Method for producing liquid crystal polyester depolymerized product, method for producing recycled liquid crystal polyester resin, method for producing recycled liquid crystal polyester molded body, and chemical recycling method

Abstract

The present invention provides a method for producing a liquid crystal polyester depolymerized product, which is useful for recycling a liquid crystal polyester product. The method for producing a liquid crystal polyester depolymerized product includes a depolymerization step for depolymerizing a liquid crystal polyester contained in a liquid crystal polyester product by means of cleavage of an ester bond so as to increase the total amount of one end, wherein the liquid crystal polyester product is depolymerized using a solvent that is in a subcritical state, and the total amount of one end of the liquid crystal polyester after depolymerization is 50 meq / kg or more.

Description

Method for producing liquid crystal polyester depolymerized product, method for producing recycled liquid crystal polyester resin, method for producing recycled liquid crystal polyester molded body, and chemical recycling method Related applications

[0001] This application claims the priority of U.S. Provisional Patent Application No. 63 / 693,840, filed on September 12, 2024 in the United States, and is incorporated herein by reference in its entirety as part of this application.

[0002] The present invention relates to a method for producing a liquid crystal polyester depolymerized product used for recycling, a method for producing a recycled liquid crystal polyester resin using the liquid crystal polyester depolymerized product obtained by the production method, a method for producing a recycled liquid crystal polyester molded body, and a chemical recycling method for liquid crystal polyester products.

[0003] Various plastic products are used in a wide range of applications such as daily necessities, textile products, industrial materials, civil engineering and construction materials, and materials for electrical and electronic components. However, a large amount of plastic products that have become unnecessary and are discarded, as well as plastic pieces generated during the manufacturing process of plastic products, are being produced. In recent years, concerns about environmental problems such as marine plastic waste have increased, and in order to build a sustainable recycling society, the construction of recycling methods such as the reuse and recycling of these waste plastics is required.

[0004] For example, Patent Document 1 (Japanese Patent No. JP4680266), Patent Document 2 (Japanese Patent No. JP3350696), and Patent Document 3 (Japanese Patent No. JP5099416) disclose methods for depolymerizing (decomposing) general-purpose polyesters typified by polyethylene terephthalate, and so-called chemical recycling techniques for producing general-purpose polyesters by repolymerizing the monomers obtained by depolymerization as raw materials are described.

[0005] Although not described in relation to recycling technology, Patent Document 4 (Japanese Patent No. JP4121188) discloses a method of reacting a wholly aromatic liquid crystal polyester resin with a lower alcohol in a supercritical state to depolymerize the wholly aromatic liquid crystal polyester resin to its repeating structural unit monomers.

[0006] Patent No. 4680266 Patent No. 3350696 Patent No. 5099416 Patent No. 4121188

[0007] On the other hand, liquid crystal polyester, known as a so-called super engineering plastic, has attracted attention in recent years due to its excellent properties such as high strength, low moisture absorption, heat resistance, chemical resistance, and electrical properties. It is widely used in various applications, and its use is expected to increase further in the future. However, unlike general-purpose polyester used in beverage bottles and the like, there is no established recycling method for liquid crystal polyester products. In fact, while Patent Documents 1 to 3 describe chemical recycling technologies for general-purpose polyester, they do not mention anything about liquid crystal polyester.

[0008] Liquid crystal polyester has a rigid molecular structure, and by highly oriented the molecular chains, properties such as high strength can be achieved in liquid crystal polyester products in the form of fibers, etc. Liquid crystal polyester products with such properties are often composed of liquid crystal polyester with a high molecular weight, and because their melt-molding properties are insufficient, it is difficult to re-melt and reuse them.

[0009] Furthermore, although Patent Document 4 describes a method for depolymerizing all-aromatic liquid crystal polyester resin, it is only described as a method for analyzing the composition of repeating structural units of all-aromatic liquid crystal polyester resin, and does not mention anything about using the resulting depolymerization product for recycling. In addition, in depolymerization methods that involve reaction with a supercritical solvent as described in Patent Document 4, it is difficult to control the depolymerization reaction, and the reaction may proceed until the monomers of the liquid crystal polyester are further decomposed, making it impossible to use for recycling.

[0010] Therefore, an object of the present invention is to provide a method for producing a liquid crystal polyester depolymer useful for recycling liquid crystal polyester products. Another object of the present invention is to provide a method for producing recycled liquid crystal polyester resin and recycled liquid crystal polyester molded articles using the liquid crystal polyester depolymer obtained by the said production method.

[0011] As a result of diligent research to achieve the above objective, the inventors of the present invention have found that a liquid crystal polyester depolymer obtained by depolymerizing liquid crystal polyester using a subcritical solvent to increase the total amount of end crystals by cleaving ester bonds can be applied to chemical recycling technology when it contains liquid crystal polyester having a specific total amount of end crystals, thus completing the present invention.

[0012] In other words, the present invention may be configured in the following embodiments. [Embodiment 1] A method for producing a liquid crystal polyester depolymer used in the production of recycled liquid crystal polyester molded articles, comprising a step of increasing the total amount of end crystals by depolymerizing the liquid crystal polyester contained in a liquid crystal polyester product by cleaving ester bonds, wherein the liquid crystal polyester product is subjected to a depolymerization reaction using a subcritical solvent, and the total amount of end crystals of the liquid crystal polyester after depolymerization is 50 meq / kg or more. [Embodiment 2] A method for producing a liquid crystal polyester depolymer according to Embodiment 1, wherein the subcritical solvent is subcritical water. [Embodiment 3] A method for producing a liquid crystal polyester depolymer according to Embodiment 1 or 2, wherein the liquid crystal polyester product contains a liquid crystal polyester containing constituent units derived from 6-hydroxy-2-naphthoic acid, and the amount of 2-naphthol produced in the liquid crystal polyester depolymer is 9.0 mol% or less (preferably 5.0 mol% or less, more preferably 3.0 mol% or less). [Aspect 4] A method for producing a liquid crystal polyester depolymer according to the method of[Aspect 7] A method for producing a liquid crystal polyester depolymer according to any one aspect of aspects 1 to 6, wherein the liquid crystal polyester product is a fiber. [Aspect 8] A method for producing a liquid crystal polyester depolymer according to any one aspect of aspects 1 to 7, wherein the total amount of liquid crystal polyester fragments contained in the liquid crystal polyester product is 50 meq / kg or less (preferably 25 meq / kg or less, more preferably 10 meq / kg or less). [Aspect 9] A method for producing a recycled liquid crystal polyester resin, comprising a polymerization step of using at least a portion of the liquid crystal polyester depolymer obtained by the method according to any one aspect of aspects 1 to 8 as at least a portion of the polymerization raw material. [Aspect 10] A method for producing a recycled liquid crystal polyester resin according to aspect 9, wherein in the polymerization step, all of the solid and / or liquid of the liquid crystal polyester depolymer is used as a mixture as at least a portion of the polymerization raw material. [Aspect 11] A method for producing a recycled liquid crystal polyester resin according to aspect 9, comprising a step of purifying the liquid crystal polyester depolymer before the polymerization step. [Aspect 12] A method for producing a recycled liquid crystal polyester molded article, comprising the step of melt-molding a recycled liquid crystal polyester resin obtained by the manufacturing method described in any one of aspects 9 to 11. [Aspect 13] A method for producing a recycled liquid crystal polyester molded article, comprising the step of melt-molding at least a portion of a liquid crystal polyester depolymer obtained by the manufacturing method described in any one of aspects 1 to 8. [Aspect 14] A method for producing a recycled liquid crystal polyester molded article according to aspect 12 or 13, wherein the recycled liquid crystal polyester molded article is a fiber, a film, or a processed product thereof.[Aspect 15] A method for chemically recycling a liquid crystal polyester product, comprising: a step of producing a liquid crystal polyester depolymer by depolymerizing the liquid crystal polyester contained in the liquid crystal polyester product by cleaving ester bonds to increase the total amount of end pieces, the depolymerization step of depolymerizing the liquid crystal polyester product using a subcritical solvent, wherein the total amount of end pieces of liquid crystal polyester contained in the liquid crystal polyester depolymer is 50 meq / kg or more; a polymerization step of polymerizing the liquid crystal polyester depolymer using at least a portion of the liquid crystal polyester depolymer as at least a portion of the polymerization raw material to synthesize a recycled liquid crystal polyester resin; and a molding step of melt-molding the obtained recycled liquid crystal polyester resin to produce a recycled liquid crystal polyester molded body. [Aspect 16] A method for chemically recycling a liquid crystal polyester product, comprising: a step of producing a liquid crystal polyester depolymer by depolymerizing the liquid crystal polyester contained in the liquid crystal polyester product by cleaving ester bonds to increase the total amount of end pieces, the depolymerization step of depolymerizing the liquid crystal polyester product using a subcritical solvent, wherein the total amount of end pieces of liquid crystal polyester contained in the liquid crystal polyester depolymer is 50 meq / kg or more; and a molding step of melt-molding at least a portion of the liquid crystal polyester depolymer to produce a recycled liquid crystal polyester molded body.

[0013] As used herein, the singular forms, “a,” “an,” and “the,” are intended to include the plural form, including “at least one,” unless the context explicitly indicates otherwise. As used herein, the terms “and / or,” “at least one,” and “one or more” include any and all combinations of the related enumerated items.

[0014] Furthermore, any combination of at least two components disclosed in the claims and / or specification is included in the present invention. In particular, any combination of two or more claims described in the claims is included in the present invention.

[0015] According to the present invention, liquid crystal polyester products can be chemically recycled. The liquid crystal polyester depolymer obtained by the manufacturing method of the present invention can be used as a polymerization raw material to produce recycled liquid crystal polyester resin. Furthermore, recycled liquid crystal polyester molded articles can be produced by melt molding the obtained recycled liquid crystal polyester resin.

[0016] [Method for producing liquid crystal polyester depolymer] The method for producing liquid crystal polyester depolymer is a step of increasing the total amount of end crystals by depolymerizing the liquid crystal polyester contained in a liquid crystal polyester product by cleaving ester bonds, and includes a depolymerization step in which the liquid crystal polyester product is depolymerized using a subcritical solvent, and the total amount of end crystals of the liquid crystal polyester after depolymerization is 50 meq / kg or more. Since the total amount of end crystals of the liquid crystal polyester contained in the liquid crystal polyester depolymer is within a specific range, it can be used as a polymerization raw material for synthesizing recycled liquid crystal polyester resin by repolymerization, or it can be used as is by melt molding to produce recycled liquid crystal polyester molded articles. Since the liquid crystal polyester depolymer is depolymerized by cleaving ester bonds, it can be used as a polymerization raw material for recycled liquid crystal polyester resin, and the recycled liquid crystal polyester resin obtained by repolymerization can be used to produce recycled liquid crystal polyester molded articles.

[0017] Liquid crystal polyester products subject to chemical recycling are products containing liquid crystal polyester. Liquid crystal polyester is a polyester that exhibits optical anisotropy (liquid crystallinity) in the molten phase. Liquid crystallinity can be determined, for example, by placing a sample on a hot stage, heating it under a nitrogen atmosphere, and observing the transmitted light of the sample with a polarizing microscope. Liquid crystal polyester may be a polyester mainly composed of structural units containing aromatic groups in the main chain, with bonds between each structural unit mainly consisting of ester bonds, but it is preferable that all structural units contain aromatic groups in the main chain, making it a fully aromatic liquid crystal polyester. For example, it may consist of structural units derived from aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc., and the chemical composition of the structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids is not particularly limited as long as it does not impair the effects of the present invention. Furthermore, within the range that does not hinder the effects of the present invention, the liquid crystal polyester may be a liquid crystal polyesteramide containing structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids. For example, preferred structural units are shown in Table 1.

[0018]

[0019] In the constituent units of Table 1, m is an integer from 0 to 2, and Y in the formula can be any of the following independently, ranging from 1 to the maximum number of substitutions possible: hydrogen atom, halogen atom (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom, etc.), alkyl group (e.g., alkyl groups with 1 to 4 carbon atoms such as methyl group, ethyl group, isopropyl group, t-butyl group, etc.), alkoxy group (e.g., methoxy group, ethoxy group, isopropoxy group, n-butoxy group, etc.), aryl group (e.g., phenyl group, naphthyl group, etc.), aralkyl group (e.g., benzyl group (phenylmethyl group), phenethyl group (phenylethyl group), etc.), aryloxy group (e.g., phenoxy group, etc.), aralkyloxy group (e.g., benzyloxy group, etc.).

[0020] More preferred structural units include those shown in Examples (1) to (20) in Tables 2, 3, and 4 below. Liquid crystal polyester may consist only of combinations of any of the structural units in the following formulas (1) to (20). If a structural unit in a formula can exhibit multiple structures, two or more such structural units may be combined and used as structural units to constitute the polymer.

[0021]

[0022]

[0023]

[0024] In the constituent units of Tables 2, 3, and 4, n is an integer of 1 or 2, and each constituent unit n=1, n=2 may exist individually or in combination, Y １ and Y ２ These may each be independently a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., a C1 to C4 alkyl group such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group, etc.), an aryloxy group (e.g., a phenoxy group, etc.), an aralkyloxy group (e.g., a benzyloxy group, etc.). Of these, hydrogen atoms, chlorine atoms, bromine atoms, or methyl groups are preferred.

[0025] Furthermore, Z can be represented by the substituent shown in the following formula.

[0026]

[0027] In one embodiment, the liquid crystal polyester may contain as a main component a constituent unit derived from a hydroxycarboxylic acid. Preferably, the liquid crystal polyester may contain a constituent unit (A) derived from hydroxybenzoic acid and a constituent unit (B) derived from hydroxynaphthoic acid. For example, a constituent unit (A) may be a constituent unit derived from 4-hydroxybenzoic acid (formula (A) below), and a constituent unit (B) may be a constituent unit derived from 6-hydroxy-2-naphthoic acid (formula (B) below). From the viewpoint of improving melt moldability, the ratio of constituent unit (A) to constituent unit (B) may preferably be in the range of 9 / 1 to 1 / 1, more preferably 7 / 1 to 1 / 1, and even more preferably 5 / 1 to 1 / 1.

[0028]

[0029]

[0030] The total content of constituent unit (A) and constituent unit (B) in the liquid crystal polyester may be, for example, 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, relative to the total amount of all constituent units.

[0031] The melting point of the liquid crystal polyester may be in the range of 250 to 380°C, preferably 255 to 370°C, more preferably 260 to 360°C, and even more preferably 260 to 350°C. In this specification, the melting point is the main absorption peak temperature observed when measured by a differential scanning calorimeter (DSC) in accordance with the JIS K 7121 test method. Specifically, 4 to 6 mg of the sample is placed in an aluminum pan and sealed in the DSC apparatus. Nitrogen is then flowed as a carrier gas at a flow rate of 200 mL / min, and the endothermic peak is measured when the temperature is raised from room temperature (e.g., 25°C) at a rate of 10°C / min. If a clear peak does not appear in the first run of the DSC measurement depending on the type of polymer, the temperature may be raised to 50°C higher than the expected flow temperature at a rate of 50°C / min, completely melted at that temperature for 3 minutes, then cooled to 50°C at a rate of 80°C / min, and then the endothermic peak is measured at a rate of 10°C / min.

[0032] The total amount of end-caps of liquid crystal polyester in a liquid crystal polyester product is not particularly limited as long as the total amount of end-caps can be increased in the depolymerization process described later. For example, it may be 50 meq / kg or less, 25 meq / kg or less, or 10 meq / kg or less. The total amount of end-caps indicates the number of polymer chains and is used as an indicator to evaluate molecular weight. A larger total amount of end-caps tends to indicate a smaller molecular weight, and a smaller total amount of end-caps tends to indicate a larger molecular weight. Considering that it is difficult to quantify all types of ends of liquid crystal polyester depending on the composition (combination of constituent units and their content ratio), in this specification, the total amount of end-caps is defined as the value obtained by dividing the total amount (meq / kg) of carboxyl group ends derived from hydroxycarboxylic acid and ends from which carbon dioxide has been removed by a decarboxylation reaction that may occur as a side reaction in the carboxyl groups derived from hydroxycarboxylic acid, per 1 kg of liquid crystal polyester product, by the molar ratio of constituent units derived from hydroxycarboxylic acid in the liquid crystal polyester, and is measured by the method described in the examples below. Even when liquid crystal polyester with a molecular weight in this range is included, chemical recycling can be performed by subjecting the liquid crystal polyester product to the depolymerization process described later. In particular, liquid crystal polyester products in the form of fibers are often composed of high molecular weight liquid crystal polyester to exhibit properties such as high strength, and it is useful to perform chemical recycling of such liquid crystal polyester products through the depolymerization process described later. Furthermore, the lower limit of the total end amount of the above-mentioned material is not particularly limited, but may be 2 meq / kg or more, 2.5 meq / kg or more, 3.3 meq / kg or more, or 5 meq / kg or more.

[0033] Furthermore, liquid crystal polyester products may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin. They may also contain inorganic substances such as titanium dioxide, kaolin, silica, and barium oxide, as well as various additives such as carbon black, colorants such as dyes and pigments, antioxidants, UV absorbers, and light stabilizers.

[0034] From the viewpoint of improving recycling efficiency, the liquid crystal polyester product may contain 50% by weight or more of liquid crystal polyester, preferably 80% by weight or more, and more preferably 90% by weight or more. Furthermore, from the viewpoint of effectively utilizing resources by using the liquid crystal polyester depolymer obtained by subjecting the liquid crystal polyester product to the depolymerization process described later as a polymerization raw material without purification or other processes, it may contain 95% by weight or more, and even more preferably 98% by weight or more.

[0035] The form of liquid crystal polyester products is not particularly limited and includes, for example, fibers, films, sheets, molded products of various shapes, and processed products thereof. Liquid crystal polyester products can be made by recovering discarded products (used products) or defective products and waste generated during the manufacturing process (e.g., scraps, fiber waste, residues, burrs, etc.).

[0036] Liquid crystal polyester products may be in the form of fibers (hereinafter sometimes referred to as "liquid crystal polyester fibers"). Examples of liquid crystal polyester fibers include mixed spun fibers obtained by mixing liquid crystal polyester with the above-mentioned thermoplastic polymer and various additives and spinning them together; composite fibers obtained by simultaneously spinning different components of liquid crystal polyester and the above-mentioned thermoplastic polymer from separated spinnerets; and non-composite fibers. Liquid crystal polyester fibers may have various oils attached to their surface. Non-composite fibers, which are not mixed spun with other materials or composite spun, are preferably used as liquid crystal polyester fibers to achieve high strength. However, because the liquid crystal polyester content, i.e., purity, in the liquid crystal polyester fibers is high, the recycling efficiency can be improved when using the chemical recycling method of the present invention. Furthermore, liquid crystal polyester fibers may be either spun yarn (untreated yarn) obtained by melt spinning, or heat-treated yarn obtained by heat treatment of the spun yarn, which promotes solid-phase polymerization of liquid crystal polyester and enhances mechanical properties such as tensile strength. In particular, since heat-treated yarns have a high molecular weight of liquid crystal polyester due to solid-phase polymerization, the chemical recycling method of the present invention, which involves obtaining a liquid crystal polyester depolymer by depolymerization using a subcritical solvent, can be suitably used. In this specification, liquid crystal polyester fibers include all fiber forms such as filaments (monofilaments, multifilaments), staple fibers, short-cut fibers, and spun yarns, and also include fabrics such as woven fabrics, knitted fabrics, and nonwoven fabrics, as well as processed products such as ropes obtained by processing such fibers.

[0037] The fibers used in liquid crystal polyester products can be recovered and used from used liquid crystal polyester fibers (e.g., untreated yarn, heat-treated yarn, or processed products thereof), leftover or waste yarns of liquid crystal polyester fibers generated during the manufacturing process (e.g., leftover liquid crystal polyester fibers remaining on paper tubes or bobbins), etc.

[0038] From the perspective of increasing the purity of the liquid crystal polyester, a step of performing a cleaning treatment or a separation treatment before subjecting the liquid crystal polyester product to a depolymerization step may be included. For example, when an oil agent, a treatment agent, or the like adheres to the surface of the liquid crystal polyester product, it may be washed and removed by a method corresponding to the type of the oil agent, the treatment agent, or the like. For example, it may be washed using a cleaning liquid according to the type of the oil agent, the treatment agent, or the like to be removed, and a cleaning liquid containing a solvent such as an acidic solvent, an alkaline solvent, an organic solvent, an aqueous solvent, and, if necessary, a cleaning agent such as a surfactant may also be used. For example, the amount of the oil agent and the treatment agent adhering to the liquid crystal polyester product to be subjected to the depolymerization step may be 0.5% by weight or less based on the weight of the entire liquid crystal polyester product from the perspective of suppressing the reaction stability in the depolymerization step and the deterioration of the performance and quality due to the inclusion of foreign substances in the liquid crystal polyester depolymerized product, the recycled liquid crystal polyester resin obtained using the same, and the recycled liquid crystal polyester molded body. When it exceeds 0.5% by weight, the above cleaning treatment may be performed to reduce the amount of the oil agent and the treatment agent adhering. In this specification, the oil agent and the treatment agent mean components adhering to the surface for improving the processability and physical properties of the liquid crystal polyester product and imparting characteristics, and components such as additives mixed with the liquid crystal polyester inside the liquid crystal polyester product do not fall under this.

[0039] Further, when the liquid crystal polyester product is a composite material containing the liquid crystal polyester and another material (for example, a fiber-reinforced plastic of the liquid crystal polyester and a reinforcing fiber, a metal-clad laminate of a film and a metal foil, etc.), the other material may be separated from the liquid crystal polyester product by a method corresponding to the type of the other material. For example, for a metal-clad laminate or the like composite with a metal material, the metal material may be removed using various etching liquids.

[0040] In the depolymerization process, a liquid crystal polyester depolymer can be obtained by using a subcritical solvent to depolymerize the liquid crystal polyester contained in the liquid crystal polyester by cleaving the ester bonds, thereby increasing the total amount of end-pieces. In this specification, a subcritical state is defined as a high-temperature, high-pressure state where at least one of the temperature and pressure is below the critical point, and the temperature and pressure are sufficiently higher than room temperature and atmospheric pressure and close to the critical point, whereas a supercritical state is defined as a high-temperature, high-pressure state where the temperature and pressure are above the critical point. Supercritical solvents are highly reactive and can cause radical reactions, making it difficult to control the depolymerization reaction. The reaction may proceed until the liquid crystal polyester monomer is further decomposed, potentially rendering the depolymer unsuitable for recycling. In contrast, subcritical solvents have high self-dissociation ability, can suppress the progression of radical reactions, and can control the depolymerization reaction, making it possible to recycle the resulting liquid crystal polyester depolymer.

[0041] From the viewpoint of improving depolymerization reactivity, subcritical protic solvents are preferred as subcritical solvents. Examples of protic solvents include water, alcohols (e.g., lower aliphatic alcohols such as methanol and ethanol, aromatic alcohols such as benzyl alcohol, etc.), alkylene glycols (e.g., ethylene glycol, propylene glycol, etc.), carboxylic acids, and amines. For example, in the case of subcritical water, the depolymerization reaction can be carried out by hydrolysis; in the case of subcritical alcohol, by alkalisis; in the case of subcritical alkylene glycol, by glycolesis; in the case of subcritical carboxylic acid, by acidolysis; and in the case of subcritical amine, by amine decomposition, by cleaving the ester bond. The critical point for water is 374°C and 22.1 MPa, the critical point for methanol is 239°C and 8.1 MPa, and the critical point for ethanol is 241°C and 6.1 MPa. However, for example, the subcritical state of these solvents may be when at least one of the temperature and pressure is below the critical point, and the temperature is 100°C or higher and the pressure is 0.1 MPa or higher.

[0042] The solvent in the subcritical state is more preferably subcritical water from the viewpoints of reducing environmental impact and ease of controlling the subcritical state. Subcritical water is water under temperature and pressure conditions where at least one of the temperature and pressure is below the critical point of 374°C and 22.1 MPa, the temperature is 100°C or higher, and the pressure is 0.1 MPa or higher. Since it does not have as high activity as supercritical water, it can suppress radical reactions. On the other hand, because its ion product is high and the concentrations of hydrogen ions and hydroxide ions are high, it exhibits strong hydrolysis and can proceed with a depolymerization reaction by cleaving the ester bonds of the liquid crystal polyester. When using subcritical water, from the viewpoints of suppressing radical reactions and promoting the depolymerization reaction by hydrolysis, the reaction temperature may be 200 to 350°C, preferably 210 to 320°C, more preferably 220 to 295°C, and even more preferably 230 to 275°C from the viewpoint of further suppressing radical reactions. Also, the reaction pressure may be 2.0 to 16.0 MPa, preferably 2.5 to 10.0 MPa, more preferably 3.0 to 8.0 MPa, and even more preferably 3.5 to 4.8 MPa from the viewpoint of further suppressing radical reactions.

[0043] In the depolymerization step, in order to accelerate the reaction, methods such as reacting under acidic or alkaline conditions, reacting in the presence of a catalyst, adding monomers constituting the liquid crystal polyester and reacting, using carbon dioxide in the supercritical state (critical point: 31°C, 7.4 MPa) in addition to the solvent in the subcritical state and reacting, reacting by irradiating with microwaves, reacting using bacteria or enzymes, or a combination of these methods can be used.

[0044] The reaction time in the depolymerization step can be appropriately adjusted according to the type of the solvent in the subcritical state, the reaction temperature and pressure, the above-described reaction acceleration methods, etc. However, from the viewpoint of suppressing radical reactions, it is preferable to react for a long time under relatively mild reaction conditions (low temperature, low pressure). For example, it may be 40 to 900 minutes, preferably 90 to 720 minutes, more preferably 150 to 600 minutes, and even more preferably 330 to 540 minutes.

[0045] In the depolymerization process, the total amount of end crystals is increased by depolymerizing the liquid crystal polyester contained in the liquid crystal polyester product, and the total amount of end crystals in the liquid crystal polyester (liquid crystal polyester after depolymerization) contained in the resulting depolymerized liquid crystal polyester product should be 50 meq / kg or more. The liquid crystal polyester (liquid crystal polyester before depolymerization) contained in the liquid crystal polyester product, which is the raw material in the depolymerization process, may have a total amount of end crystals in the range of 50 meq / kg or more, as described above. Furthermore, the rate of increase in the total amount of end crystals before and after depolymerization is not particularly limited and varies depending on the total amount of end crystals in the liquid crystal polyester before depolymerization, but for example it may be 100% or more, 200% or more, 400% or more, 600% or more, 800% or more, or 1000% or more. The rate of increase in the total amount of end crystals is calculated as (total amount of end crystals in the liquid crystal polyester after depolymerization - total amount of end crystals in the liquid crystal polyester before depolymerization) / total amount of end crystals in the liquid crystal polyester before depolymerization × 100.

[0046] The liquid crystal polyester depolymer obtained by the depolymerization process is a mixture produced by the depolymerization reaction due to the cleavage of ester bonds, and may contain monomers obtained by complete depolymerization, oligomers (e.g., polymers of 10-mers or less) or polymers obtained by partial depolymerization, or a mixture thereof. In this specification, the liquid crystal polyester after depolymerization includes not only polymers and oligomers but also monomers obtained by the depolymerization of the liquid crystal polyester, and the total end-weight of the liquid crystal polyester after depolymerization is expressed as a measured value including monomers. The liquid crystal polyester depolymer may contain depolymers produced by side reactions (e.g., radical reactions) in the depolymerization reaction due to the cleavage of ester bonds as impurities (e.g., components that are further decomposed from the liquid crystal polyester monomer and do not have the ability to form constituent units of the liquid crystal polyester). In addition, the liquid crystal polyester depolymer may contain impurities that are not involved in the depolymerization of the liquid crystal polyester (e.g., additives other than liquid crystal polyester that were contained in the liquid crystal polyester product), in addition to components that participated in the depolymerization of the liquid crystal polyester, such as monomers, oligomers, and polymers.

[0047] From the viewpoint of producing recycled liquid crystal polyester resin, it is preferable that the liquid crystal polyester depolymer contains monomers and oligomers. If the liquid crystal polyester depolymer contains monomers, it may contain multiple types of monomers. In this specification, monomers derived from different structural units of the liquid crystal polyester contained in the liquid crystal polyester product are considered to be different types of monomers, and even if they are different monomers (for example, monomers containing derivatives of hydroxyl groups or carboxyl groups), if they are monomers derived from the same structural unit, they are considered to be the same type of monomer. The components contained in the liquid crystal polyester depolymer vary depending on the composition of the liquid crystal polyester contained in the liquid crystal polyester product subjected to the depolymerization process, but if the liquid crystal polyester depolymer contains monomers, it is preferable that the content ratio of aromatic hydroxycarboxylic acids (for example, 6-hydroxy-2-naphthoic acid, etc.) is high. Even if the aromatic hydroxycarboxylic acids are of different types, their reactivity (decomposition resistance) during depolymerization and solubility during monomer recovery are similar, so even if the liquid crystal polyester depolymer contains multiple types of aromatic hydroxycarboxylic acids, it is easy to handle. The chemical structure of the liquid crystal polyester depolymer after cleavage of the ester bond may be not only hydroxyl groups and carboxyl groups, but also derivatives thereof, depending on the depolymerization method. Here, a derivative refers to a modified functional group that, even if the functional group such as a hydroxyl group or carboxyl group is modified, still possesses polymerization ability in that modified state or can be converted to a functional group such as a hydroxyl group or carboxyl group, or a monomer having such a modified functional group. If the chemical structure after cleavage of the ester bond is a derivative of a hydroxyl group or carboxyl group, it may be reacted further to convert it to a hydroxyl group or carboxyl group as needed.

[0048] In the depolymerization step, in which the depolymerization reaction is carried out using the subcritical solvent described above, depending on the composition of the liquid crystal polyester contained in the liquid crystal polyester product subjected to the depolymerization step, it is possible to selectively obtain a predetermined component as a component of the liquid crystal polyester depolymer. If it is possible to obtain a predetermined component (for example, a predetermined monomer) in a larger amount than other components, it becomes easier to isolate the predetermined component, and it can be suitably used in the synthesis of recycled liquid crystal polyester resin as described later. For example, if the liquid crystal polyester product contains a liquid crystal polyester containing constituent units derived from 4-hydroxybenzoic acid and constituent units derived from 6-hydroxy-2-naphthoic acid, the recovery rate of 6-hydroxy-2-naphthoic acid and its derivatives can be higher than the recovery rate of 4-hydroxybenzoic acid and its derivatives. For example, the recovery rate of 4-hydroxybenzoic acid and its derivatives contained in the liquid crystal polyester depolymer may be 60 mol% or less, preferably 30 mol% or less, more preferably 10 mol% or less, even more preferably 5 mol% or less, and even more preferably 0 mol%. The recovery rate of 4-hydroxybenzoic acid and its derivatives is the ratio of the amount of 4-hydroxybenzoic acid and its derivatives contained in the liquid crystal polyester depolymer to the theoretical amount produced assuming that all constituent units derived from 4-hydroxybenzoic acid in the liquid crystal polyester product are depolymerized to 4-hydroxybenzoic acid.

[0049] Furthermore, if the liquid crystal polyester product contains a liquid crystal polyester comprising structural units derived from 4-hydroxybenzoic acid and structural units derived from 6-hydroxy-2-naphthoic acid, the recovery rate of 6-hydroxy-2-naphthoic acid and its derivatives contained in the liquid crystal polyester depolymer may be 30 mol% or more, preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more. The recovery rate of 6-hydroxy-2-naphthoic acid and its derivatives is the ratio of the amount of 6-hydroxy-2-naphthoic acid and its derivatives contained in the liquid crystal polyester depolymer to the theoretical production amount assuming that all structural units derived from 6-hydroxy-2-naphthoic acid contained in the liquid crystal polyester of the liquid crystal polyester product have been depolymerized to 6-hydroxy-2-naphthoic acid.

[0050] In the depolymerization step using the aforementioned subcritical solvent, side reactions (e.g., radical reactions) can be suppressed, and the generation of impurities can be suppressed. For example, if a liquid crystal polyester product contains liquid crystal polyester containing constituent units derived from 6-hydroxy-2-naphthoic acid, the liquid crystal polyester depolymer may contain 2-naphthol as an impurity in addition to 6-hydroxy-2-naphthoic acid and its derivatives. By adjusting the conditions of the depolymerization step using the aforementioned subcritical solvent, it is possible to reduce the amount of 2-naphthol generated in the liquid crystal polyester depolymer. For example, the amount of 2-naphthol generated in the liquid crystal polyester depolymer may be 9.0 mol% or less, preferably 5.0 mol% or less, more preferably 3.0 mol% or less, and even more preferably 2.0 mol% or less. The lower limit of the amount of 2-naphthol generated in the liquid crystal polyester depolymer is not particularly limited, but may be, for example, 0.01 mol% or more. The amount of 2-naphthol produced is the ratio of the amount of 2-naphthol produced in the liquid crystal polyester depolymer to the theoretical amount produced assuming that all constituent units derived from 6-hydroxy-2-naphthoic acid contained in the liquid crystal polyester product are depolymerized to 6-hydroxy-2-naphthoic acid.

[0051] [Method for producing recycled liquid crystal polyester resin] The method for producing recycled liquid crystal polyester resin includes a step of polymerization using at least a portion of the liquid crystal polyester depolymer obtained by the above production method as at least a portion of the polymerization raw material. Since the liquid crystal polyester depolymer obtained by the above production method is depolymerized by cleavage of ester bonds, it can be polymerized to re-form ester bonds and can be used in the synthesis of recycled liquid crystal polyester resin. In this specification, recycled liquid crystal polyester resin includes liquid crystal polyester synthesized by chemical recycling via liquid crystal polyester depolymer after depolymerizing a liquid crystal polyester product, and may also include other components. For example, other components may include components other than liquid crystal polyester that were contained in the liquid crystal polyester product without purification in the intermediate steps. Here, polymerization using liquid crystal polyester depolymer includes not only monomer polymerization reactions but also polymerization reactions occurring from oligomers and polymers contained in the liquid crystal polyester depolymer.

[0052] In the polymerization process, the entire solid and / or liquid liquid of the liquid crystal polyester depolymer may be used as a mixture in at least part of the polymerization raw material. In this case, the liquid crystal polyester depolymer obtained in the depolymerization process is used directly in the polymerization process without purification.

[0053] Alternatively, the process may include a purification step to purify the liquid crystal polyester depolymer before the polymerization step. In this case, predetermined components may be separated from the liquid crystal polyester depolymer obtained in the depolymerization step, and these components may be used as at least a portion of the polymerization raw materials in the polymerization step. For example, in the purification step, if the liquid crystal polyester depolymer is a mixture containing not only monomers but also oligomers, polymers, solvents, impurities not involved in the depolymerization of the liquid crystal polyester, etc., the impurities may be removed by methods such as filtration, or the monomers, oligomers, and polymers may be separated based on differences in melting point, boiling point, molecular weight, etc.

[0054] In the polymerization process, depending on the desired composition (combination of constituent units and their content ratio), all or part of the liquid crystal polyester depolymer may be used as the polymerization raw material, or other polymerization raw materials may be added in addition to the liquid crystal polyester depolymer. Preferred alternative polymerization raw materials include virgin monomers and bio-derived monomers. The composition of the recycled liquid crystal polyester resin may be adjusted by adding monomers to the polymerization raw material in addition to the liquid crystal polyester depolymer. The polymerization raw material may have its polymerizable groups activated; for example, it may be activated into carboxylic acid derivatives such as hydroxyl group acylates, carboxyl group esters, acid halides, and acid anhydrides before being subjected to the polymerization process. Recycled liquid crystal polyester resin can be obtained by synthesizing liquid crystal polyesters of the above various compositions. The synthesized liquid crystal polyester may have the same composition as the liquid crystal polyester contained in the liquid crystal polyester product, or a new liquid crystal polyester with a different composition may be synthesized.

[0055] Polymerization may be carried out in the presence of various polymerization catalysts, for example, organotin catalysts (dialkyltin oxides, etc.), antimony catalysts (antimony trioxide, etc.), titanium catalysts (titanium dioxide, etc.), alkali metal salts or alkaline earth metal salts of carboxylic acids (potassium acetate, etc.), Lewis salts (BF ３ Examples include organic compound catalysts (such as N,N-dimethylaminopyridine and 1-methylimidazole).

[0056] [Method for Manufacturing Recycled Liquid Crystal Polyester Molded Articles] In one aspect of the present invention, the method for manufacturing a recycled liquid crystal polyester molded article includes a step of melt-molding the recycled liquid crystal polyester resin obtained by the above manufacturing method. In this specification, a recycled liquid crystal polyester molded article is a liquid crystal polyester molded article formed by chemical recycling through the depolymerization of a liquid crystal polyester product by depolymerizing the liquid crystal polyester product. The recycled liquid crystal polyester molded article is not particularly limited in type as long as it is a molded article obtained by melt-molding of liquid crystal polyester, and examples include pellets, fibers, films, various injection-molded articles, etc., which can be obtained by known or conventional manufacturing methods. Furthermore, the recycled liquid crystal polyester molded article also includes processed products obtained by processing the molded article (pellets, fibers, films, various injection-molded articles, etc.) obtained by the above melt-molding method.

[0057] When melt-molding recycled liquid crystal polyester resin, it can be melt-molded by known or conventional methods depending on the desired molded product. For example, when forming pellets, pelletizing is performed. Recycled liquid crystal polyester resin is fed into an extruder, melt-kneaded in the extruder, and then cut by known or conventional means such as the strand-cut method or the hot-cut method to obtain pellets of a predetermined size. Fibers, films, various injection-molded products, etc., can also be manufactured by known or conventional methods. When using recycled liquid crystal polyester resin for melt-molding, virgin liquid crystal polyester resin, the thermoplastic polymers mentioned above, and various additives may be added. In this specification, virgin liquid crystal polyester resin refers to unused resin, that is, non-recycled resin that has not undergone recycling.

[0058] In another aspect of the present invention, the method for producing a recycled liquid crystal polyester molded article includes a step of melt-molding the liquid crystal polyester depolymer obtained by the above production method. In this case, the liquid crystal polyester depolymer is used in melt-molding in whole or in part, without going through the polymerization step (without going through the recycled liquid crystal polyester resin). From the viewpoint of melt-molding properties, it is preferable that the liquid crystal polyester depolymer is not completely depolymerized to the monomer level, but rather partially depolymerized to contain liquid crystal polyester in a polymer state. For example, the total amount of liquid crystal polyester at the end of each piece contained in the liquid crystal polyester depolymer may be 125 meq / kg or less, and preferably 100 meq / kg or less. Also, similar to the aspect of melt-molding the recycled liquid crystal polyester resin described above, virgin liquid crystal polyester resin, the thermoplastic polymer described above, and various additives may be added when using the liquid crystal polyester depolymer in melt-molding.

[0059] The recycled liquid crystal polyester molded article may also be in the form of fibers (hereinafter sometimes referred to as "recycled liquid crystal polyester fibers"). Recycled liquid crystal polyester fibers can be obtained by melt spinning recycled liquid crystal polyester resin or liquid crystal polyester depolymer.

[0060] Melt spinning can be carried out by known methods. For example, recycled liquid crystal polyester resin or liquid crystal polyester depolymer can be melted in an extruder, then extruded from a nozzle at a predetermined spinning temperature, and wound up with a godet roller or the like to obtain spun yarn.

[0061] Furthermore, the method for producing recycled liquid crystal polyester fibers may further include a step of heat-treating the obtained spun yarn. By heat-treating the spun yarn, solid-phase polymerization of the liquid crystal polyester can be promoted, thereby improving mechanical properties such as tensile strength. In the heat-treating step, the method of heat treatment is not particularly limited; for example, it may be a batch-type heat treatment or a continuous heat treatment by conveying. In the case of batch-type heat treatment, for example, the heat treatment may be performed with the fibers wound in a package-like manner on a bobbin, or in a skein or tow-like manner. It is preferable to perform the heat treatment in a package-like manner because it simplifies the equipment and improves productivity. In the case of continuous heat treatment by conveying, the conveying method may be either contact conveying (e.g., conveyor system, support roll system, heat treatment method on heated rollers) or non-contact conveying (roll-to-roll system).

[0062] The heat treatment process can employ known methods, such as atmospheric heating and contact heating. Suitable atmospheric conditions include air, inert gases (e.g., nitrogen, argon), or combinations thereof.

[0063] The heat treatment temperature may be less than the melting point (Mp) of the spun yarn subjected to the heat treatment process in order to prevent melting. For example, it may be Mp - 50°C or higher and less than Mp°C, preferably Mp - 40°C or higher and less than Mp°C, and more preferably Mp - 30°C or higher and less than Mp°C.

[0064] In the method for manufacturing recycled liquid crystal polyester fibers, for example, an oil may be applied before the heat treatment process to improve the bundle properties of the fibers and prevent fusion during heat treatment. Furthermore, after heat treatment, a finishing oil may be applied as appropriate, depending on the intended use of the recycled liquid crystal polyester fibers.

[0065] Examples of recycled liquid crystal polyester fibers include mixed spun fibers obtained by mixing recycled liquid crystal polyester resin or liquid crystal polyester depolymer with virgin liquid crystal polyester resin, the above-mentioned thermoplastic polymer, and various additives; composite fibers obtained by simultaneously spinning different components of recycled liquid crystal polyester resin or liquid crystal polyester depolymer and the above-mentioned thermoplastic polymer from a separated spinneret; and non-composite fibers.

[0066] In this invention, even if recycled liquid crystal polyester fibers are obtained by chemically recycling liquid crystal polyester products, their strength can be increased to the same level as the liquid crystal polyester fibers before recycling. The recycled liquid crystal polyester fibers may have a strength of 18 cN / dtex or higher, preferably 20 cN / dtex or higher, and more preferably 22 cN / dtex or higher. Furthermore, there is no particular upper limit to the strength, but for example, it may be around 40 cN / dtex. In this specification, the strength of recycled liquid crystal polyester fibers refers to the tensile strength, which is the value measured by the method described in the examples below.

[0067] The fineness of the single fiber of the recycled liquid crystal polyester fiber can be appropriately selected depending on the application, etc. For example, the fineness of the single fiber may be 50 dtex or less, preferably 15 dtex or less, and more preferably 10 dtex or less. Furthermore, there is no particular lower limit to the fineness of the single fiber, but for example, it may be around 0.01 dtex.

[0068] Recycled liquid crystal polyester fibers may be monofilaments or multifilaments. In the case of multifilaments, the number of filaments can be appropriately selected depending on the application, for example, the number of filaments may be 2 to 5,000, preferably 3 to 4,000, and more preferably 5 to 3,000.

[0069] The total fineness of recycled liquid crystal polyester fibers can be appropriately selected depending on the application, etc. For example, the total fineness may be 50,000 dtex or less, preferably 10,000 dtex or less, more preferably 5,000 dtex or less, and even more preferably 2,000 dtex or less. Furthermore, there is no particular lower limit to the total fineness, but it may be, for example, around 1 dtex.

[0070] Recycled liquid crystal polyester fibers can be used in various applications as part of a fiber structure, similar to liquid crystal polyester fibers as liquid crystal polyester products before recycling. Fiber structures containing recycled liquid crystal polyester fibers can be used in any fiber form, such as staple fibers, short-cut fibers, filament yarns, spun yarns, strings, and ropes. They can also be used as various fabrics, such as nonwovens, woven fabrics, and knitted fabrics. Such fibers and fabrics can be manufactured using recycled liquid crystal polyester fibers by known methods.

[0071] The fiber structure may be a combination of recycled liquid crystal polyester fibers and other fibers, as long as the effects of the present invention are not impaired. For example, composite fibers using recycled liquid crystal polyester fibers and other fibers (e.g., blended yarns made by blending recycled liquid crystal polyester fibers and other fibers) can be used. Also, composite fabrics using recycled liquid crystal polyester fibers and other fibers (e.g., blended fabrics made by blending recycled liquid crystal polyester fibers and other fibers, or laminates of fabrics made of recycled liquid crystal polyester fibers and fabrics made of other fibers) can be used.

[0072] In addition to producing filaments by melt spinning as described above, melt molding of recycled liquid crystal polyester resin or liquid crystal polyester depolymers can also produce spin-direct nonwoven fabrics using known or conventional methods such as the melt-blown method or the spunbond method.

[0073] Recycled liquid crystal polyester fibers can be used in various forms of fiber structures for a wide range of applications, including general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various textile products. For example, they can be used in tension members (electric wires, optical fibers, umbilical cables, heater wire cores, cords for various electrical products such as earphone cords, etc.), sailcloth, ropes (marine, mountaineering, cranes, yachts, tugs, etc.), climbing ropes, land nets (safety nets, golf driving range nets, etc.), slings, safety lines, fishing lines, fishing nets, longlines, sewing threads, screen door cords, geogrids, protective gloves, ripstop for protective clothing and outdoor wear, motorcycle suits, sports rackets, strings, medical catheter reinforcement materials, sutures, screen mesh, filters, printed circuit board base fabrics, electronic equipment exterior materials, mesh conveyor belts, papermaking belts, dryer canvases, airships, balloons, airbags, speaker cones, reinforcing materials for various hoses and pipes, and advanced processed products such as rubber and plastic reinforcement materials for tires and conveyor belts.

[0074] [Chemical Recycling Method] As described above, liquid crystal polyester products can be chemically recycled by depolymerizing the liquid crystal polyester using a subcritical solvent to increase the total amount of end-pieces by cleaving ester bonds. That is, in one aspect of the present invention, a chemical recycling method for liquid crystal polyester products is a step of producing a liquid crystal polyester depolymer by depolymerizing the liquid crystal polyester contained in a liquid crystal polyester product to increase the total amount of end-pieces by cleaving ester bonds, comprising: a depolymerization step of depolymerizing the liquid crystal polyester product using a subcritical solvent, wherein the total amount of end-pieces of liquid crystal polyester contained in the liquid crystal polyester depolymer is 50 meq / kg or more; a polymerization step of polymerizing the liquid crystal polyester depolymer using at least a part of the liquid crystal polyester depolymer as at least a part of the polymerization raw material to synthesize a recycled liquid crystal polyester resin; and a molding step of melt-molding the obtained recycled liquid crystal polyester resin to produce a recycled liquid crystal polyester molded body.

[0075] Furthermore, in another aspect of the present invention, a chemical recycling method for liquid crystal polyester products is a step of producing a liquid crystal polyester depolymer by depolymerizing the liquid crystal polyester contained in the liquid crystal polyester product by cleaving ester bonds to increase the total amount of end-pieces, comprising: a depolymerization step of depolymerizing the liquid crystal polyester product using a subcritical solvent, wherein the total amount of end-pieces of liquid crystal polyester contained in the liquid crystal polyester depolymer is 50 meq / kg or more; and a molding step of melt-molding at least a portion of the liquid crystal polyester depolymer to produce a recycled liquid crystal polyester molded body.

[0076] These chemical recycling methods can be applied to the methods described above for producing liquid crystal polyester depolymers, recycled liquid crystal polyester resins, and recycled liquid crystal polyester molded articles.

[0077] The present invention will be described in more detail below 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 methods described below.

[0078] (Total end amount) Liquid crystal polyester fiber samples were freeze-dried until d90 = 100 μm or less. A large excess of n-propylamine was added to the pulverized samples, and the samples were heated and stirred at 40°C for 90 minutes to depolymerize them. The ester bonds present inside the molecular chains were depolymerized into carboxylic acid n-propylamide and hydroxyl groups, while the carboxyl groups (CEG) and hydroxyl groups present at the ends of the polymer chains remained unchanged. The depolymerized products were separated by HPLC, and the peak area of ​​the depolymerized products containing carboxyl groups was compared with a calibration curve created by HPLC analysis of each standard to quantify the amount of carboxyl ends derived from hydroxycarboxylic acid and the total amount of ends produced by the decarboxylation reaction of carboxyl groups at the ends derived from hydroxycarboxylic acid (meq / kg). For example, the amount of ends derived from 4-hydroxybenzoic acid was determined by quantifying 4-hydroxybenzoic acid and phenol, and the amount of ends 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 constituent units derived from hydroxycarboxylic acids in the liquid crystal polyester of the sample, and this value was defined as the total amount of terminals in the sample.

[0079] (Total fineness, single fiber fineness) Based on JIS L 1013:2010 8.3.1 Method A, 10m skeins of liquid crystal polyester fiber were taken using a measuring device "Wrap Reel by Motor Driven" manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd., and the weight (g) was multiplied by 1000. Three measurements were taken for each level, and the average of the three measurements 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).

[0080] (Strength, Modulus of Elasticity) Referring to JIS L 1013:2010 8.5.1, tensile tests were performed 10 times per yarn sample using an Autograph "AGS-100B" manufactured by Shimadzu Corporation, under the conditions of a test length of 20 cm and a tensile speed of 10 cm / min. The tensile strength (cN / dtex) was calculated by dividing the average value of the tensile strength (N) at the time of fracture by the total fineness (dtex) measured by the method described above. In addition, the modulus of elasticity (cN / dtex) was calculated by dividing the average value of the slope of the line connecting the two points of elongation at 0.25% and 1.00% in the strength-elongation curve obtained from the tensile test by the total fineness (dtex) measured by the method described above.

[0081] (Fiber melting point) In accordance with JIS K 7121, the melting point was measured using a differential scanning calorimeter (DSC; Shimadzu Corporation "DSC60A Plus"), and the observed main absorption peak temperature was defined as the melting point. Specifically, 1 to 10 mg of the sample was placed in an aluminum pan and sealed in the DSC apparatus. Nitrogen was then flowed through the apparatus as a carrier gas at a flow rate of 100 mL / min, and the endothermic peak originating from the liquid crystal polyester was measured when the temperature was raised from 25°C to 20°C / min.

[0082] [Examples 1-5] Liquid crystal polyester fiber (manufactured by Kuraray Co., Ltd., Vectran® HT, 1670 dtex / 300 f) was used as the liquid crystal polyester product to be recycled. The liquid crystal polyester fiber had a liquid crystal polyester content (purity) of 100% by weight, a total end weight of 6.0 meq / kg, and a melting point of 322°C. Liquid crystal polyester fiber and water were placed in a SUS316 autoclave container (capacity 500 mL) in a weight ratio of liquid crystal polyester fiber:water = 4.17:1.00, and the container was then purged with nitrogen at atmospheric pressure. In Examples 1-5, the temperature and pressure inside the container were increased while stirring until the internal temperature and pressure reached the temperatures and pressures shown in Table 5, and then the reaction was allowed to proceed for the time shown in Table 5. After the reaction, the container was cooled, and after the internal temperature fell below 60°C, the pressure was released and the container was opened. After opening, the precipitated solid and reaction solution in the container were recovered as liquid crystal polyester depolymers and separated into filtrate and filtrate by suction filtration. NMR analysis was performed on the recovered filtrates, and the recovery rates of 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA), as well as the production rate of 2-naphthol (NpOH), were calculated using the following formulas. In all of Examples 1 to 5, the monomers were depolymerized in the above reaction, so the total end-piece amount of the depolymer was 50 meq / kg or more. Recovery rate of HBA (mol%) = Amount of HBA recovered (mol) / Theoretical amount of HBA produced (mol) × 100 Recovery rate of HNA (mol%) = Amount of HNA recovered (mol) / Theoretical amount of HNA produced (mol) × 100 Production rate of NpOH (mol%) = Amount of NpOH produced (mol) / Theoretical amount of HNA produced (mol) × 100

[0083] Next, fresh HBA is added to the filtrate so that the mol ratio of 4-hydroxybenzoic acid (HBA):HNA = 73:27. In a reaction vessel equipped with a stirring blade, distillation tube, and reaction solution discharge tube, HBA, HNA, and acetic anhydride (Ac) are added. ２O) and potassium acetate (KOAc) were added in a mol ratio of 73 / 27 / 105 / 0.005. Next, the reaction vessel was purged with nitrogen, and while stirring the reaction mixture, the temperature was raised from room temperature to 160°C at a rate of 2°C / min, and reflux was carried out at 160°C for 3 hours. Next, while distilling off the evaporated liquid, the temperature was raised from 160°C to 320°C at a rate of 2°C / min, and stirring was carried out at 320°C for 1 hour. Next, the pressure inside the reaction vessel was reduced to 100 Pa over 1.5 hours and stirring continued, and when the reaction mixture reached a molten resin of the predetermined viscosity, stirring was stopped and nitrogen was introduced into the reaction vessel. Next, the reaction vessel was pressurized with nitrogen to 3 atmospheres, and the resin was removed from the discharge pipe at the bottom of the reaction vessel as strands with a diameter of 2 mm, and pelletized with a rotary cutter to obtain resin chips as recycled liquid crystal polyester resin.

[0084] After drying the resin chips with hot air at 120°C for more than 4 hours, melt extrusion was performed using a Φ15 mm twin-screw extruder at a heater temperature of 300°C, and the molten resin was supplied to the spinning head while being weighed with a gear pump. The spinning head was equipped with a spinning die with a hole diameter of 0.125 mmφ and 50 holes, and the molten resin was discharged at a discharge rate of 28 g / min and wound onto a bobbin at a winding speed of 1000 m / min to obtain recycled liquid crystal polyester fiber spun yarn (280 dtex / 50 f). At this time, a 2 wt% aqueous solution of sodium dodecyl phosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Wako Grade 1) was applied to the spun yarn from an oiling guide placed directly below the spinning die. The amount of this aqueous solution applied was 1.4 g / min, and the attachment ratio of sodium dodecyl phosphate to the spun yarn was calculated to be 0.1 wt%. The obtained recycled liquid crystal polyester fiber spun yarn had a melting point of 290°C.

[0085] Next, 4 kg of the obtained spun yarn was wound onto an aluminum bobbin and heat-treated in a sealed oven under a nitrogen atmosphere at the melting point of the spun yarn -10°C for 16 hours to obtain heat-treated recycled liquid crystal polyester fiber. The melting point, strength, and elastic modulus of the obtained heat-treated recycled liquid crystal polyester fiber are shown in Table 5.

[0086] [Comparative Example 1] Liquid crystal polyester fiber (manufactured by Kuraray Co., Ltd., Vectran® HT, 1670 dtex / 300 f) was used as the liquid crystal polyester product. The liquid crystal polyester fiber had a liquid crystal polyester content (purity) of 100% by weight, a total end weight of 6.0 meq / kg, and a melting point of 322°C. Water was added to the liquid crystal polyester fiber in a weight ratio of water:liquid crystal polyester fiber = 10:1, and the mixture was heated in an oil bath at 100°C for 100 minutes. The liquid was removed by distillation, and the remaining fiber was washed with acetone. The weight of the remaining solids did not change from the weight before the reaction (1.0 g), indicating that the depolymerization reaction did not proceed.

[0087]

[0088] Examples 1 to 5 demonstrate that liquid crystal polyester products are depolymerized using subcritical water, and the ester bonds are cleaved to depolymerize them down to the monomers, obtaining a liquid crystal polyester depolymer (total end-piece weight of 50 meq / kg or more). This allows for the synthesis of recycled liquid crystal polyester resin and the production of recycled liquid crystal polyester fibers. Thus, even liquid crystal polyester products containing high molecular weight liquid crystal polyester with low total end-piece weights can be chemically recycled.

[0089] Furthermore, in Examples 1 to 4, the generation rate of 2-naphthol, an impurity in the synthesis of recycled liquid crystal polyester resin, was reduced by adjusting the conditions of the depolymerization reaction using subcritical water. In particular, in Example 4, the generation rate of 2-naphthol was further reduced by making the temperature and pressure of the depolymerization reaction milder while extending the reaction time.

[0090] On the other hand, in Comparative Example 1, water was used instead of subcritical water, so the depolymerization reaction did not proceed, and chemical recycling was not possible.

[0091] The present invention provides a method for producing liquid crystal polyester depolymers, which allows for the chemical recycling of liquid crystal polyester products (especially waste and defective products), and enables the production of recycled liquid crystal polyester molded articles through the resulting liquid crystal polyester depolymer. The recycled liquid crystal polyester molded articles can be used in a variety of applications, such as general industrial materials, civil engineering and construction materials, various reinforcing materials, electrical and electronic component materials, and various textile products, just like the molded articles before recycling.

[0092] As described above, preferred embodiments of the present invention have been explained, but various additions, modifications, or deletions are possible without departing from the spirit of the present invention, and such are also included within the scope of the present invention.

Claims

1. A method for producing a liquid crystal polyester depolymer used in the manufacture of recycled liquid crystal polyester molded articles, comprising a step of increasing the total amount of end crystals by depolymerizing the liquid crystal polyester contained in a liquid crystal polyester product by cleaving ester bonds, wherein the liquid crystal polyester product is subjected to a depolymerization reaction using a subcritical solvent, and the total amount of end crystals of the liquid crystal polyester after depolymerization is 50 meq / kg or more.

2. A method for producing a liquid crystal polyester depolymer according to claim 1, wherein the subcritical solvent is subcritical water.

3. A method for producing a liquid crystal polyester depolymer according to claim 1, wherein the liquid crystal polyester product comprises a liquid crystal polyester containing a structural unit derived from 6-hydroxy-2-naphthoic acid, and the amount of 2-naphthol produced in the liquid crystal polyester depolymer is 9.0 mol% or less.

4. A method for producing a liquid crystal polyester depolymer according to claim 3, wherein the amount of 2-naphthol produced is 2.0 mol% or less.

5. A method for producing a liquid crystal polyester depolymer according to claim 1, wherein the liquid crystal polyester product comprises a liquid crystal polyester containing a structural unit derived from 4-hydroxybenzoic acid and a structural unit derived from 6-hydroxy-2-naphthoic acid, and the recovery rate of 4-hydroxybenzoic acid contained in the liquid crystal polyester depolymer is 60 mol% or less.

6. A method for producing a liquid crystal polyester depolymer according to claim 1, wherein the liquid crystal polyester product contains 95% by weight or more of liquid crystal polyester based on its weight.

7. A method for producing a liquid crystal polyester depolymer according to claim 1, wherein the liquid crystal polyester product is a fiber.

8. A method for producing a liquid crystal polyester depolymer according to claim 7, wherein the total amount of liquid crystal polyester fragments contained in the liquid crystal polyester product is 50 meq / kg or less.

9. A method for producing recycled liquid crystal polyester resin, comprising a polymerization step of polymerizing a liquid crystal polyester depolymer obtained by the manufacturing method described in any one of claims 1 to 8, using at least a portion of the liquid crystal polyester depolymer as at least a portion of the polymerization raw material.

10. A method for producing recycled liquid crystal polyester resin according to claim 9, wherein in the polymerization step, all of the solid and / or liquid liquid crystal polyester depolymer is used as a mixture in at least a portion of the polymerization raw materials.

11. A method for producing recycled liquid crystal polyester resin according to claim 9, comprising a step of purifying a liquid crystal polyester depolymer before the polymerization step.

12. A method for producing a recycled liquid crystal polyester molded article, comprising the step of melt-molding a recycled liquid crystal polyester resin obtained by the manufacturing method described in claim 9.

13. A method for manufacturing a recycled liquid crystal polyester molded article according to claim 12, wherein the recycled liquid crystal polyester molded article is a fiber, a film, or a processed product thereof.

14. A method for chemically recycling liquid crystal polyester products, comprising: a step of producing a liquid crystal polyester depolymer by depolymerizing the liquid crystal polyester contained in the liquid crystal polyester product by cleaving ester bonds to increase the total amount of end-pieces, the depolymerization step of depolymerizing the liquid crystal polyester product using a subcritical solvent, wherein the total amount of end-pieces of liquid crystal polyester contained in the liquid crystal polyester depolymer is 50 meq / kg or more; a polymerization step of polymerizing the liquid crystal polyester depolymer using at least a portion of the liquid crystal polyester depolymer as at least a portion of the polymerization raw material to synthesize a recycled liquid crystal polyester resin; and a molding step of melt-molding the obtained recycled liquid crystal polyester resin to produce a recycled liquid crystal polyester molded body.

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