JPH06106910A - Large sized radial tire for use on bad road - Google Patents

Abstract

PURPOSE:To improve durability of including a regenerative life and a TLB characteristic by using a cord layer, having an enclosed rubber permeable form by cord arrangement of specific twist structure, for the cord layer serving as a protector for surrounding the periphery of a belt. CONSTITUTION:A belt 1 of arranging a cord of a cord layer crossed at 15 to 30 deg., serving as the belt with a protector a4, is combined with carcass of cord arrangement orthogonal relating to a tire equatorial surface, to reinforce a tread part 3. In the protector a4, steel cords 4, 4' of two layer twist structure are used with 1 to 2 cores of twisting a filament of 93 to 120% marking factor and 0.23 to 0.40mm diameter, and when assumed (k), (m) for center virtual lines of these steel cords, (h) for bisector of these cords and (g) for boundary line, relating to an area of a part interposed by the bisector (h) and the boundary line (g), a volumetric factor of sum of a total cord sectional area of the protector, occupied by this part, is set to 5 to 40%. Further, the cord layer is buried in rubber and molded in an enclosed permeable form. Accordingly, running durability, including a bad road, particularly a TLB characteristic can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large radial tire for rough roads, and more particularly to a closed type rubber having a specific twisted structure cord arrangement as a cord layer of a protector also using a steel cord surrounding a belt using a steel cord. The present invention relates to a large radial tire for bad roads, which is advantageous in improving durability in running on rough roads by having a penetration form.

Radial tires for heavy loads such as trucks and buses using steel cords as belts and reinforcing elements for carcass are not only good roads with paved road surfaces that are complete and well managed, but also road surfaces such as construction roads. It is also used for running on rough roads in poor condition, but especially when including the latter running, there is often a problem of tread-belt separation (hereinafter abbreviated as TLB), that is, the tread rubber layer of the tire at the beginning of use. There is a disadvantage that the tread layer peels off due to breakage caused by peeling from the belt due to abnormal reduction of the service life, or otherwise cut damage of the tread accompanied by extreme poor appearance at the end of the life, and irreparable.

In many cases, such TLB is caused by external moisture intrusion into the inside of the belt cord due to the cut damage of the tread, and the conventional belt cord is poor in rubber penetration into the inside. Together, the water easily flows through the hollow inside the cord to reach the end of the cord, whereupon the interface between the rubber and the cord is deteriorated by water. Therefore, the durability of large radial tires can be improved by avoiding TLB failure due to running on a rough road.

[0004]

[Prior Art] However, as a conventional TLB countermeasure, TLB is used.
In order to reduce and reduce the cord cut of the belt, which is one of the causes of occurrence, a high-stretch cord having a double twist structure has been used as a protector surrounding the outer circumference of the belt. In this example, the case of a cord of 4 × 4 × 0.23 mm is given in Comparative Example 2 in the table below, but in this double twist structure, the twist direction of the strand and the twist direction of the cord are the same. This is the so-called Lang twist.

The use of a protector consisting of a multi-twisted cord according to the prior art can certainly reduce the cord cut and protect the cord layer of the belt directly below this cord layer because of the large elongation, but the multi-twisted cord does not Since it is difficult for rubber to penetrate into the interior, when the cut reaches the cord once, regardless of whether the cord is cut or not, it is a satisfactory solution to the occurrence of TLB due to the easy flow of water through the internal cavity of the cord. Was not obtained. In addition, in general, a highly extensible cord has a drawback that its weight per unit length is large, but its strength is low, and the price per unit weight of cord is also high.

Therefore, an object of the present invention is to solve the problem of durability including retread life, especially TLB, in a large radial tire for bad roads, advantageously and appropriately. Among the causes of TLB generation, the inventors have paid particular attention to the point of water distribution in the cord, and as a result of intensive research on its prevention, as a result, a cord having a specific twist structure in the cord layer that serves as a protector surrounding the outer circumference of the belt. It has been confirmed that the above-mentioned object can be met by using the one having a closed type rubber permeation form of the arrangement, and the present invention has been accomplished.

[0007]

According to the present invention, at least three cord layers in which steel cords are embedded in rubber in parallel are wound in an arrangement in which the cords of each layer form a relatively small angle with respect to the equatorial plane of the tire. Tire with a protector as a belt in which at least one set of mutually adjacent cord layers are laminated one on the inside of the outermost cord layer serving as a protector, the cords crossing each other at an angle of 15 to 30 °; In a radial tire with tread reinforcement combined with a carcass having a cord arrangement that is substantially orthogonal to the equatorial plane of the protector, the protector was typed within the range of 93 to 120% before the cord was twisted. Steel cord having a two-layer twist structure with one or two filaments as the core, obtained by twisting filaments with a filament diameter of 0.23 to 0.40 mm , A bisector of a virtual line passing through each cord center of the protector and a virtual line interval passing through each cord center of the cord layer of the belt adjacent inside the protector in the cross section of the belt, and the tread portion of the protector. The volume fraction of the cord, expressed as a percentage of the sum of all the cord cross-sectional areas of the protector occupying the area sandwiched by the boundary line and this area, is within the range of 5 to 40%, and
A large radial tire for bad roads, which comprises a cord layer formed by embedding the rubber in a rubber in a closed-type permeation form having a cord portion in which the rubber is completely penetrated into the inside surrounded by filaments of the cord and has no void.

In the present invention, the two-layer twist structure is more preferably 2 + 7 or 2 + 6 twist. Tread section 2
It is practically preferable that the protector has an arrangement width of 30 to 80% of the width, and if it is narrower than 30%, the important cuts cannot easily be protected and if it is wider than 80%, it will not be cut. It will cover extra places where there are very few, making the tires heavier, and also cause cost increase.

[0009]

In the present invention, the two-layer twist of the cord used in the protector according to the present invention, particularly the filament having a filament diameter of 0.23 to 0.40 mm, which is typed within the range of 93 to 120% in the type forming ratio before the cord is twisted, has a twist angle of 10 to 20. 1 obtained by twisting at
A steel cord having two filaments as a core is preferable. Here, the twist angle is an angle formed by the axial direction of the cord and the twisting direction.

If the filament diameter is smaller than 0.23 mm, the cord does not have sufficient cut resistance against external force when a stone on the road is stepped on. On the other hand, if the filament diameter exceeds 0.40 mm, the cord is rather cut due to corrosion fatigue. Tends to decrease. If the twist angle is less than 10 °, the rubber penetration in the cord is insufficient and the voids become large, resulting in faster nucleation of TLB generation.On the other hand, if the twist angle is greater than 20 °, the rubber infiltration form will be blocked even if the patterning rate is increased. I'm glad I'm out of shape.

In the present invention, the two-layer twist structure is 2+
7, 2 + 6 or 1 + 5 twist is preferred, especially 2 + 7 with filament diameter 0.23-0.40 mm and twist angle 10-20 °
Alternatively, 2 + 6 twist is preferable. This means that when the number of cores is 3 or more, it prevents the rubber from penetrating into the cord, and when it is used for the sheath with the same or close filament diameter as the core, when it is 8 or more, the sheath filaments are stuck and the gap This is because it is difficult for the rubber to permeate due to the lack of stress, and when it is less than 5, the sheath filaments are arranged so as to be offset and the stress distribution becomes uneven.

Molding means that it is easy to permeate rubber into a cord before twisting the filament into a cord by subjecting the same shape as the filament in the twisted cord to a deformation under stress exceeding the elastic limit in advance. It is necessary for tightening, and the rubber penetration in the closed type permeation form can be more easily obtained by setting the molding rate in the range of 93 to 120%. The degree of patterning is represented by the patterning rate = B / A × 100 (%). As shown in FIG. 1, A and B in the above formula represent the maximum diameter of the filament in the cord state and the maximum diameter of the filament in the helical shape when the filament is unwound from the cord. Since it is difficult to measure the maximum diameter of the core filament in the cord state, the ideal cord diameter, that is, the maximum diameter in the cord state is 2d in the case of two filaments having the filament diameter d.

The above-mentioned filament patterning ratio needs to be at least 93%. A small type ratio means that the filament is tightened to form a cord, which reduces the gap between the filaments and deteriorates the rubber permeability.However, if the type ratio is 93% or more, the required rubber penetration Is realized. Although there is no particular upper limit on the patterning rate, it is limited to 120% due to manufacturing technology. It is necessary to keep the type ratio close to 100% or more in order to prevent water from advancing in the cord.
It is particularly preferable in terms of preventing TLB by providing an optimum rubber penetration form.
The double-layer twisted cord has an increase in raw cord elongation (called PLE) of 0.3 when the load is increased from 0.25 kgf to 5 kgf.
~ 1.5% is preferred, and elongation at break is 3.0
Codes in the range of -5.5% are especially preferred for the practice of this invention. The PLE is determined from the molding ratio and the pitch, and by setting it within the above range, it is easy to cause sufficient rubber intrusion in the rubber flow during vulcanization of the tire.

Next, the definition of the volume fraction of the cord will be explained with reference to the example of FIG. 2A. In the transverse section of the belt 1, the cord layers as protectors are attached in the order of stacking the steel cord layers from the side closer to the carcass. as it from hitting the fourth to turn represented by a _4, a virtual line k passing through the center of each cord 4 occupying this code layer a ₄
And the cord layer a ₃ ( _{third part} ) of the belt 1 which is adjacent to the inside of the cord 1.
The bisector of the virtual line m passing through the center of each cord 4'of the second cord layer) is indicated by h, and the boundary line to the tread portion 3 of the protect is indicated by g. The volume fraction of the cord is the percentage of the sum of the cross-sectional areas of all the cords 4 of the protector occupying this portion with respect to the area sandwiched by the line g. Here, the cross-sectional area of the cord 4 is the area of the shaded portion surrounded by the contour line c (thick line) of the cord 4 along the outer periphery of the filament 5 constituting the cord 4 as shown in FIG. 2B.

If the volume fraction of cord 4 is less than 5%, hit it.
The outermost code layer is the protector because the number of embedded
Bell located inside of it without playing its role
Third code layer a₃The cut easily reaches
I'm glad I got to Toburst. Here after the actual driving,
The rubber of the tire tread portion 3 is used as the cord layer a of the protector.
_FourThe number of cuts that have been stripped off of and reached this code layer
And then this code layer a_FourThe belt 1 third cord
Layer a₃Strip off on and reach that code layer as well
Measure the number of cuts made and
When the relationship between the ratio and the cord volume fraction was investigated, the result is shown in Fig. 2c.
The results shown were obtained. As you can see from this figure,
Code layer a used for_FourVolume fraction of less than 5%
When the belt layer of the belt 1 is cut and penetrates the cord layer of the protector.
Third code layer a₃Although the number of cuts reaching
When the volume fraction is 5% or more, the third cord of belt 1
Layer a₃The number of cuts leading to is drastically reduced.

When the volume fraction of the cords in the protector exceeds 40%, the cord intervals are too small in terms of tire manufacturing, and the cords tend to adhere to each other, and calendaring (rolling) is also difficult. In the present invention, the closed-type permeation form of rubber means that a portion of a cord which is completely surrounded by filaments of the cord as shown in FIG. The length in the direction is indicated by l ₁ ), and of course there is a cord portion with incomplete rubber intrusion and a gap e (l ₂ based on the length of the gap in the cord direction). However, it may be in a form in which l ₂ is 10 mm or less by alternately connecting this and a portion having no void. Where the l ₁ / l ₂ ratio is
If it is 0.14 or more, it forms a blocked permeation form. In each cross section of the cord on the I-I plane and the II-II plane which are perpendicular to the cord direction in FIG.

Since the conventional highly extensible cord does not easily penetrate the rubber, if it is likened to the void e in FIG. 3, its length (l ₂ ) becomes much longer than 10 mm, and it extends over the entire length of the cord. Therefore, the inflow of water along the cord direction easily occurs inside the cord. Contrary to this, in the cord of the present invention, since the permeation of the rubber easily takes place to form the blocked permeation form as described above, the progressive flow of water in the cord is prevented even if it occurs at the cut end, No particular adverse effects will occur. In addition, the cord of the present invention does not have the drawback that the cord has a low strength for the weight and a high price per weight, unlike the double twist cord.

The average rubber permeation rate is measured as follows. First view taken out protector i.e. code from the outermost layer a ₄ for product tire 4
After being embedded in the fluid resin P and cured as described above, a photograph is taken by cutting and buffing with a cutter along a plane R perpendicular to the cord direction including the measurement point. Before the rubber permeates, the total area of the space inside the core and the space between the core and the sheath is set to 100, and the ratio of the total area permeated by the rubber is measured to determine the rubber permeation rate at that position. Recognize. This measurement is repeated, for example, by cutting with a cutter and buffing every 1 mm, and the above-described measurement is sequentially performed for one pitch length of twist to calculate an average rubber penetration rate.

In addition to the above-mentioned points, FIG. 5 shows some examples of the laminated arrangement of the cord layers useful for reinforcing the tread. The tensile strength trunk layers a ₂ and a ₃ of the belt 1 (a in the figure) are shown. , b ₂・ b ₃ (the same figure b), c ₂・ c ₃ (the same figure c), d ₂・ d
The Young's moduli of the cords of ₃ (Figure d) are 600
When in the range of from 0 to 13500 kgf / mm ^2, when such a tread is trampled stones on the road surface, is effective in terms of the so-called envelope effect encasing it, the improvement in the TLB of so tread cut is prevented from entering Promotes the wear resistance of the tread 3 and the third cord layer a of the belt 1.
It is preferable that the influence on the crack lengths occurring in ₃ , b ₃ , c ₃ , and d ₃ can be maintained at the same level as in the conventional case.

Also in particular as shown in FIG. 5c, the belt 1
When the first code layer c ₁ is hollowed out, the same effect as that of lowering the Young's modulus of the cross code layer is obtained. Further, as shown in FIGS. 6 to 8, when the cushion rubber 6 or the soft rubber cushion rubber 7 is provided at both ends of the belt 1 between the tension-resistant trunk layers, that is, the second and third cord layers, these cords are used. Stress concentration at both ends of the layer can be prevented, which is useful for suppressing cracks in the third code layer.

(Examples) The present invention will be described in more detail with reference to Examples and Comparative Examples. Examples 1 to 8, Comparative Examples 1 and 2 , a belt 1 having four types of cord layer arrangements shown in FIGS. 5A, 5B, 5C, and 5D are shown in FIGS.
A cushion rubber 6 of the same quality as the coating rubber is interposed between the cross cord layers of the belt 1 as shown in FIG.
As shown in FIG. 8, a cushion rubber 7 made of a soft rubber of 30 kgf / cm ² having a 100% modulus which is about half of that of the coating rubber was similarly arranged.

The structure of each code layer shown in FIGS. 5a to 5d is as follows. Here, from the top to the bottom of the figure,
The order of each code layer is 3, 2, and 1. The cords of the second layer and the third layer intersect each other. a type a ₄ : 2 + 7 × 0.30 (Examples 1 and 4; see FIG. 9) 2 + 6 × 0.30 (Examples 2 and 5; see FIG. 10) 1 + 5 × 0.35 (Example 3; see FIG. 11) 1 × 3 × 0.20 + 6 × 0.38 (Comparative Example 1) 4 × 4 × 0.23 (Comparative Example 2) (62% of the maximum tread width of the tire shown in FIG. 6) a ₃ : 3 + 9 + 15 × 0.23 + 1 Young's modulus 16000 kgf / mm ² a ₂ : 3 + 9 + 15 × 0.23 + 1 Young's modulus 16000 kgf / mm ² a ₁ : 3 + 9 × 0.23 + 1 b type b ₄ : 2 + 7 × 0.30 (Example 6; 62% width of tire tread maximum width in FIG. 6) b ₃ : 3 + 9 + 15 × 0.23 + 1 Young's modulus 11000 kgf / mm ² b ₂ : 3 + 9 + 15 × 0.23 + 1 Young's modulus 11000 kgf / mm ² b ₁ : 3 + 9 × 0.23 + 1 c type c ₄ : 2 + 7 × 0.30 (Example 7; tire tread maximum of FIG. 7) width of the 62% _{width) c 3: 3 + 9 +} 15 × 0.23 + 1 Young's modulus _{^{16000 kgf / mm 2 c 2:}} 3 + 9 + 15 × 0.23 + 1 Young's modulus 16000 kgf / mm ² c _1: + 9 × 0.23 + 1 d type _{d 4: 2 + 7 × 0.30} ( Example 8; 62% the width of the tire tread maximum width of FIG. _{8) d 3: 3 + 9} + 15 × 0.23 + 1 kgf / mm 2 d 2: 3 + 9 + 15 × 0.23 + 1 kgf / mm ² d ₁ : 3 x 0.20 + 6 x 0.38

A trial tire of 1000R20VDT size having the above-mentioned belt structure was manufactured, and the rubber penetration form was measured as follows. The following characteristics were evaluated for these test tires by running on a normal road including 40% of bad road for 20,000 km at 100% load. The evaluation methods are as shown below, and the comparative example 1 (current tire) was set to 100, and the larger the index, the better the characteristics. TLB property: The size of the peeling area from the protector (outermost cord layer) of the tread rubber in the tire after actual driving is displayed as an index. The larger the index, the less peeling, and the TLB.
It shows that the property is good. Cord cutability of protector, number of tread cuts: After the actual running, peel off the tread portion of the tire directly above the cord layer of the protector, and find the number of cuts that reached this cord layer. Based on this cut number, the larger the index, the better the index is displayed, and the tread cut index is shown. Further, the presence or absence of cord breakage and the number of cord breakages were counted for each of the reached cuts, and the total number was expressed as an index so that the larger the index, the better the cord cuttability. At 1000R20, three measurement points were provided on the circumference, and the size of each measurement point was measured in a region having a width of 9 cm and a length of 20 cm along the circumferential direction.

Edge length of third cord layer of belt: Third length
The cord layer of the protector is peeled off on the cord layer, and the cord end of the third cord layer is exposed. The control tire was set to 100 and indexed such that the shorter the tire, the larger the index. Abrasion resistance: Measured groove depth A at the time of new article, certain mileage Xkm
After running, the depth B of the remaining groove is measured and the difference A−B is obtained.
As a result, X / (A-B) can be calculated and the running distance until the tire is completely worn can be predicted from this, and this is indexed, and the larger the value, the better the display. Table 1 shows the structure of the test tire and the evaluation results.

[0025]

[Table 1]

The comparative example is an example of double twist. Example 1,
2, 6 to 8 each have a molding rate of 96%, and Example 3 has 98%.
And, Examples 4 and 5 are 101%, which shows that a sufficient imprinting rate close to 100% affects the closed form.

[0027]

As described above in the examples and comparative examples, the present invention is applied to a large radial tire for bad roads before the outermost cord layer of the belt, that is, the protector surrounding the belt 1 is twisted into the cord. 1 to 2 filaments obtained by twisting a modeled filament as a core 2
A twisted cord having a layered twist structure is used for a cord volume fraction of 5 to 5.
It is embedded in rubber with good permeability in the range of 40%,
As a result, by making the permeation of rubber into the cord into a closed form, the durability of large radial tires for bad roads, especially the TLB property, in running on bad roads can be advantageously improved. Is unsatisfactory and has disadvantages such as a decrease in code strength and an increase in price, which is extremely advantageous.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a molding rate.

2A and 2B are explanatory views of the volume fraction of the belt cord, and c is the number of cuts reaching the outermost cord layer with respect to the volume fraction of the cord and the number of cuts penetrating this and reaching the third cord layer. It is a graph which shows the relationship of the ratio with.

FIG. 3 is an explanatory diagram showing a rubber infiltration form.

FIG. 4 is an explanatory diagram of a procedure for measuring the rubber penetration rate of a cord.

5A, 5B, 5C, and 5D are explanatory views showing a cross-sectional structure of a belt composed of a four-layer cord.

FIG. 6 is a partial cross-sectional view (cross-section not shown) of a main part of a tire showing an embodiment of the present invention in which the belts of FIGS. 5a and 5b are arranged.

FIG. 7 is a partial cross-sectional view (cross-section not shown) of a main part of a tire showing an embodiment of the present invention in which the belt of FIG. 5c is arranged.

FIG. 8 is a partial cross-sectional view (section not shown) of a main part of a tire showing an embodiment of the present invention in which the belt of FIG. 5d is arranged.

FIG. 9 is a cross-sectional view of a cord showing a 2 + 7 twist structure.

FIG. 10 is a cross-sectional view of a cord showing a 2 + 6 twist structure.

FIG. 11 is a cross-sectional view of a cord showing a 1 + 5 twist structure. 1 Belt 2 Carcass 3 Tread 4, 4'Steel cord 5 Filament 6 Cushion rubber 7 Soft rubber cushion rubber a ₁ , b _1, c ₁ , d ₁ Belt 1st cord layer a ₂ , b ₂ , c ₂ , d ₂ belt second code layer _{a 3, b 3, c 3} , d 3 belt third cord layer _{a 4, b 4, c 4} , d 4 belt outermost cord layer (= protector)

Claims (2)

[Claims] 1. At least three cord layers in which steel cords are embedded in rubber in parallel are wound and laminated in an arrangement in which the cords of each layer form a relatively small angle with respect to the equatorial plane of the tire, and serve as a protector. On the inner side of the outer cord layer, at least one pair of mutually adjacent cord layers are arranged as belts in which the cords cross each other at an angle of 15 to 30 °, together with the protector, and substantially to the equatorial plane of the tire. In a radial tire with a tread reinforcement that is combined with a carcass with a cord arrangement orthogonal to the protector, the protector has a filament diameter of 0.23 to 0.40 mm A steel cord having a two-layer twist structure having one or two filaments as a core, which is obtained by twisting filaments, is pulled in a cross section of the belt. The area between the bisector of the imaginary line passing through each cord center of the protector and the imaginary line passing through each cord center of the belt cord layer adjacent to the inside of the protector, and the boundary line to the tread portion of the protector , The cord volume fraction expressed by the percentage of the total cord cross-sectional area of the protector occupying this portion is 5 to
Within a range of 40%, and the infiltration of rubber into the inside surrounded by the filament of the cord is composed of a cord layer formed by embedding it in the rubber in a closed penetrating form having a cord portion having no void. Large radial tire for rough roads. 2. The radial tire according to claim 1, wherein the two-layer twist structure is 2 + 7 or 2 + 6 twist.