JP2012171555A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire which excels from the viewpoint of environments and of which the degradation in the uniformity is suppressed without decreasing durability.SOLUTION: The pneumatic tire includes a carcass 1 as a skeleton, which comprises one or more carcass plies extending in a toroidal form between a pair of bead cores 5. The carcass ply cord comprises a hybrid cord of a filament of cellulose fiber and a filament of nylon twisted together. The hybrid cord in a green tire shows a thermal shrinkage of 1.0% or more and 4.0% or less at 170°C.

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, it is known that when nylon is applied to a carcass reinforcing cord, the tire uniformity deteriorates 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. Therefore, as a carcass cord for high-performance tires and run-flat tires, cellulose fibers typified by rayon are generally used, but since rayon is highly elastic, when rayon is used alone for a carcass cord, There is a drawback that ride comfort is reduced.

For rayon, environmental pollution due to the occurrence of CS ₂ and toxicity of Zn used in the manufacturing process are problems. Due to this, the number of manufacturers is decreasing 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). ).

JP 2010-058740 A (Claims etc.)

  However, as described above, depending on the fiber type used for the carcass reinforcing cord, the thermal shrinkage rate during vulcanization may increase, and the tire uniformity may deteriorate. Therefore, there has been a demand for the realization of a tire that is excellent in environmental characteristics and suppresses deterioration of uniformity without impairing durability.

  Accordingly, an object of the present invention is to provide a pneumatic tire that solves the above-mentioned problems by improving the carcass cord, has excellent environmental performance, and suppresses deterioration of uniformity without impairing durability.

  As a result of intensive studies, the present inventor has used a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon as the carcass cord, and defines the value of the thermal contraction rate of the hybrid cord within a specific range. Thus, the inventors have found that the above problems can be solved, and have completed the present invention.

That is, the present invention is a pneumatic tire having a carcass made of one or more carcass plies extending in a toroid shape between a pair of left and right bead cores,
The carcass ply cord is a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon, and the heat shrinkage rate of the hybrid cord in a green tire at 170 ° C. is 1.0% or more. It is characterized by 4.0% or less.

  In the tire of the present invention, the ratio of the dtex number of nylon to the total dtex number of the hybrid cord is preferably 20 to 50%. Further, 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 preferably 1.2% or less. Furthermore, 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 equal intervals in the tire circumferential direction is within 0.55%. Is preferred.

  According to the present invention, the above configuration makes it possible to realize a pneumatic tire that is excellent in environmental performance and in which deterioration of uniformity is suppressed without impairing durability.

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

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 1 made of a single carcass ply extending in a toroidal shape across a pair of left and right bead portions 11 as a skeleton, and the crown portion has 2 The belt layers 2a and 2b are provided.

  The carcass 1 is one in the illustrated example, but may be two or more, and preferably one or two. Further, the belt layers 2a and 2b 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, it is important to use, as the carcass ply cord, a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon (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.

  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 tire according to the present invention, such a hybrid cord is used as a carcass ply cord, and particularly when a run-flat tire is used, the rise of the vertical spring during normal running is suppressed and the riding comfort is kept good. Further, the run-flat running durability can be improved by suppressing the bending of the tire during the run-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, in addition to the combination of materials used for the hybrid cord, the heat shrinkage rate at 170 ° C. of the hybrid cord in the green tire is 1.0% to 4.0%, particularly 2.0%. It is important that the content is not less than 3.0%. By setting the thermal contraction rate of the hybrid cord at 170 ° C. within the above range, it is possible to suppress tightening due to excessive thermal contraction of the carcass ply cord during vulcanization, and to suppress deterioration of tire uniformity. It becomes possible. In addition, since appropriate rigidity can be ensured, it is possible to obtain a tire having excellent environmental performance, durability, and uniformity.

  In the present invention, the ratio of the dtex number of nylon to the total dtex number of the hybrid cord is preferably 20 to 50%, particularly preferably 30 to 40%. If the ratio of nylon in the hybrid cord is smaller than this range, thermal shrinkage as a hybrid cord is reduced, and if it is larger than this range, the tensile elastic modulus is lowered, which is not preferable. 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.

  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. That is, when the thermal contraction rate at 175 ° C. of the hybrid cord is ε (175 ° C.) and the thermal contraction rate at 165 ° C. is ε (165 ° C.), the following formula: ε (175 ° C.) − Ε (165 ° C.) Assume that ≦ 1.2% holds. 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, the smaller this difference, the better.

  Furthermore, in the present invention, 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, the difference between the maximum value and the minimum value is 0. It is preferably within 55%, particularly within 0.40%. This difference is preferably as small as possible, that is, as the value of the heat shrinkage rate is uniform in the tire circumferential direction, it is preferable.

  In the present invention, examples of a method for adjusting the thermal contraction rate of the hybrid cord include a method for controlling tension and temperature in an adhesive treatment (dip treatment) process. Specifically, the conditions at the time of cord heat treatment are important, and the maximum tension at the time of cord heat treatment is 1000 g or less per cord, and in the final zone (so-called baking zone) of the heat treatment zones consisting of multiple stages. By setting the tension to 50% or less of the maximum tension, a hybrid cord satisfying the heat shrinkage rate condition according to the present invention can be obtained. Furthermore, it is preferable to set the maximum temperature during the cord heat treatment to 180 ° C. or higher. 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 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 3 and the layer layer 4 are arranged on the outer side in the tire radial direction of the belt layers 2a and 2b. However, these arrangements are arbitrary in the present invention and are not provided. May be. The cap layer 3 and the layer layer 4 are both rubberized organic fiber cords arranged substantially parallel to the tire circumferential direction. As shown in the figure, the cap layer 3 includes the belt layer 2a, The layer layer 4 is arranged in at least one layer in both end regions of the belt layers 2a and 2b.

  As shown in the figure, a bead core 5 is embedded in each of the pair of bead portions 11 of the tire of the present invention, and the carcass 1 is folded around the bead core 5 from the inside of the tire to the outside and locked. Further, a tread portion 12 is disposed on the outer periphery of the crown portion of the belt layers 2 a and 2 b, and a sidewall portion 13 is disposed on the side portion of the carcass 1. 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 245 / 40R18. The carcass was composed of one carcass ply using a carcass ply cord having the specifications shown in the following table. 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.

<Measurement method of thermal shrinkage in green tire>
The cords of the green tires of each example and comparative example were extracted from 10 locations evenly in the tire circumferential direction. The cord length to be extracted was 250 mm or more. One end of the cord was fixed, a 50 g load was applied, and the cord length was measured. The cord length at this time was L1 (mm). Next, this is put into a dryer at 50 ° C. with a load applied, the temperature is raised at a speed of 8 ° C./min, and the cord length (L2 (mm)) at a predetermined temperature is measured. did. From these measurement results, the thermal contraction rate was calculated based on the following formula, and the average value of 10 cords was obtained.
(Heat shrinkage) = (L1-L2) / L1 × 100 (%)

<RFV measurement>
Each of the test tires obtained was assembled on a rim having a rim size of 8 1/2 J, and under the conditions of an internal pressure of 200 kPa and a load load of 497 kg, a radial force variation (RFV) according to the uniformity measurement method defined in JASO C 607 (2000). Was measured. 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.

<Tire durability under high load>
Each test tire obtained was assembled on a rim having a rim size of 81 / 2J, and a durability test was conducted under conditions of an internal pressure of 300 kPa, a load load of 1170 kg, a temperature of 38 ° C., and a speed of 60 km / h until the tire failed. The distance was measured. The results are displayed as an index with the travel 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.
The results are also shown in the table below.

  As shown in the above table, each example in which a hybrid cord formed by twisting a filament made of rayon and a filament made of nylon was used as a carcass ply cord, and the thermal contraction rate of the hybrid cord was adjusted within a predetermined range. In the test tire, it was confirmed that the RFV was suppressed to a low value without impairing the durability.

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

Claims (4)

In a pneumatic tire having a skeleton of a carcass made of one or more carcass plies extending in a toroidal shape between a pair of left and right bead cores,
The carcass ply cord is a hybrid cord formed by twisting a filament made of cellulose fiber and a filament made of nylon, and the heat shrinkage rate of the hybrid cord in a green tire at 170 ° C. is 1.0% or more. A pneumatic tire characterized by being 4.0% or less.   The pneumatic tire according to claim 1, wherein the ratio of the dtex number of nylon to the total dtex number of the hybrid cord is 20 to 50%.   The pneumatic tire according to claim 1 or 2, wherein a difference between a heat shrinkage rate at 175 ° C and a heat shrinkage rate at 165 ° C of the hybrid cord in the green tire is 1.2% or less.   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%. The pneumatic tire according to any one of?

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