JPS6215104A - Radial tire - Google Patents

Abstract

PURPOSE:To improve both low heat build-up and durability by allowing a tread to be made of a rubber composition which is composed of styrene-butadiene rubber and the like, the amount of combined styrene of which is specified, where the thickness of the tread is specified in a radial tire for buses and the like. CONSTITUTION:A tread 2 made of a rubber composition which is composed of styrene-butadiene rubber, or polybutadiene rubber by weight of 80-0, the amount of combined styrene of which is less than 20%, natural rubber or polyisoprene rubber by weight of 20-100, carbon black by weight of 45-70, iodine absorption of which is more than 60kg/g, and of softening agent by weight of 0-30. In addition, the thickness D of the tread 2 is specified to be 2.5-4.0 times the thickness 'd' from a belt 3 to the bottom of a tread groove 4. This configuration allows such factors as resistance to partial wear, low heat build-up, resistance to separation and durability, to be improved.

Description

Detailed Description of the Invention (a) Field of Industrial Application The present invention relates to radial tires that are mainly installed on heavy-duty vehicles such as trucks, buses, and trailers, as well as passenger cars. This relates to a radial tire that generates less heat and has greater durability.

However, when conventional tires are continuously driven for a long period of time under high load, high slip and frequent turning conditions, uneven wear occurs. In other words, premature wear of the entire shoulder rib of the tire tread or the outer shoulder rib, local wear of the center rib, or so-called railway wear occur, and these things progress to uneven wear at an accelerated pace, shortening the wear life of the tire. It becomes shorter and the vibration characteristics deteriorate.

As a countermeasure against such uneven wear, various methods have been proposed such as devising the tread pattern and making the ground pressure of the tread uniform. Furthermore, as shown in JP-A-58-161605 or JP-A-56-128201, uneven wear can be prevented by using styrene-butadiene rubber or a rubber composition in which styrene-butadiene rubber is blended with a liquid polymer as the tread rubber. It is proposed to do so.

In addition, as a method to prevent a decrease in tire durability due to separation caused by tire heat generation, the tread part of the tire has a two-layer structure consisting of a tread cap and a tread base, and the tread base rubber has no wear resistance. A method of using inferior rubber with low heat build-up, a method of dividing the tread into a center part and a halter part, and constructing the center part with a rubber composition with low heat build-up, a method of reducing the radius of curvature of the crown part of the tread, etc. It has been known.

(C) Problems to be Solved by the Invention Conventional tread rubber compositions mainly composed of styrene-butadiene rubber are effective to a certain extent in preventing uneven wear, but this tread rubber composition has a high exothermic temperature. However, when running, the tires generate heat at a high temperature, making it easy for separation to occur and reducing the durability of the tires.

With conventional tread rubber compositions, it is impossible to achieve both uneven tire wear resistance and durability due to low heat generation. In particular, by combining conventional tread rubber with high uneven wear resistance and low heat generation rubber, the tread part can be formed into a two-layer structure of cap and base, or a two-layer structure of center and side. Improvement in both abrasion resistance and durability is not sufficient. For example, if a rubber with high uneven wear resistance is used as the cap rubber and a rubber with low heat generation is used as the base rubber, if the base rubber becomes exposed on the tread surface during the middle to late stages of tire use, rapid wear and uneven wear will occur. This will actually shorten the life of the tire.

Therefore, in view of the above-mentioned drawbacks of conventional radial tires, an object of the present invention is to provide a tire having a highly durable tread that has high uneven wear resistance, low heat generation, and little separation. .

(d) Means for solving the problem When selecting a tread rubber composition for the purpose of improving uneven wear resistance of a tire, wear resistance under harsh conditions such as high ground pressure and high slip ratio is important. It is necessary to use a large rubber composition. As shown in FIG. 2, the amount of rubber wear increases rapidly as the ground pressure and slip ratio increase, so uneven wear tends to occur when tires are used with high ground pressure and high slip ratio.

As a result of measuring the amount of wear and exothermic temperature of various rubber compositions under extremely severe conditions, the present inventor found that styrene-butadiene rubber with a bound styrene content of 20% or less in natural rubber or polyisoprene rubber had a content of 0 to 80%. It has been found that the compounded rubber has a small amount of wear under severe conditions, has a relatively low exothermic temperature, and when used as tread rubber, has little uneven wear. However, the above-mentioned rubber composition has a rather large heat generation property, and
If this is used as is in the tread of a radial tire with a conventional structure, there is a risk that durability will decrease due to heat generation.

Therefore, as a result of extensive research into the relationship between tire structure and the decrease in durability due to heat generation, we have found that by reducing the tread thickness, as shown in Figure 3, it is possible to significantly lower the tire heat generation temperature. , and when the tread thickness is decreased, the wear life of the tire decreases by that amount, but the degree of decrease in the wear life is much smaller than expected from the decrease in the thickness of the tread rubber, and the heat generation of the tire decreases. The inventors have discovered that the effect of improving tire durability by lowering the temperature is far greater, and have completed the present invention.

That is, in the present invention, the tread rubber has a bound styrene content of 20%.
80 to 0 parts by weight of the following styrene-butadiene rubber or polybutadiene rubber, 20 to 100 parts by weight of natural rubber or polyisoprene rubber, 45 to 70 M parts of carbon black with an iodine adsorption amount of eomy/y or more, 0 to 0 parts by weight of a softener. 30 parts by weight of the composition, and the tread thickness is 1.
The gist is a radial tire characterized by having a thickness 2.5 to 4 times the thickness from the surface to the bottom of the tread groove.

As the rubber having good uneven abrasion resistance used in the tread of the radial tire of the present invention, a rubber composition having high abrasion resistance particularly under severe conditions of high ground pressure and high slip rate is used. The rubber components in the rubber composition include:
Natural rubber or polyisoprene rubber alone or a mixture thereof, or butadiene rubber or styrene rubber.
A compound containing butadiene rubber is used. natural rubber.

Polyisoprene rubber has good low heat generation properties, and
l? - The styrene-butadiene rubber to be blended preferably has a bound styrene content of 20% or less. When the amount of bound styrene exceeds 20%, wear resistance rapidly decreases. A rubber composition blended with butadiene rubber that does not contain styrene also has good abrasion resistance under severe conditions, particularly under conditions of high slip ratio.

The blending amount of styrene-butadiene rubber or butadiene rubber must be 80 parts by weight or less based on 100 parts by weight of the total rubber, and more preferably 60 to 30 parts by weight. 80
If the amount exceeds the weight part, the heat generation temperature will increase, and if this is used as a tread rubber, the durability of the tire will decrease, and problems will also occur in terms of rubber mixing and extrusion processability.

The carbon black to be added to the rubber composition has an iodine adsorption amount of 60//f or more, more preferably 12015//f or more. If the iodine adsorption amount is lower than 60/g, even if the amount of carbon black is increased, there is no effect of improving the wear resistance and uneven wear resistance of the tread rubber under conditions of high ground pressure and high slip ratio. The amount of carbon black to be blended is preferably 45 to 70 parts by weight, more preferably 45 to 60 parts by weight, based on 100 parts by weight of the rubber content. If this amount is less than 45 parts by weight, the abrasion resistance of the rubber will be low and 70 parts by weight.
If the amount exceeds the weight part, the heat generation temperature of the rubber will be high and the processability will be poor.

Addition of a softener to a rubber composition for a tread increases the friction coefficient of the rubber composition and reduces the amount of slip during tire running, thereby preventing uneven wear of the tread and improving the processability of the rubber.

The amount of softener added is 0 to 30 parts by weight per 100 parts by weight of rubber.
Parts by weight are appropriate, and 5 to 20 parts by weight is more preferred. If the amount added exceeds 30 parts by weight, the rubber becomes too soft and wear resistance decreases.

Butadiene rubber generally requires higher amounts of softener.

A tread using the above rubber composition has excellent abrasion resistance and uneven abrasion resistance, but if the conventional tire structure is maintained, the heat generation temperature of the rubber is high and a decrease in tire durability is inevitable. Therefore, by setting the ratio D/d of the tire tread thickness D to the thickness d from the first side of the belt to the bottom of the tread groove to 2.5 to 4, it is possible to suppress the heat generation of the tire and improve the durability of the tire. can.

The thickness D of the tread (2) of the tire (1) shown in Figure 1 varies from the bottom of the belt (3) to the bottom of the tread groove (4), depending on the type and size of the tire. The thickness d of the rubber is approximately constant depending on the diameter of the tire, regardless of the type of tire, and is about 3 mm for small tires for passenger cars and about 5 mm for large tires for trucks. If this thickness is too thin, the rubber will crack from the bottom of the tread groove, the steel belt will rust, and separation will occur easily.If this thickness is too thick, the tire's heat generation temperature will be high and the durability of the tire will be reduced. Most of the tires have the thickness shown above.

The tread thickness D of conventional tires is D/d=4.0~
6.5, but the radial tire of the present invention can significantly reduce the heat generation of the tread rubber by reducing the tread thickness D to a range of D/d = 2.5 to 4. This can improve tire durability. If the value of D/d is less than 2.5, the tread becomes too thin and the wear life of the tire is worse than that of conventional tires, and if the value of D/d is greater than 4, the effect of suppressing heat generation is small. However, the tread using the wear-resistant rubber of the present invention generates a large amount of heat, making it impossible to prevent a decrease in tire durability. By setting the value of D/d between 2.5 and 4, an increase in heat generation in the tread can be prevented even if a rubber composition with high wear resistance but slightly high heat generation is used in the tread. This makes it possible to prevent a decrease in tire durability.

(e) Function The radial tire of the present invention uses a special wear-resistant rubber composition as the tread rubber, and since the rubber composition has a slightly high heat generation property, in order to prevent a decrease in tire durability due to this, The tread thickness of this tire is smaller than that of conventional tires, and we will analyze how reducing the tread thickness affects the tire's lifespan.

As the tread thickness of a tire decreases, the allowable amount of wear until the tread reaches its wear limit decreases, and the possible mileage of the tire decreases accordingly.

FIG. 4 shows the relationship between tread thickness and tire mileage for tires with tire size 1000R2014PR. When the tread wears to the final wear position and the tire reaches the end of its wear life, the tire mileage is approximately 2.6 x 10 km when the tread thickness is 20 mm, while it is approximately 1.0 km when the tread thickness is 14 mm. 9 x 106 km, the possible mileage is reduced by only about 28% for a 51% reduction in the effective groove depth of the tread. This is because the thinner the tread, the higher the rigidity of the riff, the less movement, and the lower the temperature at which the tread generates heat, improving wear resistance. Furthermore, the thinner the tread is, the more the uneven wear resistance is improved.

However, if the tread thickness is 12mm and the effective groove depth is reduced by 68%, the mileage of the tire will be 1.3X10.
5/c shoulder and the life span is reduced by about 52%.

On the other hand, there is a linear relationship between the tire tread thickness and the tire heat generation temperature, as shown in Figure 2, and the tire durability improves due to a decrease in the heat generation temperature due to a decrease in the tread thickness. This results in a much better wear life than the tire wear life calculated from the decrease in thickness.

(f″) Examples Various rubber compositions were subjected to wear tests, friction tests and heat generation tests, and the results are shown in Table 1.

In addition to the ingredients listed in Table 1, the rubber composition includes 3 parts by weight of zinc white,
1 part by weight each of stearic acid, anti-aging agent, and vulcanization accelerator C2, and 2 parts by weight of sulfur are included.

In Table 1, the wear test was carried out using a Lambourn abrasion tester in accordance with the BS standard 908 Part AD method, with a ground pressure of 2.4.8 at 9/14 and a slip ratio of 12.
．． 48.80% and measure the amount of wear, and calculate the reciprocal of the amount of wear when the rubber of formulation 1, which contains only natural rubber as the rubber component, is 1%.
00 and expressed as an index. The larger the index, the better the wear resistance.

In the friction test, a friction and wear tester FT703 manufactured by Script Seisakusho was used to measure the dynamic friction coefficient of a dry road surface at a ground pressure of 6 kq/c-, and the coefficient of dynamic friction of the dry road surface was expressed as an index, with the rubber of compound 1 being 100. The larger the index, the larger the friction coefficient.

The heat generation test was conducted using a Gutdrich flexometer, with a rotation speed of 180 Orpm, a load of 48 Lbs, and a stroke of 0.1.
751nch, the temperature rise on the sample surface after vibration for 25 minutes at a room temperature of 40°C was measured and displayed.

Among the raw material rubbers of the compounded rubber in Table 1, A to F of SBR and G and H of BR are as follows.

5BRA: Emulsion polymerization S, BR (bonded styrene 23.5%
) SBRB: Solution polymerization SBR (//25%) SB
RC: /l (tt 18%
) SBRD: Oil extension solution polymerization 5BR (// 18%
) SBRE: 〃 (〃 13%)
SBRF: Solution polymerization 5BR (〃 5%) BRG:
Solution-polymerized high-cis BR BRH: Solution-polymerized low-cis BR The blended carbon blacks E to L in Table 1 are as follows.

Carbon black I:IEF Iodine adsorption amount 43~
74 Carbon Black J:HAF'/
80'/Carbon Black K: l5AF
'/ 120 // Carbon black L:
SAF // 145 // Among the rubber compositions in Table 1, the value of the abrasion test result is 4 kti
/ c! , 100 or more under the condition of slip ratio 80%, 100 or more under the condition of ground pressure 8kq/crl and slip ratio 48%.
As mentioned above, a material satisfying 120 or more and a heat generation test temperature of 31°C or less under the conditions of a ground pressure of 8 kg/d and a slip ratio of 80% is suitable for use as the tread rubber of the radial tire of the present invention, and the first All the abrasion test results of the rubber compositions that fall within the limited range of the rubber formulation of the present invention in the table above satisfy this preferable condition.

FIG. 2 shows the relationship between the wear amount, ground pressure, and slip ratio based on the test results shown in Table 1.

Among the rubber compositions in Table 1, the preferred blend for the radial tire and tread rubber of the present invention is 5.30°: 137.40
using rubber as the tread rubber, tire size 11R
A radial tire of the present invention having a size of 22,514D was manufactured and subjected to a drum test I and a running test, and the results are shown in Table 2 as Examples 1 to 5.

In addition, among the rubber compositions in Table 1, formulation t, 8.11, which is not suitable as the tread rubber of the radial tire of the present invention.
, 24 were similarly used to manufacture the same tires and subjected to drum tests and actual running tests, and the results are also shown as Comparative Examples (1 to 5) in Table 2. Furthermore, similar tests were conducted using the same tread rubber compositions as in Examples 1 and 3, but with thicker treads, and the results are also shown in Table 2 as Comparative Examples 6 and 7.

The drum test is based on the US automobile safety standard FMVSS1.
The test was carried out under the driving conditions specified in the No. 19 durability test, and the durability was expressed as the speed at which the tire failed. The tire temperature was determined by measuring the temperature at the end of the belt on the tread shoulder at a speed of 72 km/h.

In the actual driving test, the tires were run on the wheels of a trailer.
The reciprocal of the difference in the amount of wear between the normally worn part of the shoulder part and the early worn part of the ribs partially outside the shoulder was determined and expressed as an index, with the tire of Comparative Example 1 set as 100. The larger the index, the better the uneven wear resistance.

The wear life was defined as the time when the outside rib of the shoulder part became undriveable due to premature wear, and was expressed as an index with the tire of Comparative Example 1 set as 100. The higher the index, the better the wear life.

The tread thickness was expressed as the ratio D/d of the tread thickness D and the thickness d from the top surface of the belt to the bottom of the tread groove.

(g) Effects of the Invention According to the radial tire of the present invention, the rubber composition used as the tread rubber has high wear resistance, especially under harsh conditions of high ground pressure and high slip ratio. Because of its high durability, the amount of wear is small and uneven wear is less likely to occur even when the tires are mounted and driven continuously over long distances under heavy loads, high slip conditions, and frequent turns. Although the heat generation of the tread rubber is slightly higher than normal tread rubber due to the thinness of the tread, the heat generation temperature of the tread does not become high and is approximately the same as that of conventional tires. There is no decrease in tire durability due to Furthermore, even though the tread thickness is made thinner, there is almost no decrease in the wear life as would be expected from a decrease in the tread thickness, and overall the wear life and durability of the tire are improved.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a radial tire of the present invention. Figure 2 is a graph showing the relationship between rubber ground pressure, slip rate and wear amount, Figure 3 is a graph showing the relationship between tire tread thickness and tire heat generation temperature, and Figure 4 is a graph showing tread thickness and tire running. It is a graph showing the relationship between distances.

Claims (5)

[Claims] (1) Tread rubber is styrene-butadiene rubber or polybutadiene rubber with a bound styrene content of 20% or less
0 parts by weight, natural rubber or polyisoprene rubber 20-1
00 parts by weight, 45 to 70 parts by weight of carbon black with an iodine adsorption amount of 60 mg/g or more, and 0 to 30 parts by weight of a softener, and the tread thickness is 2 times the thickness from the top surface of the belt to the bottom of the tread groove. A radial tire characterized by being .5 to 4 times larger. (2) The amount of styrene-butadiene rubber or polybutadiene rubber in the rubber composition is 60 to 30 parts by weight, and the amount of natural rubber or polyisoprene rubber is 40 to 70 parts by weight.
The radial tire according to claim 1, which is in parts by weight. (3) The iodine adsorption amount of the carbon black is 120 mg/
The radial tire according to claim 1, wherein the radial tire has a tire weight of at least g. (4) The amount of carbon black in the rubber composition is 45
The radial tire according to claim 1, wherein the amount is 60 parts by weight. (5) The radial tire according to claim 1, wherein the amount of the softener contained in the rubber composition is 5 to 30 parts by weight.