JPH11200154A - Conjugated fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems in conventional polyester fibers containing particles at a high concentration and produce a high-strength conjugated fiber having high color developing properties. SOLUTION: This conjugated fiber is a core-sheath type conjugated fiber containing a core and a sheath components which are polyester-based polymers. The content of particles in the fiber is >=15 wt.% and the core component polyester is obtained by copolymerizing isophthalic acid with an ethylene oxide adduct to bisphenol A as copolymerization components in a molar fraction of 10.0<=Fa+Fb<=20.0 and 1.0<=Fb<=5.0 (Fa is the molar fraction of the isophthalic acid based on the total acid component of the copolyester; Fb is the molar fraction of the ethylene oxide adduct to the bisphenol A based on the total glycol component in the copolyester). The intrinsic viscosity of the core component is lower than that of the sheath component by >=0.35.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conjugate fiber and a method for producing the same. More specifically, the present invention relates to a polyester-based composite fiber containing particles, particularly high-specific-gravity particles, in a core component, which has high specific gravity, high strength, and has high black or chromatic coloring properties and a method for producing the same. Things.

[0002]

2. Description of the Related Art The technique of incorporating particles into polyester fibers at a high concentration is a useful technique as a means for imparting further functions to the inherent mechanical properties, thermal properties, and affordability of polyester. The functions to be provided include, for example, high specific gravity, low specific gravity, shielding and reflection of visible light and other electromagnetic waves. In particular, high specific gravity fibers have been demanded as general industrial fibers such as fishing nets, ropes, and wave breaking nets, and as interior decoration fibers such as curtains and blackout curtains. This is because the effect of catching, mooring, wave-dissipation, etc. is enhanced by suppressing product flare due to ocean currents and tides in marine applications. This is to create a calm atmosphere through prevention.

[0003] Further, many of these uses are conventionally generally used as chromatic or black fibers by dyeing or dying. It is known in the industry that not only the interior decoration but also the fishing net has a certain catch amount in a specific color tone.

[0004] In terms of high specific gravity fibers, in some fishing nets, composite fibers using nylon as a sheath component and lead metal as a core component have been put to practical use. However, in the case of a composite fiber containing nylon as a sheath component and lead metal as a core component, the core portion (lead metal portion) is not sufficiently stretched at the time of stretching, so that an intermittent state in which the core portion is cut occurs, and as a result, The fiber diameter in the longitudinal direction of the fiber fluctuates greatly, and the thick and thin fibers become non-uniform fibers and become low-strength fibers. Therefore, it is difficult to use these composite fibers alone for practical use, and they are used in combination with high-strength fibers. However, in this case, there is a problem that the twisting property at the time of net-making is reduced.

Japanese Patent Application Laid-Open No. 62-15327 discloses a high specific gravity composite fiber having a thermoplastic polymer containing fine lead alloy particles as a core component in order to solve the above-mentioned problem. However, in the case of a fiber using a lead metal or a lead alloy, lead damage occurs during incineration or after disposal, so that it cannot be easily used from the viewpoint of environmental pollution.

From these viewpoints, Japanese Patent Application Laid-Open No. 8-33792
No. 4 proposes a core-sheath type composite fiber in which particles made of a lead-free metal or a compound thereof are mixed with a thermoplastic polymer as a core component.

However, according to these conventional techniques, voids generated between the core component particles and the thermoplastic polymer during stretching cannot be controlled, and only conjugate fibers having a low specific gravity and a low coloring property can be obtained. I couldn't. Further, the conjugate fiber according to JP-A-8-337924 has no compatibility at the interface between the core component and the sheath component, and the core component and the sheath component can be easily peeled off with tweezers or the like.
There is also a problem that the coloring property is deteriorated due to light scattering on the peeling surface, and it cannot be used in fields such as fishing nets, curtains, and blackout curtains.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems in the prior art and to provide both high strength, high specific gravity, high color development and abrasion resistance. Another object of the present invention is to provide a conjugate fiber useful as a high specific gravity fiber for general industrial use or interior decoration. The fiber strength targeted in the present invention is 4.5 g / d or more,
The fiber specific gravity is 1.54 or more.

[0009]

Means for Solving the Problems To solve the above problems, the conjugate fiber of the present invention mainly has the following constitution. That is, a core-sheath type conjugate fiber in which the core component and the sheath component are polyester polymers, and the particle content in the conjugate fiber is 1%.
5% by weight or more, wherein the core component polyester is obtained by copolymerizing an ethylene oxide adduct of isophthalic acid and bisphenol A as a copolymer component at a mole fraction of the following formula, and the intrinsic viscosity of the core component polyester is higher than that of the sheath component polyester. It is a composite fiber characterized by being lower than 0.35.

10.0 ≦ Fa + Fb ≦ 20.0 1.0 ≦ Fb ≦ 5.0 (wherein Fa is the mole fraction (%) of isophthalic acid with respect to all acid components of the copolymerized polyester, and Fb is the copolymerized polyester. Is the mole fraction (%) of the ethylene oxide adduct of bisphenol A with respect to all the glycol components of the present invention.) The method for producing a conjugate fiber of the present invention has the following configuration. That is, a core component polymer, which is a polyester polymer obtained by copolymerizing ethylene oxide adduct of isophthalic acid and bisphenol A with the above molar fraction, and a sheath component polymer, which is a polyester polymer which is not substantially copolymerized, are used. And a core-sheath conjugate spinning process in which the core component polymer contains high specific gravity particles in an amount of 40% by weight or more, and stretching, heat treatment, and relaxation treatment.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The conjugate fiber of the present invention is a core-sheath conjugate fiber. By using a core-sheath type, particles can be made to exist at a high concentration in one component, so that the mechanical properties can be maintained by the other component. In addition, since these particles are contained in the core component, these particles are not exposed on the fiber surface, and prevent abrasion of high-order processing equipment such as twisted yarn, weaving, and knitting mesh, and pass through these processes. It is preferable because the properties are good and the high functionality of the particles can be exhibited. In this case, although particles may be contained in the sheath component, in order to maintain high strength, the particle content of the sheath component is preferably 2.0% by weight or less, more preferably 1.0% by weight or less. preferable. From this viewpoint, it is preferable to use a substantially concentric core-sheath composite, thereby maximizing the thickness of the sheath, improving strength and durability, and enhancing the functionality by the particles contained in the core component. Can be achieved. The composite form may be a triple or quadruple multiple concentric composite or a multi-core composite, but a simple double concentric composite is preferred from the viewpoint of strength and durability.

[0013] The core component and the sheath component of the conjugate fiber of the present invention are polyester-based polymers (hereinafter sometimes referred to as polyester). By using a polyester polymer as the core component and the sheath component, a fiber having high strength and good wear resistance can be obtained. Further, by using both components as a polyester-based polymer, the separation of the interface between the two components can be suppressed, and it can be made suitable for a field requiring high strength and color development.

The polyester polymer referred to in the present invention is:
It is a polyester polymer having ethylene terephthalate, trimethylene terephthalate, tetramethylene terephthalate, or ethylene naphthalate as a main repeating unit.

The composite fiber of the present invention is effective when the high-functional particles are contained in the composite fiber in a content of 15% by weight or more. If the amount is less than 15% by weight, the intended functionality of the present invention, for example, a specific gravity of 1.54 or more cannot be obtained.
When the purpose is a high specific gravity, the content of the high specific gravity particles in the conjugate fiber is preferably 20% by weight or more. However, if the content is too high, it is difficult to achieve high strength, which is another object of the present invention,
For this purpose, the content is preferably 35% by weight or less,
30% by weight is more preferred. In the conjugate fiber of the present invention, the particle content of the polyester as the core component is preferably 40% by weight or more in order to easily increase the specific gravity.

In the present invention, high color development can be easily obtained, and the color tone is not changed by the fluctuation of manufacturing conditions.
On the other hand, in order to prevent the thermal decomposition of the core component from intensifying and deteriorating the spinning properties, the copolymer composition of the polyester of the core component, the copolymer mole fraction thereof, and the intrinsic viscosity were further studied. As a copolymerization component, an ethylene oxide adduct of isophthalic acid and bisphenol A is copolymerized as a copolymerization component so as to satisfy the following formula: 10.0 ≦ Fa + Fb ≦ 20.0 1.0 ≦ Fb ≦ 5.0, and It has been found that it is effective to make the intrinsic viscosity 0.35 or more lower than that of the sheath component polyester.

Here, the mole fraction means the mole fraction Fa of the isophthalic acid component to the total acid components of the core component polyester.
(Mol%) and the molar fraction Fb (mol%) of the ethylene oxide adduct component of bisphenol A with respect to all glycol components of the core polyester. Isophthalic acid component,
By copolymerizing the ethylene oxide adduct of bisphenol A, it is possible to obtain a low-melting-point, low-crystalline polyester having good heat resistance, and to suppress voids generated in the core component. Can be achieved.
In particular, although a low melting point can be achieved only by using an isophthalic acid component mainly used for lowering the melting point, voids can be suppressed stably and, as a result, high color developability cannot be maintained. In the present invention, the suppression of voids was successfully stabilized by further copolymerizing an ethylene oxide adduct of bisphenol A with an isophthalic acid component. This ingredient is
At first glance, it has a low specific gravity characteristic that is opposite to high specific gravity due to its bulky molecular structure, but in the present invention, this is used as a low crystallization component, and a core component that triggers void generation It is believed that the crystallization of was suppressed.

The copolymerization ratio at this time is such that Fa + Fb is 1
Less than 0.0 (mol%) or Fb is 1.0 (mol%)
If the ratio is less than 2, the high color development aimed at by the present invention cannot be obtained stably, and if Fa + Fb exceeds 20.0 (mol%), or if Fb is 5.0 (mol%). If it exceeds, the desired spinnability of the present invention cannot be satisfied. A more preferred range is that Fa + Fb is 15.0.
(Mol%) or less, Fb is 3.0 (mol%) or more and 4.5
(Mol%) or less.

Further, the intrinsic viscosity of the core component polyester of the conjugate fiber of the present invention is made 0.35 or more lower than that of the sheath component polyester, so that the stress at the time of stretching is concentrated on the sheath component and the structure formation of the core component is suppressed. The effect of suppressing the occurrence of is obtained. On the other hand, the intrinsic viscosity of the polyester used for the core component is 0.1 from the viewpoint of the spinning property and the stability of the composite state.
It is preferably at least 56.

The polyester used for the sheath component is preferably polyethylene terephthalate of 0.91 or more from which high strength and abrasion resistance can be easily obtained, and the intrinsic viscosity is more preferably 1.0 or more.

Further, it is preferable that the polyester used for the sheath component contains substantially no copolymer component. Here, the phrase "contains substantially no copolymerization component" means that not more than 1% by weight of an ester-forming molecule besides the ester-forming molecule which is the main repeating unit before the completion of polyester polymerization. Say. In order to obtain high strength and abrasion resistance, the content of particles of the polyester polymer as the sheath component is preferably 2% by weight or less, more preferably 0.5% by weight.
The following is more preferred.

The composite fiber of the present invention preferably contains a pigment in the core component and / or the sheath component, or is preferably dyed. These make the effect of high color development of the present invention more apparent. Known pigments include inorganic pigments such as carbon black and iron oxide, and organic pigments such as phthalocyanine, perinone, and perylene. As the dye, a known disperse dye is used. Dyes and pigments can be combined.

In the case of original fibers using carbon black as the pigment, the L value is preferably 24 or less, more preferably 22 or less, in order to make the color tone black. When the composite fiber of the present invention is used for fishing nets, it is preferable that the L value is 24 or less in order to obtain high catchability without giving a caution to the fish. Also, when used as a dark curtain, setting the L value to 24 or less eliminates the feeling of white blur in the entire dark curtain, making it suitable as a light-shielding dark curtain. A more preferable carbon black content for satisfying both the L value and the strength is 0.1 to 0.7% by weight based on the whole fiber. 0.1
If the amount is less than 0.7% by weight, it is difficult to obtain the strength.

In the present invention, the effect when particles are contained for the purpose of increasing the specific gravity becomes more apparent. In this case, particles having a specific gravity of 2.5 or more are used. As such high specific gravity particles, metal particles such as barium, titanium, aluminum, iron, copper, and tungsten, and metal compounds such as titanium dioxide, zinc oxide, barium sulfate, and ferric oxide are preferably used. Among these particles, barium sulfate is particularly preferred because it suppresses polymer flow abnormalities in the polymer piping, the inside of the pack and the mouthpiece, and the aggregation in the polyester polymer, thereby preventing a decrease in operability.

The particle size and the particle size distribution of the particles to be contained are not particularly limited, but it is necessary that the yarn formability is good from the viewpoint of fiberization, and the particle size distribution is as small as possible. It is preferable to use uniform particles. For this purpose, the average particle size is preferably 1.0 μm or less.

Next, the method for producing the conjugate fiber of the present invention will be described.

In the production method of the present invention, a polyester system obtained by copolymerizing an ethylene oxide adduct of isophthalic acid and bisphenol A so as to satisfy the following formula: 10.0 ≦ Fa + Fb ≦ 20.0 1.0 ≦ Fb ≦ 5.0 Using a core component polymer which is a polymer and a sheath component polymer which is a polyester polymer which is not substantially copolymerized, a core-sheath composite spinning is carried out by incorporating particles in the core component polymer in an amount of 40% by weight or more. Thereby, it is possible to exhibit high functionality by the particles, stable and high color developing properties and good spinning properties, which are the objects of the present invention as described above.

An example of a method for producing a polyester used as a core component will be described. The copolymerized polyester having an intrinsic viscosity of 0.5 to 0.8 and the added particles obtained by a conventional polymerization method are respectively weighed, melt-kneaded by a twin-screw extruder or the like, and then extruded from a nozzle to form a pellet. Obtained by cutting into. At this time, the pigment can be mixed simultaneously or sequentially with the added particles. The particle-containing polyester cut into pellets may be dried as it is and used for spinning, or may be subjected to spinning after a high degree of polymerization by solid phase polymerization. Alternatively, at the time of spinning, it is also possible to weigh and mix with a separately prepared masterbatch mixed with a pigment at a high concentration.

On the other hand, the polyester used as the sheath component is preferably one obtained by subjecting a polyester obtained by a conventional polymerization method to solid-phase polymerization to increase the degree of polymerization. At this time, the polyester of the sheath component is preferably polyethylene terephthalate having an intrinsic viscosity of 1.0 or more, from which high strength and abrasion resistance can be easily obtained, and the intrinsic viscosity is more preferably 1.2 or more. Also,
It is preferable not to positively mix the copolymer component. At the time of spinning, a pigmented master batch in which a pigment is mixed at a high concentration separately prepared with the sheath component can be measured and mixed to be colored.

The intrinsic viscosity of the core polyester is preferably 0.35 or more lower than that of the sheath polyester.
By lowering the intrinsic viscosity of the core component, the stress at the time of stretching is concentrated on the sheath component, the fluidity of the core component is improved, and the effect of suppressing fine voids can be obtained.

In the production method of the present invention, it is necessary that the particle content of the polyester as the core component is 40% by weight or more. If it is less than 40% by weight, the high strength and high color developability targeted by the present invention cannot be obtained.

When the production method of the present invention is applied to a high specific gravity fiber, high specific gravity particles having a specific gravity of 3.0 or more are mixed in the conjugate fiber in order to easily obtain a target fiber specific gravity of 1.54 or more. Is preferably contained as a particle content of 15% by weight or more.

The polyester for the core component and the polyester for the sheath component are melted by separate extruders, respectively, and then guided to a composite spinning pack to form a composite stream in a composite spinneret in a desired composite form. And discharged from the spinneret.

The composite ratio of the core component / sheath component is preferably 20/80 to 70/30 in order to satisfy the target strength and the function of the blended particles in the present invention.

The discharged core-sheath composite yarn is cooled to a solidification temperature or lower. In this case, it is preferable that the cooling be performed by delay cooling through a heating atmosphere region provided immediately below the spinneret, then be introduced into the cooling region, blow cooling air, and pass through the spinning tube to form a yarn.

The temperature in the heating atmosphere is 120 to 350.
° C, the length may be 5 to 300 cm, and the conditions of this heating atmosphere range include the viscosity of the spun yarn, the thickness of the single fiber,
What is necessary is just to select according to setting conditions, such as a draft rate and the number of single fibers.

In the above-mentioned cooling zone, the temperature of 120 ° C.,
What is necessary is just to blow the gas below 15 degreeC at the speed of 15-50 m / min. The condition of the cooling region may be selected according to the setting conditions such as the viscosity of the spun yarn, the thickness of the single fiber, the draft rate, and the number of single yarns.

By setting the conditions in the heating atmosphere region and the cooling region within the above ranges, the cooling orientation pattern of the spun yarn can be made appropriate.

Passing through the heating atmosphere zone and the cooling zone,
A spinning oil agent is applied to the spun yarn cooled and solidified by cold air, wound around a rotating roller, and then once wound and stretched, or continuously stretched without winding. The spinning speed is 2,000 m / min.
500 m / min or less is preferable.

The spun composite fiber yarn is drawn, heat-treated,
Relaxed and wound up.

As-spun fibers have low strength and require stretching. Stretching is preferably performed in two or more stages in terms of spinning properties and high strength.

The stretching temperature is set so that the core component polyester is not sufficiently heated to prevent voids from increasing and the specific gravity from becoming difficult to be increased, while the crystallization of the core progresses and the stretching of the core after the second stage. From the viewpoint of preventing voids from being formed and lowering the specific gravity, the temperature of the yarn to be subjected to the first-stage drawing is set at 10 ° C.
It is preferable that the temperature be 0 ° C or higher and 150 ° C or lower.

The drawn composite fiber yarn is then heat-treated. Fine voids generated in the core in the stretching step by heat treatment are collected. At this time, the heat treatment temperature should be at least -20 ° C of the melting point of the core component and at least 20 ° C lower than the melting point of the sheath component, so that the state of void formation is stable against fluctuations in spinning conditions such as fluctuations in the heat treatment temperature. However, it is preferable because a certain high color developing quality can be maintained.

The heat-treated composite fiber yarn is relaxed and wound up. By performing the relaxation treatment before winding, the stress applied to the core portion can be reduced, the fine voids can be further reduced, and the color development can be sufficiently achieved. For this purpose, the relaxation rate is preferably 2% or more.

[0045]

The present invention will be described below in detail with reference to examples. In addition, the physical property in an Example was measured as follows.

[Specific gravity] It was measured using a specific gravity bottle.

[Strength] After leaving the sample in a temperature control room at 20 ° C. and 65% RT for 24 hours or more, a test length of 25 cm and a take-up speed of 3 were measured using a Tensilon tensile tester manufactured by Orientec Co., Ltd.
An SS curve was obtained at 0 cm / min, and the strength and elongation were calculated.

[Intrinsic viscosity] The particles were removed by centrifugation.
A sample having a polymer amount of 8 g was dissolved in 100 ml of orthochlorophenol, the solution viscosity (η) was measured at 25 ° C. using an Ostwald viscometer, and the intrinsic viscosity (IV) was calculated by the following approximate formula.

IV = 0.0242 · ηrp + 0.2634 where ηrp = (t × d) / (t ₀ × d ₀ ) t: Fall time of solution (second) t ₀ : Fall time of orthochlorophenol (second) d: density of solution (g / cc) d ₀ : density of orthochlorophenol (g / cc) [L value] The color tone (L value) of the winding package was measured by an SM color computer manufactured by Suga Test Instruments Co., Ltd. .

(Examples 1 to 9 and Comparative Examples 1 to 5) Isophthalic acid copolymerization rate (Fa) and ethylene oxide adduct of bisphenol A (Fb) with intrinsic viscosity of 0.66
Of polyethylene terephthalate (PET) with various changes as shown in Tables 1-2, carbon black was added to the dried chips in an amount of 0.2% by weight and high specific gravity particles having an average particle size of 0.7 μm and a specific gravity of 4%. The melt was kneaded with a twin-screw extruder while adding and mixing the precipitated barium sulfate in the amount shown in Table 1 and then discharged from a 3.0 mmφ die, cooled and cut to obtain a core component. A chip to be used was obtained. However, only in Example 8, titanium oxide having an average particle diameter of 0.5 μm and a specific gravity of 3.9 was used as high specific gravity particles.
A core chip was prepared by melt-kneading by weight%. Further, the core component chip was dried with a rotary vacuum dryer at a temperature of 110 ° C. for 12 hours or more to reduce the moisture content of the chip to 0.004% or less. The intrinsic viscosity was 0.60 to 0.62.

The polyester used as the sheath component is polyethylene terephthalate (PE) having an intrinsic viscosity of 1.30 and a water content of 0.003% or less, which is obtained by ordinary solid-state polymerization.
T) A chip and a soaked master batch containing 10% by weight of carbon black were continuously weighed and mixed at a ratio of 45: 1 to prepare a chip. The ratio of carbon black in the sheath component was 0.22% by weight. However, only Comparative Example 4 used polyethylene terephthalate having an intrinsic viscosity of 0.92.

The polymer for the core and sheath components is melted in separate extruder type spinning machines and then guided into a composite spin pack,
From the core-sheath composite spinneret, the fiber was spun into a concentric composite fiber. The core / sheath composite ratio was 40/60 by weight. The melting point of the core component is + 30 ° C., and that of the sheath component is 29 ° C.
Each was melted at 0 ° C. and spun by a composite spin pack heated to 290 ° C.

The spinneret has two rows of circular holes and a hole diameter of 0.9 m.
mΦ, number of holes is 60 holes, 30 cm directly below the base
And heated so that the in-cylinder atmosphere temperature became 320 ° C. The ambient temperature in the cylinder is 10c from the base
m and a position 1 cm away from the outermost yarn.

An annular chimney having a length of 40 cm was attached to the bottom of the heating cylinder, and a cool air of 40 m / min was blown from the periphery of the yarn at 25.degree. Next, after applying the oil agent, the yarn speed was controlled by a take-up roller of 560 m / min, and then the film was continuously drawn without being wound once.

The stretching was performed by three pairs of Nelson-type rollers at a draw ratio of 3.5 times at the first step and 1.5 times at the second step.
After the step stretching, the film was wound with a 3% relaxation between the next Nelson rollers. The take-up roller temperature was set to 130 ° C., the first-stage stretching was performed between the take-up roller and the first stretch roller heated to 170 ° C., and the first stretch roller and the second stretch roller heated to the temperature shown in Table 1 Between two
Step stretching was performed. The next Nelson roller was used without heating. The amount of polymer discharged was adjusted so that the total fineness of the drawn yarn was 1200 denier. The winding amount was 5 kg.

In addition, between the take-up roller and the first drawing roller, 1.5 kg / cm ² of compressed air was sprayed on the composite fiber yarn.

The evaluation result of the conjugate fiber thus obtained was
It is shown in Tables 1-2.

[0058]

[Table 1]

[Table 2] In each of the examples, the strength was 4.5 g / d or more and the specific gravity was 1.54.
As described above, the L value of 24 or less is satisfied (Table 1), but Comparative Example 1 in which the particle content of the core component is low and the particle content of the entire fiber is low.
Has a low specific gravity, and Comparative Examples 2 and 3 use a polyester having a copolymerization ratio not satisfying the present invention as a core component, and therefore have low color developability (Table 2). In Comparative Example 4, the intrinsic viscosity difference between the core component and the sheath component was less than 0.35, and the L value was high even when the temperature of the second stretching roller was high. In Comparative Example 5, since the copolymerization ratio was too high, the spinnability was poor and the yarn could not be sampled (Table 2).

When the L value of the package was changed by opening and closing the door of the casing for keeping the second stretching roller warm, a phenomenon of a clear change was observed in Comparative Examples 2, 3, and 5. It was lacking in stability of high color development (Table 2).

When the TiO ₂ of Example 8 was used as the high specific gravity particles, the polymer pipe tended to be blocked by the accumulation of particles in about 5 days.

[0061]

The composite fiber of the present invention has high strength and high color development while containing particles at a high concentration. In addition, the present composite fiber can be obtained in a good thread-making state. In particular, it is extremely useful as a fiber for general industrial use such as fishing nets, ropes, curtains, curtains, etc., which require a high specific gravity, and a fiber for interior decoration.

Claims (5)

[Claims] 1. A core-sheath type conjugate fiber in which the core component and the sheath component are polyester polymers, wherein the conjugate fiber has a particle content of 15% by weight or more, and the core component polyester is isophthalic acid as a copolymerization component. And a copolymer fiber comprising an ethylene oxide adduct of bisphenol A at a molar fraction represented by the following formula, wherein the intrinsic viscosity of the core component polyester is 0.35 or more lower than that of the sheath component polyester. 10.0 ≦ Fa + Fb ≦ 20.0 1.0 ≦ Fb ≦ 5.0 (wherein, Fa is the mole fraction (%) of isophthalic acid with respect to all the acid components of the copolyester, and Fb is the total glycol of the copolyester. The molar fraction (%) of the ethylene oxide adduct of bisphenol A with respect to the components.) 2. The conjugate fiber according to claim 1, wherein the core component and / or the sheath component contain a pigment. 3. A dye according to claim 1, wherein the dye is dyed.
The conjugate fiber according to the above. 4. The high specific gravity particles are barium, titanium, aluminum, iron, copper, tungsten, titanium dioxide, zinc oxide,
The composite fiber according to any one of claims 1 to 3, wherein the fiber is at least one selected from the group consisting of barium sulfate and ferric oxide. 5. A core component polymer which is a polyester polymer obtained by copolymerizing an ethylene oxide adduct of isophthalic acid and bisphenol A at a mole fraction represented by the following formula, and a sheath component which is a substantially non-copolymerized polyester polymer. A method for producing a conjugate fiber, comprising using a polymer, comprising a core component polymer containing particles in an amount of 40% by weight or more and subjecting the core to a sheath-composite spinning, stretching, heat treatment, and relaxation treatment. 10.0 ≦ Fa + Fb ≦ 20.0 1.0 ≦ Fb ≦ 5.0 (Fa is the molar fraction (%) of isophthalic acid with respect to the total acid component of the copolymerized polyester, and Fb is bisphenol with respect to the total glycol component of the copolymerized polyester. It is the mole fraction (%) of the ethylene oxide adduct of A.)