JPH0115406B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention has a tread portion of two or more layers with specific physical properties, has a good balance of wear resistance, cut resistance, chipping resistance, and durability, and is particularly suitable for large-scale applications with high loads. This invention relates to pneumatic radial tires. [Conventional technology] With the increasing use of radial large tires in Japan and overseas, radial tires for trucks and buses are high-performance tires, so the required characteristics are high speed, low fuel consumption, and long life. , durability on rough roads, etc. are required to the utmost, and the demands from users themselves tend to be diversified. Among them, high-load lug tires in particular are being used in a variety of ways, from the traditional conditions of use mainly on rough roads or unpaved roads such as road construction sites and quarry sites, to recently used conditions mainly on paved roads. It is becoming widespread. That is, there is an increasing demand for large radial tires with high load lugs that can run as fast as possible on paved roads as well as unpaved roads, and the situation is such that it cannot be met with mere conventional single-purpose specifications. For example, in terms of the materials used, it is difficult to achieve both wear resistance, which is required for paved roads, and cut resistance and chipping resistance, which are required for rough roads or non-paved roads. Including durability as a characteristic, it is difficult to provide all functions to a single cap lead, and it is impossible to satisfy market demands. There are two possible approaches to meeting these demands: improving the material and improving the structure. First, as an approach from the material formulation aspect, as shown in Japanese Patent Application Laid-Open No. 101503/1983, optimization of carbon properties such as nitrogen adsorption amount, dibutyl phthalate absorption amount, and coloring power is necessary. Although there is technology that can achieve both abrasion resistance, cut resistance, and chipping resistance, such single tread rubber alone cannot achieve the high speed and high speed that are currently required for high-load lug tires.
At present, it has not yet reached the point where it satisfies the ultimate values for long life and rough road durability. On the other hand, in terms of structural design, in tires with a single-compound tread structure, which is typical of conventional technology, if too much emphasis is placed on wear resistance, the heat generation of the rubber increases, leading to problems with tread separation in the early stages of driving. Chipping during the middle to final stages of driving can cause abnormal wear, while placing emphasis on chipping resistance, low fuel consumption, and high-speed durability can lead to a reduction in wear life, including initial wear, resulting in tires that are not fully satisfactory. It was difficult to obtain Under these circumstances, technologies aimed at improving durability are currently being established.
54-38004 and Japanese Patent Application Laid-open No. 58-128904, a base tread rubber is placed between the cap lead and the belt, in addition to the cap lead, and the base tread rubber has low heat generation. Thermal durability is improved by ensuring a certain level of rigidity and rigidity. However, at present, the conventional technology of a two-layer treaded structure that simply aims to improve durability is no longer satisfactory, and while maintaining the durability level, it is now possible to extend the lifespan by improving wear resistance and improve early wear. It is desired to develop a large pneumatic radial tire with improved cut resistance and chipping resistance from the beginning to the end of life. [Object of the Invention] An object of the present invention is to provide a preferably large-sized pneumatic radial tire designed to satisfy all of tire wear resistance, cut resistance, chipping resistance, and durability. [Configuration of the Invention] The configuration of the present invention is that in a pneumatic radial tire having at least two layers of tread rubber, the volume of the outermost tread layer (layer A) is 25 to 50% of the total volume of the tread, and The volume of the inner tread layer (B layer) is 30 to 30% of the total tread volume.
75%, and 300% modulus of A layer and 20
The loss tangent tan δ at ℃ is made larger than those of the B layer, the 300% modulus of the A layer is 120 to 160 Kg/cm ² , the tan δ is 0.18 or more, and the B layer is made larger.
300% modulus is 80~120Kg/cm ² , and the tanδ is
The gist of this is that it is between 0.14 and 0.18. The present invention will be explained in more detail below. First, we will explain why two or more tread layers having specific physical properties are necessary to satisfy all of the objectives of the present invention, such as abrasion resistance, cut resistance, chipping resistance, and durability. Wear as used in the present invention is a phenomenon in which the tread groove portion is continuously reduced due to rubber being removed from the tread surface as fine abrasion particles under normal running conditions. On the other hand, chipping is a phenomenon that occurs when extremely high loads and high torques are applied, and the rubber on the tread surface is partially removed in a layer with a thickness of about 0.5 to 2.00 mm. It is known that chipping does not occur in the early stages of running, but occurs during the middle to final stages of running when the rubber in the tread hardens due to heat or stress fatigue. Furthermore, when this stress fatigue reaches its limit, the mesh density of the tread portion increases. Network density can be obtained by measuring rubber swelling density, but it is generally measured on the stress-strain curve.
It is known that 300% modulus can be used instead. Regarding the physical properties of the material used for the tread, it is important that the mesh density does not exceed a certain limit.
When we investigated the increase in mesh density due to this stress fatigue with the distance traveled, we found that the mesh density of the rubber gradually increased and that the 300% modulus also increased with the distance traveled. In addition, in order to prevent this increase, the rubber composition used in the tread was changed within an allowable range, but when running under the same conditions, the increase rate of 300% modulus was similar, and it reached its limit from the middle to the end of running. It was concluded that in order not to exceed this value, it is necessary to keep the initial 300% modulus below a certain value, that is, it is necessary to set an appropriate 300% modulus. However, if the mesh density of the entire tread portion is set too low, the overall modulus including the tread surface portion will decrease, and the deformation of the entire tread portion will increase, resulting in a decrease in wear resistance. It is tied to In this way, research using actual tires has shown that the performance required of the tread portion of large radial tires for high loads is different between the initial stage of running and the final stage after stress fatigue. It has been found that the following conditions are necessary to prevent cutting and chipping from the beginning to the final stage and to improve wear resistance and durability. (1) The outermost layer (referred to as the A layer) near the ground plane of the tread section has slightly high hysteresis loss and heat generation, but has excellent wear resistance and a high mesh density (300% high modulus). ). (2) The part near the groove of the tread section (approximately the layer adjacent to the inside of the A layer) that wears out at the end of running (called the B layer) has a modulus of 300% to prevent cutting and chipping. Set it low,
In addition to lowering the mesh density at the beginning of the run,
This is a part that has a big impact on durability, so
The hysteresis loss is set lower than that of the rubber of the A layer. (3) More preferably, a third layer (referred to as C layer) is provided between the groove and the belt. This C layer is not used until it wears out, and is therefore the part that requires the most durability, so the hysteresis loss is set to the lowest, and wear resistance is not considered, but the performance for trauma resistance is set above the limit. do. This improves retreadability and increases durability when used after retreading. The ratio of each layer to the total volume of the tread is 25 for layer A.
-50%, B layer should be 30-75%. In addition, when providing the C layer, the ratio of the C layer is 0 to 20%,
Preferably it is 5 to 20%. Further, it is preferable that the C layer gauge does not exceed the tread groove lower gauge. Here, the volume ratio of each layer is calculated as the cumulative volume ratio between both shoulders by dividing the tire cross section into n equal parts with a width m at equal intervals, and setting the thickness of the cap tread rubber layer in each part to ai, bi, and ci. This is what I did. Next, the rubber composition used in the present invention needs to be a rubber composition that satisfies the functions of each tread rubber layer, and therefore contains at least 70 parts by weight of natural rubber, synthetic isoprene rubber, or these rubbers. It is preferable that the blend rubber is selected from blend rubber containing polybutadiene rubber or styrene-butadiene rubber. In addition, for 100 parts by weight of rubber, the tread A layer has a nitrogen surface area (N ₂ SA) of 125 to 150.
m ² /g, dibutyl phthalate absorption (DBP) 105-130ml/100g, coloring power (vs. Industry
Beferencl Black #3) Contains 40 to 60 parts by weight of highly reinforcing carbon of 110% or more, and for the Toledo B layer, N ₂ SA 110 to 125 m ² /g, DBP 80 to 120
ml/100g, reinforcing carbon with coloring power of 110% or more
30 to 50 parts by weight, and for the Toledo C layer, N ₂ SA 70 to 110 m ² /g, DBP 80 to 120 ml /
100g, 40~ reinforcing carbon with over 100% coloring strength
It is preferable to mix 60 parts by weight. Furthermore, the physical property values of the rubber composition used in the present invention are 300% for the tread A layer.
A modulus of 120 to 160 Kg/cm ² and a tan δ of 0.18 or more are required. For the treaded B layer, a 300% modulus of 80 to 120 Kg/cm ² and a tan δ of 0.14 to 0.18 are required, and the treaded C layer is used. 300 in case
It is preferable that the % modulus is 100 to 140 Kg/cm ² and the tan δ is 0.14 or less. Here, regarding the Toread B layer, which plays the most important role in the present invention, the abnormal wear phenomenon due to cuts and chipping that occur during to the final stage of driving by non-impaired road users, and the overall tire wear including general road users. Due to lifespan issues, etc.,
The vol ratio is important, and as a result of conducting actual driving tests under various conditions of varying degrees of severity and varying the vol ratio of the Toledo B layer, we found that it was possible to obtain the results under very severe usage conditions such as unpaved roads or rough roads. If the Vol ratio is less than 30%, abnormal wear phenomena due to cutting and chipping will occur in the A layer before reaching the B layer, while if it is more than 75%, although these abnormal wear phenomena due to chipping will be satisfied,
This is undesirable as it reduces tire life. If 50 parts by weight or more of carbon with N ₂ SA of 125 m ² /g or more and DBP of 120 ml/100 g or more is added to the Toledo B layer, the cutting and chipping properties at the middle to end of running will be significantly impaired, and tan δ is 0.18 or more, which raises concerns about durability. On the other hand, if it is less than 30 parts by weight, there will be no problem in terms of durability, but it will shorten the life of the tire.
A similar problem occurs when carbon with an N ₂ SA of 110 m ² /g or less and a DBP of 80 ml / 100 g or less is used. Next, regarding the tread A layer, in balance with the tread B layer, it is necessary to ensure functionality and volume that will not reduce tire life or cause abnormal wear due to cuts and chipping in the early stages of running. Therefore, the Vol ratio should be kept below 50% to prevent abnormal wear, and 25% to ensure tire life.
It is necessary to set the above settings. Furthermore, since this is the tread layer closest to the ground plane, carbon black with a small particle size of N ₂ SA of 125 m ² /g or more is preferred in order to fully exhibit its wear resistance function. In addition,
Adding more than 60 parts by weight of carbon with N ₂ SA of 150 m ² /g or more and DBP of 130 ml / 100 g or more is undesirable from the viewpoint of mixing processability, and is also undesirable from a functional standpoint as it causes abnormal wear due to chipping at the beginning of running. . Conversely, N ₂ SA125m ² /g, below:
If the DBP is less than 105 ml/100 g, the reinforcing properties of carbon black itself will be insufficient in terms of wear resistance, and even more so if the loading is as low as 40 parts by weight or less, it will be difficult to demonstrate the original wear resistance function. When using the third tread C layer, especially under severe usage conditions such as heavy loads or high speeds, the role of the tread C layer is also important, so the Vol ratio in the total tread should be less than 5%. If it exceeds 20%, durability will be insufficient, and if it exceeds 20%, the lifespan will be significantly reduced due to external damage at the end of wear. Furthermore, if the tread C layer is placed beyond the bottom groove tread gauge, the tread C layer will be exposed on the tread surface at the end of wear, which is unfavorable in terms of appearance. Furthermore, in order to set the hysteresis loss to the lowest, N ₂ SA
Carbon with a density of 110m ² /g or more is undesirable.
Carbon with a density of 70 m ² /g or less is undesirable because physical properties deteriorate significantly due to thermal factors associated with running. If the amount of carbon black added is 60 parts by weight or more, it will not be possible to achieve a tan δ of 0.14 or less, resulting in insufficient durability. Moreover, if the amount is less than 40 parts by weight, the modulus will be insufficient and the critical performance for trauma resistance cannot be secured. Hereinafter, the structure of the present invention will be explained with reference to the drawings. The figure is a cross-sectional view of the tire of the present invention, and the cap tread consists of three layers, with the outermost tread layer (A layer) 1 on the tread surface and the inner tread layer (B layer) on the inside.
layer) 2, and further therein the innermost tread layer (C layer) 3
A belt layer 4 and a carcass 5 consisting of four layers are provided adjacent to the C layer 3, and a liner 6 is provided on the innermost side. Also, a _i , b _i ,
c _i indicates the thickness of the mi-th layer A, layer B, and layer C when the tread portion is divided into m equal parts. Hereinafter, the effects of the present invention will be explained with reference to Examples. EXAMPLE A radial tire with the three-layer tread structure shown in the figure was manufactured and various performance tests were conducted. The rubber composition used for each layer A, B, and C of the tire is shown in Table 1 based on 100 parts by weight of rubber selected from natural rubber, synthetic isoprene rubber, or a blended rubber consisting of polybutadiene rubber or styrene-butadiene rubber. Contains an appropriate amount of various carbon blacks, 3 parts by weight of stearic acid, 3 parts by weight of zinc, 2 parts by weight of an anti-aging agent, and appropriate parts of sulfur and a vulcanization accelerator, and the various materials shown in Table 1. A rubber composition having the following characteristics was prepared, in which the 300% modulus was measured according to the JIS K6301 method, and the tan δ was measured using a dynamic viscoelasticity measuring machine.
The values are shown at a frequency of 20Hz, a dynamic strain of 10%±2%, and a temperature of 20℃. Furthermore, the wear index value is the same as that of Comparative Example 1.
The index value is set to 100, and the amount of wear was measured using a Lambourn abrasion tester. The tires used have a tread section divided into four parts,
Carcass and belt are made of steel cord layer
A 1000R20 14PR lug type steel radial tire is manufactured, and the rubber compositions listed in Table 1 are assigned to each tread rubber layer, and the rubber layer division ratio is varied to improve wear resistance, cut resistance, chipping resistance, and conducted an actual vehicle evaluation regarding durability.
The results are shown in Table 2. First of all, regarding durability, we calculate the step at which failure occurs when the load is cumulatively increased in the time steps shown in the table below and the vehicle is run at a constant speed of 55 km/HR.
An indoor durability test was conducted in accordance with the conditions of FMV-SS No. 119, and Comparative Example 1 was set as 100 and expressed as an index. The better the durability, the higher the numerical value.

[Table] Next, regarding wear resistance, among various severity tests, average speed of 55 km / HR, load of 120%, good road user with about 99% paving ratio, and average speed of 30 km / HR
An actual vehicle test was conducted on a user on a rough road with HR, load of 140%, and unpaved ratio of 20% or more, and the distance traveled until the remaining groove was 3.2 m/m was expressed as an index with Comparative Example 1 set as 100. The larger the value, the better the wear resistance and the longer the tire life. In addition, regarding cut resistance and chipping resistance, we conducted an external appearance check with the rough road users mentioned above.
Cut resistance is the number of injuries that enter the cut surface.
On the other hand, chipping resistance was evaluated by the degree of occurrence of peeling phenomenon on the tread surface, and calculated as a ratio when Comparative Example 1 was set as 100. The larger the value, the better the cut resistance and pitting resistance.

【table】

【table】

[Table] From the results in Table 2, it can be seen that the abrasion resistance, cut resistance, chipping resistance, and durability are all superior to Comparative Example 1, which does not have the B layer.
In addition, Comparative Example 2, in which the volume ratio of layer B exceeded 75%, had poor abrasion resistance and cut resistance on paved roads;
Comparative example 3 in which the layer is more than 50% and the B layer is less than 30%
It can be seen that the abrasion resistance, chipping resistance, and durability of unpaved roads are inferior.

[Brief explanation of drawings]

The figure is a sectional view of the radial tire of the present invention. 1... Outermost tread layer (A layer), 2... Inner tread layer (B layer), 3... Innermost tread layer (C
layer), 4...belt layer, 5...carcass, 6...
liner.

Claims (1)

[Claims] 1 In a pneumatic radial tire having at least two layers of tread rubber, the outermost tread layer (A
The volume of the inner tread layer (B layer) adjacent to the A layer is 30 to 75% of the total tread volume, and the volume of the A layer is 300% of the total tread volume. The modulus and loss tangent at 20℃ are made larger than those of the B layer, and the 300% modulus of the A layer is increased to 120 to 160 kg/
cm ² , the tan δ is 0.18 or more, the 300% modulus of the B layer is 80 to 120 Kg/cm ² , and the tan δ is 0.14 to 0.18.