JPH0112684B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a radial tire for heavy vehicles, and more particularly to a steel belt radial tire for heavy vehicles that is reinforced with a steel belt, is lightweight, has excellent durability, and has significantly improved rolling resistance. In radial tires for heavy vehicles that use steel cord as a belt, the belt consists of two tension-resistant layers that sandwich the circumferential line of the tire and form an arrangement of cords that intersect with each other, and a layer that overlaps with this to provide protection. A three-layer structure with an outer breaker layer satisfies the requirements for strength, but in actual use, the distortion at both side edges of the belt (hereinafter referred to as belt ends according to common usage) is often excessive.
Since this impairs the durability of the tire, it is a common practice in tire design to further arrange the above-mentioned tension layer and another layer between the carcass and the belt, which side-detach with the breaker layer. In other words, regarding the durability of the belt, conventional tires of this type generally use a four-layer belt with a pair of buffer layers made of soft, low heat generation rubber between the carcass and the belt. By omitting or removing one unnecessary steel cord layer,
It was not possible to make tires lighter and more fuel efficient. One of the reasons why distortion increases at the belt end in a three-layer laminated belt is due to the large compressive deformation of the buffer layer placed between the carcass, and as a countermeasure to this problem, increasing the hardness of the rubber improves the heat generation properties. Because of this, it does not meet expectations for durability. In order to solve the above-mentioned problems, the present applicant proposed in Japanese Patent Application No. 58623/1983 that if the composition contains short fibers of syndiotactic-1,2-polybutadiene, Focusing on the fact that it is possible to obtain a buffer layer that has a high elastic modulus and does not worsen heat generation, we have developed a steel belt radial tire for heavy vehicles that uses this buffer layer to achieve lighter weight and lower fuel consumption. However, even with such a tire, there was still room for improvement, particularly in terms of fuel efficiency, that is, reduction of rolling resistance. In other words, the syndiotactic technique described in the specification of the earlier application
1,2-polybutadiene short fibers have a maximum hysteresis loss associated with the glass transition temperature (30 to 40 degrees Celsius) of the amorphous portion in the range of 30 to 120 degrees Celsius, which is the tire heat generation temperature under normal tire usage conditions. However, if it were possible to reduce this hysteresis loss, rolling resistance could be further improved. In view of the current situation, the present inventors decided to use rubber that has sufficient elastic modulus and significantly reduces heat generation for the buffer layer of a steel belt radial tire for heavy vehicles that has a three-layer laminated belt. As a result of intensive research aimed at providing a steel belt radial tire for heavy vehicles that is lightweight, highly durable, and has extremely low rolling resistance,
The present invention has been achieved by discovering that the desired radial tire can be obtained by using a rubber composition made by blending a specific amount of carbon black and specific microorganic short fibers into rubber for the buffer layer. It came to this. That is, the present invention provides a toroidal carcass comprising rubberized cord plies arranged along the radial plane of the tire or in a plane intersecting the radial plane at a small angle;
In a radial tire equipped with a belt made of a rubberized steel cord layer surrounding the outer periphery of the crown of the carcass, the belt is arranged in a cord arrangement that intersects with the tire circumferential line at an angle of 30 degrees or less to the circumferential line. The belt has a laminated structure consisting of three layers: two tension layers and an outermost breaker layer arranged on top of the tension layers at a cord angle of 30 degrees or less with respect to the circumferential line of the tire. Between the carcass and the lower surface of both sides, natural rubber, synthetic polyisoprene rubber, butyl rubber, halogenated butyl rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, ethylene-propylene-diene ternary copolymer rubber, and acrylonitrile-butadiene rubber are used. At least one selected from the group consisting of copolymer rubber
100 parts by weight of seed rubber to 10 parts by weight of carbon black
~100 parts by weight and the glass transition temperature of the amorphous portion is lower than 30°C or higher than 120°C,
The melting point of the crystal part is 160℃ or higher, the average short fiber length is 0.8 to 30 μm, and the average short fiber diameter is 0.02 to 30 μm.
A heavy-duty material with a pair of wedge-shaped buffer layers made of a rubber composition containing 3 to 30 parts by weight of microorganic short fibers having a diameter of 0.8 μm and a ratio of average short fiber length to average short fiber diameter of 8 to 400. This invention relates to steel belt radial tires for vehicles. In the present invention, the microorganic short fibers to be blended into the buffer layer are those whose amorphous portion has a glass transition temperature lower than 30°C or higher than 120°C, an average short fiber length of 0.8 to 30 μm, and an average short fiber diameter of 0.8 to 30 μm. 0.02〜
0.8 μm, the ratio of average short fiber length to average short fiber diameter is 8 to 400, and the melting point of the crystal part is
160℃ or higher, such as polyvinylidene chloride,
Polyvinylidene fluoride, poly-p-tert-butylstyrene, p-chlorostyrene, dichlorostyrene, poly-α-methylstyrene, poly-2-methylstyrene, poly-2,5-dimethylstyrene,
Polytrimethylstyrene, poly-p-phenylstyrene, poly-o-vinylbenzyl alcohol,
Poly-p-vinylbenzyl alcohol, isotactic polypropylene, poly-4-methyl-
Short fibers made of 1-pentene, polyvinylnaphthalene, polyoxymethylene, polybisphenol A carbonate, 1,4-poly-2,3-dimethylbutadiene, etc. Here, the glass transition temperature of the amorphous part is lower than 30℃ or
The reason for setting the temperature higher than 120℃ is that the heat generation temperature of the tire when running under normal usage conditions is 30℃ to 120℃.
This is because short fibers having the glass transition temperature of the amorphous portion within this range usually have a large hysteresis loss. Furthermore, the glass transition temperature of rubber is approximately -
Since the temperature is around 50°C, micro organic short fibers with a glass transition temperature lower than 30°C are more preferable in consideration of affinity with rubber. In addition, the average short fiber length of the above microorganic short fibers is
The reason why the average short fiber diameter is 0.8 to 30 μm, the average short fiber diameter is 0.02 to 0.8 μm, and the ratio of the average short fiber length to the average short fiber diameter is 8 to 400 is as follows. If the average short fiber length is less than 0.8 μm, the crack growth resistance of the resulting rubber composition will not be sufficiently improved, and if it exceeds 30 μm, workability such as kneading with a Banbury mixer will be significantly reduced, which is not preferred. If the average short fiber diameter is less than 0.02 μm, the micro short fibers will be cut and become too short during kneading or sheeting with rolls, and if it exceeds 0.8 μm, the stress per surface area of the short fibers will increase and the rubber This is not preferable because there is a risk that the adhesive surface with the rubber composition will be destroyed, and as a result, the resulting rubber composition will have a large degree of creep and its bending resistance will decrease. If the ratio of the average short fiber length to the average short fiber diameter is less than 8, the original characteristics of short fiber reinforcement, such as high reinforcing properties, cut resistance, and crack growth resistance, will decrease significantly, and if it exceeds 400, the short fiber This is not preferable because the stress applied during operation is greater than the strength, and the short fibers are likely to be cut. In addition, the melting point of the crystal part of the microorganic short fibers must be 160℃ or higher, which is necessary not only during tire running but also during tire manufacturing, which can reach over 100 degrees. This is because if the short microfibers melt and harden again, their morphology will change and there is a risk that the desired reinforcing effect cannot be expected. Further, it is more preferable that the maximum diameter of the microorganic short fibers is 10 μm or less, and if microorganic short fibers with a diameter exceeding 10 μm are present, they will become fracture nuclei and the rubber will be easily destroyed. Microorganic short fibers are 3 parts per 100 parts by weight of rubber.
~30 parts by weight is blended, but in this case, two or more types of the above-mentioned micro organic short fibers may be blended. If the amount is less than 3 parts by weight, little effect can be expected and is not preferred, while if it exceeds 30 parts by weight, the workability will be significantly reduced, which is not preferred. Furthermore, microorganic short fibers can be produced, for example, in the following manner. Taking isotactic polypropylene as an example, polymerized powdered isotactic polypropylene is swollen and crushed in n-hexane at 60°C to form a slurry.
It is ejected from a nozzle at a pressure of 110 kg/cm ² to form micro short fibers. This is again dispersed in n-hexane, mixed with polymer cement, stirred, and then passed through a normal rubber drying process to form a masterbatch. At this time, the length, diameter, and length/diameter ratio of the microorganic short fibers obtained can be changed by controlling the solvent used for swelling, the temperature at that time, the pressure at the time of jetting from the nozzle, etc. is possible. In addition, microorganic short fibers are used as a masterbatch because it is relatively easy to uniformly disperse short fibers in rubber, but short fibers are directly mixed into rubber together with commonly used compounding agents such as carbon black. It is also possible to do so. Although the case of isotactic polypropylene has been described here, other microorganic short fibers can also be obtained in a similar manner by swelling them with a relatively poor solvent and crushing them into a slurry form. Of course, it is also possible to mix a good solvent and a poor solvent and adjust the composition to a suitable composition. In the present invention, it is necessary to mix 10 to 100 parts by weight of carbon black with respect to 100 parts by weight of rubber in the buffer layer. If the amount is less than 10 parts by weight, the strength at break of the resulting rubber composition will be reduced, which is undesirable, and if it exceeds 100 parts by weight, the workability will be significantly reduced, which is not preferred. In the present invention, in addition to the microorganic short fibers and carbon black mentioned above, compounding agents such as a vulcanizing agent, an accelerator, an accelerating aid, fillers such as silica, and a softening agent are added to the buffer layer in the usual amounts. It can be blended as long as it is within the range. In the present invention, the above-mentioned buffer layer has physical properties after vulcanization, and a tensile modulus x of 20 to 40 kg/
cm ² and compressive modulus y is tensile modulus x
It is more preferable to set the following formula (1) according to the value of . y>1.1x+18 (Kg/cm ² )...(1) Here, x is the value at 100% expansion (Kg/cm ² ), and y is 20
Value at % compression (Kg/cm ² ). In addition, in the present invention, the outermost breaker layer in the belt structure has a breaking elongation of 4%.
High elongation steel cord of 3 x 7 x 0.225, pitch 4(S)/6
(S) It is preferable to use a steel cord with a breaking strength of 175 kg/piece and a breaking elongation of 8%. It is known that the use of such high-strength steel cords can improve trauma resistance due to improved enveloping properties against foreign objects accidentally stepped on by the tread, but on the other hand, strain at the belt end can be It gets bigger and bigger. Therefore, it has been practically extremely difficult to use such high elongation steel cords in conventional buffer layers, but high elongation steel cords are preferably used in the buffer layers used in the present invention. This makes it possible to significantly improve the tire's trauma resistance. Now, in accordance with conventional practice, the carcass ply cords in the present invention may be general organic fiber or other fiber cords, or sometimes steel cords among metals, but the cord arrangement necessary for the radial structure , the arrangement is along the radial plane of the tire or a plane that intersects with this at a slight angle. The belt that surrounds the outer periphery of the crown part of the toroidal carcass using carcass ply for reinforcement, has two tensile layers with an angle of 30 degrees or less, more preferably 10 to 25 degrees, to the circumferential line of the tire. The cord arrangement, which intersects each other with the circumferential line at an angle of 30° or less, more preferably 10 to 25°, to the tire circumferential line, and the outermost breaker layer that overlaps this tensile layer. The cord arrangement is made of steel cord, and the twisting structure and other specifications of this cord may be as conventionally used. The present invention will be explained in detail below with reference to Examples. Examples 1 to 9, Comparative Examples 1 to 28 30 parts by weight of synthetic polyisoprene rubber
parts by weight of HAF carbon black, 2 parts by weight of aroma oil, 2 parts by weight of stearic acid and
A rubber composition containing 10 parts by weight of each of the 37 types of microorganic short fibers shown in the table was kneaded for 5 minutes in a Banbury mixer (50 rpm) at a rubber temperature of 155°C, and then 4 parts by weight of zinc white, 0.6 parts by weight of N-
Thirty-seven rubber compositions were prepared by blending oxydiethylene-2-benzothiazole sulfenamide and 3 parts by weight of sulfur. These rubber compositions were evaluated in terms of impact resilience and working history of short fibers, as well as the rolling resistance of tires using these rubber compositions as wedge-shaped buffer layers, and the results are shown in Table 1. The evaluation method is as follows. (Average impact resilience) Impact resilience was evaluated at 30°C, 60°C, 90°C and 120°C in accordance with BS903 Part 19, and the value is the average of these results. However, if the materials of the short microfibers are different, the elastic modulus will not necessarily be the same even if the blending amount is the same, so it is difficult to clearly express the effects of the present invention by simply comparing each rubber composition. be. Therefore synthetic polyisoprene rubber
For 100 parts by weight, 2 parts by weight of aroma oil, 2
Parts by weight of stearic acid, 1 part by weight of zinc white, 0.1
parts by weight of N-oxydiethylene-2-benzothiazolesulfenamide, 3 parts by weight of sulfur
Several types of rubber compositions containing varying amounts of HAF carbon black were prepared, and
The elastic modulus and rebound resilience at 120°C were measured, and a master curve was created by plotting the elastic modulus on the horizontal axis and the rebound resilience on the vertical axis at each temperature. From these master curves, read the rebound resiliency of the rubber composition reinforced only with carbon black, which corresponds to the elastic modulus of the micro short fiber reinforced rubber composition to be evaluated, and take this rebound resiliency as 100 to determine the elastic modulus of the rubber composition to be evaluated at a certain temperature. The rebound elasticity of the micro short fiber reinforced rubber composition was measured. The higher the value, the better. (Work history of short fibers) The average length and average diameter of the micro organic short fibers in the raw rubber are measured in advance, and then, after creating a rubber composition as described above, the average length and average diameter of the micro organic short fibers are measured. The diameter was determined, and if these values were 85% or more of the average length and average diameter of the raw rubber, they were marked as ○, and if they did not reach 85%, they were marked as ×. (Rolling resistance) A tire of size 1000R20, 14PR equipped with three laminated belts consisting of two tension layers and one breaker layer was placed on a drum with a diameter of 3 m at an internal pressure of 7.25.
Kg/cm ² and a load of 2425 Kg at a speed of 50 Km/hr for a certain period of time, then after a certain period of time with the drum drive clutch released, after a certain period of time with the drum drive clutch free. The rotational speed of the drum was compared with the rotational speed of only the drum without a tire set, and the rolling resistance of the tire was expressed in units of force. At this time, we investigated using several types of rubber compositions with different elastic moduli that did not contain microorganic staple fibers and varied only carbon black in the wedge-shaped buffer layer of a similar 1000R20 tire, and investigated the elastic modulus. A master curve was created with the horizontal axis as rolling resistance and the vertical axis as rolling resistance. From this master curve, the rolling resistance value of a tire using a rubber composition reinforced only with carbon black, which corresponds to the elastic modulus of the rubber composition reinforced with micro organic short fibers used for the wedge-shaped buffer layer of the tire to be evaluated, is calculated. The reading was expressed as an index as follows. The higher the value, the better. Rolling resistance of a tire reinforced only with carbon black / Rolling resistance of a tire reinforced with micro organic short fibers x 10
0 The average diameter and average length of the microorganic short fibers were determined as follows. After extruding raw rubber (or rubber composition) containing microorganic short fibers using a capillary rheometer under the conditions of L/D = 4, 100°C, and 20 sec ^-1 , it is extruded at 4 kg/cm ² in a vulcanization can. , vulcanize at 150°C for 1 hour. Ultrathin sections were cut from this vulcanizate in the direction perpendicular to the extrusion direction and in the average direction, and the diameter and length of the short microfibers were measured using an electron microscope. The average diameter and average length were calculated using the following formula: = Σniri/Σni = Σnili/Σni where: Average diameter: Average length ri: Short fiber diameter li: Short fiber length ni: Short fiber with diameter ri or length li Number of fibers Σni: 300

【table】

[Table] As is clear from Table 1, it can be seen that the steel belt radial tire for heavy vehicles of the present invention has significantly improved rolling resistance. FIG. 1 shows a test tire used to confirm the effects of the present invention. In the drawing, 1 is a carcass, 2 is a three-layer belt, 2a and 2b are tension layers, 2c is a breaker layer, and 3 is a breaker layer. It is a wedge-shaped buffer layer. The size of this test tire is 1000R20, and its specifications are as follows. Carcass 11 steel cords with a cord diameter of 1.09 mm and a number of wires of 28.
Consists of one ply of rubber-coated blind weave with a thread count of 25.4 mm arranged at a cord angle of 0° to the tire circumferential direction. belt

[Table] Examples 10 to 12, Comparative Examples 29 to 34 Isotactic polypropylene of various forms as shown in Table 2 was used as microorganic short fibers at 10% by weight per 100 parts by weight of synthetic polyisoprene rubber.
Nine types of rubber compositions were prepared by mixing parts by weight and other compounding ingredients in the same manner as in Example 1, and the presence or absence of roll baggies when kneading with a 10-inch roll was evaluated for roll workability. The average rebound resilience was determined in the same manner as in Example 1. Next, tires were made using these rubber compositions in the wedge-shaped buffer layer in the same manner as in Example 1, and the drum durability was determined at a speed of 60 Km/hr, an internal pressure of 7.25 Kg/cm ² , a load of JIS 100%, and a constant side force (1400 Kg). The distance traveled until the tire breaks on the drum was determined under these conditions. The results are shown in Table 2.

[Table] As is clear from Table 2, the steel belt radial tire for heavy vehicles of the present invention has good workability and excellent durability. Examples 13 to 15, Comparative Examples 35 to 37 Rubber compositions having the formulation contents shown in Table 3 (the amount shown is in parts by weight) were prepared, and the roll workability, average rebound resilience, and drum durability were evaluated in Examples. Ten
It was evaluated in the same way. The results are shown in Table 3.

【table】

[Table] As is clear from Table 3, the steel belt radial tire for heavy vehicles of the present invention has good workability and excellent durability. Examples 16 to 22, Comparative Examples 38 to 42 Rubber compositions with the compounding contents shown in Table 4 (the compounding amount indicates parts by weight) were prepared, and the tensile modulus (x) at 100% elongation and 20% compression were determined. The compression modulus (y) of was measured. Next, drum durability was evaluated in the same manner as in Example 10 using these rubber compositions. The results are shown in Table 4.

【table】

[Table] As is clear from Table 4, it is reinforced with micro organic short fibers and has a tensile modulus (x) of 20~
40Kg/cm ² and compression modulus (y) is y > 1.1x
It can be seen that the steel belt radial tire for heavy vehicles of the present invention using a wedge-shaped buffer layer satisfying +18 has excellent durability.

[Brief explanation of drawings]

FIG. 1 is a left half sectional view of a tire according to an example of the present invention. 1...Carcass, 2...Belt, 2a, 2b...
... Tension layer, 2c... Precaution layer, 3... Wedge-shaped buffer layer.

Claims (1)

[Scope of Claims] 1. A toroidal carcass consisting of rubberized cord plies arranged along the radial plane of the tire or a plane intersecting this at a slight angle, and a rubberized steel surrounding the outer periphery of the crown of this carcass. In a radial tire equipped with a belt consisting of a cord layer, the belt has two tension-resistant layers arranged in a cord arrangement that intersect with each other and sandwich the circumferential line at an angle of 30 degrees or less to the circumferential line of the tire; It has a laminated structure consisting of three layers, the outermost breaker layer is arranged on top of the above tension layer at a cord angle of 30 degrees or less with respect to the belt line, and natural rubber is placed between the carcass and the lower surface of both sides of this belt. , synthetic polyisoprene rubber, butyl rubber, halogenated butyl rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, ethylene-propylene-diene terpolymer rubber, and acrylonitrile-butadiene copolymer rubber. For 100 parts by weight of one type of rubber, 10 to 100 parts by weight of carbon black and the glass transition temperature of the amorphous part are lower than 30°C or higher than 120°C, and the melting point of the crystal part is 160°C or higher, and the average shortness is Fiber length 0.8
~30 μm, an average short fiber diameter of 0.02 to 0.8 μm, and a ratio of average short fiber length to average short fiber diameter of 8 to 400. A steel belt radial tire for heavy vehicles that features a wedge-shaped buffer layer. 2 Micro organic short fibers include polyvinylidene chloride, polyvinylidene fluoride, poly-P-tert-butylstyrene, P-chlorostyrene, dichlorostyrene,
Poly-α-methylstyrene, poly-2-methylstyrene, poly-2,5-dimethylstyrene, polytrimethylstyrene, poly-p-phenylstyrene, poly-o-vinylbenzyl alcohol, poly-p-vinylbenzyl alcohol , isotactic polypropylene, poly-4-methyl-1-
Pentene, polyvinylnaphthalene, polyoxymethylene, polybisphenol A carbonate,
The steel belt radial tire for heavy vehicles according to claim 1, which is 1,4-poly-2,3-dimethylbutadiene. 3. The steel belt radial tire for heavy vehicles according to claim 1 or 2, wherein the breaker layer is a high elongation steel cord having a tensile elongation at break of 4% or more.