JPS58149803A - Radial tire with improved endurance - Google Patents

Abstract

PURPOSE:To prevent corrosion of a steel belt due to rainwater by using an open twist steel cord with a specific rate of elongation, for a belt layer steel cord, and by using a blended rubber which is formed by matching a specific amount of a liquid rubber having an active radical, for a buried rubber. CONSTITUTION:3-5 filament strings of a belt layer steel cord which is composed of a rubber coated steel cord surrounding the crown outer circumferential part of carcass are twisted and made into an open twisted steel cord 1 with 0.1-0.4% rate of elongation extersive in 0.2-5kg loading range per cord, for this usage. A blended rubber obtained by matching a liquid rubber with viscosity average molecular weight of 500-50,000 having a polarity functional group such as hydroxyl group, with polymer molecules such as polybutadiene etc., in 2- 30wt% in comparison with other rubber components, is used as a buried rubber. By the above-said composition, both the uniformity and the endurance of tire can be improved.

Description

Detailed Description of the Invention This invention uses so-called open-stranded steel cords for the steel cords in the tire belt layer, and contains liquid rubber with active groups in the embedded rubber, thereby producing a steel radial with significantly improved durability. Regarding tires.

In general, the belt layer of radial tires, including passenger car tires, has high rigidity and strength, making it highly wear resistant.
A wide variety of steel cords are used, which exhibit excellent performance characteristics such as handling stability.

Here, the steel cord has a so-called layered structure in which several strands of 3 to 5 filaments are twisted together, or a so-called layered structure in which multiple filaments are arranged concentrically and twisted. Twisted structures are widely used, and the belt layer is constructed by aligning these steel cords in parallel and embedding them in a telecom. In conventional steel cords, the filaments are twisted together in a close-packed manner, which inevitably creates gaps within the cord that are difficult for rubber to penetrate. When a tire using such a steel cord in its belt layer receives a cut on its surface, rainwater enters through the cut and reaches the gap in the cord, causing corrosion of the steel cord. Furthermore, the rainwater becomes water vapor due to heat generation during running, and this spreads in the longitudinal direction of the cord within the gap, causing the corrosion to spread along the cord. As a result, the fatigue resistance of the cord and the adhesion between the cord and the rubber deteriorate. This has the disadvantage of reducing power and causing premature tire failure.

In order to solve this problem, a method is proposed in which the steel cord is treated with a rubber dipping solution in which unvulcanized rubber is dissolved in a solvent that is compatible with rubber (Japanese Unexamined Patent Publication No. 15488/1988) before rubberizing it with a calender. ), although it is effective in reducing the gap between the steel cords, it has the disadvantage that the process is very complicated. There is also a method of lowering the viscosity of buried rubber by blending liquid low molecular weight polyisoprene (Japanese Patent Application Laid-open No. 54-36385). do not have. There is also a method of lowering the viscosity by increasing the amount of softener in the embedded rubber, but this will significantly impair the crack resistance at the ends of the belt.

Therefore, recently, so-called open twisted steel cord (Japanese Patent Laid-Open No. 55-90692), in which the distance between the filaments has been widened to make it easier for embedded rubber to flow into the steel cord, has been used in the belt layer of a tire (Japanese Patent Laid-Open No. 55-90692). 4800
Publication No. 8) has been proposed. Here, the open twisted steel cord is one in which all the filaments (1) are twisted together with a predetermined spacing between them (as shown in the cross-sectional view in Fig. 1). It easily penetrates into the interior through gaps and completely covers all filament surfaces, eliminating the above-mentioned corrosion problem of steel cords.

However, such steel cord exhibits high elongation in the longitudinal direction due to its twisted structure. That is, FIG. 2 shows the relationship between the elongation of a steel cord and the load, where A indicates an open twisted steel cord and B indicates a conventional steel cord. In the figure, an open stranded steel cord is stretched with a relatively low load up to a certain elongation and thereafter behaves substantially the same as a conventional steel cord. Therefore, it has been found that when such open twisted steel cords are used in the belt layer, the following problems occur in tire manufacturing.

Normally, tires whose carcass ply is made of organic fiber cords such as nylon or polyester undergo a post, air, and inflation process (hereinafter referred to as PCI process) in which the carcass plies are cooled and held at a constant internal pressure for a predetermined period of time to prevent heat shrinkage of these fiber cords after vulcanization. ). In this case, the carcass ply cords are stretched outward in the radial direction, but in tires using conventional steel cords for the belt layer, the expansion of the carcass ply cords is restrained due to the "gathering effect" because the length of time is extremely small. The radial dimension is held constant.However, in tires using open-stranded steel cords in the belt layer, the elongation of the carcass ply cord cannot be sufficiently suppressed, allowing uneven elongation in the radial direction, and causing the belt ply cord itself to elongate. Together with the non-uniformity, the uniformity of the tire is significantly impaired.

As a result of intensive research into this problem, the inventors found that the non-uniformity of the tire is related to the degree of openness of the steel cord, that is, the elongation in the load range of 0.2 to 5, and that this elongation is 0. It has been found that when the amount is less than .4%, the heterogeneity is hardly inhibited. However, on the other hand, it has also been found that in such open-stranded steel cords, penetration of embedded rubber is insufficient due to the narrow filament spacing of the cord. Based on this knowledge, the inventors conducted further research and found that by blending a predetermined amount of liquid rubber with active groups into the embedded rubber of an open-stranded steel cord with a relatively small degree of openness and an elongation of 0.4 or less, steel It penetrates into the interior of the cord, improves the adhesion of the steel cord, and also significantly improves the crack growth resistance required at the ends of the belt layer, making it possible to improve the durable life of the tire.

Therefore, the present invention solves the problem of tire unevenness by using open twisted steel cords in the belt layer, and also improves the adhesion between the cord and rubber and the crack growth resistance of the embedded rubber in the belt layer, thereby extending the durability life. Our aim is to provide superior radial tires.

The present invention relates to a radial tire comprising a carcass with a radial structure and a belt layer made of rubberized steel cords surrounding the outer periphery of the crown portion of the carcass (a) The steel cords of the belt layer are made of 3 to 5 filaments twisted together. It is an open-stranded steel cord with an elongation of O11 to 0.4% in the immediate load range of 0.2 to 5% per cord (b) The embedded rubber in the belt layer is a liquid containing active groups. Rubber to other diene rubber components
The radial tire is characterized in that it contains ~80 parts by weight.

First, the open twisted steel cord used in the present invention is
Elongation in the load range of 0.2 to 5-5% per piece is 0.1 to 4%
It is. In other words, in Figure 2, 5 - elongation under load (bi
0.2 Elongation at immediate load (a'+ is subtracted from elongation (
ba) is within the range of 0.1 to 4%. The elongation is 0.
If it exceeds 4%, the untwisting rate of the cord will increase before and after the process of topping the steel cord with rubber, reducing the workability of the subsequent process. Allowing the tire to stretch and disrupt the uniformity of the tire. Moreover, if the elongation is less than 0.1, it becomes substantially the same as a conventional steel cord, and penetration of rubber becomes extremely difficult.

In addition, the diameter of the filament constituting the open twisted steel cord used in the present invention is preferably 0.12 to 0.4 mm; if it is too small, the strength will decrease, while if it is too large, the fatigue resistance will decrease. do. The filament is usually made of brass or plated with brass, but may be coated with an alloy containing copper, zinc, tin, nickel, and cobalt. The thickness of the plating here is usually 0, ~α7#
Use the one. In addition, the twist pitch of the open twisted resteel cord is set to 8fi or more to maintain productivity and strength during cord manufacturing, and 15fi to maintain fatigue resistance.
The following is desirable.

Next, the liquid rubber used in the present invention is a polymer such as polybutadiene or polyisoprene having polar functional groups such as a hydroxyl group, a carboxyl group, or an amino group in the molecule. By mixing this liquid rubber with other diene rubbers, the viscosity of the buried rubber is lowered, allowing it to smoothly penetrate into the gaps inside the steel cord during the vulcanization process, and co-vulcanizing with other diene rubbers. Not only the basic properties of the vulcanized rubber but also the crack growth resistance of the rubber, which is a required property at the end of the belt layer, are further improved. In addition, since it has polar active groups such as hydroxyl or carboxyl groups, it has a high affinity with the steel cord surface, increasing the adhesive interface and strengthening the chemical bond between the rubber and steel cord, which prevents the rubber from peeling off at the edge of the belt layer. can be effectively prevented.

In the present invention, the viscosity average molecular weight of the liquid rubber is 50
0-50. OOO, and its blending amount is 2 to 30 parts by weight based on other diene rubber components. If the viscosity average molecular weight is less than 500, the viscosity of the embedded rubber becomes too low, resulting in a decrease in workability and also in the physical properties of the vulcanized rubber. On the other hand, if it exceeds 50,000, the viscosity cannot be lowered and the penetration of the rubber into the internal voids of the steel cord becomes insufficient. If the amount is more than 30 parts by weight, the workability and physical properties of the vulcanized rubber will be reduced, while if it is less than 2 parts by weight, the viscosity cannot be reduced sufficiently, and in either case, the object of the present invention cannot be achieved.

Furthermore, the liquid rubber desirably contains 1 to 15 active groups per molecule in order to increase the affinity with the steel cord and not to impede compatibility with other diene rubbers. In other words, the more active groups per molecule, the higher the affinity with steel cord, but conversely, the compatibility with other diene rubbers deteriorates, reducing the co-vulcanization effect, and the physical properties of the vulcanized rubber deteriorate. By decreasing.

In addition, in the present invention, other diene rubber components used in the embedded rubber include natural rubber, synthetic polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber, or two or more of these types, metal materials, etc. However, natural rubber or synthetic polyisoprene rubber is particularly desirable from the viewpoint of crack growth resistance and heat generation properties.

Furthermore, the embedded rubber is appropriately blended with commonly used compounding agents, fillers, vulcanizing agents, and the like.

The present invention will be described in detail below with reference to examples.

Example 1 As a carcass, five steel filaments (5 steel filaments (
Tires were prototyped using two plies in which various open twisted steel cords having the IX5) structure were embedded in a rubber composition in which liquid rubber containing carboxyl groups or hydroxyl groups was mixed with natural rubber. The steel filament used was one plated with brass (63% copper, 37% zinc) to a thickness of 0.25 μm and a diameter of 0.25 μm. Regarding the above tires, the untwist change rate of the open twisted steel cord, the presence or absence of sheet curl, the degree of rubber penetration into the steel cord of the buried rubber, the degree of rust occurrence of the steel cord after running in a drum filled with salt water, / raker edge separation RFV (radial 7-os variation) and LFV (lateral
Force variation) I was carefully evaluated and the results are shown in Table 2. The basic composition used for the buried rubber is the first one.
As shown in the table.

(a) Amount of change in untwisting of the steel cord The amount of change in untwisting of the steel cord per 6 m was measured before and after the tonoping process in which the steel cord was embedded in rubber. Table 2 shows that the elongation increases by 7-1, and the elongation increases by 8. The amount of change in twist and recovery also increases, and becomes particularly significant when the elongation is 0.5 or more. Further, if the elongation is 05 or more, curling of the ply becomes significant after the steel cord topping step.

(Degree of penetration of rubber into the inside of the c4 steel cord: When the prototype tire is disassembled and the steel cord of the belt is taken out with the rubber attached, and when five cord filaments are twisted, it is 27.
3 strands, 2/2 strands for 4 strands, 2 for 3 strands
The steel cord was cut open and the inside of the steel cord was observed under a microscope, and the degree of rubber penetration was determined by determining what percentage of the total exposed metal portion corresponded to the inside of the steel cord. FIG. 8 shows the relationship between the elongation of the cord and the degree of rubber penetration. In the figure, the numbers 2, 5, 10, and 30 indicate the amount of carboxyl group-containing liquid polyisoprene rubber (Kuraprene L I R-30) added. It is observed that the degree of rubber penetration increases with the amount added.

Holes are drilled from the inner surface of the tire at 4 locations in the circumferential direction of the tire, and 3 locations in the 6ζ radial direction of the tread portion at each location, for a total of 12 locations, using a drill with a diameter of 3 mm to penetrate through the tread surface. Assemble the tire into a rim, and pour 500 cc of 10% salt water into the inner surface of the tire to fill it to a predetermined internal pressure. After running the tire for 20,000 km under the durability test conditions of the OT standard FMVS S 109 in the United States, the tread of the tire was removed using a breaker. The average value obtained by dividing the length of rust generated along the steel cord around the drill hole by the total length of each cord is defined as the steel cord rust occurrence degree. , 1st
Table note 1) 2.24-trimethyl-1,2-dihydroquinoline Note 2) N-cyclohexyl-2-benzothiazylsulfenamide) Breaker edge separation resistance salt water filled drum running test Before measuring the degree of occurrence, the breaker edge was disassembled, the length of the rubber crack growing from the breaker edge was measured, and the relative value with respect to the comparative tire (Test No. 7) was expressed as an index. The larger the index, the smaller the crack strength and the better the quality.

A tire assembled with 9mm and filled with an internal pressure of 20-Kq/i was pressed against a drum under a load of 375cm, and the drum was rotated to measure stress changes in the horizontal direction and riding direction with respect to the axle. The relative value to number 7) is indicated by an index. The smaller the index, the better.

150 layers vertically (cord arrangement direction), 1 horizontally. OOO■ bias cut sheet (number of steel cord strokes i1L)
7E15m) from the horizontal plane (angle 21°)
If the distance of the sled is 5 or more, curling is included, 5fi
If it was less than that, it was determined that there was no curling.

In Example 1 of the present invention (test numbers 1 to 4) in Table 2, the amount of change in untwisting of the steel cord tends to increase as the elongation of the steel cord (elongation in the load range of 02 to 51 g) increases. However, it is recognized that the degree of cord rust occurrence and breaker-edge separation resistance after running on the salt water drum were considerably improved compared to the comparative example (Test No. 7).

Example 2 Example 1 by keeping the elongation of the steel cord constant and varying the amount of liquid polyisoprene rubber containing carboxyl groups.
A prototype tire was manufactured in the same manner. The results are shown in Table 2, test numbers 14-16 and 3. As the amount of liquid polyisoprene rubber added increases, the degree of rust occurrence of the cord and the resistance to breaker-edge separation tend to improve, but if the amount is increased too much, there is a tendency for tire uniformity to decrease.

Example 3 Tires were trial-produced in the same manner as in Example 1, with the elongation of the steel cord kept constant and the amount of liquid polybutadiene rubber containing hydroxyl groups added. The results are shown in Table 2, test number 1.
As the amount of liquid polybutadiene rubber shown in Nos. 7 to 19 is increased, the degree of rust occurrence and breaker edge separation properties of the guard cord tend to improve, but if the amount is increased too much, it will have a negative effect on tire uniformity.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an open twisted steel cord, Fig. 2 is a graph for explaining the elongation of the steel cord, and Fig. 3 is a graph showing the elongation of the steel cord and the degree of rubber penetration. Patent application/Person Sumitomo Rubber Industries Co., Ltd. Agent
Patent Attorney Yoshihira Nakamura ALB2345 Growth (%) Diagram 2 Procedural Amendment (Mr. Kazuo Wakasugi, Commissioner of the Ship's Patent Office Yamahan 1937)
7 Year Patent Application No. 31125 3, Relationship with the case of the person making the amendment Column 6 of the detailed description of the invention in the patent applicant's specification, Contents of the amendment (1) Specification, page 13, line 19 "Exposed metal section Correct "sa" to "metal rubber ambiguous length." (2) In the carboxyl group-containing polyisoprene column of test number 13 in Table 2, page 16, the text ``rlOJ'' was changed to ``10''.
Corrected to Note 1. (3) On page 17, line 15, ``The smaller the number, the more j.'' is corrected to ``The larger the j.''

Claims (1)

[Scope of Claims] (1) A radial tire comprising a carcass with a radial structure and a belt layer made of rubberized steel cords surrounding the outer periphery of the crown portion of the carcass, (a) the belt layer has 3 to 3 steel cords. It is made by twisting 5 filaments, and each cord has 0.2 to 5 filaments.
It is an open twisted steel cord with an elongation of 0.1 to 0.4 seconds in the KF load range. The radial tire (2) according to claim 1, wherein the active group is a carboxyl group or a hydroxyl group, wherein the liquid rubber has a viscosity average molecular weight of 500. ~50. The radial tire (4) liquid rubber according to claims 1 to 2, which is in the range of O00, contains 1 to 15 active groups per molecule and has a viscosity average molecular weight of 15,000 to 50,000. The radial tire (5) according to claims 1 to 3, which is a polyisoprene rubber, has a viscosity average content of 1-10 hydroxyl groups per molecule.
The radial tire according to claims 1 to 3, which is polybutadiene rubber with a molecular weight of OOO to 5,000.