Liquid crystal polyester fiber and method for producing the same

Abstract

Provided are liquid crystal polyester fibers that generate less gas when heated and that have excellent hue. The liquid crystal polyester fibers have a total carboxy end group amount (total CEG amount) of not more than 5.0 meq / kg and have a ketone bond amount of not more than 0.05 mol%. For example the liquid crystal polyester fibers may have a melting point of not more than 380°C. The liquid crystal polyester fibers may have a strength of less than 18 cN / dtex. Further, the liquid crystal polyester fibers may contain a liquid crystal polyester which has not less than 50 mol% of a structural unit derived from 4-hydroxybenzoic acid.

Description

Related Application

[0001] This application claims the priority of Japanese Patent Application No. 2021-166307 filed on October 8, 2021, and the entire content thereof is incorporated herein by reference and made a part of this application.

Technical Field

[0002] The present invention relates to liquid crystal polyester fibers and a method for producing the same.

Background Art

[0003] Conventionally, as an intermediate material used for manufacturing fiber-reinforced composite materials, a composite yarn containing reinforcing fibers and thermoplastic fibers (in the case of an intermediate material for fiber-reinforced composite materials, thermoplastic fibers may be hereinafter referred to as fusion fibers because they are thermally fused in a subsequent process) is known. For example, Patent Document 1 (Japanese Patent Laid-Open No. 1-280031) discloses a method for producing a flexible composite fiber useful for composite products, which comprises laminating and bundling reinforcing multifilaments and thermoplastic multifilaments. Patent Document 2 (Japanese Patent Laid-Open No. 2013-237945) discloses a composite yarn in which continuous reinforcing fibers and continuous thermoplastic resin fibers are mixed and suitable for molding a resin composite material. Patent Document 3 (Japanese Patent Laid-Open No. 4-73227) discloses a method for producing a mixed yarn for a thermoplastic composite of continuous thermoplastic fibers and continuous reinforcing fibers.

[0004] Such a composite yarn containing continuous reinforcing fibers and continuous thermoplastic fibers is generally more flexible than a prepreg (a tape-like or cloth-like material obtained by coating or covering a tow or fabric of reinforcing fibers with a thermosetting resin) used as a precursor of a fiber-reinforced composite material, or an intermediate material obtained by melt-impregnating a tow or fabric of reinforcing fibers with a thermoplastic resin. Also, it is easy to form fabrics with various three-dimensional deformations such as tubular and dome shapes by weaving, knitting, etc. Therefore, it can be effectively used as a raw material for sheet-like fiber-reinforced molded articles having three-dimensional shape features such as duct tubes and automobile bumpers.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In such molded articles, there are many applications where vibration occurs, such as the above-mentioned duct tubes and automobile bumpers. Therefore, by using liquid crystal polyester fibers made of a thermoplastic resin with excellent vibration damping properties as reinforcing fibers or fusing fibers, it is expected that a molded article with excellent vibration damping properties can be obtained.

[0007] However, when using liquid crystal polyester fibers as fusing fibers, when heated to a temperature at which fusing processing is possible, thermal decomposition gas is generated from the liquid crystal polyester fibers, and a large number of bubbles are generated inside and on the surface of the obtained fiber-reinforced molded article, leading to problems such as a decrease in strength and poor appearance.

[0008] In addition, there is a problem that the hue of the liquid crystal polyester fiber (being yellowish) leads to poor appearance of the molded article.

[0009] The present invention solves the above problems, and an object thereof is to provide a liquid crystal polyester fiber that can produce a molded article with excellent hue and does not generate bubbles when used as a fusing fiber and heated for fusing.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve the above object, the inventors of the present invention have found that when heated to a predetermined temperature, thermal decomposition gas generated from liquid crystal polyester fibers causes a decarboxylation reaction at the carboxy group when a carboxy group is present at the terminal of the liquid crystal polyester constituting the liquid crystal polyester fibers. Furthermore, it has been found that a ketone bond generated by a side reaction exists in the liquid crystal polyester constituting the liquid crystal polyester fibers, and that the ketone bond affects the hue of the liquid crystal polyester fibers, leading to the completion of the present invention.

[0011] That is, the present invention can be configured in the following aspects. 〔Aspect 1〕 Liquid crystal polyester fibers having a total carboxy end amount (total CEG amount) of 5.0 meq / kg or less (preferably 4.0 meq / kg or less, more preferably 3.0 meq / kg or less, still more preferably 2.5 meq / kg or less, and even more preferably 2.0 meq / kg or less), and a ketone bond amount of 0.05 mol% or less (preferably 0.04 mol% or less, more preferably 0.03 mol% or less). 〔Aspect 2〕 The liquid crystal polyester fibers according to Aspect 1, having a melting point of 380°C or less (preferably 250 to 350°C, more preferably 260 to 300°C). 〔Aspect 3〕 The liquid crystal polyester fibers according to Aspect 1 or 2, having a strength of less than 18 cN / dtex (preferably 2 to 16 cN / dtex, more preferably 6 to 12 cN / dtex). 〔Aspect 4〕 The liquid crystal polyester fibers according to any one of Aspects 1 to 3, containing a liquid crystal polyester having a structural unit derived from 4-hydroxybenzoic acid in an amount of 50 mol% or more (preferably 53 mol% or more, more preferably 60 mol% or more). 〔Aspect 5〕 The liquid crystal polyester fiber according to any one of Aspects 1 to 4, wherein the total terminal amount is 50 meq / kg or more (preferably 55 meq / kg or more, more preferably 60 meq / kg or more). [Aspect 6] A method for producing a liquid crystal polyester fiber according to any one of Aspects 1 to 5, comprising at least a step of melt-kneading a liquid crystal polyester in an extruder and a step of discharging the melt-kneaded product from a nozzle and spinning it. [Aspect 7] The production method according to Aspect 6, wherein in the melt-kneading step, the thermal history TH represented by the following formula (1) is 250 to 1100 (preferably 300 to 1000, more preferably 350 to 950, still more preferably 400 to 900).

Number

[0012] In addition, any combination of at least two components disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, any combination of two or more of the claims described in the claims is included in the present invention.

Advantages of the Invention

[0013] According to the liquid crystal polyester fiber of the present invention, generation of gas during heat melting can be suppressed, and a molded article with few bubbles and excellent hue can be manufactured.

Brief Description of the Drawings

[0014] This invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and the drawings are for illustrative and explanatory purposes only and should not be used to define the scope of this invention. The scope of this invention is determined by the appended claims. The drawings are not necessarily shown to scale and are exaggerated for the purpose of showing the principles of the present invention.

Figure 1

Modes for Carrying Out the Invention

[0015] [Liquid Crystal Polyester Fiber] The liquid crystal polyester fiber of the present invention is composed of a liquid crystal polyester. Examples of the liquid crystal polyester include structural units derived from aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc. As long as the effects of the present invention are not impaired, the structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not particularly limited in terms of their chemical structure. Further, within a range that does not inhibit the effects of the present invention, the liquid crystal polyester may contain structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids. For example, preferred structural units include the examples shown in Table 1.

[0016]

Table 1

[0017] In the structural units of Table 1, m is an integer from 0 to 2, and Y in the formula is, within the range of 1 to the maximum number of substituents possible, each independently a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.), and the like.

[0018] More preferred structural units include the structural units described in Examples (1) to (18) shown in Table 2, Table 3, and Table 4 below. When the structural units in the formula are structural units that can represent a plurality of structures, two or more such structural units may be combined and used as the structural units constituting the polymer.

[0019]

Table 2

[0020]

Table 3

[0021]

Table 4

[0022] In the constituent units of Table 2, Table 3 and Table 4, n is an integer of 1 or 2, and each constituent unit n = 1, n = 2 may exist alone or in combination. Y1 and Y2 are each independently a hydrogen atom, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (for example, a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (for example, a phenyl group, a naphthyl group, etc.), an aralkyl group (for example, a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (for example, a phenoxy group, etc.), an aralkyloxy group (for example, a benzyloxy group, etc.). Among these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferable.

[0023] Further, examples of Z include substituents represented by the following formula.

[0024]

Chemical formula

[0025] The liquid crystal polyester may preferably be a combination having a naphthalene skeleton as a constituent unit. It is particularly preferable to contain both a constituent unit (A) derived from hydroxybenzoic acid and a constituent unit (B) derived from hydroxynaphthoic acid. For example, the following formula (A) may be mentioned as the constituent unit (A), and the following formula (B) may be mentioned as the constituent unit (B). From the viewpoint of improving the melt moldability, the ratio of the constituent unit (A) to the constituent unit (B) may preferably be in the range of 9 / 1 to 1 / 1, more preferably 7 / 1 to 1 / 1, and even more preferably 5 / 1 to 1 / 1.

[0026] [Chemical formula]

[0027] [Chemical formula]

[0028] Also, the total of the constituent unit of (A) and the constituent unit of (B) may be, for example, 65 mol% or more with respect to all the constituent units, more preferably 70 mol% or more, and even more preferably 80 mol% or more. In the polymer, a liquid crystal polyester in which the constituent unit of (B) is particularly 4 to 45 mol% is preferable.

[0029] In addition, the liquid crystal polyester contains a structural unit derived from 4-hydroxybenzoic acid as an aromatic hydroxycarboxylic acid, and may contain a structural unit derived from an aromatic dicarboxylic acid and a structural unit derived from an aromatic diol. For example, at least one selected from the group consisting of the following formula (C) and the following formula (D) may be used as the structural unit derived from an aromatic dicarboxylic acid, and at least one selected from the group consisting of the following formula (E) and the following formula (F) may be used as the structural unit derived from an aromatic diol. Preferably, a liquid crystal polyester containing a structural unit (A) (the above formula (A)) derived from 4-hydroxybenzoic acid, a structural unit (C) (the following formula (C)) derived from terephthalic acid as an aromatic dicarboxylic acid, a structural unit (D) (the following formula (D)) derived from isophthalic acid, and a structural unit (E) (the following formula (E)) derived from 4,4'-dihydroxybiphenyl as an aromatic diol; a liquid crystal polyester containing a structural unit (A) (the above formula (A)) derived from 4-hydroxybenzoic acid, a structural unit (C) (the following formula (C)) derived from terephthalic acid as an aromatic dicarboxylic acid, a structural unit (D) (the following formula (D)) derived from isophthalic acid, a structural unit (E) (the following formula (E)) derived from 4,4'-dihydroxybiphenyl as an aromatic diol, and a structural unit (F) (the following formula (F)) derived from hydroquinone may be used, etc.

[0030]

Chemical formula

[0031]

Chemical formula

[0032]

Chemical formula

[0033]

Chemical formula

[0034] The liquid crystal polyester may contain a structural unit derived from 4-hydroxybenzoic acid, preferably may contain 50 mol% or more, more preferably 53 mol% or more, and even more preferably 60 mol% or more. The upper limit of the content of the structural unit derived from 4-hydroxybenzoic acid in the liquid crystal polyester is not particularly limited, and may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

[0035] The melting point of the liquid crystal polyester used in the present invention (hereinafter sometimes referred to as Mp0) is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, and even more preferably 260 to 360°C. Also, from the viewpoint of using the obtained liquid crystal polyester fiber as a heat-sealing fiber, the melting point of the liquid crystal polyester is more preferably 250 to 330°C, and even more preferably 260 to 320°C. Here, the melting point refers to the main absorption peak temperature measured by a differential scanning calorimeter (DSC; "TA3000" manufactured by Mettler) in accordance with the JIS K 7121 test method. Specifically, after taking 10 to 20 mg of the sample and enclosing it in an aluminum pan in the DSC apparatus, nitrogen is flowed at 100 mL / min as a carrier gas, and the endothermic peak when the temperature is raised at 20°C / min is measured. When a clear peak does not appear in the 1st run in the DSC measurement depending on the type of polymer, the temperature is raised at 50°C / min to a temperature 50°C higher than the expected flow temperature, completely melted at that temperature for 3 minutes, then cooled to 50°C at a cooling rate of 80°C / min, and thereafter the endothermic peak is measured at a heating rate of 20°C / min.

[0036] In addition, the liquid crystal polyester fiber may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin as long as the effects of the present invention are not impaired. Further, it may contain inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, colorants such as carbon black, dyes and pigments, and various additives such as antioxidants, ultraviolet absorbers, and light stabilizers.

[0037] The liquid crystal polyester fiber of the present invention may contain a metal catalyst that acts on the decarboxylation reaction of aromatic carboxylic acid. However, from the viewpoint of suppressing side reactions, for example, the contents of copper, cobalt, and palladium may be less than 10 weight ppm, preferably less than 5 weight ppm, more preferably less than 1 weight ppm.

[0038] The liquid crystal polyester fiber of the present invention may contain 50% by weight or more of liquid crystal polyester, preferably 80% by weight or more, more preferably 90% by weight or more, still more preferably 95% by weight or more, and even more preferably 99.9% by weight or more.

[0039] The liquid crystal polyester fiber of the present invention has a total carboxy end group amount (total CEG amount) of 5.0 meq / kg or less. In the present invention, the total CEG amount means the amount of carboxy groups present at the ends of the molecules constituting the liquid crystal polyester fiber with respect to 1 kg of the liquid crystal polyester fiber, and is a value measured by the method described in the examples below. For example, as the carboxy groups present at the polymer terminals in the liquid crystal polyester, structural units derived from monomers having carboxy groups such as aromatic hydroxycarboxylic acids and aromatic dicarboxylic acids form the polymer terminals, and the carboxy groups remaining without reacting in such structural units present at the polymer terminals may be used.

[0040] From the perspective of suppressing the amount of gas generated during heating, the total CEG amount of the liquid crystal polyester fiber of the present invention is preferably 4.0 meq / kg or less, more preferably 3.0 meq / kg or less, still more preferably 2.5 meq / kg or less, and even more preferably 2.0 meq / kg or less. The lower limit of the total CEG amount is not particularly limited, but for example, it may be 0.1 meq / kg or more.

[0041] The liquid crystal polyester fiber of the present invention has a ketone bond content of 0.05 mol% or less. In the present invention, the ketone bond content means the ratio of the molar amount of ketone bonds to the total molar amount of ester bonds and ketone bonds (molar amount of ketone bonds / (molar amount of ester bonds + molar amount of ketone bonds)), and is a value measured by the method described in the examples below. The inventors of the present invention have found that when the liquid crystal polyester resin is melt-processed, ketone bonds are generated from ester bonds due to side reactions, and that the ketone bonds affect the hue of the liquid crystal polyester fiber. Therefore, the liquid crystal polyester fiber of the present invention suppresses the generation of ketone bonds. From the perspective of achieving excellent hue, the ketone bond content may preferably be 0.04 mol% or less, and more preferably 0.03 mol% or less. The lower limit of the ketone bond content is not particularly limited, but for example, it may be 0.005 mol% or more.

[0042] Generally, liquid crystal polyester fibers can exhibit very high mechanical properties by increasing the molecular weight of the polymer by heat-treating the spun yarn obtained by melt spinning and subjecting it to solid-phase polymerization. However, in the present invention, a liquid crystal polyester fiber having a strength sufficient to be processed as a fused fiber for manufacturing a fiber-reinforced molded body may be used. For example, the liquid crystal polyester fiber of the present invention may be a spun yarn, or may be a heat-treated yarn subjected to solid-phase polymerization within a range that does not impair the effects of the present invention. Considering that the melting point of the liquid crystal polyester fiber increases from the melting point (Mp) of the spun yarn by solid-phase polymerization, when the liquid crystal polyester fiber of the present invention is used as a fused fiber, it is preferably a spun yarn.

[0043] The liquid crystal polyester fiber of the present invention may have a total chain end amount of 50 meq / kg or more, preferably 60 meq / kg or more, more preferably 70 meq / kg or more. The total chain end amount indicates the number of polymer chains and is used as an index for evaluating the molecular weight. Considering that it is difficult to quantify all types of ends depending on the composition of the liquid crystal polyester, in the present invention, the total chain end amount is the total amount (meq / kg) of the carboxy group end derived from hydroxycarboxylic acid and the end in which carbon dioxide has been eliminated by decarboxylation reaction in the carboxy group derived from hydroxycarboxylic acid per 1 kg of the liquid crystal polyester fiber, divided by the molar ratio of the structural unit derived from hydroxycarboxylic acid to all the structural units in the liquid crystal polyester (molar amount of the structural unit derived from hydroxycarboxylic acid / molar amount of all the structural units), and is a value measured by the method described in the examples below. When the total chain end amount is within the above range, the polymerization of the liquid crystal polyester does not proceed more than necessary and the molecular weight is relatively low, so it can be used as a fused fiber. The upper limit of the total chain end amount is not particularly limited, but if the molecular weight is too low, the strength required for processing the fiber may not be obtained. Therefore, for example, it may be 100 meq / kg or less, preferably 90 meq / kg or less.

[0044] From the viewpoint of using the liquid crystal polyester fiber of the present invention as a fused fiber, it is not necessary to have a high strength. For example, the strength may be less than 18 cN / dtex, preferably 2 to 16 cN / dtex, more preferably 6 to 12 cN / dtex. In the present invention, the strength of the liquid crystal polyester fiber refers to the tensile strength and is a value measured by the method described in the examples below.

[0045] From the viewpoint of using the liquid crystal polyester fiber of the present invention as a fused fiber, the melting point may be 380 °C or lower, preferably 250 to 350 °C, more preferably 260 to 300 °C. The melting point of the liquid crystal polyester fiber is a value measured by the method described in the examples below.

[0046] The liquid crystal polyester fiber of the present invention can appropriately select the fineness of a single fiber according to its use and the like. For example, the fineness of a single fiber may be 0.5 to 50 dtex, preferably 1.0 to 35 dtex, more preferably 1.0 to 15 dtex, and even more preferably 1.5 to 10 dtex.

[0047] The liquid crystal polyester fiber of the present invention may be a monofilament or a multifilament. In the case of a multifilament, the number of filaments can be appropriately selected according to its use and the like. For example, the number of filaments may be 2 to 5000, preferably 3 to 4000, and more preferably 5 to 3000.

[0048] The liquid crystal polyester fiber of the present invention can appropriately select the total fineness according to its use and the like. For example, the total fineness may be 1 to 50000 dtex, preferably 5 to 10000 dtex, more preferably 10 to 2000 dtex, and even more preferably 10 to 600 dtex.

[0049] In the liquid crystal polyester fiber of the present invention, the amount of CO2 gas generated, measured by the examples described below, may be 2.0 mmol / kg or less, preferably 1.5 mmol / kg or less, and more preferably 1.0 mmol / kg or less.

[0050] Since the liquid crystal polyester fiber of the present invention can suppress the amount of ketone bonds to a low level, it has excellent hue. For example, the L * value may be 78 or more, preferably 79 or more, and more preferably 80 or more. The L * value refers to the L * a * b * value representing the lightness in the color system of L * value, which is measured by the method described in the examples below. The L * value becomes brighter as the numerical value is larger and darker as the numerical value is smaller. The upper limit of the L * value is not particularly limited, but may be 85 or less, for example.

[0051] For reasons not yet clear, the liquid crystal polyester fiber of the present invention can suppress the amount of ketone bonds to a low level, and thus can reduce the surface roughness of the fiber. The surface roughness of the liquid crystal polyester fiber affects the processability when used as a fused fiber and the adhesiveness with the reinforcing fiber, leading to a deterioration in physical properties. For example, the surface roughness Ra may be 1.0 μm or less, preferably 0.8 μm or less, and more preferably 0.6 μm or less. The lower limit of the surface roughness Ra is not particularly limited, and may be, for example, 0.1 μm or more. The surface roughness Ra is the arithmetic mean roughness measured in accordance with JIS B 0601-2001, and represents the average value of the absolute value of the deviation from the average line to the roughness curve in the roughness curve of the reference length, indicating the uneven state of that section. Note that the surface roughness Ra is measured by the method described in the examples below.

[0052] [Method for producing liquid crystal polyester fiber] The method for producing the liquid crystal polyester fiber of the present invention is not particularly limited as long as the total CEG amount and the ketone bond amount of the liquid crystal polyester fiber can be adjusted to specific amounts as described above, and may include at least a step of melt-kneading the liquid crystal polyester in an extruder and a step of discharging the melt-kneaded product from a nozzle for spinning.

[0053] As a method for adjusting the total CEG amount and the ketone bond amount of the liquid crystal polyester fiber, for example, a method of adjusting the heating temperature and residence time in the extruder in relation to the melting point of the input liquid crystal polyester can be mentioned. For example, in the method for producing the liquid crystal polyester fiber of the present invention, in the melt-kneading step, the heat history TH represented by the following formula (1) may be 250 to 1100. [Number] In the formula, Mp0 is the melting point (°C) of the liquid crystal polyester, x is the time (minutes) defined such that x = 0 when the liquid crystal polyester is introduced into the extruder, x = 1, 2,... during residence, and x = M when the melt-kneaded product is discharged from the nozzle, and T x (T1, T2,..., TM ) is the heating temperature (°C) per minute during the residence time from input to discharge, and y is the residence time (minutes) in the heating temperature range where T x ≦(Mp0 + 10). However, when M and y are not integers, they are rounded to integers for calculation, and M is an integer that satisfies M≧y + 1.

[0054] As described later, TH represented by the above formula (1) indicates an index related to the thermal history of how much the liquid crystal polyester is exposed to a high temperature at which decarboxylation reaction of carboxy groups at the molecular ends and side reactions of ester bonds occur during the residence time from when the liquid crystal polyester is introduced into the extruder until it is discharged from the nozzle as a melt-kneaded product.

[0055] The inventors of the present invention have found that when a liquid crystal polyester fiber having a carboxy group at the end of the liquid crystal polyester is heated as a fused fiber, a decarboxylation reaction occurs at the carboxy group and carbon dioxide is generated as a thermal decomposition gas. Therefore, in the method for producing a liquid crystal polyester fiber, it has been found that by melt-kneading at a high temperature for a long time in an extruder, the decarboxylation reaction of the carboxy group at the molecular end can be advanced in advance and the carboxy group at the molecular end can be reduced. However, it has also been found that when melt-kneading at a high temperature for a long time, side reactions of the ester bonds of the liquid crystal polyester occur and ketone bonds are formed. Therefore, in the present invention, by adjusting the thermal history of the liquid crystal polyester by heating temperature and residence time in relation to its melting point, it is possible to advance the decarboxylation reaction of the carboxy group at the molecular end while suppressing side reactions of the ester bonds.

[0056] A method for producing liquid crystal polyester fibers will be described below with reference to FIG. 1. FIG. 1 is a schematic diagram showing an apparatus 100 used for producing liquid crystal polyester fibers according to an embodiment of the present invention. As shown in FIG. 1, the apparatus 100 includes an extruder 10, a gear pump 30, a spinning head 40, and a pipe 20 connecting these components. The extruder 10 includes a hopper 11 for introducing liquid crystal polyester, a barrel 12, a screw 13 rotating within the barrel 12, and a vent 14. FIG. 1 illustrates the equipment necessary for explaining the method for producing liquid crystal polyester fibers of the present invention, but the apparatus 100 may be provided with other equipment as necessary.

[0057] In FIG. 1, the solid liquid crystal polyester introduced from the hopper 11 is transported in the X direction, which is the advancing direction, within the barrel 12 by the rotation of the screw 13 and is heated by known heating means such as a heater installed in the barrel 12. In addition to the heat transfer from the heating means, mechanical energy such as friction and shear is efficiently imparted between the inner wall of the barrel 12 and the screw 13, causing the solid liquid crystal polyester to melt as it progresses in the X direction. Thereafter, the molten liquid crystal polyester is metered by the gear pump 30, passes through the pipe 20, is transported to the spinning head 40, is discharged through the nozzle 41 at a predetermined spinning temperature, and the resulting yarn is wound up to produce liquid crystal polyester fibers. Note that the liquid crystal polyester may be introduced into the extruder 10 as a resin composition containing the above-described thermoplastic polymer, various additives, catalysts, etc.

[0058] As the thermal history of the liquid crystal polyester in the apparatus 100, the thermal history that affects the decarboxylation reaction of the carboxy group at the molecular end and the side reaction of the ester bond can be grasped by TH represented by the above formula (1). First, the liquid crystal polyester introduced from the hopper 11 starts to stay with x = 0 (minutes). Within the barrel 12, the liquid crystal polyester is heated as it progresses in the X direction. When grasping the heating temperature T in the apparatus 100 every minute with x being an integer of 1 or more x for the heating temperature T xrepresents the temperature of the apparatus 100 at the location where the liquid crystal polyester is located x minutes after the liquid crystal polyester is introduced into the extruder 10 within the residence time M. The location x minutes after introduction is represented by a location that is separated from the introduction location by a distance in the X direction by which the liquid crystal polyester is transported in x minutes. This distance can be calculated from the volume of the apparatus 100, the transport speed of the screw 13, the transport speed of the gear pump 30, a predetermined time x minutes, and the like.

[0059] In the above formula (1), the residence time M represents the time during which the liquid crystal polyester stays within the apparatus 100 from when the liquid crystal polyester is introduced from the hopper 11 into the extruder 10 until the liquid crystal polyester is discharged from the nozzle 41 as a melt-kneaded product. The residence time M can be calculated based on the volume of the entire apparatus 100 from when the liquid crystal polyester is introduced until it is discharged, the transport speed of the gear pump 30, etc. For example, the volume of the entire apparatus (in FIG. 1, barrel 12 + pipe 20 + gear pump 30 + spinning head 40) [cm 3 / {(rotation speed of the gear pump [RPM] × transport capacity per rotation of the gear pump [cm 3 )}, and when it is not an integer, it is rounded to an integer for calculation.

[0060] Immediately after being introduced into the hopper 11, the heating temperature T x has not risen sufficiently with respect to the melting point Mp0 and does not affect the thermal history. Therefore, among the residence time M, the thermal history up to the time y (minutes) during which the liquid crystal polyester stays in the initial low-temperature region where the melting point (Mp0) of the liquid crystal polyester + 10 °C or lower is not considered. Therefore, in the above formula (1), the sum starting from x = y + 1 is calculated. y can be calculated based on the volume of the apparatus, the transport speed of the gear pump, the region set at a low temperature, etc., and when it is not an integer, it is rounded to an integer for calculation.

[0061] In order to promote the decarboxylation reaction of the carboxy groups at the terminals of the liquid crystal polyester, it is preferable to heat and melt at a temperature exceeding the melting point (Mp0) of the liquid crystal polyester + 10°C. In the extruder, in order to change the liquid crystal polyester from the solid state to the molten state as it moves in the X direction, it is common to increase the temperature for each region in the X direction. Therefore, when heating and melting at a temperature exceeding Mp0 + 10°C, the temperature in the extruder 10 is set to start at a temperature of Mp0 + 10°C or lower, and then the set temperature is increased in the X direction to a temperature exceeding Mp0 + 10°C. Further, when being transported from the extruder 10 toward the spinneret 40, from the viewpoint of adjusting the viscosity of the molten liquid crystal polyester, outside the extruder 10 (the pipe 20, the gear pump 30, and the spinneret 40), the temperature may be lower than the maximum temperature in the extruder 10, but it is preferable to heat at a temperature exceeding Mp0 + 10°C. In that case, when x is from 1 to y, T x is T x satisfying the relationship of ≤ (Mp0 + 10), and when x is from y + 1 to M, T x are all T x satisfying the relationship of > (Mp0 + 10). Therefore, TH is, among the residence time M, for all cases of time x where T x > (Mp0 + 10), the sum of the temperatures obtained by adding the positive value of T x - (Mp0 + 10).

[0062] When heating at a temperature exceeding the melting point (Mp0) of the liquid crystal polyester + 10°C, in addition to the decarboxylation reaction, side reactions of the ester bonds also proceed simultaneously. Therefore, T x - (Mp0 + 10) in the above formula (1) is an index meaning how high a temperature the liquid crystal polyester is exposed to as the temperature conditions for the decarboxylation reaction of the carboxy groups at the molecular terminals and the side reactions of the ester bonds. That is, TH means an index regarding the heat history indicating how much the liquid crystal polyester is exposed to a high temperature such that the decarboxylation reaction of the carboxy groups at the molecular terminals and the side reactions of the ester bonds occur during the residence time from when it is introduced into the extruder 10 until it is discharged from the nozzle 41 as a melt-kneaded product.

[0063] When the value of TH is too large, that is, when the heating temperature in the extruder is too high and / or the residence time is too long, side reactions of the ester bonds of the liquid crystal polyester occur excessively, the formation of ketone bonds cannot be suppressed, the amount of ketone bonds increases, and the hue and surface roughness of the fiber tend to deteriorate. Note that when the value of TH is relatively large, the decarboxylation reaction of the carboxy groups at the ends of the liquid crystal polyester proceeds sufficiently, so the total CEG amount becomes small and the amount of gas generated during heating is small. On the other hand, when the value of TH is too small, that is, when the heating temperature in the extruder is too low and / or the residence time is too short, the decarboxylation reaction of the carboxy groups at the ends of the liquid crystal polyester hardly proceeds, the carboxy groups at the molecular ends cannot be reduced, the total CEG amount increases, and the amount of gas generated during heating tends to increase. Note that when the value of TH is relatively small, the amount of ketone bonds does not increase, so the hue and surface roughness of the fiber do not deteriorate.

[0064] From the viewpoint of reducing the carboxy groups at the molecular ends, TH may preferably be 300 or more, more preferably 350 or more, and still more preferably 400 or more. Also, from the viewpoint of suppressing the formation of ketone bonds, TH may preferably be 1000 or less, more preferably 950 or less, and still more preferably 900 or less.

[0065] From the viewpoint of reducing the carboxy groups at the molecular ends, the residence time M may be 6 minutes or more, preferably 8 minutes or more, and more preferably 10 minutes or more. Also, from the viewpoint of suppressing the formation of ketone bonds, it may be 40 minutes or less, preferably 30 minutes or less, and more preferably 25 minutes or less. Also, regarding the time y during which the liquid crystal polyester stays in the initial low-temperature region of the melting point (Mp0) + 10 °C or lower of the liquid crystal polyester in the residence time M, there is no particular limitation, but it may be 1 minute or more, preferably 2 minutes or more, and may also be 5 minutes or less.

[0066] T xThe maximum temperature may be Mp0 + 30°C or higher, preferably Mp0 + 40°C or higher, more preferably Mp0 + 50°C or higher, and even more preferably Mp0 + 55°C or higher, from the viewpoint of reducing the carboxy groups at the molecular terminals. Also, from the viewpoint of suppressing the formation of ketone bonds, it may be Mp0 + 100°C or lower, preferably Mp0 + 90°C or lower, and more preferably Mp0 + 85°C or lower.

[0067] In the extruder 10, since the decarboxylation reaction is proceeding, carbon dioxide is generated as a pyrolysis gas. From the viewpoints of removing the carbon dioxide generated by the decarboxylation reaction outside the system and further promoting the decarboxylation reaction, and reducing the inclusion of the generated gas as bubbles in the fiber, for example, it is preferable to connect a vacuum pump or the like to the vent 14 of the extruder 10 and degas by depressurizing the inside of the extruder 10. For example, the degree of vacuum may be 100 kPa or lower in absolute pressure, preferably 80 kPa or lower, and more preferably 60 kPa or lower.

[0068] As the extruder 10, known extruders such as a single-screw extruder and a multi-screw extruder (two or more axes) can be used, and a twin-screw extruder is preferable from the viewpoints of improving kneading properties and degassing properties.

[0069] After obtaining a melt-kneaded product containing the liquid crystal polyester in the extruder 10, it may be metered by the gear pump 30, supplied to the spinneret 40, and discharged from the nozzle 41 for melt spinning. The melt spinning can be carried out by a known or conventional method, and can be obtained by discharging from the nozzle at a predetermined spinning temperature and winding it up by a godet roller or the like.

[0070] [Fiber structure] The liquid crystal polyester fiber of the present invention can be used as a fusion fiber for manufacturing a molded body using it as a matrix. When using it as a fusion fiber, a fiber structure containing the liquid crystal polyester fiber in at least a part can be used as an intermediate material for manufacturing the molded body.

[0071] The fiber structure containing the liquid crystal polyester fiber of the present invention can be used in any fiber form such as staple fiber, short cut fiber, filament yarn, spun yarn, cord, rope, etc., and can also be used as various fabrics such as non-woven fabric, woven fabric, knitted fabric using the liquid crystal polyester fiber. Such fibers and fabrics can be produced using the liquid crystal polyester fiber by known methods.

[0072] The fiber structure of the present invention may combine the liquid crystal polyester fiber with other fibers as long as the effects of the present invention are not impaired. For example, a composite yarn using the liquid crystal polyester fiber and other fibers (for example, a mixed yarn in which the liquid crystal polyester fiber and other fibers are mixed) can be used. Further, a composite fabric using the liquid crystal polyester fiber and other fibers (for example, a mixed fabric in which the liquid crystal polyester fiber and other fibers are mixed, a laminate of a fabric made of the liquid crystal polyester fiber and a fabric made of other fibers, etc.) can be used. When the fiber structure is used for the production of a reinforced fiber molded body (fiber reinforced composite material), the fiber structure may be a composite yarn or composite fabric containing a reinforcing fiber as other fibers.

[0073] The type of the reinforcing fiber is not particularly limited as long as its melting point is higher than that of the liquid crystal polyester fiber of the present invention. For example, at least one selected from the group consisting of glass fiber, carbon fiber, liquid crystal polyester fiber, aramid fiber, polyparaphenylene benzobisoxazole fiber, polyparaphenylene benzobisimidazole fiber, polyparaphenylene benzobisthiazole fiber, ceramic fiber, and metal fiber can be mentioned. These reinforcing fibers may be used alone or in combination of two or more.

[0074] [Molded body] In the present invention, the molded article may be any article that can be obtained by molding a fibrous structure. For example, it may be a molded article that does not contain reinforcing fibers and is obtained by molding a fibrous structure, or it may be a reinforced fiber molded article obtained by molding a fibrous structure together with reinforcing fibers. Since the fibrous structure can be made flexible, it is possible to form molded articles having various three-dimensional shapes such as cylindrical and dome-shaped by weaving, knitting, etc.

[0075] The molded article can be obtained by heating and molding the fibrous structure at a temperature equal to or higher than the melting point of the liquid crystal polyester fiber. The molding method is not particularly limited as long as the liquid crystal polyester fiber is melted and integrated, and a known molding method for molded articles can be used. The liquid crystal polyester fiber of the present invention is excellent in hue and can suppress the generation of bubbles when heat-fused, so that a molded article having excellent appearance can be obtained.

[0076] In addition, since the liquid crystal polyester constituting the matrix of the molded article is excellent in vibration damping properties, the obtained molded article is excellent in vibration damping properties and can be effectively used in applications where vibration occurs, such as duct tubes and automobile bumpers.

Examples

[0077] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by these. In the following examples and comparative examples, various physical properties were measured by the following methods.

[0078] (Total fineness, single fiber fineness) Based on JIS L 1013:2010 8.3.1 Method A, using a measuring instrument "Wrap Reel by Motor Driven" manufactured by Dai-ichi Kagaku Seiki Co., Ltd., the liquid crystal polyester fiber was wound around a bobbin of 1 m per turn × 100 turns (total 100 m), and its weight (g) was multiplied by 100, and two measurements were taken for each level, and the average value was taken as the total fineness (dtex) of the obtained liquid crystal polyester fiber. Also, the quotient obtained by dividing this value by the number of filaments was taken as the single fiber fineness (dtex).

[0079] (Melting point of fiber and resin chips (granular molded bodies)) Measurement was carried out in accordance with JIS K 7121 using a differential scanning calorimeter (DSC; manufactured by Mettler, "TA3000"), and the main absorption peak temperature observed was taken as the melting point. Specifically, after taking 10 - 20 mg of the sample and enclosing it in an aluminum pan in the DSC apparatus, nitrogen was flowed as the carrier gas at a flow rate of 100 mL / min, and the endothermic peak derived from the liquid crystal polyester was measured when the temperature was raised from 25°C at a rate of 20°C / min.

[0080] (Strength) With reference to JIS L 1013:2010 8.5.1, using an autograph "AGS - 100B" manufactured by Shimadzu Corporation, a tensile test was conducted 6 times for each yarn sample under the conditions of a test length of 10 cm and a tensile speed of 10 cm / min. The average tensile strength (cN) was divided by the total fineness (dtex) measured by the above method to calculate the strength (cN / dtex).

[0081] (Total CEG amount) The liquid crystal polyester fiber sample was cryogenically pulverized until d90 = 100 μm or less (d90: the particle diameter at which the cumulative volume in the particle size distribution is 90%). An excessive amount of n - propylamine was added to the pulverized sample, and heat - stirring treatment was carried out at 40°C for 90 minutes to decompose the sample. In this case, the ester bonds present inside the polymer chain were decomposed into carboxylic acid n - propylamide and hydroxy groups, and the carboxy groups (CEG) and hydroxy groups present at the ends of the polymer chain remained unchanged as carboxy groups and hydroxy groups. Therefore, the decomposition products were separated by HPLC method, and the peak area of the decomposition product having a carboxy group was compared with the calibration curve prepared by HPLC analysis of each standard to quantify the carboxy - terminal amount (meq / kg) derived from each monomer. For example, the CEG amount derived from monocarboxylic acids such as 4 - hydroxybenzoic acid and 6 - hydroxy - 2 - naphthoic acid was determined by directly quantifying 4 - hydroxybenzoic acid and 6 - hydroxy - 2 - naphthoic acid, and terephthalic acid, isophthalic acid, and 2,The amount of CEG derived from a divalent carboxylic acid such as 6-naphthalenedicarboxylic acid is determined by quantifying a substance in which one carboxy group is amidated, such as terephthalic acid mono n-propylamide, isophthalic acid mono n-propylamide, or 2,6-naphthalenedicarboxylic acid mono n-propylamide. The total of all carboxy terminal amounts contained in each sample was defined as the total carboxy terminal amount (total CEG amount) (meq / kg) of that sample.

[0082] (Total terminal amount of all fragments) Similar to the measurement of the total CEG amount described above, the liquid crystal polyester fiber sample was decomposed using n-propylamine, and the total amount (meq / kg) of the carboxy terminal amount derived from hydroxycarboxylic acid and the terminal amount generated by the decarboxylation reaction of the carboxy group at the terminal derived from hydroxycarboxylic acid was quantified. For example, the terminal amount derived from 4-hydroxybenzoic acid is determined by quantifying 4-hydroxybenzoic acid and phenol, and the terminal amount derived from 6-hydroxy-2-naphthoic acid is determined by quantifying 6-hydroxy-2-naphthoic acid and 2-naphthol. In order to consider the terminal amounts derived from diols and dicarboxylic acids other than hydroxycarboxylic acids, the total of the terminal amounts derived from hydroxycarboxylic acids was divided by the molar ratio of the structural units derived from hydroxycarboxylic acids to all the structural units in the liquid crystal polyester of the sample, and the value obtained was defined as the total terminal amount (meq / kg) of that sample.

[0083] (Amount of ketone bonds) The amount of ketone bonds was calculated by the thermal decomposition gas chromatography method described in Polymer Degradation and Stability, 76, 85-94 (2002). Specifically, using a thermal decomposition apparatus (manufactured by Frontier Lab Co., Ltd., "PY2020iD"), the liquid crystal polyester fiber sample was heated in the presence of tetramethylammonium hydroxide (TMAH) to generate gas by thermal decomposition / methylation. This gas was analyzed using gas chromatography (manufactured by Agilent Technologies, Inc., "GC-6890N"), and the amount of ketone bonds (mol%) was calculated from the peak area derived from ketone bonds and the peak area derived from ester bonds.

[0084] (Hue (L * value)) L * The L value was measured using a spectrophotometer "CM-3700A" manufactured by Konica Minolta, Inc., under the conditions of regular reflection processing: SCE, measurement diameter: LAV (25.4 mm), UV condition: 100% Full, field of view: 2 degrees, and main light source: C light source.

[0085] (Surface roughness Ra) Using a laser microscope manufactured by Keyence Corporation (controller unit "VK-X200", measurement unit "VK-X210"), at a magnification of 3000 times (objective lens 150 times × 20), for 10 points in the fiber longitudinal direction, with a reference length of 0.8 mm, the arithmetic mean roughness (Ra) of the fiber surface (conforming to the definition described in JIS B 0601:2001) was measured, and the average value of the 10 points was taken as the surface roughness Ra (μm) of the present invention.

[0086] (CO2 gas generation amount) The amount of CO2 gas generated when the liquid crystal polyester fiber was heated was evaluated by the thermal decomposition GC-BID method. Specifically, first, the liquid crystal polyester fiber was cryogenically pulverized until d90 = 100 μm or less to obtain an analysis sample. Using a GC (gas chromatograph) apparatus equipped with a pyrolyzer in the sample introduction section and a BID (dielectric barrier discharge ionization detector) in the gas detector, CO2 was separated, detected, and quantified from the gas generated by treating at 300 °C for 10 minutes. The measurement was performed 3 times for the same sample, and the average value was taken as the amount of CO2 gas generated (mmol / kg) from that sample.

[0087] (Foaming property evaluation) Using a circular knitting machine (manufactured by Maruzen Industries Co., Ltd., "MR-1", diameter 10 cm, 28 gauge), a knitted fabric of liquid crystal polyester fiber was produced. Three pieces of this fabric cut into a square with a side length of 10 cm were stacked. On the other hand, a SUS304 metal plate with a thickness of 1 mm and a square hole with a side length of 10 cm was placed on a polyimide film (manufactured by Ube Industries, Ltd., Upilex-S, 125S) prepared as a release film. After placing the three-layered knitted fabric in the square hole, a second polyimide film (the same as above) was placed on the metal plate. This was clamped from above and below with a flat heating press device at a pressure of 0.1 MPa or less and heated by contact for 5 minutes at the melting point of the liquid crystal polyester fiber + 20°C. Then, after applying a pressure of 2 MPa for 1 minute, the pressure was released to the atmosphere and cooled to 100°C or less to obtain a resin plate derived from liquid crystal polyester fiber, which is a sample for appearance evaluation. The front and back of a square area with a side length of 6 cm in the center of this sample for appearance evaluation were observed with a magnifying glass, and the number of bubbles with a major axis of 1 mm or more was counted.

[0088] [Example 1] Chips (granular molded bodies) of a liquid crystal polyester (α) (Mp0: 281°C) in which the structural units (A) and (B) represented by the following formula have (A) / (B) = 73 / 27 (molar ratio) were used. These chips were charged into a Φ15 mm twin-screw extruder (manufactured by Technovel Corporation, "KZW15TW-45MG-NH(-700)"), melt-kneaded at a maximum temperature of 365°C, and the melt-kneaded material was supplied to the spinneret while being metered by a gear pump. Here, the residence time and temperature profile from the twin-screw extruder to the spinneret were set as shown in Table 5, and TH was adjusted to 553. At this time, a vacuum pump (dry pump manufactured by Orion Machine Co., Ltd., "KRF40A-V-01B") was connected via a metal pipe from the vent part in the middle of the twin-screw extruder, and the resin non-filled space in the twin-screw extruder was depressurized to 60 kPa. The spinning head is equipped with a spinneret having a pore diameter of 0.1 mmφ, a land length of 0.14 mm, and 40 holes. The molten kneaded material was discharged from the spinneret at a discharge rate of 22.0 g / min and wound onto a bobbin at a winding speed of 1000 m / min to obtain liquid crystal polyester fibers (spinning raw yarn). At this time, an aqueous solution of 2 wt% sodium dodecyl phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako special grade) was applied to the spinning raw yarn from an oiling guide arranged immediately below the spinneret. The application amount of this aqueous solution was 1.4 g / min, and the adhesion ratio of sodium dodecyl phosphate to the spinning raw yarn was 0.1 wt% in calculation. The analysis results of the obtained liquid crystal polyester fibers are shown in Table 7.

[0089] [Chemical formula]

[0090] [Table 5]

[0091] The calculation method of TH will be described taking the production conditions of Example 1 as an example. Table 5 shows the heating temperature T every minute at the residence time M in Example 1 x , T in formula (1) x -(Mp0 + 10), and the numerical values of TH. In Example 1, since Mp0 is 281°C, T x ≦(Mp0 + 10) is satisfied when x where T x is 260°C is 1 to 2. Therefore, the residence time y is 2, and when x is y + 1 (that is, 3) or more, T x -(Mp0 + 10) shows a positive numerical value. And as the numerical value of TH, when x is y + 1 to M (that is, 3 to 14), all the numerical values of T x -(Mp0 + 10) are added together to calculate 553. The same calculation was performed in the following examples and comparative examples.

[0092] [Example 2] After setting the maximum temperature in the twin-screw extruder to 340 °C, a liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1 except that TH was adjusted to 403 by changing the temperature profile. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0093] [Example 3] After setting the residence time to 11 minutes and the maximum temperature in the twin-screw extruder to 340 °C, TH was adjusted to 335 by changing the temperature profile. A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1 except that a spinneret with a hole diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes was used and the melt-kneaded product was discharged at a discharge rate of 28.0 g / min and wound up at a winding speed of 500 m / min. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0094] [Example 4] After setting the residence time to 27 minutes and the maximum temperature in the twin-screw extruder to 360 °C, a liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1 except that TH was adjusted to 996 by changing the temperature profile. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0095] [Example 5] After setting the residence time to 11 minutes and the maximum temperature in the twin-screw extruder to 360 °C, TH was adjusted to 435 by changing the temperature profile. A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1 except that a spinneret with a hole diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes was used and the melt-kneaded product was discharged at a discharge rate of 56.0 g / min. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0096] [Example 6] After setting the residence time to 27 minutes and the maximum temperature in the twin-screw extruder to 340 °C, by changing the temperature profile, TH was adjusted to 836. Using a spinneret with a hole diameter of 0.125 mmφ, a land length of 0.175 mm, and 20 holes, the molten kneaded product was discharged at a discharge rate of 11.0 g / min. Five out of the 20 discharged filaments were separated and wound up at a winding speed of 1000 m / min. In other respects, the liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0097] [Example 7] After setting the residence time to 27 minutes and the maximum temperature in the twin-screw extruder to 360 °C, by changing the temperature profile, TH was adjusted to 926. In other respects, the liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 6. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0098] [Example 8] The chips of liquid crystal polyester (α) were put into a Φ30 mm single-screw extruder (manufactured by Osaka Seiki Co., Ltd., "3VSE-30-32N type"), melt-kneaded at a maximum temperature of 340 °C, and the melt-kneaded product was supplied to the spinning head while being metered by a gear pump. Here, the residence time and temperature profile from the single-screw extruder to the spinning head were set as shown in Table 6, and TH was adjusted to 452. The spinning head was equipped with a spinneret with a hole diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes. In other respects, the liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1, except that the melt-kneaded product was discharged from the spinneret at a discharge rate of 28.0 g / min and wound up at a winding speed of 500 m / min. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0099]

Table 6

[0100] [Example 9] Instead of the liquid crystal polyester (α) described in Example 1, a liquid crystal polyester (β) (Mp0: 348 °C) in which the molar ratio of each structural unit represented by the following formula is (A) / (C) / (D) / (E) = 65 / 10 / 5 / 20 was used, and the residence time was set to 21 minutes and the maximum temperature in the twin-screw extruder was set to 380 °C. Then, by changing the temperature profile, a liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1 except that TH was adjusted to 308. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0101]

Chemical formula

[0102] [Example 10] Instead of the liquid crystal polyester (α) described in Example 1, a liquid crystal polyester (γ) (Mp0: 315 °C) in which the molar ratio of each structural unit represented by the following formula is (A) / (C) / (D) / (E) / (F) = 54 / 15 / 8 / 16 / 7 was used, and the residence time was set to 21 minutes and the maximum temperature in the twin-screw extruder was set to 360 °C. Then, by changing the temperature profile, a liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1 except that TH was adjusted to 375. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0103]

Chemical formula

[0104] [Comparative Example 1] A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1 except that the residence time was set to 11 minutes, the maximum temperature in the twin-screw extruder was set to 310 °C, then the temperature profile was changed to adjust TH to 160, and a melt-kneaded product was discharged at a discharge rate of 28.0 g / min using a spinneret with a pore diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes and wound up at a winding speed of 500 m / min. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0105] [Comparative Example 2] A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1, except that the maximum temperature in the twin-screw extruder was set to 310 °C and then the temperature profile was changed to adjust TH to 193. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0106] [Comparative Example 3] A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 6, except that the residence time was set to 5 minutes, the maximum temperature in the twin-screw extruder was set to 310 °C, and then the temperature profile was changed to adjust TH to 56. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0107] [Comparative Example 4] A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 1, except that the residence time was set to 22 minutes, the maximum temperature in the twin-screw extruder was set to 370 °C, then the temperature profile was changed to adjust TH to 1355, and a spinneret with a pore diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes was used to extrude the melt-kneaded product at a discharge rate of 14.0 g / min and wind it up at a winding speed of 250 m / min. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0108] [Comparative Example 5] A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Example 8, except that the residence time was set to 11 minutes, the maximum temperature in the single-screw extruder was set to 340 °C, and then the temperature profile was changed to adjust TH to 246. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0109] [Comparative Example 6] A liquid crystal polyester fiber (spinning raw yarn) was obtained in the same manner as in Comparative Example 5, except that the residence time was set to 23 minutes, the maximum temperature in the single-screw extruder was set to 360 °C, and then the temperature profile was changed to adjust TH to 1284. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0110]

Table 7

[0111] As shown in Table 7, in Examples 1 to 10, since the thermal history of the liquid crystal polyester was adjusted by the heating temperature and the residence time in relation to its melting point, the total CEG amount could be reduced and the ketone bond amount could be suppressed. Therefore, the liquid crystal polyester fibers of Examples 1 to 10 can suppress the gas generation amount, and the resin plate produced using them can suppress the generation of bubbles. Further, the obtained liquid crystal polyester fibers are excellent in hue and can reduce the surface roughness, and thus can be suitably used for producing a molded body excellent in appearance and physical properties.

[0112] On the other hand, in Comparative Examples 1 to 3 and 5, since the thermal history of the liquid crystal polyester is small, the ketone bond amount can be suppressed, but the total CEG amount cannot be sufficiently reduced. Therefore, the liquid crystal polyester fibers of Comparative Examples 1 to 3 and 5 generate more CO2 gas than those of Examples 1 to 10, and more bubbles are generated in the resin plate produced using them as compared with these examples.

[0113] In Comparative Examples 4 and 6, since the thermal history of the liquid crystal polyester is large, the total CEG amount can be reduced, but a large amount of ketone bonds are generated. Therefore, the liquid crystal polyester fibers of Comparative Examples 4 and 6 have a lower L * value and are inferior in hue compared to Examples 1 to 10. Further, the liquid crystal polyester fibers of Comparative Examples 4 and 6 have a larger surface roughness Ra compared to Examples 1 to 10.

Industrial Applicability

[0114] The liquid crystal polyester fiber of the present invention can suppress the generation of gas during heating and is excellent in hue, and thus can be used as a fusion fiber for producing a molded body (for example, a fiber-reinforced composite material).

[0115] As described above, the preferred embodiments of the present invention have been described with reference to the drawings. However, various additions, changes, or deletions are possible without departing from the spirit of the present invention, and such are also included within the scope of the present invention.

Explanation of Reference Numerals

[0116] 100 ··· Device 10 ··· Extruder 11 ··· Hopper 12 ··· Barrel 13 ··· Screw 14 ··· Vent 20 ··· Pipe 30 ··· Gear Pump 40 ··· Spinning Head 41 ··· Nozzle X ··· Flow Direction

Claims

1. A liquid crystal polyester fiber having a total carboxy terminal amount (total CEG amount) of 5.0 meq / kg or less and a ketone bond amount of 0.05 mol% or less.

2. The liquid crystal polyester fiber according to Claim 1, having a melting point of 380°C or less.

3. The liquid crystal polyester fiber according to Claim 1 or 2, having a strength of less than 18 cN / dtex.

4. The liquid crystal polyester fiber according to Claim 1 or 2, comprising a liquid crystal polyester having a structural unit derived from 4-hydroxybenzoic acid in an amount of 50 mol% or more.

5. The liquid crystal polyester fiber according to Claim 1 or 2, having a total piece end amount of 50 meq / kg or more.

6. A method for producing a liquid crystal polyester fiber according to Claim 1 or 2, comprising at least a step of melt-kneading a liquid crystal polyester in an extruder and a step of discharging the melt-kneaded product from a nozzle and spinning it.

7. The production method according to Claim 6, wherein in the melt-kneading step, the thermal history TH represented by the following formula (1) is 250 to 1100. 【Number 1】 wherein, Mp ０ is the melting point (°C) of the liquid crystal polyester, x is defined as x = 0 at the time of charging the liquid crystal polyester into the extruder, x = 1, 2,... during residence, and x = M at the time of discharging from the nozzle of the melt-kneaded product, and is the time (minutes), T ｘ (T １ , T ２ ,..., T Ｍ ) is the heating temperature (°C) per minute in the residence time from charging to discharging, and y is the residence time (minutes) in the heating temperature range where T ｘ ≤ (Mp ０ +10). However, when M and y are not integers, they are rounded to integers for calculation, and M is an integer satisfying M ≥ y + 1.

8. The production method according to Claim 6, wherein the extruder is a twin-screw extruder.

9. A fiber structure comprising at least a part of the liquid crystal polyester fiber according to Claim 1 or 2.

10. The fiber structure according to Claim 9, further comprising a reinforcing fiber.

11. A method for producing a molded article, wherein the fiber structure according to Claim 9 is heated and molded at a temperature equal to or higher than the melting point of the liquid crystal polyester fiber.

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