JP2009167584A - Liquid crystal polyester fiber, method for producing the same, and use of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a liquid crystal polyester fiber having a high strength, the method comprising a step of heat treatment at a lower temperature, a liquid crystal polyester fiber obtained by the production method, and preferable use of the same. <P>SOLUTION: In the method for producing the liquid polyester fiber, the liquid crystal polyester satisfies the following features: a glass transition temperature and a melting point are observed by differential scanning calorimetry (DSC); and a flow initiation temperature is 250°C or higher, which is followed by a heat treatment at 230°C or lower. The liquid crystal polyester fiber obtained by the production method has a high strength of 10 (cN/dtex) or more, and can be preferably used for various industrial materials, e.g. nonwoven fabrics. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal polyester fiber, a method for producing a liquid crystal polyester fiber, and its use.

Liquid crystal polyester fibers are attracting attention as high-strength and high-modulus fibers, and many studies have been made so far. Since liquid crystal polyester has the property of exhibiting anisotropy in the molten state, when the liquid crystal polyester is melt-spun, if the conditions for extrusion from the spinneret nozzle are optimized, stretching is not required and relatively high A strong liquid crystal polyester fiber can be obtained. And in order to obtain liquid crystal polyester fiber of higher strength, it is usual to further heat-treat the melt-spun liquid crystal polyester fiber.
By the heat treatment, the liquid crystalline polyester maintains a fiber state, the degree of polymerization is increased, and the crystallization proceeds. As a result, high strength liquid crystalline polyester fibers can be obtained. However, the heat treatment performed in the production of such a liquid crystal polyester fiber requires a relatively high temperature condition, and in the heat treatment under such a high temperature condition, the obtained liquid crystal polyester fiber single yarns are A problem has been pointed out, such as the occurrence of sticking and inferior single fiber separation (see, for example, Patent Document 1). Further, the heat treatment requiring high temperature conditions as described above has a difficulty in productivity, and depending on the type of the liquid crystal polyester fiber, a heat treatment requiring a considerably long time is required.
In order to improve such problems, various manufacturing methods have been proposed so far. For example, Patent Document 2 proposes a manufacturing method in which a fiber made of a liquid crystal polymer (liquid crystal polymer fiber) is heat-treated in a tension state of 1 g / d or more. Patent Document 3 proposes a manufacturing method in which liquid crystal polyester fibers are deposited in a loop shape, and then the obtained fiber deposit is passed through a heat treatment furnace and heat-treated.

No. 58-502227 (2nd page, upper right column, lines 8-12) JP-A-3-260114 (Claims) JP-A-5-222611 (Claims)

However, the liquid crystal polyester fiber manufacturing methods disclosed in Patent Document 2 and Patent Document 3 are also subjected to heat treatment at about 285 ° C., and there is room for improvement in the temperature conditions. Such liquid crystal polyester fiber production is not capable of sufficiently suppressing the sticking between single yarns, etc., and can produce high-strength liquid crystal polyester fiber under lower temperature conditions from the viewpoint of improving productivity. A method was sought.
Accordingly, an object of the present invention is to provide a method for producing a liquid crystal polyester fiber that enables the production of a liquid crystal polyester fiber having a high strength by heat treatment under a lower temperature condition than the conventional method for producing a liquid crystal polyester fiber. is there. Another object of the present invention is to provide a high-strength liquid crystal polyester fiber obtained by the production method.

  As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.

That is, the present invention provides the following <1>.
<1> a step of obtaining fibers from liquid crystal polyester that satisfies the following requirements (a) and (b):
Heat-treating the fiber at a temperature of 230 ° C. or lower;
(A) A glass transition temperature and a melting point are observed by differential scanning calorimetry (b) a flow start temperature is 250 ° C. or higher.

The inventors of the present invention are able to produce high-strength liquid crystal polyester fibers even under low temperature conditions of 230 ° C. or lower by using fibers made of liquid crystal polyester that satisfies the requirements (a) and (b). I came to find it. In the following description, the former process may be referred to as “spinning process” and the latter process as “heat treatment process”.

Furthermore, the present invention provides the following <2> to <5> as preferred embodiments according to the above <1>.
<2> The liquid crystal polyester has monomer units derived from phthalic acid and / or monomer units derived from isophthalic acid, and the total of these monomer units is 20 mol% or more with respect to the total of all monomer units. A method for producing a liquid crystal polyester fiber according to <1>, which is polyester;
<3> The method for producing a liquid crystal polyester fiber according to <1> or <2>, wherein the liquid crystal polyester is a liquid crystal polyester having a glass transition temperature of 150 ° C. or less determined by differential scanning calorimetry;
<4> The method for producing a liquid crystal polyester fiber according to any one of <1> to <3>, wherein the liquid crystal polyester is a liquid crystal polyester having a melting point of 250 ° C. or higher obtained by differential scanning calorimetry;
<5> In the heat treatment, when the strength of the fiber before the heat treatment is T _X (cN / dtex) and the strength of the liquid crystal polyester fiber after the heat treatment is T _Y (cN / dtex), T _Y / T _X The method for producing a liquid crystal polyester fiber according to any one of <1> to <4>, which is a heat treatment satisfying a relationship of ≧ 2.

Moreover, this invention provides the following <6>-<7> as liquid crystal polyester fiber obtained by one of the said manufacturing methods. Furthermore, this invention provides the following <8> as a suitable use of this liquid crystalline polyester fiber.
<6> Liquid crystal polyester fiber obtained by the method for producing a liquid crystal polyester fiber according to any one of <1> to <5>;
<7> Liquid crystalline polyester fiber according to <6>, wherein the tensile strength at 23 ° C. is 10 (cN / dtex) or more;
<8> A nonwoven fabric comprising <6> or <7> liquid crystal polyester fiber;

  The liquid crystal polyester fiber production method of the present invention can produce high-strength liquid crystal polyester fiber by a heat treatment under a low temperature condition, compared to a conventionally proposed production method. And according to the heat processing of such low temperature conditions, the liquid crystal polyester fiber excellent in single yarn separation property can be manufactured. The high-strength liquid crystal polyester fiber obtained by the present invention can be applied to various industrial uses and is extremely useful industrially.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings as necessary.

<Liquid crystal polyester>
First, the liquid crystal polyester applied to the present invention will be described.
The liquid crystal polyester is a polyester called a thermotropic liquid crystal polymer, and forms a melt exhibiting optical anisotropy at a temperature of 450 ° C. or lower.
The liquid crystal polyester applied to the present invention is an aromatic polyester, aromatic-aliphatic polyester, or the like, in which aromatic groups or aromatic groups and aliphatic groups bond ester groups (—COO— or —OCO—). Connected as a group. Further, in this liquid crystal polyester, an aromatic poly (ester-amide) having an amide group (—CONH— or —NHCO—) as a part of the bonding group, and a carbonate group (—OCOO—) as a part of the bonding group. Aromatic polyester-carbonates having) can also be used as the liquid crystalline polyester of the present invention.
In order to satisfy the above requirements (a) and (b), the residues connected by a linking group containing an ester group are preferably aromatic groups, and the total of the residues constituting the liquid crystal polyester Is more preferably 50 mol% or more of an aromatic group, more preferably 80 mol% or more of an aromatic group, and a wholly aromatic polyester or wholly aromatic in which substantially all residues are aromatic groups. The group poly (ester-amide) or wholly aromatic polyester-carbonate is particularly preferred. The aromatic group is preferably a monocyclic aromatic group, and details of such a suitable liquid crystal polyester will be described later.

Next, the requirements (a) and (b) will be described.
(A) represents that the glass transition temperature and the melting point are observed by differential scanning calorimetry (hereinafter, sometimes referred to as “DSC measurement”). The DSC measurement in (a) refers to performing calorimetric measurement from room temperature (about 23 ° C.) to 400 ° C. at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere. In the calorimetric profile of the DSC chart thus measured, an endothermic pattern (hereinafter, sometimes referred to as “Tg pattern”) based on the glass transition temperature (hereinafter, sometimes referred to as “Tg”) and a melting point (hereinafter, referred to as “Tg pattern”). The liquid crystal polyester in which an endothermic peak based on “Tm” (sometimes referred to as “Tm peak” in some cases) is observed is a liquid crystal polyester that satisfies the requirement (a).
Here, the Tg pattern and the Tm peak will be described with reference to FIG. FIG. 1 is a schematic diagram of a DSC chart of a typical liquid crystal polyester in which the x-axis represents temperature (higher as it goes to the right) and the y-axis represents temperature change indicating endothermic heat generation. In the calorimetric profile of the liquid crystal polyester, as the temperature rises from room temperature, first, a “step change” in which heat absorption occurs is observed based on Tg. And such an endothermic endothermic pattern is referred to as a Tg pattern in the present invention. In order to obtain Tg from such a Tg pattern, it is usually necessary to use an analysis means based on “Method for measuring transition temperature of plastic” in JIS K7121 (1987). This will be briefly described with reference to FIG. 2 (an enlarged schematic diagram of a Tg pattern). First, two auxiliary straight lines L1 and L2 obtained by extending the base line on the high temperature side (heat generation side) and the base line on the low temperature side (heat absorption side) of the Tg pattern are drawn. Next, an endothermic change amount (ΔTh) between L1 and L2 is obtained. Then, a half value (1 / 2ΔTh) of ΔTh is obtained, shifted from L2 by 1 / 2ΔTh toward the heat generation side, and a third auxiliary straight line (Lh) parallel to L2 is drawn. And the temperature value of the intersection of Lh and a calorific profile becomes Tg. The Tm peak based on Tm is an endothermic peak observed on the higher temperature side than the Tg pattern. The temperature value at the apex of this Tm peak is Tm. Note that the change in the endothermic amount of the Tg pattern and the change in the endothermic amount of the Tm peak in this DSC measurement are determined by a parameter called the SN ratio of the DSC measurement. The S / N ratio refers to the ratio of the heat difference between the signal components of DSC measurement and the heat difference between the noise components. It is assumed that the Tg pattern is observed when a heat absorption amount change pattern (step change) with an SN ratio of 30 or more is observed on the heat absorption side in DSC measurement. On the other hand, it is assumed that the Tm peak is observed when a peak with an SN ratio of 50 or more is observed on the endothermic side on the higher temperature side than the Tg pattern.

The Tg of the liquid crystal polyester applied to the present invention is usually observed in the range of 80 ° C. or higher and lower than 250 ° C., but a liquid crystal polyester having a Tg of 150 ° C. or lower is particularly preferable for application to the present invention.
On the other hand, the Tm peak is observed on the higher temperature side than the Tg pattern as described above. In the present invention, a liquid crystal polyester having an apex (Tm) of 250 ° C. or higher is preferable, and a liquid crystal polyester of 280 ° C. or higher is more preferable.

The flow start temperature of (b) is an index representing the molecular weight of liquid crystal polyesters well known in the art (Naoyuki Koide, “Liquid Crystalline Polymer Synthesis / Molding / Application—”, pages 95 to 105, see MC, published on June 5, 1987), liquid crystalline polyester is processed into powder and filled into a capillary rheometer fitted with a die with an inner diameter of 1 mm and a length of 10 mm, and 9.8 MPa (100 kg / cm) ² ) The load is applied and the melt viscosity is measured using a flow tester while extruding the liquid crystalline polyester at a heating rate of 4 ° C./min, and the temperature is obtained when a melt viscosity of 4800 Pa · s (48000 poise) is obtained. . The liquid crystalline polyester applied to the present invention requires that the flow start temperature be 250 ° C. or higher. This is because in the method for producing a liquid crystal polyester fiber of the present invention, the spinnability is improved when the fiber (fiber-shaped liquid crystal polyester) is obtained by melt spinning the liquid crystal polyester before the heat treatment. When the flow start temperature is less than 250 ° C., even when measures such as increasing the discharge amount are taken during melt spinning, yarn breakage tends to be severe and stable spinning tends to be relatively difficult.

As described above, the liquid crystal polyester satisfying the requirements (a) and (b) can realize high strength of the liquid crystal polyester fiber by heat treatment under a low temperature condition as described later.
Although the cause of the effect is not necessarily clear, the present inventors have estimated as follows. That is, in the liquid crystal polyester in which Tg is observed in the DSC measurement, the micro-Brownian motion of the polyester molecules tends to be relatively active by heat treatment, and the high temperature conditions such as the vicinity of the melting point as in the conventional manufacturing method. The orientation of the liquid crystal polyester can be controlled without using the bottom. Moreover, since the liquid crystal polyester in which Tm is observed is a liquid crystal polyester having a crystal structure, the crystallinity thereof is increased after the heat treatment, and high strength of the liquid crystal polyester fiber is easily achieved. Therefore, it is estimated that high-strength liquid crystal polyester fibers can be obtained even by heat treatment under relatively low temperature conditions.

  In order to improve the strength of the liquid crystal polyester fiber by using a heat treatment under a lower temperature condition, it is preferable to use a liquid crystal polyester having a low Tg, and as described above, use a liquid crystal polyester having a Tg of 150 ° C. or less. Is particularly preferred. Furthermore, when heat treatment is performed in the vicinity of the melting point, the single yarns easily stick to each other. Therefore, a liquid crystal polyester in which Tm is expressed on the higher temperature side is preferable, and the temperature difference between Tg and Tm is 100 ° C. or more. preferable. When this temperature difference is 100 ° C. or more, the method for producing a liquid crystal polyester fiber of the present invention can sufficiently prevent single yarns from sticking together to obtain a high-strength liquid crystal polyester fiber.

Next, preferable ones among the liquid crystal polyesters applied to the present invention will be described in detail.
In order for the liquid crystal polyester to satisfy the requirement (b), an aromatic liquid crystal polyester in which the residue in the liquid crystal polyester mainly has an aromatic group is preferable. In particular, in order to satisfy the requirement (a), an aromatic liquid crystal having a relatively flexible segment capable of expressing Tg and a relatively high crystallinity segment capable of expressing Tm. Polyester is more preferred.
As a suitable aromatic liquid crystal polyester having such two types of segments,
(P1) A monomer unit derived from an aromatic hydroxycarboxylic acid (hereinafter referred to as “aromatic hydroxycarboxylic acid unit”), a monomer unit derived from an aromatic diol (hereinafter referred to as “aromatic diol unit”) and a fragrance. An aromatic liquid crystal polyester comprising monomer units derived from an aromatic dicarboxylic acid (hereinafter referred to as “aromatic dicarboxylic acid units”);
(P2) an aromatic liquid crystal polyester comprising different types of aromatic hydroxycarboxylic acid units;
In particular, the aromatic polyester (P1) is particularly preferable for satisfying the requirement (a).
In addition, the monomer unit derived from a specific monomer means, in other words, a structural unit formed when the monomer is used for polymerization as described later.

Examples of suitable monomers for deriving these monomer units include the following.
Examples of the aromatic hydroxycarboxylic acid include parahydroxybenzoic acid, metahydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, 2-hydroxy-3-naphthoic acid, 1-hydroxy-4-naphthoic acid, 4-hydroxy -4'-carboxydiphenyl ether, 2,6-dichloro-parahydroxybenzoic acid, 2-chloro-parahydroxybenzoic acid, 2,6-difluoro-parahydroxybenzoic acid, 4-hydroxy-4'-biphenylcarboxylic acid, etc. Can be mentioned. In the production of the aromatic liquid crystal polyester, the aromatic hydroxycarboxylic acid may be used alone or in combination of two or more selected from the above examples.
Among these, parahydroxybenzoic acid and / or 2-hydroxy-6-naphthoic acid are preferable because they are easily available and the resulting liquid crystal polyester fiber tends to have higher strength.

Examples of the aromatic diol include hydroquinone, resorcin, methylhydroquinone, chlorohydroquinone, nitrohydroquinone, 4,4′-dihydroxybiphenyl, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, In addition to 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene and the like, bis- (4-hydroxyphenyl) ketone and bis- (4-hydroxy-3) which are aromatic diols to which two aromatic groups can be conjugated , 5-dimethylphenyl) ketone, bis- (4-hydroxy-3,5-dichlorophenyl) ketone, bis- (4-hydroxyphenyl) ether, bis- (4-hydroxyphenyl) sulfide, bis- (4-hydroxyphenyl) ) Sulfones etc. I can make it.
An aromatic diol in which two aromatic groups are bonded with an aliphatic group can also be used.
Specifically, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 2,2-bis (4-hydroxy-3,5) -Dichlorophenyl) propane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 2,2-bis (4-hydroxy-3-chlorophenyl) propane, bis- (4-hydroxyphenyl) methane, bis- (4-hydroxy-3,5-dimethylphenyl) methane, bis- (4-hydroxy-3,5-dichlorophenyl) methane, bis- (4-hydroxy-3,5-dibromophenyl) methane, bis- (4- Hydroxy-3-methylphenyl) methane, bis- (4-hydroxy-3-chlorophenyl) methane, 1,1-bis (4-hydroxyphenyl) Cyclohexane. Thus, when an aromatic diol in which two aromatic groups are bonded with an alkylene group is used, the alkylene group is partially introduced into the molecular chain of the liquid crystal polyester. If there are many such alkylene groups, the flow start temperature of the liquid crystalline polyester may be lowered. Therefore, the amount of use of these aromatic diols can be determined so as to satisfy the requirement (b). is necessary.
In the production of the aromatic liquid crystal polyester, the aromatic diol may be used alone or in combination of two or more selected from the above examples. Among them, an aromatic diol selected from the group consisting of 4,4′-dihydroxybiphenyl, hydroquinone, resorcin, and 2,6-dihydroxynaphthalene is easily available, and the resulting liquid crystal polyester fiber has higher strength. It is preferable because it is easy.

Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, methylterephthalic acid, and methylisophthalic acid. In addition to the above, diphenyl ether-4,4′-dicarboxylic acid, 2,2′-diphenylpropane-4,4′-dicarboxylic acid and the like, which are aromatic dicarboxylic acids in which two aromatic groups can be conjugated, may also be used. Good. In the production of the aromatic liquid crystal polyester, the aromatic dicarboxylic acid may be used as one kind selected from the above examples, or may be used in combination of two or more kinds.
Among these, when an aromatic dicarboxylic acid selected from the group consisting of terephthalic acid, isophthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid is used, the Tg and Tm of the liquid crystal polyester can be relatively easily controlled, and the above (a) It is preferable for obtaining a liquid crystal polyester that satisfies the above requirements. These aromatic dicarboxylic acids also have an advantage that they are easily available.

  A monomer in which the phenolic hydroxyl group of the aromatic hydroxycarboxylic acid or aromatic diol as exemplified above is replaced with an amino group, that is, an aromatic amine having an aromatic aminocarboxylic acid or phenolic hydroxyl group is used as part of the monomer. If a liquid crystal polyester is produced, the resulting product is a liquid crystal poly (ester-amide). When producing a liquid crystal polyester, if diphenyl carbonate or the like is used as a reaction reagent, a carbonate group is added to some of the bonding groups. A liquid crystal polyester-carbonate having the above is obtained. However, if there is an amide group or a carbonate group as the linking group, among the requirements of (a), there is a tendency that a liquid crystal polyester in which Tm is not observed is obtained. It is necessary to adjust the amount of carbonic acid ester group introduced. Also from this point, the liquid crystalline polyester applied to the present invention is preferably a wholly aromatic liquid crystalline polyester in which the bonding group is substantially composed only of an ester group and the residue is substantially composed of an aromatic group.

Next, a preferred liquid crystal polyester, an aromatic liquid crystal polyester comprising an aromatic hydroxycarboxylic acid unit, an aromatic diol unit and an aromatic dicarboxylic acid unit, which satisfies the above requirements (a) and (b) This will be described more specifically.
In order for the liquid crystal polyester to exhibit Tm, a segment having high crystallinity may be introduced into the liquid crystal polyester molecule as described above. Specifically,

(I) Increasing the content ratio of monomer units derived from parahydroxybenzoic acid.
(Ii) Increasing the content ratio of 2,6-naphthalene residues in the residues.
(Iii) Increasing the content ratio of segments in which aromatic diols and aromatic dicarboxylic acids are alternately copolymerized.

According to the above, the obtained liquid crystal polyester easily develops Tm. That is, the monomer unit derived from parahydroxybenzoic acid is easy to improve the crystallinity of the liquid crystal polyester, and the 2,6-naphthalene residue has high so-called packing properties such that the aromatic rings overlap and become dense. The crystallinity is easy to improve, and the segment in which the aromatic diol and the aromatic dicarboxylic acid are alternately copolymerized tends to improve the crystallinity by increasing the regularity of the liquid crystal polyester molecule. These (i), (ii) and (iii) (hereinafter referred to as “(i) to (iii)”) are all advantageous in that Tm is expressed.

On the other hand, in order to obtain a liquid crystal polyester that expresses Tg, among the above-described monomer units, a monomer unit that gives a bent structure to the molecular chain of the liquid crystal polyester (hereinafter sometimes referred to as “bending monomer unit”) may be introduced. Specifically, when the bending monomer unit is introduced in an amount of 20 mol% or more with respect to the total of all the monomer units, the liquid crystal polyester obtained easily develops Tg. Examples of such bent monomer units include monomer units derived from phthalic acid and monomer units derived from isophthalic acid among aromatic dicarboxylic acid units, and monomer units derived from resorcin are used as aromatic diol units. Can be mentioned. And when it is a liquid crystal polyester which has 20 mol% or more of total content (copolymerization ratio) of such a bending monomer unit, temperature reduction of Tg becomes easy.
As the liquid crystal polyester applied to the present invention, it is more preferable to introduce a monomer unit derived from phthalic acid and / or a monomer unit derived from isophthalic acid among the bent monomer units.

  Accordingly, if the Tm of the liquid crystal polyester is controlled by the introduction amount of the above (i) to (iii) and the linking group (the above-mentioned amide group, carbonate ester group), and the Tg is controlled by the copolymerization ratio of the bending monomer unit, It becomes easy to obtain a liquid crystal polyester that satisfies the requirements (a) and (b). The copolymerization ratio is 30 to 80 mol% aromatic hydroxycarboxylic acid units, 10 to 35 mol% aromatic diol units, and 10 to 35 mol% aromatic dicarboxylic acid units (in addition, aromatic hydroxycarboxylic acid units). The total of the aromatic diol unit and the aromatic dicarboxylic acid unit is 100 mol%. The liquid crystal polyester composed of such a combination of monomer units is relatively easy to control Tg and Tm, and high strength liquid crystal polyester fibers can be obtained by the production method of the present invention.

Among them, monomer units derived from parahydroxybenzoic acid and / or 2-hydroxy-6-naphthoic acid, which are suitable aromatic hydroxycarboxylic acid units,
Monomer units derived from an aromatic diol selected from the group consisting of 4,4′-dihydroxybiphenyl, hydroquinone, resorcin, and 2,6-dihydroxynaphthalene, which are suitable aromatic diol units;
Monomer units derived from aromatic dicarboxylic acids selected from terephthalic acid, isophthalic acid, phthalic acid and 2,6-naphthalenedicarboxylic acid, which are suitable aromatic dicarboxylic acid units;
Since the liquid crystal polyester is a wholly aromatic liquid crystal polyester that does not contain an alkylene group in the molecular chain, the requirement (b) is easily satisfied, and the liquid crystal polyester itself has high heat resistance. is there.

<Method for producing liquid crystal polyester>
As described above, the amount of the liquid crystal polyester comprising a combination of monomer units suitable for expressing Tg and Tm is determined so that each monomer for inducing each monomer unit has a desired copolymerization ratio. Can be obtained by polymerization.

  Here, the manufacturing method of liquid crystalline polyester is demonstrated easily. First, raw material monomers for liquid crystal polyester are selected so as to obtain a desired combination of monomer units, and these are melt polymerized to obtain a relatively low molecular weight prepolymer. In order to obtain this prepolymer, for example, the phenolic hydroxyl group of an aromatic hydroxycarboxylic acid and an aromatic diol is acylated with an acid anhydride to give an acylated product (acylated aromatic hydroxycarboxylic acid and acylated aromatic diol) and Thereafter, the acyl group of the acylated product and the carboxyl group of the aromatic dicarboxylic acid and the acylated aromatic hydroxycarboxylic acid may be melt-polymerized so as to cause a transesterification reaction. As such melt polymerization, a polymerization method disclosed in JP-A No. 2002-220444 or JP-A No. 2002-146003 can be applied. In order to obtain a liquid crystal polyester fiber having higher strength, a liquid crystal polyester (prepolymer) having a relatively low molecular weight is obtained by such melt polymerization, and the prepolymer is further increased in molecular weight by solid phase polymerization. It is preferable to obtain a liquid crystal polyester by polymerization. In this case, the flow start temperature of the prepolymer is preferably 228 ° C to 238 ° C, more preferably 232 to 236 ° C. When the flow initiation temperature of the prepolymer is less than 228 ° C. or exceeds 238 ° C., an unmelted product is likely to be generated in the resin after solid-phase polymerization, and it is relatively difficult to spin the liquid crystalline polyester into a fiber. May be.

Here, the solid phase polymerization will be briefly described.
The prepolymer obtained by the melt polymerization is cooled to about room temperature to form a solid, and then the solid is pulverized and processed into powder such as powder or flakes. The prepolymer powder preferably has an average particle size of 1 mm or less, and more preferably an average particle size of 0.1 to 1 mm. The average particle diameter here is a value calculated by observing the particle diameters of a plurality of powders (prepolymer powders) by observing the appearance with an optical microscope and averaging the measured values of the particle diameters. .

  Thereafter, the prepolymer powder is solid-phase polymerized by heating it in the form of a powder to obtain a high molecular weight liquid crystal polyester. When solid state polymerization is performed in this way to increase the molecular weight, both the flow start temperature and Tm of the liquid crystal polyester can be improved. In particular, it is preferable to set the flow start temperature of the liquid crystalline polyester to 250 ° C. or higher by performing this solid phase polymerization. The reaction conditions for the solid phase polymerization vary depending on the type of liquid crystal polyester applied and the desired flow start temperature value, and therefore it is preferable to optimize appropriately by preliminary experiments and the like. Alternatively, the liquid crystalline polyester during the solid phase polymerization may be sampled every predetermined time to obtain the flow start temperature, and the solid phase polymerization may be stopped when the flow start temperature reaches 250 ° C. or higher.

<Liquid crystal polyester fiber and manufacturing method thereof>
Next, the manufacturing method of the liquid crystalline polyester fiber of this invention is demonstrated.
In order to obtain the liquid crystal polyester fiber, first, the liquid crystal polyester as described above is melt-spun to obtain a fiber shape, and in order to achieve high strength of the obtained fiber, the liquid crystal in the fiber shape A production method having a heat treatment step of heat-treating polyester at a temperature of 230 ° C. or lower is applied. Here, the fiber obtained through the spinning process is hereinafter referred to as “liquid crystal polyester fiber 1”.

  In the spinning step, first, the liquid crystalline polyester is melted at a flow start temperature or higher. The upper limit value of the temperature related to melting is set by the Tm of the applied liquid crystal polyester. Suitably, it is (Tm + 50) ° C. or lower, preferably (Tm + 30) ° C. or lower. The melted liquid crystal polyester is formed into a fiber shape by being discharged from a suitable spinneret nozzle, and the liquid crystal polyester fiber 1 is formed by further cooling. The formed liquid crystal polyester fiber 1 can be continuously obtained by winding the liquid crystal polyester fiber 1 using a winding bobbin or the like. The hole diameter of the spinneret nozzle is usually about 0.05 to 1.0 mm, preferably 0.1 to 0.5 mm. Further, the discharge rate from the spinneret is usually 1 to 40 g / min, preferably 10 to 30 g / min, and the discharge rate is preferably adjusted within a range in which yarn breakage does not occur during melt spinning.

By spinning in this way, the liquid crystal polyester fiber 1 in which the liquid crystal polyester is oriented and crystallized can be obtained. However, in order to suppress the decomposition of the liquid crystalline polyester itself as much as possible, the melting time of the liquid crystalline polyester in the spinning process is preferably shorter, and the transport time of the molten liquid crystalline polyester is preferably set as low as possible. A commercially available melt spinning apparatus (for example, multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd.) can be used for such melt spinning. If such a melt spinning apparatus is used, it is easy to shorten the melting time of the liquid crystal polyester, and it is also possible to shorten the transfer time for making the melted liquid crystal polyester into a fiber shape. In addition, if the melt spinning apparatus is equipped with a heating means in front of the spinneret nozzle so that the melted liquid crystal polyester is immediately discharged from the spinneret nozzle, the melting time is shortened and the transfer time is shortened. Can be made compatible.
Further, in order to impart higher orientation to the liquid crystal polyester constituting the liquid crystal polyester fiber 1, the shear rate at the spinneret nozzle is preferably 10 ³ sec ⁻¹ or more, and further, the spinneret nozzle The smaller the pore diameter, the better. Moreover, when winding the discharged liquid crystalline polyester fiber 1 using a winding bobbin, it is so preferable that the winding speed is large. The number of holes in the spinneret nozzle is not particularly limited, and may be appropriately selected depending on the type of melt spinning apparatus to be used and the required production amount.

  In addition, the liquid crystalline polyester used for melt spinning includes various kinds of particles such as a light-proofing agent, carbon black, and titanium oxide within a range that does not adversely affect the spinnability in producing the liquid crystalline polyester fiber 1 and the heat treatment described later. Further, colorants such as pigments and dyes, antistatic agents, antioxidants and the like can be added.

  Since the liquid crystal polyester fiber 1 thus obtained has a strength of about 5 to 8 (cN / dtex) as it is, it has a relatively higher strength than organic fibers made of polyester other than nylon or liquid crystal polyester. It is expensive. However, the liquid crystal polyester fiber 1 obtained by using the liquid crystal polyester that satisfies the requirements (a) and (b) can dramatically improve the strength of the liquid crystal polyester fiber by the subsequent heat treatment.

  In the heat treatment of the liquid crystal polyester fiber 1, the liquid crystal polyester fiber 1 discharged from the spinneret nozzle is also passed through the heating furnace as it is, and after the liquid crystal polyester fiber 1 is wound around the winding bobbin, The liquid crystal polyester fiber 1 may be heated together with the bobbin, or the liquid crystal polyester fiber 1 may be drawn from the take-up bobbin and heated. In consideration of ease of operation and productivity, the bobbin heating type is preferable.

  As the atmospheric gas related to the heat treatment, air, oxygen, carbon dioxide gas, or a mixed gas thereof can be used in addition to an inert gas such as nitrogen or argon. However, since liquid crystal polyester tends to be easily hydrolyzed, it is preferably a dehumidified atmosphere gas, and the dew point of the atmosphere gas is more preferably −20 ° C. or less, and particularly preferably −50 ° C. or less.

  In the heat treatment for increasing the strength of the liquid crystal polyester fiber 1, the treatment time can be appropriately optimized depending on the treatment temperature and the intended properties of the liquid crystal polyester fiber to be obtained, but is generally about 1 to 20 hours. . The treatment time is preferably a short time in terms of productivity and energy consumption. In order to shorten the treatment time, it is preferable to perform multi-stage heat treatment. Typically, heat treatment is performed at about 120 to 150 ° C. for 0.5 to 1 hour, then at 180 to 200 ° C. for 0.5 to 3 hours, and further at 210 to 230 ° C. for 1 to 5 hours. Can be mentioned. Even in such a multi-stage heat treatment, the maximum value of the treatment temperature needs to be 230 ° C. or less. The maximum value of the treatment temperature may be set in consideration of the rate of increase in strength before and after the heat treatment described later, but is typically 200 ° C. or higher.

  The liquid crystal polyester fiber 1 is applied with a liquid crystal polyester that satisfies the requirements of the above (a) and (b), so that a high strength can be obtained even by heat treatment under a low temperature condition of 230 ° C. or less as described above. It is possible to obtain liquid crystal polyester fibers. And the manufacturing method of the liquid crystalline polyester fiber of the present invention is better than the conventional manufacturing method having a heat treatment step that employs a temperature condition near the melting point of the liquid crystalline polyester, which makes it easier to glue single yarns together. It becomes possible to prevent. Moreover, since the manufacturing method of the liquid crystalline polyester fiber of this invention is a heat processing on low temperature conditions, it contributes also to energy saving, Therefore It is advantageous also in terms of production.

The strength of the liquid crystal polyester fiber thus obtained is greatly improved before and after the heat treatment. Specifically, when the strength of the liquid crystal polyester fiber 1 is T _X (cN / dtex) and the strength of the liquid crystal polyester fiber after the heat treatment is T _Y (cN / dtex), T _Y / T _X ≧ 2. be able to. And the liquid crystal polyester fiber which heat-processed in this way can implement | achieve the high intensity | strength more than 10 (cN / dtex) easily.

  Thus, by the heat treatment under a low temperature condition of 230 ° C. or less, the production method of the present invention in which a liquid crystal polyester fiber having extremely high strength can be obtained while satisfactorily preventing sticking of single yarns is obtained by the conventional liquid crystal This cannot be easily achieved by the polyester fiber manufacturing method, and is based on the inventors' original knowledge. The strength of the liquid crystal polyester fiber means strength obtained by measurement using an autograph (AG-1 KNIS manufactured by Shimadzu Corporation) at a measurement temperature of 23 ° C., a sample interval of 20 cm, and a tensile speed of 20 cm / min.

The liquid crystalline polyester fiber of the present invention may be a fiber obtained by core-sheath type composite yarn, bimetal type composite yarn, sea-island type or split type composite yarn, or may be an ultrafine fiber.
The cross-sectional shape of the fiber is not particularly limited, and conventionally known shapes such as a triangular cross-section, a multi-oval cross-section, a flat cross-section, and a hollow fiber can be widely applied in addition to a circular cross-section. The cross-sectional shape of such a fiber can be appropriately set to a desired shape depending on the shape of the spinneret nozzle used in the spinning step.

<Uses of liquid crystal polyester fiber>
In addition, the liquid crystalline polyester fiber obtained by the present invention not only has the characteristics of high strength, but also the characteristics of the liquid crystalline polyester itself, that is, low water absorption, low dielectric property, vibration damping, dimensional stability, heat resistance, chemical resistance. Are well maintained, and are useful for fishery materials such as fish nets, tegus and ropes, fiber optic cords and printed circuit board reinforcements, rubber reinforcements such as tire cords and belts, and plastic and concrete reinforcements. It is. It can also be used as clothing material such as protective clothing and gloves.
Moreover, the liquid crystalline polyester fiber of the present invention can be twisted with a fiber made of another polymer to form a composite fiber and used for various applications.

Furthermore, the liquid crystal polyester fiber obtained by the present invention can be used after being processed into any form. Examples thereof include filament yarn, cut fiber, spun yarn, rope-like material, and fabric (woven fabric, knitted fabric, nonwoven fabric, etc.). Among these, in the manufacturing method of a nonwoven fabric, it can be set as a polymorphous sheet | seat, such as a dry nonwoven fabric, a needle felt, a spunlace, and a spun bond. For example, when manufacturing a wet nonwoven fabric, it is preferable to use a cut fiber having a single fiber diameter of 5 dtex or less and a fiber length of 3 mm to 10 mm.
In particular, since the liquid crystal polyester fiber has a relatively low dielectric property, an excellent electrical property effect can be obtained when it is made of a non-woven fabric, and it can be suitably applied as an insulating material for a circuit board. Of course, in this case, it may be used in combination with other fibers.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is defined by the terms of the claims, and further includes meanings equivalent to the description of the claims and all modifications within the scope.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  In the synthesis of the following liquid crystal polyester, the glass transition temperature (Tg), melting point (Tm) and flow start temperature of the liquid crystal polyester to be measured were measured according to the following methods.

(Measurement of glass transition temperature and melting point)
For the liquid crystal polyester to be measured, a calorimetric profile was measured under the conditions described above using a differential scanning calorimetry system “DSC6200” manufactured by Seiko Instruments Inc., and the glass transition temperature (Tg) was determined from the obtained calorimetric profile. The melting point (Tm) was determined.

(Flow start temperature)
The flow start temperature was also measured as described above. That is, a flow tester (manufactured by Shimadzu Corporation, CFT-500 type) was used, and about 2 g of liquid crystal polyester was filled in a capillary rheometer equipped with a die having an inner diameter of 1 mm and a length of 10 mm. Then, while applying a load of 9.8 MPa (100 kg / cm 2) and extruding the liquid crystalline polyester from the nozzle at a heating rate of 4 ° C./min, the temperature at which the melt viscosity is 4800 Pa · s (48000 poise) is measured. Was defined as the flow start temperature.

The characteristic (strength) evaluation of the liquid crystal polyester fiber was performed as follows.
(Tensile strength)
The tensile strength of the liquid crystal polyester fiber was measured by using Autograph AG-1KNIS manufactured by Shimadzu Corporation at a sample interval of 20 cm and a tensile speed of 20 cm / min.

(Synthesis Example 1)
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 828 g (6.0 mol) of parahydroxybenzoic acid and 559 g (3.0 of 4,4′-dihydroxybiphenyl) were added. Mol), 498 g (3.0 mol) of isophthalic acid and 1348 g (13.2 mol) of acetic anhydride were added, and these were stirred. Next, 0.19 g of 1-methylimidazole was added to the mixture after stirring, and the inside of the reactor was sufficiently replaced with nitrogen gas, and then the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream. The temperature was maintained and refluxed for 1 hour. Thereafter, the temperature was raised to 320 ° C. over 2 hours and 50 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the reaction was considered to be completed when 75 minutes passed at 320 ° C., and the contents were taken out. It was.

  Next, the taken-out contents were cooled to room temperature and then pulverized by a pulverizer to obtain a prepolymer powder having a particle size of about 0.1 mm to about 1 mm. A part of the obtained prepolymer powder was taken out and its flow initiation temperature was measured.

  Then, this prepolymer powder was heated from 25 ° C. to 200 ° C. over 1 hour, then heated from this temperature to 232 ° C. over 5 hours, and further kept at the same temperature for 3 hours. I let you. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 258 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Moreover, when the DSC measurement was implemented about the powder of liquid crystalline polyester, the glass transition temperature (Tg) was 128 degreeC and melting | fusing point (Tm) was 310 degreeC. In addition, the ratio with respect to the sum total of all the monomer units of the monomer unit calculated | required from the used raw material monomer is 50 mol% of aromatic hydroxycarboxylic acid (parahydroxybenzoic acid) units, and 25 mol of aromatic diol (4,4'-dihydroxybiphenyl) units. %, The aromatic dicarboxylic acid (isophthalic acid) unit is 25 mol%, and the bending monomer unit (monomer unit derived from isophthalic acid) is 25 mol%.

(Synthesis Example 2)
In the same manner as in Synthesis Example 1, a prepolymer powder having a flow start temperature of 230 ° C. was obtained. Next, the prepolymer powder was heated from 25 ° C. to 200 ° C. over 1 hour, then heated from this temperature to 220 ° C. over 5 hours, and further kept at that temperature for 3 hours. I let you. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 241 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Moreover, when the DSC measurement was implemented about the powder of liquid crystalline polyester, the glass transition temperature (Tg) was 125 degreeC and melting | fusing point (Tm) was 305 degreeC. The ratio of the monomer units to the total of all the monomer units and the ratio of the bent monomer units are the same as those of the liquid crystal polyester of Synthesis Example 1.

(Synthesis Example 3)
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 911 g (6.6 mol) of parahydroxybenzoic acid and 409 g (2.2 mol) of 4,4′-dihydroxybiphenyl were added. Mol), 91 g (0.55 mol) of isophthalic acid, 274 g (1.65 mol) of terephthalic acid, and 1235 g (12.1 mol) of acetic anhydride were added and stirred. Next, 0.17 g of 1-methylimidazole was added to the mixture after stirring, and the inside of the reactor was sufficiently replaced with nitrogen gas, and then heated to 150 ° C. over 15 minutes under a nitrogen gas stream, The temperature was maintained and refluxed for 1 hour. Thereafter, 1.7 g of 1-methylimidazole was further added, and then the temperature was raised to 320 ° C. over 2 hours and 50 minutes while distilling off distilling by-product acetic acid and unreacted acetic anhydride. The time at which an increase in torque was observed was regarded as the end of the reaction, and the contents were taken out.

  Next, after the taken-out contents were cooled to room temperature, they were pulverized by a pulverizer to obtain a prepolymer powder having a particle size of about 0.1 mm to about 1 mm. A part of the obtained prepolymer powder was taken out and its flow initiation temperature was measured.

  Then, this prepolymer powder was heated from 25 ° C. to 250 ° C. over 1 hour, then heated from this temperature to 285 ° C. over 5 hours, and further kept at that temperature for 3 hours. I let you. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 327 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Further, when DSC measurement was performed on the liquid crystalline polyester powder, the melting point (Tm) was 340 ° C., and the glass transition temperature (Tg) was not observed. In addition, the ratio with respect to the sum total of all the monomer units of the monomer unit calculated | required from the used raw material monomer is 60 mol% of aromatic hydroxycarboxylic acid (parahydroxybenzoic acid) units, and 20 mol of aromatic diol (4,4′-dihydroxybiphenyl) units. %, Aromatic dicarboxylic acid (isophthalic acid and terephthalic acid) units are 20 mol%, and bending monomer units (monomer units derived from isophthalic acid) are 5 mol%.

(Synthesis Example 4)
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 941 g (5.0 mol) of 2-hydroxy-6-naphthoic acid and 273 g (2.5 mol) of 4-aminophenol were added. ), 415.3 g (2.5 mol) of isophthalic acid and 1123 g (11 mol) of acetic anhydride were added, and these were stirred. Next, after sufficiently replacing the inside of the reactor with nitrogen gas, the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream, and the temperature was maintained as it was and refluxed for 3 hours. Thereafter, the temperature was raised to 320 ° C. over 2 hours and 50 minutes while distilling off distilling by-product acetic acid and unreacted acetic anhydride. The time at which an increase in torque was observed was regarded as the end of the reaction, and the contents were taken out.

  Next, the taken-out contents were cooled to room temperature and then pulverized by a pulverizer to obtain a prepolymer powder having a particle size of about 0.1 mm to about 1 mm. A part of the obtained prepolymer powder was taken out and its flow initiation temperature was measured.

  Then, the prepolymer powder was heated from 25 ° C. to 180 ° C. over 1 hour, then heated from this temperature to 220 ° C. over 5 hours, and further kept at that temperature for 3 hours for solid phase polymerization. It was. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 272 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Further, when DSC measurement was performed on the liquid crystalline polyester powder, the glass transition temperature (Tg) was 129 ° C., and the melting point (Tm) was not clearly observed. 50 mol% aromatic hydroxycarboxylic acid (2-hydroxy-6-naphthoic acid) units, 25 mol% units derived from aromatic amines having hydroxyl groups (4-aminophenol), 25 mol% aromatic dicarboxylic acid units (isophthalic acid) The bending monomer unit (monomer unit derived from isophthalic acid) is 25 mol%.

(Synthesis Example 5)
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 828 g (6.0 mol) of p-hydroxybenzoic acid and 559 g (3. 0 mol), 498 g (3.0 mol) of isophthalic acid and 1348 g (13.2 mol) of acetic anhydride were added, and these were stirred. Next, 0.19 g of 1-methylimidazole was added to the mixture after stirring, and the inside of the reactor was sufficiently replaced with nitrogen gas, and then the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream. The temperature was maintained and refluxed for 1 hour. Then, the temperature was raised to 320 ° C. over 2 hours and 50 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the reaction was considered to be completed when 65 minutes passed at 320 ° C., and the contents were taken out. It was.

  Next, the taken-out contents were cooled to room temperature and then pulverized by a pulverizer to obtain a prepolymer powder having a particle size of about 0.1 mm to about 1 mm. A part of the obtained prepolymer powder was taken out and its flow initiation temperature was measured.

  Then, this prepolymer powder was heated from 25 ° C. to 200 ° C. over 1 hour, then heated from this temperature to 249 ° C. over 5 hours, and further kept at the same temperature for 3 hours. I let you. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 266 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Moreover, when the DSC measurement was implemented about the powder of liquid crystalline polyester, the glass transition temperature was 128 degreeC and melting | fusing point was 313 degreeC. In addition, the ratio with respect to the sum total of all the monomer units of the monomer unit calculated | required from the used raw material monomer is 50 mol% of aromatic hydroxycarboxylic acid (p-hydroxybenzoic acid) units, aromatic diol (4,4'-dihydroxybiphenyl) units. 25 mol%, aromatic dicarboxylic acid (isophthalic acid) units are 25 mol%, and bending monomer units (monomer units derived from isophthalic acid) are 25 mol%.

(Synthesis Example 6)
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 828 g (6.0 mol) of parahydroxybenzoic acid and 559 g (3.0 of 4,4′-dihydroxybiphenyl) were added. Mol), 498 g (3.0 mol) of isophthalic acid and 1348 g (13.2 mol) of acetic anhydride were added, and these were stirred. Next, after sufficiently replacing the inside of the reactor with nitrogen gas, the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream, and the temperature was maintained as it was and refluxed for 3 hours. Thereafter, the temperature was raised to 320 ° C. over 2 hours and 50 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the reaction was considered to be completed when 85 minutes passed at 320 ° C., and the contents were taken out. It was.

  Next, the taken-out contents were cooled to room temperature and then pulverized by a pulverizer to obtain a prepolymer powder having a particle size of about 0.1 mm to about 1 mm. A part of the obtained prepolymer powder was taken out and its flow initiation temperature was measured.

  Then, this prepolymer powder was heated from 25 ° C. to 200 ° C. over 1 hour, then heated from this temperature to 245 ° C. over 5 hours, and further kept at the same temperature for 3 hours. I let you. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 267 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Moreover, when the DSC measurement was implemented about the powder of liquid crystalline polyester, the glass transition temperature was 128 degreeC and melting | fusing point was 313 degreeC. In addition, the ratio with respect to the sum total of all the monomer units of the monomer unit calculated | required from the used raw material monomer is 50 mol% of aromatic hydroxycarboxylic acid (parahydroxybenzoic acid) units, and 25 mol of aromatic diol (4,4'-dihydroxybiphenyl) units. %, The aromatic dicarboxylic acid (isophthalic acid) unit is 25 mol%, and the bending monomer unit (monomer unit derived from isophthalic acid) is 25 mol%.

(Synthesis Example 7)
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 828 g (6.0 mol) of p-hydroxybenzoic acid and 559 g (3. 0 mol), 498 g (3.0 mol) of isophthalic acid and 1348 g (13.2 mol) of acetic anhydride were added, and these were stirred. Next, after sufficiently replacing the inside of the reactor with nitrogen gas, the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream, and the temperature was maintained as it was and refluxed for 3 hours. Thereafter, the temperature was raised to 320 ° C. over 2 hours and 50 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the reaction was regarded as completed when 90 minutes passed at 320 ° C., and the contents were taken out. It was.

  Next, the taken-out contents were cooled to room temperature and then pulverized by a pulverizer to obtain a prepolymer powder having a particle size of about 0.1 mm to about 1 mm. A part of the obtained prepolymer powder was taken out and its flow initiation temperature was measured.

  Then, the temperature of this prepolymer powder was raised from 25 ° C. to 200 ° C. over 1 hour, then raised from this temperature to 244 ° C. over 5 hours, and further kept at that temperature for 3 hours. I let you. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 267 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Moreover, when the DSC measurement was implemented about the powder of liquid crystalline polyester, the glass transition temperature (Tg) was 128 degreeC and melting | fusing point (Tm) was 312 degreeC. In addition, the ratio with respect to the sum total of all the monomer units of the monomer unit calculated | required from the used raw material monomer is 50 mol% of aromatic hydroxycarboxylic acid (parahydroxybenzoic acid) units, and 25 mol of aromatic diol (4,4'-dihydroxybiphenyl) units. %, The aromatic dicarboxylic acid (isophthalic acid) unit is 25 mol%, and the bending monomer unit (monomer unit derived from isophthalic acid) is 25 mol%.

(Synthesis Example 8)
In a reactor equipped with a stirrer, a torque meter, a nitrogen gas inlet tube, a thermometer and a reflux condenser, 828 g (6.0 mol) of parahydroxybenzoic acid and 559 g (3.0 of 4,4′-dihydroxybiphenyl) were added. Mol), 498 g (3.0 mol) of isophthalic acid and 1348 g (13.2 mol) of acetic anhydride were added, and these were stirred. Next, 0.19 g of 1-methylimidazole was added to the mixture after stirring, and the inside of the reactor was sufficiently replaced with nitrogen gas, and then the temperature was raised to 150 ° C. over 15 minutes under a nitrogen gas stream. The temperature was maintained and refluxed for 1 hour. Thereafter, the temperature was raised to 320 ° C. over 2 hours and 50 minutes while distilling off the by-product acetic acid and unreacted acetic anhydride, and the reaction was regarded as completed when 90 minutes passed at 320 ° C., and the contents were taken out. It was.

  Next, the taken-out contents were cooled to room temperature and then pulverized by a pulverizer to obtain a prepolymer powder having a particle size of about 0.1 mm to about 1 mm. A part of the obtained prepolymer powder was taken out and its flow initiation temperature was measured. As a result, it was 241 ° C.

  Then, this prepolymer powder was heated from 25 ° C. to 200 ° C. over 1 hour, then heated from this temperature to 243 ° C. over 5 hours, and further kept at the same temperature for 3 hours. I let you. The powder after the solid phase polymerization was cooled to obtain a liquid crystalline polyester powder. It was 268 degreeC when the flow start temperature of the obtained liquid crystalline polyester was measured similarly to the above. Moreover, when the DSC measurement was implemented about the powder of liquid crystalline polyester, the glass transition temperature (Tg) was 128 degreeC and melting | fusing point (Tm) was 312 degreeC. In addition, the ratio with respect to the sum total of all the monomer units of the monomer unit calculated | required from the used raw material monomer is 50 mol% of aromatic hydroxycarboxylic acid (parahydroxybenzoic acid) units, and 25 mol of aromatic diol (4,4'-dihydroxybiphenyl) units. %, The aromatic dicarboxylic acid (isophthalic acid) unit is 25 mol%, and the bending monomer unit (monomer unit derived from isophthalic acid) is 25 mol%.

Example 1
The liquid crystal polyester obtained in Synthesis Example 1 was granulated into a pellet shape that is easy to fiberize in the spinning process. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 310 ° C. The spinneret used had a hole diameter of 0.3 mm and a number of holes of 24, and was wound at a discharge rate of 25 g / min and a spinning speed of 400 m / min. The spinning yarn was wound around a metal bobbin and heat-treated at 150 ° C. for 1 hour, from 150 ° C. to 230 ° C. for 80 minutes, and at 230 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn A are shown in Table 1.

(Example 2)
The liquid crystalline polyester obtained in Synthesis Example 2 was granulated into pellets. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 310 ° C. The spinneret used had a hole diameter of 0.3 mm and a number of holes of 24, and was wound at a discharge rate of 25 g / min and a spinning speed of 400 m / min. This spinning yarn was wound around a metal bobbin and heat-treated at 150 ° C. for 1 hour, from 150 ° C. to 220 ° C. for 70 minutes, and at 220 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn B are shown in Table 1.

(Example 3)
The liquid crystalline polyester obtained in Synthesis Example 5 was granulated into pellets. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 315 ° C. The spinneret used had a hole diameter of 0.3 mm and a number of holes of 24, and was wound at a discharge rate of 25 g / min and a spinning speed of 400 m / min. The spinning yarn was wound around a metal bobbin and heat-treated at 150 ° C. for 1 hour, from 150 ° C. to 230 ° C. for 80 minutes, and at 230 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn D are shown in Table 1.

Example 4
The liquid crystalline polyester obtained in Synthesis Example 6 was granulated into a pellet shape that is easy to fiberize in the spinning process. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 315 ° C. The spinneret used had a hole diameter of 0.3 mm and a number of holes of 24, and was wound at a discharge rate of 25 g / min and a spinning speed of 400 m / min. The spinning yarn was wound around a metal bobbin and heat-treated at 150 ° C. for 1 hour, from 150 ° C. to 230 ° C. for 80 minutes, and at 230 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn E are shown in Table 1.

(Example 5)
The liquid crystalline polyester obtained in Synthesis Example 7 was granulated into a pellet shape that is easy to fiberize in the spinning process. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 315 ° C. The spinneret used had a hole diameter of 0.3 mm and a number of holes of 24, and was wound at a discharge rate of 25 g / min and a spinning speed of 400 m / min. The spinning yarn was wound around a metal bobbin and heat-treated at 150 ° C. for 1 hour, from 150 ° C. to 230 ° C. for 80 minutes, and at 230 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn F are shown in Table 1.

(Example 6)
The liquid crystalline polyester obtained in Synthesis Example 8 was granulated into a pellet shape that is easy to fiberize in the spinning process. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 315 ° C. The spinneret used had a hole diameter of 0.3 mm and a number of holes of 24, and was wound at a discharge rate of 25 g / min and a spinning speed of 400 m / min. The spinning yarn was wound around a metal bobbin and heat-treated at 150 ° C. for 1 hour, from 150 ° C. to 230 ° C. for 80 minutes, and at 230 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn G are shown in Table 1.

(Comparative Example 1)
The liquid crystalline polyester obtained in Synthesis Example 2 was granulated into a pellet shape that is easy to fiberize in the spinning process. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 300 ° C. A spinneret having a hole diameter of 0.3 mm and a number of holes of 24 was used at a discharge rate of 25 g / min. However, the yarn was severely broken and could not be wound around the bobbin. Therefore, the strength of the fiber could not be measured.

(Comparative Example 2)
The liquid crystalline polyester obtained in Synthesis Example 3 was processed into pellets by granulation and then melt-spun at 370 ° C. using a 30 mm diameter screw type extruder. A spinneret having a hole diameter of 0.2 mm and a hole number of 150 was used and wound up at a spinning speed of 600 m / min. The spinning yarn was wound around a metal bobbin and heat-treated at 150 ° C. for 1 hour, from 150 ° C. to 230 ° C. for 80 minutes, and at 230 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn C are shown in Table 1.

(Comparative Example 3)
The liquid crystalline polyester obtained in Synthesis Example 4 was granulated into a pellet shape that is easy to fiberize in the spinning process. Next, using a multifilament apparatus polymer mate V manufactured by Chubu Chemical Machinery Co., Ltd., the material was passed through a filter made of stainless steel and melt-spun at 310 ° C. The spinneret used had a hole diameter of 0.3 mm and 24 holes, and was wound at a discharge rate of 20 g / min and a spinning speed of 300 m / min. The spinning yarn was wound around a metal bobbin and heat treated at 150 ° C. for 1 hour, from 150 ° C. to 230 ° C. for 80 minutes, and at 230 ° C. for 5 hours. The evaluation results of the obtained heat treated yarn D are shown in Table 1.

※１ ＤＳＣ測定でＴｇが観測された場合を「○」、観測されない場合を「×」とした。
※２ ＤＳＣ測定でＴｍが観測された場合を「○」、観測されない場合を「×」とした。
※３ 糸切れが激しい場合の紡糸性を「×」、ボビンに巻き取れる程度の紡糸性を有していた場合を「○」とした。
※４ 加熱処理の最高温度を示す。

* 1 “○” indicates that Tg was observed by DSC measurement, and “×” indicates that Tg was not observed.
* 2 “○” indicates that Tm is observed by DSC measurement, and “×” indicates that Tm is not observed.
* 3 The spinnability when the yarn breakage is severe is indicated as “X”, and the spinnability that can be wound around the bobbin is indicated as “◯”.
* 4 Indicates the maximum temperature for heat treatment.

  A liquid crystal polyester fiber using a liquid crystal polyester having a glass transition temperature (Tg) and a melting point (Tm) observed by DSC measurement and having a flow initiation temperature of 250 ° C. or higher is subjected to heat treatment under a lower temperature condition than before. It has been found that the liquid crystal polyester fiber obtained after the treatment has a very high strength (10 cN / dtex or more) (Examples 1 to 6). On the other hand, even when the same raw material monomer was used, the liquid crystalline polyester having a flow start temperature lower than 250 ° C. could not be melted to form a fiber (Comparative Example 1). Moreover, the fiber using the liquid crystal polyester in which either Tg or Tm is not observed was inferior in strength to the liquid crystal polyester of Example 1 (Comparative Examples 2 and 3).

It is a schematic diagram showing the calorimetric profile of the DSC chart of a typical liquid crystal polyester. It is a model drawing showing the principal part of the analysis means which calculates | requires Tg from a Tg pattern.

Claims (8)

A step of obtaining fibers from liquid crystal polyester that satisfies the following requirements (a) and (b):
Heat-treating the fiber at a temperature of 230 ° C. or lower;
A method for producing a liquid crystal polyester fiber, comprising:
(A) Glass transition temperature and melting point are observed by differential scanning calorimetry (b) Flow start temperature is 250 ° C. or higher.   The liquid crystal polyester has a monomer unit derived from phthalic acid and / or a monomer unit derived from isophthalic acid, and the total of these monomer units is a liquid crystal polyester of 20 mol% or more based on the total of all structural units. The method for producing a liquid crystal polyester fiber according to claim 1.   The method for producing a liquid crystalline polyester fiber according to claim 1 or 2, wherein the liquid crystalline polyester is a liquid crystalline polyester having a glass transition temperature of 150 ° C or lower determined by differential scanning calorimetry.   The method for producing a liquid crystal polyester fiber according to any one of claims 1 to 3, wherein the liquid crystal polyester is a liquid crystal polyester having a melting point determined by differential scanning calorimetry of 250 ° C or higher. In the heat treatment, when the strength of the fiber before the heat treatment is T _X (cN / dtex) and the strength of the liquid crystal polyester fiber after the heat treatment is T _Y (cN / dtex), T _Y / T _X ≧ 2. It is heat processing which satisfy | fills a relationship, The manufacturing method of the liquid-crystal polyester fiber as described in any one of Claims 1-4 characterized by the above-mentioned.   A liquid crystal polyester fiber obtained by the method for producing a liquid crystal polyester fiber according to any one of claims 1 to 5.   The liquid crystalline polyester fiber according to claim 6, wherein the tensile strength at 23 ° C is 10 (cN / dtex) or more.   A non-woven fabric comprising the liquid crystal polyester fiber according to claim 6 or 7.

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