JP2013226982A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire which solves problems by improving a carcass cord, and which is environment friendly, and especially, has improved tire strength without impairing tire durability.SOLUTION: A pneumatic tire has a carcass 2 as a framework, consisting of one carcass ply or more extending in a toroidal form between a pair of bead cores 1 buried in right and left pair of bead sections 11 respectively. The cord of at least one carcass ply in carcass plies is a hybrid cord formed by twisting a filament made of a cellulose fiber and a filament made of a nylon fiber together. Absolute dry fineness A (dtex) of the cellulose fiber, absolute dry fineness B of the nylon fiber, and the tensile strength C(N) of the hybrid cord pulled out from a tire, satisfy relation expressed by C>(5×A+8×B) ×0.007.

Description

  The present invention relates to a pneumatic tire (hereinafter also simply referred to as “tire”), and more particularly to a pneumatic tire according to an improvement in a carcass reinforcing cord.

  Conventionally, when nylon fiber is applied to a carcass reinforcing cord, it is known that the uniformity of the tire is deteriorated due to large thermal shrinkage during vulcanization. Therefore, in recent years, it has become the mainstream to use cellulose fibers and polyester fibers having a low thermal shrinkage rate as a material for reinforcing cords for carcass.

  However, when polyester fiber is applied to high-performance tires or run-flat tires that are expected to be used in high-speed or high-load environments, durability is insufficient due to low adhesion at high temperatures. There was a problem. For this reason, as a carcass cord for high-performance tires and run-flat tires, cellulose fibers typified by rayon having high dimensional stability are generally used. However, since rayon is highly elastic, rayon can be used alone as a carcass cord. When used in a cord, there is a problem that the rigidity of the tire increases and the ride comfort deteriorates. In addition, since the rayon cord does not have a heat shrinking force, the effect of suppressing bending in a high temperature environment such as during high speed running cannot be obtained, and it cannot contribute to the improvement of tire durability at high temperatures.

Furthermore, for rayon, environmental pollution due to the generation of CS ₂ and toxicity of Zn used in the production process are becoming problems, and due to this, the number of manufacturers has decreased year by year. Supply has become insufficient, and prices have risen accordingly. Against this background, it can be said that reducing the amount of rayon used for high-performance tires and run-flat tires is one measure for solving environmental problems. On the other hand, as one of the techniques for reducing the use amount of such rayon, it has been proposed to use a hybrid cord including rayon instead of rayon as a carcass ply cord (see, for example, Patent Document 1). ).

  Patent Document 2 defines the value of the heat shrinkage stress at 177 ° C. for each of the hybrid cord of cellulose fiber and nylon used for the carcass ply cord after the adhesive treatment and after being extracted from the product tire. A run flat tire is disclosed.

JP 2010-058740 A (Claims etc.) JP 2011-068342 A (Claims etc.)

  However, in the case of a hybrid cord formed by combining cellulose fibers and nylon fibers having greatly different elongations, the tensile strength is low, and when this cord is applied to a carcass, the strength (fracture energy) of the tire is reduced. This low tire strength can be compensated for by increasing the number of carcass shots. In that case, the rubber ratio (void ratio) contained in the carcass ply is reduced, and the tire durability test is performed. Another problem is that adhesion failure starting from a large number of parts is observed, and the durability of the tire is lowered. Accordingly, it has been desired to establish a technique for improving the tire strength without deteriorating the durability and the tire durability.

  Accordingly, an object of the present invention is to provide a pneumatic tire which solves the above problems by improving the carcass cord and is excellent in environmental performance, and in particular, has improved tire strength without impairing tire durability.

  As a result of intensive studies, the inventor used a hybrid cord obtained by twisting a filament made of cellulose fiber and a filament made of nylon fiber as the carcass cord, and the tensile strength value of the hybrid cord was determined by cellulose fiber and nylon fiber. The present invention has been completed by finding that the above-mentioned problems can be solved by prescribing within a specific range in relation to the degree of dryness of the fiber.

That is, the present invention is a pneumatic tire having a skeleton of a carcass made of one or more carcass plies extending in a toroid shape between a pair of bead cores embedded in a pair of left and right bead portions,
The cord of at least one of the carcass plies is a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon fiber, and the dryness A (dtex) of the cellulose fiber The absolute dryness B (dtex) of the nylon fiber and the tensile strength C (N) of the hybrid cord extracted from the tire are represented by the following formula (1),
C> (5 × A + 8 × B) × 0.007 (1)
It is characterized by satisfying the relationship indicated by.

In the present invention, when the cord diameter of the hybrid cord is D (mm) and the number of driving of the at least one carcass ply in the bead portion is E (lines / 50 mm), F = (1−D × E / 50) × 100 (%) The ratio of the rubber contained in the carcass ply in the bead portion is preferably more than 15% and less than 40%. In the present invention, the cord diameter D (mm) of the hybrid cord is expressed by the following formula (2),
D <0.0001 × (A + B) +0.45 (2)
Is preferably satisfied.

  Furthermore, in the present invention, the cord diameter D (mm) of the hybrid cord is preferably more than 0.5 mm and less than 1.0 mm. Furthermore, the number of upper twists of the hybrid cord is preferably in the range of 20-50 times / 10 cm, the number of lower twists of the nylon fiber is preferably in the range of 0-50 times / 10 cm, and the cellulose fiber The number of under twists is preferably in the range of 0-50 times / 10 cm.

  According to the present invention, by adopting the above-described configuration, it is possible to realize a pneumatic tire that is excellent in environmental performance, and in particular, has improved tire strength without impairing tire durability.

It is a width direction sectional view showing an example of the pneumatic tire of the present invention. It is explanatory drawing which concerns on the calculation method of the cord diameter of the carcass ply cord and the number of driving in an Example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view in the width direction showing an example of the pneumatic tire of the present invention. The pneumatic tire of the present invention shown in the figure has a carcass 2 made of a single carcass ply extending in a toroid shape between a pair of bead cores 1 embedded in a pair of left and right bead portions 11, respectively, and a crown thereof. Two belt layers 3a and 3b are provided on the outer side in the tire radial direction.

  The carcass 2 is one in the illustrated example, but may be two or more, and preferably one or two. Further, the belt layers 3a and 3b are formed by rubber coating a plurality of steel cords arranged at an angle of, for example, 15 to 40 ° with respect to the tire circumferential direction, and are two layers in the illustrated example. However, the number of layers may be three or more, for example, two to four layers.

  In the present invention, as a carcass ply cord, it is important to use a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon fiber (aliphatic polyamide). By using such a hybrid cord as the carcass ply cord, it is possible to reduce the amount of rayon used and to make the tire excellent in environmental performance. In addition, the effect of improving the fatigue properties in comparison with the rayon cord can be obtained.

  Cellulose fibers such as rayon and lyocell are not very high in heat shrinkage stress, but are highly rigid.Nylon fiber is low in rigidity but high in heat shrinkage stress. In addition, a hybrid cord having low initial rigidity can be obtained. In the tire of the present invention, by using such a hybrid cord as a carcass ply cord, particularly in the case of a run flat tire, the rise of the vertical spring during normal running is suppressed by the effect of containing nylon, thereby improving the riding comfort. While maintaining good, it is possible to improve the run-flat running durability by suppressing the deflection of the tire in a high-temperature environment during the run-flat running. Further, even in a tire that is not a run-flat tire, high-speed durability can be improved by suppressing growth in the radial direction of the tire in a high-temperature environment during high-speed running.

  Furthermore, in the present invention, a combination of cellulose fiber and nylon fiber is used as the two types of organic fibers constituting the hybrid cord, so that resorcinol, which has been conventionally used as an adhesive at the time of dip cord production, is used. An RFL-based adhesive liquid using formaldehyde latex (RFL) can be used, and there is also an advantage that adhesion can be ensured by treatment with one type of adhesive. 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 fibers and nylon fibers, adhesiveness cannot be ensured unless two types of adhesives are used, and when two types of adhesives are used, the number of dip treatment steps In addition, there is a possibility that a side reaction may occur by mixing two kinds of adhesives, and in any case, it is not sufficient in practice.

  Here, examples of the cellulose fiber used in the present invention include rayon, lyocell, and cupra. Examples of nylon fibers include 66 nylon, 6 nylon, 4, 6 nylon, and the like.

In the present invention, in addition to the combination of materials used for the hybrid cord, the absolute dryness A (dtex) of the cellulose fiber, the absolute dryness B (dtex) of the nylon fiber, and the tensile strength of the hybrid cord extracted from the tire C (N) is represented by the following formula (1),
C> (5 × A + 8 × B) × 0.007 (1)
It is important to satisfy the relationship indicated by. The conventional rayon / nylon fiber hybrid cord has an ideal tension that is multiplied by the fineness when the rayon yarn strength is 5.0 cN / dtex and the nylon fiber yarn strength is 8.0 cN / dtex. It has only a tensile strength of about 60% of the strength, and therefore sufficient tire strength could not be obtained. If the present inventor is a hybrid cord that can maintain a tensile strength of 70% or more with respect to the ideal tensile strength, that is, if the tensile strength C satisfies the above formula (1), It has been found that a sufficient tire strength can be maintained when the cord is applied to a carcass ply. In the present invention, the value of the tensile strength C of the hybrid cord satisfying the above formula (1) is adjusted as appropriate within the scope of the present invention by the rubber ratio F, the cord diameter D, and the cord twist coefficient described later. Can be obtained.

  In the present invention, when the cord diameter of the hybrid cord is D (mm) and the number of driving in the bead portion of the carcass ply using this hybrid cord as the carcass ply cord is E (lines / 50 mm), F = ( It is preferable that the ratio of the rubber contained in the carcass ply in the bead portion defined by 1−D × E / 50) × 100 (%) is more than 15% and less than 40%. If the ratio F of the rubber contained in the carcass ply is too large, the strength as the carcass ply may not be maintained, which is not preferable. On the other hand, if the rubber ratio F is too small, a sufficient amount of rubber cannot be secured between the cords, causing separation due to insufficient adhesion during the durability test, and there is a risk that sufficient durability cannot be obtained. is there. Accordingly, the rubber ratio F is preferably more than 15% and less than 40%, more preferably 20% or more and 30% or less.

In the present invention, the cord diameter D (mm) of the hybrid cord is expressed by the following formula (2),
D <0.0001 × (A + B) +0.45 (2)
Is preferably satisfied. Since the hybrid cord is formed by twisting fibers having different elongations, the cross-section of the hybrid cord tends to be a cross-section from a perfect circle. Therefore, the cord diameter D (mm) is also D = 0.0001 × The (A + B) +0.50 was very thick compared to the conventional fibers. On the other hand, in the present invention, by improving the number of twists of the cord, the twisting conditions and the heat treatment conditions, a cord satisfying the above formula (2) can be obtained, thereby making it possible to keep the cord diameter small. It has become. Therefore, since the ratio F of the rubber can be increased if the number of driving is the same, durability can also be improved. If the cord diameter is too small, sufficient tensile strength may not be obtained. On the other hand, if the cord diameter is too large, the weight increases. Specifically, the cord diameter D (mm) is preferably more than 0.5 mm and less than 1.0 mm, and more preferably more than 0.5 mm and 0.8 mm or less.

  In the present invention, the number of twists of the hybrid cord is preferably in the range of 20 to 50 times / 10 cm. As for the number of twists of the cord, the smaller the number of upper twists, the higher the tensile strength and the smaller the cord diameter, which is preferable. However, if the amount is too small, the fatigue property deteriorates, so 20-50 times / 10 cm is preferable. . More preferably, the number of twists of the hybrid cord is 35 to 45 times / 10 cm. If the number of twists exceeds 50 times / 10 cm, the cord diameter becomes thick and the weight increases, which is not preferable.

  Furthermore, in the present invention, the number of twisted nylon fibers and cellulose fibers constituting the hybrid cord is preferably in the range of 0 to 50 times / 10 cm. The smaller the number of lower twists, the greater the tensile strength. However, if the number is too small, the fatigue properties of the cord will be reduced. Therefore, the tire strength is increased, while the tire durability is deteriorated. The number of twists of nylon fibers and cellulose fibers is more preferably in the range of 20 to 40 times / 10 cm.

  A hybrid cord satisfying the above physical property conditions can be obtained by appropriately adjusting the number of twists of the cord, twisting conditions, and heat treatment conditions. As the twisting machine, there are types such as a ring twisting machine and a twisting machine called a direct twisting machine that continuously performs a lower twisting and an upper twisting, but it is preferable to perform twisting with a high twisting tension regardless of the apparatus. On the other hand, when twisting with a high twist tension, the rayon filament rubs and the tensile strength decreases. Must be kept to a minimum. As a means for obtaining high twist tension, although depending on the apparatus, such as increasing the number of rotations or increasing the weight of the traveler, any method may be used.

  As the heat treatment conditions, it is preferable to increase the cord tension during the heat treatment. However, if the tension is too high, the heat shrinkage rate increases, and the cord may shrink during tire vulcanization and the uniformity may deteriorate, so it is necessary to select appropriate tension conditions. As an adhesive to be applied to the cord during the heat treatment, an RFL-based adhesive liquid using resorcin / formaldehyde / latex (RFL) which has been conventionally used can be used, and when the adhesion amount of the adhesive is increased. The tensile strength of the cord decreases. On the other hand, when the adhesion amount is lowered, the tensile strength is increased, but the adhesiveness is lowered. Therefore, it is important to set an appropriate adhesion amount.

  In the tire of the present invention, when there are two or more carcass plies, the cord of at least one of the carcass plies only needs to be a hybrid cord that satisfies the above-described conditions. An effect can be obtained. Preferably, all the carcass ply cords are hybrid cords that satisfy the above conditions. 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, in the illustrated example, the cap layer 4 and the layer layer 5 are disposed on the outer side in the tire radial direction of the belt layers 3a and 3b. However, these arrangements are arbitrary in the present invention and are not provided. May be. The cap layer 4 and the layer layer 5 are both rubberized organic fiber cords arranged substantially parallel to the tire circumferential direction. As shown in the figure, the cap layer 4 includes the belt layer 3a, At least one layer is arranged over the entire width of 3b, and the layer layer 5 is arranged in at least one layer in both end regions of the belt layers 3a and 3b.

  As shown in the figure, a bead core 1 is embedded in each of the pair of bead portions 11 of the tire of the present invention, and the carcass 2 is folded around the bead core 1 from the inside of the tire to the outside to be locked. Further, a bead filler 6 is disposed outside the bead core 1 in the tire radial direction. Furthermore, a tread portion 12 is disposed on the outer periphery of the crown portion of the belt layers 3 a and 3 b, and a sidewall portion 13 is disposed on the side portion of the carcass 2. Furthermore, a tread pattern is appropriately formed on the surface of the tread portion 12, and an inner liner (not shown) is formed on the innermost layer. Furthermore, 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.

  The present invention can be applied to a so-called run-flat tire in which a side reinforcing rubber layer having a crescent cross section is disposed inside the carcass 1 in the side wall portion 13 in addition to the normal tire as shown in the drawing.

Hereinafter, the present invention will be described in more detail with reference to examples.
A pneumatic tire as shown in FIG. 1 was produced at a tire size of 225 / 45R18. The carcass was composed of a single carcass ply using a hybrid cord formed by twisting a filament made of cellulose fiber and a nylon fiber having the specifications shown in the following table as a carcass ply cord. Here, the cordonka rayon was used as the cellulose fiber constituting the hybrid cord, and nylon 66 manufactured by Asahi Kasei Co., Ltd. was used as the nylon fiber. Further, the belt was composed of two steel belt layers arranged in an intersecting manner at an angle of ± 40 ° with respect to the tire circumferential direction. Furthermore, a cap layer and a layer layer formed by rubber-drawing organic fiber cords (material: nylon) arranged substantially parallel to the tire circumferential direction were arranged one by one.

<Absolute dryness>
The absolute dry fineness of the used cellulose fiber and nylon fiber was measured in accordance with the test method for positive fineness of JIS L1017. However, since it is an absolute dryness, the Rc (official moisture content) term was set to zero.

<Tensile strength>
The tensile strength of the carcass ply cord extracted from the tire was measured in accordance with the test method for the tensile strength of JIS L1017 when absolutely dry. Since it is a hybrid cord, the drying method was based on rayon.

<Cord diameter and number of driving>
As shown in FIG. 2, the tire was cut at a location (dotted line portion) 1 mm in height from the upper end of the bead core 1, and the cord diameter and the number of drivings of the carcass ply cord were calculated from the cross section. The cord diameter was measured as the diameter of the circumscribed circle of the cord in accordance with the cord diameter regulations of the steel cord.

<Number of twists>
The number of primary twists of each cord and the number of primary twists of cellulose fibers and nylon fibers were determined according to JIS L1017.

<Tire strength>
The tire strength of each test tire obtained was measured in accordance with JIS D4230. The results are shown as an index with the tire of Comparative Example 1 as 100. A larger index value indicates a higher tire strength and is better.

<Tire durability under high load>
For tire durability, each test tire obtained was assembled on a rim having a rim size of 71 / 2J, and a durability test was performed under the conditions of an internal pressure of 300 kPa, a load load of 1040 kg, a temperature of 38 ° C., and a speed of 60 km / h. Was evaluated by measuring the distance to failure. The results are shown as an index with the running distance of the tire of Comparative Example 1 as 100. The larger the index value, the higher the durability of the tire and the better.
These results are also shown in the table below.

  As shown in the above table, in the tires of the respective examples in which the hybrid cord satisfying the relationship represented by the formula (1) according to the present invention is used for the carcass ply cord, the tire of the comparative example not satisfying this is used. In comparison, it was confirmed that the tire strength was improved without impairing the tire durability.

1 Bead core 2 Carcass 3a, 3b Belt layer 4 Cap layer 5 Layer layer 6 Bead filler 11 Bead portion 12 Tread portion 13 Side wall portion

Claims (7)

In a pneumatic tire having a carcass made of one or more carcass plies extending in a toroidal shape between a pair of bead cores embedded in a pair of left and right bead parts, respectively,
The cord of at least one of the carcass plies is a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon fiber, and the dryness A (dtex) of the cellulose fiber The absolute dryness B (dtex) of the nylon fiber and the tensile strength C (N) of the hybrid cord extracted from the tire are represented by the following formula (1),
C> (5 × A + 8 × B) × 0.007 (1)
A pneumatic tire characterized by satisfying the relationship indicated by.   When the cord diameter of the hybrid cord is D (mm) and the number of driving of the at least one carcass ply in the bead portion is E (lines / 50 mm), F = (1−D × E / 50) × 100 The pneumatic tire according to claim 1, wherein a ratio of rubber contained in the carcass ply in the bead portion defined by (%) is more than 15% and less than 40%. The cord diameter D (mm) of the hybrid cord is expressed by the following formula (2),
D <0.0001 × (A + B) +0.45 (2)
The pneumatic tire according to claim 1 or 2, which satisfies:   The pneumatic tire according to any one of claims 1 to 3, wherein a cord diameter D (mm) of the hybrid cord is more than 0.5 mm and less than 1.0 mm.   The pneumatic tire according to any one of claims 1 to 4, wherein an upper twist number of the hybrid cord is in a range of 20 to 50 times / 10 cm.   The pneumatic tire according to any one of claims 1 to 5, wherein the number of twists of the nylon fiber is in a range of 0 to 50 times / 10 cm.   The pneumatic tire according to any one of claims 1 to 6, wherein the number of twists of the cellulose fiber is in the range of 0 to 50 times / 10 cm.

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