Method for recycling liquid-crystal polyester products and method for selecting recycling method

Abstract

Provided is a recycling method with which the recycling rate of liquid-crystal polyester products is heightened and energy consumption is reduced. The recycling method is for selectively recycling a liquid-crystal polyester product. In cases where the liquid-crystal polyester product is a low-molecular-weight liquid-crystal polyester product in which a liquid-crystal polyester contained therein has a total one-end content exceeding 12.5 meq / kg, then the low-molecular-weight liquid-crystal polyester product is materially recycled. In cases where the liquid-crystal polyester product is a high-molecular-weight liquid-crystal polyester product in which a liquid-crystal polyester contained therein has a total one-end content of 12.5 meq / kg or less, then the high-molecular-weight liquid-crystal polyester product is chemically recycled.

Description

Recycling method for liquid crystal polyester products and method for selecting recycling method Related applications

[0001] This application claims the priority of Japanese Patent Application No. 2024-165166 filed on September 24, 2024, and the entire content thereof is incorporated herein by reference and cited as part of this application.

[0002] The present invention relates to a recycling method for liquid crystal polyester products and a method for selecting a 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, interest in environmental problems such as marine plastic waste has increased, and in order to build a sustainable recycling-based society, the construction of recycling methods such as the reuse and recycling of these waste plastics is required.

[0004] For example, material recycling and chemical recycling of products such as polyamides and polyesters have been studied. For example, regarding material recycling technology, Patent Document 1 (Japanese Patent No. 4163084) discloses a recycled high-functional spun yarn obtained by using 5 to 95% by mass of high-functional short fibers obtained by recycling used high-functional fiber products such as wholly aromatic polyamide fibers by crushing and then opening the fibers. Further, Patent Document 2 (Japanese Patent No. 7267821) discloses a method for producing recycled meta-type wholly aromatic polyamide fibers by redissolving and spinning a fiber structure composed of meta-type wholly aromatic polyamide fibers.

[0005] Regarding chemical recycling technology, Patent Document 3 (Japanese Patent No. 4680266) discloses a method for depolymerizing polyester by irradiating a molded product or waste containing polyester with microwaves in the presence of ethylene glycol containing sodium hydroxide.

[0006] 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, and is widely used in various applications, with its usage expected to increase further in the future. Patent document 4 (Japanese Patent No. 4720306) describes that when liquid crystal resin fibers such as liquid crystal polyester are subjected to heat treatment or solid-phase polymerization after melt spinning, their ΔHm1 (heat of fusion at the endothermic peak, as measured by differential calorimetry) becomes significantly larger, and their recyclability decreases.

[0007] Patent No. 4163084 Patent No. 7267821 Patent No. 4680266 Patent No. 4720306

[0008] However, unlike the fully aromatic polyamides described in Patent Documents 1 and 2, and the general-purpose polyesters described in Patent Document 3, research into recycling methods for liquid crystal polyester products has not progressed. Although Patent Document 4 describes the recyclability of liquid crystal polyester fibers, it only states that some specific liquid crystal polyester fibers can be used for recycling, and does not describe a method for recycling other liquid crystal polyester products as well.

[0009] 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 their melt-molding properties are insufficient, making it difficult to reuse them by melt-molding. On the other hand, chemical recycling technologies that use depolymers with a melt-moldtable molecular weight obtained by chemical decomposition (depolymerization), or resins obtained by repolymerizing monomers obtained by depolymerization as raw materials, make it possible to recycle all liquid crystal polyester products without distinguishing whether or not they are difficult to melt-mold. However, chemical recycling involves a step of depolymerizing liquid crystal polyester, which not only increases the number of steps but also consumes high energy for the depolymerization conditions, so it is not necessarily a perfect method from the perspective of building a sustainable circular society.

[0010] Therefore, the object of the present invention is to provide a recycling method that reduces energy consumption while increasing the recycling rate of liquid crystal polyester products.

[0011] The inventors of the present invention, after diligent research to achieve the above objective, discovered that by using a combination of recycling technologies—specifically, material recycling when the total amount of liquid crystal polyester fragments contained in liquid crystal polyester products exceeds a certain threshold, and chemical recycling otherwise—it is possible to increase the recycling rate while reducing energy consumption, thus completing the present invention.

[0012] In other words, the present invention may be configured in the following embodiments. [Embodiment 1] A method for selectively recycling liquid crystal polyester products, wherein if the liquid crystal polyester product is a low molecular weight liquid crystal polyester product in which the total amount of liquid crystal polyester fragments contained is greater than 12.5 meq / kg, the low molecular weight liquid crystal polyester product is materially recycled, and if the liquid crystal polyester product is a high molecular weight liquid crystal polyester product in which the total amount of liquid crystal polyester fragments contained is 12.5 meq / kg or less, the high molecular weight liquid crystal polyester product is chemically recycled. [Embodiment 2] The recycling method according to Embodiment 1, wherein the chemical recycling comprises: a depolymerization step of producing a liquid crystal polyester depolymer by depolymerizing the liquid crystal polyester contained in the high molecular weight liquid crystal polyester product until the total amount of liquid crystal polyester fragments contained is 50 meq / kg or more by cleaving ester bonds; a polymerization step of synthesizing a recycled liquid crystal polyester resin by polymerizing using at least a part of the liquid crystal polyester depolymer as at least a part of the polymerization raw material; and a molding step of producing a recycled liquid crystal polyester molded body by melt molding the obtained recycled liquid crystal polyester resin. [Aspect 3] A recycling method according to Aspect 1, wherein the chemical recycling comprises: a depolymerization step of producing a liquid crystal polyester depolymer by depolymerizing liquid crystal polyester contained in a high molecular weight liquid crystal polyester product until the total amount of end pieces is 50 meq / kg or more by cleaving ester bonds; and a molding step of producing a recycled liquid crystal polyester molded body by melt molding at least a portion of the liquid crystal polyester depolymer. [Aspect 4] A recycling method according to Aspect 2 or 3, wherein the cleaving of ester bonds in the depolymerization step is carried out by at least one depolymerization method selected from the group consisting of glycolysis, hydrolysis, and alkalisis.[Aspect 5] A recycling method according to any one of aspects 1 to 4, wherein the material recycling includes a recovery step of recovering a low molecular weight liquid crystal polyester product such that the liquid crystal polyester content is 95% by weight or more, and a molding step of melt-molding the recovered low molecular weight liquid crystal polyester product to produce a recycled liquid crystal polyester molded body. [Aspect 6] A recycling method according to aspect 5, wherein in the material recycling, the low molecular weight liquid crystal polyester product used in the molding step is a liquid crystal polyester chip-like material having a bulk density of 0.15 to 1.20 g / mL (preferably 0.30 to 1.15 g / mL, more preferably 0.55 to 1.10 g / mL, even more preferably 0.65 to 1.08 g / mL, and even more preferably 0.85 to 1.05 g / mL) and an average maximum length of 3 to 30 mm (preferably 3.5 to 20 mm, more preferably 5 to 15 mm). [Aspect 7] A recycling method according to any one aspect of aspects 1 to 6, wherein the liquid crystal polyester product contains 70% by weight or more (preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more) of liquid crystal polyester fibers relative to its weight. [Aspect 8] A recycling method according to any one aspect of aspects 1 to 7, wherein the liquid crystal polyester product is a sling belt. [Aspect 9] A recycling method according to any one aspect of aspects 1 to 8, wherein the liquid crystal polyester product contains liquid crystal polyester that includes constituent units derived from 4-hydroxybenzoic acid and / or constituent units derived from 6-hydroxy-2-naphthoic acid, and the total content of these is 40 mol% or more (preferably 50 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.[Aspect 10] A method for selecting a recycling method for a liquid crystal polyester product based on the total amount of liquid crystal polyester fragments contained in the liquid crystal polyester product, comprising the step of determining whether to apply the liquid crystal polyester product to material recycling if the total amount of fragments is greater than 12.5 meq / kg, and whether to apply the liquid crystal polyester product to chemical recycling if the total amount of fragments is 12.5 meq / kg or less.

[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 the specification and / or drawings 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 recycling method of the present invention, liquid crystal polyester products can be recycled while increasing the recycling rate and reducing the energy consumption associated with recycling.

[0016] This invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are for illustrative and explanatory purposes only and should not be used to define the scope of this invention. The scope of this invention is defined by the appended claims. A flowchart of a recycling method for liquid crystal polyester products according to one embodiment. A flowchart of material recycling according to one embodiment. A flowchart of chemical recycling according to one embodiment.

[0017] [Recycling Method for Liquid Crystal Polyester Products] The present invention provides a method for selectively recycling liquid crystal polyester products. In this method, if the liquid crystal polyester product is a low-molecular-weight liquid crystal polyester product with a total end-cap amount of liquid crystal polyester exceeding 12.5 meq / kg, the low-molecular-weight liquid crystal polyester product is materially recycled. If the liquid crystal polyester product is a high-molecular-weight liquid crystal polyester product with a total end-cap amount of liquid crystal polyester of 12.5 meq / kg or less, the high-molecular-weight liquid crystal polyester product is chemically recycled. Figure 1 is a flowchart of a liquid crystal polyester product recycling method according to one embodiment. In this invention, by using the total end-cap amount of liquid crystal polyester contained in the liquid crystal polyester product as a judgment indicator to determine whether to apply material recycling or chemical recycling, it is possible to make all liquid crystal polyester products eligible for recycling, thereby increasing the recycling rate while reducing energy consumption associated with recycling. More specifically, low molecular weight liquid crystal polyester products with a total end-grain weight exceeding 12.5 meq / kg can be molded without depolymerization, making them suitable for material recycling that reduces energy consumption. On the other hand, high molecular weight liquid crystal polyester products with a total end-grain weight of 12.5 meq / kg or less are difficult to mold as is, so they can be applied to chemical recycling to improve the recycling rate.

[0018] The total end weight indicates the number of polymer chains and is used as an indicator for evaluating molecular weight. A larger total end weight tends to indicate a smaller molecular weight, while a smaller total end weight tends to indicate a larger molecular weight. Considering that it is difficult to quantify all types of ends in liquid crystal polyester depending on the composition (combination of constituent units and their content ratios), in this specification, the total end weight 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. The recycling method may further include a step of determining the total end weight of liquid crystal polyester contained in the liquid crystal polyester product.

[0019] Liquid crystal polyester products 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 are all aromatic liquid crystal polyesters containing aromatic groups in the main chain. 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, examples of preferred structural units are shown in Table 1.

[0020]

[0021] 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.).

[0022] 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.

[0023]

[0024]

[0025]

[0026] 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 ２These 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.

[0027] Furthermore, Z can be represented by the substituent shown in the following formula.

[0028]

[0029] 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.

[0030]

[0031]

[0032] The liquid crystal polyester contained in the liquid crystal polyester product may contain a constituent unit derived from 4-hydroxybenzoic acid (constituent unit (A)) and / or a constituent unit derived from 6-hydroxy-2-naphthoic acid (constituent unit (B)), and the total content of constituent unit (A) and constituent unit (B) may be 40 mol% or more of the total amount of all constituent units, preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more.

[0033] 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.

[0034] 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.

[0035] Liquid crystal polyester products 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 allowing the liquid crystal polyester products to be recycled as is without washing or separation treatments, they may contain 95% by weight or more, and even more preferably 98% by weight or more.

[0036] The form of liquid crystal polyester products is not particularly limited and can include, for example, fibers, films, sheets, molded products of various shapes, and processed products thereof. Liquid crystal polyester products can be made from products that have become unnecessary and been discarded (used products), or from defective products and waste generated during the manufacturing process (e.g., scraps, fiber scraps, residues, burrs, etc.) that have been recovered. For example, fibers as liquid crystal polyester products can be made from used liquid crystal polyester fibers (e.g., untreated yarn, heat-treated yarn, or processed products thereof), or from leftover or waste yarn of liquid crystal polyester fibers generated during the manufacturing process (e.g., leftover liquid crystal polyester fibers remaining on paper tubes or bobbins) that have been recovered. Films as liquid crystal polyester products can be made from used liquid crystal polyester films (e.g., raw film rolls before processing, processed films, or processed products thereof), or from scraps and leftover rolls remaining on winding cores generated during the film manufacturing process, metal-clad laminate manufacturing process, and circuit board manufacturing process, etc.

[0037] Liquid crystal polyester products may contain 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 polymers and various additives and then spinning; composite fibers obtained by simultaneously spinning different components of liquid crystal polyester and the above-mentioned thermoplastic polymers from a segmented spinneret; and non-composite fibers, etc. In addition, various sizing agents may adhere to the surface of the liquid crystal polyester fibers. For liquid crystal polyester fibers, in order to exhibit high strength, non-composite fibers that are not mixed or composite spun with other materials are preferably used. However, since the content of liquid crystal polyester in the liquid crystal polyester fibers, that is, the purity is high, the recycling rate can be improved when using the recycling method of the present invention. Further, the liquid crystal polyester fibers may be either spun raw yarns (untreated yarns) obtained by melt spinning or heat-treated yarns obtained by heat-treating the spun raw yarns and having enhanced mechanical properties such as tensile strength due to the progress of solid-phase polymerization of liquid crystal polyester. Since the untreated yarn contains liquid crystal polyester having a molecular weight that enables melt spinning, the total terminal amount per piece tends to exceed 12.5 meq / kg and can be applied to material recycling. On the other hand, since the molecular weight of liquid crystal polyester is increased by solid-phase polymerization in the heat-treated yarn, the total terminal amount per piece tends to be 12.5 meq / kg or less and can be applied to chemical recycling.

[0038] In this specification, liquid crystal polyester fibers include those having all fiber forms such as filaments (monofilaments, multifilaments), staple fibers, short-cut fibers, spun yarns, etc. Liquid crystal polyester products may be fiber structures such as one-dimensional structures such as strings, belts, cords, ropes, etc. and two-dimensional structures such as fabrics, knitted fabrics, non-woven fabrics, etc. obtained by processing such fibers. Among these fiber structures, from the viewpoint of improving the recycling rate, as liquid crystal polyester products, it is preferable to use a sling belt having a high content of liquid crystal polyester fibers and being easy to recover.

[0039] From the perspective of improving the recycling rate, the liquid crystal polyester product may contain 70% by weight or more of liquid crystal polyester fibers based on its weight, preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more.

[0040] From the perspective of enhancing the purity of the liquid crystal polyester, the liquid crystal polyester product may be subjected to a process of performing a cleaning treatment or a separation treatment before being applied to each recycling. For example, when an oil agent, a treatment agent, etc. adhere 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, etc. For example, it may be washed using a cleaning liquid according to the type of the oil agent, the treatment agent, etc. to be removed, and a cleaning liquid containing a solvent such as an acidic solvent, an alkaline solvent, an organic solvent, an aqueous solvent, etc., and a cleaning agent such as a surfactant as needed may also be used. Further, when the liquid crystal polyester product is a composite material containing liquid crystal polyester and other materials (for example, a fiber reinforced plastic of liquid crystal polyester and reinforcing fibers, a metal-clad laminate of a film and a metal foil, etc.), the other materials may be separated from the liquid crystal polyester product by a method corresponding to the type of the other materials. For example, for a metal-clad laminate, etc. that is composite with a metal material, the metal material may be removed using various etching liquids.

[0041] The liquid crystal polyester product may be subjected to a process of performing a pulverization treatment or a cutting treatment so as to have a suitable shape for being applied to each recycling. For the pulverization treatment or the cutting treatment, for example, scissors, a guillotine cutter, a slitter, a pulverizer, etc. can be selected and used according to the shape of the liquid crystal polyester product. The process of performing the pulverization treatment or the cutting treatment may be used in combination with the process of performing the above-mentioned cleaning treatment or separation treatment. In that case, the order of the two processes is not particularly limited, but it is preferable that the process of performing the cleaning treatment or separation treatment is performed after the process of performing the pulverization treatment or cutting treatment.

[0042] (Material Recycling) In the recycling method of the present invention, low molecular weight liquid crystal polyester products having a total end-piece content of liquid crystal polyester exceeding 12.5 meq / kg are subject to material recycling. In this specification, material recycling is a recycling technology that melts and molds at least a portion of the recovered liquid crystal polyester product without going through a depolymerization step that depolymerizes the liquid crystal polyester contained in the liquid crystal polyester product. The depolymerization step is a process that processes the liquid crystal polyester to cause a depolymerization reaction with the intention of reducing its molecular weight, and the decomposition of liquid crystal polyester that occurs as a side reaction during melt molding does not fall under the category of depolymerization in the depolymerization step.

[0043] Material recycling is not particularly limited as long as it is a method for obtaining a recycled liquid crystal polyester molded article using a low molecular weight liquid crystal polyester product. For example, it may include a step of recovering a low molecular weight liquid crystal polyester product so that the liquid crystal polyester content is 95% by weight or more, and a molding step of melt-molding the recovered low molecular weight liquid crystal polyester product to produce a recycled liquid crystal polyester molded article. Figure 2 is a flowchart of material recycling according to one embodiment. Since material recycling does not involve a step of depolymerizing the liquid crystal polyester in the liquid crystal polyester product, by recovering a low molecular weight liquid crystal polyester product with few impurities in the recovery step, the physical properties of the recycled liquid crystal polyester molded article obtained in the molding step can be made equivalent to those of a liquid crystal polyester molded article obtained by melt-molding virgin liquid crystal polyester resin. In this specification, virgin liquid crystal polyester resin refers to unused resin, that is, non-recycled resin that has not undergone recycling.

[0044] In the recovery process, high-purity liquid crystal polyester products such as liquid crystal polyester fibers may be selected and recovered, or the liquid crystal polyester products may be subjected to the above-mentioned washing and separation processes to increase their purity and then recovered. The recovered low molecular weight liquid crystal polyester product may preferably have a liquid crystal polyester content of 98% by weight or more, more preferably 99% by weight or more.

[0045] The low molecular weight liquid crystal polyester product used in the molding process may be a liquid crystal polyester chip-like material with a bulk density of 0.15 to 1.20 g / mL and an average maximum length of 3 to 30 mm, from the viewpoint of enabling efficient melt-kneading in the extruder when an extruder is used for melt molding and obtaining a high-quality recycled liquid crystal polyester molded article.

[0046] A method for producing liquid crystal polyester chips may include an integration step of forming an integrated body by integralizing a recovered low molecular weight liquid crystal polyester product (which may, if necessary, be subjected to the pulverization or cutting steps described above), and a cutting step of cutting the integrated body to produce chips having a bulk density of 0.15 to 1.20 g / mL and an average maximum length of 3 to 30 mm.

[0047] In the integration process, the recovered low molecular weight liquid crystal polyester products are integrated by thermoforming and / or adhesive molding to obtain an integrated body. The integrated body may be a one-dimensional molded body such as a string, or a two-dimensional molded body such as a sheet.

[0048] In thermoforming, recovered low molecular weight liquid crystal polyester products can be integrated by heat treatment. The heating temperature can be appropriately set according to the melting point of the low molecular weight liquid crystal polyester product used. If the melting point of the low molecular weight liquid crystal polyester product is Tm, the heating temperature may be, for example, Tm-5 to Tm+40°C, preferably Tm to Tm+30°C, and more preferably Tm+5 to Tm+25°C. Before thermoforming, if necessary, a melting point determination step may be performed to determine the melting point of the low molecular weight liquid crystal polyester product to be heated in advance.

[0049] In thermoforming, a low molecular weight liquid crystal polyester product with reduced moisture content may be used in advance. For example, the moisture content of the low molecular weight liquid crystal polyester product may be 500 ppm or less, preferably 400 ppm or less, more preferably 300 ppm or less, even more preferably 200 ppm or less, even more preferably 100 ppm or less, and particularly preferably 50 ppm or less.

[0050] Furthermore, during thermoforming, a heat press treatment may be performed as needed. By performing the heat press treatment, the liquid crystal polyester resin may be fused and integrated. The heat press treatment may be a single-wafer method or a continuous method such as roll-to-roll. Specifically, examples include a method of pressing the material into a sheet using a hot plate, a method of pressing the material into a sheet using a hot roll, and a method of pressing the material into a sheet by sandwiching it between wire mesh or a metal belt.

[0051] The press pressure for the hot pressing process may be, for example, 0.5 to 20 MPa as a surface pressure, preferably 1 to 15 MPa, and more preferably 1.5 to 10 MPa. In the case of roll-to-roll pressing, the value obtained by converting the linear pressure to surface pressure may be used. The pressing time may be, for example, 1 to 10 minutes, preferably 1.5 to 8 minutes, and more preferably 2 to 7 minutes. The hot pressing process may be performed only during thermoforming, but may also be performed after the degassing process if necessary.

[0052] If necessary, a degassing press treatment may be performed as a degassing treatment, and the degassing press treatment may be performed with the surface pressure described above for, for example, 3 to 20 times, preferably 5 to 15 times. The pressing time per time may be, for example, 1 to 30 seconds, preferably 2 to 25 seconds, more preferably 3 to 20 seconds.

[0053] During thermoforming, it is preferable to bring the release-treated equipment into contact with the low molecular weight liquid crystal polyester product to prevent the molten liquid crystal polyester resin from adhering to the equipment used. For example, it is preferable that the metal plates and hot rolls used in the heat press process be treated with a release agent such as a fluorine coating or a silicone coating. Alternatively, the press process may be performed via a release material such as a fluorine sheet, silicone sheet, or polyimide film.

[0054] Thermoforming and degassing are preferably carried out under an inert gas atmosphere or vacuum.

[0055] Furthermore, if the low molecular weight liquid crystal polyester product contains fibers, the resulting chip-like material may have at least part of a shape derived from the liquid crystal polyester fibers. For example, if liquid crystal polyester fibers are aligned in substantially one direction or arranged randomly and subjected to heat pressing, the integrated body after heat pressing and the chip-like material obtained from the integrated body may have part of a shape derived from the liquid crystal polyester fibers (e.g., the outer edge).

[0056] For example, the liquid crystal polyester fibers to be thermoformed may be thermoformed in a pre-aligned state. For example, aligned liquid crystal polyester fibers may be twisted together, and the twisted fiber bundle may be thermoformed into a rod shape in a hot air furnace. Alternatively, if the low molecular weight liquid crystal polyester product contains fibers, the fiber bundle, which is made by twisting aligned liquid crystal polyester fibers as needed, may be covered on the outside with a thermoplastic resin sheet (for example, a liquid crystal polyester sheet, the above-mentioned thermoplastic resin that can be mixed with liquid crystal polyester, etc.), and the whole may be integrated by heating the covering to melt the thermoplastic resin. The thermoplastic resin sheet may have the same melting point as the low molecular weight liquid crystal polyester product, but it is preferable that it has a lower melting point than the low molecular weight liquid crystal polyester product.

[0057] In one embodiment of the integration process, if the raw material molded body is in the shape of a long fiber or film, twisting may be applied to form a twisted cord, and then the twisted cord may be compressed to form a crimped twisted cord as an integrated body. Heating may also be applied before and / or after twisting (for example, during compression), and by softening with heat, the twisting and / or crimping can be made easier. For example, a raw material molded body in the shape of a continuous fiber may be twisted to form a continuous twisted yarn, then molded by heat pressing to form an integrated body, and then chip-like objects of a predetermined size may be formed by the cutting process described later. The formation of the twisted yarn, the formation of the integrated body, and the cutting process may be performed by the same apparatus or by separate apparatuses.

[0058] For example, in one embodiment of such an integration process, a twisted cord manufacturing apparatus may be used that comprises a supply unit which serves as the starting point for twisting a long raw material molded body, and a rotary compression unit which applies a twist to the raw material molded body sent from the supply unit by rotation and applies a concave indentation by point compression to form a crimped twisted cord with a concave indentation. The rotary compression unit may comprise a rotary unit and a compression unit equipped within the rotary unit. In the supply unit, the raw material molded body is clamped, thereby becoming the starting point for twisting the raw material molded body, and the rotation in the rotary unit applies a twist to the raw material molded body. In the compression unit, a crimped twisted cord can be formed by point compression by clamping the raw material molded body with a predetermined pressing force through a pair of compression rollers. In this case, a heating unit and an intermediate feeding unit may be provided between the supply unit and the rotary compression unit (in this case, the intermediate roller of the intermediate feeding unit becomes the starting point for twisting the raw material molded body). Furthermore, the cutting process described later can be performed by a chip-shaped material manufacturing apparatus that further comprises a cutting unit for cutting the crimped twisted cord sent from the rotary compression unit to a predetermined length.

[0059] In adhesive molding, recovered low molecular weight liquid crystal polyester products can be integrated using an adhesive such as a sizing agent. After adhesive molding, the above-mentioned thermoforming may be performed as needed.

[0060] The proportion of the adhesive used in adhesive molding should be within a range that allows control of the bulk density of the chip-shaped material. For example, the solid content of the adhesive may be 0.1 to 5% by weight of the total, and preferably 0.5 to 4% by weight.

[0061] The adhesive may be applied to the low molecular weight liquid crystal polyester product by immersion, coating, or spraying. In particular, if the low molecular weight liquid crystal polyester product contains fibers, the sizing agent may be applied to the aligned fibers by immersion, coating, or spraying to integrate them.

[0062] The adhesive is not particularly limited as long as it can integrate the low molecular weight liquid crystal polyester product, but examples of known or conventional adhesives include polyurethane adhesives, polysiloxane adhesives, polyamide adhesives, polyolefin adhesives, and epoxy adhesives.

[0063] The integrated body after integral molding may be subjected to a cutting process. The cutting process is not particularly limited as long as it does not impair the effects of the present invention, and can be carried out by, for example, scissors, a push cutter, a fan cutter, a slitter, etc. By cutting, chip-like objects formed to predetermined dimensions can be obtained.

[0064] The resulting liquid crystal polyester chips have specific bulk density and dimensions, and when an extruder is used for melt molding, they can be efficiently melt-kneaded in the extruder, allowing for the production of high-quality recycled liquid crystal polyester molded articles. Therefore, such liquid crystal polyester chips may be used in the molding process.

[0065] The bulk density of the liquid crystal polyester chips may be 0.15 to 1.20 g / mL, preferably 0.30 to 1.15 g / mL, more preferably 0.55 to 1.10 g / mL, even more preferably 0.65 to 1.08 g / mL, and even more preferably 0.85 to 1.05 g / mL. When the bulk density of the liquid crystal polyester chips is 0.15 g / mL or higher, the feedability when feeding the chips into the extruder and the ability to grip the extruder screw are excellent, and the melt-kneading properties in the extruder tend to be good. When the bulk density is 1.20 g / mL or lower, the inclusion of foreign matter in the chips is reduced, and the physical properties of the molded article obtained from the chips tend to improve. In this specification, the bulk density of liquid crystal polyester chips is calculated by pouring the liquid crystal polyester chips into a measuring container without using a funnel, and then measuring the weight of the chips in the measuring container using an electronic balance without compressing the chips by tapping or the like, and expressing it as the bulk density per unit area of ​​the measuring container.

[0066] The dimensions of the liquid crystal polyester chip-like material may be 3 to 30 mm in average maximum length, preferably 3.5 to 20 mm, and more preferably 5 to 15 mm. When the average maximum length is 3 mm or more, the chip-like material tends to have excellent feedability when fed into a melt extruder and excellent gripping into the extruder screw. When the average maximum length is 30 mm or less, the chip-like material also tends to have excellent feedability when fed into a melt extruder and excellent gripping into the extruder screw. In this specification, the maximum length of the liquid crystal polyester chip-like material can be measured by measuring the largest length from one end to the other in the projected area when the chip-like material is placed on a flat surface. Simple methods for measuring this include using electronic calipers, a stereomicroscope with a scale, or an automatic shape measuring machine.

[0067] In the molding process, recycled liquid crystal polyester molded articles can be produced by melt-molding the recovered low-molecular-weight liquid crystal polyester product. The type of recycled liquid crystal polyester molded article is not particularly limited as long as it is a molded article obtained by melt-molding liquid crystal polyester, and examples include pellets, fibers, films, and various injection-molded articles, which can be obtained by known or conventional manufacturing methods. The molding process is preferably a process of melt-extruding the above-mentioned liquid crystal polyester chip-like material. Virgin liquid crystal polyester resin may be mixed with the low-molecular-weight liquid crystal polyester product used in the molding process, and the form of the virgin liquid crystal polyester resin may include powder, pellets, or chips. In addition, various thermoplastic polymers and various additives may be used in the molding process along with the low-molecular-weight liquid crystal polyester product, depending on the desired recycled liquid crystal polyester molded article.

[0068] The process of melt-extruding liquid crystal polyester chips can be carried out by known or conventional methods depending on the target molded product. For example, when forming pellets, a pelletizing process is performed. In the pelletizing process, in order to suppress the thermal degradation of the liquid crystal polyester melted in the extruder, it is preferable to set the melt-kneading temperature to a temperature of Tm + 30°C or lower, where Tm is the melting point of the liquid crystal polyester chips. Here, the melt-kneading temperature refers to the temperature at which the resin is melt-kneaded by the screw of the extruder, and specifically refers to the set temperature of the extruder.

[0069] Furthermore, in order to perform degassing during melt-kneading, it is preferable to provide a vent in the extruder and remove the air from inside the extruder cylinder with a vacuum pump. For example, the extruder may be divided into a solid zone, a solid-molten mixture zone, and a molten zone, and degassing may be performed at a vent port provided in any of these zones at a pressure of, for example, 0 to 90 kPa (preferably 0 to 80 kPa, more preferably 0 to 70 kPa). Degassing may be performed at least in the molten zone, and preferably at all of the vent ports.

[0070] After melting and kneading, the material is discharged from the extruder and then cut by known or conventional means such as strand cutting or hot cutting to obtain pellets of a predetermined size.

[0071] Furthermore, the melt-kneading temperatures described above in the pelletizing process can also be used for fibers, films, and various injection-molded articles. In addition, during melt-kneading, degassing by venting as described above may be performed as needed.

[0072] In the process of melt-extruding liquid crystal polyester chips, chips with reduced moisture content may be used in advance. For example, the moisture content of the chips may be 500 ppm or less, preferably 400 ppm or less, more preferably 300 ppm or less, more preferably 200 ppm or less, more preferably 100 ppm or less, and more preferably 50 ppm or less.

[0073] The resulting recycled liquid crystal polyester molded article may contain virgin liquid crystal polyester resin, and the proportion of virgin liquid crystal polyester resin in the recycled liquid crystal polyester molded article may be 5 to 97% by weight, preferably 10 to 96% by weight, and more preferably 20 to 95% by weight.

[0074] The resulting recycled liquid crystal polyester molded article may contain thermoplastic polymers such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin. It 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.

[0075] 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 recovered low molecular weight liquid crystal polyester products (preferably in the form of liquid crystal polyester chips).

[0076] In material recycling, when obtaining recycled liquid crystal polyester fibers, it is preferable to use a low molecular weight liquid crystal polyester product in which the total amount of liquid crystal polyester at the end of each flake is 50 meq / kg or more, from the viewpoint of obtaining heat-treated yarn with improved melt-spinning properties and mechanical properties through subsequent heat treatment.

[0077] Melt spinning can be carried out by known methods. For example, a low molecular weight liquid crystal polyester product (preferably in the form of liquid crystal polyester chips) is melted in an extruder, then extruded from a nozzle at a predetermined spinning temperature, and wound up by a godet roller or the like to obtain a spun yarn.

[0078] 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).

[0079] 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.

[0080] 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.

[0081] 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.

[0082] Examples of recycled liquid crystal polyester fibers include non-composite fibers made using only low molecular weight liquid crystal polyester products as raw materials; mixed spun fibers obtained by mixing low molecular weight liquid crystal polyester products with virgin liquid crystal polyester resin, the above-mentioned thermoplastic polymers, and various additives; and composite fibers obtained by simultaneously spinning different components of low molecular weight liquid crystal polyester products and the above-mentioned thermoplastic polymers from separated spinnerets.

[0083] In this invention, even if recycled liquid crystal polyester fibers are obtained by material recycling of low molecular weight liquid crystal polyester products, the 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Recycled liquid crystal polyester fibers can be used in various applications as part of fiber structures, similar to liquid crystal polyester fibers as liquid crystal polyester products before recycling. Fiber structures containing recycled liquid crystal polyester fibers can be used as any one-dimensional structure, such as staple fibers, short-cut fibers, filament yarns, spun yarns, strings, ropes, and sling belts. They can also be used as two-dimensional structures, including various fabrics such as nonwovens, woven fabrics, and knitted fabrics made from recycled liquid crystal polyester fibers. Such one-dimensional and two-dimensional structures can be manufactured using recycled liquid crystal polyester fibers by known methods.

[0088] 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.

[0089] In addition to producing filaments by melt spinning as described above, in the melt molding of low molecular weight liquid crystal polyester products, spin-direct nonwoven fabrics such as the melt-blown method and the spunbond method can be produced by known or conventional methods.

[0090] 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.

[0091] (Chemical Recycling) In the recycling method of the present invention, high molecular weight liquid crystal polyester products with a total end-piece amount of liquid crystal polyester of 12.5 meq / kg or less are subject to chemical recycling. In this specification, chemical recycling is a recycling technology in which at least a portion of the liquid crystal polyester depolymer obtained by depolymerizing the liquid crystal polyester contained in the liquid crystal polyester product is melt-molded with or without a polymerization process.

[0092] Chemical recycling is not particularly limited as long as a recycled liquid crystal polyester molded article can be obtained via a liquid crystal polyester depolymer obtained by depolymerizing the liquid crystal polyester contained in a high molecular weight liquid crystal polyester product. For example, it may include at least a depolymerization step to produce a liquid crystal polyester depolymer by depolymerizing the liquid crystal polyester contained in a high molecular weight liquid crystal polyester product until the total amount of end pieces is 50 meq / kg or more by cleaving the ester bonds. Figure 3 is a flowchart of chemical recycling according to one embodiment. Since the liquid crystal polyester depolymer is depolymerized by cleaving the ester bonds, it can be used as a polymerization raw material for liquid crystal polyester, and can be repolymerized to synthesize recycled liquid crystal polyester resin, and this recycled liquid crystal polyester resin can be used in the manufacture of a recycled liquid crystal polyester molded article. Therefore, as shown in Figure 3, the liquid crystal polyester depolymer obtained in the depolymerization step can be used as a polymerization raw material for synthesizing recycled liquid crystal polyester resin by repolymerization and subjected to the polymerization step, or it can be subjected to a molding step in which it is melt-molded as is.

[0093] In the depolymerization step, the liquid crystal polyester contained in the high molecular weight liquid crystal polyester product is depolymerized by cleaving the ester bonds until the total amount of end pieces is 50 meq / kg or more, thereby obtaining a liquid crystal polyester depolymer. The depolymerization method is not particularly limited as long as it can depolymerize by cleaving the ester bonds of the liquid crystal polyester. Examples include hydrolysis using water as a solvent, alcoholosis using alcohol (e.g., lower aliphatic alcohols such as methanol and ethanol, aromatic alcohols such as benzyl alcohol, etc.) as a solvent, glycolysis using alkylene glycol (e.g., ethylene glycol, propylene glycol, etc.) as a solvent, acidolysis using carboxylic acid, transesterification using low molecular weight ester compounds, and amine decomposition using amine compounds. Among these depolymerization methods, the cleavage of ester bonds in the depolymerization step may be carried out by at least one depolymerization method selected from the group consisting of glycolysis, hydrolysis, and alcoholosis.

[0094] For example, in the alkylesis depolymerization method, the alcohol can be an aliphatic alcohol such as methanol, ethanol, propanol (e.g., 1-propanol), butanol (e.g., 1-butanol), pentanol (e.g., 1-pentanol), hexanol (e.g., 1-hexanol), 2-ethylhexanol, or an aromatic alcohol such as benzyl alcohol. These can be used individually or in combination of two or more. In the case of lower aliphatic alcohols with about 1 to 4 carbon atoms, since their boiling point is low, it is preferable to pressurize the reaction in order to impart thermal energy. Considering the high boiling point and reactivity, from the viewpoint of reacting at a higher temperature, the glycolesis depolymerization method using alkylene glycol as the solvent is more preferable. In the glycolesis depolymerization method, alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or their alkyl ether compounds (e.g., diethylene glycol monomethyl ether) can be used. These can be used individually or in combination of two or more. In depolymerization methods using alcoholosis and / or glycolysis, a solvent can be appropriately selected from the above-mentioned alcohols and alkylene glycols depending on the boiling point, reactivity, and solubility of the depolymer (e.g., monomer).

[0095] In the above depolymerization method, in order to promote the reaction, methods such as reacting under acidic or alkaline conditions, reacting in the presence of a catalyst, reacting by adding monomers that constitute the liquid crystal polyester, reacting at high temperature using a solvent in a subcritical or supercritical state, reacting by irradiating with microwaves, reacting using bacteria or enzymes, or a combination of these methods can be used.

[0096] In the depolymerization step, the reaction may be carried out under alkaline conditions using the alcoholesis or glycolysis method. Alkaline conditions can also be achieved by adding an alkali metal salt. Examples of alkali metal salts include hydroxides, carbonates, or bicarbonates of alkali metals such as sodium, potassium, or lithium, which may be used individually or in combination of two or more. Of these, sodium hydroxide, potassium hydroxide, and sodium carbonate are preferred. For example, in the depolymerization method using the alcoholesis or glycolysis method, the depolymerization step may involve heat treatment under alkaline conditions using alcohol or alkylene glycol as a solvent. In particular, in the microwave heat treatment described above, the reaction can be efficiently controlled by carrying out the reaction under alkaline conditions.

[0097] In the depolymerization step, the reaction temperature can be adjusted according to the boiling point of the solvent in the alcoholesis method or the glycolesis method. For example, the temperature of the heat treatment may be 120°C or higher, preferably 140°C or higher, and more preferably 150°C or higher. For example, when ethylene glycol is used as the solvent, it can be heated up to 197°C, and can be adjusted as appropriate considering the desired degree of depolymerization of the liquid crystal polyester. The heat treatment may be carried out at atmospheric pressure or under pressure. The time for the heat treatment can also be adjusted as appropriate considering other reaction conditions and the desired degree of depolymerization of the liquid crystal polyester. For example, it may be 1 minute to 5 hours, preferably 3 minutes to 1 hour, and more preferably 5 minutes to 30 minutes.

[0098] The liquid crystal polyester depolymer obtained by the depolymerization step is a mixture produced by the depolymerization reaction due to the cleavage of ester bonds, and the total end-piece weight should be 50 meq / kg or more. It 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 total end-piece weight of the liquid crystal polyester depolymer is expressed as a measured value including monomers. It is preferable that the liquid crystal polyester depolymer does not substantially contain decomposition products produced by reactions other than the depolymerization reaction due to the cleavage of ester bonds, but decomposition products produced by side reactions in the depolymerization reaction due to the cleavage of ester bonds may be included as impurities (e.g., in an amount of about 0.1% by weight or less). Furthermore, the liquid crystal polyester depolymer may contain impurities that are not involved in the depolymerization of liquid crystal polyester (e.g., components other than liquid crystal polyester that were contained in the liquid crystal polyester product), in addition to components that participated in the depolymerization of liquid crystal polyester, such as monomers, oligomers, and polymers.

[0099] 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 of the liquid crystal polyester before depolymerization. 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 of liquid crystal polyester after depolymerization - total amount of end crystals of liquid crystal polyester before depolymerization) / total amount of end crystals of liquid crystal polyester before depolymerization × 100.

[0100] From the viewpoint of producing recycled liquid crystal polyester resin, it is preferable that the liquid crystal polyester depolymer contains monomers and oligomers. The components contained in the liquid crystal polyester depolymer vary depending on the composition of the liquid crystal polyester contained in the high molecular weight liquid crystal polyester product subjected to the depolymerization process, but it may contain, for example, at least one monomer selected from the group consisting of 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and their derivatives. 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. If the liquid crystal polyester depolymer contains monomers, it is preferable that the content ratio of aromatic hydroxycarboxylic acids (for example, 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, etc.) is high. Even if different types of aromatic hydroxycarboxylic acids exist, their reactivity (resistance to decomposition) during depolymerization and solubility during monomer recovery are similar, making liquid crystal polyester depolymers easy to handle even if they contain multiple types of aromatic hydroxycarboxylic acids. From this viewpoint, the content ratio of aromatic hydroxycarboxylic acids in liquid crystal polyester depolymers may be, for example, 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 100% by weight. The chemical structure of the liquid crystal polyester depolymer after cleavage of the ester bond may be not only a hydroxyl group or a carboxyl group, but also derivatives thereof, depending on the depolymerization method. If the chemical structure after cleavage of the ester bond is a derivative of a hydroxyl group or a carboxyl group, it may be further reacted to convert it to a hydroxyl group or a carboxyl group as needed.

[0101] In one aspect of the present invention, chemical recycling includes a depolymerization step for producing the above-mentioned liquid crystal polyester depolymer; a polymerization step for synthesizing a recycled liquid crystal polyester resin by polymerizing at least a portion of the liquid crystal polyester depolymer as at least a portion of the polymerization raw materials; and a molding step for producing a recycled liquid crystal polyester molded article by melt molding the obtained recycled liquid crystal polyester resin. In this specification, the recycled liquid crystal polyester resin includes liquid crystal polyester synthesized by chemical recycling via a liquid crystal polyester depolymer obtained by depolymerizing a high molecular weight liquid crystal polyester product once, and may also contain other components. For example, other components may include components other than liquid crystal polyester that were contained in the high molecular weight liquid crystal polyester product without purification in the intermediate steps. Here, polymerization using the liquid crystal polyester depolymer includes not only the polymerization reaction of monomers, but also the polymerization reaction that occurs from oligomers and polymers contained in the liquid crystal polyester depolymer.

[0102] In the polymerization process, the entire 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.

[0103] Alternatively, the process may include a step of purifying 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, and impurities not involved in the depolymerization of the liquid crystal polyester, 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.

[0104] The purification process may include a solvent removal step to remove the solvent used in the depolymerization process. If the liquid crystal polyester depolymer contains monomers, removing the solvent can improve the recovery rate of the monomers. Examples of solvents used in the depolymerization process include alcohols when depolymerization is performed by the alcoholis method, and alkylene glycols when depolymerization is performed by the glycolisis method. In the solvent removal step, depending on the type of solvent, the solvent can be removed by means such as letting the liquid crystal polyester depolymer stand or heating it to evaporate it.

[0105] The purification process may include a precipitation step in which the depolymer is precipitated by neutralization. When the liquid crystal polyester depolymer is dissolved in a solution and the solution is acidic or alkaline, it can be purified by adding a base or acid, respectively, to neutralize it and precipitate the liquid crystal polyester depolymer. In the precipitation step, it is preferable that a poor solvent for the liquid crystal polyester depolymer is present, and the process may include adding a poor solvent such as water before the precipitation step. The purification process may also include filtering the depolymer precipitated after the precipitation step.

[0106] When the purification process includes a solvent removal step and a precipitation step, it is preferable to perform the precipitation step after the solvent removal step in order to further improve the monomer recovery rate.

[0107] 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.

[0108] 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).

[0109] In the molding process, recycled liquid crystal polyester resin can be used and melt-molded using known or conventional methods, similar to the molding process in material recycling described above, depending on the desired molded product. 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.

[0110] In another aspect of the present invention, chemical recycling includes a depolymerization step for producing the above-described liquid crystal polyester depolymer and a molding step for producing a recycled liquid crystal polyester molded article by melt-molding at least a portion of the liquid crystal polyester depolymer. 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 the liquid crystal polyester 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 above-described thermoplastic polymer, and various additives may be added when using the liquid crystal polyester depolymer in melt molding.

[0111] Recycled liquid crystal polyester molded articles, whether chemically recycled or materially recycled, are not particularly limited in type as long as they are molded articles obtained by melt molding of liquid crystal polyester, and include pellets, fibers, films, various injection-molded articles, etc., which can be obtained by known or conventional manufacturing methods. In the molding process of chemical recycling, the contents described in the molding process of material recycling above can be applied to recycled liquid crystal polyester resin or liquid crystal polyester depolymer instead of low molecular weight liquid crystal polyester products (preferably liquid crystal polyester chips). In particular, recycled liquid crystal polyester fibers can be suitably produced in chemical recycling as well as in material recycling.

[0112] Thus, the above recycling method can recycle liquid crystal polyester products while increasing the recycling rate and reducing energy consumption associated with recycling, and can also be used as a recycling system including the equipment used in each of the above processes.

[0113] [Method for Selecting Recycling Method] In one aspect of the present invention, a method for selecting a recycling method for a liquid crystal polyester product is also included based on the total amount of liquid crystal polyester fragments contained in the product. The method for selecting a recycling method includes a step of determining whether to apply the liquid crystal polyester product to material recycling if the total amount of liquid crystal polyester fragments contained in the product is greater than 12.5 meq / kg, and whether to apply the liquid crystal polyester product to chemical recycling if the total amount of liquid crystal polyester fragments is 12.5 meq / kg or less. In the present invention, it has been found that the total amount of liquid crystal polyester fragments contained in a liquid crystal polyester product can be used as a judgment indicator to select whether to apply material recycling or chemical recycling.

[0114] In selecting a recycling method, it may be possible to indirectly determine the total amount of liquid crystal polyester at the end of each flake by considering other physical properties of the liquid crystal polyester product, but the method may also include a step of measuring the total amount of liquid crystal polyester at the end of each flake contained in the liquid crystal polyester product.

[0115] 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.

[0116] (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.

[0117] (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.

[0118] (Strength) 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.

[0119] [Reference Example 1] Virgin chips of liquid crystal polyester (melting point: 278°C), composed of 73 / 27 (mol%) constituent units derived from 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, were hot-air dried at 120°C for more than 4 hours. Then, they were fed into a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd.) for melt-kneading, and the molten mixture was supplied to the spinning head. The spinning head was equipped with a nozzle with a hole diameter of 0.10 mmφ and 50 holes. The spinning head temperature was set to 320°C, and the molten mixture was discharged at a discharge rate of 28 g / min. The mixture was wound onto bobbins at a winding speed of 1000 m / min, yielding 10 5 kg rolls of liquid crystal polyester fiber spun yarn (untreated yarn). 4 kg of the 5 kg spun yarn was unwound from each bobbin and rewound onto aluminum bobbins for use in the heat treatment described in Reference Example 2 below. One kilogram of leftover yarn from each of the ten 5 kg bobbins was used as the liquid crystal polyester fiber for Reference Example 1, which is a liquid crystal polyester product to be recycled. The obtained liquid crystal polyester fiber for Reference Example 1 had a total end weight of 71.4 meq / kg, a melting point of 290°C, and a liquid crystal polyester content (purity) of 100% by weight.

[0120] [Reference Example 2] Four kilograms of spun yarn, wound onto aluminum bobbins obtained in Reference Example 1, were heat-treated in a sealed oven under a nitrogen atmosphere at 270°C for 16 hours to obtain heat-treated liquid crystal polyester fibers. The heat-treated yarns from the ten 4kg bobbins obtained were used as the liquid crystal polyester fibers for Reference Example 2, which are liquid crystal polyester products to be recycled. The obtained liquid crystal polyester fibers for Reference Example 2 had a total end weight of 6.0 meq / kg, a melting point of 322°C, and a liquid crystal polyester content (purity) of 100% by weight.

[0121] [Example 1] Of all the yarns described in Reference Examples 1 and 2 above, the liquid crystal polyester fiber of Reference Example 1 had a total end weight of more than 12.5 meq / kg, so it was applied to material recycling as follows.

[0122] First, the liquid crystal polyester fibers (spun yarn) from Reference Example 1 were cut on a bobbin using a utility knife, and liquid crystal polyester fibers approximately 10 cm in length were recovered to form a molded raw material. Next, a polyimide film was placed on a metal plate as a heat-resistant release material, and a metal frame (12 cm long, 12 cm wide, 1.5 mm thick) was placed on top of the polyimide film. The liquid crystal polyester fibers were aligned as the molded raw material and placed inside the metal frame, with the polyimide film placed on top. The recovered liquid crystal polyester fibers were then heat-pressed 10 times at 300°C and 2.2 MPa for 10 seconds each using metal hot plates positioned above and below to degas them, and then heat-pressed for 3 minutes. Following the heat pressing, the entire metal frame was transferred to a cooling press machine for cooling to obtain a sheet-like material made from the recovered liquid crystal polyester fibers. The obtained sheet-like material was cut using a cutter to obtain a rectangular prism-shaped chip-like material with a thickness of approximately 1.5 mm, a long side of approximately 10 mm, and a short side of approximately 3 mm. The average maximum length of these chip-like materials was 10.4 mm, and the bulk density was 0.80 g / mL. The obtained chip-like materials had a fibrous shape on their outer edges.

[0123] The obtained chip-like material was hot-air dried at 120°C for more than 4 hours, and then fed into a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd.). The extruder was able to melt and knead the fed chip-like material at 300°C without the screw running idle, and the molten mixture was supplied to the spinning head. The spinning head was equipped with a nozzle with a hole diameter of 0.10 mmφ and 50 holes, and the spinning head temperature was set to 330°C. The molten mixture 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 spun yarn of recycled liquid crystal polyester filament. Furthermore, 500 m of the obtained spun yarn was wound at a winding density of 0.6 g / cm². ３ The recycled liquid crystal polyester filament was wound onto an aluminum bobbin and heat-treated in a sealed oven under a nitrogen atmosphere at 300°C for 16 hours to obtain heat-treated yarn. The strength of the obtained recycled liquid crystal polyester filament was 23.0 cN / dtex.

[0124] Of all the yarns described in Reference Examples 1 and 2 above, the liquid crystal polyester fiber in Reference Example 2 was applied to chemical recycling as follows, since the total end weight of the fibers was 12.5 meq / kg or less.

[0125] To a solution in which sodium hydroxide was completely dissolved in ethylene glycol, liquid crystal polyester fibers were added in a weight ratio of ethylene glycol:sodium hydroxide:liquid crystal polyester fibers = 9.50:0.75:1.00, and the mixture was heated in an oil bath at 160°C for 12 minutes until the liquid crystal polyester fibers were completely dissolved. The liquid containing ethylene glycol was removed by distillation, and distilled water was added in an amount 10 times the weight of the liquid crystal polyester fibers to completely dissolve them and obtain a yellow liquid. While cooling the liquid to 5°C, 3.5 g of 6 mol / L hydrochloric acid was added dropwise. When the reaction solution became acidic, a white solid precipitated. The solid was collected by filtration and vacuum-dried overnight at 80°C. This yielded a pale yellow powder solid (4-hydroxybenzoic acid (HBA):6-hydroxy-2-naphthoic acid (HNA) = 68.4:31.6 (mol ratio), with other components at 0.0 wt%) as a liquid crystal polyester depolymer.

[0126] Next, new HBA is added to this depolymerization mixture so that the mol ratio of 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 ２ O) 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.

[0127] 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. 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 280°C for 16 hours to obtain heat-treated recycled liquid crystal polyester fiber. The obtained heat-treated recycled liquid crystal polyester fiber had a strength of 24.0 cN / dtex.

[0128] In Example 1, all liquid crystal polyester fibers could be recycled as liquid crystal polyester products (high recycling rate), and since both material recycling and chemical recycling were used in combination, with material recycling applied to liquid crystal polyester fibers that were suitable for material recycling, energy consumption due to chemical recycling was minimized, resulting in a small overall environmental impact.

[0129] [Reference Example 3] Virgin chips of liquid crystal polyester (melting point: 309°C), composed of 60 / 20 / 15 / 5 (mol%) constituent units derived from 6-hydroxy-2-naphthoic acid, 2,6-naphthalenedicarboxylic acid, hydroquinone, and 4,4'-dihydroxybiphenyl, were hot-air dried at 120°C for more than 4 hours. Then, they were fed into a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd.) for melt-kneading, and the molten mixture was supplied to the spinning head. The spinning head was equipped with a nozzle with a hole diameter of 0.10 mmφ and 50 holes, and the spinning head temperature was set to 340°C. The molten mixture was discharged at a discharge rate of 28 g / min and wound onto a bobbin at a winding speed of 1000 m / min, yielding 10 spun yarns (untreated yarns) of liquid crystal polyester fiber in 5 kg rolls. Four kilograms of spun yarn were unwound from each 5 kg bobbin and rewound onto aluminum bobbins for use in the heat treatment described in Reference Example 4 below. One kilogram of the remaining yarn from each of the 10 bobbins (5 kg each) was used as the liquid crystal polyester fiber for Reference Example 3, which is a liquid crystal polyester product to be recycled. The obtained liquid crystal polyester fiber for Reference Example 3 had a total end weight of 99.7 meq / kg, a melting point of 310°C, and a liquid crystal polyester content (purity) of 100% by weight.

[0130] [Reference Example 4] Four kilograms of spun yarn, wound onto aluminum bobbins obtained in Reference Example 3, were heat-treated in a sealed oven under a nitrogen atmosphere at 290°C for 24 hours to obtain heat-treated liquid crystal polyester fibers. The heat-treated yarns from the ten 4kg bobbins obtained were used as the liquid crystal polyester fibers for Reference Example 4, which are liquid crystal polyester products to be recycled. The obtained liquid crystal polyester fibers for Reference Example 4 had a total end weight of 12.4 meq / kg, a melting point of 349°C, and a liquid crystal polyester content (purity) of 100% by weight.

[0131] [Example 2] Of all the yarns described in Reference Examples 3 and 4 above, the liquid crystal polyester fiber of Reference Example 3 had a total end weight of more than 12.5 meq / kg, so it was applied to material recycling as follows.

[0132] First, the liquid crystal polyester fibers (spun yarn) from Reference Example 3 were cut on a bobbin using a utility knife, and liquid crystal polyester fibers approximately 10 cm in length were recovered to form a molded raw material. Next, a polyimide film was placed on a metal plate as a heat-resistant release material, and a metal frame (12 cm long, 12 cm wide, 1.5 mm thick) was placed on top of the polyimide film. The liquid crystal polyester fibers were aligned as the molded raw material and placed inside the metal frame, with the polyimide film placed on top. The recovered liquid crystal polyester fibers were then heat-pressed 10 times at 320°C and 2.2 MPa for 10 seconds each using metal hot plates positioned above and below to degas them, and then heat-pressed for 3 minutes. Following the heat pressing, the entire metal frame was transferred to a cooling press machine for cooling to obtain a sheet-like material made from the recovered liquid crystal polyester fibers. The obtained sheet-like material was cut using a cutter to obtain a rectangular prism-shaped chip-like material with a thickness of approximately 1.5 mm, a long side of approximately 10 mm, and a short side of approximately 3 mm. The average maximum length of these chip-like materials was 10.4 mm, and the bulk density was 0.80 g / mL. The obtained chip-like materials had a fibrous shape on their outer edges.

[0133] The obtained chip-like material was hot-air dried at 120°C for more than 4 hours, and then fed into a Φ15 mm twin-screw extruder (manufactured by Technovel Co., Ltd.). The extruder was able to melt and knead the fed-in chip-like material at 340°C without the screw running idle, and the molten mixture was supplied to the spinning head. The spinning head was equipped with a nozzle with a hole diameter of 0.10 mmφ and 50 holes, and the spinning head temperature was set to 340°C. The molten mixture 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 spun yarn of recycled liquid crystal polyester filament. Furthermore, 500 m of the obtained spun yarn was wound at a winding density of 0.6 g / cm². ３ The recycled liquid crystal polyester filament was wound onto an aluminum bobbin and heat-treated in a sealed oven under a nitrogen atmosphere at 290°C for 24 hours to obtain heat-treated yarn. The strength of the obtained recycled liquid crystal polyester filament was 28.0 cN / dtex.

[0134] Of all the yarns described in Reference Examples 3 and 4 above, the liquid crystal polyester fiber in Reference Example 4 was applied to chemical recycling as follows, since the total end weight of the fibers was 12.5 meq / kg or less.

[0135] To a solution in which sodium hydroxide was completely dissolved in ethylene glycol, liquid crystal polyester fibers were added in a weight ratio of ethylene glycol:sodium hydroxide:liquid crystal polyester fibers = 9.50:0.75:1.00, and the mixture was heated in an oil bath at 160°C for 240°C until the liquid crystal polyester fibers were completely dissolved. The liquid containing ethylene glycol was removed by distillation, and distilled water was added in an amount 10 times the weight of the liquid crystal polyester fibers to completely dissolve them and obtain a yellow liquid. While cooling the liquid to 5°C, 3.5 g of 6 mol / L hydrochloric acid was added dropwise. When the reaction solution became acidic, a white solid precipitated. The solid was collected by filtration and vacuum-dried overnight at 80°C. This yielded a pale yellow powder solid (6-hydroxy-2-naphthoic acid (HNA): 2,6-naphthalenedicarboxylic acid (NDCA): hydroquinone (HQ): 4,4'-dihydroxybiphenyl (BP) = 68.6:22.1:4.1:5.2 (mol ratio), with other components at 0.12 wt%) as a liquid crystal polyester depolymer.

[0136] Next, new reagents are added to this depolymerization mixture in a mol ratio of HNA:NDCA:HQ:BP = 60:20:16.5:5, and the mixture is then placed in a reaction vessel equipped with a stirring blade, distillation tube, and reaction solution discharge tube, and the HNA, NDCA, HQ, BP, and Ac are added. ２O and KOAc were added in a mol ratio of 60 / 20 / 16.5 / 5 / 110 / 0.005. Next, the reaction vessel was purged with nitrogen, and while stirring the reaction mixture, the temperature was raised from room temperature to 165°C at a rate of 2°C / min, and reflux was carried out at 165°C for 2 hours. Next, while distilling off the evaporated liquid, the temperature was raised from 165°C to 350°C at a rate of 2°C / min, and stirring was carried out at 350°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.

[0137] 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 340°C, and the molten resin was supplied to the spinning head while being weighed by 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 spun yarn (280 dtex / 50 f) of recycled liquid crystal polyester fiber. 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 calculated adhesion ratio of sodium dodecyl phosphate to the spun yarn was 0.1 wt%. The obtained spun yarn of recycled liquid crystal polyester fiber had a melting point of 308°C. 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 290°C for 24 hours to obtain heat-treated recycled liquid crystal polyester fiber. The obtained heat-treated recycled liquid crystal polyester fiber had a strength of 27.9 cN / dtex.

[0138] In Example 2, all liquid crystal polyester fibers could be recycled as liquid crystal polyester products (high recycling rate), and since material recycling and chemical recycling were used in combination, with material recycling applied to liquid crystal polyester fibers that were suitable for material recycling, energy consumption due to chemical recycling was minimized, resulting in a small overall environmental impact.

[0139] [Comparative Example 1] All the yarns described in Reference Examples 1 and 2 above were subjected to chemical recycling. In the same manner as the chemical recycling in Example 1, all of the liquid crystal polyester fibers in Reference Examples 1 and 2 were depolymerized, and a new monomer was added to the resulting depolymer to polymerize and obtain recycled liquid crystal polyester resin. Then, the recycled liquid crystal polyester resin was melt-spun and heat-treated to obtain heat-treated yarn of recycled liquid crystal polyester fibers. In Comparative Example 1, all liquid crystal polyester fibers as liquid crystal polyester products could be recycled, but because everything was chemically recycled, high energy was consumed and the overall environmental impact was large.

[0140] [Comparative Example 2] All the yarns described in Reference Examples 1 and 2 above were applied to material recycling. In the same manner as in the material recycling in Example 1, all of the liquid crystal polyester fibers in Reference Examples 1 and 2 were used as raw material molded bodies, and after obtaining chip-like materials via sheet-like materials, the obtained chip-like materials were fed into an extruder and subjected to melt spinning. However, stable melt extrusion was not possible, and it was not possible to obtain spun yarn of recycled liquid crystal polyester fibers. In Comparative Example 2, an attempt was made to recycle all liquid crystal polyester fibers as liquid crystal polyester products, but recycling was not possible.

[0141] [Comparative Example 3] All the yarns described in Reference Examples 3 and 4 above were subjected to chemical recycling. In the same manner as the chemical recycling in Example 2, all of the liquid crystal polyester fibers in Reference Examples 3 and 4 were depolymerized, and a new monomer was added to the resulting depolymer to polymerize and obtain recycled liquid crystal polyester resin. Then, the recycled liquid crystal polyester resin was melt-spun and heat-treated to obtain heat-treated yarn of recycled liquid crystal polyester fibers. In Comparative Example 3, all liquid crystal polyester fibers as liquid crystal polyester products could be recycled, but because everything was chemically recycled, high energy was consumed and the overall environmental impact was large.

[0142] [Comparative Example 4] All the yarns described in Reference Examples 3 and 4 above were applied to material recycling. In the same manner as in the material recycling in Example 2, all of the liquid crystal polyester fibers in Reference Examples 3 and 4 were used as raw material molded bodies, and after obtaining chip-like materials via sheet-like materials, the obtained chip-like materials were fed into an extruder and subjected to melt spinning. However, stable melt extrusion was not possible, and it was not possible to obtain spun yarn of recycled liquid crystal polyester fibers. In Comparative Example 4, an attempt was made to recycle all liquid crystal polyester fibers as liquid crystal polyester products, but recycling was not possible.

[0143] The recycling method of the present invention can recycle all liquid crystal polyester products (especially waste and defective products), and can increase the recycling rate while reducing energy consumption. Therefore, it can promote recycling and contribute to the creation of a sustainable circular society.

[0144] 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 selectively recycling liquid crystal polyester products, wherein if the liquid crystal polyester product is a low-molecular-weight liquid crystal polyester product with a total end-to-end amount of liquid crystal polyester contained in it exceeding 12.5 meq / kg, the low-molecular-weight liquid crystal polyester product is materially recycled; and if the liquid crystal polyester product is a high-molecular-weight liquid crystal polyester product with a total end-to-end amount of liquid crystal polyester contained in it of 12.5 meq / kg or less, the high-molecular-weight liquid crystal polyester product is chemically recycled.

2. A recycling method according to claim 1, wherein the chemical recycling comprises: a depolymerization step of producing a liquid crystal polyester depolymer by depolymerizing liquid crystal polyester contained in a high molecular weight liquid crystal polyester product until the total amount of end pieces is 50 meq / kg or more by cleaving ester bonds; a polymerization step of synthesizing a recycled liquid crystal polyester resin by polymerizing using at least a portion of the liquid crystal polyester depolymer as at least a portion of the polymerization raw material; and a molding step of producing a recycled liquid crystal polyester molded body by melt molding the obtained recycled liquid crystal polyester resin.

3. A recycling method according to claim 1, wherein the chemical recycling comprises: a depolymerization step of producing a liquid crystal polyester depolymer by depolymerizing liquid crystal polyester contained in a high molecular weight liquid crystal polyester product until the total amount of end pieces is 50 meq / kg or more by cleaving ester bonds; and a molding step of producing a recycled liquid crystal polyester molded body by melt molding at least a portion of the liquid crystal polyester depolymer.

4. A recycling method according to claim 2 or 3, wherein the cleavage of the ester bond in the depolymerization step is carried out by at least one depolymerization method selected from the group consisting of glycolysis, hydrolysis, and alkalisis.

5. A recycling method according to any one of claims 1 to 3, wherein the material recycling includes a recovery step of recovering a low molecular weight liquid crystal polyester product such that the liquid crystal polyester content is 95% by weight or more, and a molding step of melt-molding the recovered low molecular weight liquid crystal polyester product to produce a recycled liquid crystal polyester molded body.

6. A recycling method according to claim 5, wherein, in the material recycling, the low molecular weight liquid crystal polyester product subjected to the molding step is a liquid crystal polyester chip having a bulk density of 0.15 to 1.20 g / mL and an average maximum length of 3 to 30 mm.

7. A recycling method according to any one of claims 1 to 3, wherein the liquid crystal polyester product contains 70% by weight or more of liquid crystal polyester fibers relative to its weight.

8. A recycling method according to any one of claims 1 to 3, wherein the liquid crystal polyester product is a sling belt.

9. A recycling method according to any one of claims 1 to 3, wherein the liquid crystal polyester product comprises a liquid crystal polyester having constituent units derived from 4-hydroxybenzoic acid and / or constituent units derived from 6-hydroxy-2-naphthoic acid, wherein the total content thereof is 40 mol% or more of the total amount of all constituent units.

10. A method for selecting a recycling method for a liquid crystal polyester product based on the total amount of liquid crystal polyester fragments contained in the liquid crystal polyester product, comprising the step of determining whether to apply the liquid crystal polyester product to material recycling if the total amount of fragments exceeds 12.5 meq / kg, and whether to apply the liquid crystal polyester product to chemical recycling if the total amount of fragments is 12.5 meq / kg or less.

Images