Cleaning method and cleaning solvent for polyester polymerization equipment

Abstract

An object of the present invention is to provide a cleaning method and a cleaning solvent for a polyester polymerization apparatus that can efficiently clean the polymerization apparatus, enable reuse of the cleaning solvent, and suppress odor when cleaning the polyester polymerization apparatus. [Solution] The present invention relates to a method for cleaning a polymerization apparatus used to produce polyesters, characterized by cleaning the polymerization apparatus at a temperature of 150 to 400°C using a cleaning solvent containing a mono-substituted ethylene glycol having an aromatic group.

Description

[Technical Field]

[0001] The present invention relates to a cleaning method and a cleaning solvent for a polyester polymerization apparatus. [Background technology]

[0002] Crystalline polyesters such as polyethylene terephthalate and polybutylene terephthalate and liquid crystalline polyesters have been widely used in various applications due to their excellent physical and chemical properties. Liquid crystalline polyesters, in particular, have excellent mechanical properties such as heat resistance and rigidity, chemical resistance, and dimensional accuracy, and are therefore increasingly used in a variety of applications, including not only molded products but also fibers and films.

[0003] For example, known polycondensation methods for producing liquid crystal polyesters include (1) a process in which a mixture of monomers is reacted with an acylating agent such as acetic anhydride to acylate hydroxyl groups and amino groups contained in the monomers, and (2) a melt polymerization process in which the mixture of monomers acylated in process (1) is heated in a molten state to perform polycondensation while distilling off lower fatty acids such as acetic acid (Patent Document 1), and a polymerization process in which the melt polymerization process and solid-state polymerization process are combined (Patent Document 2).

[0004] In the process of producing such polyesters, when the polyesters are extracted from the polymerization apparatus after production, it is not possible to extract all of them, and some of them remain on the inner walls of the polymerization apparatus, etc. Therefore, a cleaning process is required to wash and remove these residues.

[0005] Among polyesters, many studies have been conducted on methods for cleaning melt polymerization equipment in the production process of liquid crystal polyester (Patent Documents 3 and 4). However, when aliphatic glycols such as tetraethylene glycol (hereinafter referred to as "TEG") are used as cleaning solvents, the cleaning effect is insufficient, and many impurities derived from the solvent are generated during cleaning, making it difficult to reuse the solvent. In addition, cleaning with TEG produces a strong odor, which is a problem in terms of workability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 3-59067 [Patent Document 2] Japanese Patent Application Publication No. 3-281656 [Patent Document 3] Japanese Patent Application Publication No. 5-295392 [Patent Document 4] Japanese Patent Application Publication No. 2023-172359 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a cleaning method and a cleaning solvent for a polyester polymerization apparatus that can efficiently clean a polymerization apparatus, enable reuse of the cleaning solvent, and suppress odor when cleaning a polyester polymerization apparatus. Another object of the present invention is to provide a method for producing polyesters that includes a step using the above cleaning method. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into cleaning methods and cleaning solvents for polyester polymerization apparatuses and have found that by using mono-substituted ethylene glycols having an aromatic group as a cleaning solvent, polyesters in a polymerization apparatus can be quickly dissolved, the amount of impurities generated by thermal decomposition is small, so that the cleaning solvent can be reused, and odors can be suppressed, thereby completing the present invention.

[0009] That is, the present invention includes the following preferred embodiments. [1] A method for cleaning a polymerization apparatus used to produce polyesters, characterized by cleaning the polymerization apparatus at a temperature of 150 to 400°C using a cleaning solvent containing a mono-substituted ethylene glycol having an aromatic group. [2] The monosubstituted ethylene glycols having an aromatic group are represented by the formula (A) and / or the formula (B) [ka] [ka] [In the formula, R1 and R2 each independently represent an alkyl group having 1 to 30 carbon atoms or a hydrogen atom, and m and n each independently represent an integer of 1 to 30.] The method according to [1], wherein the compound is represented by the formula: [3] The method according to [1] or [2], wherein the mono-substituted ethylene glycol having an aromatic group is phenyl diglycol. [4] The method according to any one of [1] to [3], wherein the polyester is a liquid crystal polyester. [5] The liquid crystal polyester is represented by the formula (I) and / or the formula (II) [ka] The method according to [4], wherein the liquid crystal polyester contains a repeating unit represented by the formula: [6] The liquid crystal polyester is represented by the formula (I) and the formula (II) [ka] The method according to [4] or [5], wherein the liquid crystal polyester contains a repeating unit represented by the formula: [7] The liquid crystal polyester is represented by the formula (I) to the formula (IV): [ka] [In the formula, Ar1 and Ar2 each represent a divalent aromatic group] The method according to [4] or [5], wherein the liquid crystal polyester contains a repeating unit represented by the formula: [8] In the repeating units represented by formulas (III) and (IV), Ar1 and Ar2 are each independently represented by formulas (1) to (4): [ka] The method according to [7], wherein each of the repeating units is one or more types selected from aromatic groups represented by the following formula: [9] A method for producing polyesters, comprising the steps of cleaning a polyester polymerization apparatus by the method according to any one of [1] to [8], and polymerizing polyesters in the polyester polymerization apparatus after cleaning.

[10] A cleaning solvent for cleaning polyester polymerization equipment, comprising a monosubstituted ethylene glycol having an aromatic group.

[11] The monosubstituted ethylene glycols having an aromatic group are represented by the formula (A) and / or the formula (B): [ka] [ka] [In the formula, R1 and R2 each independently represent an alkyl group having 1 to 30 carbon atoms or a hydrogen atom, and m and n each independently represent an integer of 1 to 30.] The cleaning solvent according to

[10] , which is a compound represented by the formula:

[12] The cleaning solvent according to

[10] or

[11] , wherein the mono-substituted ethylene glycol having an aromatic group is phenyl diglycol.

[13] The cleaning solvent according to any one of

[10] to

[12] , wherein the polyester is a liquid crystal polyester. [Effects of the Invention]

[0010] According to the cleaning method and cleaning solvent of the present invention, polyester polymerization equipment can be efficiently cleaned, the cleaning solvent can be reused, and odor can be suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the process of the present invention, when washing the polyester polymerization apparatus, a washing solvent containing a mono-substituted ethylene glycol having an aromatic group is used from the viewpoint of washing efficiency and thermal stability.

[0012] In the method of the present invention, the mono-substituted ethylene glycol having an aromatic group used for washing the polyester polymerization apparatus is preferably a compound represented by formula (A) and / or formula (B). [ka] [ka] [In the formula, R1 and R2 each independently represent an alkyl group having 1 to 30 carbon atoms or a hydrogen atom, and m and n each independently represent an integer of 1 to 30.]

[0013] Of these, the aromatic group-containing monosubstituted ethylene glycols used for cleaning a polyester polymerization apparatus are more preferably the compounds represented by formula (A) from the viewpoint of cleaning efficiency.

[0014] In formula (A), from the viewpoint of ease of availability of the compound, R1 is preferably an alkyl group having 1 to 30 carbon atoms or a hydrogen atom, more preferably an alkyl group having 1 to 20 carbon atoms or a hydrogen atom, even more preferably an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, and particularly preferably a hydrogen atom.

[0015] In formula (A), m is preferably an integer of 1 to 30, more preferably an integer of 1 to 10, even more preferably an integer of 1 to 5, particularly preferably an integer of 2 to 4, and most preferably 2, from the viewpoint of achieving an excellent balance between high boiling point and thermal stability.

[0016] In formula (B), from the viewpoint of ease of availability of the compound, R2 is preferably an alkyl group having 1 to 30 carbon atoms or a hydrogen atom, more preferably an alkyl group having 1 to 20 carbon atoms or a hydrogen atom, even more preferably an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, and particularly preferably a hydrogen atom.

[0017] In formula (B), n is preferably an integer of 1 to 30, more preferably an integer of 1 to 10, even more preferably an integer of 1 to 5, and particularly preferably 2, from the viewpoint of achieving an excellent balance between high boiling point and thermal stability.

[0018] The compounds represented by formula (A) and / or formula (B) may be used alone or in combination, and may further contain other compounds within the scope of the present invention.

[0019] Specific examples of monosubstituted ethylene glycols having an aromatic group that can be used to clean a polyester polymerization apparatus in the method of the present invention include those derived from formula (A): phenyl glycol, ethylene glycol mono-m-tolyl ether, ethylene glycol mono-p-tolyl ether, phenyl diglycol, triethylene glycol monophenyl ether, tetraethylene glycol monophenyl ether, pentaethylene glycol monophenyl ether, hexaethylene glycol monophenyl ether, polyethylene glycol monophenyl ether (wherein m has a distribution but is, for example, 20 to 30), polyoxyethylene octylphenyl ether (wherein m has a distribution but is, for example, about 10), and polyethylene glycol mono-4-nonylphenyl ether (wherein m has a distribution but is, for example, about 18). These may be used alone, or two or more of them may be used in combination. Among these, in terms of excellent cleaning properties and thermal stability, it is more preferable to use one or more selected from the group consisting of phenyl glycol, ethylene glycol mono-m-tolyl ether, ethylene glycol mono-p-tolyl ether, phenyl diglycol, triethylene glycol monophenyl ether, tetraethylene glycol monophenyl ether, and pentaethylene glycol monophenyl ether, it is particularly preferable to use one or more selected from the group consisting of phenyl diglycol, triethylene glycol monophenyl ether, and tetraethylene glycol monophenyl ether, and it is most preferable to use phenyl diglycol.

[0020] Further, examples of those derived from formula (B) include benzyl glycol, benzyl diglycol, triethylene glycol monobenzyl ether, tetraethylene glycol monobenzyl ether, pentaethylene glycol monobenzyl ether, hexaethylene glycol monobenzyl ether, and polyethylene glycol monobenzyl ether (where n has a distribution, but is, for example, about 20). These may be used alone or in combination of two or more. Among these, in terms of excellent cleaning properties and thermal stability, it is more preferable to use one or more selected from the group consisting of benzyl glycol, benzyl diglycol, triethylene glycol monobenzyl ether, tetraethylene glycol monobenzyl ether, and pentaethylene glycol monobenzyl ether, and it is particularly preferable to use benzyl diglycol.

[0021] The boiling point of the cleaning solvent is preferably 150 to 450°C, more preferably 200 to 420°C, and even more preferably 250 to 400°C, from the viewpoints of enabling cleaning at high temperatures and being easily available.

[0022] The cleaning temperature of the polymerization apparatus is preferably between -100°C and +30°C of the boiling point of the cleaning solvent, and more preferably between -50°C and +10°C of the boiling point of the cleaning solvent. Specifically, the cleaning temperature is 150 to 400°C, preferably 200 to 380°C, and more preferably 250 to 350°C. When the cleaning temperature exceeds the boiling point of the cleaning solvent, the polymerization apparatus may be sealed and cleaning may be performed under pressure. Furthermore, to further shorten the cleaning time, cleaning is preferably performed under stirring.

[0023] The washing time is not particularly limited, but is typically 1 to 20 hours, preferably 2 to 15 hours. Here, the washing time means the time from when the temperature reaches a predetermined washing temperature.

[0024] The cleaning solvent used in cleaning the polyester polymerization apparatus of the present invention may be recovered after the cleaning step is completed and stored for the next cleaning.

[0025] The recovered washing solvent can be used as is as a whole or part of the washing solvent in the next washing step, or it may be used after distillation under atmospheric pressure or reduced pressure to remove non-volatile components as a distillation residue, or after removing a low-boiling fraction that has a boiling point below the washing temperature at atmospheric pressure. Removal of the low-boiling fraction has the advantage of facilitating washing at high temperatures. The removal of the low-boiling fraction may be performed during the washing step.

[0026] The recovered cleaning solvent may be reused as a cleaning solvent either alone or by mixing with a mono-substituted ethylene glycol having an aromatic group that has no history of cleaning (i.e., has never been used as a cleaning solvent for a polyester polymerization apparatus) in the next cleaning.

[0027] The polyesters produced in the polymerization apparatus used in the cleaning method of the present invention are polymers whose polymer chains have repeating units linked by ester groups. Specific examples of polyesters include polyethylene terephthalate, polyethylene naphthalate, liquid crystal polyester, polypropylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polybutylene naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, polyethylene diphenyl ether, polyglycolic acid, and copolymer polyesters thereof. Among these, the cleaning method and cleaning solvent of the present invention are suitable for use with polyesters that have excellent chemical resistance. Examples of polyesters with excellent chemical resistance include one or more selected from polyethylene terephthalate, polyethylene naphthalate, liquid crystal polyester, and polybutylene terephthalate, and are particularly suitable for use with liquid crystal polyester.

[0028] Hereinafter, a liquid crystalline polyester, which is one type of polyester produced in a polymerization apparatus used in the cleaning method of the present invention, and a method for producing the same and a polymerization apparatus will be described.

[0029] Liquid crystal polyesters are polyesters that form a melt phase with optical anisotropy (exhibit liquid crystal properties), and include wholly aromatic polyesters in which aromatic rings are linked by ester bonds (-CO-O- or -O-CO-), wholly aromatic poly(ester-amides) in which some of the ester bonds of the wholly aromatic polyesters are replaced by amide bonds (-CO-NH- or -NH-CO-), and wholly aromatic polyesters in which some of the ester bonds are replaced by alkyl bonds (-(CH2) x -) (x is any integer).

[0030] The liquid crystalline polyesters are liquid crystalline polyesters that form an anisotropic melt phase, referred to by those skilled in the art as thermotropic liquid crystalline polyesters.

[0031] The anisotropic melt phase can be confirmed by conventional polarized light examination using crossed polarizers. More specifically, the anisotropic melt phase can be confirmed by observing the sample on a Leitz hot stage under a nitrogen atmosphere at 40x magnification using a Leitz polarized microscope. Liquid crystal polyesters are optically anisotropic, i.e., they transmit light when examined between crossed polarizers. If a sample is optically anisotropic, polarized light will be transmitted even when it is stationary.

[0032] The liquid crystal polyester preferably has a crystalline melting temperature of 150 to 400°C, more preferably 220 to 370°C, and even more preferably 270 to 350°C, as measured by a differential scanning calorimeter.

[0033] If the crystalline melting temperature of the liquid crystal polyester is lower than 150°C, the heat resistance will be poor, and if it is higher than 400°C, the molding processability will tend to decrease, which is undesirable.

[0034] In this specification and claims, the "crystalline melting temperature" is determined from the crystalline melting temperature peak temperature measured using a differential scanning calorimeter (hereinafter abbreviated as DSC) at a heating rate of 20 ° C. / min. More specifically, a sample of liquid crystalline polyester is measured at a temperature rise rate of 20 ° C. / min from room temperature to the endothermic peak temperature (Tm1), and then the sample is held at a temperature 20 to 50 ° C. higher than Tm1 for 10 minutes. The sample is then cooled to room temperature at a temperature drop rate of 20 ° C. / min, and the endothermic peak is measured again at a temperature rise rate of 20 ° C. / min. The temperature at the peak top is taken as the crystalline melting temperature of the liquid crystalline polyester. For example, a Seiko Instruments Inc. Exstar 6000 or the like can be used as a measuring instrument.

[0035] Examples of polymerizable monomers constituting the structural units of liquid crystal polyester include aromatic hydroxycarboxylic acids, aromatic dicarboxylic acids, aromatic diols, aromatic aminocarboxylic acids, aromatic hydroxyamines, aromatic diamines, aliphatic diols, and aliphatic dicarboxylic acids.Such polymerizable monomers may be used alone or in combination of two or more.Preferably, at least one polymerizable monomer having a hydroxyl group and a carboxyl group is used.

[0036] Specific examples of aromatic hydroxycarboxylic acids include 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 2-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 5-hydroxy-2-naphthoic acid, 7-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, 4'-hydroxyphenyl-4-benzoic acid, 3'-hydroxyphenyl-4-benzoic acid, 4'-hydroxyphenyl-3-benzoic acid, and alkyl, alkoxy, or halogen-substituted derivatives thereof, as well as ester-forming derivatives thereof such as acylation products, ester derivatives, and acid halides. Among these, one or more compounds selected from the group consisting of 4-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid are preferred from the viewpoint of ease of adjusting the heat resistance and melting point of the resulting liquid crystal polyester.

[0037] Specific examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-dicarboxybiphenyl, 3,4'-dicarboxybiphenyl, and 4,4"-dicarboxyterphenyl, as well as alkyl, alkoxy, or halogen-substituted derivatives thereof, and ester-forming derivatives thereof, such as ester derivatives and acid halides. Among these, from the viewpoint of effectively enhancing the heat resistance of the resulting liquid crystal polyester, one or more compounds selected from the group consisting of terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid are preferred, and terephthalic acid and 2,6-naphthalenedicarboxylic acid are more preferred.

[0038] Specific examples of aromatic diols include hydroquinone, resorcinol, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl ether, and 2,2'-dihydroxybinaphthyl, as well as ester-forming derivatives thereof such as alkyl, alkoxy, or halogen-substituted derivatives and acylated derivatives thereof. Among these, from the viewpoint of excellent reactivity during polymerization, one or more compounds selected from the group consisting of hydroquinone, resorcinol, 4,4'-dihydroxybiphenyl, and 2,6-dihydroxynaphthalene are preferred, and one or more compounds selected from the group consisting of hydroquinone, 4,4'-dihydroxybiphenyl, and 2,6-dihydroxynaphthalene are more preferred.

[0039] Specific examples of aromatic aminocarboxylic acids include 4-aminobenzoic acid, 3-aminobenzoic acid, 6-amino-2-naphthoic acid, alkyl-, alkoxy-, or halogen-substituted derivatives thereof, and ester-forming derivatives thereof such as acylated products, ester derivatives, and acid halides.

[0040] Specific examples of aromatic hydroxyamines include 4-aminophenol, N-methyl-4-aminophenol, 3-aminophenol, 3-methyl-4-aminophenol, 4-amino-1-naphthol, 4-amino-4'-hydroxybiphenyl, 4-amino-4'-hydroxybiphenyl ether, 4-amino-4'-hydroxybiphenylmethane, 4-amino-4'-hydroxybiphenyl sulfide, and 2,2'-diaminobinaphthyl, as well as ester-forming derivatives thereof such as alkyl, alkoxy, or halogen-substituted derivatives thereof, and acylated derivatives thereof. Among these, 4-aminophenol is preferred from the viewpoint of the heat resistance of the resulting liquid crystal polyester.

[0041] Specific examples of aromatic diamines include amide-forming derivatives such as 1,4-phenylenediamine, 1,3-phenylenediamine, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene, alkyl-, alkoxy- or halogen-substituted derivatives thereof, and acylated derivatives thereof.

[0042] Specific examples of the aliphatic diol include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, and acylated derivatives thereof. Also, a polymer containing an aliphatic diol, such as polyethylene terephthalate or polybutylene terephthalate, may be reacted with the aromatic oxycarboxylic acid, aromatic dicarboxylic acid, aromatic diol, and their acylated derivatives, ester derivatives, acid halides, etc.

[0043] Specific examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, fumaric acid, maleic acid, and 1,4-cyclohexanedicarboxylic acid. Among these, oxalic acid, succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid are preferred from the viewpoint of excellent reactivity during polymerization.

[0044] The polymerizable monomers forming the structural units of the liquid crystal polyester may contain, as other copolymerization components, dihydroxyterephthalic acid, 4-hydroxyisophthalic acid, 5-hydroxyisophthalic acid, trimellitic acid, 1,3,5-benzenetricarboxylic acid, pyromellitic acid, or alkyl, alkoxy, or halogen-substituted derivatives thereof, as well as ester-forming derivatives thereof, such as acylated products, ester derivatives, and acid halides, within the scope of the present invention. The amount of these polymerizable monomers used is preferably 10 mol % or less of the total structural units forming the liquid crystal polyester.

[0045] The liquid crystal polyester may contain a thioester bond as long as it does not impair the object of the present invention. Polymerizable monomers that provide such bonds include mercapto aromatic carboxylic acids, aromatic dithiols, and hydroxy aromatic thiols. The content of these polymerizable monomers is preferably 10 mol% or less of the total structural units constituting the liquid crystal polyester.

[0046] Polymers combining these repeating units may or may not form an anisotropic molten phase depending on the monomer structure, composition ratio, and sequence distribution of each repeating unit in the polymer. However, the liquid crystal polyesters produced in the polymerization apparatus used in the cleaning method of the present invention are limited to those that form an anisotropic molten phase.

[0047] Specific examples of the combination of polymerizable monomers that form the constituent units of the liquid crystal polyester include the following. 1) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid, 2) 4-hydroxybenzoic acid / terephthalic acid / 4,4'-dihydroxybiphenyl, 3) 4-hydroxybenzoic acid / terephthalic acid / isophthalic acid / 4,4'-dihydroxybiphenyl, 4) 4-hydroxybenzoic acid / terephthalic acid / isophthalic acid / 4,4'-dihydroxybiphenyl / hydroquinone, 5) 4-hydroxybenzoic acid / terephthalic acid / hydroquinone, 6) 6-hydroxy-2-naphthoic acid / terephthalic acid / hydroquinone, 7) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid / terephthalic acid / 4,4'-dihydroxybiphenyl, 8) 6-hydroxy-2-naphthoic acid / terephthalic acid / 4,4'-dihydroxybiphenyl, 9) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid / terephthalic acid / hydroquinone, 10) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid / terephthalic acid / hydroquinone / 4,4'-dihydroxybiphenyl, 11) 4-hydroxybenzoic acid / 2,6-naphthalenedicarboxylic acid / 4,4'-dihydroxybiphenyl, 12) 4-hydroxybenzoic acid / terephthalic acid / 2,6-naphthalenedicarboxylic acid / hydroquinone, 13) 4-hydroxybenzoic acid / 2,6-naphthalenedicarboxylic acid / hydroquinone, 14) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid / 2,6-naphthalenedicarboxylic acid / hydroquinone, 15) 4-hydroxybenzoic acid / terephthalic acid / 2,6-naphthalenedicarboxylic acid / hydroquinone / 4,4'-dihydroxybiphenyl, 16) 4-hydroxybenzoic acid / terephthalic acid / 4-aminophenol, 17) 6-hydroxy-2-naphthoic acid / terephthalic acid / 4-aminophenol, 18) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid / terephthalic acid / 4-aminophenol, 19) 4-hydroxybenzoic acid / terephthalic acid / 4,4'-dihydroxybiphenyl / 4-aminophenol, 20) 4-hydroxybenzoic acid / terephthalic acid / ethylene glycol 21) 4-hydroxybenzoic acid / terephthalic acid / 4,4'-dihydroxybiphenyl / ethylene glycol, 22) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid / terephthalic acid / ethylene glycol 23) 4-hydroxybenzoic acid / 6-hydroxy-2-naphthoic acid / terephthalic acid / 4,4'-dihydroxybiphenyl / ethylene glycol 24) 4-Hydroxybenzoic acid / terephthalic acid / 2,6-naphthalenedicarboxylic acid / 4,4'-dihydroxybiphenyl.

[0048] Among these, liquid crystal polyesters consisting of structural units derived from polymerizable monomers 1), 9), 10), and 14) are preferred because they have excellent performance such as mechanical strength of the liquid crystal polyester itself and are easy to clean using the cleaning method of the present invention.

[0049] In one preferred embodiment, a liquid crystalline polyester containing a total of 90 mol% or more of repeating units represented by formula (I) and formula (II) is preferably used, and a liquid crystalline polyester composed of repeating units represented by formula (I) and formula (II) is more preferably used. The repeating units represented by formula (I) account for 50 to 90 mol%, preferably 55 to 85 mol%, more preferably 60 to 80 mol%, and even more preferably 70 to 75 mol%. The repeating units represented by formula (II) account for 10 to 50 mol%, preferably 15 to 45 mol%, more preferably 20 to 40 mol%, and even more preferably 25 to 30 mol%. [ka]

[0050] In another preferred embodiment, a liquid crystal polyester resin containing repeating units represented by formulas (I) to (IV) is suitably used. [ka]

[0051] Here, the repeating unit represented by formula (III) may be a plurality of types of repeating units each containing a different Ar1, and the repeating unit represented by formula (IV) may be a plurality of types of repeating units each containing a different Ar2. That is, the repeating unit represented by formula (III) may be a plurality of repeating units, such as a repeating unit having one type of Ar1 and a repeating unit having another type of Ar1, and similarly, the repeating unit represented by formula (IV) may be a plurality of repeating units, such as a repeating unit having one type of Ar2 and a repeating unit having another type of Ar2. Furthermore, the term "aromatic group" refers to an aromatic group that is a 6-membered monocyclic ring or a fused ring having two rings.

[0052] The total composition ratio (mol %) of the repeating units represented by formula (I) and formula (II) is 30 to 80 mol %, preferably 32 to 78 mol %, more preferably 34 to 76 mol %, and even more preferably 36 to 74 mol %. The repeating units represented by formula (III) and formula (IV) are each 10 to 35 mol %, preferably 11 to 34 mol %, more preferably 12 to 33 mol %, and even more preferably 13 to 32 mol %. The repeating units represented by formula (III) and formula (IV) are preferably in substantially equimolar amounts.

[0053] It is more preferred that the repeating units represented by formulas (III) to (IV) are each independently one or more repeating units in which Ar1 and Ar2 are selected from the aromatic groups represented by formulas (1) to (4): It is particularly preferred that the repeating unit represented by formula (III) is a repeating unit in which Ar1 is an aromatic group represented by formula (1) and / or formula (3), and that the repeating unit represented by formula (IV) is a repeating unit in which Ar2 is an aromatic group represented by formula (1) and / or formula (4). [ka]

[0054] The method for producing the liquid crystal polyester is not particularly limited, and the liquid crystal polyester can be produced by a known polycondensation method in which a polymerizable monomer forms an ester bond. Usually, a melt polymerization method, a solution polymerization method, a slurry polymerization method, a solid-phase polymerization method, or a combination of two or more of these methods is used, and a melt polymerization method or a combination of a melt polymerization method and a solid-phase polymerization method is preferably used.

[0055] In melt polymerization, the monomers are first heated to form a melt of reactants, and the reaction is continued to produce a molten polyester, with vacuum applied to facilitate removal of volatile by-products (e.g., acetic acid, water, etc.) produced in the final stage of condensation.

[0056] Slurry polymerization is a process in which the reaction is carried out in the presence of a heat exchange fluid, and the solid product is obtained in a state suspended in the heat exchange medium.

[0057] The solid-state polymerization method is a method in which the reaction is carried out by heating at a temperature 10 to 120°C lower than the liquid crystal formation temperature of the polyester obtained by the polycondensation reaction under reduced pressure or vacuum in an inert gas stream such as nitrogen gas. The reaction may be carried out at a constant temperature or may be gradually increased to a higher temperature. The heating method is not particularly limited, and microwave heating, heater heating, etc. may be used.

[0058] The polymerizable monomer components used in producing the liquid crystal polyester can be subjected to the reaction at room temperature in a modified form in which the hydroxyl groups are acylated, i.e., as lower acylated products. The lower acyl groups preferably have 2 to 5 carbon atoms, more preferably 2 or 3 carbon atoms. Particularly preferred is a method in which an acetylated product of the monomer component is used in the reaction.

[0059] The lower acylated monomer may be one which has been previously synthesized by separate acylation, or may be produced in the reaction system by adding an acylating agent such as acetic anhydride to the monomer during the production of the liquid crystal polyester resin.

[0060] The polycondensation reaction is preferably carried out at a temperature of 150 to 400°C, preferably 250 to 370°C, under normal pressure and / or reduced pressure, and a catalyst may be used as necessary.

[0061] Specific examples of the catalyst include organotin compounds (dialkyltin oxides such as dibutyltin oxide, diaryltin oxides, etc.), titanium dioxide, antimony trioxide, organotitanium compounds (alkoxytitanium silicates, titanium alkoxides, etc.), alkali and alkaline earth metal salts of carboxylic acids (potassium acetate, sodium acetate, etc.), Lewis acids (BF3, etc.), gaseous acid catalysts such as hydrogen halides (HCl, etc.), and the like.

[0062] The amount of the catalyst used is preferably 1 to 1000 ppm, more preferably 5 to 200 ppm, based on the mass of the monomer.

[0063] The liquid crystal polyester obtained by such a polycondensation reaction is extracted in a molten state from a polymerization reaction vessel, and then processed into pellets, flakes, or powder, and is subjected to molding or melt-kneading.

[0064] The liquid crystal polyester in the form of pellets, flakes, or powder may be heat-treated in a substantially solid state under reduced pressure, in vacuum, or in an atmosphere of an inert gas such as nitrogen or helium, in order to increase the molecular weight and improve the heat resistance.

[0065] The temperature of the heat treatment is not particularly limited as long as the liquid crystal polyester does not melt, but is preferably 260 to 380°C, more preferably 280 to 350°C.

[0066] The polymerization apparatus to be cleaned in the present invention is not particularly limited, and either a vertical or horizontal reactor can be used, but specifically, a polymerization apparatus having an internal stirring blade, baffles, a raw material inlet, a distillation pipe, a pressure reduction port, a nitrogen inlet, a polymer outlet, etc. is preferably used. The material of the polymerization apparatus is preferably corrosion-resistant to acylation reaction products, etc., and specific examples include stainless steels such as SUS316, SUS316L, SUS317, and duplex stainless steel, nickel-molybdenum alloys such as Hastelloy (registered trademark) B and Hastelloy (registered trademark) C, impermeable graphite, titanium, zirconium, GL, and tantalum.

[0067] In the cleaning method of the present invention, a polymerization apparatus after producing a polyester such as the liquid crystal polyester described above is cleaned using a mono-substituted ethylene glycol having an aromatic group as a cleaning solvent, whereby the polyester in the polymerization apparatus can be quickly dissolved and efficiently cleaned. Furthermore, the cleaning solvent of the present invention can be reused and has the effect of suppressing odor.

[0068] Polyesters are polymerized in the polyester polymerization apparatus after cleaning. By polymerizing polyesters using the polyester polymerization apparatus cleaned by the cleaning method according to the above embodiment, polyesters can be produced efficiently. That is, the present invention also relates to a method for producing polyesters, which includes the steps of cleaning the polyester polymerization apparatus by the cleaning method according to the above embodiment, and polymerizing polyesters in the polyester polymerization apparatus after cleaning. [Example]

[0069] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples in any way.

[0070] The synthesis examples of the liquid crystal polyesters used in the Examples and Comparative Examples are described below. The abbreviations for the compounds in the synthesis examples are as follows.

[0071] [Monomers used in the synthesis of liquid crystal polyester] POB: 4-hydroxybenzoic acid BON6: 6-hydroxy-2-naphthoic acid BP: 4,4'-dihydroxybiphenyl HQ: Hydroquinone TPA: Terephthalic acid NDA: 2,6-naphthalenedicarboxylic acid

[0072] Synthesis Example 1 (LCP1) A 2 L reactor equipped with a stirrer with a torque meter and a distillation tube was charged with POB, BON6, HQ, and NDA in the composition ratio shown in Table 1 so that the total amount was 6.5 mol. Furthermore, 1.03 times the moles of acetic anhydride relative to the amount (moles) of hydroxyl groups in all monomers was charged, and deacetic acid polymerization was carried out under the following conditions.

[0073] [Table 1]

[0074] The temperature was raised from room temperature to 150°C in a nitrogen gas atmosphere over 1 hour and maintained at that temperature for 30 minutes. The temperature was then raised to 350°C over 7 hours while distilling off the by-product acetic acid, and the pressure was then reduced to 10 mmHg over 80 minutes. The polymerization reaction was terminated when a predetermined torque was reached, and the contents of the reactor were removed and crushed to obtain pellets of liquid crystal polyester resin. The amount of acetic acid distilled during polymerization was nearly the theoretical value. The crystalline melting temperature (Tm) of the resulting pellets was 321°C.

[0075] Synthesis example 2 (LCP2) A 2 L reaction vessel equipped with a stirrer with a torque meter and a distillation tube was charged with POB and BON6 in a total amount of 6.5 mol in the composition ratio shown in Table 2, and 1.03 times the moles of acetic anhydride relative to the amount (moles) of hydroxyl groups in all monomers. Deacetic acid polymerization was carried out under the following conditions.

[0076] [Table 2]

[0077] The temperature was raised from room temperature to 150°C in a nitrogen gas atmosphere over 1 hour and maintained at that temperature for 30 minutes. Next, the temperature was rapidly raised to 210°C while distilling off the by-product acetic acid and maintained at that temperature for 30 minutes. The temperature was then raised to 325°C over 5 hours, and the pressure was then reduced to 10 mmHg over 90 minutes. The polymerization reaction was terminated when a predetermined torque was reached, and the contents of the reactor were removed and crushed to obtain liquid crystal polyester resin pellets. The amount of acetic acid distilled during polymerization was nearly the theoretical value. The crystalline melting temperature (Tm) of the resulting pellets was 278°C.

[0078] Synthesis Example 3 (LCP3) A 2 L reactor equipped with a stirrer with a torque meter and a distillation tube was charged with POB, BON6, HQ, BP, and TPA in a total amount of 6.5 mol in the composition ratio shown in Table 3, and 1.03 times the moles of acetic anhydride relative to the amount (moles) of hydroxyl groups in all monomers. Deacetic acid polymerization was carried out under the following conditions.

[0079] [Table 3]

[0080] The temperature was raised from room temperature to 150°C in a nitrogen gas atmosphere over 1 hour and maintained at that temperature for 30 minutes. The temperature was then raised to 350°C over 7 hours while distilling off the by-product acetic acid, and the pressure was then reduced to 5 mmHg over 80 minutes. The polymerization reaction was terminated when a predetermined torque was reached, and the contents of the reactor were removed and crushed into pellets of liquid crystal polyester resin. The amount of acetic acid distilled during polymerization was nearly the theoretical value. The crystalline melting temperature (Tm) of the resulting pellets was 335°C.

[0081] Synthesis Example 4 (LCP4) A 2 L reactor equipped with a stirrer with a torque meter and a distillation tube was charged with POB, BON6, HQ, and TPA in the composition ratio shown in Table 4 so that the total amount was 6.5 mol. Further, 1.03 times the moles of acetic anhydride relative to the amount (moles) of hydroxyl groups in all monomers was charged, and deacetic acid polymerization was carried out under the following conditions.

[0082] [Table 4]

[0083] The temperature was raised from room temperature to 150°C in a nitrogen gas atmosphere over 1 hour and maintained at that temperature for 30 minutes. The temperature was then raised to 350°C over 7 hours while distilling off the by-product acetic acid, and the pressure was then reduced to 10 mmHg over 80 minutes. The polymerization reaction was terminated when a predetermined torque was reached, and the contents of the reactor were removed and crushed into pellets of liquid crystal polyester resin. The amount of acetic acid distilled during polymerization was nearly the theoretical value. The crystalline melting temperature (Tm) of the resulting pellets was 332°C.

[0084] The cleaning solvents used in the examples and comparative examples are shown below. Phenyl diglycol: Tokyo Chemical Industry Co., Ltd., phenyl diglycol (boiling point: 298°C, specific gravity: 1.12) Tetraethylene glycol (TEG): Tetraethylene glycol (boiling point: 328°C, specific gravity: 1.13), manufactured by Tokyo Chemical Industry Co., Ltd.

[0085] Examples 1 to 3 and Comparative Examples 1 to 6 (1-1) Calculation of dissolution rate Using pellets of the liquid crystal polyesters (LCP1 to 3) obtained in Synthesis Examples 1 to 3, test specimens (cross section: 12.7 mm×3.2 mm, length: 12.0 mm, weight: approximately 0.6 g) were prepared using an injection molding machine.

[0086] Each test piece was placed in a 500 ml four-neck glass flask equipped with a half-moon stirring blade, a T-shaped distillation tube, and a thermometer, and 300 ml of the cleaning solvent shown in Table 5 was added and stirred at a speed of 100 rpm.

[0087] The temperature was then raised to the temperature shown in Table 5, and the mixture was kept at that temperature for 6 hours while stirring, after which the dissolution rate of the test piece was calculated using the following formula. The results are shown in Table 5. Dissolution rate (%) = (weight of test piece at the time of preparation - weight of test piece after 6 hours) / weight of test piece at the time of preparation × 100

[0088] (1-2) Measurement of solvent concentration after cleaning [Phenyldiglycol] High performance liquid chromatography (HPLC) was performed under the following conditions, and the concentration of phenyl diglycol solvent was calculated from the area % of the HPLC chart. The results are shown in Table 5. <High-Performance Liquid Chromatography (HPLC)> Equipment: Shimadzu Corporation LC-2010C Column model number: L-Column 5C18 Fluid volume: 1.0 mL / min Solvent ratio: MeOH / H2O (pH 2.3) = 35 / 65 (15 min) → 3 min → 100 / 0 (3 min) → 9 min → 35 / 65 (5 min), gradient analysis Wavelength: 229nm Column temperature: 50℃

[0089] [TEG] Gas chromatography (GC) was performed under the following conditions, and the TEG solvent concentration was calculated from the area % of the GC chart. The results are shown in Table 5. <Gas chromatography (GC)> Equipment: Shimadzu Corporation GC-2014 Column model number: G-100 1.2mm x 40m 5μm Carrier gas: He Column flow rate: 20 mL / min Internal standard: dimethyl phthalate Detector and inlet temperature: 280°C Column temperature: 170℃ Injection mode: Split (split ratio 50) Analysis time: 15 minutes

[0090] (1-3) Calculation of impurity rate of solvent after cleaning The impurity rate of each cleaning solvent was calculated using the following formula: The results are shown in Table 5. Solvent impurity rate (%) = 100 (%) - solvent concentration after washing (%)

[0091] Examples 4 to 7 and Comparative Example 7 (2-1) Calculation of dissolution rate Regarding the polymerization apparatus used in the polymerization reactions of Synthesis Examples 1 to 4 (LCP1 to LCP4), after each polymerization reaction was completed, 1600 g of phenyl diglycol was charged into each 2 L reaction vessel and stirred at a speed of 100 rpm.

[0092] The temperature was then raised to 297°C and maintained at that temperature for 6 hours while stirring. The dissolution rate in the reaction vessel was calculated using the following formula. The results are shown in Table 6. Dissolution rate (%) = (weight of resin adhering to the reaction vessel and stirring blade before starting cleaning - weight of resin adhering to the reaction vessel and stirring blade after 6 hours) / weight of resin adhering to the reaction vessel and stirring blade before starting cleaning x 100

[0093] (2-2) Measurement of solvent concentration after cleaning The solvent concentrations of phenyl diglycol and TEG after washing were measured in the same manner as in (1-2) above. The results are shown in Table 6.

[0094] (2-3) Calculation of impurity rate of solvent after cleaning The impurity rate of the washing solvent was calculated in the same manner as in (1-3) above. The results are shown in Table 6.

[0095] Sensory evaluation (checking odor) In the cleaning methods of Examples 2 and 3 and Comparative Examples 4 and 6, odors detected at a location approximately 1 m away from the experimental device were confirmed by six panelists.

[0096] The odor was evaluated according to the following criteria, and the results are shown in Table 7. [Evaluation criteria] ○: No odor △: Odor is noticeable but very weak ×: Strong odor

[0097] [Table 5]

[0098] [Table 6]

[0099] [Table 7]

[0100] As shown in Tables 5 and 6, the Examples using phenyl diglycol, a monosubstituted ethylene glycol having an aromatic group, as the cleaning solvent had a high LCP dissolution rate and excellent cleaning effectiveness. On the other hand, the Comparative Examples using TEG as the cleaning solvent had poor cleaning effectiveness and contained a large amount of solvent-derived impurities generated by thermal decomposition, making it difficult to reuse.

[0101] As shown in Table 7, it can be seen that when phenyldiglycol, which is a monosubstituted ethylene glycol having an aromatic group, is used as a cleaning solvent, odor is suppressed.

Claims

1. A method for cleaning a polymerization apparatus for producing polyesters, characterized by cleaning the polymerization apparatus in which polyesters have been produced, using a cleaning solvent containing a mono-substituted ethylene glycol having an aromatic group at a temperature of 150 to 400°C.

2. The monosubstituted ethylene glycols having an aromatic group are represented by the formula (A) and / or the formula (B): 【Chemistry 1】 【Chemistry 2】 [In the formula, R １ and R ２ each independently represents an alkyl group having 1 to 30 carbon atoms or a hydrogen atom, and m and n each independently represent an integer of 1 to 30. The method according to claim 1, wherein the compound is represented by the formula:

3. 2. The method of claim 1, wherein the monosubstituted ethylene glycol having an aromatic group is phenyl diglycol.

4. The method of claim 1 , wherein the polyester is a liquid crystalline polyester.

5. The liquid crystal polyester is represented by formula (I) and / or formula (II): 【Transformation 3】 The method according to claim 4, wherein the liquid crystal polyester comprises a repeating unit represented by the formula:

6. The liquid crystal polyester is represented by the formula (I) and the formula (II): 【Chemistry 4】 5. The method according to claim 4, wherein the liquid crystal polyester contains 90 mol % or more of repeating units represented by the formula:

7. The liquid crystal polyester is represented by the formula (I) to the formula (IV): 【Transformation 5】 [In the formula, Ar １ and Ar ２ each represents a divalent aromatic group. The method according to claim 4, wherein the liquid crystal polyester comprises a repeating unit represented by the formula:

8. The repeating units represented by formulas (III) and (IV) are Ar １ and Ar ２ are each independently represented by the formulas (1) to (4) 【Transformation 6】 The method according to claim 7, wherein each repeating unit is one or more types selected from aromatic groups represented by the following formula:

9. A method for producing polyesters, comprising the steps of cleaning a polyester polymerization apparatus by the method according to any one of claims 1 to 8, and polymerizing polyesters in the polyester polymerization apparatus after cleaning.

10. A cleaning solvent for cleaning polyester polymerization equipment, comprising a mono-substituted ethylene glycol having an aromatic group.

11. The monosubstituted ethylene glycols having an aromatic group are represented by the formula (A) and / or the formula (B): 【Transformation 7】 【Transformation 8】 [In the formula, R １ and R ２ each independently represents an alkyl group having 1 to 30 carbon atoms or a hydrogen atom, and m and n each independently represent an integer of 1 to 30. The cleaning solvent according to claim 10, which is a compound represented by the formula:

12. 11. The cleaning solvent of claim 10, wherein the mono-substituted ethylene glycol having an aromatic group is phenyl diglycol.

13. The cleaning solvent according to claim 10, wherein the polyester is a liquid crystal polyester.

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