JPH03161515A - Conjugate fiber of multilayered structure - Google Patents

Abstract

PURPOSE:To obtain the subject fiber, having the innermost and outermost layers respectively composed of polyester ether and polyamide and a dispersion mixture of both as an interlayer and excellent in high strength, high modulus, dimensional stability, etc. CONSTITUTION:The objective fiber, composed of three layers of (A) the innermost layer, composed of a polyester ether consisting essentially of poly(ethylene-1,2-diphenoxyethane-p,p'-dicarboxylate) having >=0.7 intrinsic viscosity [eta], >=170X10<-3> birefringence ( n) and >=1.365g/cm<3> density and accounting for 30-90wt.% of the objective fiber, (B) the outermost layer composed of a polyamide having >=2.8 relative viscosity (etar) in sulfuric acid, >=45X10<-3> birefringence ( n) and >=1.135g/cm<3> density and (C) a dispersion mixture obtained by dispersing and mixing the components (A) with (B) at (30/70)-(70/30) weight ratio and having >=6.0g/d strength, <=20% elongation, >=90g/d initial resistance to stretching and <=5% dry heat shrinkage factor at 150 deg.C.

Description

[Detailed description of the invention]

[Field of Industrial Use] The present invention relates to a multilayer composite fiber suitable for industrial material use, particularly as a rubber reinforcing material. For more details, see high strength,
A core component and sheath that have excellent mechanical properties such as high modulus and improved dimensional stability, and also cause deterioration in adhesion to rubber, heat resistance in rubber, and durability of core-sheath composite fibers. It is an object of the present invention to provide a multi-layer composite fiber for use in rubber reinforcing materials, which has improved interface peeling with other components. [Prior art] Poly(ethylene-1,2-diphenoxyethane-1),
P'-dicarboxylate) polyester ether fibers have high modulus, high strength, high elastic modulus, and high heat resistance in rubber, and are therefore widely used in various industrial material applications. In particular, the development of applications for rubber reinforcing materials and levers for tire cords, power transmission belts, conveyor bells, etc. is progressing. In the past, many attempts have been made to improve the adhesion to rubber, which is a drawback of fibers such as polyethylene, non-terephthalate, and polyester ether. Composite fibers that are coated and have appropriate physical properties are disclosed in JP-A-1-972.
It is described in Publication No. 11. JP-A-1-972il
The publication describes a composite &a fiber, which is a composite fiber having a polyester core and a nylon 66 sheath, and in which the degree of polymerization of each polymer and the proportion of the core polymer are specified. [Problems to be Solved by the Invention] Although the composite fiber described in JP-A-1-97211 has considerably improved adhesion, durability, etc., it cannot be used in some applications, such as tires for passenger cars that run at high speed. However, even better durability and ride comfort were required. In addition, polymers such as polyethylene terephthalate l/=}- and polyester ether have poor compatibility with polyamides such as nylon 6 and nylon 6G, so if they are produced using a normal yarn-making method, they will have a core-sheath composite structure. It was easy to peel and break at the interface between both bolamers, and it did not have sufficient durability for practical use. During the rolling process, tire cord processing process such as twisting and dipping, tire vulcanization process, and repeated 12 elongation compression fatigue during tire running, the core-sheath interface is destroyed, which is expected from the original core-sheath composite fiber. The problem is that performance cannot be obtained. The purpose of the present invention is to overcome the problems of the prior art, which has excellent adhesion to rubber, has high modulus and dimensional stability superior to polyester, and has the following characteristics: The object of the present invention is to provide a composite fiber suitable for reinforcing rubber, which has heat resistance (hereinafter referred to as heat resistance in rubber) and fatigue resistance. Particularly, the object is to provide a composite fiber that provides sufficient durability against the peeling of the volima at the core-sheath composite interface (2), which has not been achieved with conventional techniques. [Means and actions for solving the problem] This book The structure of the invention is that, in a multilayer composite fiber, the innermost layer is made of poly(ethylene-ethylene).
1,2-diphenoxyethane-P,■)'-dicarboxylate), the outermost layer is made of polyamide, and the polyester ether is formed between the innermost layer and the outermost layer. An intermediate layer is formed in which polyamide and polyamide are dispersed and mixed in phase h, and at least 3
It is a composite fiber consisting of layers, A. The polyester ether component forming the innermost layer has an intrinsic viscosity [η] of 0, 7 or more, and a birefringence of 170×10
-' or more, the density is 1,365 g/ern" or more, and the proportion of the entire composite fiber is 30-90% by weight; B. The polyamide fraction forming the outermost layer is sulfuric acid Viscosity (η') is 2.8 or more, birefringence (Δn) is 45X10
C. The polyester ether and polyamide forming the intermediate layer are dispersed and mixed in a weight ratio of 30:70 to 70:30. The multi-layered composite fiber has a strength of 6.0 g/denier or more, an elongation of 20% or less, an initial tensile resistance of 90 g/denier or more, and a 150°C dry heat shrinkage rate of 5% or less. The multilayer structure composite fiber according to the present invention has the above structure,
In particular, regarding the durability of the core-sheath composite interface, which is the object of the present invention and which could not be achieved with the prior art, the peeling durability of the core-sheath composite interface between the innermost layer component (hereinafter referred to as the core component) and the outermost layer component (hereinafter referred to as the sheath component) is particularly important. This can be achieved by appropriately providing an intermediate layer in which the core component and the sheath component are mutually dispersed and mixed.
It also has high modulus and dimensional stability that surpasses polyester.
and significantly improved heat resistance in rubber, etc., can be achieved by combining the characteristics of the polyester fibers and polyamide fiber portions forming the core and sheath within a specific range. The contents and effects of each element constituting the present invention will be explained in detail below. The core component of the multilayer composite fiber according to the present invention is substantially poly(ethylene-1,2-diphenoxyethane-P,P'
-dicarboxylate), and copolymerized with less than 10 mol% of a third component other than bis-1,2-(para-carboxyphenoxy)ethane and ethylene glycol in the polymer chain. including those that have been In order to obtain the strength of the multilayer composite fiber according to the present invention of 6.0 g/denier or more, the intrinsic viscosity [η] of the core component polyester ether fiber is set to 0.0 g/denier. 7 or more, preferably 0
．． It has a high viscosity of 8 or more. The polyamide that is the sheath component is polybramid, polyhexamethylene adipamide, polytetramethylene adipamide,
Polyhexamethylene sebamide, polyhexamethylene dodecamide, and other common polyamides can be used, and polymers obtained by blending or partially copolymerizing the above-mentioned polymers can also be used, but polyhexamethyleneazibamide is particularly preferred. The polyamide sheath component bolima is also made to have a high degree of polymerization in order to obtain a high-strength conjugate fiber required for industrial use, and has a sulfuric acid relative viscosity (ηr) of 2.8 or more, preferably 3.0 or more. It is preferred that the polyamide partially contain a copper salt and other organic or inorganic compounds as thermal antioxidants. In particular, copper salts such as copper iodide, copper acetate, copper chloride, and copper stearate are used in an amount of 30 to 500 ppm as copper, potassium iodide,
Alkali metal halide such as potassium bromide is 0.01~
It is preferable that the content of phosphorus is 0.51 ift% and/or 10 to 500 ppm of organic or inorganic phosphorus compounds. The intermediate layer provided between the core component and the sheath component of the multilayer composite fiber according to the present invention is formed by dispersing and mixing the core component polymer and the sheath component polymer in a weight ratio of 30:70 to 70:30. The portions of the layer that have a ratio outside this range are considered to be the core component and the sheath component, respectively. The intermediate layer preferably has an area of 5 to 30% of the total cross-sectional area of the filament. If the intermediate layer, which is a mutually dispersed mixture of the core component and the sheath component, exceeds 30% of the total cross-sectional area of the filament, the characteristics of the core-sheath composite fiber of the present invention, such as modulus, dimensional stability, heat resistance in rubber, etc. Improvements may not be sufficient. On the other hand, if it is less than 5%, although the improvement effect of core-sheath interface peeling durability, which is a feature of the present invention, is recognized, it may not reach the point where there is a significant difference. The proportion of polyester ether as a core component of the multilayer composite fiber according to the present invention is 30 to 90% by weight, and the proportion of polyamide as a sheath component is 10 to 70% by weight. A portion of each of these proportions is mixed to form an intermediate layer. If the core component is less than 30% by weight, the desired modulus and dimensional stability of the composite fiber cannot be achieved to a level superior to that of conventional polyester fibers. On the other hand, when the core content exceeds 90% by weight, the intermediate layer and sheath layer become thinner, and improvements in the durability of the core-sheath composite interface, the adhesion between the composite fiber and rubber, and the heat resistance in the rubber occur. It's not enough. The multilayer composite fiber according to the present invention is characterized in that both the polyester ether core fiber and the polyamide sheath fiber are highly oriented and crystallized. In other words, the birefringence of the polyester ether cored fiber is 170X10-"
That's all. If it is less than 170 x 10-', the strength of the composite fiber is 6. 0g
It is not possible to achieve L below /d. On the other hand, the polyamide sheath or split fiber has a highly oriented birefringence of 45 x 10-1 or more, preferably 50 x 1,0'' or more.If the birefringence is less than 45 x 10-'', the composite fiber has a high initial tensile resistance. cannot be obtained. The density of the polyester ether powder is 1.365 or more, preferably i,380 or more. The dimensional stability of the composite fiber and the heat resistance in rubber cannot be improved unless the density exceeds the specified value. The density of the polyamide sheath component is also 1,135g/e m' or more, 1.140g/c
It is preferable that it is highly crystallized with m3 or more. The multilayer structure composite fiber according to the present invention characterized by i-1 as described above has a high strength of 6.0 g/denier or more and 90 g/denier.
It has an initial tensile resistance of denier or higher, and an elongation of 20%.
It is as follows. More preferable (composite fiber properties of 7 are strength 7, O
g/denier or more, initial tensile resistance of 1.00 g/denier or more, and elongation of 8 to 1.6%, which can be achieved by appropriately combining the above conditions. The composite fiber according to the present invention having the following two characteristics is produced by the novel method shown below. The polymer of the polyester ether core component of the multilayer composite fiber according to the present invention has an intrinsic viscosity [η] of 0.7 or more, usually 0. 8 or more substantially poly(ethylene-1.2-
Diphenoxyethane-P,P'-dicarboxylate)
A volima consisting of is used. The polyamide sheath component volima has a sulfuric acid relative viscosity (ηr) of 2.
A polymer with a high polymerization degree of 8 or more, usually 3.0 or more is used. The antioxidant is usually added during the polymerization or spinning process. The intermediate layer formed between the core component and the sheath portion is formed by a weight ratio of the core component borimer and the sheath portion bolamer at a weight ratio of 30:70 to 70.
In order to stably make the intermediate layer mixed with each other at a ratio of 70:30 to 5 to 30% of the total cross-sectional area of the filament, it is necessary to Blend and melt each (method of compounding within a lump sum, ■ After melting the core component z3 and sheath polymer respectively,
A method in which the core component and part of the sheath or sheath polymer are introduced into a kneading device installed before the back introduction part, kneaded, and compounded in the nozzle; ■ After melting the core and sheath polymers respectively, There is a method in which the material is introduced into a die pack and compounded while being kneaded in the die, or a part of the bolymer near the core-sheath composite interface is kneaded after being compounded in the die. For example, in the case of method (2) above, a polyester ether borimer is used as the core, a polyamide bolymer is used as the sheath, and an intermediate layer is formed in which the core and sheath are mutually dispersed and mixed. , three extruder-type spinning machines are used for melt spinning the blended polymer. A core component polyester ether polymer, a sheath component polyamide polymer, and a blend polymer to form an intermediate layer in which the core component polymer and the sheath component polymer are mutually dispersed and mixed are melted using three extruders. The polyester ether and polyamide polymer are mutually inserted between the composite spinning bag and the composite spinning nozzle). Spun as a three-layer composite fiber with polyamide dispersively mixed in the middle layer and the sheath component. In the case of method (2) above, the core and sheath parts are melted using two extruders, one part of each part is mixed at a predetermined mixing ratio, and a kneading device installed before the bag introduction part is used. The core component volima and the sheath component volima are mutually dispersed and mixed (2
After forming a molten polymer, it is introduced into a composite spinning bag and passed through a composite spinning nozzle to form a polyester ether core, an intermediate layer in which polyester ether and polyamide polymer are mutually dispersed and mixed between the core component and the sheath component, and a sheath component. It is also possible to spin a composite fiber with one or three layers of polyamide. In the case of the above method (■), the core bolumina and the sheath component volima are divided into 2 parts.
Each component is melted using a base extruder, introduced into a composite bag, and a portion of each component is kneaded in the bag so that the core component and sheath component are mutually mixed. Le ink II -y J-
Polyester ether core,
Spun as a three-layer composite fiber with an intermediate layer of polyester ether and polyamide mutually dispersed and mixed between the core and sheath components, and polyamide as the sheath component, or melt the core and sheath components. Guide the volima directly to the compound nozzle,
A part of both of the bolimers is passed through a porous metal filter provided in the base to form a molten bollima in which the core component and the sheath component are mutually dispersed and mixed, thereby performing cross-wire and compounding at the same time. It is possible to spin a three-layer composite fiber comprising an intermediate layer in which polyester ether and polyamide polymer are mutually dispersed and mixed in the middle, and polyamide in the sheath component. The spinning speed is 1000 m/min or more, preferably 150 m/min.
The speed shall be 0 m/min or higher. 10cm directly below the spinneret
200°C or more over a distance of 1 m, preferably 200°C or more
A heating atmosphere of 50° C. or more and 400° C. or less is created by providing a heat retaining cylinder and a heating cylinder. After passing through the above-mentioned heated atmosphere, the spun yarn is quenched and solidified with cold air, and after being applied with an oil agent, it is taken off at a take-off port that controls the spinning speed. Control of the heating atmosphere directly below the spinneret is extremely important in order to maintain the stringiness during high-speed spinning of the present invention. The taken-off undrawn yarn is usually drawn continuously without being wound once, or the undrawn yarn is once wound and then drawn in a separate process. In the multilayer composite fiber according to the present invention, the peeling durability of the core-sheath composite interface is significantly improved due to the shape of the intermediate layer in which the core polymer and the sheath component polymer are mutually dispersed and mixed, and thereby the fatigue resistance is significantly improved. be done. It should be noted that the modulus and dimensional stability of the composite fiber are significantly improved by high-speed spinning of 1000 m/min or more, preferably 1500 m/min or more, as described above. Perhaps the difference in spinning tension between the polyamide sheath component and the polyester ether component the core component, and the difference in stretching behavior between the polyamide component and the polyester ether component, can be explained by the differences between the core component and the sheath component polymer. It is thought that the above effect is remarkable due to the gradual absorption by the mixed intermediate layer. Next, the undrawn yarn is continuously heated to 170°C or higher, preferably 2°C.
It is hot rolled at a temperature of 00 to 240°C. The stretching is carried out in two or more stages, preferably three or more stages, and the stretching ratio is 1.
It is in the range of 4 to 5.0 times, preferably 1.4 to 4.0 times. The fiber thus obtained has the characteristics of the multilayer composite fiber of the present invention. The definitions and measurement methods of each fiber characteristic and cord characteristic of the multilayer composite fiber according to the present invention are as follows. Characteristics of polyester ether core component fiber (a) Intrinsic viscosity [η]: A sample was dissolved in orthomerolphenol and measured at 25°C using an Ostwald viscometer. (b) Density: Measured at 25° C. using a density gradient tube prepared with carbon tetrachloride as a heavy liquid and n-heptane as a light liquid. The polyamide sheath component of the sample was dissolved and removed with formic acid, and the polyester ether core fiber component was measured. (c) Birefringence: Using a transmission quantitative microscope manufactured by Carl Zeiss Jena (East Germany), the average birefringence observed from the side of the fiber was determined by the interference fringe method. For the sample, the polyamide component, which is the main component of the sheath, was dissolved and removed with formic acid, and the polyester core fiber portion was measured. Characteristics of polyamide sheath component fibers (a) Relative viscosity of sulfuric acid (ηr): 0.25 g of a sample was dissolved in 25 cc of 98% sulfuric acid and measured at 25°C using an Ostwald viscometer. (Expression) Birefringence: Using a transmission quantitative interference microscope manufactured by Carl Zeiss Jena Co., Ltd., only the polyamide sheath portion was measured at 211 intervals from the side of the fiber toward the center using the interference M method17, and the average value was calculated. I asked for it. (c) Preparation: The density of the composite fiber and polyester ether core fiber fraction was measured, and the density of the polyamide fiber fraction was calculated using the composite ratio. Characteristics of composite fibers (a) Strength, elongation, and initial tensile resistance Strength, elongation, and initial tensile resistance are determined according to the definition and measurement method of JIS-L1017. The specific conditions are as follows. Take the sample into a rough shape, leave it in a temperature-controlled room at 20°C and 65% R K-1 for more than 24 hours, and then
U T T, - 4 1,'' type tensile testing machine (manufactured by Orientec (■)), sample length 25 cm, tensile speed 30
Measured in ern/min

[7. (Ex) Density: Measured in the same manner as in the above-mentioned polyester ether 4.'; Characteristics (ex) of the woven fiber. (c) Dry heat shrinkage rate Two samples were taken in a general shape, left in a temperature-controlled room at 20°C and 65% RH for more than 24 hours, and then measured by applying a load equivalent to the O, Ig/d of the sample. A sample of length L0 is processed under tension in an oven at 150@C for 30 minutes. The sample after treatment was air-dried and left in the above temperature and humidity control room for 24 hours or more {7, then the above load was applied again and measured [7] Calculated from the length L using the following formula. Dry heat shrinkage rate (%) (L.-L)/I. Characteristics of 6X100 composite fiber cord (a) Strength, elongation, initial tensile resistance: Measured in the same manner as in the above characteristics of composite fiber (a). Intermediate elongation refers to the elongation at which strength is shown as determined by the formula below. (6.75X D X n ) / (1500X2)
K g However, D two-drawn medium yarn weave n: number of yarns combined and twisted, for example, drawn yarn weave], cord 1 0 0 0/2 made of two 500 denier yarns combined and twisted is 6. 75Kg
The elongation at the time is the intermediate elongation. (1) Dry heat yield = Measured in the same manner as in (3) of the properties of composite fibers except that the heat treatment temperature was 177°C. (c) GY fatigue life: Compliant with JIS-L1017-1.3.2, A method. However, the tlb angle was set to 90°. (2) GD fatigue: J Is-L10]. 7-4.3.2.2 quasi 1!13
T,ta. However, (7 elongation was 6.3%, compression J was 2.6%. (e) Adhesiveness: According to JIS-L1017-3.3.1A method. (f) Heat-resistant adhesiveness: during vulcanization The heat treatment was carried out at 70℃ for 60 minutes, except for the above (
Evaluation was made in the same manner as in section e). (g) Heat resistance in rubber: Dip cords lined up on a rubber sheet were sandwiched between separately prepared rubber sheets in a sandwich shape, and heated to 170°C under a pressure of 50 kg/cm for 3 hours. The cord strength was measured before and after the treatment, and the strength retention rate was determined to determine the fatigue resistance. [Example] Example 1 Polyester ether with intrinsic viscosity (η) of 0 and 9, and copper iodide Polyhexamethylene adipamide (N66: sulfuric acid relative thickness ηr 3.4) containing 0.02% by weight and 0.1% by weight of potassium iodide was melted in a 40Φ extruder type spinning machine, and the above polyester ether was melted. Volima blended with N66 at a weight ratio of 5:5 is 30
Melt with a Φ extruder type spinning machine, introduce the three types of bolimar into a composite pack, and use a three-layer core-sheath composite spinneret to form polyester ether in the core, and polyester ether as the core component and the sheath in the boundary layer between the core and sheath components. It was spun as a polyamide conjugate fiber with an intermediate layer, a sheath and a sheath in which the component polyamides were dispersed and mixed with each other. Table 1 shows the intermediate layer in which the core component and the core-sheath component are dispersed and mixed with each other, and the proportions of the core and sheath. The cap used had a hole diameter of 0.6 mmΦ and 120 holes. The polymer temperature is 295℃ for polyester ether, 293℃ for mixed polymer of polyester ether and N66, and 295℃ for N66.
Each was melted at 90°C and spun at a spinning pack temperature of 295°C. A 20 cm heating cylinder was attached directly below the mouthpiece, and the atmosphere inside the cylinder was heated to 320°C. The atmosphere temperature inside the cylinder is the atmosphere temperature measured at a position 10 cm below the mouth surface and 1 cm away from the outermost peripheral thread. An annular chimney with a length of 40 cm was installed under the heating cylinder, and cold air was blown at 25° C. at 40 m/min from around the yarn at right angles to the yarn to cool it. After applying an oil agent, the yarn speed was controlled with a take-up roll rotating at the speed shown in Table 1, and then the yarn was drawn continuously without being wound up. The film was stretched in three stages using four pairs of Nelson rolls, then heat-treated between two pairs of Nelson rolls while being relaxed by 3%, and then wound up. The take-up roll temperature is 60°C, the first stretching roll temperature is 120°C, and the second stretching roll temperature is 1.
The temperature of the third stretching roll was 230°C, the tension adjustment roll after stretching was not heated, the first stage stretching ratio was 70% of the total stretching ratio, and the remainder was divided into two stages for stretching. The yarn was produced by varying the spinning speed, total draw ratio, etc., and the discharge amount was changed in accordance with the spinning speed and draw ratio so that the fineness of the drawn yarn was about 500 denier. The obtained drawn yarn is 3
The yarn was doubled to a denier of 1,500. The spinning conditions, the obtained drawn yarn properties, and the fiber structure parameters are as shown in Table 1. In addition, commercially available polyethylene terephthalate (PET) fiber for tire cords (15
00-288-702C), and nylon 66 fiber (
1260-204-1781) are also shown in Table 1. Example 2 The drawn yarn and PET fiber obtained in Example 1 were twisted and twisted in opposite directions at 40T/lOc.
Multiply by m to obtain a raw code of 1 5 0 0/2. However, the number of twists for N66 fiber is 39T/10cm, and 1
The raw code was 2 6 0/2. The raw cord made of the highly durable composite fiber according to the present invention was made into a dipped cord by applying an adhesive and heat-treating it in a conventional manner using a dipping machine manufactured by Ritzler. The dip liquid contained a portion of an adhesive consisting of 20% resorcinol, formalin, and latex, and was adjusted so that about 4% of the adhesive component adhered to the cord. The heat treatment was carried out at 225° C. for 80 seconds while stretching the dip cord so that the intermediate elongation was 5%. The raw cord made of N66 fibers was subjected to heat treatment conditions similar to those for the composite fibers of the present invention, and was stretched so that the intermediate elongation was approximately 9%, which is applied to ordinary N66 tire cords. In addition, the raw cord made of PET fibers is subjected to a two-bath adhesive treatment using a conventional method, heat treated at 240°C for 120 seconds, and stretched so that the intermediate elongation is approximately 5%, which is applied to ordinary PET tire cord. did. The thus obtained dipped cord was simultaneously evaluated for tire cord properties such as heat resistance in rubber, adhesion, and fatigue resistance, and the results are shown in Table 2. The composite fiber dipped cord of the present invention has high modulus and dimensional stability superior to conventional polyester dipped cords, and has significantly improved fatigue resistance and heat resistance in rubber.
This shows that it is a high-strength dip cord with heat-resistant adhesive properties. (Left below) Hon゜Liess in-te C$”llO Chile: J・l+2-J
-7t. '4:'19:'-PH66: f irono-66 PO: 1 polyester, 8 strands, 1 oleate) Table 2 [Effects of the invention] The multilayer composite fiber according to the present invention is superior to conventional polyester fibers. The heat resistance and adhesion properties in rubber, especially the heat resistance adhesion properties and fatigue resistance after being subjected to high temperature history, have been significantly improved.
It is a multilayer composite fiber that has extremely high durability and has a high modulus and dimensional stability of 1K, which was not possible even with polyester fibers. When the multilayer composite fiber according to the present invention is used as a tire cord, for example, it has extremely good durability during tire running, and also has high durability because the core-sheath interface does not break due to repeated stretching and compression fatigue during tire running. has. Therefore, a relatively large light truck and 1 rack,
It is ideal as a tire reinforcement material for bus tire cords, as well as tire reinforcement cords for racing cars and high-speed passenger cars that require high-speed durability. Furthermore, since the multilayer composite fiber according to the present invention has the excellent characteristics listed in (1) and (2), it can be used not only in rubber reinforcing materials other than tire cords, such as power transmission belts, rubber hoses, air springs, etc., but also in general industrial materials. , for example, thread, seat bell 1.
Useful for fishing nets, robes, etc.

Claims (1)

[Claims] In the multilayer composite fiber, the innermost layer is poly(ethylene-1,2-diphenoxyethane-P,P'-
dicarboxylate), the outermost layer is made of a polyamide component, and an intermediate layer in which the polyester ether and polyamide are mutually dispersed and mixed is formed between the innermost layer and the outermost layer. ,
A composite fiber consisting of at least three layers, A. The polyester ether component forming the innermost layer has an intrinsic viscosity [η] of 0.7 or more and a birefringence (Δn) of 17
0x10^-^3 or more, density 1.365g/cm^3
It has the above characteristics and accounts for 30 to 30% of the total composite fibers.
B. The polyamide component forming the outermost layer has a sulfuric acid relative viscosity (ηr) of 2.8 or more, a birefringence (Δn) of 45×10^-^3 or more, and a density of 1.135.
g/cm^3 or more; C. The polyester ether and polyamide forming the intermediate layer are mutually dispersed and mixed at a weight ratio of 30:70 to 70:30; A multilayer composite fiber having a strength of 6.0 g/denier or more, an elongation of 20% or less, an initial tensile resistance of 90 g/denier or more, and a 150° C. dry heat shrinkage rate of 5% or less.