JPS6348722B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a pneumatic tire with excellent performance. Multifilament yarns such as rayon, nylon, and polyester, or cords made of twisted steel wire are used as reinforcing materials for pneumatic automobile tires, and the carcass of the tire is made of a ply of rubber-coated cords. . Among the above tires, tires using nylon cords have the disadvantage that if they are left on a car for a long time, they will develop so-called spot flats, which are caused by deformation due to contact with the ground, and the ride quality will be poor due to the spot flats when the tires are first resumed driving. In addition, rayon cord has low strength, and steel cord has a large weight per unit strength. Polyester cords, on the other hand, have become widely used in recent years as they do not have the above drawbacks. However, as the development of automobile roads and the speed of driving have progressed, there has been a demand for improved quality of polyester cords, and some problems have been raised. Chief among these problems is improving the dimensional stability and uniformity of the tire without compromising its fatigue resistance. When using a tire that uses polyester cord for the carcass ply, when compressed air is injected into the tire cavity formed by attaching the rim to the bead of the tire, tension is applied to the cord and it stretches. This causes the tire to expand, which is called inflation growth. Accompanying this inflation growth, the tread rubber and side rubber are also stretched, resulting in a decrease in the wear resistance and crack resistance of the tire. Therefore, in order to reduce inflation growth, it is desirable to reduce the constant load elongation rate of the polyester cord. On the other hand, in the tire manufacturing process, for example, in the radial tire manufacturing process, a large number of arranged cords are coated with rubber and then cut in a direction perpendicular to the length of the cord. 1 to 10 cords are overlapped and joined to make a long cut cord, this cut cord is cut to a certain length along the cord, and this fixed length cord is made into 1 to 5 cords on a drum forming machine. The carcass ply is overlapped and joined to form a cylindrical carcass ply, and the open ends of the carcass ply are folded back and locked so as to wrap around the annular bead assemblies in contact with each of the open ends. Next, the diameter of the bead assembly is expanded while narrowing the interval to form a toroidal shape, and then a belt ply, tread rubber, and side rubber are polymerized on the outer surface of the carcass ply to form a green tire.
This green tire is placed in a mold, and the inner surface of the green tire is pressurized with hot water or steam to extend the cord, which is then heated from the inner and outer surfaces of the tire to vulcanize and mold.Then, to prevent the cord from shrinking, The tire is cooled by performing so-called post-inflation, in which compressed air is sealed in the inner cavity of the tire, and then the tire is removed from the mold. The above manufacturing process is similar to the manufacturing of bias tires. In the above tire manufacturing process, the cutting cord and cutting cord joint part during carcass ply formation are
It has greater rigidity than other parts. Furthermore, if there are variations in the spacing or angle of the cord arrangement, when forming a cylindrical carcass ply into a toroidal shape, the proportion of expansion of the portion with high rigidity becomes small, resulting in a large difference in rigidity. As described above, the locally non-uniform stiffness of the carcass ply results in non-uniform tensions acting on the cord during the post-inflation process, resulting in uneven elongation of the cord. In addition, the rise in tire temperature during vulcanization varies depending on the thickness of the rubber and the temperature distribution is not necessarily uniform, resulting in uneven heating contraction of the cord. Coupled with the non-uniformity of the tire, the elongation of the cord also becomes non-uniform during the above-mentioned post-inflation, and the non-uniformity of the elongation of the cord further promotes the local non-uniformity of the stiffness of the tire. When a vehicle is driven with tires that have locally uneven stiffness as described above, the amount of deflection varies periodically, causing abnormal vibrations and poor ride comfort. The vehicle shakes periodically and becomes unstable. Since the non-uniformity of the tire in the tire manufacturing process described above is due to the high dry heat shrinkage rate of the polyester cord, it is desired that the dry heat shrinkage rate of the cord is low. 2.3 as an indication of the dimensional stability of the code.
It is expressed by the dimensional stability coefficient, which is the sum of the elongation rate (%) under a load of g/d and the dry heat shrinkage rate (%) when heated at 150°C for 30 minutes. However, the constant load elongation rate and the dry heat shrinkage rate are in an antinomic relationship, and as the constant load elongation rate increases, the dry heat shrinkage rate decreases.
For example, the conventionally used 1500 denier/2 made of polyethylene terephthalate with an intrinsic viscosity of 0.9.
The dimensional stability factor of a cord with a twist factor of 2190 is 9.0
It is in the range of ~9.5%, and depending on the heating conditions, the dry heat shrinkage rate increases even if the constant load elongation rate is reduced.
The dimensional stability factor remains unchanged. As mentioned above, in order to obtain a tire with excellent uniformity, a polyester cord with a small constant load elongation rate and a small dry heat shrinkage rate, that is, a small dimensional stability coefficient, is required. If the cord is heat-treated for a long time in order to reduce the stability coefficient, the strength and fatigue resistance of the cord will be significantly reduced, and the performance as a tire cord will not be obtained. In addition, in order to reduce the dimensional stability coefficient, if a polyester with a relatively low degree of polymerization with an intrinsic viscosity of 0.8 or less is used as a raw material, or if the twist coefficient is reduced, the fatigue resistance will decrease and it will not be practical. I can't get the correct code. As a result of intensive research into the relationship between the degree of crystal orientation and dimensional stability of polyester cords with a high degree of polymerization, the present inventors found that cords manufactured with filaments with different birefringence between the center and surface portions have the following characteristics: It has been found that a tire with good stability and a carcass formed of cords with good dimensional stability can solve the above-mentioned tire problems. Based on the above knowledge, the present applicant has previously proposed that the ratio of the birefringence of the surface portion to the birefringence of the filament center be 1.03 to 1.15 using the formula K
= T x √ (K is the twist coefficient, T is the average number of twists of top and bottom twists per 10 cm, D is the indicated denier of the cord), and the twist is applied to a range of 800 to 2500, and Elongation rate (%) at 2.3g/d and 150℃,
A tire carcass ply made of polyester cord that has been heat-treated so that the dimensional stability coefficient expressed as the sum of the dry heat shrinkage rate (%) when heated for 30 minutes is 8.5% or less. He proposed an excellent pneumatic tire (see the specification of Japanese Patent Application No. 56-30646, hereinafter referred to as the first prior invention). The filament forming the cord in this first prior invention contains 85 ethylene terephthalate components.
It consists of a polyester containing mol% or more, preferably polyethylene terephthalate, and may also be a copolymerized polyester containing 15 mol% or less of other components such as ethylene isophthalate or ethylene benzoate. The above polyester is a high polymerization degree polyester with an intrinsic viscosity of 0.8 or more measured at 25°C using orthochlorophenol as a solvent.If the intrinsic viscosity is less than 0.8, a cord with a small dimensional stability coefficient can be obtained, but the fatigue resistance and It has low strength and tires made with it have poor durability. The above-mentioned high polymerization degree polyester is spun and drawn under a relatively large tension so that the degree of orientation of the molecular chain axis in the fiber axis direction varies locally along the fiber radial direction. is larger than the central birefringence. In this first prior invention, the ratio of the birefringence of the surface portion to the birefringence of the filament center is 1.03.
A filament in the range ~1.15 is selected. If the above birefringence ratio is less than 1.03, the dimensional stability coefficient becomes large and the uniformity of the tire decreases, and if the birefringence ratio exceeds 1.15, the degree of orientation becomes relatively low and the tire becomes less uniform. The strength of the cord decreases. The filament having the above birefringence ratio range is
It can be obtained by appropriately setting various conditions such as spinning speed, stretching ratio, and stretching fixation in spinning and stretching. The thickness of the filament is preferably in the range of 1.5 to 15 deniers. The twist coefficient K when forming a cord by bundling and twisting the above filaments is expressed as T×√, and T
is the average number of twists per 10 cm of cord for first twisting using multiple filaments as strands and final twisting using multiple filaments as cords, and D is the indicated denier of the cord. be. Twist coefficient K is 800 to 2500, preferably 1300 to
If the twist coefficient is less than 800, the fatigue resistance will be low, and if it exceeds 2500, the load elongation rate will increase and the uniformity of the tire due to inflation growth will decrease. The above-mentioned cord is immersed in a latex adhesive solution, dried, and then heat-treated to improve its adhesion to rubber. The heat treatment temperature is preferably 220-250℃, the time is preferably 1-3 minutes, and the dimensional stability coefficient is 8.5.
% or less. Generally, when the heat treatment temperature is high and the time is long, the dimensional stability coefficient tends to decrease. The pneumatic tire obtained by this first prior invention has excellent wear resistance, crack resistance, and good tire uniformity, and not only provides a comfortable ride on a car but also improves the internal pressure of the tire. Hysteresis loss due to repeated deformation of expansion and compression during ground contact is small. Therefore, the temperature generated inside the tire is lowered, and rolling resistance is reduced. On the other hand, in recent years, pneumatic tires reinforced with steel cords have been used for high-speed mass transportation or for construction vehicles, but the steel cords have a high specific gravity, which increases the weight of the tires, resulting in lower fuel consumption. There was a problem with the amount being large. As a countermeasure to this problem, we are trying to reduce the weight of the tire by using special compounded rubber and reducing the thickness of the excess rubber, but if we reduce the amount of steel cord used, the safety factor of the tire will decrease. Therefore, the current situation is that we have no choice but to use the steel cord without reducing the amount. In addition, in pneumatic tires reinforced with steel cords, stress concentration acts on the interface between the rigid steel cords and flexible rubber, which tends to cause rubber peeling at the ends of the steel cords or between the breaker layers in radial tires. It was. In addition, if conventional pneumatic tires reinforced with steel cords are left in hot and humid conditions for a long time, moisture will seep between the iron material of the steel cord and the surface plating layer, causing the pneumatic tires to peel off. There was a drawback that a peeling phenomenon occurred. As a result of various studies on the strength of steel cords in pneumatic tires, the present inventors found that the strength of conventional steel cords is expressed by the following experimental formula. (A+285)W/7.86<TS<(A+335)W/7.86 (1) A=-177D-1.84N+0.02N ² (2) In the above equation (1), TS is the tensile strength of the steel cord (Kg), and W is the tensile strength of the steel cord (Kg). The weight per meter of steel cord (g/m), the denominator 7.86 is the specific gravity of iron, and (2)
In the formula, D is the diameter (mm) of the strands forming the steel cord, and N is the number of strands forming the steel cord. And the empirical formulas of (1) and (2) above are N
Applicable in the range of = 3 to 50, D = 0.15 to 0.40 mm. If D is less than 0.15 mm, it is not practical due to low industrial productivity and high cost, and if D exceeds 0.40 mm, the rigidity of the steel cord will be excessive and the tire will easily peel off. , fatigue resistance also decreases. The number N of strands in the above equation (2) is defined as the number N of strands when the wires have different diameters and are formed of m core strands and n side strands. Considering the core strand as one wire, n
Applied as +1=N. In order to solve the drawbacks of traditional pneumatic tires, the present inventors aim to reduce the weight of pneumatic tires by reducing the amount of steel cord used, reduce fuel consumption of vehicles, and reduce the weight of pneumatic tires. The above objective was achieved by improving the tensile strength of the steel cord, with the aim of reducing failures due to peeling of the steel cord. That is, the present applicant previously proposed a pneumatic tire at least partially reinforced with steel cords, in which most of the strands forming the steel cords are made of iron material with a carbon content of 0.75 to 0.85% by weight, and the steel cords are is the formula (A+345)W/7.86<TS<(A+395)W/7.86 (3) A=-177D-1.84N+0.02N ² (2) (In the above formula, D is the steel cord wire diameter mm, and N is It is characterized by having a tensile strength calculated from the number of strands in the steel cord configuration, where W is the weight of the steel cord per meter (g), TS is the tensile strength (Kg), and the denominator 7.86 indicates the specific gravity of iron. He proposed a pneumatic tire (see the specification of Japanese Patent Application No. 55-125625, hereinafter referred to as the second prior invention). Note that the applicable ranges of N and D in the above (2) are as in the conventional formula described above. In order to improve the tensile strength of the steel cord to the range expressed by equation (3) above, the carbon content in the iron material of the wire forming the steel cord should be 0.75 to 0.85%, and the carbon content of the conventional steel cord wire should be More than 0.69-0.73%. If the carbon content is less than 0.75%, the tensile strength will be low and the object of the second prior invention cannot be achieved. Also carbon content is 0.85
%, it is extremely difficult to heat treat the wire;
In addition, the steel cord has poor toughness, making it easy to break when the pneumatic tire steps on a protrusion. Steel cord strands having the above carbon content are sinus-plated to improve adhesion to rubber. The ingredient ratio of Shinchiyu is
A proportion of 60-70% copper and 30-40% zinc is preferred. If the copper content in the steel wire is less than 60%, the iron material is hard and the steel material exhibits a β phase, making it impossible to draw a steel cord wire. Also copper
If it exceeds 70%, pinholes will occur when the steel cord wire is drawn, and the surface of the thin layer will become rough, which is undesirable. What is noteworthy about this second prior invention is that the bond between the steel cord strands with high carbon content and the shiny coating is strengthened, so that even if the tire is left in high temperature and humidity, There is no destruction between the iron and the metal.
When steel wire is wet drawn in a lubricating oil, it is drawn at a higher pressure than conventional low carbon steel wire, so the steel wire is pressed and bonded in the wire drawing die. It is thought that this is because the If the tensile strength of the steel cord is smaller than the value calculated using equations (2) and (3) above, the tire reinforcement performance will decrease when the tire strength is constant, and this will reduce tire weight reduction and fuel consumption. The effect is not much different from tires using conventional steel cords,
If the object of this invention cannot be achieved, and on the other hand, the tensile strength is greater than the calculated value above, then assuming the tire strength is constant, the tensile strength must be Although the amount of steel cord used can be reduced by the increase in strength, in this case the rigidity of the tire and the rigidity of the rubber-steel cord composite are insufficient, resulting in a decrease in the wear resistance of the tire. As mentioned above, the first prior invention and the second prior invention each have their own excellent effects, but tires that use the polyester cord of the first prior invention as a carcass ply and the conventional steel cord as a breaker;
Or, in the tires in which the steel cord of the second prior invention is used as a breaker and the conventional polyester cord is used as a carcass ply, so-called belt edge separation occurs between the steel cord end at the breaker end and the rubber. This grows and becomes the cause of tire separation. This invention uses the polyester cord according to the first prior invention as a carcass ply and the steel cord according to the second prior invention as a breaker, and combines the performance of both prior inventions, resulting in an edge separator that is fatal in terms of tire performance. To provide a pneumatic tire that prevents the occurrence of shock and has excellent performance. Examples of the present invention will be described below. Example 1 Polyester cords (1500 d/2 cords) obtained by spinning and drawing a highly polymerized polyethylene terephthalate with an intrinsic viscosity of 0.9 so that the degree of crystal orientation differs between the surface and center of the filament were spliced into a carcass. The performance is shown in Table 1 below. In addition, polyester cords with different cord manufacturing conditions are also listed in Table 1 as comparative examples.

[Table] The cord fatigue resistance in Table 1 above is based on JIS-L1017
In accordance with the chemical fiber tire cord test method of Indicated. Next, the steel cord used for the breaker is
JIS-G3502 SWRS82A material (carbon content 0.75~
0.85%) strand H22 wire is plated and twisted at 400 rpm using a bunchier type double twister to make steel cord 1 x 4 x with a twist pitch of 10 mm.
0.22mm was manufactured, and the performance of the above-mentioned wire and steel cord is shown in Table 2 below. For comparison,
Wire of SWRS72A material (carbon content 0.69-0.73%)
The performance of the L22 wire and steel cord manufactured in the same manner as above is also listed.

[Table] The area reduction rates in Table 2 above are values calculated using the following formula. Area reduction rate (%) = Ao-A/Ao×100 where Ao is the cross-sectional area of the iron material, and A is the cross-sectional area of the strand. Radial tire 165-13 was manufactured using the polyester cord shown in Table 1 as the carcass layer and the steel cord shown in Table 2 as the breaker layer, and its performance is shown in Table 3 below. The parts by weight of the rubber compositions used for tire manufacture are as follows. Natural rubber 100 HAF 55 ZnO 7 Stearic acid 1 Trimethyldihydroquinone polymer 2 SiO ₂ 8 Resorcinol 2.5 Melamine derivative 2.5 Cobalt naphthenate 2.5 Sulfur 4 Dicyclohexylbenzthiazylsulfenamide 0.8

【table】

[Table] As shown in Table 3 above, the tire T1 of Example 1 has a small amount of steel cord in the breaker, which reduces the tire weight, and the polyester cord in the carcass has a small hysteresis loss. Due to the synergistic effect, the tire rolling resistance ratio,
The fuel consumption ratio has been dramatically improved, and since the tire has good uniformity, belt edge separation, which tends to occur at the breaker end of the carcass joint, is less likely to occur, and furthermore, it has excellent high-speed durability. The tire uniformity in Table 3 above is based on the automobile standard JASO-C607 established by the Society of Automotive Engineers of Japan, and the outer diameter is 851.1.
A tire with an internal pressure of 2 kg/cm ² is loaded on a drum of 366 mm.
The tire was pressed with Kg and rotated at 60 rpm, and the magnitude of the variation in force in the radial direction of the tire was measured.The average measured value was expressed in a 5-level scale, with 5th grade being the best for uniformity. The high-speed durability of the tires is based on the U.S. automobile safety standard FMVSS109, with an internal air pressure of 1.7Kg/ ^cm2 ,
The drum was run at a speed of 80 km/hour while adding a predetermined load at predetermined intervals, and the time until tire failure was measured. It is expressed as an index with the T4 measurement value using a conventional code, which is almost never used, as 100. The rolling resistance ratio was calculated by driving a 1600 c.c. passenger car equipped with the above test tires at a speed of 60 km/hour on the applicant's Tsuno Town driving test course in Miyazaki Prefecture, and when it reached a certain point, the clutch was released and the engine was turned off. Measure the distance traveled by coasting when stopped,
This value is based on the T4 coasting distance of a conventional tire as 100. The fuel consumption ratio is the fuel consumption required to travel 40 km on the above driving test course,
This is the value when the fuel consumption of T4 is set as 100. Moist heat coverage is the rate of rubber adhesion to the steel cord when each tire is left in the air at 70°C and 95% RH for two weeks, then disassembled and the breaker gap is peeled off. In the above moist heat coverage test, when observing the peeled surface, it was found that in the conventional tire T4, the metal plating layer adhered to the rubber side on the exposed surface of the steel cord, and peeling between the steel and the metal was observed. Therefore, the copper content on the rubber side and the steel cord side was measured using an X-ray microanalyzer on the peeled surface where no rubber was attached to the solid layer, and the results are shown in Table 4. Table 4 Tire symbol T1 T4 Cord side copper (%) 98.0 67.1 Rubber side copper (%) 2.0 32.9 As seen in Table 4 above, T1 of this invention
In contrast to the strong bond between iron and steel in T4, the bond in the conventional product T4 is small. It is completely unexpected that the increased strength of the steel cord of the present invention contributes to a stronger bond between iron and steel. Example 2 One layer of carcass ply was made of polyester cord (1500 denier/2 cords) made from highly polymerized polyethylene terephthalate and obtained under conditions such that the degree of crystal orientation differs between the center and surface of the filament. Radial tires T6 and T7 of size 155SR13 were manufactured using the same steel cord as the tire T1 of Example 1 as a breaker. Comparative tires T8, T9, and Tires T8, T9, and Tires T8, T9, and Tires T8, T9, and Tires T8, T9, and Tires T8, T9, and Tires similar to those in Example 2, with different polyester cord manufacturing conditions, were manufactured.
T10, the polyester cord manufacturing conditions and tire performance of the tires T6 and T7 of Example 2 and the tires T8, T9, and T10 of Comparative Examples are shown in Table 5 below.

[Table] The sidewall irregularities in Table 5 above are
The depth of the groove-like recess in the radial direction on the sidewall part that is formed when filled with internal pressure air of 2.2 kg/cm ² is measured with a caliper, and those with no recess are grade 3, and the depth of the recess is 0.03. Those with a depth of 0.03 mm or more were classified as Class 2, and those with a depth of 0.03 mm or more were classified as Class 1. Tire heat generation was explained in Example 1 above.
In a tire high-speed durability test based on FMVSS109, after running under the maximum load condition, needle thermistor thermometers were inserted into holes previously drilled at the side edges and center of the tire tread. The temperature was measured, and the average value of the temperature difference between the lower part of the tread and the room temperature at the side edges and the center was shown. As seen in Table 5 above, the birefringence ratio is 1.10.
Tires T6 and T7 of Examples have small dimensional stability coefficients and similar excellent tire performance even though the twist coefficients are different. However, Comparative Tires T8 and T9, which were manufactured using highly polymerized polyethylene terephthalate under conditions such that there was no difference between the filament center and the surface, had different dimensional stability coefficients due to the difference in twist coefficient. Tires T6 and T7 of Example 2 do not have sidewall irregularities, tire durability is the same as or better than tire T10 of the comparative example, and tire heat generation and tire rolling resistance are lower than that of the comparative example. Better than tires. The edge separation in Table 5 above is the result of dismantling the breaker part of the tire and observing the edge separation after the tire high-speed durability test.Tires T6 and T7 of Example 2 have edge separation. There is no or slight shading. Example 3 The 4-ply polyester cord PE1 of Example 1, the number of ends 22/25 mm, and the cord angle of 90 degrees were used as the carcass ply, and the core wires shown in Table 6 below were used.
Wrap side wire H35 around H20 and 3×0.20+
A 1000R20-14PR radial tire for truck buses was manufactured using a 6 x 0.25 steel cord as a breaker. The breaker cord conditions of this tire are shown in Table 6, and the breaker configuration and tire performance are shown in Table 7.

[Table] R/Ro in Table 6 above indicates the ratio of the diameter R of the steel cord end to the diameter Ro of the center of the steel cord. It was broken into pieces.

[Table] As seen in Table 7 above, even large radial tires are lightweight, have good uniformity, have low rolling resistance, and have excellent high-speed durability, making it difficult for breaker edge separation to occur. It has performance.

Claims (1)

[Scope of Claims] 1. A filament made of a high degree of polymerization polyester containing 85 mol% or more of ethylene terephthalate component and having an intrinsic viscosity of 0.8 or more, and having a ratio of birefringence at the surface to birefringence at the center of the filament from 1.03 to 1.15. , the formula K=T×√(K is the twist coefficient, T is 10cm
The twist coefficient, expressed as the average number of twists in the first and second twists (D is the code denier), is 800 or more.
2500 and has a dimensional stability coefficient of 8.5% or less, which is the sum of the elongation rate at a load of 2.3 g/d and the drying shrinkage rate when heated at 150°C for 30 minutes. As a carcass ply,
In addition, most of the wires forming the steel cord are made of iron with a carbon content of 0.75 to 0.85% by weight, and the formula (A+345)W/7.86<TS<(A+395)W/7.86 A=-177D-1.84N+0. 02N ² (In the above formula, D is the wire diameter mm of the steel cord, N is the number of wires in the steel cord configuration, W is the weight g per 1 meter of steel cord, TS is the tensile strength, and the denominator 7.86 is the iron A pneumatic tire with excellent performance characterized by using a steel cord as a breaker, which has a tensile strength calculated by the specific gravity (specific gravity). 2. A pneumatic tire with excellent performance according to claim 1, wherein the high polymerization degree polyester is polyethylene terephthalate. 3 Steel cord strands are 60-70% copper and 30% zinc
A high-performance pneumatic tire according to claim 1 or 2, coated with a proportion of ~40% of silver. 4. A composite steel cord in which the core strand wire of the steel cord is made of an iron material with a carbon content of 0.65 to 0.75%, and the side strand wire is made of an iron material with a carbon content of 0.75 to 0.85%. A pneumatic tire with excellent performance according to any of item 3. 5. A pneumatic tire with excellent performance according to any one of claims 1 to 4, wherein the ends of the steel cords are dispersed in a broom-like manner.