the blending ratio of resorcin, formalin and latex.

  In the first preferred embodiment for the dip treatment, the amine barrier layer made of isocyanate is firmly bonded to the fiber by the carrier effect by the treatment with the first treatment liquid, and the fiber and the adhesive layer adjacent to the fiber. And the deterioration of the interface between them is remarkably suppressed, and then the second treatment liquid improves the heat resistance of the RFL resin by the cross-linking modification effect of the latex with isocyanate and epoxy, and has excellent heat resistance adhesion due to the overall effect. In addition, a strong retention rate can be obtained.

  In addition, it is preferable that (B) blocked isocyanate solid content is mix | blended 40-95 weight part of said 1st process liquid with respect to 100 weight part of total solid content. If the amount is less than 40 parts by weight, the resin is not sufficiently cross-linked and sufficient heat-resistant adhesiveness cannot be obtained. If the amount is more than 95 parts by weight, the carrier component decreases, and in this case, sufficient heat-resistant adhesiveness cannot be obtained. Moreover, it is preferable that the said 2nd processing liquid is 5-40 weight part of (B) blocked isocyanate solid content with respect to 100 weight part of total solid content. If the amount is less than 5 parts by weight, the resin is not sufficiently crosslinked, and sufficient heat-resistant adhesiveness cannot be obtained. If the amount is more than 40 parts by weight, the RFL component becomes too small and sufficient initial adhesiveness cannot be obtained. Furthermore, it is preferable that the 2nd process liquid is mix | blended 0.5-10 weight part of (C) epoxy compound solid content with respect to 100 weight part of total solid content. If it is less or more than this range, good adhesion cannot be obtained.

  (E) The compound containing an oxazoline group used in the second preferred embodiment for the dip treatment is an oxazoline group (preferably a 2- A compound containing a large number of oxazoline groups). The rubber latex (F) used in the first treatment liquid together with this is preferably a styrene-butadiene-ethylenically unsaturated acid monomer copolymer latex.

  Further, the adhesion processing apparatus is not particularly limited, and can be a dipping processing apparatus normally used in the rubber industry. For example, after the cord is dip-treated in the treatment liquid, the treatment liquid is dried in the drying treatment (dry) zone at a predetermined temperature, and then the tension heat treatment (heat stretch) zone and the tension are continuously arranged. There is a method in which the physical properties of the cord are adjusted by sequentially passing through a relaxation heat treatment (heat relaxation) zone under a predetermined tension and heat setting. These devices are a single cord processor, a cord setter that can process a plurality of single cords at the same time, or a known dip processor that is commonly used in the rubber industry, such as a so-called dipping machine, that can process a weave fabric. Can do.

  By the above-mentioned adhesion treatment, the polyester cord has a rubber coverage after the peel adhesion test after the belt reinforcement layer is molded and initially vulcanized (vulcanized at 140 ° C. for 40 minutes), preferably 90% or more, more preferably Is 95% or more, more preferably 98% or more, and the rubber coverage after the peel adhesion test after overvulcanization (170 ° C. × 120 minutes vulcanization) is preferably 80% or more, more preferably 82% or more, More preferably, it becomes 85% or more.

  The polyester cord used for the belt reinforcing layers 7 and 8 has a twist number (T) of preferably more than 21 and 50 or less. Thus, by appropriately increasing the number of twists (T), the fatigue resistance of the polyester cord can be improved, and thereby the fatigue resistance can be increased. When the number of twists (T) is 21 or less, it is difficult to improve tire high-speed durability, and when it exceeds 50, it becomes difficult to maintain steering stability.

  A pneumatic radial tire having a tire size of 205 / 65R15 and having a tire structure provided with belt reinforcing layers 7 and 8 as shown in FIG. The carcass 5 is made of polyester (PET) cord 1670 dtex / 2, two plies with a driving number of 24/25 mm, and the belt 6 is steel cord 2 + 2 × 0.25 (end number 23/25 mm) with two plies (cord angle 21 degrees). And a common structure and members other than the belt reinforcing layer.

  As a polyester (PET) cord as a reinforcing cord for the belt reinforcing layer, a product of a predetermined type of “ester” manufactured by Toyobo Co., Ltd. was used as it was. The constitution and conditions of the polyester cord used in each example are as shown in Table 1 below.

  The conventional pneumatic radial tire used for comparison was a nylon cord (Ny66) instead of a polyester (PET) cord, and “Leona 66” 940 dtex / 2 manufactured by Asahi Kasei Corporation (twist number 29 × 29). Times / 10 cm) was used. That is, a twisted nylon cord obtained by adding a lower twist to a bundle of filaments having a total fineness of 940 dtx to form a yarn, and combining the two yarns and applying an upper twist in the opposite direction of the lower twist It is.

  The polyester (PET) cord as the reinforcing cord for the belt reinforcing layer was sequentially subjected to dip treatment using the following first and second treatment liquids. That is, a treatment for imparting heat-resistant adhesion was performed. In the conventional example and the comparative example 5 used for comparison, only one dipping treatment with a resorcin-formaldehyde-latex (RFL) mixed solution was performed.

  First treatment liquid: containing 1.5% by weight of a carrier (ammonia aqueous solution of p-chlorophenol / formalin resorcin condensate; Nagase ChemteX Corp. Denabond) in terms of solid content, and a blocked isocyanate aqueous solution (polyurethane pre-polymer) Polymer block, solid content 30%; Daiichi Kogyo Seiyaku Co., Ltd. Elastron BN-27) contains 22% by weight in terms of solid content.

  Second treatment liquid: Blocked isocyanate aqueous solution (polyurethane prepolymer blocked, solid content 30%; Daiichi Kogyo Seiyaku Co., Ltd. Elastron BN-27) containing 9% by weight in terms of solid content, and dispersion of epoxy compound (Sorbitol polyglycidyl ether; Nagase ChemteX Corp. Denacol EX-614) in an amount of about 1% by weight in terms of solid content, surfactant (dialkylsulfosuccinic acid ester soda salt, solid content 75%; Daiichi Kogyo Seiyaku Co., Ltd.) (Neocol P) 0.1 to 0.2% by weight in terms of solid content, and about 15% by weight of a resorcin-formalin-latex (RFL) mixed solution in terms of solid content.

  The polyester (PET) cord used for the belt reinforcing layer and the obtained tire were evaluated as follows.

  -Tensile strength (cord strength) and 2% elongation modulus: Measured by conducting a tensile test in accordance with JIS L1017 in a 22 ° C atmosphere.

  ・ Peel adhesion test: Adhesion-treated cords arranged at a density of 22 pieces / 25 mm and coated with rubber are laminated in parallel with the cord direction, 140 ° C. × 40 minutes (initial bonding), or 170 ° C. × 120 (heat resistance Adhesion) After vulcanization, a 25 mm wide peel adhesion test piece was prepared, and a peel test was carried out at a speed of 50 mm / min between layers in a 22 ° C. atmosphere using a universal testing machine. Peel adhesion strength (N / 25 mm) And the rubber coverage after peeling was visually evaluated. 100% is completely covered with rubber, and 0% is not completely covered with rubber.

High-speed tire durability: Measured as follows using a drum testing machine having a 1700 mm diameter rotating drum made of steel with a smooth surface in accordance with FMVSS109 (UTQG). The test tire was assembled to a standard rim specified by JIS under an internal pressure of 220 kPa (2.2 kgf / cm ² ), and the load was 88% of the maximum load specified by JATMA. After running in at a speed of 80 km / hr, the vehicle was allowed to cool, and after adjusting the air pressure again, the main run was performed. The running started from 120 km / hr, and thereafter, the running speed was increased by 8 km / hr every 30 minutes until the failure occurred. The total travel distance of the main travel until the occurrence of the failure is shown in Table 1 as an index with the conventional example being 100. The higher the index value, the better the high speed durability.

  Actual vehicle handling stability: Each tire was adjusted to an internal pressure of 200 kPa using a JIS standard rim and mounted on a passenger car with a displacement of 2000 cc. Then, in the test course for evaluating steering stability, three trained test drivers performed a comprehensive sensory evaluation of steering stability such as steering response, rigidity, and grip. At this time, the conventional example was set to 6 points and relative comparison was performed with a maximum of 10 points. The larger the value, the better the steering stability.

  As shown in the results of Table 1, in Examples 1 to 4, it was possible to improve actual vehicle handling stability and tire high-speed durability. In addition, the effect of reducing the weight of the tire was great. These effects were implemented in Examples 1 to 3 in which the twist coefficient was in the range of 800 to 2000, larger than that in Example 4, and more in the range of 800 to 1700. Greater than in Examples 3-4. In particular, the most remarkable effect was obtained by Example 2.

  The pneumatic radial tires of Comparative Examples 1 to 5 are the same as the tires of Examples 1 and 2 except for the configurations mentioned below. The tire of Comparative Example 1 uses a polyester (PET) cord having a nominal fineness (D) of 840 dtx, which is lower than the above-mentioned predetermined range, and a twist coefficient (K) of 691 is low. / 25 mm and significantly increased. For this reason, adhesion failure tends to occur at the cut end portion of the polyester (PET) cord, and the high-speed durability is greatly reduced. However, data are not shown, but there was no problem with handling stability. The tire of Comparative Example 2 uses a polyester (PET) cord having a nominal fineness (D) of 2200 dtx, which exceeds the above-mentioned predetermined range. As a result, although high-speed durability is improved, the tire weight is increased. Oops.

  The tire of Comparative Example 3 used a polyester (PET) cord having a twisting coefficient (K) of 661, which was lower than the above-mentioned predetermined range. As a result, the tire high speed durability was greatly reduced. This is thought to be because the fatigue resistance of the polyester (PET) cord was lowered because the number of twists of the polyester cord was as low as 19. As a result of using a polyester (PET) cord having a twist coefficient (K) of 2018 and exceeding the above-mentioned predetermined range, the tire of Comparative Example 4 has improved tire high-speed durability, but the actual vehicle handling stability Was low. This is presumably because the number of twists is excessively high at 58, and the rigidity of the tire is thus lowered.

  In Comparative Example 5, one-time dip treatment with a resorcin-formaldehyde-latex (RFL) mixed solution was performed on a polyester (PET) cord without imparting heat-resistant adhesion by immersing in the first and second treatment liquids described above. As a result, only high-speed durability was remarkably low. This is presumably because the heat-resistant adhesiveness is remarkably low, as is known from the fact that the rubber adhesion rate after overvulcanization is remarkably low.

  In the above embodiment, the belt reinforcing layer 7 covering the entire width (A + B) of the belt 6 is described. However, the belt reinforcing layer 7 is provided only in the region corresponding to both end portions (B) of the belt 6, that is, the shoulder portion. May be. That is, even if only the belt reinforcing layer 8 corresponding to the folded portion is provided, the use of the above-described polyester (PET) cord realizes improvement in steering stability and tire high-speed durability and weight reduction of the tire. be able to.

  As described above, the pneumatic radial tire of the present invention is excellent in handling stability, ride comfort, and durability and realizes weight reduction, and is particularly suitable for various types of passenger car tires.

3 ... tread part, 5 ... carcass, 6 ... belt, 7, 8 ... belt reinforcement layer T ... pneumatic radial tire

Claims (3)

A belt layer provided in the tread portion, and a belt reinforcing layer disposed on the outer side in the radial direction of the belt layer so as to cover at least both ends of the belt layer, and a fiber having a polyester single twist structure in the belt reinforcing layer In a pneumatic radial tire using a cord, as the fiber cord, (1) the nominal fineness (D) is 1000 to 2000 dtex, (2) the twist coefficient (K) represented by the following formula (I) is 700 to 2000, and (3) at least one of a blocked isocyanate aqueous solution and an epoxy compound dispersion, and a resorcin-formaldehyde-latex (RFL) mixed solution at least used for dipping.
K = T · (D / 1.38) ^1/2 …… (I);
Here, T is the number of twists per 10 cm (times / 10 cm), D is the nominal fineness (dtex) of the entire cord, and 1.38 is the specific gravity of the polyester.   When the fiber cord is rubberized with a rubber material for a belt reinforcing layer and vulcanized at 140 ° C. for 40 minutes and then subjected to a peel test from the rubber layer, the rubber adhesion rate is 90% or more, and 170 ° C. 2. The pneumatic radial tire according to claim 1, wherein a rubber adhesion rate is 80% or more when a peel test from a rubber layer is performed after 120 minutes of overvulcanization.   The pneumatic radial tire according to claim 1 or 2, wherein a twist number (T) per 10 cm of the fiber cord is greater than 21 and 50 or less.

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