JP2002371435A - Method for producing conjugate fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber having both of high sedimentation property and sufficient fiber strength free from problem on net production processing and having excellent endurance and weather resistance without lowering strength even when used as a fishing net for a long period. SOLUTION: In this method for producing a conjugate fiber, out conjugate spinning is carried by using a thermoplastic polymer having >=1 specific gravity and containing 50-85 wt.% non-lead-based inorganic fine particles having >=3 specific gravity as a core component and using a polyester as a sheath component, heat-drawing the resultant conjugate fiber and then heat-treating the drawn fiber at a temperature not lower than (melting point or softening point-60) deg.C of thermoplastic polymer of the core component and not higher than (melting point or softening point-10) deg.C of the sheath component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conjugate fiber having a high specific gravity and a high strength and suitable for use in industrial materials, and particularly to a conjugate fiber suitable for fishing nets which has no problem of marine environmental pollution and has excellent durability. .

[0002]

2. Description of the Related Art Conventionally, as a fishery material represented by fishing nets, fishing ropes, etc., it is superior to natural fiber products in terms of water resistance, corrosion resistance, strength, abrasion resistance and durability. Synthetic resin fiber products exhibiting such properties have been used. However, the water content is lower than that of natural fiber products, and the specific gravity is relatively low, so that the sedimentation in seawater and the shape retention against tidal current are unsatisfactory, and there are many restrictions on its use. Was.

[0003] Various proposals have been made to overcome such difficulties, but the technique of increasing the specific gravity of fibers and ropes themselves to increase their sedimentation in water has received the most attention.
As a means for increasing the specific gravity of fibers and ropes themselves, there is a technique of kneading metallic lead or a compound thereof into fibers. There is a possibility that it may fall off from seawater or elute into seawater during use as a fishing net, causing a problem of lead pollution. Further, when the used fishing net is discarded, there is a possibility that a similar pollution problem may occur such that harmful components including lead remain after incineration, and there is a problem that it cannot be easily disposed of. On the other hand, as a means not using a lead compound, for example, vinylidene chloride-based fibers having a relatively large specific gravity have been used. However, with the development of the net-making technology, high-strength fibers that can be stably provided for high-speed net-making. As a result, vinylidene chloride fiber has a problem of insufficient strength. In addition, fishing nets made of vinylidene chloride fiber also have a problem in that incineration is difficult due to the generation of hydrogen chloride gas during incineration. in this way,
Not only high specific gravity but also high strength and non-polluting properties are required.

[0004] Various proposals have been made to meet such demands, and as one of the means, a fiber made of a combination of a resin exhibiting high strength by drawing and a high specific gravity powder is considered. Specifically, (1) a fiber obtained by uniformly dispersing a high specific gravity powder such as zinc or lead in a synthetic filament (for example, JP-B-51-37378, JP-A-56-61936, JP-A-61-61936) No. 613) and (2) fibers obtained by mixing and dispersing a high specific gravity powder in a resin having a low softening point and further mixing the mixture with a resin for imparting strength (for example, Japanese Patent Publication No. 57-20407). (3) Cored fibers (for example, Japanese Patent Application Laid-Open No. 58-4819) in which a mixture of a low softening point resin and a high specific gravity powder is used as a core layer and a resin layer for imparting strength is used as a sheath layer. .

However, the proposal (1) has a drawback that when the specific gravity of the fiber is sufficiently increased, the amount of powder added increases, and the strength of the fiber itself decreases in inverse proportion to the improvement in the specific gravity. . Further, in the proposal of (2), the low softening point resin mixed with the powder is extended in the drawing direction of the fiber to be partially and irregularly buried and unevenly distributed, and thus the production of the fiber is complicated. In addition, there is a restriction that the amount of the high specific gravity powder to be contained with the same fiber diameter as compared with the proposal of the above (1) is naturally reduced, so that the degree of increase in specific gravity is significantly restricted. Furthermore, the proposal (3) not only has disadvantages such as a decrease in yarn quality and a decrease in durability due to an increase in interfacial distortion due to incompatibility at the interface between different kinds of resins, but also has a problem in that a resin having a low softening point has However, since the high specific gravity powder is not uniformly dispersed, only a powder having a high fiber fineness can be obtained.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide both high sedimentability and sufficient fiber strength without any problem in net making, and excellent durability which does not decrease in strength even when used as a fishing net for a long time. To provide a fiber having weather resistance.

[0007]

That is, the present invention provides a thermoplastic polymer having a specific gravity of 1 or more containing 50 to 85% by weight of lead-free inorganic fine particles having a specific gravity of 3 or more, and a polyester sheath. After the composite spinning as a component and heat drawing, heat treatment is performed at a temperature of not less than (melting point or softening point -60) ° C of the thermoplastic polymer of the core component and not more than (melting point or softening point of -10) ° C of the polyester of the sheath component. A method for producing a conjugate fiber, characterized in that:

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The composite fiber obtained by the present invention is
2. Specific gravity of 1.5 or more, toughness of 60 or more, and strength of 3.
5 g / denier or more. When the specific gravity of the conjugate fiber is less than 1.5, it is difficult to achieve high sedimentation in seawater and the shape retention of the fishing net, and when the strength is less than 3.5 g / denier, high speed is obtained. It is not practical because the fibers are damaged during net making. The toughness is indicated by the product of the strength and the elongation. When the value is less than 60, that is, when the elongation is low, the fatigue and durability against tides and waves are low, and the fishing net is not used. From such a viewpoint, a fiber having a specific gravity of 1.55 or more, a strength of 4.0 g / denier or more, and a toughness of 80 or more is desired.

In the present invention, in order to increase the specific gravity of the fiber, it is essential to contain lead-free inorganic fine particles having a specific gravity of 3 or more. When using inorganic fine particles having a specific gravity of less than 3, it is necessary to increase the content of the inorganic fine particles in the fiber and to increase the composite ratio of the core component in the composite fiber in order to achieve the target fiber specific gravity. , Even if the fiber of the desired fiber specific gravity is obtained, spinnability,
Since processability such as stretchability is poor and only a fiber having low fiber strength can be obtained, it is not suitable for use as a fishing net.

Examples of the type of the inorganic fine particles include fine particles of a lead-free metal or fine particles of a compound thereof. "Lead-free metal" refers to metals other than metals that are extremely susceptible to environmental problems, such as lead and tin. Specifically, titanium, iron, copper, zinc, silver, barium, zirconium,
Examples thereof include metals such as manganese, antimony, and tungsten, and oxides and salts thereof. In the present invention, the inorganic fine particles can be appropriately selected from such metals, oxides, salts, and the like as desired, but the specific gravity of the fine particles, the dispersibility of the fine particles in the polymer, and the thermal decomposition of the polymer are reduced. It is preferable to use titanium dioxide, iron oxide, barium sulfate or the like from the viewpoint of non-catalytic property without promoting. Further, not only one kind of the inorganic fine particles but also two or more kinds can be used in combination.

The content of the inorganic fine particles in the core component is 5%.
It must be 0-85% by weight. The content is 5
When the content is less than 0% by weight, the ratio of the core component in the conjugate fiber must be increased in order to obtain the desired fiber specific gravity, and only a fiber having a low fiber strength can be obtained. On the other hand, if the content exceeds 85% by weight, the polymer melt fluidity at the time of spinning becomes poor, and yarn breakage frequently occurs.

The average particle diameter of the primary particles is preferably 5 μm or less. Particle size is 5
If it exceeds μm, thread breakage and fluff will tend to occur frequently during spinning and stretching. If the particle size is too small, when adding the fine particles to the polymer, heat agglomeration occurs due to the heat generated during the molding process, and conversely, the particles become coarse. Agglomeration is likely to occur and troubles such as clogging of lines are likely to occur frequently. Therefore, the average particle size of the primary particles of the inorganic fine particles is 0.1.
It is preferably at least 05 μm.

First, the case where iron oxide is used as the inorganic fine particles will be described. Iron oxide includes black magnetite, ie magnetite (Fe3 O4), brown γ-type hematite, red-brown α-type hematite, and the like. For fishing net fibers such as fixed nets, if the hue is black, the fish is alert. Therefore, it is preferable to use magnetite which can give a good result to the catch and exhibit black color. When magnetite is used in combination with other inorganic fine particles, if 20% by weight or more of the whole inorganic fine particles to be used is magnetite, the dyeing treatment or the like can be simplified or omitted. There is nothing wrong with using polyester.

The particle shape of the iron oxide is spherical, octahedral, hexahedral, polyhedral, etc., and any shape can be used. Is most desirable and desirable. In particular, when a large amount of inorganic fine particles are added to a polymer, the use of spherical fine particles has a remarkable effect, and the occurrence of filter clogging during spinning due to agglomeration is small, and yarn breakage during spinning and drawing. Also less.

Further, the iron oxide may be subjected to a surface coating treatment with an organic or inorganic compound such as silica or ferrite, and if fine particles subjected to the surface coating treatment are used, the heat of the polymer may be reduced. Decomposition is suppressed,
It is preferable because the fine particle dispersibility can be further improved.

Iron oxide may be used alone as the inorganic fine particles contained in the core component. However, if the content exceeds 50% by weight in the core component, iron oxide having an appropriate particle shape and particle diameter is used. Even when used, contamination may occur due to thermal agglomeration in the line during melt extrusion, and in severe cases, troubles such as pipe clogging may occur. It is preferable to use iron oxide as the inorganic fine particles contained in the core component and to use iron oxide in combination with other fine particles in order to obtain a content exceeding 50% by weight. Particularly when producing fine denier yarn, the residence time in the molten polymer line becomes longer,
This may cause line clogging troubles.

Other fine particles used in combination with iron oxide have a specific gravity of 3
As described above, it is preferable to select a primary particle having an average particle diameter of 5 μm or less, having little thermal cohesion, and not being expensive. Preferred examples are titanium dioxide, zinc oxide, barium sulfate, alumina, ferrite,
Examples thereof include lithopone, copper oxide, and magnesium oxide. Among them, titanium dioxide is particularly preferable in terms of dispersibility of the inorganic fine particles in the core component. The mixing ratio when iron oxide and titanium dioxide are used in combination is such that the total content with respect to the core component is 50-8.
If the amount is within the range of 5% by weight, the desired fiber can be obtained without any significant troubles, such as good spinnability and stretchability, even if arbitrarily changed. An example of a suitable mixing ratio is iron oxide / titanium dioxide = 20/80 to 70/30 (weight ratio). For example, when the total amount of fine particles in the core component is 7
In the case of 0% by weight, iron oxide is 30% by weight and titanium dioxide is 40% by weight, and when the total amount is 60% by weight, iron oxide is 30% by weight and titanium dioxide is 30% by weight.
The hue of the obtained fiber is preferable.

As described above, the content of the fine particles in the core component is as high as 50% by weight or more, and when iron oxide is added in high content therein, titanium dioxide is added in combination. It is clear that the target fiber can be obtained in a state where there is no trouble such as line clogging during melt extrusion, the dispersibility in the core component is good, the yarn breakage during the process is small, and the A rating is high. This is the first finding that the inventors have made in various studies.

Next, the case where titanium dioxide is used as the inorganic fine particles will be described. An object of the present invention is to provide a fishing net fiber having both excellent mechanical properties and a high specific gravity, and at the same time to provide a fishing net fiber capable of coping with various hues. However, as described above, when a high content of colored fine particles such as iron oxide is used as the inorganic fine particles, it is difficult to freely change the hue. However, when titanium dioxide is used as the inorganic fine particles, titanium dioxide is used. Is white, and such white fine particles are added to the core component, and the desired hue can be obtained without disturbing the color of the core component by blending a desired color pigment or the like with the polyester as the sheath component. Can be expressed.

Titanium dioxide has three forms, anatase type, rutile type, and brookite type, depending on the crystal form.
Generally, anatase type and rutile type are used as pigments. In particular, an anatase type is mainly used for synthetic fibers due to the relationship between the hardness affecting the abrasion in the process and the dispersibility in a solvent or a dispersion medium, but the specific gravity is high and the light resistance is excellent. In this respect, it is preferable to use the rutile type in the present invention. in this case,
The rutile type has a higher Moth hardness than the anatase type, and there is a concern that problems such as abrasion in the process may occur.However, in the composite fiber of the present invention, the core component containing inorganic fine particles is sheathed. Since it is substantially covered with the components, there is no problem such as abrasion of the nozzle cap at the time of spinning or abrasion damage of guides and rollers during the working process.

Even when titanium dioxide is added at a high content in a polymer as compared with other inorganic fine particles, thermal aggregation does not easily occur during melt extrusion of the polymer, and contamination due to contamination in the molten polymer line is caused. Clogging hardly occurs, filter clogging during spinning is small, and yarn breakage during spinning / drawing is also small. The surface of the titanium dioxide may be coated with an inorganic or organic compound such as titanium, alumina, or silica, and heat resistance and fine particle dispersibility can be obtained by using fine particles coated with the surface. Is further preferred since it can be further improved.

Titanium dioxide may be used alone,
It may be used in combination with other fine particles having a specific gravity of 3 or more and an average particle diameter of 5 μm or less. Even if the fine particles used together tend to cause the above-described problem of thermal aggregation, improvement in dispersibility can be expected by using titanium dioxide at 15% by weight or more, particularly at 40% by weight or more. As other fine particles, for example, zinc oxide, alumina, barium sulfate, lithopone, magnesium oxide, and the like, which are less toxic than tin oxide (tinite), can be used. In addition, since titanium dioxide easily promotes deterioration of the thermoplastic polymer constituting the core component by excitation of titanium atoms by ultraviolet rays, it is preferable to use an antioxidant together.

In the present invention, the thermoplastic polymer constituting the core component needs to have a specific gravity of 1 or more. When the specific gravity of the thermoplastic polymer is less than 1, in order to increase the specific gravity of the fiber, the content of the fine particles must be increased, which further disturbs the process condition.

In addition, when a polymer containing a high content of inorganic fine particles is generally melt-spun, a problem arises in that the spinning condition is extremely deteriorated due to a unique viscous behavior. Such a viscous behavior indicates a so-called thixotropic property in which the melt viscosity is high under low shear, while the melt viscosity is low under high shear. The shear rate is in the order of 100 sec -1 at the inlet where the polymer containing the inorganic fine particles at a high content is supplied to the spinning pack, but is 10 2 sec-in the flow dividing plate distributed to the nozzle holes. With a nozzle which is extruded by being merged with an order of 1 and further with a polymer which is a sheath component, it reaches an order of 10 3 sec -1. A polymer stream having a remarkable thixotropic property causes a large unevenness in the melt viscosity under such a large change in the shear rate, the discharge amount around a single nozzle fluctuates, and the balance between the core and the sheath is lost. It will be difficult. As a result of studying this point in the present invention, it has been found that the melt viscosity of the polyester as the core component and the sheath component containing a large amount of inorganic fine particles is important. That is, the shear rate at 300 ° C. is 1.0 × 1
The ratio (a / b) of the melt viscosity a of the core component to the melt viscosity b of the polyester as the sheath component is in the range of 5.0 to 0.05 in the entire range of 01 to 5 × 10 2 sec -1. Is desirable. Only when the melt viscosity ratio of the core component and the sheath component is within such a range, the merging of the core component and the sheath component containing a large amount of inorganic fine particles is performed smoothly, and the operability such as composite spinning and stretchability is also improved. . In addition, the inorganic fine particles are uniformly dispersed in the thermoplastic polymer constituting the core component, so that the desired composite fiber can be produced with good operability. The preferred melt viscosity ratio (a / b) is 1.5 to
0.8.

In order to adjust the melt viscosity ratio (a / b), it is desirable to first set the intrinsic viscosity of the polymer of the sheath component after suppressing the thixotropic properties of the core component as much as possible. As means for suppressing the thixotropic property of the core component,
To increase the particle diameter by selecting a spherical one to reduce the surface area of the inorganic fine particles, or to reduce the addition ratio of the inorganic fine particles by selecting one having the highest specific gravity as possible; aptitude of the molecular weight and melting point of the polymer of the core component Addition of a coupling agent to improve the affinity between the polymer of the core component and the inorganic fine particles.

The conditions described above, ie, specific gravity, melting point,
As thermoplastic polymers satisfying the melt viscosity, polyamides such as nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, etc .; polyethylene terephthalate
And polyesters such as polybutylene terephthalate and polyhexamethylene terephthalate.

When the inorganic fine particles are added at a high level as in the present invention, the wettability between the inorganic fine particles and the polymer and the dispersibility in the polymer are good, and the spinnability and the stretchability are the best. It is preferable to use a thermoplastic polymer, and from this viewpoint, in the present invention, it is preferable to use a polyamide, particularly a polyamide containing nylon 6 as a main component. As a preferred example, the degree of polymerization of nylon 6 has a number average molecular weight of about 22,000 or less, especially 20,000 or less.
It is preferably at least 000. If the degree of polymerization is too high, the melt viscosity of the core component to which inorganic fine particles are added at a high level becomes too high, which may cause troubles or poor dispersion of the inorganic fine particles. Further, when melt-extruding a polymer to which inorganic fine particles are added in a high amount to form a fiber, if the melt viscosity is too high, troubles in equipment are liable to occur frequently and, at the same time, thread breakage frequently occurs, which is not preferable. On the other hand, if the degree of polymerization is too low, the melt viscosity becomes too low with respect to the sheath component, making it difficult to form the core-sheath interface.

In addition, when a polyamide is used as the thermoplastic polymer constituting the core component, the core component preferably has a water content of 500 ppm or less, particularly 300 ppm or less. When a large amount of inorganic fine particles are contained in a water-absorbing polymer such as polyamide, when the moisture content is high,
There is a problem that the fluidity is extremely lowered at the time of melting and the process condition is significantly impaired. In general, polyamide is used with a water content of about 500 to 1000 ppm, but in the present invention in which a large amount of inorganic fine particles are contained, special consideration must be given. Further, the polyamide may be copolymerized with a small amount of the third component, or may contain small amounts of additives, stabilizers and the like.

Although the main purpose of use of the composite fiber of the present invention is for fishing, fishing nets are used outdoors, so weather resistance over time is an important issue. Anything that causes a drop and poses a practical problem cannot be used. When a polyamide containing a large amount of the above-mentioned inorganic fine particles is used as a core component, there is a possibility that a decrease in fiber strength occurs when the polyamide is used as a fishing net for a long time. 0.01
By adding a copper salt such as copper iodide as a heat stabilizer in a range of not less than 0.1% by weight, especially not more than 0.1% by weight and not more than 2% by weight, a decrease in fiber strength over time does not cause a practical problem. Be improved.

In the present invention, the polyester which is a sheath component is preferably a polyester containing polyethylene terephthalate or polybutylene terephthalate as a main component. Further, a small amount of the third component may be copolymerized in such a polyester, for example, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid,
4'-diphenylmethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 4,4'-diphenylisopropylidenedicarboxylic acid, 1,2-diphenoxyethane-4 ', 4 "-dicarboxylic acid, anthracenedicarboxylic acid, 2, 5-pyridine dicarboxylic acid, diphenoxy ketone dicarboxylic acid, 5-sodium sulfoisoltalic acid, dimethyl 5-sodium sulfoisophthalate,
Aromatic dicarboxylic acids such as tetrabutylphosphonium sulfoisophthalic acid; malonic acid, succinic acid, adipic acid,
Aliphatic dicarboxylic acids such as azelaic acid and sebacic acid; alicyclic dicarboxylic acids such as decalin dicarboxylic acid and cyclohexanedicarboxylic acid; hydroxy such as β-hydroxyethoxybenzoic acid, p-oxybenzoic acid, hydroxypropionic acid and hydroxyacrylic acid Carboxylic acids; carboxylic acids derived from these ester-forming derivatives; aliphatic lactones such as ε-caprolactone; aliphatic diols such as trimethylene glycol, hexamethylene glycol, neopentyl glycol, diethylene glycol, and polyethylene glycol; hydroquinone catechol , Naphthalene diol, resorcinol, bisphenol A, bisphenol A ethylene oxide adduct, bisphenol S, bisphenol S ethylene oxide adduct, etc. And aliphatic diols such as cyclohexanedimethanol. One or more of these third components may be copolymerized.

The polyester of the present invention may further comprise trimellitic acid within a range where the polyester is substantially linear.
Polyvalent carboxylic acids such as trimesic acid, pyromellitic acid and tricarballylic acid; glycerin, trimethylolethane,
Polyhydric alcohols such as trimethylolpropane and pentaerythritol may be contained. The polyester may contain additives such as a fluorescent whitening agent and a stabilizer. In particular, it is important to maintain the weather resistance of the entire conjugate fiber, that is, the strength retention over time, at a better level.
Bonblack may be contained in the polyester which is the sheath component.

The intrinsic viscosity [η] of the polyester is preferably 0.7 or more. The limiting viscosity is 3 in an equal weight mixed solvent of phenol / tetrachloroethane.
This is a value measured at 0 ° C. In ordinary clothing fibers,
The intrinsic viscosity of polyethylene terephthalate is 0.60
In contrast to the use of about 0.65, in the present invention, a polyester having a higher degree of polymerization than a normal degree of polymerization is used in order to develop the desired fiber strength. When the intrinsic viscosity is less than 0.7, the fiber specific gravity is 1.5 or more, the fiber strength is 3.5 g / denier or more, and the toughness is 6 or more.
It is difficult to satisfy any of the conditions of 0 or more. If the composite ratio of the sheath component and the core component is changed and the sheath component is made rich, the fiber specific gravity cannot reach the target level. As a result, the fiber strength and toughness did not reach the target levels. That is, by using a polyester having an intrinsic viscosity of 0.7 or more as the sheath component, one satisfying all of the fiber strength, toughness, and specific gravity was obtained.

The limiting viscosity in the present invention is the limiting viscosity of polyester which is a sheath component in the fiber after spinning. That is, when the degree of polymerization is reduced by thermal decomposition or hydrolysis during spinning, it is needless to say that the fiber must be formed using a polyester having a somewhat higher degree of polymerization in consideration of the degree.

In the present invention, a colorant is added to the polyester which is a sheath component to obtain a hue suitable for fishing net use as described above, and the polyester has a heat resistance that can withstand the melt spinning temperature of the polyester. Organic pigments and inorganic pigments can be used as appropriate. Specifically, carbon black, anthraquinone brown colorant, anthraquinone purple colorant, benzoquinone red colorant, and ordinary colorant for original use can be used, and these colorants can be used alone or in combination of two or more. Addition rate of 0.1 to 5% by weight in combination
May be blended with the polyester. When the amount of the colorant is less than 0.1% by weight, it is difficult to obtain a netted yarn for fishing nets exhibiting a sufficient “hue” or “gloss”, and the amount exceeds 5% by weight. This is not preferred because the reduction in strength is increased.

In particular, most of the hue of the currently required dipped yarn for fishing nets is black. In such a case, carbon black is added to the sheath component polyester in an amount of 1 to 3% by weight.
It is preferable to add. Carbon black has an effect of absorbing ultraviolet rays and preventing deterioration of polyester, and can prevent weather resistance of fibers, that is, a decrease in fiber strength over time, and can exhibit a synergistic effect. It is also possible to dye the fibers in a desired color after forming the fibers.

The conjugate fiber of the present invention has a cross-sectional shape in which the core component containing the above-mentioned inorganic fine particles is substantially covered with the sheath component polyester. Here, the “substantially covered cross-sectional shape” indicates that 60% or more, preferably 80% or more of the fiber surface circumference is occupied by the sheath component. In the present invention, the core component is completely covered with the sheath component in order to further prevent friction of the guide and the roller and yarn breakage in the spinning / drawing process and to solve the problem of interface delamination between the core component and the sheath component. Preferably, the cross-sectional shape includes a concentric core-sheath type, an eccentric core-sheath type, and the like.

The composite weight ratio of the core component and the sheath component is the former /
The latter = 20/80 to 70/30, preferably the former / latter = 20/80 to 50/50. If the composite weight ratio of the sheath component is too small, the fiber strength is reduced. On the other hand, if the composite weight ratio of the sheath component is too large, the effect of increasing the fiber specific gravity cannot be sufficiently exhibited.

The method for obtaining the conjugate fiber of the present invention is not particularly limited, but the polyester, which is the sheath component, and the core component are heated and melted in separate melting systems, and each is heated in a conventional extrusion spinning apparatus. To a spinneret, the two components are combined just before the spinneret according to a desired core-in-sheath composite shape, the extruded yarn is wound, further stretched and heat-treated. In addition, a method of immediately stretching without being wound after being extruded from a spinneret, or a method of extruding from a spinneret, winding at high speed, and forming a product as it is can also be used.

Specifically, a so-called POY or FOY stretching method in which the film is taken up at a speed of about 4000 m / min or less and then wound and then stretched, or a spin-drawing method in which the film is stretched without winding, or 4000 m / min. The above-described DSY method of taking out at a high speed, or a method of providing a heater between a nozzle and a taking-off roller in the DSY method, and taking out while stretching is adopted. Among them, preferred are 300 to 4000 m / min, and more preferred is 600 to 4000 m / min.
This is a method of drawing and stretching at 2000 m / min (either FOY or spin draw), followed by heat treatment. When the speed is less than 300 m / min, the degree of orientation of the undrawn yarn is low, and it is necessary to increase the draw ratio to obtain a desired fiber strength. As a result, many voids are generated in the fiber, High specific gravity may not be achieved sufficiently. On the other hand, in the case where the film is taken out in a so-called DSY region where the speed exceeds 4000 m / min, the target physical properties may be obtained without performing the stretching heat treatment operation. It is inevitable that the fiber strength is reduced as compared with the method.

The stretching may be one-stage stretching or two-stage stretching. Further, since the stretching ratio varies depending on the spinning speed, it cannot be uniquely specified, but it is preferable to employ a ratio of about 75 to 85% of the ratio leading to breakage. In particular, a characteristic point in the production of the fiber of the present invention is a heat treatment after drawing.
That is, the thermoplastic polymer constituting the core component has a melting point of not less than (melting point -80) ° C.
5) It is characterized in that the heat treatment is performed at a temperature of not more than ℃. If the heat treatment temperature is set higher within a range in which fluff is not generated, a fiber having a higher specific gravity of the fiber, and having higher strength and toughness can be obtained. By heating at a temperature close to or higher than the melting point of the thermoplastic polymer constituting the core component, the voids around the inorganic fine particles in the fiber generated during drawing while the fiber is contracted are repaired to some extent. It is also presumed that the crystallization of the sheath component that expresses the mechanical properties of the fiber is promoted by increasing the heat treatment temperature.

When the heat treatment temperature exceeds (melting point -5) ° C. of the polyester as the sheath component, thread breakage occurs frequently, and when the temperature is lower than (melting point −80) ° C. of the thermoplastic polymer constituting the core component, the above-mentioned case occurs. It is difficult to sufficiently repair the voids around the inorganic fine particles. A preferred heat treatment temperature is not lower than (melting point -60) ° C of the thermoplastic polymer constituting the core component and not higher than (melting point -10) ° C of the polyester as the sheath component. As a specific example, when the thermoplastic polymer constituting the core component is nylon 6, the heat treatment temperature is 160 ° C. or more and 255 ° C.
It is desirable to make the following.

Further, in order to stabilize the stretching and to suppress the generation of voids around the inorganic fine particles, the heating at the time of stretching is performed in addition to a contact heating method such as a heat roll or the like. It is preferable to use a contact heating method in combination. In this method, the core component is stretched at a temperature sufficiently higher than the melting point of the thermoplastic polymer constituting the core component in a state in which the fluidity of the core component is increased. 350 ° C or more when
It is preferable to perform heat stretching using a temperature steam jet of preferably 400 ° C. or more, more preferably 430 ° C. or more. Incidentally, the temperature of the steam jet does not indicate the heat treatment temperature itself in the present invention.
The heat treatment temperature in the present invention means a contact heating temperature. From these findings, it is necessary that the melting point of the thermoplastic polymer constituting the core component be higher than the melting point of the polyester which is the sheath component by 20 ° C. or more, particularly 30 ° C. or more, and the melting point of the thermoplastic polymer is inevitably 200 ° C. or higher is required.

The conjugate fiber of the present invention can be used for a wide variety of applications either alone or in combination with other fibers. When mixed with other fibers, mixed fibers, plying, ply twisting, interweaving, interlacing, and any other means can be used, and the obtained fabric is subjected to various post-processing if necessary. It can be used for various applications. Preferred applications of the composite fiber of the present invention include gill nets, trawl nets, trawl nets, and constructions that make the most of the characteristics of a polyester fiber having an unprecedented high specific gravity, practically strong fiber strength, and toughness. It is suitable for various fish net applications such as nets and floor nets. Particularly, it is most suitable for fixed netting of salmon, yellowtail, tuna, horse mackerel, mackerel, sardine, sea bass, squid and the like.

As a fiber other than the above-mentioned fish net, it can be applied to various types of industrial materials, such as a silt protector used in civil engineering work and the like, and a polyester fiber having an unprecedented high specific gravity performance. In addition to industrial materials, applications to non-clothing fields such as curtains and black screens are also suitable.

[0045]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. In addition, each physical property value in an Example is measured by the following method. (1) Intrinsic viscosity [η] of polyester: Measured at 30 ° C. using an equal weight mixed solvent of phenol and tetrachloroethane. (2) Number average molecular weight of nylon: HL manufactured by Waters Inc.
It was measured by GPC chromatogram according to C-510. (3) Average particle size of inorganic fine particles: Measured by a centrifugal automatic particle size distribution analyzer CAPA-500 manufactured by Horiba, Ltd. (4) Fiber specific gravity: Measured at 20 ° C. by a density gradient method using carbon tetrachloride and normal hexane. (5) Fiber strength, elongation and toughness: Using a tensile tester (Autograph IM-100) manufactured by Shimadzu Corporation, 2
It was measured at 0 ° C. and 65 RH%. The toughness is indicated by the product of the strength at break and the elongation. (6) Melt Viscosity of Polymer (Poise) Measured at 300 ° C. using a Capillograph 1C manufactured by Toyo Seiki Co., Ltd.

Example 1 Nylon 6 powder having a number average molecular weight of 11,000 (P1011F, manufactured by Ube Industries, Ltd.) was used as the thermoplastic polymer constituting the core component, and the inorganic fine particles of the core component had an average particle diameter of 0.2 μm. Spherical magnetite powder [Toda Kogyo Co., Ltd.
Product, surface ferrite coated product, specific gravity 5.0] 30% by weight, and titanium dioxide [rutile type, specific gravity 4.2], manufactured by Titanium Industry Co., Ltd., having an average particle diameter of 0.35 μm, 40% by weight. The mixture was melt-kneaded with a twin-screw kneader as a core component, extruded into strands, cut into strands, pelletized, and vacuum-dried at 90 ° C. to a water content of 180 ppm. On the other hand, polyethylene terephthalate having an intrinsic viscosity [η] = 0.80 containing 0.08% by weight of titanium dioxide was used as a sheath component, and the polyester was melt-polymerized and pelletized by a conventional method.

The core component and the sheath component are melt-extruded by separate melt extruders, and are spun at a nozzle so as to form a concentric core-sheath type having a spinning temperature of 295 ° C. and a composite weight ratio (core component / sheath component) of 1/2. They were merged, discharged using a nozzle having a nozzle diameter of 0.4 mmφ and 8 holes, and wound up at a speed of 1000 m / min. At this time, the intrinsic viscosity [η] of the polyethylene terephthalate of the sheath component forming the composite fiber obtained was 0.7.
It was 5.

The obtained spun yarn is heated at a hot roller temperature of 80.
At a hot plate temperature of 140 ° C. and a draw ratio of 4.0, followed by heat treatment at a hot roller temperature of 180 ° C. while inserting 3% overfeed, followed by 75 denier.
And a multifilament of 8 filaments was wound up. When the cross-sectional shape of the multifilament yarn was observed with a microscope, the core-sheath composite ratio was almost constant in any of the fibers and also in the length direction, and there was no fluff. No trouble was observed in the spinning / drawing process. The fiber specific gravity of the drawn yarn was 1.58, the strength was 4.5 g / denier, and the toughness was 67.5.

When the drawn yarn was combined to form a net, and the net was put into the sea and observed, it was found that the fiber had good sedimentation, had little net shaking in the sea, had excellent durability, and was suitable as a fish net. Was confirmed.

It was also found that the fiber specific gravity of the drawn yarn obtained by changing the heat treatment temperature during drawing was different. As a result of drawing the spun yarn obtained under the above-mentioned spinning conditions under the following conditions, a drawn yarn having the following physical properties was obtained.

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[Table 1]

The higher the processing temperature at the time of the shrinking treatment, the better the fiber properties can be obtained. However, if the processing temperature is extremely high, it is not preferable because the stretching fuzz occurs frequently.

The fiberization was carried out in the same manner as described above, except that the magnetite powder was replaced with the above-mentioned magnetite powder having a surface coated and non-coated magnetite powder (specific gravity: 5.0, manufactured by Toda Kogyo KK). As a result, the fiber specific gravity of the drawn yarn was 1.53, which was slightly lower than that in the case of using a surface-coated product.

Example 2 A composite fiber (drawn yarn) was produced in the same manner as in Example 1 except that 0.2% by weight of copper iodide was added to the core component, and the strength retention of the obtained drawn yarn was obtained. Was measured. As the evaluation means, the intensity retention after irradiation of carbon fade at 83 ° C. for 400 hours and the xenon weather irradiation at 83 ° C.
The intensity retention after irradiation for 00 hours was examined. As a result, the average intensity retention of n = 5 after 400 hours of carbon fade irradiation was about 86%, and the average intensity retention of n = 5 after 400 hours of xenon weather irradiation was about 84%. On the other hand, the composite fiber (stretched yarn) obtained in Example 1 had an average strength retention of about 42% when n = 5 after 400 hours irradiation with carbon fade, and n after 400 hours irradiation with xenon weather. = 5, the average strength retention was about 36%.

Examples 3 to 6 Magnetite powder 5 was used as the inorganic fine particles contained in the core component.
A mixture of 0% by weight and 20% by weight of titanium dioxide in a total of 70% by weight (Example 3), a mixture of 20% by weight of magnetite powder and 50% by weight of titanium dioxide in a total of 70% by weight (Example 4), and magnetite powder 10% by weight, 60% by weight titanium dioxide
(Example 5) was mixed with magnetite powder 3
A composite fiber was obtained in the same manner as in Example 2 except that a mixture of 0% by weight and 20% by weight of titanium dioxide in a total of 50% by weight was used (Example 6). No trouble in processability
Moreover, fibers having good fiber properties were obtained. The hue of the composite fiber obtained in Example 4 was gray, which was slightly different from black. The hue of the composite fiber obtained in Example 5 was whitish gray.

Examples 7 and 8 In Example 2, the composite weight ratio of the core component and the sheath component was changed except that the intrinsic viscosity [η] of the polyethylene terephthalate as the sheath component was set to 0.85 (Example 7). (Example 8) except that was changed to (core component / sheath component) = 1/1 to obtain a conjugate fiber. In each case, there was no trouble in processability, and fibers having good fiber properties were obtained. Tables 1 and 2 show various physical properties of the composite fiber in each example.

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[Table 2]

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[Table 3]

Examples 9 to 10 In Example 2, instead of titanium dioxide, zinc oxide having an average particle size of 1.0 μm (specific gravity 5.5) was used (Example 9), and alumina having an average particle size of 2.0 μm was used. (Specific gravity 3.98)
A conjugate fiber was obtained in the same manner except for using (Example 10). In each case, the processability was good except that some fluff was generated during spinning, and the fiber properties were also good (see Tables 1 and 2).

Examples 11 to 12 Composite fibers were obtained in the same manner as in Example 2, except that the number of cores was 3 (Example 11) and the number of cores was 4 (Example 12). In each case, the processability was good, and the fiber properties were also good.

Example 13 In Example 2, nylon 6 having a number average molecular weight of 22,000 was used instead of nylon 6 having a number average molecular weight of 11,000.
A composite fiber was obtained in the same manner except that [P1022 manufactured by Ube Industries, Ltd.] was used. Tables 1 and 2 show various physical properties of the obtained conjugate fiber.

Example 14 Polyethylene terephthalate having an intrinsic viscosity [η] = 0.70
G as a thermoplastic polymer constituting a core component, 70% by weight of barium sulfate (specific gravity: 4.35) having an average particle diameter of 0.5 μm is used as inorganic fine particles of the core component, and the core component is melted by a twin-screw kneader. The mixture was kneaded and extruded into a strand, and the strand was cut and pelletized. On the other hand, intrinsic viscosity [η] containing 0.08% by weight of titanium dioxide as a sheath component
Polyethylene terephthalate having a ratio of 0.80 was used, and the polyester used was melt-polymerized and pelletized by a conventional method.

The core component and the sheath component are melt-extruded by separate melt extruders, and are spun at a nozzle so as to form a concentric core-sheath type having a spinning temperature of 295 ° C. and a composite weight ratio (core component / sheath component) of 1/2. They were merged, discharged using a nozzle having a nozzle diameter of 0.4 mmφ and 8 holes, and wound up at a speed of 1000 m / min. At this time, the intrinsic viscosity [η] of the polyethylene terephthalate of the sheath component forming the composite fiber obtained was 0.7.
It was 5.

The obtained spun yarn is heated to a hot roller temperature of 80.
At a hot plate temperature of 140 ° C. and a draw ratio of 4.0, followed by heat treatment at a hot roller temperature of 180 ° C. while inserting 3% overfeed, followed by 75 denier.
And a multifilament of 8 filaments was wound up. When the cross-sectional shape of the multifilament yarn was observed with a microscope, the core-sheath composite ratio was almost constant in any of the fibers and also in the length direction, and there was no fluff. No trouble was observed in the spinning / drawing process. The fiber specific gravity of the drawn yarn was 1.52, the strength was 4.1 g / denier, and the toughness was 61.5.

When the drawn yarn was combined into a net to form a net and placed in the sea and observed, it was found that the fiber had good sedimentation, reduced net shaking in the sea, had excellent durability, and was suitable as a fish net. Was confirmed.

Comparative Example 1 A polyethylene terephthalate chip having an intrinsic viscosity [η] of 0.65 before spinning was used as a sheath component, and spinning was performed so that the intrinsic viscosity [η] after spinning became 0.60. Except for this, a composite fiber was obtained in the same manner as in Example 2. as a result,
During spinning and stretching, fluff was slightly generated, and the viscosity of the sheath component was low, so that the fiber strength was as low as 2.5 g / denier.
Was inferior to the fiber obtained in the above.

Comparative Example 2 15% by weight of a magnetic iron mineral and titanium dioxide 1 as inorganic fine particles
A conjugate fiber was obtained in the same manner as in Example 2, except that a mixture of 5% by weight was used. The spinning / drawing process was good and the fiberization was possible, but the fiber specific gravity was 1.45, which was inferior to the fiber obtained in Example 2.

Comparative Examples 3 and 4 In Example 2, silicon dioxide particles having an average particle diameter of 0.1 μm and a specific gravity of 2.2 were used instead of titanium dioxide (Comparative Example 3), and an average particle diameter of 1.0 μm and a specific gravity of 2 were used. A composite fiber was obtained in the same manner as in Example 2 except that the kaolin particles of Comparative Example 4 were used (Comparative Example 4). In each case, fluff was generated frequently, and the spinning property and stretchability were not so good. The specific gravity of each of the obtained composite fibers was also at a lower level than the fiber obtained in Example 2.

Comparative Examples 5 to 6 The same as Example 2 except that the composite weight ratio (core component / sheath component) was changed to 15/85 (Comparative Example 5) and 15/85 (Comparative Example 6). To perform composite spinning. In Comparative Example 5, the fiberization was good, but the fiber specific gravity performance was inferior. In Comparative Example 6, the spinnability and stretchability were poor, and fluff and breakage occurred frequently, and it was not possible to obtain a fiber of a level that could be evaluated for performance. Tables 1 and 2 show the results of these comparative examples.

Example 15 Nylon 6 powder having a number average molecular weight of 11,000 (P1011F, manufactured by Ube Industries, Ltd.) was used as the thermoplastic polymer constituting the core component, and the inorganic particles of the core component had an average particle diameter of 0.35 μm. Titanium dioxide [Titanium Industry Co., Ltd.
, Specific gravity 4.2] 70% by weight, and melt-kneaded as a core component with a twin-screw kneader, extruded into strands, cut the strands into pellets, and reduced the water content to 460 ppm by nitrogen circulation at 100 ° C. I made it. On the other hand, intrinsic viscosity [η] = 0.80 containing 1.5% by weight of carbon black (manufactured by Tegusa) having an average particle size of 0.03 μm as a sheath component.
Polyethylene terephthalate was used, and the polyester was melt-polymerized and pelletized by a conventional method.

The core component and the sheath component were spun and drawn in the same manner as in Example 2 to obtain a conjugate fiber. The intrinsic viscosity [η] of polyethylene terephthalate, which is the sheath component of the composite fiber, was 0.75. The fiber specific gravity is 1.57,
The strength was 4.6 g / denier, and the elongation was 18%.

Example 16 A conjugate fiber was obtained in the same manner as in Example 15, except that the content of titanium dioxide was 55% by weight. The specific gravity of the obtained composite fiber is 1.53, the strength is 5.2 g / denier, and the elongation is 2
0%, and both spinnability and stretchability were excellent.

Example 17 In Example 15, titanium dioxide 5 was used as the inorganic fine particles.
A conjugate fiber was obtained in the same manner except that a mixture of 0% by weight, 20% by weight of zinc oxide having an average particle diameter of 1.0 μm and a specific gravity of 5.5 was used. The specific gravity of the obtained conjugate fiber was 1.58, the strength was 4.5 g / denier, and the elongation was 15%. Although some fluff occurred during spinning, it was excellent in stretchability and excellent for use in fishing nets. Had performance.

Example 18 In Example 15, titanium dioxide 5 was used as the inorganic fine particles.
A composite fiber was obtained in the same manner except that a mixture of 0% by weight, 20% by weight of alumina having an average particle diameter of 2.0 μm and a specific gravity of 3.9 was used. The specific gravity of the obtained conjugate fiber was 1.56, the strength was 4.5 g / denier, and the elongation was 15%. Although some fluff occurred during spinning, it was excellent in stretchability and excellent for fishing net use. Had performance.

Example 19 In Example 15, titanium dioxide 5 was used as the inorganic fine particles.
A composite fiber was obtained in the same manner except that a mixture of 0% by weight, 20% by weight of barium sulfate having an average particle diameter of 0.6 μm and a specific gravity of 4.3 was used. The specific gravity of the obtained composite fiber is 1.57,
The strength was 4.5 g / denier and the elongation was 14%. Although some fluff was generated during spinning, it had excellent stretchability and excellent performance for fishing net use. Examples 15 to 19
Tables 3 and 4 show the respective component constitutions, fiber physical properties and the like of the conjugate fiber obtained in the above.

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[Table 4]

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[Table 5]

Example 20 Nylon 6 powder having a number average molecular weight of 11,000 was used as a thermoplastic polymer constituting a core component, and 60% by weight of titanium dioxide having an average particle diameter of 0.35 μm was used as inorganic fine particles of the core component. (Moisture percentage: 100 ppm), intrinsic viscosity [η] containing 0.08% by weight of titanium dioxide = 0.
Using 95 extruded polyethylene terephthalate as a sheath component, melt extruding with separate extruders, a nozzle having a concentric core-sheath type having a spinning temperature of 300 ° C. and a composite weight ratio (core component / sheath component) of 1/1. Part, nozzle diameter 0.5mmφ, 20
Discharge was performed using a 0-hole nozzle. The discharge yarn is passed through a heating zone of 20 cm length and 380 ° C. provided immediately below the nozzle, and then cooled at 25 ° C. with a cooling air flow of 7 Nm 3 per minute.
A spinning oil is applied with an oiling roller, and a spinning speed of 600
Withdrawn at m / min.

Subsequently, without winding the yarn, stretching and heat treatment were carried out in the following manner and wound. Stretching: After heating with a hot roll at 110 ° C., the film is stretched by 4.3 times while injecting heated steam at 400 ° C. Heat treatment: 3% between hot roll at 220 ° C. and relaxation roll
Heat shrink treatment. As a result, the process stability was good, and a highly practical fiber having 1004 denier, strength of 4.0 g / denier, elongation of 18% and specific gravity of 1.62 was obtained.

Example 21 Nylon 6 powder having a number average molecular weight of 12,000 was used as a thermoplastic polymer constituting a core component. As inorganic fine particles of the core component, 25% by weight of titanium dioxide having an average particle size of 0.35 μm and an average particle size of 0 were used. Carbon black (manufactured by Tegusa Co., Ltd.) was prepared as a core component using a mixture of 50% by weight of 0.2 μm α-type hematite powder (manufactured by Toda Kogyo KK, specific gravity 5.2). A polyethylene terephthalate having an intrinsic viscosity [η] of 1.0 containing 0% by weight was melt-extruded with a separate extruder as a sheath component, and a spinning temperature of 300 was used.
℃, the composite weight ratio (core component / sheath component) 1/2 concentric core-sheath type merge at the nozzle part, nozzle diameter 0.6m
Discharge was performed using a nozzle of mφ and 100 holes. The discharged yarn was passed through a heating zone of 380 ° C., 20 cm in length provided directly below the nozzle, cooled with a cooling air of 7 Nm 3 per minute at 25 ° C., applied a spinning oil with an oiling roller, and spun at a spinning speed of 600 m. / Min.

Subsequently, without winding the yarn, stretching and heat treatment were carried out in the following manner and wound. Stretching: After heating with a hot roll at 110 ° C, stretched 4.8 times in one step while injecting heated steam at 450 ° C. Heat treatment: 4% between 210 ° C hot roll and relaxation roll
Heat shrink treatment. As a result, the process stability was good, and a highly practical fiber having 1002 denier, strength of 5.5 g / denier, elongation of 19% and specific gravity of 1.62 was obtained.

Comparative Example 7 A conjugate fiber was produced in the same manner as in Example 20 except that the temperature of the heated steam was set at 300 ° C., and as a result, the strength was 3.3.
g / denier, elongation 20%, specific gravity 1.54, but a fiber with a fiber strength less than the present invention was obtained.
It is thought to be due to the insufficient flowability of the thermoplastic polymer constituting the core component during stretching, and frequent breakage occurred during stretching.

Examples 22 to 23 and Comparative Example 8 The heat treatment temperature after stretching was 245 ° C. (Example 22), 160 ° C.
A composite fiber was manufactured in the same manner as in Example 20, except that the temperature was set to 25 ° C (Example 23) and 256 ° C (Comparative Example 8). As a result, in Example 22, a composite fiber having a strength of 4.2 g / denier, an elongation of 21%, a specific gravity of 1.63, and a high strength and a high specific gravity could be obtained. In Example 23, the strength was 3.
A composite fiber having a density of 7 g / denier, an elongation of 15% and a specific gravity of 1.53 was obtained. In Comparative Example 8, some of the fibers were fused and broken.

Comparative Example 9 In Example 1, when the water content of the core component was changed to 650 ppm, screws fell off from the nozzle holes and spinning was impossible at all.

Comparative Example 10 In Example 5, the particle size of titanium dioxide was set to 0.02 μm.
A chip was prepared in the same manner as in Example 5, except that the spinning was performed, and composite spinning was attempted. When the shear rate is 1 × 10 1 sec-1,
The melt viscosity of the core component is 30 × 10 3 poise, the melt viscosity of the sheath component is 7.0 × 10 3 poise, and the shear rate is 5 × 1.
At 02 sec-1, the melt viscosity of the core component is 0.08 × 10
The melt viscosity of the 3 poise and sheath components was 7.0 × 10 3 poise. That is, a / b means that the shear rate is 1 × 10 1 sec.
At the time of -1, it is 4.3, and the shear rate is 5.times.10@2 sec.
At the time of -1, it was 0.02. At this time, single yarn breakage frequently occurred on the nozzle surface, and spinning was impossible.

[0086]

According to the present invention, a composite fiber comprising a core component to which specific inorganic fine particles are added at a high content and a sheath component made of polyester is obtained, which has both unprecedented high strength and high specific gravity, and is used for a fixed net. A conjugate fiber having no pollution problem and having a suitable hue can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masao Kawamoto 892 Sakuhi-shi, Saijo-shi, Ehime Prefecture Inside Kuraray Co., Ltd. (72) Eiichi Sasakawa 1-12-39 Umeda, Kita-ku, Osaka Kuraray F Term (reference) 2B106 AA08 4L041 AA07 BA02 BA06 BA21 BC20 BD02 CB03

Claims (1)

[Claims] 1. A method for preparing lead-free inorganic fine particles having a specific gravity of 3 or more
A composite polymer comprising 85% by weight of a thermoplastic polymer having a specific gravity of 1 or more as a core component and a polyester as a sheath component is subjected to composite spinning, and after heat drawing, is subjected to (melting point or softening point −60) ° C. of the core component thermoplastic polymer. As described above, a method for producing a conjugate fiber, wherein a heat treatment is performed at a temperature of (melting point or softening point −10) ° C. or lower of the polyester of the sheath component.