JP2012179943A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire suppressed in degradation of RFV or a flat spot when a hybrid cord using a cellulose fiber is used for a carcass ply, and is applied to an envelope structure.SOLUTION: This pneumatic radial tire uses a carcass 4 toroidally extending between a pair of right and left bead cores 6 as a skeleton, and includes a belt 8 arranged in the outside in a tire radial direction of a crown part of the carcass. A carcass ply cord is a hybrid cord formed by intertwining a filament formed of a cellulose fiber with a filament formed of nylon. At least one sheet out of the carcass ply includes a body part extending between the bead cores, and a folded part folded from the inside toward the outside in the tire width direction around the bead cores; an end of the folded part is inserted in the inside of the belt in the tire radial direction; and insertion length of the end of the folded part is 10-23 mm.

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more particularly, to a pneumatic radial tire according to a carcass reinforcing cord and improved arrangement conditions.

  As carcass cords for high performance tires and run flat tires, cellulose fibers typified by rayon have been generally used. However, with respect to rayon, environmental pollution in the manufacturing process has become a problem, and the number of manufacturers producing it has decreased, and the price has increased accordingly. For this reason, it has been proposed to use a hybrid code including rayon instead of rayon as a carcass ply code based on a request for response to environmental problems and specification optimization.

  On the other hand, with regard to the tire structure, in recent years, studies have been made in the direction of simplifying the structure from the viewpoint of improving rolling resistance. As a ply structure, a single carcass ply is used, and this is arranged around the bead core. An increasing number of cases adopt a structure (so-called envelope structure) in which the folded end is disposed inside the belt disposed in the tread portion (see, for example, Patent Document 1).

JP 2001-030712 A (Claims etc.)

  However, when the carcass ply using the hybrid cord is applied to an envelope structure using the one carcass ply, radial force variation (RFV) and a flat spot may be deteriorated. . Here, RFV indicates the magnitude of force fluctuation in the tire radial direction, and is one of the indices of tire uniformity. The flat spot refers to a phenomenon in which, after the tire generates heat by running and is cooled in a state where a load is applied, the roundness of the tire collapses and vibration is generated when the running starts again.

  Therefore, an object of the present invention is to provide a pneumatic radial tire that suppresses deterioration of RFV and flat spots when a hybrid cord using cellulose fibers such as rayon is used for a carcass ply and applied to an envelope structure. There is to do.

  As a result of intensive studies, the present inventor has found that the deterioration of the RFV and the flat spot is caused by a lack of insertion amount under the belt at the folded end of the carcass ply in the envelope structure. The inventors have found that the above problems can be solved by appropriately defining the material, and have completed the present invention.

That is, the pneumatic radial tire of the present invention has a carcass made of one or more carcass plies extending in a toroidal shape between a pair of left and right bead cores, and is disposed on the outer side in the tire radial direction of the crown portion of the carcass. In a pneumatic radial tire including a belt composed of one or more belt layers,
The carcass ply cord is a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon,
At least one of the carcass plies includes a main body portion extending between the bead cores and a folded portion that is folded from the inner side to the outer side in the tire width direction around the bead core, and the end of the folded portion is the belt. And the insertion length of the end of the folded portion is in the range of 10 to 23 mm.

  In the present invention, the ratio of the dtex number of nylon to the total dtex number of the hybrid cord is 20 to 50%, and the thermal shrinkage rate at 170 ° C. of the hybrid cord in a green tire is 1.0% or more. It is preferable that it is 4.0% or less. In addition, the difference between the maximum value and the minimum value when the heat shrinkage rate at 170 ° C. of the hybrid cord in the green tire is measured at 10 points at equal intervals in the tire circumferential direction is within 0.55%. Is preferred.

  Furthermore, in the present invention, it is preferable that the difference between the heat shrinkage rate at 175 ° C. and the heat shrinkage rate at 165 ° C. of the hybrid cord in the green tire is 1.2% or less. Further, the hybrid cord extracted from the product tire has a heat shrinkage stress (cN / dtex) at 177 ° C. of 0.10 cN / dtex or more and a tensile elastic modulus at 3% strain at 25 ° C. of 12 cN / It is preferable that it is dtex or more. The tire of the present invention is suitable as a run flat tire.

  According to the present invention, with the above-described configuration, air that suppresses deterioration of RFV and flat spots when a hybrid cord using cellulose fibers such as rayon is used for a carcass ply and is applied to an envelope structure. It has become possible to realize a radial tire with an inside. Since the amount of rayon used can be reduced in the tire of the present invention, it can be said that the tire of the present invention is excellent in environmental performance.

It is a width direction one side sectional view showing an example of the pneumatic radial tire of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional side view in the width direction showing a run-flat tire as an example of the pneumatic radial tire of the present invention. The illustrated tire of the present invention includes a pair of left and right bead portions 1, a pair of sidewall portions 2 that are continuous from the bead portion 1 to the outside in the tire radial direction, and a grounding portion that extends between the pair of sidewall portions 2. A carcass 4 comprising one or more carcass plies that extend in a toroidal shape between a pair of bead parts 1 and reinforce each of these parts 1, 2, 3; A side reinforcing rubber layer 5 having a crescent-shaped cross section disposed inside the carcass 4.

  In the illustrated tire, a bead filler 7 is disposed on the outer side in the tire radial direction of the ring-shaped bead core 6 embedded in the bead portion 1, and on the outer side in the tire radial direction of the crown portion of the carcass 4. A belt 8 composed of two belt layers is arranged. Further, on the outer side in the tire radial direction of the belt 8, a belt reinforcing layer 9A covering the entire belt 8 and a pair of belt reinforcing layers 9B covering only both ends of the belt reinforcing layer 9A are disposed.

  In the illustrated example, the carcass 4 is composed of one carcass ply formed by coating a plurality of carcass ply cords arranged parallel to each other with a coating rubber. In the tire of the present invention, the number of plies of the carcass 4 is Is not limited to this. As shown in the figure, in the tire of the present invention, at least one of the carcass plies constituting the carcass 4 has a main body portion 14 </ b> A extending in a toroidal shape between a pair of bead cores 6, and the tire width around each bead core 6. It has a so-called envelope structure in which the folded portion 14B is folded from the inner side to the outer side, and the end of the folded portion 14B is inserted inside the belt 8 in the tire radial direction.

  In the present invention, the insertion length x of the end of the folded portion 14B to the inner side in the tire radial direction of the belt 8 is in the range of 10 to 23 mm, preferably 10 to 20 mm, more preferably 12 to 20 mm. The point is important. When the carcass has the above-described envelope structure, in particular, the envelope structure composed of one carcass ply as shown in the figure, the insertion length x of the end of the folded portion 14B is defined within the above range, so that a specific material described later The desired effect of the present invention can be obtained in combination with the hybrid cord. If the insertion length x at the end of the folded portion 14B to the inner side of the belt 8 is insufficient, the ground contact shape changes. If the insertion length x is too long, the warp of the belt increases. However, the RFV and flat spot will deteriorate.

  In the present invention, a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon is used as the carcass ply cord in combination with the adoption of the carcass structure. As a carcass ply cord for high-performance tires and run-flat tires, this hybrid cord is used in place of the conventional rayon cord, reducing the amount of rayon used and making the tire excellent in environmental performance It became possible.

  Cellulose fibers such as rayon and lyocell are not very high in heat shrinkage stress but high in rigidity. Nylon is low in rigidity but high in heat shrinkage stress. In addition, a hybrid cord with low initial rigidity can be obtained. In the present invention, such a hybrid cord is used as a carcass ply cord, and particularly in the case of a run flat tire, the rise of the vertical spring during normal running is suppressed and the ride comfort is kept good, and the run comfort is maintained. It is possible to improve the run-flat running durability by suppressing the deflection of the tire during flat running.

  Furthermore, in the present invention, resorcin / formaldehyde which has been conventionally used as an adhesive for dip cord production by using a combination of cellulose fiber and nylon as the two types of organic fibers constituting the hybrid cord. An RFL-based adhesive liquid using latex (RFL) can be used, and an advantage that adhesion can be ensured by treatment with one type of adhesive is also obtained. Organic fibers based on polyester or aramid, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polytrimethylene terephthalate (PTT), have poor adhesion to rubber due to their chemical properties. In order to ensure, for example, pretreatment with blocked isocyanate or epoxy resin or the like is required, and the number of man-hours during the adhesive coating process increases. In addition, when using aramid fiber or polyketone fiber, it is inferior to cellulose fiber or nylon fiber, so in order to secure fatigue, it must be twisted to a high twist, and the number of twisting processes is reduced. In addition to increasing, the diameter of the hybrid cord may become too thick. As a result, in the combination of organic fibers other than cellulose fiber and nylon, the adhesion cannot be secured unless two types of adhesives are used, and when two types of adhesives are used, the number of dip treatment steps is reduced. In addition, the side reaction may occur by mixing two types of adhesives, and in any case, it is not sufficient in practice.

  In the present invention, the ratio of the dtex number of nylon to the total dtex number of the hybrid cord is 20 to 50% by mass, particularly 30 to 40% by mass, and the hybrid cord in a green tire is at 170 ° C. The thermal shrinkage rate is preferably 1.0% to 4.0%, particularly preferably 2.0% to 3.0%. If the ratio of nylon in the hybrid cord is smaller than this range, the heat shrinkage stress as the hybrid cord becomes smaller, and if it is larger than this range, the tensile elastic modulus becomes lower. By setting the ratio of nylon in the hybrid cord within this range, 50% or more of highly elastic cellulose fibers are contained, which can contribute to improvement in tire durability. Also, if the nylon ratio is less than 20% and the thermal shrinkage of the cord is less than 1.0%, the cord shrinkage during vulcanization is too small and the slack of the carcass ply cord in the bead folded portion during molding Is not resolved, and the radial force variation (RFV) of the tire becomes large. On the other hand, if the thermal contraction rate of the cord exceeds 4.0%, the thickness of the rubber in the vicinity of the cord becomes non-uniform due to tightening due to excessive thermal contraction of the ply cord during vulcanization, and the RFV becomes large.

  In the present invention, the difference between the maximum value and the minimum value when the thermal shrinkage rate at 170 ° C. of the hybrid cord in the green tire is measured at 10 points at equal intervals in the tire circumferential direction is 0.55. %, Particularly within 0.5%, more preferably within 0.4%. This difference is preferably as small as possible. Exceeding the above range is not preferable because RFV is deteriorated.

  Furthermore, in the present invention, the difference between the heat shrinkage rate at 175 ° C. and the heat shrinkage rate at 165 ° C. of the hybrid cord in the green tire is 1.2% or less, particularly 0.8% or less. It is preferable. This is because the deterioration of uniformity can be suppressed as the fluctuation of the heat shrinkage rate near the vulcanization temperature of the tire is smaller. Therefore, this difference is preferably as small as possible. Exceeding the above range is not preferable because the RFV is deteriorated.

  Furthermore, in the present invention, it is preferable that the thermal contraction stress (cN / dtex) at 177 ° C. of the hybrid cord extracted from the product tire is 0.10 cN / dtex or more. By having the heat shrinkage stress in this range, it is possible to make the ride comfort and the run-flat running durability during normal running in the run-flat tire as described above highly compatible. If the thermal contraction stress at 177 ° C. of the hybrid cord extracted from the product tire is less than 0.10 cN / dtex, the run-flat running durability becomes insufficient. The higher the heat shrinkage stress, the better, for example, 0.12 to 0.25 cN / dtex. Here, the heat shrinkage stress at 177 ° C. of the tire drawn cord is generated in the cord at 177 ° C. when the cord in the section of the carcass cord sandwiched between the bead cores is drawn and heated at a heating rate of 5 ° C./min. It can be obtained as stress.

  Moreover, as such a hybrid cord, as a cord extracted from a product tire, a tensile elastic modulus at 1% strain at 25 ° C. is 45 cN / dtex or less, particularly 18 to 35 cN / dtex, and 3% strain at 25 ° C. The tensile modulus at the time is preferably 12 cN / dtex or more, particularly 15 to 30 cN / dtex. Since the longitudinal spring is desired to be small at the time of low strain, the tensile elastic modulus at 1% strain is preferably 45 cN / dtex or less for the tire pulling cord. This corresponds to, for example, a value equal to or lower than the tensile elastic modulus of rayon. On the other hand, in order to obtain the effect of suppressing the bending at the time of high strain, the tensile elastic modulus at the time of 3% strain is preferably set to 12 cN / dtex or more with the tire drawing cord. This corresponds to, for example, the same or higher value of the same tensile elastic modulus of rayon.

  In the present invention, the method for adjusting the heat shrinkage stress and the tensile elastic modulus of the hybrid cord includes a method for controlling the tension and temperature during the adhesive treatment (dip treatment). For example, a high tension is applied. However, by performing the dipping process, the value of the heat shrinkage stress of the cord can be increased. Further, by performing the dipping process at a low temperature, the value of the heat shrinkage stress of the cord can be increased. That is, although there is a range of physical property values unique to each organic fiber, a hybrid cord having desired physical properties can be obtained by controlling the above dip treatment conditions to adjust the physical property value within the range. is there.

  In the present invention, the number of twists of the two organic fibers constituting the hybrid cord is 30 to 60 times / 10 cm, and the number of twists of the hybrid cord is 25 to 60 times / 10 cm. preferable. By setting the number of twists and the number of upper twists of the hybrid cord within this range, the target tensile elastic modulus can be realized.

  In the tire of the present invention, it is only important to satisfy the conditions relating to the above carcass, and other details of the tire structure and the material of each member are not particularly limited, and are appropriately selected from conventionally known ones Can be configured.

  For example, the belt layer is usually composed of a rubberized layer of a cord that extends at an angle of 10 ° to 40 ° with respect to the tire equatorial plane, and preferably a rubberized layer of a steel cord. The belt 8 is formed by laminating the cords constituting the layers so as to cross each other with the equator plane interposed therebetween. In the illustrated example, the belt 8 includes two belt layers. However, in the tire of the present invention, the number of belt layers constituting the belt 8 is not limited to this. The belt reinforcing layers 9A and 9B are usually made of rubberized layers of cords arranged substantially parallel to the tire circumferential direction. However, in the present invention, the belt reinforcing layers 9A and 9B are not necessarily provided. Alternatively, a belt reinforcing layer having a different structure may be provided.

  Furthermore, in the tire of the present invention, a tread pattern is appropriately formed on the surface of the tread portion 3, and an inner liner (not shown) is formed in the innermost layer. In the tire of the present invention, as the gas filled in the tire, normal or air having a changed oxygen partial pressure, or an inert gas such as nitrogen can be used.

Hereinafter, the present invention will be described in more detail with reference to examples.
A side reinforcing type run-flat tire as shown in FIG. 1 was produced at a tire size of 225 / 45R17. The carcass is composed of one carcass ply having the specifications shown in the following table, and has a so-called envelope structure in which the end of the folded portion is inserted inside the belt in the tire radial direction. The belt was composed of two belt layers arranged in an intersecting manner at an angle of ± 30 ° with respect to the tire circumferential direction.

<RFV measurement>
Each test tire was assembled on a rim having a rim size of 71 / 2J, and radial force variation (RFV) was measured according to the uniformity measurement method defined in JASO C 607 (2000) under the conditions of an internal pressure of 200 kPa and a load load of 4410 N. . The results are shown as an index with the RFV of the tire of Comparative Example 1 as 100. The smaller the index value, the higher the uniformity (uniformity) of the tire and the better. The results are also shown in the table below.

  As shown in the above table, a hybrid cord formed by twisting a filament made of rayon and a filament made of nylon is used as a carcass ply cord, and the insertion length of the folded portion end of the carcass ply below the belt is 10 to 23 mm. It was confirmed that the RFV was suppressed to a low value in the test tires of the examples. On the other hand, in Comparative Example 2 in which the insertion length of the folded portion end of the carcass ply is 25 mm, the insertion length is long, so that the shoulder region is higher in the tire radial direction than the tire center region. Thus, it can be seen that RFV is getting worse.

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 4 Carcass 5 Side reinforcement rubber layer 6 Bead core 7 Bead filler 8 Belt 9A, 9B Belt reinforcement layer

Claims (6)

A carcass composed of one or more carcass plies extending in a toroidal shape between a pair of left and right bead cores is provided as a skeleton, and a belt composed of one or more belt layers disposed on the outer side in the tire radial direction of the crown portion of the carcass is provided. In pneumatic radial tires,
The carcass ply cord is a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon,
At least one of the carcass plies includes a main body portion extending between the bead cores and a folded portion that is folded from the inner side to the outer side in the tire width direction around the bead core, and the end of the folded portion is the belt. A pneumatic radial tire characterized by being inserted inside the tire in the radial direction of the tire and having an insertion length of the end of the folded portion in the range of 10 to 23 mm.   The ratio of the dtex number of nylon to the total dtex number of the hybrid cord is 20 to 50%, and the thermal shrinkage rate at 170 ° C. of the hybrid cord in a green tire is 1.0% to 4.0%. The pneumatic radial tire according to claim 1.   The difference between the maximum value and the minimum value when the thermal contraction rate at 170 ° C of the hybrid cord in a green tire is measured at 10 points at equal intervals in the tire circumferential direction is within 0.55%. Or the pneumatic radial tire of 2.   The pneumatic radial according to any one of claims 1 to 3, wherein a difference between a heat shrinkage rate at 175 ° C and a heat shrinkage rate at 165 ° C of the hybrid cord in a green tire is 1.2% or less. tire.   The hybrid cord extracted from the product tire has a heat shrinkage stress (cN / dtex) at 177 ° C. of 0.10 cN / dtex or more and a tensile elastic modulus at 3% strain at 25 ° C. of 12 cN / dtex or more. The pneumatic radial tire according to any one of claims 1 to 4.   It is a run flat tire, The pneumatic radial tire as described in any one of Claims 1-5.

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