JPH0536526B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high modulus polyamide tire cord with improved stress resistance and dimensional stability. Polyamide tire cord is highly strong, has excellent stress resistance, and has excellent adhesion to rubber.
Although it has been useful as a reinforcing cord for relatively large bias tires, it is actually rarely used as a cord for radial tires because it has a low modulus and lacks dimensional stability. On the other hand, among textile cords, polyester cords with high modulus and excellent dimensional stability are widely used, and rayon cords are also used in some cases. However, compared to polyamide cord, these materials have inferior durability such as heat resistance in rubber, adhesion to rubber, and fatigue resistance, so they are not suitable for relatively large radial tires used under harsh conditions. It is not recommended to apply to Therefore, if the durability of polyamide tire cords could be further improved, along with the modulus and dimensional stability at the same level as polyester cords, it would be possible to apply them to relatively large radial tires. Development has been required for a long time. Therefore, as a result of intensive studies in order to achieve the above object, the present inventors specifically selected polyhexamethylene adipamide as the fiber material, and created a drawn yarn made by imparting a unique fiber structure to the polyhexamethylene adipamide. It was discovered that a polyamide tire cord with high strength (T/D), medium elongation (MDE), dry heat (177°C) shrinkage rate (ΔS ₂ ), and fatigue resistance (GY and GD) can be obtained by , arrived at the present invention. That is, the present invention essentially provides a polyamide tire cord made by twisting and twisting drawn polyhexamethylene adipamide yarns and subjecting them to tension heat treatment, in which each single yarn has a relative viscosity (ηr) of 3.0 or more and a fineness (d) of 1.0 to 4.0, the birefringence (Δn) is 52×10 ^-3 or more, and the birefringence (Δn _S ) of the surface layer within the fiber cross section is lower than the birefringence (Δn _C ) of the inner layer. The present invention provides a polyamide tire cord characterized by: The polyamide fiber used in the polyamide tire cord of the present invention differs from conventional polyamide fibers in that the single filament fineness is fine and the birefringence of the surface layer of the fiber cross section is lower than the birefringence of the inner layer. Furthermore, the polyamide tire cord of the present invention differs from conventional ones in that it has a lower intermediate elongation and a lower shrinkage rate, and has extremely improved high modulus properties and dimensional stability. Furthermore, the polyamide tire cord of the present invention has a thin single yarn fineness and is flexible, and the birefringence of the surface layer in the cross section of the fiber is lower than the birefringence of the inner layer, and the surface layer is more flexible. Another feature is that it exhibits excellent resistance to fatigue when subjected to repeated bending deformation, and this feature provides excellent performance when used as a reinforcing cord for relatively large tires that are subject to large repeated deformations. . The fibers forming the polyamide tire cord of the present invention are substantially composed of polyhexamethylene adipamide, and 95 mol% or more of all repeating units in the polymer molecular chain are hexamethylene adipamide and contain less than 5 mol% of a copolymer component. You may do so. Examples of other polyamide components that can be copolymerized include ε-caproamide, polyhexamethylene sebamide, polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, and polyxylylene phthalamide. If the copolymer component is contained in an amount of 5 mol % or more, the crystallinity will decrease and the dimensional stability will decrease, which is not preferable. 25℃ for polyhexamethylene adipamide;
Polymers with a high degree of polymerization having a sulfuric acid relative viscosity (ηr) measured at a polymer concentration of 1% by weight of 3.0 or more, particularly 3.2 or more are preferred for obtaining the high-strength yarn of the present invention. Furthermore, since the polyamide of the present invention is used for tire cords, it is preferable to add an antioxidant to the polyamide for the purpose of imparting sufficient durability against heat, oxygen, etc. Antioxidants are usually blended into polyamide. Various copper salts, halogenated metal salts, amine type and phenolic type organic antioxidants, etc. are used.
Furthermore, an anti-dissipating agent, a pigment, an antistatic agent, etc. can be added as necessary. The manufacturing process of the polyamide tire cord of the present invention is roughly divided into the following four steps. (1) Polyhexamethylene adipamide is melt-spun, and ηr is 3.0 or more, fineness is 2 to 10 deniers, density (ρ) is 1.135 or more, and birefringence (Δn) is 40×.
10 ^-3 or more, and the birefringence of the surface layer (hereinafter abbreviated as Δn _S ) in the fiber cross section is lower than the birefringence of the inner layer (hereinafter abbreviated as Δn _C ) is produced. Process. (2) The above-mentioned undrawn yarn is hot-stretched at a draw ratio of 2.5 times or less and at a limit draw ratio of 85% or more to obtain a fineness of 1.0 to 4.0 deniers, Δn≧52×10 ^-3 ,
A process of producing a drawn yarn having the characteristics of Δn _S −Δn _C <<0, preferably strength (T/D) ≥7.5 g/d, and dry heat shrinkage rate at 150°C (ΔS ₁ ) ≤2%. . (3) A step of twisting the above-mentioned drawn yarn to have a twist coefficient of 1300 to 2200 to obtain a raw cord. (4) Apply adhesive to the above raw cord as necessary,
Then, the step of performing tension heat treatment to obtain a treated cord. Next, the manufacturing process of the polyamide tire cord of the present invention will be explained in detail. First of all, FIG. 1 is a process diagram showing the spinning process of polyamide fibers forming the polyamide cord of the present invention.
Melted at 290-305℃, output amount per hole (single hole output amount) from spinneret 1 with hole diameter 0.1-0.4 mm 1.0~
It is spun at a rate of 3.0 g/min to become spun yarn Y. A heating cylinder 3 of 5 to 30 cm is installed directly below the spinneret 1, and a heating cylinder 3 of 5 to 30 cm is installed, and the temperature is higher than the melting point of the polyamide polymer and lower than 400°C.
The atmosphere inside the heating cylinder is usually heated to 260-350℃ 2
After the spun yarn is passed through the yarn, it is immediately cooled and solidified by blowing cold air at 10 to 50°C in the cooling cylinder 4. Next, the yarn is cooled and solidified, and after passing through the yarn guide duct 5, an oil agent is applied to the yarn by the oil supply device 6, and then
It is taken off by take-off rollers 7 and 8 which rotate at a surface speed of not less than m/min, preferably from 5000 m/min to 7500 m/min.
Next, the diameter of the spinneret hole is adjusted so that the spinning draft, which is expressed as the ratio between the yarn take-up speed and the discharge linear speed when the molten polymer is spun out from the spinneret hole, is in the range of 100 to 400.
The single-hole discharge amount and take-up speed are determined, and the yarn is spun and taken to form a taken-up yarn 9. Furthermore, in the above method, installing a heating cylinder directly under the spinneret and providing a slow cooling zone is advantageous when producing the relatively highly oriented and highly crystallinity undrawn yarn of the present invention by a high-speed spinning method. It also has a remarkable effect on improving the stretching condition and improving quality. That is, by satisfying the above-mentioned conditions for spinning and drawing, each single yarn has a relative viscosity of 3.0 or more, a fineness of 1.0 to 4.0 denier, and a birefringence of 52×10 ^-3
As described above, a polyamide fiber made of polyhexamethylene adipamide, which is suitable for a tire cord and has a property in which the birefringence of the surface layer portion within the fiber cross section is lower than the birefringence of the inner layer portion, is obtained. The polyamide fibers used in the polyamide tire cord of the present invention have a single filament fineness of 4 denier or less, preferably 3.0 denier or less, and are thinner than ordinary commercially available polyamide fibers for tire cords. This means that during melt spinning, the polyamide fiber of the present invention consisting essentially of polyhexamethylene adipamide
When the discharge amount per hole from the die hole increases, it is difficult to rapidly cool the material in the cooling zone, the residence time in the crystallization temperature range becomes longer, and a large amount of spherulites are likely to be produced. If a large amount of spherulites are produced, this can be observed as a devitrification phenomenon in the drawn yarn when no degreasing agent is included, but such drawn yarn cannot be drawn normally and does not become a high-strength yarn. As mentioned above, in the spinning method of the present invention, a slow cooling zone is provided directly under the spinneret for the purpose of improving spinning stability, but it is necessary to uniformly rapidly cool the spinning material immediately after leaving the spinneret. Specified fineness. For example, methods of lowering the cold air temperature or increasing the cooling rate for rapid cooling are as follows.
If it is attempted to adopt such conditions that a sufficient effect can be obtained, the yarn will not be cooled uniformly, making it impossible to obtain an undrawn yarn having the properties aimed at by the present invention. In this way, by reducing the fineness of the single filaments and adopting high-speed spinning conditions in which the fibers are passed through a slow cooling atmosphere, the birefringence (Δn _{S ) of the surface layer in the fiber cross-section of the undrawn polyamide yarn is changed from the birefringence (Δn S} ) of the inner layer in the fiber cross section. It has a unique performance that is lower than Δn _C ). The density (ρ), birefringence (Δn), and birefringence distribution in the fiber cross section were measured using the following method. Δn: Using a Nikon Corporation XTP-11 polarizing microscope,
The measurement was carried out using white light as a light source and using the normal Bereck compensator method. ρ: Measured at 25°C using a density gradient tube prepared using carbon tetrachloride as a heavy liquid and toluene as a light liquid. Birefringence distribution within the fiber cross section: By measuring the average refractive index distribution observed from the side of the fiber using the interference fringe method obtained using a transmission quantitative interference microscope manufactured by Carl Zeiss Air (Germany). I asked. Next, the polyamide undrawn yarn obtained by the above method is taken off by high-speed take-off rolls 7 and 8, and then
Either the material is wound up on a bobbin and then stretched, or it is stretched continuously without being wound up. The drawing method is preferably a multi-stage drawing method in order to stably obtain high-strength polyamide fibers, but the drawn yarn 9 is
Since a relatively high degree of orientation has already been achieved, the total stretching ratio is 2.5 times or less, usually 2.0 to 1.5 times, and a one-stage stretching method can also be adopted. In addition, to obtain high strength yarn, 85% of the limit drawing ratio
As described above, each sample is stretched at a high stretching ratio, preferably 90 to 96%, and the stretching ratio of each sample is determined so that the residual elongation is 12 to 18%. Note that the limit stretching ratio is the highest stretching ratio at which the film can be stretched for 2 minutes or more without cutting. The drawn polyamide yarn produced by this method has a single filament fineness of 1 to 4 deniers, maintains the properties of Δn≧52×10 ^-3 and Δn _S −Δn _C <0 given in the spinning process, and has the above-mentioned properties. It has excellent T/D and ΔS ₁ . The polyamide drawn yarn thus obtained has a low shrinkage rate and differs from conventional polyamide fibers in that the birefringence of the surface layer is lower than the birefringence of the inner layer. In particular, the fibers of the present invention are obtained by additionally drawing undrawn yarns spun at high speed.Usually, when high-speed spinning is used, the birefringence of the cross section of the fiber tends to be highly oriented in the surface layer. When applied to fibers, even polyhexamethylene adipamide fibers have insufficient fatigue resistance. This is because the surface layer is cooled during the spinning cooling process, becomes highly oriented from this area, and is most susceptible to spinning tension. However, the drawn polyamide yarn of the present invention, in which the surface layer portion has a lower birefringence than the inner layer portion, is produced under the spinning conditions of the present invention, that is, the mutual combination of spinning temperature, single hole discharge rate, heating cylinder, cooling method, take-up speed, spinning draft, etc. It can be said that this is a unique characteristic expressed by Next, the drawn yarn obtained by the above method is twisted in a conventional manner to obtain a green cord. However, it is preferable that the twist coefficient K expressed by the following formula is 1300 to 2200, particularly 1500 to 1800. K=T√ (Here, T is the number of twists and D is the fineness of the raw cord.) The smaller the twist coefficient, the higher the modulus and the lower the shrinkage, but the fatigue resistance will decrease, so polyamide tire cord is not used as a tire carcass material. When used, a twist coefficient of about 2000 to 2200 is usually adopted. On the other hand, since the polyamide cord made of the fibers of the present invention has extremely excellent fatigue resistance, it can be used with a lower twist coefficient. As a result, in addition to the high modulus and low shrinkage properties originally possessed by the fibers of the present invention, the aforementioned effect of reducing the twist coefficient is added, further emphasizing the characteristics. Next, the raw cord is woven as it is or after being woven into a sudare shape, and then preferably a tire cord adhesive is applied.
For example, an RFL (resorcinol-formalin-latex) solution is applied. The amount of adhesive applied is 1 to 6%, usually 2 to 5%. The adhesive is then dried by passing through a heating oven (dry zone) and then subjected to tension heat treatment, which are usually carried out successively. In order to make the polyamide tire cord of the present invention a high modulus cord, it is subjected to tension treatment so that the MDE is 8% or less, preferably 5.5 to 7.5%. At this time, the stretching rate should be 7% to 20%. The heat treatment temperature is 230-250°C, preferably 230-240°C, and the heat treatment time is 60-240 seconds, preferably 60-150 seconds. Tension processing is usually carried out in two stages, with the first stage hot and
A method of applying tension in the zone and lowering or relaxing the tension in the subsequent normal zone is adopted, but it is sufficient to satisfy the above-mentioned stretching rate as a total. In order to set the MDE of polyamide tire cord within the above range, conditions are selected by correlating the properties of the polyamide fibers, the twist coefficient of the raw cord, the stretch rate during tension heat treatment, and the heat treatment temperature, but the maximum tension during cord heat treatment ( stretch tension)
The amount is 0.5 to 3 g/d, preferably 1.0 to 2.5 g/d. The thus obtained polyamide tire cord of the present invention has excellent performance such as strength (T/D) ≧6.5 g/d, medium elongation (MDE) = 5.5 to 8%, and dry heat shrinkage rate (ΔS ₂ ) ≦4%. This is a high modulus tire cord with good fatigue resistance and dimensional stability. A polyamide tire cord having the above characteristics is suitable as a carcass material for a relatively large radial tire, and a high-performance tire with excellent handling stability and durability can be obtained. Furthermore, when used in conventional relatively large bias tires, due to their high modulus, the amount of deformation during tire rotation under high loads is small, and it is effective in reducing noise generation during running. The definition and measurement method of the characteristics according to the present invention are as follows. (a) Tensile strength T/D, elongation E; as defined by JIS-L1017. In a room with temperature and humidity controlled at 20℃ and 65%RH.
After standing for 24 hours, using a "Tensilon" UTM-4L tensile tester (manufactured by Toyo Baldwin Co., Ltd.),
Measurement was performed with a sample length of 25 cm and a tensile speed of 30 cm/min. (b) Intermediate elongation MDE: Perform a tensile test on the tire cord in the same manner as the T/D described above to obtain a load-elongation rate curve. In the load-elongation curve, when the atomic fineness is D and the number of twisted yarns is n, the elongation under load of 5.36×D×n/2 (Kg) is determined and this is defined as MDE.
MDE is a parameter that is practically used as a guideline for tire cord modulus.
The smaller the MDE, the higher the modulus. (c) Dry heat shrinkage rate ΔS ₁ , ΔS ₂ ; Corresponds to 0.1 g/d of the sample after rolling the sample into a comb and leaving it in a room controlled at 20°C and 65% RH for 24 hours. A sample of length l ₀ measured under load is heated at 150℃ (ΔS ₁ ) for raw yarn and 177℃ for cord in a non-tensioned state.
After being left in an oven at .degree. C. (ΔS ₂ ) for 30 minutes, it was taken out from the oven, left in the temperature and humidity control room for 4 hours, and the load was applied again to calculate the measured length l ₁ using the following formula. ΔS = (l ₀ ~ _{l 1} ) / l ₀ × 100 (%) Fatigue resistance was determined by the Gutdrich tube fatigue test (JIS L-1017, 1321 (method A)) and the Guddrich disk fatigue test (JIS L- The excellent performance of the code of the present invention can be confirmed by model evaluation methods such as 1017, 1322). The present invention will be specifically explained below using Examples. Example 1 Polyhexamethylene adipamide chips with ηr = 3.25 containing 0.03% by weight of cuprous iodide and 0.5% by weight of potassium iodide were heated at 295°C using an extruder type spinning machine.
It was spun with The spinning take-off device is the same as in FIG. The diameter of the spinnerets was as shown in Table 1, and spinning was carried out using spindles with different numbers of holes and varying the discharge rate from each hole. An 80 cm heating cylinder was attached below the cap, and a slow cooling zone was established with the ambient temperature controlled at 300°C. After passing through the slow cooling zone, the spun yarn was rapidly cooled through a 20 cm annular cooling chimney installed directly below the heating cylinder. From the cooling chimney, cold air at 20°C was blown onto the yarn from the outer periphery at a speed of 30 m/min. After solidification, the yarn was applied with a lubricant using an oil supply device, and then taken up with a take-up roll and wound up once. At this time, by changing the take-up speed as shown in Table 1, undrawn yarns with various values of Δn and ρ were obtained. For comparison, an undrawn yarn that was immediately cooled and taken off without passing through the slow cooling zone after removing the heating cylinder under the spinneret was also collected. The fineness of the undrawn yarn after drawing is approximately
It was stretched while doubling the yarn to 1260 denier. Roll temperature is FR: 60℃, 1DR: 100℃,
2DR: 230°C, RR: non-heating, and the number of threads wound around the roll was 5T, 8T, 8T, and 5T, respectively. 1DR
A 50cm HP (thermal plate) was attached to the 2DR and the temperature was set to 235℃. The stretching ratio was 94% of the limit stretching ratio, 2
The stretch ratio of the rows was set to 1.20 times. A 6% relaxation was performed between 2DR and RR. Table 1 also shows these spinning conditions, undrawn yarn characteristics, stretching ratio, and drawn yarn characteristics. Next, the above drawn yarn is twisted per 10cm for both the first twist and the second twist.
The 39T and/or 35T yarns were twisted together to make a raw cord. The raw cord was treated with Computeritor RFL adhesive manufactured by Ritzler (USA) and heat set. Heat setting was performed by applying tension at 240°C for 50 seconds (hot zone), followed by 1% relaxation at 240°C for 50 seconds (normal zone). The stretch rate was varied depending on the intermediate elongation of the treated cord.
The twisting conditions, cord processing conditions, and obtained cord characteristics are also shown in Table 1.

【table】

【table】

[Table] As is clear from the results in Table 1, the cords of the present invention (Nos. 3 to 6) have low intermediate elongation, low shrinkage, and excellent fatigue resistance. On the other hand, when low speed spinning conditions are adopted (Nos. 1 and 2), Δn _S becomes higher than Δn _C ,
In particular, the dry heat shrinkage (ΔS ₂ ) and fatigue resistance of the tire cord are significantly reduced. Furthermore, even under high-speed spinning conditions, Δn _S becomes larger than Δn _C when the single yarn fineness is increased (No. 7) and when the spinneret diameter is increased and the draft rate is increased (No. 8). Code characteristics become unsatisfactory.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the manufacturing process of polyhexamethylene adipamide fiber. 1: Spinneret, 2: Atmosphere inside the heating cylinder, 3: Heating cylinder, 4: Cooling cylinder (annular chimney), 5: Yarn guide duct, 6: Oil supply device, 7, 8: Take-up roll, 9: Take-up yarn.

Claims (1)

[Claims] 1. A polyamide tire cord made by substantially twisting and twisting drawn polyhexamethylene adipamide yarns and subjecting them to tension heat treatment, each single yarn having a relative viscosity of 3.0 or more,
A polyamide tire having a fineness of 1.0 to 4.0 denier, a birefringence of 52×10 ^-3 or more, and having a property that the birefringence of the surface layer in the fiber cross section is lower than the birefringence of the inner layer. code.