JPH0514642B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pneumatic radial tire for heavy vehicles such as trucks and buses that has improved resistance to uneven wear. Pneumatic radial tires for heavy vehicles have many advantages over pneumatic bias tires for heavy vehicles, such as superior wear resistance, wet resistance, and puncture resistance, so they are used on paved roads and highways. Its use has been rapidly expanding in recent years as the equipment has become more fully equipped. As tires for high-speed roads, rib-type tires are used in which ribs in a zigzag pattern extending in the circumferential direction of the tire are provided on the tire tread surface in consideration of traction, braking performance, general wear resistance, and heat resistance. There is. Such ribs are normally continuous in the circumferential direction of the tire, but sometimes they are separated by grooves along the width direction of the tire, making them discontinuous in the circumferential direction. It has become known that when pneumatic radial rib type tires for heavy vehicles are continuously driven in a straight line over long distances at high speeds, uneven wear, that is, railway wear, which has never been seen before, occurs. This railway wear refers to the convex portion of the circumferential rib 2 that extends in the width direction of the tire T toward the tread main groove 1 that extends in a zigzag shape along the circumferential direction of the tread of the tire T, as shown in FIG. Uneven wear occurs locally from area A near the apex of 3, which is accelerated and eventually creates a step h with width W in the cross section shown in Figure 6, and this area A of uneven wear is , and then gradually increase as the traveling distance (number of meters) increases, and eventually connect with the adjacent area A and continue on the circumference of the tire T. Further, as the traveling distance increases, the step h and the width W increase. Such uneven wear is generally called railway wear, and the resulting shoulder sagging of the tread main groove 1 not only makes the appearance of the tire T unsightly, but also impairs the function of the ridgeline of the rib 2 divided by the tread main groove 1. This adversely affects dependent tire performance, especially traction and braking performance, and significantly shortens tire life. This uneven wear begins to occur only near the apex of the convex part 3 of the circumferential rib 2 forming a zigzag shape, and the concave corner 4 of the circumferential rib 2 facing in the width direction of the tire T is the starting point. However, as the uneven wear progresses, the corner portion 4 will eventually be affected by railway wear. This railway wear is a peculiar phenomenon that occurs when metal cords with extremely high rigidity are used as belt reinforcement materials or when ribbed tires are used for continuous high-speed running. Due to the fact that it is less likely to occur when used on rough roads with severe wear and tear,
The cause of this is that the tire T towards the tread main groove 1 is
It is said that this is because the vicinity of the apex on the convex portion 3 side of the circumferential rib 2 extending in the width direction of the tire is subjected to stress concentration in the width direction of the tire during continuous high-speed running. From this point of view, attempts have been made to improve the shape of conventional tread patterns. For example, the amplitude of the main grooves arranged in a zigzag manner in the circumferential direction of the tire, the method of making the circumferential pitch small, that is, the shape close to a straight groove, and the method of making the main grooves smaller than the tread grooves as described in Japanese Patent Application Laid-open No. 52-44904. A method in which independent thin stress relaxation grooves 5 are provided in the circumferential rib as shown in FIG.
As described in the specification of No. 128807, a circumferential rib is provided near the apex of the overhanging convex portion of the circumferential rib with a separation groove 6 substantially parallel to the rib ridgeline near the apex as shown in FIG. There is also a method of attaching stress relieving ribs 7 that form part of the tread surface. However, improving the shape of the tread pattern such as the stress-relieving grooves 5 and stress-relieving ribs 7 alone cannot reduce railway wear.Also, railway wear can be improved by making the shape closer to a straight groove, but the tire Currently, this method cannot be implemented because it degrades wet performance, which is one of the most important required characteristics. In view of the current situation, the present inventors aimed to obtain a tire with a tread that significantly improves uneven wear resistance, especially railway wear resistance, without sacrificing the wet performance of a heavy-duty radial tire.
As a result of detailed research from both the compounding and tread pattern aspects, we found that when a natural rubber compound composition is applied to tread rubber, railway wear occurs regardless of the tread pattern shape (zigzag shape other than straight grooves). However, an SBR blend composition containing a styrene-butadiene copolymer, natural rubber, and/or other diene rubber as the rubber component can effectively prevent railway wear within a certain tread pattern shape range. It has been found that the objects of the invention can be advantageously achieved. That is, the heavy-duty pneumatic radial tire of the present invention includes at least two breaker layers that intersect with each other at a relatively small angle to the tire circumferential direction, and at least one carcass layer that is arranged at substantially 90 degrees to the tire circumferential direction. In a radial tire reinforced with layers, the tread rubber layer placed outside the breaker layer is composed of two layers, and the cap tread portion placed outside the crown portion has a zigzag-shaped tread continuous in the tire circumferential direction on its tread surface. It has at least one main groove, and as shown in FIG. 4, the width 9 of the main groove is 2 to 10% of the tire tread width, the amplitude 10 is 15 to 50% of the main groove width 9, and The length 11 is in the range of 60 to 220% of the main groove width 9, and the rubber component in the cap lead portion is composed of a styrene-butadiene copolymer, natural rubber, and/or other diene rubber, The amount of polymer blended is 30 to 70% by weight, and the extract obtained by continuous extraction with acetone for 24 hours is 10% by weight.
A rubber composition having a maximum elongation at break of 490% or more at 100°C is arranged below, and a composition having a lower loss tangent than the cap lead rubber, preferably 70%, is placed in the base rubber part inside the cap lead part. %
A composition having the following loss tangent is arranged to cover the entire width of the breaker layer in the tire radial direction, and a cushion rubber having a lower loss tangent than the rubber layer constituting the breaker layer, preferably 50%
It is characterized in that a cushion rubber having the following loss tangent is disposed between the end of the breaker layer and the carcass ply. Furthermore, as for the compounding composition of the cap lead rubber part, the amount of styrene-butadiene copolymer as a rubber component is 40 to 60% by weight, and the amount of vulcanized rubber extracted is 8% by weight or less, and the maximum at rupture at 100 ° C. More preferably, the elongation is 510% or more. Instead of the natural rubber compound that has traditionally been used exclusively as tread rubber for radial tires for heavy vehicles, we have used a blend of natural rubber (NR) and styrene-butadiene copolymer rubber (SBR) to make SBR account for at least 30% by weight of the rubber component. As a result, railway wear resistance is significantly improved. Moreover, this effect can be achieved by replacing some or all of the natural rubber with other diene rubbers such as polybutadiene rubber, polyisoprene rubber, butyl rubber, halogenated butyl rubber, and one type of ethylene-propylene-diene terpolymer selected from the group. Alternatively, the effect can be achieved even if two or more types are substituted. It is not clear why railway wear improves rapidly when SBR exceeds 30% by weight, but one reason may be that the state of dispersion of SBR in the rubber changes. The amount of SBR added is
As will be described later, the content should be 70% by weight or less in order to suppress heat generation. In addition, suppressing the amount of low molecular weight organic compounds such as extracts of capturing rubber, ie, aromatic oil and stearic acid, also contributes to improving railway wear. However, the railway wear improvement effect obtained by reducing the extract to 10% by weight or less is only exhibited when SBR is blended as described above. In the present invention, the carbon black used for the cap lead is IA80 (mg/
g), a furnace black with a DBP of 100 (ml/100g) or more is preferred, and an IA of 120 (mg/g) or more is more preferred. The groove width 9, amplitude 10, and pitch length 11 of the tread main groove 1 will be described in detail below when the SBR blend composition is applied to the tread rubber. If the groove width 9 is less than 2% of the tread width, it will be difficult to drain water when wet, and if it exceeds 10%, the ground pressure will be uneven between the rib end facing the main groove and the rib center, and other unevenness will occur. This will cause wear and further reduce the wear resistance, so if the tread width is
10%, more preferably within 4-8% of the tread width. Next, amplitude 10 and pitch length 11 are also important; if amplitude 10 is less than 15% of main groove width 9, or pitch length 11 exceeds 220% of main groove width, the main groove will have a shape close to a straight groove. This will reduce traction and braking performance when wet. On the other hand, if the amplitude 10 exceeds 50% of the main groove width 9 or the pitch length 11 becomes less than 60% of the main groove width, railway wear cannot be avoided even when the SBR blend composition is applied. Therefore, in the present invention, the amplitude is set to 15 to 15 of the main groove width.
50%, pitch length 60-220%. Furthermore, the main groove width 9 is 4% to 8% of the tire tread width, and the amplitude is 10%.
If it is 25 to 40% of the main groove 9 and the pitch length is 100 to 180% of the main groove width, it is more advantageous that railway wear can be prevented even when the running speed of the vehicle is particularly high. . In order to prevent railway wear between the main grooves or between the main groove and the tread edge, one or more narrow grooves substantially parallel to the main groove may be arranged with narrow groove widths that contact each other during load rolling. Since the wet performance of the tire is improved, the number of main grooves can be reduced. When the structure of the present invention as described above is applied to a radial tire for heavy vehicles, in order to ensure that the tire can withstand high-speed running, the base rubber portion inside the cap tread portion has a loss tangent that is smaller than that of the cap tread rubber. It is necessary to arrange a cushion rubber having a lower loss tangent than the rubber layer constituting the breaker layer so as to cover the entire outer width of the breaker layer in the tire radial direction. When this SBR blend composition is applied to a tored, it is inferior in terms of heat generation compared to a natural rubber composition, and there is a concern that heat separation may occur. Therefore, the above two requirements are necessary to suppress heat generation and prevent this. Become. In accordance with the above, the SBR blend composition
It is also important to suppress the amount of SBR to 70% by weight or less in terms of suppressing heat generation. Furthermore, if the SBR blend composition applied to cap treads is simply increased in SBR content, the maximum elongation at break at high temperature will decrease; ) may also occur, so it is also important that the maximum elongation at break at 100° C. of the SBR blend composition used for the cap lead is 490% or more, preferably 510% or more. Methods to increase this maximum elongation include (1) slightly reducing the amount of sulfur than the amount normally used, (2) adding softeners and resins, and (3) adding a portion of the SBR amount to low molecular weight (viscosity average Molecular weight 5000~
200000) Replace with SBR, etc. This will be explained in more detail below with reference to Examples. Examples The compounding composition of the cap lead rubber is 9 types in Table 1, and the coating rubber of the breaker layer and the breaker interlayer rubber are the rubber compositions No. 2 in Table 2.
10. Various tires shown in Table 4 were trial produced using the four types of base tread rubber and cushion rubber shown in Table 3. The base rubber was arranged so as to cover the entire outer width of the breaker layer in the tire radial direction. Both tires are rib type steel radial tires shown in Figure 5 with size 10.00R20 14PR tire width 180mm. Table 4 shows the results of performance tests conducted on these tires. Carbon black used in Tables 1 to 3
HAF IA is 80 (mg/g), DBP is 104 (ml/100g)
It is. Here, IA refers to the amount of iodine adsorbed by carbon black (unit: mg/g), and the measurement method is JIS
By K6221. DBP is the dibutyl phthalate (DBP) absorption value of carbon black measured according to the method described in ASTM D-2424 (unit: ml/
100g). The measurement methods for the evaluation items listed in Tables 1 to 4 are as follows. <Extracted amount> After cutting the tored rubber into cubes of approximately 1 mm on a side, approximately 1 g was precisely weighed (A) and extracted with acetone continuously for 24 hours using a Soxhlet extractor, and from the weight of the obtained extract (B) /A×100 (weight%). <Maximum elongation at break> After slicing the tored rubber into approximately 2mm thick
It was punched into the shape of DIN-3 and subjected to a tensile test in an atmosphere of 100℃ using an Instron type tensile tester.
The maximum elongation at break was expressed as "%". <Loss tangent> The viscoelastic spectrometry was performed using a test piece prepared by slicing treaded rubber to a thickness of about 2 mm, or cutting out a sheet of about 2 mm thick from the breaker interlayer rubber to a length of 20 mm and a width of 5 mm. Meter (Viscoelastic manufactured by Iwamoto Seisakusho)
Test conditions: initial strain 5%, dynamic amplitude 2%, frequency 50
Measured at Hz, 25°C. Note that the loss tangent is calculated using the following formula based on the above measurement conditions. tan δ (loss tangent) = E″/E′ where E′ is the dynamic storage modulus E″ is the dynamic loss modulus. <Wet resistance> After filling the test tire with an internal pressure of 7.25 kg/m ² and mounting it on a large truck and adjusting the load so that the wheel weight was 2425 kg, the test tire was placed on an asphalt pavement for 1 to 2 hours.
Sprinkle water in an amount that creates a water film of mm, and then
Sudden braking was applied at a speed of 80 km/h, and the distance taken until the vehicle stopped, that is, the braking distance, was measured. It was expressed as an index using the following formula. The higher the index value, the better. Braking distance of tire No. 1 / braking distance of test tire x 100 <Railway wear rate> The test tire was filled with an internal pressure of 7.25 kg/m ² and attached to the front wheel of a large truck. , load/constant loading,
70% highway, 30% local road, 80% highway
After traveling 40,000 km at a vehicle speed of 40 km/h on ordinary roads, the degree of railway wear was measured. The left and right positions of the tires were changed every 5000 km. The degree of railway wear occurrence is evaluated by the level difference h and the railway wear width w as shown in FIG. 6, and is expressed as an index as shown in the following equation. The smaller the index value, the better. h x w / ho x wo x 100 ho: step difference in tire No. 1 wo: width of railway wear on tire No. 1 h: step difference w in test tire w: width of railway wear in test tire <heat resistance> Test tires and Tire No. 1 were tested on an actual vehicle under harsh running conditions (internal pressure 7.25Kg/cm ² , load 2425Kg+)
30%), and after running for 100,000 km, we dissected the belt and compared the cracks at the end of the belt. The index of the results was calculated using the following formula. Here, the larger the index, the better. Length of belt end crack of tire No. 1 / Length of belt end crack of test tire x 100

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[Table] From Table 4, it can be understood that the synergistic effect of reducing railway wear is exhibited only by the pattern shape and SBR blend composition range of the present invention. Improving the pattern shape alone has little effect on reducing railway wear, but when combined with an SBR blend composition, the effect increases dramatically.
(Refer to Tire No. 1, 2, 3, 5) Even if the SBR blend composition is applied to the cap tread, increasing the main groove width and amplitude and shortening the pitch length will reduce the mechanical input to the tread rubber. Due to large changes, the effectiveness of SBR rubber decreases,
If the main groove width and amplitude are made smaller and the pitch length is made longer, wet and skid resistance will be impaired. (Tire No.
1, 4, 5, 6) Looking at tires No. 7 to 12, in order to achieve both railway wear resistance, wet resistance, and heat resistance,
It can be confirmed that the amount of SBR blended is 30 to 70 parts by weight. Examples of tires No. 9, 13, and 17 have cap lead.
In the case of an SBR blend composition,
This shows that the effect of extraction amount contributing to railway wear cannot be ignored. Next, five types of tires No. 9, 10, 11, 12, and 17 were each filled with an internal pressure of 7.25 kg/cm ² and mounted on a large truck, and the load was adjusted so that the wheel weight was 2425 kg. After running the test tire on a rough road at 50,000 kg, we observed the size of cracks that occurred in the ribs of the tire tread and the condition of the ribs to confirm the durability of the rib tear. The results were evaluated based on the length of cracks that occurred in the tread ribs. Tire No. with the highest maximum elongation at break at 100℃
The three types of tires No. 9, 10, and 17 had no cracks at all, and tire No. 11 had only a few cracks with an average length of 5 mm, but tire No. 12 had cracks with an average length of 40 mm. Rib blistering also occurred in the area. High-speed rib-type radial tires with excellent railway abrasion resistance do not sacrifice other performance unless the maximum elongation at high temperature fracture is 490% or more, such as tires No. 9, 10, 11, and 17. You can get it without having to do it. As described above, by the present invention, for the first time, a dramatic improvement in railway wear, which had been considered difficult in the past, has been achieved.

[Brief explanation of drawings]

Fig. 1 is a partial plan view of a conventional pneumatic radial rib tire for heavy vehicles, Figs. FIG. 4 is a partial plan view of a tire for explaining the tread grooves of a tire according to the present invention. FIG. 5 is an example of a tire according to the present invention. FIG. 6 is a sectional view of the left half of FIG. 6, which is an explanatory diagram of the degree of railway wear occurrence. 1... Tread main groove, 2... Circumferential rib, 3... Overhanging convex portion, 4... Corner, 5... Stress relaxation groove, 6... Separation groove, 7... Stress relaxation rib, 8... Thin groove, 9... Main groove width ,
10... Amplitude, 11... Pitch length, 12... Base tread rubber, 13... Cushion rubber, 14... Breaker layer, 15... Breaker interlayer rubber, h... Step, w... Railway wear width.

Claims (1)

[Claims] 1. Reinforced by at least two breaker layers intersecting each other at a relatively small angle to the tire circumferential direction and at least one carcass layer disposed at substantially 90° to the tire circumferential direction. In a radial tire, the tread rubber layer arranged on the outside of the breaker layer is composed of two layers, and the cap tread part arranged on the outside of the crown part has at least one main tread in a zigzag shape continuous in the tire circumferential direction on its tread surface. The groove width of the main groove is 2 to 10 times the width of the tire tread.
%, the amplitude is in the range of 15 to 50% of the width of the main groove, the pitch length is in the range of 60 to 220% of the width of the main groove, and the rubber component is styrene in the cap lead part.
Consisting of butadiene copolymer, natural rubber and/or other diene rubber, the blending amount of styrene-butadiene copolymer is 30 to 70% by weight, and the extract obtained by continuous extraction with acetone for 24 hours is 10% by weight. Maximum elongation at break at 100℃ is 490%
The above rubber composition is arranged, and a composition having a loss tangent of 70% or less compared to the cap tread rubber is applied to the base rubber part inside the cap tread part over the entire width of the breaker layer outward in the tire radial direction. furthermore, a cushion rubber having a loss tangent of 50% or less compared to the rubber layer constituting the breaker layer is arranged between the end of the breaker layer and the carcass ply. Pneumatic radial tires for heavy vehicles.