Liquid crystal polyester fiber and method for producing the same

Abstract

The present invention provides a liquid crystal polyester fiber in which gas generation during heating is suppressed. The total carboxyl terminal amount (total CEG amount) of the liquid crystal polyester fiber is 5.0 meq / kg or less, and the strength is 18 cN / dtex or more. For example, the initial elastic modulus deviation of the liquid crystal polyester fiber may be 3.0% or less. In addition, the liquid crystal polyester fiber may include a liquid crystal polyester having a structural unit derived from 4-hydroxybenzoic acid of 50 mol% or more.

Description

[0001] Related Applications

[0002] This application claims the benefit of priority based on Japanese Patent Application No. 2020-070885 filed in Japan on April 10, 2020, the entire content of which is incorporated herein by reference. Technical Field

[0003] The invention relates to liquid crystal polyester fiber and a method for producing the same. Background Art

[0004] At present, fiber-reinforced composite plastics using liquid crystal polyester fibers having high strength and better vibration attenuation than metal wires, glass fibers, carbon fibers, etc. as reinforcing fibers have been reported as components of structures exposed to vibrations such as bicycles, automobiles, railway vehicles, airplanes, and wind turbines. For example, Patent Document 1 (Japanese Patent Publication No. 2016-125051) discloses a sheet-like article having at least one outermost surface provided with a layer containing wholly aromatic polyester fibers and a matrix resin, wherein the layer contains 0.1 to 80% by weight of wholly aromatic polyester fibers relative to the total weight thereof, and the unit area weight of the wholly aromatic polyester fibers is 20 to 4000 g / m 2 The matrix resin contains more than 85 wt % of thermosetting resin relative to its total weight, and the thickness of the layer is 0.03 to 50 mm.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-125051 Summary of the invention

[0008] Technical problem to be solved by the invention

[0009] However, in Patent Document 1, a vibration damping component is manufactured by molding a sheet at a temperature above the softening point of a thermosetting resin and below the curing temperature, and then curing it at a temperature above the curing temperature. When a fiber-reinforced composite plastic using liquid crystal polyester fibers is manufactured by such a heating process, bubbles formed by thermal decomposition gas generated by the liquid crystal polyester fibers are generated in the plastic at a specific heating temperature or above. Therefore, in order to maintain the physical properties such as mechanical properties and appearance of the obtained fiber-reinforced composite plastic, the resin is limited to a resin that can be processed at a relatively low temperature, and there is a problem that it cannot be combined with a resin that requires a high temperature for molding, such as a polycarbonate resin.

[0010] The present invention has been made based on the above problems, and an object of the present invention is to provide a liquid crystal polyester fiber and a method for producing the same, which can obtain a high-quality fiber-reinforced composite plastic without generating bubbles during the production of the fiber-reinforced composite plastic.

[0011] Methods used to solve technical problems

[0012] The inventors of the present invention have conducted in-depth research to achieve the above-mentioned purpose. As a result, it was found that the bubbles generated in the plastic are caused by the thermal decomposition gas generated by the liquid crystal polyester fiber. When there is a carboxyl group at the molecular end of the liquid crystal polyester constituting the liquid crystal polyester fiber, it will trigger a decarboxylation reaction in the carboxyl group. In addition, in order to reduce the amount of carboxyl groups at the molecular end that are the main cause of gas generation, repeated research was conducted. As a result, it was found that for liquid crystal polyester fibers, in order to improve the strength, it is necessary to heat treat the spinning raw yarn and perform solid phase polymerization. However, if the temperature at which solid phase polymerization is effectively performed is reached in a state with a large amount of water, hydrolysis will be caused in the ester bond in the polymer chain, and the amount of carboxyl groups at the end will increase. Further, based on these insights, it was found that by performing solid phase polymerization after adjusting the amount of water, a liquid crystal polyester fiber with a small amount of carboxyl groups at the end can be obtained, thereby completing the present invention.

[0013] That is, the present invention can be constituted in the following aspects.

[0014] [Method 1]

[0015] A liquid crystal polyester fiber having a total carboxyl terminal amount (total CEG amount) of 5.0 meq / kg or less (preferably 4.5 meq / kg or less, more preferably 4.0 meq / kg or less) and a strength of 18 cN / dtex or more (preferably 20 cN / dtex or more, more preferably 23 cN / dtex or more).

[0016] [Method 2]

[0017] The liquid crystal polyester fiber according to aspect 1 has an initial elastic modulus deviation of 3.0% or less (preferably 2.5% or less, more preferably 2.0% or less).

[0018] [Method 3]

[0019] The liquid crystal polyester fiber according to embodiment 1 or 2, comprising a liquid crystal polyester having 50 mol % or more (preferably 53 mol % or more, more preferably 60 mol % or more) of a structural unit derived from 4-hydroxybenzoic acid.

[0020] [Method 4]

[0021] The liquid crystal polyester fiber according to any one of aspects 1 to 3, wherein

[0022] The CEG amount of the carboxyl group at the end of the carboxyphenyl group is 4.0 meq / kg or less (preferably 3.5 meq / kg or less, more preferably 3.0 meq / kg or less).

[0023] [Method 5]

[0024] A method for producing a liquid crystal polyester fiber, which is a method for producing the liquid crystal polyester fiber described in any one of methods 1 to 4, and the method at least comprises:

[0025] A step of preheating the spinning raw yarn of the liquid crystal polyester fiber at 80 to 220° C. (preferably 85 to 210° C., more preferably 90 to 205° C.); and

[0026] a step of subjecting the preheated raw yarn to solid phase polymerization at 230° C. or higher (preferably 240° C. or higher, more preferably 250° C. or higher);

[0027] At least in the solid phase polymerization step, the spinning raw yarn is fed at an elongation ratio of 1.000 to 1.200 times (preferably 1.001 to 1.150 times, more preferably 1.002 to 1.100 times, and further preferably 1.003 to 1.050 times) and solid phase polymerized.

[0028] [Method 6]

[0029] The method for producing a liquid crystal polyester fiber according to Embodiment 5, wherein

[0030] The preheating and the solid phase polymerization are performed while the spinning raw yarn is conveyed in a roll-to-roll manner.

[0031] [Method 7]

[0032] A method for producing a liquid crystal polyester fiber, which is a method for producing the liquid crystal polyester fiber described in method 1, comprising: a step of solid-phase polymerization of a spinning precursor of the liquid crystal polyester fiber at a temperature of 230° C. or above (preferably 240° C. or above, and more preferably 250° C. or above); in the solid-phase polymerization step, heat treatment is intermittently performed while the spinning precursor is wound on a bobbin; when the heat treatment temperature reaches 230° C., the amount of moisture contained in the gas generated by the heat-treated yarn of the spinning precursor supplied to the solid-phase polymerization step is less than 1 g (preferably less than 0.1 g, and more preferably less than 0.01 g) per kilogram of yarn per minute.

[0033] [Method 8]

[0034] The method for producing a liquid crystal polyester fiber according to any one of aspects 5 to 7, wherein

[0035] The strength ratio before and after the solid phase polymerization step is 1.5 times or more (preferably 1.8 times or more, more preferably 2.0 times or more).

[0036] [Method 9]

[0037] The method for producing a liquid crystal polyester fiber according to any one of aspects 5 to 8, wherein

[0038] The moisture regain of the spun yarn subjected to the solid phase polymerization step is 200 ppm or less (preferably 180 ppm or less, more preferably 150 ppm or less).

[0039] [Method 10]

[0040] A fiber structure comprising the liquid crystal polyester fiber according to any one of aspects 1 to 4 at least in a part.

[0041] It should be noted that any combination of at least two constituent elements 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 claims recorded in the claims is also included in the present invention.

[0042] Effects of the Invention

[0043] According to the liquid crystal polyester fiber of the present invention, generation of gas can be suppressed during heating, and a fiber-reinforced composite plastic with few bubbles and good quality can be produced.

[0044] Furthermore, according to the production method of the present invention, a liquid crystal polyester fiber having a small total carboxyl terminal amount (total CEG amount) can be produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention can be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and the accompanying drawings are for illustration and description only and should not be used to determine the scope of the present invention. The scope of the present invention is determined by the attached claims.

[0046] Figure 1 This is a schematic diagram of the process for producing the liquid crystal polyester fiber of Example 1.

[0047] Explanation of symbols

[0048] 1 Unwinder

[0049] 2 First Roller

[0050] 3 Heat treatment furnace

[0051] 4 Second Roller

[0052] 5 Coiler

[0053] 6a, 6b, 6c, 6d, 6e, 6f heating zones

[0054] 7 Furnace pipe

[0055] 8 Control Unit DETAILED DESCRIPTION

[0056] [Liquid crystal polyester fiber]

[0057] The liquid crystal polyester fiber of the present invention is composed of liquid crystal polyester. As a liquid crystal polyester, it is formed by repeating structural units derived from, for example, aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc., and as long as the effect of the present invention is not impaired, the chemical structure of the structural unit derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids is not particularly limited. In addition, within the scope of not impairing the effect of the present invention, the liquid crystal polyester may also include structural units derived from aromatic diamines, aromatic hydroxylamines or aromatic aminocarboxylic acids. For example, as preferred structural units, the examples shown in Table 1 can be cited.

[0058] [Table 1]

[0059]

[0060] (Wherein, X in the formula is selected from the following structures)

[0061]

[0062] (wherein, m = 0 to 2, Y = selected from hydrogen, halogen, alkyl, aryl, aralkyl, alkoxy,

[0063] Substituents of aryloxy and aralkyloxy groups)

[0064] In the structural unit of Table 1, m is an integer of 0 to 2, and Y in the formula may 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, a tert-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, a phenethyl group, etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyl group, etc.), etc., which are independently selected from the group consisting of:

[0065] More preferred structural units include the structural units described in Examples (1) to (18) shown in Tables 2, 3 and 4 below. When the structural unit in the formula is a structural unit that can exhibit multiple structures, two or more such structural units may be combined and used as a structural unit constituting a polymer.

[0066] [Table 2]

[0067]

[0068] [Table 3]

[0069]

[0070] [Table 4]

[0071]

[0072] In the structural units of Table 2, Table 3 and Table 4, n is an integer of 1 or 2, and each structural unit n=1, n=2 may exist alone or in combination, and Y1 and Y2 are each independent and may 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, a tert-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 (benzyl), a phenethyl group (phenylethyl)), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.), etc. Among them, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

[0073] In addition, as Z, substituents represented by the following chemical formulas can be mentioned.

[0074] [Chemical formula 1]

[0075]

[0076] The liquid crystal polyester may preferably be a combination having a naphthalene skeleton as a structural unit. It is particularly preferred to include both a structural unit (A) derived from hydroxybenzoic acid and a structural unit (B) derived from hydroxynaphthoic acid. For example, the following formula (A) may be cited as the structural unit (A), and the following formula (B) may be cited as the structural unit (B). From the viewpoint of improving melt moldability, the ratio of the structural unit (A) to the structural unit (B) may be preferably in the range of 9 / 1 to 1 / 1, more preferably 7 / 1 to 1 / 1, and further preferably 5 / 1 to 1 / 1.

[0077] [Chemical formula 2]

[0078]

[0079] [Chemical formula 3]

[0080]

[0081] In addition, the total amount of the structural units of (A) and (B) can be, for example, 65 mol% or more, more preferably 70 mol% or more, and further preferably 80 mol% or more relative to all structural units. In the polymer, liquid crystal polyesters in which the structural units of (B) are 4 to 45 mol% are particularly preferred.

[0082] In addition, the liquid crystal polyester may include a structural unit derived from 4-hydroxybenzoic acid as an aromatic hydroxycarboxylic acid, a structural unit derived from an aromatic dicarboxylic acid, and a structural unit derived from an aromatic diol. For example, as a structural unit derived from an aromatic dicarboxylic acid, at least one selected from the following formula (C) and the following formula (D) can be used, and as a structural unit derived from an aromatic diol, at least one selected from the following formula (E) and the following formula (F) can be used. Preferred are: a liquid crystal polyester comprising a structural unit (A) derived from 4-hydroxybenzoic acid (the above formula (A)), a structural unit (C) derived from terephthalic acid as an aromatic dicarboxylic acid (the following formula (C)), a structural unit (D) derived from isophthalic acid (the following formula (D)), and a structural unit (E) derived from 4,4'-dihydroxybiphenyl as an aromatic diol (the following formula (E)); a liquid crystal polyester comprising a structural unit (A) derived from 4-hydroxybenzoic acid (the above formula (A)), a structural unit (C) derived from terephthalic acid as an aromatic dicarboxylic acid (the following formula (C)), a structural unit (D) derived from isophthalic acid (the following formula (D)), a structural unit (E) derived from 4,4'-dihydroxybiphenyl as an aromatic diol (the following formula (E)), and a structural unit (F) derived from hydroquinone (the following formula (F)).

[0083] [Chemical formula 4]

[0084]

[0085] [Chemical formula 5]

[0086]

[0087] [Chemical formula 6]

[0088]

[0089] [Chemical formula 7]

[0090]

[0091] The liquid crystal polyester may contain a structural unit derived from 4-hydroxybenzoic acid, preferably 50 mol% or more, more preferably 53 mol% or more, and further 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, for example, it may be 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

[0092] The melting point (hereinafter sometimes referred to as Mp0) of the liquid crystal polyester suitable for the present invention is preferably in the range of 250 to 380°C, more preferably 255 to 370°C, further preferably 260 to 360°C, and further preferably 260 to 330°C. It should be noted that the melting point here is the main absorption peak temperature measured and observed using a differential scanning calorimeter (DSC; "TA3000" manufactured by Mettler) according to the JIS K 7121 test method. Specifically, in the above-mentioned DSC device, 10 to 20 mg of the sample is taken and sealed in an aluminum pan, and nitrogen as a carrier gas is circulated at 100 mL / min, and the endothermic peak when the temperature is increased at 20°C / min is measured. Depending on the type of polymer, when no clear peak appears in the first run of DSC measurement, the temperature is raised at 50°C / min to a temperature 50°C higher than the expected flow temperature. After complete melting at this temperature for 3 minutes, the polymer is cooled to 50°C at a cooling rate of 80°C / min, and then the endothermic peak is measured at a heating rate of 20°C / min.

[0093] It should be noted that, within the scope of not impairing the effects of the present invention, thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyetheretherketone, fluororesin, etc. may be added to the above-mentioned liquid crystal polyester. In addition, various additives such as inorganic substances such as titanium oxide, kaolin, silicon dioxide, barium oxide, colorants such as carbon black, dyes or pigments, antioxidants, ultraviolet absorbers, and light stabilizers may also be included.

[0094] The liquid crystal polyester fiber of the present invention may contain 50% by weight or more of the liquid crystal polyester, preferably 80% by weight or more, more preferably 90% by weight or more, further preferably 95% by weight or more, and further preferably 99.9% by weight or more.

[0095] The total carboxyl terminal amount (total CEG amount) of the liquid crystal polyester fiber of the present invention is 5.0 meq / kg or less. The total carboxyl terminal amount (total CEG amount) is a value measured by the method described in the examples described later, and is composed of the amount of carboxyl groups present at the molecular ends in the molecules that mainly constitute the liquid crystal polyester fiber in 1 kg of fiber. For example, as a carboxyl group present at the polymer end in the liquid crystal polyester, it can be a carboxyl group: a structural unit derived from a monomer having a carboxyl group such as an aromatic hydroxycarboxylic acid and an aromatic dicarboxylic acid forms a polymer end, and a carboxyl group that remains in such a structural unit present at the polymer end without reacting.

[0096] From the viewpoint 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 4.5 meq / kg or less, more preferably 4.0 meq / kg or less. The lower limit of the total CEG amount is not particularly limited, and may be, for example, 0.1 meq / kg or more.

[0097] For the liquid crystal polyester fiber of the present invention, from the viewpoint of suppressing the amount of gas generated during heating, the CEG amount of the carboxyl group at the end of the carboxylphenyl group (-Ph-COOH (wherein: other substituents may also be present on Ph)) in the carboxyl group at the end of the molecule may be 4.0 meq / kg or less, preferably 3.5 meq / kg or less, and more preferably 3.0 meq / kg or less. Since the carboxyl group at the end of the carboxylphenyl group is derived from a monomer having a carboxylphenyl group, such as 4-hydroxybenzoic acid, terephthalic acid, isophthalic acid, etc. (arbitrarily, the phenyl group in the carboxylphenyl group may have a halogen atom, an alkyl group, an alkoxy group, an aryl group, an aralkyl group, an aryloxy group, an aralkyloxy group, etc.), it is a chemical structure that is particularly prone to decarboxylation reaction, and therefore, it is preferred to reduce the CEG amount of the carboxyl group at the end of the carboxylphenyl group. The lower limit of the CEG amount of the carboxyl group at the end of the carboxylphenyl group is not particularly limited, and for example, it may be 0.1 meq / kg or more.

[0098] For the liquid crystal polyester fiber of the present invention, from the viewpoint of suppressing the amount of gas generated during heating, the ratio of the CEG amount of the carboxyl group at the carboxyphenyl terminal to the total CEG amount may be 90% or less, preferably 85% or less, and more preferably 80% or less. The lower limit of the ratio of the CEG amount of the carboxyl group at the carboxyphenyl terminal to the total CEG amount is not particularly limited, and may be, for example, 5% or more.

[0099] The strength of the liquid crystal polyester fiber of the present invention is 18 cN / dtex or more. In addition, from the viewpoint of improving the mechanical strength of the fiber-reinforced composite plastic using the liquid crystal polyester fiber as a reinforcing fiber, the strength may preferably be 20 cN / dtex or more, more preferably 23 cN / dtex or more. In addition, the upper limit of the strength is not particularly limited, for example, about 35 cN / dtex. In the present invention, the strength of the liquid crystal polyester fiber refers to the tensile strength, which is a value measured by the method described in the embodiments described later.

[0100] From the viewpoint of improving the mechanical properties of the entire fiber-reinforced composite plastic, the strength deviation of the liquid crystal polyester fiber of the present invention may be 3.0% or less, preferably 2.7% or less, and more preferably 2.3% or less. In addition, the lower limit of the strength deviation is not particularly limited, for example, about 0.1%. It should be noted that the strength deviation is a value measured by the method described in the examples described later.

[0101] From the viewpoint of improving dimensional stability, the initial elastic modulus of the liquid crystal polyester fiber of the present invention may be 100 cN / dtex or more, preferably 300 cN / dtex or more, and more preferably 500 cN / dtex or more. The upper limit of the initial elastic modulus is not particularly limited, for example, about 1000 cN / dtex. It should be noted that the initial elastic modulus represents the slope of the straight line between the two points of elongation 0.25% and 1.00% in the connection strength-elongation curve, and is a value measured by the method described in the embodiments described later.

[0102] From the viewpoint of improving the mechanical properties of the fiber-reinforced composite plastic as a whole, the initial elastic modulus deviation of the liquid crystal polyester fiber of the present invention may be 3.0% or less, preferably 2.5% or less, and more preferably 2.3% or less. In addition, the lower limit of the initial elastic modulus deviation is not particularly limited, for example, about 0.1%. Such an initial elastic modulus deviation can be achieved by continuous heat treatment in the manufacturing method of the liquid crystal polyester fiber described later. It should be noted that the initial elastic modulus deviation is a value measured by the method described in the embodiments described later.

[0103] The melting point of the liquid crystal polyester fiber of the present invention may be 290 to 400° C., preferably 300 to 380° C., and more preferably 305 to 350° C. For the liquid crystal polyester fiber, the melting point thereof rises from the melting point of the spinning raw yarn (hereinafter sometimes referred to as Mp) by solid phase polymerization. It should be noted that the melting point of the liquid crystal polyester fiber is a value measured by the method described in the examples described later.

[0104] The single fiber fineness of the liquid crystal polyester fiber of the present invention can be appropriately adjusted according to the application etc., and for example, the single fiber fineness may be 0.5 to 50 dtex, preferably 1.0 to 35 dtex, more preferably 1.0 to 15 dtex, and further preferably 1.5 to 10 dtex.

[0105] 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 may be appropriately adjusted according to the application, for example, the number of filaments may be 5 to 5000, preferably 10 to 4000, and more preferably 30 to 3000.

[0106] The total fineness of the liquid crystal polyester fiber of the present invention can be appropriately adjusted according to the application etc., and for example, the total fineness may be 10 to 50,000 dtex, preferably 15 to 30,000 dtex, and more preferably 25 to 10,000 dtex.

[0107] [Method for producing liquid crystal polyester fiber]

[0108] The inventors of the present invention have found that even if a liquid crystal polyester with a total CEG amount adjusted in advance is spun, it is not possible to produce the liquid crystal polyester fiber described above. If solid phase polymerization is performed in a state where the spinning precursor contains water, hydrolysis is caused in the ester bonds in the polymer chain, resulting in an increase in the amount of terminal carboxyl groups. Therefore, in the production method of the present invention, a liquid crystal polyester fiber with a small amount of terminal carboxyl groups is obtained by adjusting the water content in the spinning precursor and then performing solid phase polymerization.

[0109] That is, as a method for producing the liquid crystal polyester fiber of the present invention, it includes at least a step of solid phase polymerization of the spinning precursor at 230°C or above, and as described later, the moisture content of the spinning precursor is adjusted before the solid phase polymerization step. The method of heat treatment in the solid phase polymerization step is not particularly limited, for example, it can be a continuous heat treatment based on conveyance or a heat treatment performed in an intermittent manner. From the viewpoint of suppressing the deviation of the physical properties in the longitudinal direction of the fiber, continuous heat treatment based on conveyance is preferred.

[0110] (Continuous heat treatment based on transport)

[0111] In the case of a continuous heat treatment based on conveying, the method for producing the liquid crystal polyester fiber of the present invention may at least include:

[0112] The process of preheating the spinning raw yarn of liquid crystal polyester fiber at 80 to 220°C, based on

[0113] The step of solid phase polymerizing the preheated raw yarn at 230°C or above,

[0114] At least in the solid phase polymerization step, the spinning raw yarn may be conveyed at an elongation ratio of 1.000 to 1.200 times and heat-treated.

[0115] In the continuous heat treatment based on conveying, by subjecting the spinning precursor to a preheating process under specific conditions before the solid phase polymerization process, the spinning precursor can be dried and the moisture content can be reduced. Therefore, the hydrolysis of the liquid crystal polyester can be suppressed in the subsequent solid phase polymerization process, and a liquid crystal polyester fiber with a small total CEG content and high strength can be obtained.

[0116] Furthermore, by heat-treating while continuously conveying at a specific elongation ratio, heat treatment can be performed in a more uniform environment over the entire length direction of the fiber, thereby obtaining liquid crystal polyester fibers with reduced variation in mechanical properties in the length direction of the fiber.

[0117] There is no limitation on the method of fiberizing the spinning precursor of the liquid crystal polyester fiber, and generally, fibers obtained by melt spinning can be used. Melt spinning can be performed by a known or conventional method, for example, a fiber-forming resin used to obtain the spinning precursor composed of the liquid crystal polyester can be melted in an extruder, ejected from a nozzle at a given spinning temperature, and wound up using a godet roller or the like below the solidification point to obtain the fiber.

[0118] In the preheating step, the spinning precursor can be dried by preheating the spinning precursor at 80 to 220°C. From the viewpoint of efficiently removing moisture from the spinning precursor, the preheating temperature may preferably be 85°C or higher, more preferably 90°C or higher. In addition, if the temperature at which solid phase polymerization is effectively performed is reached in a state with a lot of moisture, hydrolysis will occur and the amount of CEG will increase, so it may preferably be 210°C or lower, more preferably 205°C or lower. In addition, with respect to the preheating temperature, from the viewpoint of efficiently removing moisture according to the number of filaments of the spinning precursor, the single fiber fineness, etc., the preheating may be performed while gradually increasing the temperature within the above-mentioned temperature range.

[0119] In addition, from the viewpoint of efficiently removing the water in the spinning precursor, the preheating time may be 1 minute or more. The preheating time refers to the time for preheating the same part of the spinning precursor, and may be preferably 5 minutes or more, more preferably 10 minutes or more. The upper limit of the preheating time is not particularly limited, and may be 200 minutes or less, for example, from the viewpoint of improving the manufacturing efficiency, may be 30 minutes or less.

[0120] Preheating can be performed using a known method, such as gas atmosphere heating, contact heating, etc. As the gas atmosphere, air, an inert gas (e.g., nitrogen, argon), or a gas atmosphere composed of these can be used appropriately. In addition, from the viewpoint of removing moisture, preheating can also be performed under reduced pressure.

[0121] When preheating is performed in a gas atmosphere, water removal can be performed efficiently by using a gas atmosphere with a low dew point. The dew point may be 30° C. or lower, preferably 0° C. or lower, and more preferably -30° C. or lower.

[0122] In the solid phase polymerization process, the strength of the spinning precursor can be improved by heat-treating the spinning precursor after the preheating process at 230°C or above. From the viewpoint of efficiently improving the strength, the temperature of the solid phase polymerization may be preferably 240°C or above, and more preferably 250°C or above. In addition, in order to prevent melting, the temperature of the solid phase polymerization may be lower than the melting point (Mp) of the liquid crystal polyester fiber (spinning precursor) provided for the solid phase polymerization process, for example, within the range of 230°C or above, it may be Mp-80°C or above and lower than Mp°C, it may be preferably Mp-50°C or above and lower than Mp°C, and more preferably Mp-30°C or above and lower than Mp°C. Among them, since the melting point of the liquid crystal polyester fiber increases as the solid phase polymerization proceeds, it is sufficient to make the initial temperature in the solid phase polymerization process lower than the melting point (Mp) of the liquid crystal polyester fiber (spinning precursor). Compared with the case of heat treatment at a constant temperature, by gradually increasing the temperature of the solid phase polymerization according to the progress of the solid phase polymerization, it is possible to exceed the melting point at the time of the solid phase polymerization process at a high temperature. It should be noted that gradually or continuously increasing the temperature of the solid phase polymerization relative to time can prevent melting and improve the time efficiency of the solid phase polymerization, which is preferred from this point of view.

[0123] From the viewpoint of improving strength and improving manufacturing efficiency, the time of the solid phase polymerization step in the continuous heat treatment based on transportation can be 5 to 1000 minutes, preferably 8 to 500 minutes, more preferably 10 to 100 minutes, and further preferably 15 to 60 minutes. In addition, the solid phase polymerization can use a known method in the same manner as the above-mentioned preheating.

[0124] Solid phase polymerization in continuous heat treatment based on transportation can use known methods, such as gas atmosphere heating, contact heating and the like. As the gas atmosphere, air, inert gas (e.g., nitrogen, argon), or a gas atmosphere formed by combining them can be suitably used. In addition, solid phase polymerization can also be carried out under reduced pressure.

[0125] When solid phase polymerization is performed in a continuous heat treatment by conveyance in a gas atmosphere, water can be removed efficiently by using a gas atmosphere with a low dew point. The dew point may be 0°C or lower, preferably -20°C or lower, and more preferably -50°C or lower.

[0126] The transport treatment only needs to be carried out at least in the solid-phase polymerization process, and may also be carried out in the preheating process as desired. In the case where the transport treatment is carried out in the preheating process and the solid-phase polymerization process, the transport treatment may be carried out separately in each process. For example, after carrying out transport-based preheating as the preheating process, the fiber may be temporarily wound up, and then another transport device may be used to carry out transport-based heat treatment as the solid-phase polymerization process. Alternatively, the same transport device may be used to carry out both the preheating process and the solid-phase polymerization process. From the viewpoint of improving manufacturing efficiency, it is preferred to use the same transport device to carry out both the preheating process and the solid-phase polymerization process. In addition, in the case where the same transport device is used to carry out both the preheating process and the solid-phase polymerization process, the temperature may be temporarily lowered from the preheating temperature after preheating, and then the temperature may be increased again to carry out solid-phase polymerization, or the temperature may be directly increased from the preheating temperature to the temperature of the solid-phase polymerization process. From the viewpoint of carrying out solid-phase polymerization in a state where the amount of water is further reduced, it is preferred to directly increase the temperature from the preheating temperature to the temperature of the solid-phase polymerization process. For example, the solid phase polymerization can be performed after the preheating by controlling the temperature in the heat treatment furnace so as to be increased stepwise or continuously from the preheating temperature to the solid phase polymerization temperature.

[0127] The conveying method in the solid phase polymerization process can be carried out by any of contact conveying (for example, conveyor conveying method, support roller conveying method, heat treatment method on heated rollers) and non-contact conveying (roll-to-roll method). From the viewpoint of avoiding uneven heat caused by contact, treating in a more uniform environment, and suppressing the deviation of mechanical properties in the length direction of the fiber, it is preferred to use a heat treatment furnace to heat treat the spinning precursor while conveying it in a roll-to-roll manner. In addition, the processing path may not be a straight line, and a return roller or a guide may be configured in the device to appropriately change the length, angle, curvature, etc. of the processing path for heat treatment. In addition, the same method can also be used in the preheating process.

[0128] The spinning precursor can be transported at an elongation ratio of 1.000 to 1.200 times during the solid phase polymerization process. By stretching and transporting at a specific elongation ratio, in the case of multifilaments, the single fibers can be parallel to each other at all parts of the fiber length direction without relaxation, thereby suppressing the deviation of the mechanical properties in the fiber length direction and suppressing the reduction of strength caused by elongation. In addition, the same can be done in the preheating process.

[0129] The elongation ratio is a value indicating how many times the liquid crystal polyester fiber is elongated before and after elongation. When two rollers with a speed difference are used for elongation, it is calculated based on the speed ratio. When elongation is performed using a device that cannot be expressed by a speed ratio, such as using the load of a tension roller for extension, it is calculated based on the total fineness ratio of the fiber before and after elongation (before and after heat treatment). As long as the strength is not significantly reduced due to elongation, there is no limit to the range of the elongation ratio. From the viewpoint of aligning the single fibers with each other, it can be preferably 1.001 to 1.150 times, more preferably 1.002 to 1.100 times, and further preferably 1.003 to 1.050 times.

[0130] The stretching method is not particularly limited to a specific stretching ratio, and examples thereof include: a method in which the rotation speed of the downstream driving roller is set higher than the rotation speed of the upstream conveying roller during preheating and solid-phase polymerization in a roll-to-roll manner; a method in which a constant load is applied using a tension roller while heat treating the fiber during conveyance; a method in which the fiber is passed through a heated Nelson roller; a method in which the fiber is fixed with a pin or the like and then heat treated during conveyance, thereby stretching the fiber by utilizing the fact that the liquid crystal polyester fiber has a negative thermal expansion coefficient relative to the fiber axis direction.

[0131] It should be noted that although the stretching technology is widely known as a technology for stretching fibers while performing heat treatment, the stretching technology is a technology applied to fibers with low molecular orientation to improve the strength and elastic modulus of the yarn, and is not intended to be applied to fibers with a highly oriented high-order structure such as the liquid crystal polyester fiber of the present invention. In addition, the suitable treatment conditions are also different. In the stretching technology, in order to improve the orientation as much as possible, the stretching ratio is set to 1.5 times or more in most cases, but in the present invention, it is sufficient to stretch the single fibers to align with each other, so the stretching ratio is suitable in the range of 1.000 to 1.200 times. If the treatment is performed at a ratio exceeding this, defects are generated in the high-order structure due to the sliding of the molecular chain, etc., which easily leads to a decrease in strength. As mentioned above, since the stretching technology of the present invention is a technology different from the stretching technology, the technical term "stretching ratio" is used instead of the stretching ratio in the present invention.

[0132] In addition, the tension applied during the solid phase polymerization step can be adjusted according to the total fineness of the liquid crystal polyester fiber supplied to the solid phase polymerization step, and from the viewpoint of stabilizing the yarn path and suppressing yarn breakage, for example, it can be 0.001 to 0.06 cN / dtex, preferably 0.003 to 0.05 cN / dtex, and more preferably 0.005 to 0.04 cN / dtex. The same can be done in the preheating step.

[0133] (Batch Heat Treatment)

[0134] In the case of intermittent heat treatment, the method for producing the liquid crystal polyester fiber of the present invention comprises: performing solid phase polymerization on the spinning raw yarn of the liquid crystal polyester fiber at 230° C. or above,

[0135] In the above-mentioned solid-phase polymerization process, the above-mentioned spinning precursor is intermittently heat-treated in a state where it is wound on a bobbin. When the heat treatment temperature reaches 230°C, the amount of moisture contained in the gas generated by the above-mentioned spinning precursor supplied to the above-mentioned solid-phase polymerization process during the heat treatment can be less than 1g per kilogram of silk per minute.

[0136] In the batch heat treatment, by using a spinning precursor adjusted to a specific moisture content as the spinning precursor for the solid phase polymerization step, hydrolysis of the liquid crystal polyester can be suppressed in the solid phase polymerization step, and a liquid crystal polyester fiber with a low total CEG content and high strength can be obtained.

[0137] When the heat treatment temperature reaches 230° C., the moisture content contained in the gas generated by the spinning raw yarn during the heat treatment of the solid phase polymerization step may be preferably 0.1 g or less per kilogram of yarn per minute, and more preferably 0.01 g or less. It should be noted that the moisture content is a value measured by the method described in the examples described below.

[0138] As a method for adjusting the amount of moisture contained in the gas generated by the silk during the heat treatment at the moment when the heat treatment temperature reaches 230°C to a level below a certain level, there is no particular limitation on the specific method, and a method of continuously flowing a gas that is always dry instead of a closed heat treatment, or a method of circulating a dry gas using a circulation path equipped with a silk drying oven and a moisture removal device, etc. can be used. In addition, by using a single oven to continuously perform preheating and solid-phase polymerization of the silk, it is possible to prevent moisture in the air from adhering to the fiber. In this case, the solid-phase polymerization can be performed after the silk temperature is temporarily lowered to room temperature after the preheating step. From the viewpoint of thermal efficiency, it is preferred to perform solid-phase polymerization without cooling down the silk after the preheating step is completed but by raising the temperature.

[0139] In the solid phase polymerization process, by heat-treating the spinning precursor adjusted to a specific moisture content at 230°C or above to perform solid phase polymerization, the strength of the spinning precursor can be improved without increasing the total CEG amount. From the viewpoint of improving strength, the temperature of the solid phase polymerization may be preferably 240°C or above, and more preferably 250°C or above. In addition, in order to prevent melting, the temperature of the solid phase polymerization may be lower than the melting point (Mp) of the liquid crystal polyester fiber (spinning precursor) provided for the solid phase polymerization process, for example, within the range of 230°C or above, it may be Mp-80°C or above and below Mp°C, it may be preferably Mp-50°C or above and below Mp°C, and more preferably Mp-30°C or above and below Mp°C. Among them, since the melting point of the liquid crystal polyester fiber increases as the solid phase polymerization proceeds, it is sufficient to make the initial temperature in the solid phase polymerization process lower than the melting point (Mp) of the liquid crystal polyester fiber (spinning precursor). Compared with the case of heat treatment at a constant temperature, by gradually increasing the temperature of the solid phase polymerization according to the progress of the solid phase polymerization, it is possible to exceed the melting point at the time of the solid phase polymerization process at a high temperature. It should be noted that gradually or continuously increasing the temperature of the solid phase polymerization relative to time can prevent melting and improve the time efficiency of the solid phase polymerization, which is preferred from this point of view.

[0140] From the viewpoint of improving strength, the time of the solid phase polymerization process in the intermittent heat treatment can be 2 to 30 hours, preferably 3 to 24 hours, and more preferably 5 to 20 hours. In addition, solid phase polymerization can use known methods, such as gas atmosphere heating, contact heating and other methods. As gas atmosphere, air, inert gas (for example, nitrogen, argon) or the gas atmosphere formed by combining them can be suitably used. In addition, solid phase polymerization can also be carried out under reduced pressure.

[0141] When solid phase polymerization is performed in a batch heat treatment under a gas atmosphere, water can be removed efficiently by using a gas atmosphere with a low dew point. The dew point may be 0°C or lower, preferably -20°C or lower, and more preferably -50°C or lower.

[0142] In the batch heat treatment, for example, the heat treatment can be performed in a state where the material is wound around a bobbin in a package shape. The bobbin needs to withstand the temperature of solid phase polymerization and is preferably made of a metal such as aluminum, brass, iron, or stainless steel.

[0143] In the method for producing the liquid crystal polyester fiber of the present invention, in any mode of continuous heat treatment and intermittent heat treatment, the strength ratio of the liquid crystal polyester fiber before and after the solid phase polymerization process can be 1.5 times or more, preferably 1.8 times or more, and more preferably 2.0 times or more. The upper limit of the strength ratio of the liquid crystal polyester fiber before and after the solid phase polymerization process is not particularly limited, for example, it can be 10 times or less. Here, the strength ratio before and after the solid phase polymerization process refers to the value obtained by dividing the tensile strength of the liquid crystal polyester fiber after the solid phase polymerization process by the tensile strength of the liquid crystal polyester fiber (spinning precursor) before the solid phase polymerization process. Since the strength of the spinning precursor of the liquid crystal polyester fiber is generally less than 12cN / dtex, the strength of the liquid crystal polyester fiber can be improved by performing solid phase polymerization under appropriate conditions in which the strength ratio before and after the solid phase polymerization process reaches 1.5 times or more.

[0144] In the method for producing the liquid crystal polyester fiber of the present invention, in any mode of continuous heat treatment and intermittent heat treatment, the moisture regain (hereinafter sometimes referred to as process moisture regain) of the yarn (the yarn after the preheating process) supplied to the solid phase polymerization process can be 200ppm or less. By using the yarn adjusted to a specific process moisture regain as the yarn supplied to the solid phase polymerization process, the hydrolysis of the liquid crystal polyester can be suppressed in the solid phase polymerization process, and a liquid crystal polyester fiber with a small total CEG amount and high strength can be obtained. The process moisture regain of the yarn supplied to the solid phase polymerization process can preferably be 180ppm or less, and more preferably 150ppm or less. The lower limit of the process moisture regain of the yarn supplied to the solid phase polymerization process is not particularly limited, for example, it can be 1ppm or more. It should be noted that the process moisture regain is a value measured by the method described in the embodiments described later.

[0145] The liquid crystal polyester fiber of the present invention can be processed into a fiber structure containing the same in at least a part and used for various purposes. The fiber structure can be used as a so-called one-dimensional structure such as short fibers, chopped fibers, filament yarns, spun yarns, ropes, cords, etc., and can also be used as a two-dimensional structure such as a nonwoven fabric, a fabric, a knitted fabric using the liquid crystal polyester fiber. Such a one-dimensional structure and a two-dimensional structure can be produced by a known method using the liquid crystal polyester fiber.

[0146] The fiber structure may be composed of liquid crystal polyester fiber alone, or the liquid crystal polyester fiber may be combined with other fibers. The fiber structure may be, for example, a composite fiber using liquid crystal polyester fiber and other fibers (for example, a mixed fiber yarn formed by blending liquid crystal polyester fiber and other fibers, etc.). In addition, the fiber structure may be a composite cloth using liquid crystal polyester fiber and other fibers (for example, a mixed fiber non-woven fabric or mixed fiber woven fabric blended with liquid crystal polyester fiber and other fibers, a laminate of cloth formed by liquid crystal polyester fiber and cloth formed by other fibers, etc.).

[0147] The liquid crystal polyester fiber of the present invention can be used for applications where liquid crystal polyester fibers are generally used, and can be preferably used as a reinforcing material or a matrix material for fiber-reinforced composite plastics, particularly because gas generation during heating can be suppressed.

[0148] Example

[0149] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto. In the following examples and comparative examples, various physical properties were measured by the following methods.

[0150] (Total fineness, single fiber fineness)

[0151] Based on JIS L 1013:2010 8.3.1A method, 100 m of liquid crystal polyester fiber was wound in the form of a hank using a size measuring device "Wrap Reel by Motor Driven" manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd., and its weight (g) was multiplied by 100 times, and the measurement was performed twice for each level, and the average value was taken as the total fineness (dtex) of the obtained liquid crystal polyester fiber. In addition, the quotient obtained by dividing this value by the number of filaments was taken as the single fiber fineness (dtex).

[0152] (Melting Point)

[0153] The measurement was performed using a differential scanning calorimeter (DSC; manufactured by Mettler, "TA3000") according to JIS K 7121, and the main absorption peak temperature observed was taken as the melting point. Specifically, in the above-mentioned DSC apparatus, 10 to 20 mg of the sample was sealed in an aluminum pan, and nitrogen as a carrier gas was flowed at a flow rate of 100 mL / min, and the endothermic peak when the temperature was increased from 25°C at 20°C / min was measured.

[0154] (Strength, strength deviation)

[0155] Fifty 1-meter-long measurement samples were collected from the continuous liquid crystal polyester fiber. These measurement samples were collected from points where the entire fiber length was divided into 50 equal parts in the longitudinal direction within a range of ±0.5%.

[0156] Next, with reference to JIS L 1013:2010 8.5.1, a tensile test was carried out using a universal testing machine "AGS-100B" manufactured by Shimadzu Corporation under the conditions of a test length of 10 cm, an initial load of 2.94 mN / dtex, and a tensile speed of 10 cm / min. For 50 test specimens, the strength at each break was measured, and the average value (A1) of a total of 50 measurements was taken as the strength (cN / dtex).

[0157] Furthermore, the value obtained by dividing the standard deviation (σ1) of the 50 measurement results by the average value (A1) was multiplied by 100 and was defined as the intensity deviation (%).

[0158] Strength deviation (%) = (σ1 / A1) × 100 (1)

[0159] (Initial elastic modulus, initial elastic modulus deviation)

[0160] The slope of the straight line between the two points of elongation 0.25% and 1.00% in the connection strength-elongation curve was calculated from the results measured under the same conditions as the above strength measurement, and the average value (A2) of 50 measurements was taken as the initial elastic modulus (cN / dtex).

[0161] Furthermore, the value obtained by dividing the standard deviation (σ2) of the 50 measurement results by the average value (A2) was multiplied by 100, and the obtained value was defined as the initial elastic modulus deviation (%).

[0162] Initial elastic modulus deviation (%) = (σ2 / A2) × 100 (2)

[0163] (Process moisture regain (moisture regain of yarn subjected to solid phase polymerization process))

[0164] Liquid crystal polyester fiber samples weighing 0.2 to 0.5 g were prepared for each test object. The liquid crystal polyester fiber samples were bundled to a size small enough to fit into the sample boat of the moisture regain measuring instrument (Mitsubishi Analytech, trace moisture measuring device "CA-200" and moisture vaporization device "VA-200"), and the samples were placed in the sample boat to measure the moisture regain. In order to minimize the change of moisture during the measurement operation when the sample was at a temperature above room temperature, the time from sample preparation to placement in the moisture vaporization device was set to within 1 minute.

[0165] It should be noted that when the preheating process and the solid-phase polymerization process are directly combined, the liquid crystal polyester fibers that have been treated by canceling the heating of the area corresponding to the solid-phase polymerization process, or the liquid crystal polyester fibers that have been taken out by stopping the heating of the oven or the air flow at the stage when the preheating process is completed are used as samples, and the process moisture regain is calculated.

[0166] (Amount of water contained in the gas generated from the silk during heat treatment)

[0167] A side pipe for collecting gas was set on the gas outlet side piping of the heat treatment chamber, thereby collecting A liter of gas, and the moisture content contained in the collected gas was measured using a moisture regain meter (Mitsubishi Analytech, trace moisture measuring device "CA-200"), and the measured value was set as B grams. The weight of the heat-treated liquid crystal polyester fiber (spun raw yarn before heat treatment) was set to C kilograms, and the circulation speed of the air flow was set to D liters / minute. The moisture content W [g / (min·kg)] contained in the gas generated by the silk during the heat treatment per kilogram of silk per minute was calculated by the following formula.

[0168] W=(B×D) / (A×C) (3)

[0169] (CEG amount)

[0170] A liquid crystal polyester resin or fiber sample is freeze-pulverized to d90=100 μm or less (d90: particle size at which the cumulative volume is 90% in particle size distribution), a large excess of n-propylamine is added to the pulverized sample, and the sample is decomposed by heating and stirring at 40°C for 90 minutes. In this case, the ester bond present in the polymer chain is decomposed into carboxylic acid n-propylamide and hydroxyl groups, and the carboxyl group (CEG) and hydroxyl group present at the end of the polymer chain remain in their original state without changing from the carboxyl group and hydroxyl group, so the decomposition products are separated by HPLC, and the peak area of ​​the decomposition product having a carboxyl group is compared with the calibration curve of each standard prepared by HPLC analysis, thereby quantifying the amount of carboxyl terminal groups (meq / kg) derived from each monomer. For example, the amount of CEG derived from monocarboxylic acids such as 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid can be obtained by directly quantifying 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid; the amount of CEG derived from dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid can be obtained by quantifying a substance formed by amide formation of one carboxyl group such as terephthalic acid mono-n-propylamide, isophthalic acid mono-n-propylamide, and 2,6-naphthalenedicarboxylic acid mono-n-propylamide.

[0171] The total amount of all carboxyl terminal groups contained in each sample was taken as the total carboxyl terminal amount (total CEG amount) of the sample. In addition, the total amount of carboxyl terminal groups of carboxyphenyl groups (for example, carboxyl terminal groups derived from monomers having carboxylphenyl groups such as 4-hydroxybenzoic acid, terephthalic acid, and isophthalic acid) contained in each sample was taken as the CEG amount of carboxyl groups at the carboxyl phenyl terminals.

[0172] (CO2 gas generation)

[0173] The amount of CO2 gas generated when the liquid crystal polyester fiber is heated was evaluated by the thermal decomposition GC-BID method. Specifically, first, the liquid crystal polyester fiber was freeze-crushed to d90 = 100 μm or less to prepare a sample for analysis. A GC (gas chromatography) device equipped with a pyrolyzer and a gas detector BID (dielectric barrier discharge ionization detector) in the sample introduction section was used to separate and detect CO2 from the gas generated by treating at 300°C for 10 minutes and quantify it. The measurement was performed three times on the same sample, and the average value was taken as the amount of CO2 gas generated from the sample (meq / kg).

[0174] (Appearance evaluation of fiber-reinforced composite plastics)

[0175] First, a flat fabric with a weft density of 13 threads / 2.5 cm and a warp density of 13 threads / 2.5 cm was prepared using liquid crystal polyester fiber. The unit weight of the fabric was 180 g / m 2 , with a thickness of 0.29 mm. The fabric was cut into a square with a side length of 10 cm, and a polycarbonate film (Mitsubishi Gas Chemical Co., Ltd., "IUPILON FILM FE-2000", thickness 100 μm) cut into a square with a side length of 10 cm was overlapped on each of the upper and lower surfaces, and heated at 280°C, a temperature at which the film is completely melted, for 3 minutes, and after applying a pressure of 3 MPa for 1 minute, it was cooled to below 100°C, thereby obtaining a liquid crystal polyester fiber reinforced composite polycarbonate resin as a sample for appearance evaluation. It should be noted that the weight ratio of the fiber to the resin in the composite is 3:4. The surface and back of the central and 6 cm square area of ​​the sample for appearance evaluation were observed with a magnifying glass, and the number of bubbles with a major diameter of 1 mm or more was counted.

[0176] [Example 1]

[0177] A liquid crystal polyester (α) (Mp0: 281°C) in which the structural units (A) and (B) represented by the following formula are (A) / (B)=73 / 27 (mol ratio) was used. It was melt-extruded through an extruder, metered with a gear pump, and supplied to a polymer spinning head. At this time, the temperature from the extruder outlet to the spinning head was set to 310°C. The spinning head was equipped with a spinning nozzle with an aperture of 0.125 mmφ, a path length (land length) of 0.175 mm, and 300 holes. The polymer was ejected at an ejection amount of 168 g / min, and was wound on a bobbin at a winding speed of 1000 m / min to obtain a spinning precursor. At this time, a 2 wt% aqueous solution of sodium dodecyl phosphate (Wako Pure Chemical Industries, Ltd., Wako Grade 1) was applied to the spinning precursor from an oiling guide arranged directly below the spinning nozzle. The amount of the aqueous solution applied was 8.4 g / min, and the attachment ratio of sodium dodecyl phosphate to the spinning raw fibers was calculated to be 0.1 wt %.

[0178] [Chemical formula 8]

[0179]

[0180] Next, if Figure 1 As shown in the process diagram of , the spinning raw yarn 9 is withdrawn from the unwinder 1, and is passed through the device and wound in the order of the first roller 2, the heat treatment furnace 3, the second roller 4, and the winding machine 5, thereby performing continuous heat treatment based on transportation in a roll-to-roll manner to obtain the heat-treated yarn 10 of this embodiment. Here, the heat treatment furnace 3 has a furnace tube 7 and a control unit 8, and the furnace tube 7 is composed of a ceramic tube, and the control unit 8 has a heating unit for heating the inside of the furnace tube 7 with a gas atmosphere. The furnace tube 7 has six heating zones 6a to 6f, and each heating zone 6a to 6f can be temperature-controlled by the control unit 8, and their path lengths are the same length. The conditions for continuous heat treatment are set as follows. The rotation speed of the first roller 2 is set so that the time of passing through the furnace tube 7 of the heat treatment furnace 3 (the distance of the silk sample passing through the furnace tube 7 of the heat treatment furnace 3 / the conveying speed of the first roller 2) is 60 minutes. In addition, the rotation speed of the second roller 4 is set so that the elongation ratio (the rotation speed of the second roller 4 / the rotation speed of the first roller 2) is 1.005 times. In addition, in the heat treatment furnace 3, in a nitrogen atmosphere, the dew point is -55°C, and the temperatures of the six heating zones 6a to 6f are set to 200°C, 260°C, 260°C, 260°C, 290°C, and 290°C in the order of passing. Here, preheating is carried out at 200°C for 10 minutes in the heating zone 6a, and solid phase polymerization is carried out at 260°C to 290°C for 50 minutes in the heating zones 6b to 6f. It should be noted that in order to adjust the height of the yarn path, ceramic rollers and ceramic guides (not shown) that have been treated with matte finish are also appropriately used. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) and the analysis results in the process such as the strength before preheating and the process regain are shown in Table 5.

[0181] [Example 2]

[0182] Using the spun yarn obtained in the same manner as in Example 1, continuous heat treatment was performed twice in a roll-to-roll manner while conveying as follows.

[0183] In the first time, the rotation speed of the first roller 2 was set so that the time for passing through the furnace tube 7 of the heat treatment furnace 3 (the distance of the wire sample passing through the furnace tube 7 of the heat treatment furnace 3 / the conveying speed of the first roller 2) was 60 minutes. In addition, the rotation speed of the second roller 4 was set so that the elongation ratio (the rotation speed of the second roller 4 / the rotation speed of the first roller 2) was 1.005 times. In the heat treatment furnace 3, in a nitrogen atmosphere, the dew point was -55°C, the heating zone 6a was set to 200°C, and the other heating zones 6b to 6f were not heated.

[0184] In the second time, the treated wire collected by the coiler 5 in the first time was again arranged in the unwinder 1, and the rotation speed of the first roller 2 was set so that the time of passing through the furnace tube 7 of the heat treatment furnace 3 (the distance of the wire sample passing through the furnace tube 7 of the heat treatment furnace 3 / the conveying speed of the first roller 2) was 60 minutes. In addition, the rotation speed of the second roller 4 was set so that the elongation ratio (the rotation speed of the second roller 4 / the rotation speed of the first roller 2) was 1.005 times. In addition, in the heat treatment furnace 3, in a nitrogen atmosphere, the dew point was -55°C, the heating zone 6a was not heated, and the heating zones 6b to 6f were set to 260°C, 260°C, 260°C, 290°C, and 290°C in the order of passing.

[0185] Here, preheating was performed at 200°C for 10 minutes in heating zone 6a in the first continuous heat treatment, and solid phase polymerization was performed at 260°C to 290°C for 50 minutes in heating zones 6b to 6f in the second continuous heat treatment. It should be noted that, in order to adjust the height of the yarn path, a ceramic roller and a ceramic guide (not shown) with a rough surface finishing treatment were also appropriately used. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) and the analysis results of the process such as the strength before preheating and the process moisture regain are shown in Table 5.

[0186] [Example 3]

[0187] Heat-treated yarns were obtained in the same manner as in Example 1 except that the temperature of the heating zone 6a in the heat treatment furnace 3 was set to 100°C for the purpose of setting the preheating temperature to 100°C. The analysis results of the obtained liquid crystal polyester fibers (heat-treated yarns) and the analysis results of the processes such as the strength before preheating and the moisture regain during the process are shown in Table 5.

[0188] [Example 4]

[0189] The spinning raw yarn was obtained in the same manner as in Example 1 except that a spinning nozzle with an aperture of 0.100 mmφ, a path length of 0.140 mm, and 600 holes was used. Then, preheating and solid phase polymerization were performed in the same manner as in Example 1 to obtain heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) and the analysis results in the process such as the strength before preheating and the moisture regain in the process are shown in Table 5.

[0190] [Example 5]

[0191] The spinning raw yarn was obtained in the same manner as in Example 1 except that a spinning nozzle having an aperture of 0.150 mmφ, a path length of 0.210 mm, and 50 holes was used. Then, preheating and solid phase polymerization were performed in the same manner as in Example 1 to obtain heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) and the analysis results in the process such as the strength before preheating and the moisture regain in the process are shown in Table 5.

[0192] [Example 6]

[0193] A spinning raw yarn was obtained in the same manner as in Example 1 except that a spinning nozzle having an aperture of 0.125 mmφ, a path length of 0.175 mm, and 20 holes was used, the polymer was discharged at a discharge rate of 11.2 g / min, and the amount of sodium dodecyl phosphate aqueous solution supplied from the oiling guide was set to 0.56 g / min. Then, preheating and solid phase polymerization were performed in the same manner as in Example 1 to obtain a heat-treated yarn. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) and the analysis results in the process such as the strength before preheating and the moisture regain in the process are shown in Table 5.

[0194] [Example 7]

[0195] Four spinning heads and spinning nozzles used in Example 1 were used simultaneously, and the polymer ejected from each nozzle at an ejection amount of 168 g / min was reassembled into a filament, and wound on a bobbin at a winding speed of 1000 m / min to obtain a spinning precursor. The spinning precursor was obtained in the same manner as in Example 1 except that the step of applying the sodium dodecyl phosphate aqueous solution from the oiling guide was performed at a stage earlier than the reassembly into a filament, and was applied directly below each spinning nozzle in the same manner as in Example 1. Then, preheating and solid phase polymerization were performed in the same manner as in Example 1 to obtain a heat-treated filament. The analysis results of the obtained liquid crystal polyester fiber (heat-treated filament) and the analysis results in the process such as the strength before preheating and the process moisture regain are shown in Table 5.

[0196] [Example 8]

[0197] In the continuous heat treatment, the rotation speed of the first roller 2 was set so that the time of passing through the furnace tube 7 of the heat treatment furnace 3 (the distance of the silk sample passing through the furnace tube 7 of the heat treatment furnace 3 / the conveying speed of the first roller 2) was 960 minutes, and the rotation speed of the second roller 4 was set so that the elongation ratio (the rotation speed of the second roller 4 / the rotation speed of the first roller 2) was 1.005 times, and the heat-treated silk was obtained in the same manner as in Example 1. Here, preheating was carried out at 200°C for 160 minutes in the heating zone 6a, and solid phase polymerization was carried out at 260°C to 290°C for 800 minutes in the heating zones 6b to 6f. The analysis results of the obtained liquid crystal polyester fiber (heat-treated silk) and the analysis results of the process such as the strength before preheating and the process moisture regain are shown in Table 5.

[0198] [Example 9]

[0199] Heat-treated yarns were obtained in the same manner as in Example 1 except that the rotation speed of the second roller 4 was set to 1.100 times during the continuous heat treatment. The analysis results of the obtained liquid crystal polyester fibers (heat-treated yarns) and the analysis results of the processes such as the strength before preheating and the moisture regain during the process are shown in Table 5.

[0200] [Example 10]

[0201] Heat-treated yarns were obtained in the same manner as in Example 1 except that the rotation speed of the second roller 4 was set to 1.000 times during the continuous heat treatment. The analysis results of the obtained liquid crystal polyester fibers (heat-treated yarns) and the analysis results of the processes such as the strength before preheating and the moisture regain during the process are shown in Table 5.

[0202] [Example 11]

[0203] Instead of using the liquid crystal polyester (α) described in Example 1, a liquid crystal polyester (β) (Mp0: 348°C) having a molar ratio of each structural unit represented by the following formula of (A) / (C) / (D) / (E)=65 / 10 / 5 / 20 was used, and the temperature from the extruder outlet to the spinning head was set to 350°C. A spinning raw yarn was obtained in the same manner as in Example 1, except that the temperatures of the six heating zones 6a to 6f in the heat treatment furnace 3 were set to 200°C, 300°C, 300°C, 300°C, 330°C, and 330°C in the order of passing. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) and the analysis results of the process such as the strength before preheating and the process moisture regain are shown in Table 5.

[0204] [Chemical formula 9]

[0205]

[0206] [Example 12]

[0207] Instead of using the liquid crystal polyester (α) described in Example 1, a liquid crystal polyester (γ) (Mp0: 315°C) having a molar ratio of each structural unit represented by the following formula of (A) / (C) / (D) / (E) / (F) = 54 / 15 / 8 / 16 / 7 was used, and the temperature from the extruder outlet to the spinning head was set to 340°C. A spinning raw yarn was obtained in the same manner as in Example 1, except that the temperatures of the six heating zones 6a to 6f in the heat treatment furnace 3 were set to 200°C, 280°C, 280°C, 280°C, 310°C, and 310°C in the order of passing. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) and the analysis results of the process such as the strength before preheating and the process moisture regain are shown in Table 5.

[0208] [Chemical formula 10]

[0209]

[0210] [Comparative Example 1]

[0211] Heat-treated yarns were obtained in the same manner as in Example 1 except that the temperature of the heating zone 6a was set to 260°C. Table 5 shows the analysis results of the obtained liquid crystal polyester fibers (heat-treated yarns) and the analysis results of the spinning raw yarn strength and process moisture regain.

[0212] [Comparative Example 2]

[0213] Heat-treated yarns were obtained in the same manner as in Example 1 except that the temperature of heating zones 6b to 6f was set to 200°C during the continuous heat treatment. The analysis results of the obtained liquid crystal polyester fibers (heat-treated yarns) and the analysis results of the pre-heating strength, process moisture regain, etc. are shown in Table 5.

[0214] [Comparative Example 3]

[0215] Heat-treated yarns were obtained in the same manner as in Example 11 except that the temperature of the heating zone 6a was set to 300°C. Table 5 shows the analysis results of the obtained liquid crystal polyester fibers (heat-treated yarns) and the analysis results of the spinning raw yarn strength, process moisture regain, etc.

[0216] [Comparative Example 4]

[0217] Heat-treated yarns were obtained in the same manner as in Example 12 except that the temperature of the heating zone 6a was set to 280°C during the continuous heat treatment. The analysis results of the obtained liquid crystal polyester fibers (heat-treated yarns) and the analysis results of the spinning raw yarn strength, process moisture regain, etc. are shown in Table 5.

[0218] [Example 13]

[0219] A liquid crystal polyester (α) (Mp0: 281°C) in which the structural units (A) and (B) are (A) / (B)=73 / 27 (mol ratio) is used. It is melt-extruded by an extruder, metered by a gear pump, and the polymer is supplied to a spinning head. The temperature from the extruder outlet to the spinning head at this time is set to 310°C. The spinning head is equipped with a spinning nozzle with an aperture of 0.125 mmφ, a path length of 0.175 mm, and a number of holes of 300. The polymer is ejected at an ejection rate of 168 g / min, and is wound on a bobbin at a winding speed of 1000 m / min to obtain a spinning precursor. At this time, a 2.00 wt% aqueous solution of sodium dodecyl phosphate (manufactured by Wako Pure Chemical Industries, Ltd., Wako Grade 1) is applied to the spinning precursor from an oiling guide arranged directly below the spinning nozzle. The amount of the aqueous solution applied is 8.40 g / min, and the attachment ratio of sodium dodecyl phosphate to the spinning precursor is 0.100 wt%.

[0220] Next, 5 kg of the spun yarn was wound on an aluminum bobbin to a winding density of 0.6 g / cm 3 , using an oven in the form of a combination of two heat sources, heating nitrogen circulation and electric heating, heat treatment was carried out in a nitrogen atmosphere at a dew point of -55°C. At this time, the temperature was raised from 20°C to 220°C within 10 minutes (average 10°C / min), and from 220°C to 230°C within 1 minute (average 10°C / min). In order to measure the amount of moisture contained in the gas, it was kept at 230°C for 1 minute, and from 230°C to 250°C within 2 minutes (average 10°C / min). It was kept at 250°C for 16 hours to obtain heat-treated silk. It should be noted that at the moment of reaching 230°C, the amount of moisture contained in the gas generated by the silk during the heat treatment was 0.0022g / (min·kg). The analysis results of the obtained liquid crystal polyester fiber (heat-treated silk) are shown in Table 5.

[0221] [Comparative Example 5]

[0222] Heat-treated yarns were obtained in the same manner as in Example 13, except that the concentration of the sodium dodecyl phosphate (Wako Pure Chemical Industries, Ltd., Wako Grade 1) aqueous solution supplied from the oiling guide was set to 0.200% by weight, and the amount of the aqueous solution supplied to the spinning precursor was set to 84.0 g / min. It should be noted that the amount of moisture contained in the gas generated by the yarn during the heat treatment was 3.0 g / (min·kg) when the temperature reached 230°C. The analysis results of the obtained liquid crystal polyester fiber (heat-treated yarn) are shown in Table 5.

[0223]

[0224] As shown in Table 5, in Examples 1 and 3 to 12, the preheating was performed at 200°C or 100°C in the heating zone 6a of the heat treatment furnace 3, so that in the subsequent heating zones 6b to 6f, solid phase polymerization was performed in a state where the water content was reduced, and the total CEG amount could be reduced. In addition, in Example 2, the continuous heat treatment was divided into two times, and the preheating was performed at 200°C in the first continuous heat treatment, so that in the subsequent second continuous heat treatment, solid phase polymerization was performed in a state where the water content was reduced, and the total CEG amount could be reduced. Therefore, the liquid crystal polyester fibers of Examples 1 to 12 can suppress the amount of gas generated, and the fiber-reinforced composite plastics manufactured using the same can suppress the generation of bubbles. In addition, in Examples 1 to 9, 11 and 12, the liquid crystal polyester fibers were manufactured by controlling the specific elongation ratio and continuous heat treatment based on transportation, so the deviation of the mechanical properties in the fiber length direction can be suppressed.

[0225] On the other hand, in Comparative Examples 1, 3, and 4, the preheating to reduce the water content was not performed, but the heat treatment was performed at 260°C, 300°C, and 280°C, respectively, depending on the type of the liquid crystal polyester resin, starting from the heating zone 6a of the heat treatment furnace 3. Therefore, the total CEG amount was large. It is believed that the reason for this is that since solid phase polymerization was performed in a state with a large amount of water, hydrolysis occurred and the total CEG amount increased. Therefore, the liquid crystal polyester fibers of Comparative Examples 1, 3, and 4 generated more than twice as much CO2 gas as that of Example 1, and in the fiber-reinforced composite plastics produced using the same, more bubbles were generated than in Examples 1 to 12.

[0226] In Comparative Example 2, since heating to a temperature effective for solid phase polymerization, i.e., 230° C. or higher, was not performed, the strength after heat treatment did not reach 18 cN / dtex. It is therefore inferred that the fiber-reinforced composite plastic produced using the liquid crystal polyester fiber of Comparative Example 2 had insufficient mechanical properties.

[0227] In Example 13, the total CEG amount can be reduced by reducing the moisture content of the spinning raw yarn provided for intermittent solid phase polymerization. Therefore, the liquid crystal polyester fiber of Example 13 can suppress the amount of gas generated, and the fiber-reinforced composite plastic produced using the same can suppress the generation of bubbles.

[0228] On the other hand, in Comparative Example 5, the total CEG amount was large because the water content of the spinning raw yarns provided for solid phase polymerization was large. Therefore, the liquid crystal polyester fiber of Comparative Example 5 generated more than twice as much CO2 gas as that of Example 13, and in the fiber-reinforced composite plastic produced using the liquid crystal polyester fiber, more bubbles were generated than in Example 13.

[0229] Industrial Applicability

[0230] The liquid crystal polyester fiber of the present invention can suppress the generation of gas during heating, and thus can be suitably used as a reinforcing material for fiber-reinforced composite plastics. In addition, when mixed with rubber, resin, etc. as short fibers, the generation of gas during heating can be suppressed during molding and use, and thus can be suitably used as a filling material.

[0231] As mentioned above, the preferred embodiments of the present invention have been described, but various additions, changes, or deletions may be made without departing from the gist of the present invention, and all of these are included in the scope of the present invention.

Claims

1. A liquid crystal polyester fiber having a total carboxyl terminal amount (total CEG amount) of 5.0 meq / kg or less, a strength of 18 cN / dtex or more, and an initial elastic modulus deviation of 3.0% or less. 2 . The liquid crystal polyester fiber according to claim 1 , comprising a liquid crystal polyester having 50 mol % or more of a structural unit derived from 4-hydroxybenzoic acid.

3. The liquid crystal polyester fiber according to claim 1 or 2, wherein: The CEG amount of the carboxyl group at the terminal of the carboxyphenyl group is 4.0 meq / kg or less.

4. A method for producing a liquid crystal polyester fiber, which is a method for producing the liquid crystal polyester fiber according to any one of claims 1 to 3, the method at least comprising: The step of preheating the spinning raw yarn of the liquid crystal polyester fiber at 80 to 220°C, and a step of solid phase polymerizing the preheated raw yarn at 230° C. or higher; At least in the solid phase polymerization step, the spinning raw yarn is conveyed at an elongation ratio of 1.001 to 1.200 times and heat-treated.

5. The method for producing a liquid crystal polyester fiber according to claim 4, wherein: The preheating and the solid phase polymerization are performed while the spinning raw yarn is conveyed in a roll-to-roll method.

6. The method for producing a liquid crystal polyester fiber according to claim 4, wherein: The strength ratio before and after solid phase polymerization is more than 1.5 times.

7. The method for producing a liquid crystal polyester fiber according to claim 5, wherein: The strength ratio before and after solid phase polymerization is more than 1.5 times.

8. The method for producing a liquid crystal polyester fiber according to any one of claims 4 to 7, wherein The moisture regain of the spun raw yarn subjected to the solid phase polymerization step is 200 ppm or less. 9 . A fiber structure comprising the liquid crystal polyester fiber according to claim 1 at least in part.

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