Polybutylene terephthalate and method for producing same

Abstract

To provide polybutylene terephthalate with a desirable color tone as a resin, specifically enabling reduction of yellowish and bluish tints, and a method for producing the same.SOLUTION: A polybutylene terephthalate comprising, as copolymerization components, 0.001-0.020 mol% of butyric acid units and 0.001-0.027 mol% of succinic acid units, and having a terminal methoxy group concentration of 0.03-6.0 equivalents / ton. In a method for producing polybutylene terephthalate by reacting a dicarboxylic acid component mainly composed of dimethyl terephthalate with a diol component, 1,4-butanediol containing, in total, 50-8000 ppm of butanediol mono(4-hydroxybutyrate) and 2,7-dioxadecan-1-one, and 5-1000 ppm in total of succinic acid and a cyclic ester of succinic acid and butanediol, is used as the diol component.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to polybutylene terephthalate (hereinafter sometimes referred to as "PBT"). Specifically, the present invention relates to polybutylene terephthalate having a preferable color tone as a resin and a method for producing the same.

Background Art

[0002] Polybutylene terephthalate using terephthalic acid (hereinafter sometimes referred to as "TPA") or dialkyl terephthalate (hereinafter sometimes referred to as "terephthalic acid component" or "TPA component") as the main component of the dicarboxylic acid component and using 1,4-butanediol (hereinafter sometimes referred to as "BDO") as the main component of the diol component has excellent mechanical properties, heat resistance, moldability, and recyclability. In addition, since it has high mechanical strength and excellent chemical resistance, it is widely used as a material for industrial molded products such as connectors, relays, and switches for automobiles and electric and electronic devices. Furthermore, it is also widely used for films, sheets, fibers (filaments), etc., and accordingly, high-quality polybutylene terephthalate and a method for producing the same are required.

[0003] In order to provide molded products for various uses, techniques for improving the color tone of polybutylene terephthalate, particularly the b value (yellowness), are known. In order to solve this color tone problem, for example, a method of regulating the polycondensation temperature during PBT production has been proposed (see Patent Document 1). Regarding BDO as well, for example, it is known that the color tone of PBT is improved by reducing the content of cyclic acetals which are impurities (see Patent Document 2). However, all of them were insufficient as the effect of improving the color tone.

[0004] On the one hand, regarding terephthalic acid, in recent years, in addition to the conventional method of producing terephthalic acid using fossil fuels such as petroleum as raw materials (hereinafter referred to as "petrochemical-derived"), methods for producing terephthalic acid derived from biomass resources (referred to as "biomass-derived" in the present invention) using biomass resources as raw materials have also been developed. For example, a method has been proposed in which isobutanol is obtained from a renewable carbon source, and terephthalic acid is obtained by oxidizing p-xylene through the dehydration dimerization of isobutanol (for example, Patent Document 3). From the terephthalic acid obtained by this method, dimethyl terephthalate can be easily obtained according to a conventional method. In addition, a chemical recycling method for recovering dimethyl terephthalate by depolymerizing waste polyester has also been proposed (for example, Patent Documents 4 and 5).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide polybutylene terephthalate having a preferable color tone as a resin, specifically, having less yellowness and blueness, and a method for producing the same.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by polybutylene terephthalate containing specific amounts of specific terminal components and copolymer components, and have completed the present invention. That is, the present invention relates to the following inventions.

[0008] [1] Polybutylene terephthalate containing 0.001 to 0.020 mol% of butyric acid units and 0.001 to 0.027 mol% of succinic acid units as copolymer components, and having a terminal methoxy group concentration of 0.03 to 6.0 equivalents / ton.

[0009] [2] The polybutylene terephthalate according to [1], wherein the terminal benzaldehyde group concentration is 0.01 to 0.50 equivalents / ton.

[0010] [3] The polybutylene terephthalate according to [1] or [2], wherein the terminal methylphenyl group concentration is less than 0.30 equivalents / ton, the terminal acetyl group concentration is less than 0.10 equivalents / ton, the copolymerization amount of 1,4-pentanediol units is less than 0.006 mol%, and the copolymerization amount of 2-methyl-1,4-butanediol units is less than 0.020 mol%.

[0011] [4] In a method for producing polybutylene terephthalate by reacting a dicarboxylic acid component mainly composed of dimethyl terephthalate with a diol component, the diol component contains a total of 50 to 8000 ppm of one or two compounds represented by the following formula (1) or formula (2), and a total of 5 to 1000 ppm of one or two compounds represented by the following formula (4) or formula (5). A method for producing polybutylene terephthalate, characterized by using 1,4-butanediol.

[0012]

Chemical formula

[0013] [5] The method for producing polybutylene terephthalate according to [4], wherein 1,4-butanediol obtained by hydrogenating succinic acid or a succinic acid derivative is used as the 1,4-butanediol.

[0014] [6] The method for producing polybutylene terephthalate according to [4] or [5], wherein the content of the compound represented by the following formula (3) in the 1,4-butanediol is less than 1 ppm.

[0015] [Chemical formula]

[0016] [7] The method for producing polybutylene terephthalate according to any one of [4] to [6], wherein dimethyl terephthalate produced by chemical recycling of polyester or dimethyl terephthalate produced using biomass resources is used as the dimethyl terephthalate. [Advantages of the Invention]

[0017] The polybutylene terephthalate of the present invention has a preferable resin color tone, specifically, less yellowish or bluish color. Therefore, such polybutylene terephthalate of the present invention, a compound containing the polybutylene terephthalate of the present invention, and a molded article obtained using the same have a good color tone and high commercial value, and can be preferably used for various applications, such as electric and electronic parts, automobile parts, films, sheets, filaments, and the like. [Embodiments for Carrying Out the Invention]

[0018] Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not exceed the gist of the present invention. In addition, when the expression "~" is used in this specification, it shall be used as an expression including the numerical values or physical property values before and after it. In the present invention, the "main component" in the dicarboxylic acid component refers to a component contained in an amount of 50 mol% or more in the component. The same applies to the "main component" in the diol component. Also, unless otherwise specified, "ppm" indicates "mass ppm" except for the unit of chemical shift in NMR described later.

[0019] [Polybutylene terephthalate] In the present invention, polybutylene terephthalate (PBT) refers to a polymer having a structure in which a terephthalic acid component and a 1,4-butanediol (BDO) component are ester-bonded, and 50 mol% or more of all dicarboxylic acid components consist of the terephthalic acid component, and 50 mol% or more of all diol components consist of BDO. The proportion of the terephthalic acid component in all dicarboxylic acid components is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 95 mol% or more. Also, the proportion of BDO in all diol components is preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 95 mol% or more. When the terephthalic acid component or BDO is less than 50 mol%, the crystallization rate of PBT tends to decrease, leading to deterioration of moldability.

[0020] The PBT of the present invention is as follows: the copolymerization amount of butyric acid units is 0.001 to 0.020 mol%, the copolymerization amount of succinic acid units is 0.001 to 0.027 mol%, the terminal methoxy group concentration is 0.03 to 6.0 equivalents / ton, and preferably the terminal benzaldehyde group concentration is 0.01 to 0.50 equivalents / ton. The PBT of the present invention is obtained by using dimethyl terephthalate as the raw material dicarboxylic acid of PBT and using BDO obtained by hydrogenating succinic acid or a succinic acid derivative as the raw material BDO, as described later. Usually, the concentration of terminal methylphenyl groups is less than 0.30 equivalents / ton, the concentration of terminal acetyl groups is less than 0.10 equivalents / ton, the copolymerization amount of 1,4-pentanediol units is less than 0.006 mol%, and the copolymerization amount of 2-methyl-1,4-butanediol units is less than 0.020 mol%.

[0021] The measurement of the terminal methoxy group concentration and the terminal benzaldehyde group concentration in the PBT of the present invention can be carried out by the method described in the Examples section below.

[0022] <Butyric acid unit and succinic acid unit> One of the characteristics of the PBT of the present invention is that it is a PBT in which a specific amount of a butyric acid unit and a succinic acid unit are present as copolymerization components. The butyric acid unit of the PBT of the present invention may be referred to as being derived from the compound represented by the following formula (1) or formula (2) in the PBT raw material, particularly in the raw material BDO, from its production method. However, it is specified by the measurement method described later and is not limited to only being derived from the compound represented by the following formula (1) or formula (2) contained in the raw material. Similarly, the succinic acid unit of the PBT of the present invention may be referred to as being derived from the compound represented by the following formula (4) or formula (5) in the PBT raw material, particularly in the raw material BDO, from its production method. However, it is specified by the measurement method described later and is not limited to only being derived from the compound represented by the following formula (4) or formula (5) contained in the raw material. Here, the "unit" means a structural unit incorporated into PBT by the reaction of the monomer in the reaction process of PBT production.

[0023]

Chemical formula

[0024] Hereinafter, the compound represented by formula (1) may be referred to as "compound (1)", the compound represented by formula (2) may be referred to as "compound (2)", and the compound represented by formula (3) described later may be referred to as "compound (3)". Similarly, the compound represented by formula (4) may be referred to as "compound (4)", and the compound represented by formula (5) may be referred to as "compound (5)".

[0025] <Amount of butyric acid unit> The PBT of the present invention has a butyric acid unit content that is usually 0.001 mol%, preferably 0.002 mol%, more preferably 0.004 mol% as its lower limit, and usually 0.020 mol%, preferably 0.019 mol%, more preferably 0.018 mol% as its upper limit. When the content of the butyric acid unit is below the above lower limit, not only does the raw material purification cost increase, but the color tone of the PBT becomes more bluish, which is not preferable. On the other hand, when the content of the butyric acid unit exceeds the above upper limit, the color tone of the PBT becomes more yellowish, which is not preferable.

[0026] <Amount of succinic acid units> The PBT of the present invention has a succinic acid unit content that is usually 0.001 mol%, preferably 0.002 mol%, more preferably 0.004 mol% as its lower limit, and usually 0.027 mol%, preferably 0.026 mol%, more preferably 0.025 mol% as its upper limit. When the content of the succinic acid unit is below the above lower limit, not only does the raw material purification cost increase, but the color tone of the PBT becomes more bluish, which is not preferable. On the other hand, when the content of the succinic acid unit exceeds the above upper limit, the color tone of the PBT becomes more yellowish, which is not preferable.

[0027] <Amount of 1,4-pentanediol units and 2-methyl-1,4-butanediol units> The PBT of the present invention preferably has a content of 1,4-pentanediol units and 2-methyl-1,4-butanediol units as copolymerization components that are each below a specific amount. BDO produced by the allyl alcohol method via allyl alcohol, which involves acetoxylating propylene and hydrolyzing it to allyl acetate, contains 1,4-pentanediol and 2-methyl-1,4-butanediol as impurities due to its manufacturing process. In order for the PBT of the present invention to satisfy the above-mentioned copolymerization amounts of butyric acid units and succinic acid units, as the raw material BDO of PBT, as described below, it is preferable to use BDO obtained by subjecting succinic acid or a succinic acid derivative to a hydrogenation treatment. Thus, when BDO obtained by subjecting succinic acid or a succinic acid derivative to a hydrogenation treatment is used, in the production process of PBT, 1,4-pentanediol or 2-methyl-1,4-butanediol derived from the raw material BDO is not introduced into PBT as a copolymerization component, and the copolymerization amount of 1,4-pentanediol units is preferably less than 0.006 mol%, more preferably less than 0.003 mol%, and most preferably does not contain 1,4-pentanediol units (below the detection limit). Also, the copolymerization amount of 2-methyl-1,4-butanediol units is preferably less than 0.020 mol%, more preferably less than 0.010 mol%, and most preferably does not contain 2-methyl-1,4-butanediol units (below the detection limit), and PBT can be produced.

[0028] <Terminal methoxy group> The PBT of the present invention has a terminal methoxy group concentration of 0.03 to 6.0 equivalents / ton. The terminal methoxy groups contained in the PBT of the present invention may be referred to as terminal methoxy groups derived from the methoxy groups contained in the raw materials of PBT, particularly dimethyl terephthalate, depending on the production method thereof, but are specified by the measurement method described below and are not limited to those derived from the methoxy groups contained in dimethyl terephthalate.

[0029] The terminal methoxy group concentration of the PBT of the present invention is usually 0.03 equivalents / ton or more, preferably 0.04 equivalents / ton or more. On the other hand, the terminal methoxy group concentration of the PBT of the present invention is usually 6.0 equivalents / ton or less, preferably 5.0 equivalents / ton or less. When the terminal methoxy group concentration is lower than the above lower limit, the number of reaction sites decreases and the transesterification reaction takes an extremely long time, which is not practical. On the other hand, when the terminal methoxy group concentration exceeds the above upper limit, not only does the color tone of PBT increase in yellowness, but PBT may not reach the predetermined molecular weight during the production of PBT, and the required strength may not be obtained.

[0030] <Terminal benzaldehyde group> For the PBT of the present invention, the terminal benzaldehyde group concentration is preferably 0.01 to 0.50 equivalents / ton. The terminal benzaldehyde groups contained in the PBT of the present invention may be referred to as terminal benzaldehyde groups derived from 4-carboxybenzaldehyde (hereinafter sometimes referred to as "4CBA") contained in the raw materials of PBT, particularly in the raw material dimethyl terephthalate, from the production method thereof, but are those specified by the measurement method described later and are not limited to those derived from 4CBA.

[0031] The terminal benzaldehyde group concentration of the PBT of the present invention is preferably 0.01 equivalents / ton or more, more preferably 0.02 equivalents / ton or more, and still more preferably 0.03 equivalents / ton or more. On the other hand, the terminal benzaldehyde group concentration of the PBT of the present invention is preferably 0.50 equivalents / ton or less, more preferably 0.40 equivalents / ton or less, and still more preferably 0.30 equivalents / ton or less. When the terminal benzaldehyde group concentration is lower than the above lower limit, the color tone of PBT tends to increase in blueness. On the other hand, when the terminal benzaldehyde group concentration exceeds the above upper limit, not only does it increase in yellowness, but due to the effect of end capping, the molecular weight of PBT decreases, and the required strength may not be obtained.

[0032] <Terminal methylphenyl group> For the PBT of the present invention, the terminal methylphenyl group concentration is preferably less than 0.30 equivalents / ton. The terminal methylphenyl group is usually introduced into PBT derived from p-toluic acid contained as an impurity in the raw materials of PBT, particularly in the raw material terephthalic acid. In order for the PBT of the present invention to satisfy the aforementioned terminal methoxy group concentration, it is preferable to use dimethyl terephthalate as the dicarboxylic acid component of the raw material for PBT, as described below. Thus, when dimethyl terephthalate is used, in the manufacturing process of PBT, terminal methylphenyl groups are not introduced into PBT due to p-toluic acid in the raw material dicarboxylic acid component, and the terminal methylphenyl group concentration is preferably less than 0.30 equivalents / ton, more preferably less than 0.20 equivalents / ton, and most preferably 0 equivalents / ton of PBT can be obtained.

[0033] <Terminal acetyl group> The PBT of the present invention preferably has a terminal acetyl group concentration of less than 0.10 equivalents / ton. BDO produced by the butadiene method using butadiene as a raw material contains 1-acetoxy-4-hydroxybutane as an impurity derived from its manufacturing process. In order for the PBT of the present invention to satisfy the aforementioned copolymerization amounts of butyric acid units and succinic acid units, it is preferable to use BDO obtained by hydrogenating succinic acid or a succinic acid derivative as the raw material BDO for PBT, as described below. Thus, when BDO obtained by hydrogenating succinic acid or a succinic acid derivative is used, in the manufacturing process of PBT, terminal acetyl groups are not introduced into PBT due to 1-acetoxy-4-hydroxybutane derived from the raw material BDO, and the terminal acetyl group concentration is preferably less than 0.10 equivalents / ton, more preferably less than 0.05 equivalents / ton, and most preferably 0 equivalents / ton of PBT can be obtained.

[0034] <Intrinsic viscosity> When the PBT of the present invention is used for compounds or injection molding, the intrinsic viscosity of the PBT of the present invention is usually preferably 0.6 to 1.3 dL / g. When the intrinsic viscosity is less than 0.6 dL / g, the mechanical strength of the obtained molded product becomes insufficient, and when it exceeds 1.3 dL / g, the melt viscosity becomes high, the fluidity deteriorates, and the moldability tends to deteriorate. The intrinsic viscosity of the PBT of the present invention is more preferably 0.65 to 1.26 dL / g, and even more preferably 0.7 to 1.2 dL / g.

[0035] Also, when the PBT of the present invention is used for extrusion applications such as films, sheets or filaments, the intrinsic viscosity of the PBT of the present invention is usually preferably 0.80 to 1.60 dL / g, more preferably 0.81 to 1.50 dL / g, still more preferably 0.82 to 1.55 dL / g, particularly preferably 0.84 to 1.50 dL / g, and especially preferably 0.85 to 1.35 dL / g. When the intrinsic viscosity is less than 0.80 dL / g, the extrusion moldability deteriorates, causing resin drawdown and molding loss, and the mechanical strength of the extruded molded product such as a film becomes insufficient, or the melt viscosity becomes low and the fluidity is too high, resulting in a tendency for the extrusion moldability to deteriorate. On the other hand, when the intrinsic viscosity exceeds 1.60 dL / g, the melt viscosity increases, the fluidity deteriorates, and the extrusion moldability tends to deteriorate.

[0036] The measurement of the intrinsic viscosity of the PBT of the present invention can be carried out by the method described in the Examples section below.

[0037] <Compound> The PBT of the present invention can be made into a compound product by adding various additives or compounding materials as required after the PBT production stage or after the PBT is manufactured.

[0038] [Manufacturing Method of PBT] The method for producing PBT of the present invention is not particularly limited, and any method can be used as long as it can produce PBT satisfying the above-mentioned succinic acid unit copolymerization amount, butyric acid unit copolymerization amount, terminal methoxy group concentration, and preferably further the above-mentioned terminal benzaldehyde group concentration. Preferably, in the method for producing PBT by reacting a dicarboxylic acid component mainly composed of dimethyl terephthalate and a diol component mainly composed of BDO according to the method for producing PBT of the present invention, BDO obtained by hydrogenating succinic acid or a succinic acid derivative obtained by a direct fermentation method or a fermentation method, such as succinic anhydride, dialkyl succinate (more specifically, dialkyl succinate having an alkyl group with 1 to 4 carbon atoms, preferably 1 to 3 carbon atoms, more preferably 1 to 2 carbon atoms, and most preferably a methyl group with 1 carbon atom), etc., is used to produce PBT of the present invention. This is preferable because the effects of the present invention can be obtained more effectively. According to this method, PBT can be produced that also satisfies the above-mentioned terminal methylphenyl group concentration, terminal acetyl group concentration, 1,4-pentanediol copolymerization amount, and 2-methyl-1,4-butanediol copolymerization amount.

[0039] There are no particular restrictions on the method for producing BDO by subjecting succinic acid or a succinic acid derivative obtained by a direct fermentation method or a fermentation method to a hydrogenation treatment, and a conventionally known method can be employed.

[0040] In the method for producing PBT of the present invention, dimethyl terephthalate is not limited to dimethyl terephthalate derived from petrochemicals, and dimethyl terephthalate produced by chemical recycling of polyester (chemically recycled dimethyl terephthalate) or dimethyl terephthalate produced using biomass resources (biomass-derived dimethyl terephthalate) can be used. That is, as the dimethyl terephthalate, it is possible to use dimethyl terephthalate synthesized by oxidation of para-xylene, a petrochemical product (terephthalic acid derived from petrochemicals), terephthalic acid derived from chemical recycling obtained by recovering waste polyester and depolymerizing the recovered polyester, dimethyl terephthalate produced by methyl esterifying biomass-derived terephthalic acid obtained using para-xylene produced from isobutanol or ethanol produced from plants such as corn and sugarcane, or dimethyl terephthalate directly produced by depolymerization of waste polyester. From the perspective of aiming for a sustainable society for the global environment and future generations, it is a preferred embodiment to use those produced by chemical recycling of polyesters such as polyethylene terephthalate or polybutylene terephthalate. In particular, like Production Examples 1 to 3 described in the Examples section below, dimethyl terephthalate directly produced by depolymerization of polyester is preferable because it can reduce the number of steps in the chemical recycling process.

[0041] In the present invention, dimethyl terephthalate can use dimethyl terephthalate derived therefrom, and two or more of these may be mixed and used.

[0042] The production format when producing the PBT of the present invention may be a continuous type or a batch type.

[0043] The PBT of the present invention can be produced by a conventional method. For example, the PBT of the present invention is produced through a process of heating a dicarboxylic acid component mainly composed of dimethyl terephthalate and a diol component mainly composed of BDO obtained by hydrogenating succinic acid or a succinic acid derivative obtained by a direct fermentation method or a fermentation method to cause a transesterification reaction to obtain a low-polymerized polyester (oligomer), and then gradually reducing the pressure of the obtained oligomer and heating it to cause a melt polycondensation reaction to obtain PBT.

[0044] Although the method for producing PBT of the present invention is not limited as described above, as an example, a method of producing through the following transesterification reaction step and polycondensation reaction step can be mentioned.

[0045] <Content of the compound represented by formula (1), formula (2) or formula (3) in BDO> In order to introduce butyric acid units into PBT in the present invention, as an example, BDO containing one or two compounds represented by the following formula (1) or formula (2) can be used.

[0046]

Chemical formula

[0047] The total content of one or two compounds represented by the above formula (1) or formula (2) in the raw material BDO in the present invention (hereinafter, may be referred to as "total content of compounds (1) to (2)") has a lower limit value of usually 50 ppm, preferably 500 ppm, more preferably 1500 ppm, and an upper limit value of usually 8000 ppm, preferably 5000 ppm, more preferably 2500 ppm. When the total content of compounds (1) to (2) is less than the above lower limit value, the color tone of the obtained PBT becomes bluer, which is not preferable. On the other hand, when the total content of compounds (1) to (2) exceeds the above upper limit value, the color tone of the obtained PBT becomes yellower, which is not preferable.

[0048] The content of the compound represented by the following formula (3) (compound (3)) in the raw material BDO in the present invention is preferably less than 1 ppm. When the content of compound (3) in the raw material BDO is 1 ppm or more, the hydrolysis resistance of the obtained PBT tends to deteriorate. Note that the content of compound (3) being less than 1 ppm corresponds to being below the detection limit in the analysis of 1,4-butanediol in the examples section described later.

[0049]

Chemical formula

[0050] <Content of the compounds represented by Formula (4) and Formula (5) in BDO> In order to introduce a succinic acid unit into PBT in the present invention, as an example, BDO containing one or two compounds represented by the following Formula (4) or Formula (5) can be used.

[0051]

Chemical formula

[0052] The total content of one or two compounds represented by Formula (4) or Formula (5) in the raw material BDO in the present invention (hereinafter, may be referred to as "total content of Compounds (4) to (5)") is usually 5 ppm, preferably 50 ppm, more preferably 150 ppm as its lower limit value, and usually 1000 ppm, preferably 600 ppm, more preferably 300 ppm as its upper limit value. When the total content of Compounds (4) to (5) is lower than the above lower limit value, the color tone of the obtained PBT becomes bluer, which is not preferable. On the other hand, when the total content of Compounds (4) to (5) exceeds the above upper limit value, the color tone of the obtained PBT becomes yellower, which is not preferable.

[0053] <Dicarboxylic acid component> The dicarboxylic acid component other than dimethyl terephthalate to be subjected to the transesterification reaction is not particularly limited. For example, dialkyl phthalate, dialkyl isophthalate, dialkyl terephthalate other than dimethyl terephthalate, dialkyl 4,4'-diphenyldicarboxylate, dialkyl 4,4'-diphenyletherdicarboxylate, dialkyl 4,4'-benzophenonedicarboxylate, dialkyl 4,4'-diphenoxyethanedicarboxylate, dialkyl 4,4'-diphenylsulfonedicarboxylate, aromatic dicarboxylic acid dialkyls such as 2,6-naphthalenedicarboxylic acid; alicyclic dicarboxylic acid dialkyls such as dialkyl 1,2-cyclohexanedicarboxylate, dialkyl 1,3-cyclohexanedicarboxylate, dialkyl 1,4-cyclohexanedicarboxylate; aliphatic dicarboxylic acid dialkyls such as dialkyl malonate, dialkyl succinate, dialkyl glutarate, dialkyl adipate, dialkyl pimelate, dialkyl suberate, dialkyl azelate, dialkyl sebacate, etc. can be mentioned.

[0054] The two alkyl groups of the above dialkyl dicarboxylate may be the same or different. Also, the alkyl group may be linear or cyclic, and in the case of linear, it may be straight-chain or branched. However, since the boiling point is low and the reaction rate is fast, the alkyl group is preferably linear, and more preferably straight-chain. The number of carbon atoms of the alkyl group is preferably 4 or less, more preferably 3 or less, particularly preferably 2 or less, and most preferably a methyl group having 1 carbon atom.

[0055] Examples of dialkyl dicarboxylates other than dimethyl terephthalate include dimethyl phthalate, dimethyl isophthalate, dimethyl 4,4'-diphenyldicarboxylate, dimethyl 4,4'-diphenyletherdicarboxylate, dimethyl 4,4'-benzophenonedicarboxylate, dimethyl 4,4'-diphenoxyethanedicarboxylate, dimethyl 4,4'-diphenylsulfonedicarboxylate, and dialkyl 2,6-naphthalenedicarboxylate, etc., which are aromatic dialkyl dicarboxylates; dimethyl 1,2-cyclohexanedicarboxylate, dimethyl 1,3-cyclohexanedicarboxylate, and dialkyl 1,4-cyclohexanedicarboxylate, etc., which are alicyclic dialkyl dicarboxylates; dimethyl malonate, dimethyl succinate, dimethyl glutarate, dimethyl adipate, dimethyl pimelate, dimethyl suberate, dimethyl azelate, dimethyl sebacate, etc., which are aliphatic dialkyl dicarboxylates.

[0056] As for these dicarboxylic acid components other than dimethyl terephthalate, only one kind may be used, or two or more kinds may be mixed and used.

[0057] From the viewpoint of more effectively obtaining the effects of the present invention, the proportion of dimethyl terephthalate in all the dicarboxylic acid components is 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 95 mol% or more, and may be 100 mol%.

[0058] <Diol component> The diol components other than BDO to be subjected to the transesterification reaction are not particularly limited. For example, aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, and dibutylene glycol; alicyclic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol; polyalkylene glycols such as xylylene glycol, polyethylene glycol, polytrimethylene glycol, and polytetramethylene ether glycol; aromatic diols such as 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone, etc. can be mentioned.

[0059] Regarding these diol components other than BDO, only one kind may be used, or two or more kinds may be mixed and used.

[0060] From the viewpoint of more effectively obtaining the effects of the present invention, the proportion of BDO in all the diol components is 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 95 mol% or more, and may be 100 mol%.

[0061] <Other monomers> In the production of PBT of the present invention, further, hydroxycarboxylic acids such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, and p-β-hydroxyethoxybenzoic acid, alkoxycarboxylic acids, monofunctional components such as stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, and benzoylbenzoic acid, trifunctional or higher polyfunctional components such as tricarballylic acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, trimethylolethane, trimethylolpropane, glycerol, and pentaerythritol, etc. can be used as one or more copolymerization components.

[0062] <Transesterification reaction> As an example of the process of subjecting a dicarboxylic acid component mainly composed of dimethyl terephthalate as a raw material and a diol component mainly composed of BDO to a transesterification reaction to obtain an oligomer, a single transesterification reaction tank or a multi-stage reactor in which a plurality of transesterification reaction tanks are connected in series is used, and methanol and excess diol components generated in the reaction are removed outside the system. While the transesterification reaction rate (the ratio of the total ester groups of the raw material dicarboxylic acid component that have undergone transesterification reaction by reacting with the diol component) usually reaches 90% or more, with or without using a catalyst, under normal pressure or reduced pressure, the transesterification reaction is carried out to obtain an oligomer. Usually, the temperature of the transesterification reaction is about 210 to 230 °C, and the reaction time is about 1 to 4 hours.

[0063] <Polycondensation reaction process> As an example of the polycondensation reaction process, a single melt polycondensation tank or a plurality of melt polycondensation tanks are connected in series. For example, a multi-stage reactor composed of a completely mixed reactor equipped with a stirring blade in the first stage and a horizontal plug flow reactor equipped with a stirring blade in the second and third stages is used. A method of distilling out the diol generated while heating under reduced pressure in the presence of a catalyst is mentioned. Usually, the temperature of the polycondensation reaction is 210 to 280 °C, preferably about 220 to 250 °C, and the pressure is in a reduced pressure state of 27 kPa or less, preferably 13 kPa or less. The reaction tank may be single or multi-stage, but in order to suppress coloring and deterioration and suppress the increase of end groups such as vinyl groups, it is preferably carried out under a high vacuum of usually 1.3 kPa or less, preferably 0.3 kPa or less, in at least one reaction tank.

[0064] The PBT obtained by the polycondensation reaction is usually withdrawn in the form of strands or sheets from the outlet provided at the bottom of the polycondensation reaction vessel, and then cut with a cutter into granular forms such as pellets or chips (for example, about 3 to 10 mm in length) while being cooled with water or after being cooled with water. Alternatively, the molten resin is discharged into cold water adjusted to a predetermined temperature through a pipe from the polycondensation reaction vessel and cut with a cutter to obtain spherical bodies (about 2 to 10 mm in diameter).

[0065] <Polycondensation catalyst> When polycondensing the oligomer obtained by the transesterification reaction between the diol component and the dicarboxylic acid component, a titanium compound is usually used as the catalyst, and preferably further a Group 2A metal compound of the periodic table is used.

[0066] These catalyst components may be used in the transesterification reaction and the polycondensation reaction may be carried out as they are, or may not be used in the transesterification reaction, or only the titanium catalyst may be used and the remaining catalyst components may be added in the polycondensation stage. Furthermore, in the transesterification reaction, a part of the finally used catalyst amount may be used and appropriately added as the polycondensation reaction proceeds. In any case, in the present invention, titanium and preferably a Group 2A metal of the periodic table are inevitably contained in the finally obtained PBT, and the amount thereof will be described later.

[0067] (Examples of titanium compounds) Specific examples of the titanium compound used as the catalyst include inorganic titanium compounds such as titanium oxide and titanium tetrachloride, titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, and titanium phenolates such as tetraphenyl titanate. These may be used alone or in combination of two or more. Among these, tetraalkyl titanates are preferred, and among them, tetrabutyl titanate is preferred.

[0068] (Amount of titanium catalyst) The content of the titanium catalyst in the PBT of the present invention is preferably 5 to 200 ppm in terms of the mass ratio of titanium atoms to PBT. This amount is more preferably 10 ppm or more, still more preferably 20 ppm or more, and most preferably 25 ppm or more. Also, this amount is more preferably 190 ppm or less, still more preferably 180 ppm or less, particularly preferably 160 ppm or less, especially preferably 150 ppm or less, and most preferably 140 ppm or less. When the content of titanium is too high, deterioration of color tone, hydrolysis resistance, solution haze, and an increase in fish eyes in the resulting molded product occur. When the content of titanium is too low, the polymerizability deteriorates.

[0069] (Examples of Group 2A metal compounds) Specific examples of the Group 2A metal compounds of the periodic table used as catalysts include various compounds of beryllium, magnesium, calcium, strontium, and barium. From the viewpoints of handling ease, availability, and catalytic effect, magnesium compounds and / or calcium compounds are preferred, and particularly, magnesium compounds with excellent catalytic effects are preferred. Specific examples of magnesium compounds include magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, magnesium hydrogen phosphate, etc. Specific examples of calcium compounds include calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide, calcium hydrogen phosphate, etc. These Group 2A metal compounds of the periodic table may be used alone or in combination of two or more. Among these, magnesium acetate is preferred.

[0070] (Amount of Group 2A metal catalyst) The content of the Group 2A metal catalyst in the polyester of the present invention is not particularly limited, but is preferably 3 to 150 ppm in terms of the mass ratio of the Group 2A metal atom to PBT. This amount is more preferably 5 ppm or more, still more preferably 10 ppm or more. Also, this amount is more preferably 140 ppm or less, still more preferably 130 ppm or less, particularly preferably 120 ppm or less, and most preferably 100 ppm or less. When the content of the Group 2A metal is too high, the color tone, hydrolysis resistance, etc. deteriorate, and when it is too low, the polymerizability deteriorates. When using the acetate of the Group 2A metal in the periodic table, since the acetic acid source enters the reaction system, the amount of the Group 2A metal in PBT is preferably 100 ppm or less.

[0071] (M / Ti ratio) The molar ratio of the titanium atom to the Group 2A metal atom (Group 2A metal / titanium) contained in the PBT of the present invention is usually 0.01 to 100, preferably 0.1 to 10, more preferably 0.3 to 3, and still more preferably 0.3 to 1.5.

[0072] (Metal analysis method) The metal content such as titanium atoms in PBT can be measured using methods such as atomic emission, atomic absorption, ICP emission, etc. after recovering the metal in PBT by methods such as wet ashing.

[0073] (Other catalysts) In the production of the polyester of the present invention, separate from the above-mentioned titanium compound and Group 2A metal compound, antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, phosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, phosphorus compounds such as their esters and metal salts, reaction aids such as sodium hydroxide and sodium benzoate may be used.

Examples

[0074] Hereinafter, the present invention will be described in more detail by way of Examples and Comparative Examples. However, the present invention is not limited to the following Examples as long as the gist thereof is not exceeded.

[0075] [Raw Materials and Reagents] As the dimethyl terephthalate, dimethyl terephthalate derived from petrochemicals manufactured by SK Chemical Co., Ltd. or chemical recycled dimethyl terephthalate manufactured in Production Examples 1 to 3 described below was used. As the tetrabutyl titanate, a reagent manufactured by Tokyo Chemical Industry Co., Ltd. was used. As the terephthalic acid, medium-purity terephthalic acid derived from petrochemicals manufactured by Toray Industries, Inc. was used. As the antioxidant, Adeka Stab (AO-60) manufactured by ADEKA Corporation was used.

[0076] [Measurement and Evaluation Methods] <Analysis of 1,4-Butanediol> Using BDO added with the compound represented by the formula (1), formula (2) or formula (3) and the compound represented by the formula (4) or formula (5) as a sample, the sample was dissolved in a deuterated chloroform solvent containing a small amount of tetramethylsilane, and using an AVANCE NEO spectrometer (manufactured by Bruker) 1 the 1H NMR spectrum was measured. The content (integral value) of the compound represented by the formula (1), formula (2) or formula (3) and the compound represented by the formula (4) or formula (5) with respect to the content (integral value) of BDO was determined. The reference for the chemical shift was set such that the signal of tetramethylsilane was 0.00 ppm. In the obtained spectrum, using the integral value of the signal of the proton (δ: 1.49 ppm) bonded to the α-position carbon of the hydroxy group of BDO as a reference, and using the integral value of the signal of the proton assigned to Table 1 below for each functional group, the weight of each functional group contained in the unit weight of BDO was determined. In addition, "×" in each structural formula in Table 1 indicates the proton used as a reference when calculating the concentration.

[0077] <Intrinsic Viscosity of Polybutylene Terephthalate> The viscosity was measured using a fully automatic viscosity measuring device (model DT553, capillary type) manufactured by Sentec Co., Ltd. in the following manner. A mixed solution of phenol and 1,1,2,2-tetrachloroethane (1 / 1 mass ratio mixture) was used as the solvent. The number of seconds it took for a 1.0 g / dL PBT sample solution and the solvent alone to fall at 30°C was measured and calculated using the following formula. Intrinsic viscosity (dL / g)=((1+4K H η sp ) 0.5 -1) / (2K H C) (However, η sp =η / η0-1, where η is the time it takes for the sample solution to fall, η0 is the time it takes for the solvent to fall, C is the PBT concentration of the sample solution (g / dL), and K H is Huggins' constant. K H The value used was 0.33.)

[0078] <Color tone of polybutylene terephthalate> The color tone of polybutylene terephthalate was evaluated using a color difference meter "Z-300A" manufactured by Nippon Denshoku Co., Ltd., using the L, a, b color system. The lower the b value, the less yellowish it is, and the more preferable it is. However, if the b value is lower than -2.0, the yellowish color is reduced, but the blue color increases, making the color tone unfavorable. The evaluation criteria for the b value are as follows: ◎ -1.0≦b value≦1.0 ○ -2.0≦b value<-1.0 or 1.0 <b値≦2.0 △ b value < -2.0 or 2.0 <b値≦2.5 × 2.5 <b値、又はb値<-2.5

[0079] <Quantitative determination of butyric acid unit content, succinic acid unit content, terminal methoxy group concentration, and terminal benzaldehyde concentration in polybutylene terephthalate> PBT was dissolved in a mixed solvent of deuterated chloroform / deuterated hexafluoroisopropanol / deuterated pyridine (volume ratio 21 / 9 / 1) containing a trace amount of tetramethylsilane, and the results were analyzed using an AVANCE NEO spectrometer (manufactured by Bruker). 1The 1H NMR spectrum was measured. The reference for chemical shift was set with the signal of tetramethylsilane as 0.00 ppm. In the obtained spectrum, based on the integrated value of the signal of the proton (δ: 8.11 ppm) of the phenyl group of the terephthalic acid unit, the equivalent amount of each functional group contained in 1 ton of PBT was determined using the integrated value of the signal of the proton assigned to each of the following Table 1 for each functional group. In addition, in each structural formula in Table 1, "×" indicates the proton used as a reference when calculating the concentration.

[0080]

Table 1

[0081] In the following examples, dimethyl terephthalate was used as the raw material dicarboxylic acid component, and BDO obtained by hydrogenating succinic acid or a succinic acid derivative as the raw material BDO was used. Therefore, the terminal methylphenyl group concentration, terminal acetyl group concentration, 1,4-pentanediol unit copolymerization amount, and 2-methyl-1,4-butanediol unit copolymerization amount of the produced PBT were all below the detection limit.

[0082] [Raw material 1,4-butanediol] 1,4-Butanediol (BDO) used as a raw material for producing PBT in the following examples and comparative examples is one of the BDO obtained by hydrogenating succinic acid or a succinic acid derivative obtained by the fermentation method and purified by distillation. However, in the production process, a certain amount of Compound (1), Compound (2), and Compound (3), and Compound (4) and Compound (5) may be contained respectively. On the other hand, in the BDO (allyl alcohol method BDO) obtained by hydrolyzing butadiene from naphtha after acetoxylation, Compound (1), Compound (2), Compound (3), Compound (4), and Compound (5) were not detected. Although these contents vary depending on the manufacturing method and conditions, in the following Examples and Comparative Examples, the BDOs of both were appropriately blended and used so that the contents of Compound (1), Compound (2), Compound (3), Compound (4), and Compound (5) would be the numerical values shown in Table 2 below.

[0083] [Production Example of Chemically Recycled Dimethyl Terephthalate] <Production Example 1: Chemically Recycled Dimethyl Terephthalate 1> Referencing the method described in JP-A-2001-151934, Chemically Recycled Dimethyl Terephthalate 1 was obtained as follows. Into a flask equipped with a fraction collector, stirrer, and thermometer, 100 parts by mass of waste fibers made of polyethylene terephthalate, 100 parts by mass of ethylene glycol, and 1.5 parts by mass of sodium carbonate were placed. This flask was immersed in an oil bath at 210°C and reacted for 10 hours while extracting light-boiling components to obtain a depolymerization reaction solution 1. The obtained depolymerization reaction solution 1 was hot-filtered through a glass filter to obtain filtrate 1. To the obtained filtrate 1, 200 parts by mass of methanol and 0.5 parts by mass of sodium carbonate were added, and the mixture was reacted at 65°C for 1 hour to obtain reaction solution 2. The obtained reaction solution 2 was placed in a vacuum distillation apparatus equipped with a fraction collector, Liebig condenser, stirrer, thermometer, and pressure controller. The distillation apparatus was immersed in an oil bath, and while observing the distillate, the temperature and pressure of the oil bath were controlled to obtain a fore-fraction, a main fraction, and a residue in the order of distillation. The obtained main fraction and xylene were placed in an eggplant flask, heated to form a homogeneous solution, and then cooled to room temperature for crystallization to obtain a slurry. The obtained slurry was filtered through a glass filter to obtain a cake. The obtained cake was placed in an eggplant flask and attached to an evaporator equipped with an oil bath, and xylene was distilled off from the cake under reduced pressure to obtain a white solid. A part of the obtained white solid was extracted and analyzed by gas chromatography, and the content of dimethyl terephthalate was 99% by mass or more.

[0084] <Production Example 2: Chemically Recycled Dimethyl Terephthalate 2> Referencing the method described in Japanese Patent Application Laid-Open No. 2004-323378, dimethyl terephthalate for chemical recycling 2 was obtained as follows. Into an autoclave equipped with a stirrer and a thermometer, 100 parts by mass of waste fibers made of polyethylene terephthalate, 300 parts by mass of methanol, and 1.5 parts by mass of sodium carbonate were added. This autoclave was immersed in an oil bath at 150 °C and reacted at 1.3 MPa for 10 hours. Then, a distillation tube was attached to the autoclave, the pressure was slowly reduced to normal pressure, and the light-boiling components were distilled off to obtain a depolymerization reaction solution 1. After the temperature of the obtained depolymerization reaction solution 1 was lowered to room temperature, xylene was added, and it was immersed in an oil bath at 120 °C to obtain slurry 1. The obtained slurry 1 was filtered through a glass filter, cooled to room temperature for crystallization to obtain slurry 2. The obtained slurry 2 was subjected to solid-liquid separation by a centrifuge to obtain a cake. The obtained cake was placed in a flask equipped with a fraction collector, a stirrer, and a thermometer, and then immersed in an oil bath. While observing the distillate, the temperature and pressure of the oil bath were controlled, and from the order of distillation, a first fraction, a main fraction, and a residue were obtained. When a part of the obtained main fraction was taken out and analyzed by gas chromatography, the content of dimethyl terephthalate was 99% by mass or more.

[0085] <Production Example 3: Dimethyl Terephthalate for Chemical Recycling 3> Referencing the method described in Japanese Patent Application Laid-Open No. 2001-151934, dimethyl terephthalate for chemical recycling 3 was obtained as follows. A 100 parts by mass of polybutylene terephthalate containing a glass filler and 200 parts by mass of methanol were placed in an autoclave equipped with a stirrer and a thermometer. This autoclave was immersed in an oil bath at 170 °C and reacted at 5.5 MPa for 5 hours. Then, the autoclave was taken out of the oil bath and cooled to room temperature to obtain a depolymerization reaction solution 1. The obtained depolymerization reaction solution 1 was filtered through a glass filter to obtain a solid content. Tetrahydrofuran was added to the obtained solid content to dissolve the white solid contained in the solid content, and the glass filler was removed as a filtrate by filtration to obtain a solution 1. After the obtained solution 1 was placed in a flask equipped with a fraction collector, a stirrer, and a thermometer, it was immersed in an oil bath. While observing the distillate, the temperature and pressure of the oil bath were controlled to obtain a low-boiling component containing tetrahydrofuran, a first fraction, a main fraction, and a residue in the order of distillation. When a part of the obtained main fraction was taken out and analyzed by gas chromatography, the content of dimethyl terephthalate was 99% by mass or more.

[0086] [Example 1] [Transesterification reaction] 132 parts by mass of dimethyl terephthalate derived from petrochemicals manufactured by SK Chemical Co., Ltd. and 75 parts by mass of BDO having the contents of the compounds (1), (2), (3), (4) and (5) shown in Table 2 were supplied to a glass reaction vessel equipped with a stirrer and a distillation tube. The glass reaction vessel was depressurized to about 100 Pa, and then the operation of repressurizing to atmospheric pressure with nitrogen was repeated 3 times to replace the inside of the reaction vessel with nitrogen. Then, the reaction vessel was immersed in an oil bath at 150 °C. After confirming the dissolution of the contents, the rotation speed was set to 150 revolutions per minute. Subsequently, a butanediol mixture containing 94% by mass of BDO and 6% by mass of tetrabutyl titanate having the contents of the compounds (1), (2), (3), (4) and (5) shown in Table 2 was supplied so as to be 33 ppm by mass as titanium atoms with respect to the resulting polybutylene terephthalate. Then, the temperature of the oil bath was raised from 150 °C to 210 °C over 105 minutes to obtain a transesterification reaction solution. 44 parts by mass of a fraction was obtained in the receiver at the tip of the distillation tube. The transesterification reaction time from the addition of the BDO solution of tetrabutyl titanate until 44 parts by mass of the fraction was obtained was 210 minutes.

[0087] <Polycondensation reaction> To the obtained transesterification reaction solution, a butanediol mixture containing 70% by mass of BDO, 10% by mass of magnesium acetate tetrahydrate, and 20% by mass of water, which are the contents of compound (1), compound (2), compound (3), compound (4), and compound (5) shown in Table 2, was supplied so that the magnesium atom content was 48 ppm by mass with respect to the obtained polybutylene terephthalate. Further, a butanediol mixture containing 94% by mass of BDO and 6% by mass of AO-60, which are the contents of compound (1), compound (2), compound (3), compound (4), and compound (5) shown in Table 2, was supplied so that the AO-60 content was 530 ppm by mass with respect to the obtained polybutylene terephthalate. Furthermore, a butanediol mixture containing 94% by mass of BDO and 6% by mass of tetrabutyl titanate, which are the contents of compound (1), compound (2), compound (3), compound (4), and compound (5) shown in Table 2, was supplied so that the titanium atom content was 61 ppm by mass with respect to the obtained polybutylene terephthalate. The temperature of the oil bath was raised from 210°C to 240°C over 45 minutes, and the internal pressure of the glass reaction vessel was reduced from 101 KPa to 133 Pa over 85 minutes to conduct the polycondensation reaction. Subsequently, the internal pressure was set to full vacuum, and when the stirrer of the reaction vessel reached a predetermined stirring power, the polymerization reaction was terminated. The polycondensation reaction time from the start of pressure reduction until the stirrer was stopped was 178 minutes.

[0088] Next, after the reaction vessel was repressurized to 101 KPa with nitrogen, the pressure was increased to a predetermined pressure, and polybutylene terephthalate was extracted in a strand form from the bottom of the reaction vessel to obtain strand-shaped polybutylene terephthalate. Thereafter, using a rotary cutter, the strand was pelletized to obtain pellet-shaped polybutylene terephthalate.

[0089] The intrinsic viscosity of the obtained pellet-shaped polybutylene terephthalate was 0.988 dL / g. Regarding the color tone, the L value was 84.5, the a value was -1.0, the b value was -0.8, and the evaluation of the b value was ◎. When the NMR of the obtained polybutylene terephthalate was measured, the copolymerization amount of the butyric acid unit was 0.008 mol%, the copolymerization amount of the succinic acid unit was 0.011 mol%, the terminal methoxy group concentration was 0.20 eq / ton, and the terminal benzaldehyde group concentration was 0.04 eq / ton.

[0090] [Examples 2 to 7, Comparative Examples 1 and 2] In Example 1, the procedure was the same as in Example 1 except that dimethyl terephthalate shown in Table 2 and BDO having the contents of the compounds (1), (2), (3), (4) and (5) shown in Table 2 were used.

[0091] [Comparative Example 3] A slurry obtained by mixing 75.44 parts by mass of petrochemical-derived medium-purity terephthalic acid manufactured by Toray Industries, Inc. and 122.77 parts by mass of BDO having the contents of the compounds (1), (2), (3), (4) and (5) shown in Table 2 was charged into an esterification reaction tank set at 150°C in advance. Subsequently, a butanediol mixture containing 94% by mass of BDO having the contents of the compounds (1), (2), (③), (4) and (5) shown in Table 2 and 6% by mass of tetrabutyl titanate was supplied so as to be 38 ppm by mass as titanium atoms with respect to the obtained polybutylene terephthalate. The temperature in the tank was raised from 150°C to 210°C over 90 minutes and then held at 210°C for 60 minutes. During this period, the esterification reaction was advanced while removing the by-produced water in the rectification column. When the distilled by-produced water reached 41 parts by mass, the esterification reaction was terminated. The esterification reaction time in Table 2 was defined as the time from the start of the temperature increase in the tank to the point when the distilled water reached 21 parts by mass.

[0092] Subsequently, the entire amount of the oligomer obtained was transferred through a pipe from the lower part of the esterification reaction tank to a polycondensation reaction tank set at 210°C in advance. A butanediol mixture containing 70% by mass of BDO, 10% by mass of magnesium acetate tetrahydrate, and 20% by mass of water, which would result in the contents of compound (1), compound (2), compound (3), compound (4), and compound (5) shown in Table 2, was supplied so that the magnesium atom content was 12 ppm by mass based on the resulting polybutylene terephthalate. While stirring, the temperature inside the tank was raised from 210°C to 240°C over 45 minutes, and the pressure was gradually reduced from normal pressure to 67 Pa over 90 minutes. Then, 240°C and 67 Pa were maintained. When a predetermined torque was reached, the stirrer was stopped and the pressure was restored. After that, the resin was extruded in a strand shape from the lower part of the polycondensation reaction tank through a die head, cooled with a water-flow type slider, and cut into PBT pellets (major axis: about 3 mm, minor axis: about 2 mm, length: about 4 mm) with a rotary cutter. Note that the polycondensation time described in Table 2 represents the time from when the temperature inside the tank was raised to when a predetermined torque was reached, with the starting point being set to zero.

[0093] In Examples 1 to 7 and Comparative Examples 1 to 3, the transesterification reaction time (or esterification reaction time) and polycondensation reaction time, as well as the evaluation of the terminal methoxy group concentration, copolymerization amount of butyric acid units, copolymerization amount of succinic acid units, terminal benzaldehyde group concentration, intrinsic viscosity, L value, a value, and b value of the obtained polybutylene terephthalate, were summarized in Table 2. In Table 2 below, "derived from petrochemicals" is abbreviated as "derived from petrochemicals", and dimethyl terephthalate for chemical recycling is described as "CR-DMT".

[0094]

Table 2

[0095] From Table 2, it can be seen that when the copolymerization amount of butyric acid units in polybutylene terephthalate is 0.001 to 0.020 mol%, the copolymerization amount of succinic acid units is 0.001 to 0.027 mol%, and the terminal methoxy group concentration is 0.03 to 6.0 equivalents / ton, the evaluation of the b value is ◎, and the polybutylene terephthalate has a good color tone with less yellowness and blueness. In addition, such polybutylene terephthalate with a good color tone can be produced by reacting a dicarboxylic acid component mainly composed of dimethyl terephthalate with a diol component to produce polybutylene terephthalate. As the diol component, the total content of compounds (1) to (2) and the total content of compounds (4) to (5) are within a specific range, and preferably 1,4-butanediol containing no compound (3) is used. This effect can be similarly effectively exerted when using dimethyl terephthalate derived from chemical recycling as the raw material dimethyl terephthalate, not limited to dimethyl terephthalate derived from petrochemicals.

Claims

1. A polybutylene terephthalate containing 0.001 to 0.020 mol% of butyric acid units and 0.001 to 0.027 mol% of succinic acid units as copolymerization components, and having a terminal methoxy group concentration of 0.03 to 6.0 equivalents / ton.

2. The polybutylene terephthalate according to claim 1, having a terminal benzaldehyde group concentration of 0.01 to 0.50 equivalents / ton.

3. The polybutylene terephthalate according to claim 1 or 2, wherein the terminal methylphenyl group concentration is less than 0.30 equivalents / ton, the terminal acetyl group concentration is less than 0.10 equivalents / ton, the copolymerization amount of 1,4-pentanediol units is less than 0.006 mol%, and the copolymerization amount of 2-methyl-1,4-butanediol units is less than 0.020 mol%.

4. In a method for producing polybutylene terephthalate by reacting a dicarboxylic acid component mainly composed of dimethyl terephthalate with a diol component, the diol component contains a total of 50 to 8000 ppm of one or two compounds represented by the following formula (1) or formula (2), and a total of 5 to 1000 ppm of one or two compounds represented by the following formula (4) or formula (5). The method for producing polybutylene terephthalate is characterized by using 1,4-butanediol. 【Chemical 1】

5. The method for producing polybutylene terephthalate according to claim 4, wherein the 1,4-butanediol used is 1,4-butanediol obtained by hydrogenating succinic acid or a succinic acid derivative.

6. The method for producing polybutylene terephthalate according to claim 4 or 5, wherein the content of the compound represented by the following formula (3) in the 1,4-butanediol is less than 1 ppm. 【Chemical Formula 2】

7. The method for producing polybutylene terephthalate according to claim 4 or 5, wherein the dimethyl terephthalate used is dimethyl terephthalate produced by chemical recycling of polyester or dimethyl terephthalate produced using biomass resources.

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