JP2637516B2 - Pneumatic radial tire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radial tire reinforced by a so-called open twisted structure cord using improved steel filaments.

(Prior Art) In a pneumatic tire reinforced with a steel cord, there is a problem that the durability of a product is shortened due to corrosion of a steel filament due to moisture entering the tire. Therefore, metal plating is applied to the filament surface,
A so-called open twist structure that allows rubber to penetrate into the cord (see RESEARCH DISCLOSURE, JUNE 1978, page 33)
As a result, the corrosion resistance of the steel cord is improved.

(Problems to be Solved by the Invention) In the case of a steel cord having a metal-plated filament and poor rubber permeability, if the steel cord is used under conditions where repeated strain is applied, plating due to friction between filaments in the cord occurs. Due to the rapid wear of the layer, the anticorrosion effect is lost due to the exposure of the iron base, and in the open twisted cord, only a small tension is applied to the cord during the rubber coating calendar, the gap between the filaments narrows, and the rubber inside the cord The problem remains where plastics and plastics are difficult to penetrate.

On the other hand, Japanese Utility Model Laid-Open Publication No. Sho 61-108397 discloses an open twisted steel cord in which a steel cord is twisted into a substantially elliptical helical shape in order to improve rubber infiltration. Due to the large elongation, the gap between the filaments constituting the cord is narrowed, and the penetration of rubber or plastic into the cord is prevented.

Japanese Patent Application Laid-Open No. Sho 62-170594 discloses that the mold ratio is divided into at least two or more units having different mold ratios, the mold ratio is set to 1.65 at the maximum value, 1.05 at the minimum value, and the difference between the maximum value and the minimum value is 0.20 to 0.40
However, since the spiral shape of the filament is not optimized, there is a problem that the workability of the cord and the rubber penetration property are reduced.

Therefore, an object of the present invention is to propose a pneumatic tire having an excellent durability life reinforced with an open twisted structure steel cord having improved corrosion intrusion resistance by improving rubber penetration.

(Means for Solving the Problems) The present invention provides a tread portion including a tread portion, a pair of side portions connected by both shoulders of the tread portion, and a pair of bead portions formed on an inner periphery of the side portion. In a radial tire having a carcass reinforced with a belt buried inside, an elliptical helical winding is formed, and the ellipse is represented by the following formula (x / a) ² + (y / b) ² = 1 where b / a: 0.70 to Having an open twist structure represented by 1 × n, wherein 3 to 6 filaments each consisting of 3 to 6 filaments represented by 0.90 are represented by n;
A pneumatic radial tire, wherein at least one of the belt and the carcass is reinforced with a steel cord having a tensile elongation at a load of 5 kg in a range of 0.3 to 1.4%.

Also, when conducting the test, the tensile elongation P ₂ at a load of 2 kg of the cord
And the tensile elongation at 5 kg load P ₅ is P ₂ ≦ 0.947 P ₅ −
0.043, more preferably P ₂ ≦ 0.947 P ₅ −0.0
83 and the gap between adjacent filaments
Advantageously, at least one is at a different distance.

In the present invention, the filament diameter of the steel cord is preferably 0.15 to 0.45 mm, and more preferably 0.15 to 0.
In the range of 40 mm, the twist pitch is preferably provided in the range of 6 to 20 mm.

The steel cord according to the present invention has, for example, a so-called open twist structure in which five filaments 1 are formed into an elliptical helical shape and the filaments 1 are spaced apart, as shown in FIG.

Here, the elliptical helical winding refers to a helical winding along the periphery of the ellipsoid, and the ellipse is characterized by following the above equation.

The steel cord according to the present invention is a straightening roller having an open twisted structure cord obtained by linearly forming and twisting 3 to 6 filaments at a shaping rate of 105 to 140%, and having a bending deflection rate of 12.5% or more. By passing through.

Here typed rate the cord diameter when twisted the same filament and the filament in many dense and d _c, the code size after typed and d _f is _{used, (d f / d c)} × 100
(%). When the filament has an elliptical helical shape Further, the bending deflection rate is calculated by using a group of rollers arranged as shown in FIG. 2 and calculating a bending deflection amount δ (mm) and a center distance L (mm) of the rollers (δ / L) × 100 (%). Is represented by

In addition, the reason why the bending deflection rate is set to 12.5% or more is that if the bending deflection rate is less than 12.5%, the winding shape of the filament becomes close to a circle from an ellipse,
This is because the infiltration of rubber is deteriorated. When the distance L between the roller centers was set to 2.0 times or more of the cord twist pitch length, the infiltration of the rubber was improved probably due to the displacement of the elliptical helical winding of the filament.

Furthermore, if the operating conditions of the straightening roller are set as described above, a compressive residual stress is applied to the surface of the filament constituting the cord, so that the corrosion fatigue property of the filament can be improved.

(Operation) The number of filaments that compose the steel cord is 3 to
The reason why the number of wires is limited to six is that if one or two wires are used as a reinforcing material, the strength per cord is too low for the same wire diameter, and if the wire strength is the same, the wire diameter becomes too large and the fatigue resistance deteriorates, and This is because the use of one or two filaments does not have the effect of improving the rubber infiltration property by forming the filament into an elliptical shape.

On the other hand, if the number of filaments is 7 or more, the cord diameter becomes large, the reinforcing layer by the cord becomes thick, and it is uneconomical. The filaments fall into the cord to form a two-layer state, the rubber permeability into the cord becomes poor, and heat is generated. This is because the sex becomes worse. Although it is conceivable to reduce the filament diameter, it is not preferable because the drawability is deteriorated. Therefore, the diameter of the filament is 0.15 to 0.45 mm, preferably 0.15 to 0.45 mm.
In the range of 0.40 mm, the filament can be manufactured economically, and the mechanical fatigue durability when used as a cord is in a practical range and is suitable.

Next, the steel cord used for reinforcing the product or the steel cord extracted from the product is composed of an elliptical helical filament, and the ellipse is represented by the following formula (x / a) ² + (y / b) ² = 1 However, by adopting the shape represented by b / a: 0.70 to 0.90, the tensile elongation of the cord at a load of 5 kg is reduced, and the tensile elongation at a load of 2 kg, which is an indicator of rubber penetration into the cord, is also reduced. Therefore, the present inventors have newly found that the decrease in the gap between filaments can be suppressed and the infiltration of rubber can be greatly improved.

That is, by using the elliptical helical filament according to the above formula, the tensile elongation under a load of 2 kg can be reduced, and the penetration of rubber can be improved. FIG. 3 shows a cord (a) to which a compressive residual stress is applied by a straightening roller composed of an elliptical helical filament and a cord (ii) composed of a helical filament, each having a relative humidity of 90% and a temperature of 25 ° C. 3 shows the results of a rotary bending fatigue test performed under the same atmosphere. From the figure, it was also found that the fatigue life was improved by applying the compressive residual stress.

In order to further increase the penetration of rubber between filaments, the relationship between the tensile elongation P ₂ (%) at a load of ₂ kg and the tensile elongation P ₅ (%) at a load of 5 kg is expressed as P ₂ ≦ 0.947 P ₅ − It is preferably 0.043. More preferably, P ₂ ≦ 0.947 P ₅ −0.083.

Further, by randomly arranging the filaments and making at least one gap between the filaments different, it is possible to reduce the elongation strain under a load of 2 kg and to improve the rubber penetration.

(Example) Steel cord manufacturing example Five filaments having a diameter of 0.23 mm are aligned and spirally shaped by a hammering plate so that the diameter becomes 1.15 times the cord diameter of the close-packed cord structure. Subsequently, five molded filaments were twisted to form a cord having an open twist structure. Next, the cord was passed through straightening rollers arranged in a staggered manner shown in FIG. 2 to change the filament from a cylinder to a helix of an elliptic cylinder. The staggered arrangement of the straightening rollers in this case is such that the bending deflection (δ) shown in FIG. 2 is 4.2 mm and the distance between the roll centers (L) is 24 mm.
The total number of rolls was 13. FIG. 4 illustrates a cross section of the obtained cord. Further, as shown in FIG. 5 (a), the filament was in the shape of an elliptical helix, and the penetration rate of rubber into the cord was almost 100%. The details of the obtained steel cord are shown in Table 1 as No. 3.

On the other hand, when the bending deflection of the straightening roller is 6.8 mm and the distance L between the roll centers is 24 mm, the filament becomes a flat ellipse including a straight line portion as shown in FIG. 20%. The details of the obtained steel cord are shown in Table 1 as No. 2.

Steel cords Nos. 2 to 8 shown in Table 1 were prepared by slightly changing the conditions of the production method disclosed above. 1 × 5 × 0.2 for tire performance evaluation in the same way
5, 1 × 5 × 0.28, 1 × 5 × 0.30, 1 × 4 × 0.20, 1 ×
A 3 × 0.20 steel cord was also prepared. Here, 0.25 of (1 × 5 × 0.25) display means that the filament diameter is 0.
Indicates 25 mm.

The results of a study on the rubber penetration and corrosion fatigue resistance of an open twisted steel cord (1 × 5 × 0.23 mm) made of filaments according to the conditions shown in Table 1 are also shown in the same table.

The rubber infiltration property was as follows. A 1 × 5 steel cord was embedded in a vulcanizable natural rubber composition sheet containing 50 parts by weight of carbon black (HAF), and a temperature of 145 was applied under a pressure of 20 kg / cm ^2.
After vulcanization at 30 ° C. for 30 minutes, the cord was cut at 5 mm intervals in the length direction, and 10 cord sections were observed with an optical microscope for the degree of penetration of rubber into the cord. In addition, the corrosion fatigue resistance was evaluated by applying a bending strain of 0.5% to a bare cord not covered with rubber in an atmosphere of 90% relative humidity and a temperature of 25 ° C. Exponential notation. The larger the index, the longer the fatigue life and the better the corrosion fatigue resistance.

Example 1 Three kinds of 1s manufactured according to the steel cord manufacturing example.
X5 steel cords and closed-twisted 1x5 steel cords were used for reinforcing belts of radial tires for passenger cars having a tire size of 165SR13, and four types of tires were prototyped under the conditions shown in Table 2. Note that the tire of Example 3 is the tire of Example 1,
Cording was adjusted so that belt strength was the same as 2.

A hole of 3 mm in diameter reaching the metal cord of the belt part was made in the ground part of these tires, and the tires were run 1,000 km on the ground. Then, the tires were immersed in a 5% NaCl aqueous solution tank for one day. For a total of 40,000 km and then the internal pressure
The tire was dissected after it was lowered to 1.3 kg / cm ² and ran 20,000 km on a constant mountain slope.

1. Corrosion resistance: A metal cord corresponding to the position of the hole in the tire is sampled, and how long the adhesive interface with the embedded rubber has reduced adhesion is evaluated as the corrosion length of the cord. The corrosion length of the tire metal cord of tire No. 13 was represented by an index using the following equation, with the corrosion length of the tire metal cord being 100.

The larger the value, the better the result.

Example 2 According to Table 3, radial tires for passenger cars having a tire size of 195 / 70R14 having three different carcasses were prototyped. No. 4 steel cords in Table 1 were used for the belts.

In the comparative example, a polyethylene terephthalate fiber cord of 1000d / 2 as a carcass (cord strength 21.5kg)
Was used in two layers, with the bead portion turned up at a height of 55.0 lines / 50 mm.

In Example 4, a steel cord of 1 × 3 × 0.20 (mm) (cord strength 29.0 kg) was further layered, and the number of shots was 60/50 mm.
, The bead portion folded height was reduced. Example 5
, A steel cord of 1 × 4 × 0.20 (mm) (cord strength: 38.0 kg) was used as one layer at the same bead turning height as that of Example 4 at 45/50 mm.

After running these three types of tires for 100,000 km, the growth length of the cracks at the end of the carcass ply and the incidence of trauma on the side wall were investigated. The index was evaluated. The larger the index, the better the result.

In addition, the rolling resistance was evaluated in accordance with JIS D0202, and a driver's feeling test was conducted on the test course for operability and riding comfort. In each case, the larger the index, the better the results.

 Table 3 shows the results of these evaluations.

Example 3 No. 1 and No. 6 steel cords in Table 1 and N
A steel cord of 1 × 5 × 0.30 structure (filament diameter 0.30 mm) manufactured in the same manner as o.4, that is, the winding shape of the filament is elliptical, the minor axis / major axis ratio of the ellipse is 0.81, and the elongation under a load of 5 kg is 0.54. The radial tires for heavy load (for trucks and buses) are cords with elongation of 0.41% at% 2kg load.
A prototype tire was manufactured using the outermost layer of the ply belt on the tread side in 1000R2014.

The three layers other than the outermost layer of the belt were all 3 × 0.20
A steel cord having a structure of + 6 × 0.38 was used. The first layer, which is the innermost layer, was buried at a rate of 18/50 mm, and the second and third layers were buried at a rate of 28/50 mm.

Then, the steel cord of No. 1 and the steel cord of No. 6 were buried at a driving number of 52 wires / 50 mm, respectively, to obtain Comparative Example 3 and Example 6, respectively. The remaining steel cords were buried at a driving number of 34 wires / 50 mm, and this was used as Example 7.

After running these three types of tires for 150,000 km, the corrosion resistance was evaluated. As a result, in the belt outermost layer of the comparative example 3 tire, internal corrosion of the cord progressed everywhere. The tire showed good results with no progress of corrosion.

Example 4 A heavy duty truck / bus radial tire 1000R20-14PR was used as an evaluation tire. As shown in Table 4 below, the belt structure of this tire is 3 × 0.20 mm + 6 × 0.
38mm steel cord in the first layer with a density of 9 wires / 25m
m and 14/25 mm for the second to fourth layers, respectively, and the first layer is driven at 23 ° and the second to fourth layers are driven at 70 ° with respect to the circumferential direction of the tire. The carcass ply structure is
As shown in Table 4, in the control tire of Comparative Example 4, 3 + 9 × 0.23 mm + 1 steel cords were arranged at an angle of 90 ° with respect to the tire circumferential direction at a driving density of 8 wires / 25 mm. In Table 4, steel cords to which each carcass ply was applied were arranged at the same angle with respect to the circumferential direction and with the number of shots determined to match the case strength of the control tire of Comparative Example 4.

The following performance evaluations were performed on the prototype tire.

Fretting resistance From the prototype tire (the same method for running tires and new tires), the cord of the carcass cord layer with rubber from one bead to the other bead is pulled out and cut in half at the crown center. Next, the rubber is dissolved and removed with a solvent, and the filament is loosened one by one. For each of the unraveled filaments, sandwich the crown center end and bead side end with a chuck, break the cord with a tensile tester,
Set the broken surface on a microscope so that it can be seen from directly above, take an enlarged photograph, cover the enlarged photograph with a piece of graph paper, draw a circle along the edge of the part where fretting does not occur, and draw a circle without fretting. The value obtained by averaging 10 parts of cords obtained by measuring the part where fretting occurred in the abraded part in units of μm is the amount of fretting.

The fretting resistance in Table 4 shows that this value is indicated as an index so that the smaller the fretting amount is, the larger the control tire of Comparative Example 4 is set to 100.

As shown in FIG. 6, the test method of hanging the rubber cord 3 taken out of the tire on three pulleys 4 having a diameter of 40 mm was applied to the three pulleys 4 as shown in FIG. A tensile load is applied to the weight 6 equivalent to 10%, and the three pulleys are repeatedly moved 20 cm to the left and right to repeatedly apply bending strain to the cords to cause the cords to fatigue-rupture. The value obtained as the number of breaks, and the degree of decrease in comparison with new tires assuming that the code of a new tire is 100, is the degree of decrease in corrosion fatigue resistance. The degree of decrease in corrosion fatigue resistance shown in Table 4 is indicated by an index value with the above value taken as the control tire of Comparative Example 4 being 100, and the larger the value, the better the corrosion fatigue resistance.

Carcass ply end durability The tread rubber of the prototype tire is buffed, and the bead durability is evaluated in a state where the belt layer does not fail due to the heat generated by the belt layer. Specifically, load each prototype tire with JIS 200% load, speed
Turned on the drum under the conditions of 60 km / h and internal pressure of 7.25 kg / cm ² , the separation occurred at the tip of the carcass ply cord, and the drum travel distance when the vibration increased became the respective travel distance, the control of Comparative Example 1 It was indicated by an index in comparison with that of a tire. The larger the value, the better the endurance of the carcass ply end.

Sidewall trauma resistance The steel cord used for the prototype tire is embedded vertically and vertically in rubber with a thickness of 3 mm, a width of 50 mm, and a length of 300 mm. Ten percent of tension is applied, a 20 kg blade is naturally dropped from above at right angles to the cord direction, and the side wall damage resistance is compared based on the cutting height. Table 1 shows the properties of the control tire of Comparative Example 1 as 100, and the larger the value, the better the side trauma resistance.

Weight reduction effect A steel cord used for the prototype tire is made up of a ply treat composite made up of carcass coating rubber,
In order to obtain the same strength as the ply treat of the control tire of Comparative Example 1 as a composite, the effect of weight reduction by reducing the number of shots when the number of shots of each trial treatment was changed was determined by the treat weight used per tire. Is shown as a control tire contrast index. The smaller the value, the better the weight reduction effect.

 The above evaluation results are shown in Table 4.

From Table 4, the examples are all excellent in comparison with the comparative examples.
It can be seen that a remarkable effect is particularly exhibited in the fretting resistance.

(Effects of the Invention) According to the present invention, since the penetration of rubber inside the cord is significantly improved and the corrosion fatigue property of the filament itself is also improved, it has extremely excellent corrosion fatigue resistance, especially for passenger cars or A cord suitable for reinforcing a belt or a carcass of a pneumatic radial tire for a truck or bus can be provided.

[Brief description of the drawings]

 FIG. 1 is a sectional view of a steel cord according to the present invention, FIG. 2 is a schematic view of a straightening roller, FIG. 3 is a graph showing the relationship between the cord structure and fatigue life, and FIGS. FIG. 5 (a) and (b) are cross-sectional views of the filament, and FIG. 6 is an explanatory view of the corrosion fatigue resistance reduction test method. 1 ... filament

Claims (3)

(57) [Claims] A tread portion, a pair of side portions connected by both shoulders of the tread portion, and a pair of bead portions formed on an inner periphery of the side portion, are reinforced with a belt embedded inside the tread portion. In the radial tire having the carcass described above, an elliptical helical shape is formed, and the ellipse is represented by the following formula (x / a) ² + (y / b) ² = 1, where b / a is 3 to 6 represented by 0.70 to 0.90. 3 to 6 filaments having an open twist structure represented by 1 × n,
A pneumatic radial tire, wherein at least one of the belt and the carcass is reinforced with a steel cord having a tensile elongation at a load of 5 kg in a range of 0.3 to 1.4%. 2. The tensile elongation P of a steel cord at a load of 2 kg.
The relationship between ₂ and the tensile elongation at 5 kg load P ₅ is P ₂ ≦ 0.947 P ₅ −
The tire according to claim 1, wherein the tire satisfies 0.043. 3. The steel cord of claim 1, wherein at least one of the gaps between adjacent filaments is at a different distance.
Or the tire according to 2.