JPH0223362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a radial pneumatic tire reinforced with steel cords. In recent years, pneumatic tires reinforced with steel cord have been used for high-speed mass transportation or for construction vehicles, but the steel cord has a high specific gravity, which increases the weight of the tire, resulting in lower fuel consumption. There was a problem with getting bigger. As a countermeasure, 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. On the other hand, in pneumatic tires reinforced with steel cords, stress concentration occurs at 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. Ta. In addition, if conventional pneumatic tires reinforced with steel cords are left in hot and humid conditions for a long time, moisture will penetrate 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. The present inventors measured the tensile strength and cord weight of a large number of steel cords with various diameters and numbers of wires forming the steel cord in a pneumatic tire, and input these measured values into a computer. As a result of finding the relationship, the carbon content is 0.65-0.75%
The tensile strength of a conventional steel cord using strands made of iron material is expressed by the following empirical formula, which consists of the basic strength and a supplementary term as a shape factor that causes a decrease in strength in relation to the structure of the cord. I found out. (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 A is the shape factor of the tensile strength determined by the structure of the cord (Kg/mm ² ), 285 and 335 are the lower and upper limits of the basic strength of the baseline, W is the weight per meter of steel cord (g/m), the denominator 7.86 is the density of iron (g/cm ³ ), and formula (2) D is the diameter (mm) of the strands forming the steel cord, and N is the number of strands forming the steel cord. The experimental formulas for (1) and (2) above are: N = 3 to 50, D = 0.15
Applicable in the range of ~0.40mm. In other words, when the number of strands N is less than 3, the bending hardness of the cord becomes uneven in the longitudinal direction, and the parts with low bending hardness are bent intensively when the tire runs, making it easy to break due to fatigue. If there are more than 50 cords, the belt or ply becomes too rigid and bends at the cut end, causing the cut end to spring up and cause separation, which can lead to failure. reach. 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
+1=N is applied, and the diameter of the core strand is calculated assuming that it is the same diameter as the diameter of the side strand strand. In order to solve the shortcomings of traditional pneumatic tires, this invention reduces the weight of pneumatic tires by reducing the amount of steel cord used, reduces fuel consumption of vehicles, and reduces the delamination of pneumatic tires. The purpose is to reduce failures due to The above object has been achieved by improving the tensile strength of the steel cord. That is, the present invention provides a radial pneumatic tire at least partially reinforced with steel cords, in which most of the wires forming the steel cords are made of iron material with a carbon content of 0.75 to 0.85% by weight, and the wires are made of copper. It is coated with 60-70% zinc and 30-40% zinc, and the steel cord has 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, A is the shape factor Kg/mm ² for the tensile strength of the steel cord, and D is the strand diameter of the steel cord.
mm, N is the number of strands composing the steel cord,
W is the weight of the steel cord per meter (g), TS is the tensile strength and breaking load due to tension (kg), and the denominator 7.86 is the density of iron (g/cm ³ ). It is a radial type pneumatic tire. In addition, the applicable range of N and D in the above formula (2) is:
Similar to the conventional formula described above, N = 3 to 50 pieces, D =
If N is 2 or less, the bending hardness of the cord will be uneven, if it is 51 or more, a spring-up phenomenon will occur at the cut end of the belt or ply, and if D is less than 0.15 mm, the bending hardness of the cord will be uneven. This increases the cost and makes it impractical, and if it exceeds 0.40 mm, tire delamination increases. Next, the process of deriving the above equations (2) and (3) will be explained. Conventional tensile strength TS (Kg) of steel cord
is the tensile strength t (Kg/mm ² ) of the steel cord and 1
The product of the cord weight per m is the density (7.86g/
cm ³ ), but according to the inventor's knowledge, the strength of the steel cord (Kg/mm ² ) is as shown in Figure 7. The smaller the number of strands, the smaller the number of strands, the larger the strands tend to be. Therefore, regarding steel cords that are judged to have the effects of the present invention in terms of tensile strength and toughness, we prepared data on a large number of steel cords with different diameters, numbers of strands, and tensile strengths, and analyzed the data. When the relationship was determined by arithmetic processing using a computer, the following regression equation was obtained: t=-177D-1.84N+0.02N ² +370 (4), and the correlation coefficient was 0.922. In order to increase this correlation coefficient to 0.990, the constant 370 in equation (4) above needs a width of ±25, making the upper limit value 395 and the lower limit value 345. The above equation (2) is the variable term A on the right side of the above equation (4), and these equations (2), (4) and the constant
From the relationship of 370±25, the relationship A+345<t<A+395 (5) is obtained, and in this equation (5), TS=t・W/7.86
By substituting the relationship, the above equation (3) can be obtained. In addition, the tensile strength of conventional steel cord
Equation (1) for TS was obtained in the same manner. 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 strands forming the steel cord must be increased to increase the basic strength.
The carbon content is 0.75 to 0.85%, which is higher than the carbon content of conventional steel cord wires, which is 0.69 to 0.73%. If the carbon content is less than 0.75%, its tensile strength is small;
The purpose of this invention cannot be achieved. Furthermore, if the carbon content exceeds 0.85%, heat treatment of the wire becomes extremely difficult, and the steel cord becomes less tough, making it more likely to break when a 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 not preferable. What is noteworthy about this invention is that the bond between the steel cord strands with high carbon content and the steel cord coating is strengthened, so that even if the tire is left in high temperature and humidity, it can be
There is no destruction between the two. this is,
In order to wet-draw steel wire in a lubricating oil, it is necessary to draw the steel wire at a higher pressure than conventional steel wire in order to achieve the same area reduction as conventional low-carbon steel wire. This is thought to be due to the fact that the steel wire is press-bonded to the steel wire. 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, assuming the tire strength is constant, and this will reduce the effect of reducing tire weight and lowering fuel costs. The effect is not much different from tires using conventional steel cords, and the purpose of this invention cannot be achieved.On the other hand, if the tensile strength is larger than the calculated value above, then if the tire strength is constant, it will not be as good as tires using conventional steel cords. In order to maintain the same strength as a tire using cord, the amount of steel cord used can be reduced by the amount of improved tensile strength, but in this case, the rigidity of the tire and the rigidity of the rubber-steel cord composite are insufficient. As a result, the wear resistance of the tire decreases. The steel cord of this invention can be twisted into various structures like conventional steel cords, and can be used in the carcass, breaker, and chief parts of pneumatic tires.
Used at appropriate locations on the sidewall. It may also be used in conjunction with conventional low-strength steel cord. Examples of the present invention will be described below. The steel cord wires used in this example were JIS-G3502 SWRS82A material (carbon content 0.80 to 0.85%) and conventional SWRS72A material (carbon content 0.69 to 0.73%) as shown in Table 1 below. It's a shiny piece of paper.

[Table] The area reduction rates in Table 1 above are values calculated using the following formula. Area reduction rate (%)=A ₀ −a/A ₀ ×100 where A ₀ is the cross-sectional area of the iron material and the cross-sectional area of the a-wire. The parts by weight of the rubber compositions used in the production of tires in Examples 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 Dicyclohexylbenzthiazyl sulfenamide 0.8 Example 1 H22A, H22B, L22A in Table 1 We manufactured four types of steel cords (1 x 4 x 0.22 mm) with a twist pitch of 10 mm (Fig. 1) using four types of L22B strands using a buncher-type double twister at 4000 rpm, and evaluated the performance of these steel cords. It is shown in Table 2.

[Table] Radial tire 165-13 was manufactured using the above four types of steel cords as a breaker layer and a polyester cord as a carcass layer, and the performance thereof is shown in Table 3.

【table】

[Table] The high-speed durability in Table 3 above is
These are the results of the drum test specified in FMVSS No. 109. 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. The distance traveled by coasting after stopping is measured, and the value is based on the coasting distance of the conventional tire TL22B being set 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 TL22B 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. As seen in Table 3 above, the tire of this invention
TH22A, TH22B are conventional tires TL22A,
Compared to TL22B, rolling resistance and fuel consumption are lower, and moisture heat coverage is larger. In the moist heat coverage test mentioned above, when observing the peeling surface, it was found that in the conventional products TL22A and TL22B, the metal plating layer adhered to the rubber side on the exposed surface of the steel cord, causing peeling between the iron and the metal. . 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] As seen in Table 4 above, this invention
TH22A has a strong bond between iron and steel, while the conventional product TL22A has a weak bond. The strength of the steel cord of this invention has been improved.
It is completely unexpected that it contributes to strengthening the bond between iron and steel. As a result, the amount of steel cord used in one tire can be reduced, and fuel consumption can be reduced. Example 2 Using four H22A strands shown in Table 1, steel cords with different preform ratios of 1 x 4 x 0.22 mm were manufactured using a tubular type twisting machine, and the steel cords were used as the breaker layer in Example 1. Manufactured similar tires. For comparison, a tire was manufactured using L22A. The performance of this steel cord is 5th.
Table 6 shows the tire test results.

【table】

[Table] Note that the above R/R ₀ is the ratio of the cord end diameter to the cord diameter (see Figure 3). The air permeability was determined by molding the above rubber composition to a length of cm, width of 2.5 cm, and thickness of 1.25 cm, and sandwiching one steel cord in the longitudinal direction between two of the molded products. Vulcanize in a mold at 160℃ for 20 minutes, then grind each lengthwise end by 0.5cm using a grinder.
This is the value obtained by injecting Kg/cm ² of air and measuring the amount of air leaking from the other end using a flowmeter.

[Table] The drum test ratio is the distance until tire failure in a drum test rotating at a circumferential speed of 182 km/hour, with the conventional tire TL22A set as 100, and indicates high-speed durability. As shown in Table 6 above, with under-preformed products like TH22A ₆₀ , the cut ends of the steel cord are dispersed, making it difficult for the edges of the breaker layer to peel off, improving high-speed durability, and with products like TH22A ₁₂₀ . Over-preformed wires allow rubber to penetrate between the wires, resulting in the best high-speed durability. Example 3 Using H22A and L22A strands in Table 1,
Core strand made of four wires twisted (twist pitch 10)
Pitch 7 side strands around 20 mm)
A steel cord 7+4 x 0.22 mm stranded in mm was manufactured and its performance is shown in Table 7.

【table】

[Table] Next, the core strand (twisting pitch: 10 mm) using the wires H20 and L20 in Table 1 as the core strand wire, and the side strand (twisting pitch: 10 mm) using the wires CH35, CH38, and CL38 as the side strand wires. A steel cord was manufactured by combining the steel cord with a pitch of 18 mm, and its performance is shown in Table 8.

[Table] A 1200R20 large radial tire was manufactured by combining the steel cords shown in Table 7 above as a carcass layer and the steel cords shown in Table 8 as a breaker layer, and the structure and performance thereof are shown in Table 9.

【table】

[Table] In Table 9, the peel force ratio and wet heat coverage are as follows:
The peeling state between the second and third breaker layers is shown, and the rust area ratio is the value of the fourth breaker layer after 2000 km of driving on rough roads. The carcass strength retention rate of the above tires T2 and T4 after running for 150,000 km is shown in the graph of FIG. As shown in Figure 6, in order to find out that there is a difference in the strength retention rate of the carcass cord after driving 150,000 km between the tire T2 of the present invention and the conventional tire T4, we observed the cross section of the cord and found that the tire T4 showed no fretting. This phenomenon was observed and the steel wire was significantly worn compared to tire T2. That is, by mixing strands with a high carbon content with strands with a low carbon content, the fatigue resistance of the cord is significantly improved. As shown in Table 9, tire T1, in which a cord with a large side strand gap was used in the breaker layer, had significantly improved high-speed durability and peeling force of the breaker layer. Tires T1 and T2 also consume less fuel and have improved high-speed durability and load capacity. Tire T3 has the cord ends of the breaker layer dispersed in the shape of bamboo bags, and has significantly improved high-speed durability.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views of the steel cords of Examples 1 and 2, Figure 3 is a side view showing the cord ends of Examples 2 and 3 having broom shapes, and Figures 4 and 5 are examples of the examples. Figure 6 is a cross-sectional view of the steel cord of Example 3.
FIG. 7 is a graph showing the relationship between the number of strands N of the steel cord, the strand diameter D, and the tensile strength t of the steel cord.

Claims (1)

[Claims] 1. A radial pneumatic tire at least partially reinforced with steel cords, in which most of the strands forming the steel cords have a carbon content of 0.75.
~0.85% by weight iron material, 60~70% copper wire
%, zinc with a ratio of 30 to 40%, and the steel cord is coated with ^the formula In the above formula, A is the shape factor Kg/mm ² for the tensile strength of the steel cord, D is the wire diameter of the steel cord, 0.15 to 0.40 mm, and N is the number of wires making up the steel cord, 3 to 50. , W is steel cord 1
The weight per meter is g, TS is the tensile strength and breaking load due to tension in kg, and the denominator 7.86 is the density of iron in g/
A radial pneumatic tire characterized by having a tensile strength calculated in cm ³ ). 2. The radial pneumatic tire according to claim 1, wherein a steel cord is used as the breaker layer. 3. The radial pneumatic tire according to claim 1, wherein steel cord is used for the breaker layer and the carcass layer. 4. Claim No. 4, wherein the core strand wire of the steel cord is made of an iron material with a carbon content of 0.65 to 0.75% by weight, and the side strand wire is a composite steel cord made of an iron material with a carbon content of 0.75 to 0.85% by weight. The radial pneumatic tire according to any one of items 1 to 3. 5. The radial pneumatic tire according to any one of claims 1 to 4, wherein the ends of the steel cord are distributed in a broom-like manner.