Liquid crystal polyester fiber and production method for the same

Abstract

To provide a liquid crystal polyester fiber in which generation of gas during heating is suppressed and which is excellent in hue.SOLUTION: The liquid crystal polyester fiber has 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. For example, the liquid crystal polyester fiber may have a melting point of 380°C or less. Furthermore, the liquid crystal polyester fiber may have a strength of less than 18 cN / dtex. Furthermore, the liquid crystal polyester fiber may comprise a liquid crystal polyester having 50 mol% or more of a structural unit derived from 4-hydroxybenzoic acid.SELECTED DRAWING: None

Description

Related Applications

[0001] This application claims priority to Patent Application No. 2021-166307, filed in Japan on October 8, 2021, the entire contents of which are incorporated herein by reference as part of this application. [Technical Field]

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

[0003] Conventionally, composite yarns containing reinforcing fibers and thermoplastic fibers (in the case of intermediate materials for fiber-reinforced composite materials, the thermoplastic fibers are heat-fused in a later process and are therefore sometimes referred to as fused fibers hereinafter) have been known as intermediate materials used in the production of fiber-reinforced composite materials. For example, Patent Document 1 (JP 1-280031 A) discloses a method for producing flexible composite fibers useful for composite products, which comprises bundling reinforcing multifilaments and thermoplastic multifilaments into a layered composite. Patent Document 2 (JP 2013-237945 A) discloses composite yarns containing a blend of continuous reinforcing fibers and continuous thermoplastic resin fibers, which are suitable for molding resin composite materials. Patent Document 3 (JP 4-73227 A) discloses a method for producing a blended yarn for a thermoplastic composite of continuous thermoplastic fibers and continuous reinforcing fibers.

[0004] Such composite yarns containing continuous reinforcing fibers and continuous thermoplastic fibers are more flexible than prepregs (tape- or fabric-like materials in which a thermosetting resin is applied or coated onto reinforcing fiber tows or fabrics) generally used as precursors to fiber-reinforced composite materials, or intermediate materials in which a reinforcing fiber tow or fabric is melt-impregnated with a thermosetting resin, and can easily be formed into fabrics with various three-dimensional deformations, such as cylindrical or dome shapes, by weaving, knitting, etc. Therefore, they can be effectively used as raw materials for sheet-shaped fiber-reinforced moldings with three-dimensional shapes, such as duct tubes and automobile bumpers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 1-280031 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-237945 [Patent Document 3] Japanese Patent Application Publication No. 4-73227 Summary of the Invention [Problem to be solved by the invention]

[0006] Such molded articles have many applications where vibrations occur, such as the above-mentioned duct tubes and automobile bumpers. Therefore, by using liquid crystal polyester fibers made of liquid crystal polyester, which is a thermoplastic resin with excellent vibration damping properties, as reinforcing fibers or fusion fibers, it is expected that molded articles with excellent vibration damping properties can be obtained.

[0007] However, when liquid crystal polyester fibers are used as fusible fibers, pyrolysis gas is generated from the liquid crystal polyester fibers when they are heated to a temperature at which fusion processing is possible, and a large number of bubbles are generated inside and on the surface of the obtained fiber-reinforced molding, which leads to a decrease in strength and a poor appearance, which is a problem.

[0008] Furthermore, there has been a problem that the hue (yellowishness) of the liquid crystal polyester fiber leads to poor appearance of the molded product.

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a liquid crystalline polyester fiber which, when used as a fusible fiber and subjected to heat fusion, does not generate bubbles and can be used to produce a molded article having excellent hue. [Means for solving the problem]

[0010] As a result of intensive research to achieve the above object, the inventors of the present invention have found that the pyrolysis gas generated from a liquid crystal polyester fiber when heated to a predetermined temperature is triggered by a decarboxylation reaction of a carboxy group present at the terminal of the liquid crystal polyester constituting the liquid crystal polyester fiber. Furthermore, they have found that the liquid crystal polyester constituting the liquid crystal polyester fiber contains a ketone bond formed by a side reaction, and that the ketone bond affects the hue of the liquid crystal polyester fiber, leading to the completion of the present invention.

[0011] That is, the present invention can be configured in the following manner. [Aspect 1] A liquid crystal polyester fiber having a total carboxyl terminal 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, even more preferably 2.5 meq / kg or less, and still 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 fiber according to aspect 1, having a melting point of 380° C. or lower (preferably 250 to 350° C., more preferably 260 to 300° C.). Aspect 3 The liquid crystal polyester fiber 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 A liquid crystal polyester fiber according to any one of aspects 1 to 3, comprising a liquid crystal polyester having 50 mol % or more (preferably 53 mol % or more, more preferably 60 mol % or more) of structural units derived from 4-hydroxybenzoic acid. Aspect 5 A liquid crystal polyester fiber according to any one of aspects 1 to 4, wherein the total amount of one terminal 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 the liquid crystalline polyester fiber according to any one of aspects 1 to 5, comprising at least the steps of melt-kneading a liquid crystalline polyester in an extruder, and discharging the melt-kneaded mixture from a nozzle and spinning it. Aspect 7 A method for producing a liquid crystal polyester fiber according to a sixth embodiment, 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, and even more preferably 400 to 900):

number

[0012] It should be noted that any combination of at least two elements disclosed in the claims and / or the specification and / or the drawings is included in the present invention, and in particular any combination of two or more of the claims set forth in the claims is included in the present invention. [Effects of the Invention]

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

[0014] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and description purposes and should not be used to define the scope of the present invention, which is defined by the appended claims. The drawings are not necessarily drawn to scale and may be exaggerated to illustrate the principles of the present invention. [Figure 1] 1 is a schematic diagram illustrating a method for producing a liquid crystal polyester fiber according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Liquid crystal polyester fiber] The liquid crystal polyester fiber of the present invention is composed of a liquid crystal polyester. The liquid crystal polyester is composed of structural units derived from, for example, aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc., and the structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not particularly limited in terms of their chemical structure, as long as the effects of the present invention are not impaired. Furthermore, the liquid crystal polyester may contain structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids, as long as the effects of the present invention are not impaired. For example, preferred structural units are shown in Table 1.

[0016] [Table 1]

[0017] In the structural units in Table 1, m is an integer of 0 to 2, and Y in the formula, in the range of 1 to the maximum number of possible substitution, each independently represents 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, a 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), an aralkyloxy group (for example, a benzyloxy group, etc.).

[0018] More preferred structural units include the structural units described in Examples (1) to (18) in the following Tables 2, 3, and 4. When the structural unit in the formula is a structural unit that can exhibit multiple structures, two or more of such structural units may be combined and used as structural units that constitute the polymer.

[0019] [Table 2]

[0020] [Table 3]

[0021] [Table 4]

[0022] In the structural units of Tables 2, 3, and 4, n is an integer of 1 or 2, and each of the structural units n=1 and n=2 may exist alone or in combination, and Y1 and Y2 may each independently be 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, or a t-butyl group), 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), an aralkyloxy group (e.g., a benzyloxy group), etc. Among these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

[0023] Furthermore, examples of Z include substituents represented by the following formulas.

[0024] [ka]

[0025] The liquid crystal polyester may preferably be a combination having a naphthalene skeleton as a structural unit. It is particularly preferred to contain both a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, the structural unit (A) may be represented by the following formula (A), and the structural unit (B) may be represented by the following formula (B). From the viewpoint of improving melt moldability, the ratio of the structural unit (A) to the structural 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] [ka]

[0027] [ka]

[0028] The total of the structural units (A) and the structural units (B) may be, for example, 65 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more, based on the total structural units. Liquid crystal polyesters in which the structural units (B) account for 4 to 45 mol % of the polymer are particularly preferred.

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

[0030] [ka]

[0031] [ka]

[0032] [ka]

[0033] [ka]

[0034] The liquid crystal polyester may contain structural units derived from 4-hydroxybenzoic acid, preferably 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 structural units derived from 4-hydroxybenzoic acid in the liquid crystal polyester is not particularly limited, but may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

[0035] The melting point (hereinafter sometimes referred to as Mp0) of the liquid crystalline polyester used in the present invention is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, and even more preferably 260 to 360°C. Furthermore, from the viewpoint of using the resulting liquid crystalline polyester fiber as a fusible fiber, the melting point of the liquid crystalline polyester may be more preferably 250 to 330°C, and even more preferably 260 to 320°C. The melting point here refers to the main absorption peak temperature observed when measured using a differential scanning calorimeter (DSC; Mettler TA3000) in accordance with JIS K 7121. Specifically, a 10 to 20 mg sample is placed in an aluminum pan and sealed in the DSC apparatus. Nitrogen is flowed as a carrier gas at 100 mL / min, and the endothermic peak is measured when the temperature is increased at 20°C / min. If a clear peak does not appear in the first run of DSC measurement due to the type of polymer, it is recommended to increase the temperature at 50°C / min to a temperature 50°C higher than the expected flow temperature, allow it to completely melt at that temperature for 3 minutes, then decrease the temperature to 50°C at a rate of 80°C / min, and then measure the endothermic peak at a heating rate of 20°C / min.

[0036] The liquid crystal polyester fiber may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, fluororesin, etc., within the range that does not impair the effects of the present invention. Furthermore, the liquid crystal polyester fiber may contain various additives such as inorganic substances such as titanium oxide, kaolin, silica, barium oxide, etc., colorants such as carbon black, dyes, and pigments, 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. From the viewpoint of suppressing side reactions, the content of copper, cobalt, and palladium may be less than 10 ppm by weight, preferably less than 5 ppm by weight, and more preferably less than 1 ppm by weight.

[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, even more preferably 95% by weight or more, and still more preferably 99.9% by weight or more.

[0039] The liquid crystal polyester fiber of the present invention has a total carboxyl terminal amount (total CEG amount) of 5.0 meq / kg or less. In the present invention, the total CEG amount means the amount of carboxyl groups present at the terminals of the molecules constituting the liquid crystal polyester fiber per 1 kg of the liquid crystal polyester fiber, and is a value measured by the method described in the Examples below. For example, the carboxyl group present at the polymer terminal in the liquid crystal polyester may be a carboxyl group remaining unreacted in a structural unit present at the polymer terminal, which is formed by a structural unit derived from a monomer having a carboxyl group, such as an aromatic hydroxycarboxylic acid or an aromatic dicarboxylic acid.

[0040] In order to suppress the amount of gas generated during heating, the liquid crystal polyester fiber of the present invention may have a total CEG content of preferably 4.0 meq / kg or less, more preferably 3.0 meq / kg or less, even 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 content is not particularly limited, but may be, for example, 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 refers to 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 discovered that when a liquid crystal polyester resin is melt-processed, ketone bonds are generated from ester bonds as a side reaction, and that the ketone bonds affect the hue of the liquid crystal polyester fiber. Therefore, the liquid crystal polyester fiber of the present invention has suppressed generation of ketone bonds. From the viewpoint of achieving excellent hue, the ketone bond content may preferably be 0.04 mol% or less, more preferably 0.03 mol% or less. The lower limit of the ketone bond content is not particularly limited, but may be, for example, 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 through heat treatment of the raw spun yarn obtained by melt spinning and solid-phase polymerization. However, in the present invention, the liquid crystal polyester fiber may have a strength sufficient to be processed into a fusible fiber for producing a fiber-reinforced molding. For example, the liquid crystal polyester fiber of the present invention may be a raw spun yarn, or may be a heat-treated yarn that has been solid-phase polymerized to an extent 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 raw spun yarn due to solid-phase polymerization, the liquid crystal polyester fiber of the present invention is preferably a raw spun yarn when used as a fusible fiber.

[0043] The liquid crystal polyester fiber of the present invention may have a total one-terminal amount of 50 meq / kg or more, preferably 60 meq / kg or more, and more preferably 70 meq / kg or more. The total one-terminal amount indicates the number of polymer chains and is used as an index for evaluating molecular weight. Considering the difficulty of quantifying all types of terminals in a liquid crystal polyester depending on its composition, in the present invention, the total one-terminal amount is defined as the value obtained by dividing the total amount (meq / kg) of carboxyl group terminals derived from hydroxycarboxylic acid and terminals resulting from decarboxylation of carboxyl groups derived from hydroxycarboxylic acid, per 1 kg of liquid crystal polyester fiber, by the molar ratio of hydroxycarboxylic acid-derived structural units to all structural units in the liquid crystal polyester (molar amount of hydroxycarboxylic acid-derived structural units / molar amount of all structural units), and is measured by the method described in the Examples below. When the total one-terminal 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, making it suitable for use as a fusible fiber. There is no particular upper limit to the total amount of single terminals. However, if the molecular weight is too low, the strength required for processing the fibers may not be obtained. Therefore, for example, it may be 100 meq / kg or less, and preferably 90 meq / kg or less.

[0044] The liquid crystal polyester fiber of the present invention does not need to have high strength from the viewpoint of use as a fusible fiber, and may have a strength of, for example, 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 tensile strength, and is a value measured by the method described in the examples below.

[0045] From the viewpoint of use as a fusible fiber, the liquid crystal polyester fiber of the present invention may have a melting point of 380° C. or lower, preferably 250 to 350° C., and 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 single fiber fineness of the liquid crystal polyester fiber of the present invention can be appropriately selected depending on the application, etc., and may be, for example, 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 depending on the application, etc. For example, the number of filaments may be 2 to 5,000, preferably 3 to 4,000, and more preferably 5 to 3,000.

[0048] The total fineness of the liquid crystal polyester fiber of the present invention can be appropriately selected depending on the application, etc., and may be, for example, 1 to 50,000 dtex, preferably 5 to 10,000 dtex, more preferably 10 to 2,000 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 as measured in the examples described later 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] The liquid crystal polyester fiber of the present invention has an excellent hue because the amount of ketone bonds can be kept low. * The value may be 78 or more, preferably 79 or more, and more preferably 80 or more. * The value is the L standardized by the International Commission on Illumination (CIE). * a * b * L, which represents the lightness of the color system * The value is measured by the method described in the Examples below. * The larger the value, the brighter the image, and the smaller the value, the darker the image. * The upper limit of the value is not particularly limited, but may be, for example, 85 or less.

[0051] The liquid crystal polyester fiber of the present invention can reduce the surface roughness of the fiber, possibly due to the ability to keep the ketone bond content low, although the reason is unclear. The surface roughness of the liquid crystal polyester fiber affects the processability and adhesion to reinforcing fibers when used as a fusible fiber, leading to a decrease 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, but 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 is the average absolute value of the deviation from the mean line to the roughness curve, representing the unevenness of a section of a roughness curve over a reference length. The surface roughness Ra is measured by the method described in the Examples below.

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

[0053] The total CEG amount and ketone bond amount of the liquid crystal polyester fiber can be adjusted, for example, by adjusting the heating temperature and residence time in the extruder in relation to the melting point of the liquid crystal polyester to be added. For example, in the method for producing the liquid crystal polyester fiber of the present invention, the thermal history TH represented by the following formula (1) may be 250 to 1100 in the melt-kneading step.

number

[0054] As will be described later, TH represented by the above formula (1) is an index relating to the thermal history, which indicates the extent to which the liquid crystal polyester is exposed to a high temperature that causes a decarboxylation reaction of the carboxyl groups at the molecular terminals and a side reaction of the ester bonds during the residence time from when the liquid crystal polyester is introduced into the extruder until when it is discharged from the nozzle as a molten mixture.

[0055] The inventors of the present invention have found that when a liquid crystal polyester fiber containing carboxyl groups at its terminals is heated as a fusible fiber, a decarboxylation reaction occurs at the carboxyl groups, generating carbon dioxide as a pyrolysis gas. Therefore, they have found that, in a method for producing a liquid crystal polyester fiber, melt-kneading the fiber in an extruder at high temperatures for a long period of time can advance the decarboxylation reaction of the carboxyl groups at the molecular terminals and reduce the number of carboxyl groups at the molecular terminals. However, they have also found that melt-kneading at high temperatures for a long period of time can cause a side reaction of the ester bonds in the liquid crystal polyester to form ketone bonds. Therefore, in the present invention, by adjusting the thermal history of the liquid crystal polyester by the heating temperature and residence time in relation to its melting point, it is possible to advance the decarboxylation reaction of the carboxyl groups at the molecular terminals while suppressing the side reaction of the ester bonds.

[0056] The method for producing a liquid crystal polyester fiber will be described below with reference to FIG. 1. FIG. 1 is a schematic diagram showing an apparatus 100 used for producing a liquid crystal polyester fiber according to one 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 piping 20 connecting these components. The extruder 10 includes a hopper 11 for charging the liquid crystal polyester, a barrel 12, a screw 13 that rotates within the barrel 12, and a vent 14. Although FIG. 1 illustrates the equipment necessary for explaining the method for producing a liquid crystal polyester fiber of the present invention, the apparatus 100 may include other equipment as needed.

[0057] In FIG. 1 , solid liquid crystalline polyester introduced from a hopper 11 is transported in the X direction, i.e., the direction of travel, within a barrel 12 by the rotation of a screw 13, and is heated by a known heating means, such as a heater, installed in the barrel 12. Furthermore, in addition to heat transfer from the heating means, mechanical energy, such as friction and shear, is efficiently applied between the inner wall of the barrel 12 and the screw 13, causing the solid liquid crystalline polyester to melt as it travels in the X direction. The molten liquid crystalline polyester is then metered by a gear pump 30, passed through a pipe 20, transported to a spinning head 40, and extruded through a nozzle 41 at a predetermined spinning temperature. The resulting yarn is wound to produce a liquid crystalline polyester fiber. The liquid crystalline polyester may be introduced into the extruder 10 as a resin composition containing the above-mentioned thermoplastic polymer, various additives, a catalyst, and the like.

[0058] The thermal history of the liquid crystal polyester in the apparatus 100, which influences the decarboxylation reaction of the carboxyl groups at the molecular terminals and the side reaction of the ester bonds, can be grasped by TH represented by the above formula (1). First, the liquid crystal polyester introduced from the hopper 11 starts to stay at x=0 (minutes). In the barrel 12, the liquid crystal polyester is heated as it advances in the X direction. The heating temperature T in the device 100 per minute is expressed as x, where x is an integer of 1 or more. x When determining the heating temperature T xindicates the temperature of the apparatus 100 at a point where the liquid crystalline polyester is located x minutes after the liquid crystalline polyester is introduced into the extruder 10, during the residence time M. The point x minutes after introduction is represented by a point in the X direction that is the distance the liquid crystalline polyester is transported from the introduction point 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, the predetermined time x minutes, etc.

[0059] In the above formula (1), the residence time M represents the time during which the liquid crystalline polyester resides in the apparatus 100 from when the liquid crystalline polyester is introduced into the extruder 10 from the hopper 11 until when the liquid crystalline polyester is discharged as a molten mixture from the nozzle 41. The residence time M can be calculated from the volume of the entire apparatus 100 from when the liquid crystalline polyester is introduced until when it is discharged, the transport speed of the gear pump 30, and the like. For example, the residence time M can be calculated from the volume [cm 3 ] of the entire apparatus (in FIG. 1 , the barrel 12 + the piping 20 + the gear pump 30 + the spinning head 40). 3 ] / {(Gear pump rotation speed [RPM] x Transport capacity per gear pump rotation speed [cm 3 ])}, and if it is not an integer, it is rounded to the nearest integer.

[0060] Immediately after being put into the hopper 11, the heating temperature T x Since the temperature does not rise sufficiently above the melting point Mp0 and does not affect the thermal history, the thermal history up to the time y (minutes) during which the liquid crystalline polyester stays in the initial low-temperature region below the melting point (Mp0) + 10°C of the liquid crystalline polyester is not taken into consideration during the residence time M. Therefore, in the above formula (1), the sum is calculated from x = y + 1. y can be calculated from the volume of the device, the transport speed of the gear pump, the region set at a low temperature, etc. If y is not an integer, it is rounded to the nearest integer.

[0061] In order to promote the decarboxylation reaction of the terminal carboxy groups of the liquid crystal polyester, it is preferable to heat and melt the liquid crystal polyester at a temperature exceeding the melting point (Mp0) + 10°C of the liquid crystal polyester. In order to convert the liquid crystal polyester from a solid state to a molten state in the X direction within the extruder, it is common to increase the temperature in each region toward the X direction. Therefore, when heating and melting at a temperature exceeding Mp0 + 10°C, the temperature within the extruder 10 is set to start at a temperature equal to or lower than Mp0 + 10°C, and then the set temperature is increased toward the X direction to a temperature exceeding Mp0 + 10°C. Furthermore, from the viewpoint of adjusting the viscosity of the molten liquid crystal polyester when transported from the extruder 10 toward the spinning head 40, the temperature outside the extruder 10 (piping 20, gear pump 30, and spinning head 40) may be equal to or lower than the maximum temperature within the extruder 10, but it is preferable to heat the liquid crystal polyester at a temperature exceeding Mp0 + 10°C. In this case, when x is 1 to y, T x is T x ≦(Mp0+10) and T when x is y+1~M x Both are T x > (Mp0+10). Therefore, TH is the time T x For all times x that satisfy the relationship >(Mp0+10), a positive value of T x -(Mp0+10) is added together to show the total temperature.

[0062] When heated at a temperature exceeding the melting point (Mp0) + 10°C of the liquid crystal polyester, a side reaction of the ester bond occurs in addition to the decarboxylation reaction. x -(Mp0+10) is an index indicating how high a temperature the liquid crystalline polyester has been exposed to, as a temperature condition that causes a decarboxylation reaction of the carboxy groups at the molecular terminals and a side reaction of the ester bonds. That is, TH is an index related to the thermal history that indicates how high a temperature the liquid crystalline polyester has been exposed to, during the residence time from when it is fed into the extruder 10 until it is discharged from the nozzle 41 as a molten mixture, that causes a decarboxylation reaction of the carboxy groups at the molecular terminals and a side reaction of the ester bonds.

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

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

[0065] The residence time M may be 6 minutes or more, preferably 8 minutes or more, and more preferably 10 minutes or more, from the viewpoint of reducing the carboxyl groups at the molecular terminals. Furthermore, 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. Furthermore, within the residence time M, the time y during which the liquid crystal polyester resides in the initial low-temperature region of the melting point (Mp0) of the liquid crystal polyester + 10°C or less is not particularly limited, but may be 1 minute or more, preferably 2 minutes or more, and may be 5 minutes or less.

[0066] T xFrom the viewpoint of reducing the carboxyl groups at the molecular terminals, the 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 suppressing the formation of ketone bonds, the maximum temperature may be Mp0+100°C or lower, preferably Mp0+90°C or lower, and more preferably Mp0+85°C or lower.

[0067] As the decarboxylation reaction proceeds in the extruder 10, carbon dioxide is generated as a pyrolysis gas. From the viewpoint of removing the carbon dioxide generated by the decarboxylation reaction from the system and further promoting the decarboxylation reaction, and from the viewpoint of reducing the inclusion of the generated gas as bubbles in the fibers, it is preferable to degas the extruder 10 by, for example, connecting a vacuum pump or the like to a vent 14 of the extruder 10 and reducing the pressure inside the extruder 10. For example, the degree of vacuum may be 100 kPa or less, preferably 80 kPa or less, and more preferably 60 kPa or less, in absolute pressure.

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

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

[0070] [Fiber structure] The liquid crystal polyester fiber of the present invention can be used as a fusible fiber for producing a molded body using the same as a matrix. When used as a fusible fiber, a fiber structure at least partially containing the liquid crystal polyester fiber can be used as an intermediate material for producing 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, string-like material, rope, etc., and can also be used as various fabrics using the liquid crystal polyester fiber such as nonwoven fabric, woven fabric, knitted fabric, etc. 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 be a combination of liquid crystal polyester fiber and other fibers, as long as the effects of the present invention are not impaired. For example, a composite yarn using liquid crystal polyester fiber and other fibers (e.g., a mixed yarn in which liquid crystal polyester fiber is mixed with other fibers) can be used. Also, composite fabrics using liquid crystal polyester fiber and other fibers (e.g., mixed fabrics in which liquid crystal polyester fiber is mixed with other fibers, and laminates of fabrics made of liquid crystal polyester fiber and fabrics made of other fibers) can be used. When the fiber structure is used to produce a reinforced fiber molding (fiber-reinforced composite material), the fiber structure may be a composite yarn or composite fabric containing reinforcing fibers as other fibers.

[0073] The reinforcing fiber is not particularly limited as long as it has a melting point higher than that of the liquid crystal polyester fiber of the present invention, and examples thereof include 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. 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 fiber structure, and may be, for example, a molded article that does not contain reinforcing fibers, which is obtained by molding a fiber structure, or a reinforced fiber molded article that is obtained by molding a fiber structure together with reinforcing fibers. Because the fiber structure can be made flexible, it is possible to form molded articles in various three-dimensional shapes, such as cylindrical or dome-shaped, by weaving, knitting, etc.

[0075] The molded article can be obtained by heating and molding the fiber 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 any known molding method for a molded article can be used. The liquid crystal polyester fiber of the present invention has excellent hue and can suppress the generation of bubbles during heat fusion, so that a molded article with excellent appearance can be obtained.

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

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. 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 A method, the liquid crystal polyester fiber was wound onto a skein of 1m x 100 skeins (total 100m) using a measuring device "Wrap Reel by Motor Driven" manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd., and the weight (g) was multiplied by 100 and measured twice per level, and the average value was taken as the total fineness (dtex) of the obtained liquid crystal polyester fiber. 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 molding)) The melting point was determined using a differential scanning calorimeter (DSC; Mettler, "TA3000") in accordance with JIS K 7121. Specifically, 10 to 20 mg of a sample was placed in an aluminum pan and sealed in the DSC apparatus. Nitrogen was then introduced as a 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) Referring to JIS L 1013:2010 8.5.1, a tensile test was conducted six times for each yarn sample using an autograph "AGS-100B" manufactured by Shimadzu Corporation under conditions of a test length of 10 cm and a tensile speed of 10 cm / min, and the average tensile strength (cN) was divided by the total fineness (dtex) measured by the above-mentioned method to calculate the strength (cN / dtex).

[0081] (Total CEG amount) A liquid crystal polyester fiber sample was freeze-pulverized to a d90 of 100 μm or less (d90: particle size at which the cumulative volume in the particle size distribution is 90%), and the pulverized sample was decomposed by adding a large excess of n-propylamine and heating and stirring at 40°C for 90 minutes. The ester bonds present within the polymer chain were decomposed into carboxylic acid n-propylamide and hydroxyl groups, while the carboxyl groups (CEG) and hydroxyl groups present at the ends of the polymer chain remained unchanged. Therefore, the decomposition products were separated by HPLC, and the amount of carboxyl terminals (meq / kg) derived from each monomer was quantified by comparing the peak areas of the decomposition products containing carboxyl groups with calibration curves prepared by HPLC analysis of each standard sample. For example, the amount of CEG derived from monocarboxylic acids such as 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid can be determined by quantifying these acids directly, while the amount of CEG derived from dicarboxylic acids such as terephthalic acid, isophthalic acid, and 6-naphthalenedicarboxylic acid can be determined by quantifying substances in which one carboxy group is amidated, such as terephthalic acid mono-n-propylamide, isophthalic acid mono-n-propylamide, and 2,6-naphthalenedicarboxylic acid mono-n-propylamide. The sum of all carboxyl terminals contained in each sample was taken as the total amount of carboxyl terminals (total CEG amount) (meq / kg) for that sample.

[0082] (Total end amount) As with the measurement of the total CEG content, the liquid crystal polyester fiber sample was decomposed using n-propylamine, and the total amount (meq / kg) of carboxyl terminals derived from hydroxycarboxylic acids and the total amount of terminals resulting from the decarboxylation of the terminal carboxyl groups derived from hydroxycarboxylic acids was quantified. For example, the amount of terminals derived from 4-hydroxybenzoic acid was determined by quantifying 4-hydroxybenzoic acid and phenol, and the amount of terminals derived from 6-hydroxy-2-naphthoic acid was determined by quantifying 6-hydroxy-2-naphthoic acid and 2-naphthol. To account for the amount of terminals derived from diols and dicarboxylic acids other than hydroxycarboxylic acids, the total amount of terminals derived from hydroxycarboxylic acids was divided by the molar ratio of hydroxycarboxylic acid-derived structural units to all structural units in the liquid crystal polyester sample, and the value was used to determine the total amount of terminals (meq / kg) for that sample.

[0083] (ketone binding amount) The ketone bond content was calculated by pyrolysis gas chromatography as described in Polymer Degradation and Stability, 76, 85-94 (2002). Specifically, a liquid crystal polyester fiber sample was heated in the presence of tetramethylammonium hydroxide (TMAH) using a pyrolysis apparatus (Frontier Labs, PY2020iD) to generate gas through pyrolysis / methylation. This gas was analyzed using gas chromatography (Agilent Technologies, GC-6890N), and the ketone bond content (mol%) was calculated from the peak areas derived from ketone bonds and ester bonds.

[0084] (Hue (L * value)) L * The values ​​were measured using a spectrophotometer "CM-3700A" manufactured by Konica Minolta, Inc. under the following conditions: specular reflection treatment: SCE, measurement diameter: LAV (25.4 mm), UV conditions: 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"), the arithmetic mean roughness (Ra) (based on the definition in JIS B 0601:2001) of the fiber surface was measured at a magnification of 3000x (objective 150x x 20) at 10 points in the longitudinal direction of the fiber with a reference length of 0.8 mm, and the average value of the 10 points was taken as the surface roughness Ra (μm) in the present invention.

[0086] (CO2 gas generation amount) The amount of CO2 gas generated when liquid crystal polyester fiber was heated was evaluated using the pyrolysis GC-BID method. Specifically, the liquid crystal polyester fiber was first frozen and crushed until its d90 was 100 μm or less to prepare the analytical sample. This was then treated at 300°C for 10 minutes using a GC (gas chromatograph) equipped with a pyrolyzer in the sample introduction section and a BID (dielectric barrier discharge ionization detector) as the gas detector, and CO2 was separated, detected, and quantified from the resulting gas. Measurements were performed three times on the same sample, and the average value was used as the amount of CO2 gas generated from that sample (mmol / kg).

[0087] (Foaming evaluation) A liquid crystal polyester fiber knit fabric was produced using a circular knitting machine (Maruzen Sangyo Co., Ltd., "MR-1," 10 cm diameter, 28 gauge). This fabric was cut into 10 cm squares and stacked three times. A 1 mm thick SUS304 metal plate with a 10 cm square hole was placed on top of a polyimide film (Ube Industries, Ltd., Upilex-S, 125S) prepared as a release film. The three-ply knit fabric was then placed in the square hole, and a second polyimide film (same as above) was placed on top of the metal plate. The resulting fabric was sandwiched from above and below in a flat-plate heating press at a pressure of 0.1 MPa or less and heated at 20°C above the melting point of the liquid crystal polyester fiber for 5 minutes. A pressure of 2 MPa was then applied for 1 minute, and the fabric was then cooled to below 100°C in the atmosphere to obtain a liquid crystal polyester fiber-derived resin plate for appearance evaluation. The front and back of a square area measuring 6 cm on a side 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 liquid crystal polyester (α) (Mp0: 281°C) with the structural units (A) and (B) shown in the formula below, (A) / (B) = 73 / 27 (molar ratio), were used. The chips were fed into a Φ15mm twin-screw extruder (Technovel Corporation, "KZW15TW-45MG-NH(-700)"), melt-kneaded at a maximum temperature of 365°C, and metered with a gear pump while being fed to the spinning head. The residence time and temperature profile from the twin-screw extruder to the spinning head were set as shown in Table 5, and the TH was adjusted to 553. At this time, a vacuum pump (Orion Machinery Co., Ltd., dry pump, "KRF40A-V-01B") was connected to the vent midway through the twin-screw extruder via a metal tube, and the resin-free space in the twin-screw extruder was depressurized to 60 kPa. The spinning head was equipped with a spinneret with a hole diameter of 0.1 mm, a land length of 0.14 mm, and 40 holes. The molten mixture was discharged from the spinneret at a rate of 22.0 g / min and wound onto a bobbin at a winding speed of 1000 m / min to obtain liquid crystal polyester fiber (raw spun yarn). At this time, a 2 wt% aqueous solution of sodium dodecyl phosphate (Wako Pure Chemical Industries, Ltd., Wako Grade 1) was applied to the raw spun yarn from an oiling guide located directly below the spinneret. The application rate of this aqueous solution was 1.4 g / min, and the calculated deposition ratio of sodium dodecyl phosphate to the raw spun yarn was 0.1 wt%. The analytical results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0089] [ka]

[0090] [Table 5]

[0091] The calculation method of TH will be described using the manufacturing conditions of Example 1 as an example. Table 5 shows the heating temperature T per minute at the residence time M in Example 1. x , T in Eq. (1) xIn Example 1, Mp0 is 281°C, so T x The condition that ≦(Mp0+10) is satisfied is T x When x is 1 to 2 and the temperature is 260°C, the residence time y is 2. When x is y+1 (i.e., 3) or more, T x -(Mp0+10) indicates a positive value. And as the value of TH, T when x is y+1~M (i.e., 3~14) x By adding up all the values ​​of -(Mp0+10), it is possible to calculate 553. The same calculations were made in the following examples and comparative examples.

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

[0093] [Example 3] A liquid crystal polyester fiber (raw spun 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 340°C, the temperature profile was changed to adjust the TH to 335, and a spinneret with a hole diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes was used to extrude the molten mixture at a discharge rate of 28.0 g / min and wind it up at a take-up speed of 500 m / min. The analytical results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0094] [Example 4] A liquid crystalline polyester fiber (raw spinning yarn) was obtained in the same manner as in Example 1, except that the residence time was set to 27 minutes, the maximum temperature in the twin-screw extruder was set to 360°C, and the temperature profile was changed to adjust the TH to 996. Table 7 shows the analysis results of the obtained liquid crystalline polyester fiber.

[0095] [Example 5] A liquid crystal polyester fiber (raw spun 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 360°C, the temperature profile was changed to adjust the TH to 435, and a spinneret with a hole diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes was used to extrude the molten mixture at a discharge rate of 56.0 g / min. The analytical results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0096] [Example 6] Liquid crystal polyester fiber (raw spinning yarn) was obtained in the same manner as in Example 1, except that the residence time was set to 27 minutes, the maximum temperature in the twin-screw extruder was set to 340°C, the temperature profile was changed to adjust the TH to 836, and a spinneret with a hole diameter of 0.125 mmφ, a land length of 0.175 mm, and 20 holes was used to extrude the molten mixture at a throughput of 11.0 g / min, and 5 of the 20 extruded filaments were separated and wound up at a winding speed of 1000 m / min. The analytical results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0097] [Example 7] A liquid crystalline polyester fiber (raw spinning yarn) was obtained in the same manner as in Example 6, except that the residence time was set to 27 minutes, the maximum temperature in the twin-screw extruder was set to 360°C, and the temperature profile was changed to adjust the TH to 926. The analytical results of the obtained liquid crystalline polyester fiber are shown in Table 7.

[0098] [Example 8] Chips of liquid crystal polyester (α) were fed into a Φ30 mm single-screw extruder (Osaka Seiki Co., Ltd., "3VSE-30-32N type"), melt-kneaded at a maximum temperature of 340 ° C, and the molten mixture was supplied to the spinning head while being metered with 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 the 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, and the molten mixture 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. Except for this, a liquid crystal polyester fiber (raw spun yarn) was obtained in the same manner as in Example 1. The analytical results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0099] [Table 6]

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

[0101] [ka]

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

[0103] [ka]

[0104] [Comparative Example 1] A liquid crystal polyester fiber (raw spun 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, the temperature profile was changed to adjust the TH to 160, and a spinneret with a hole diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes was used to extrude the molten mixture at a discharge rate of 28.0 g / min and wind it up at a take-up speed of 500 m / min. The analytical results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0105] Comparative Example 2 A liquid crystal polyester fiber (raw spinning 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 the temperature profile was changed to adjust the TH to 193. The analysis results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0106] Comparative Example 3 A liquid crystalline polyester fiber (raw spinning 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 the temperature profile was changed to adjust the TH to 56. The analytical results of the obtained liquid crystalline polyester fiber are shown in Table 7.

[0107] Comparative Example 4 A liquid crystal polyester fiber (raw spun 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, the temperature profile was changed to adjust the TH to 1355, and a spinneret with a hole diameter of 0.1 mmφ, a land length of 0.14 mm, and 100 holes was used to extrude the molten mixture at a discharge rate of 14.0 g / min and wind it up at a take-up speed of 250 m / min. The analytical results of the obtained liquid crystal polyester fiber are shown in Table 7.

[0108] Comparative Example 5 A liquid crystalline polyester fiber (raw spinning 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 the temperature profile was changed to adjust the TH to 246. The analytical results of the obtained liquid crystalline polyester fiber are shown in Table 7.

[0109] Comparative Example 6 A liquid crystalline polyester fiber (raw spinning 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 the temperature profile was changed to adjust the TH to 1284. The analysis results of the obtained liquid crystalline polyester fiber are shown in Table 7.

[0110] [Table 7]

[0111] As shown in Table 7, in Examples 1 to 10, the thermal history of the liquid crystal polyester was adjusted by the heating temperature and residence time in relation to its melting point, thereby reducing the total CEG amount and suppressing the amount of ketone bonds. Therefore, the liquid crystal polyester fibers of Examples 1 to 10 were able to suppress the amount of gas generation, and the resin plates produced using them were able to suppress the generation of bubbles. Furthermore, the obtained liquid crystal polyester fibers had excellent hue and small surface roughness, so they can be suitably used to produce molded articles with excellent appearance and physical properties.

[0112] On the other hand, in Comparative Examples 1 to 3 and 5, the thermal history of the liquid crystal polyester was small, so the amount of ketone bonds was suppressed, but the total amount of CEG was not sufficiently reduced. Therefore, the liquid crystal polyester fibers of Comparative Examples 1 to 3 and 5 generated more CO2 gas than Examples 1 to 10, and the resin plates produced using them also generated more bubbles than those of these Examples.

[0113] In addition, in Comparative Examples 4 and 6, the total CEG amount can be reduced because the thermal history of the liquid crystal polyester is large, but the amount of ketone bonds is large. Therefore, the liquid crystal polyester fibers of Comparative Examples 4 and 6 have a higher L than those of Examples 1 to 10. * The liquid crystal polyester fibers of Comparative Examples 4 and 6 have a large surface roughness Ra compared to Examples 1 to 10. [Industrial Applicability]

[0114] The liquid crystal polyester fiber of the present invention can suppress gas generation during heating and has excellent color hue, and therefore can be used as a fusible fiber for producing a molded product (for example, a fiber-reinforced composite material).

[0115] As described above, a preferred embodiment of the present invention has been described with reference to the drawings, but various additions, modifications, or deletions can be made without departing from the spirit of the present invention, and such additions, modifications, or deletions are also included within the scope of the present invention. [Explanation of symbols]

[0116] 100...device 10. Extruder 11 Hopper 12 barrels 13···screw 14. Vent 20 Piping 30 Gear pump 40 Spinning head 41 Nozzle X: Flow direction

Claims

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

2. 2. The liquid crystal polyester fiber according to claim 1, wherein the melting point is 380° C. or less.

3. 3. The liquid crystal polyester fiber according to claim 1, wherein the tenacity is less than 18 cN / dtex.

4. 4. The liquid crystal polyester fiber according to claim 1, comprising a liquid crystal polyester having 50 mol % or more of constitutional units derived from 4-hydroxybenzoic acid.

5. 5. The liquid crystal polyester fiber according to claim 1, wherein the total amount of one terminal is 50 meq / kg or more.

6. A method for producing the liquid crystal polyester fiber according to any one of claims 1 to 5, comprising at least the steps of melt-kneading a liquid crystal polyester in an extruder, and discharging the molten mixture from a nozzle to spin the mixture.

7. 7. The method for producing a liquid crystal polyester fiber according to claim 6, wherein in the melt-kneading step, a thermal history TH represented by the following formula (1) is 250 to 1100: [Equation 1] In the formula, Mp ０ is the melting point (°C) of the liquid crystal polyester, x is the time (minutes) when x = 0 is defined as the time when the liquid crystal polyester is introduced into the extruder, x = 1, 2, ... is defined as the time during retention, and x = M is defined as the time when the molten kneaded product is discharged from the nozzle, and T ｘ (T １ , T ２ , ..., T Ｍ ) is the heating temperature (°C) per minute during the residence time from the time of addition to the time of discharge, and y is the heating temperature (°C) per minute after the time of addition. ｘ ≦(Mp ０ +10), where M and y are integers and are rounded up or down to the nearest integer, and M is an integer that satisfies M≧y+1.

8. The method for producing a liquid crystal polyester fiber according to claim 6 or 7, 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 any one of claims 1 to 5.

10. The fiber structure according to claim 9 , further comprising reinforcing fibers.

11. A method for producing a molded article, comprising heating the fiber structure according to claim 9 or 10 at a temperature equal to or higher than the melting point of the liquid crystal polyester fiber to mold the fiber structure.

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