JP7563531B2 - Polybutylene terephthalate and its manufacturing method - Google Patents

Description

The present invention relates to polybutylene terephthalate (hereinafter sometimes abbreviated as "PBT"), and more particularly to PBT which has a favorable polymer color tone and generates little acetic acid when heated, and a method for producing the same.
The present invention also relates to a PBT composition using this PBT, which can be suitably used for electric/electronic parts, automobile parts, etc., a method for producing the same, and a molded article and a method for producing the same.

PBT, which uses terephthalic acid (hereinafter sometimes abbreviated as "TPA") as the main dicarboxylic acid component and 1,4-butanediol (hereinafter sometimes abbreviated as "BDO") as the main diol component, has excellent mechanical properties, heat resistance, moldability and recyclability, and has high mechanical strength and excellent chemical resistance, so it is widely used as a material for industrial molded products such as connectors, relays and switches for automobiles and electrical and electronic devices. It is also widely used in films, sheets, fibers (filaments), etc., and as a result, there is a demand for high-quality PBT and a manufacturing method for it.

Methods for producing 1,4-butanediol, the raw material of PBT, include the butadiene process, which uses butadiene as the raw material, and the Reppe process, which reacts acetylene with formaldehyde.
However, BDO produced by any of these methods contains impurities specific to each method, and these impurities can cause problems such as deterioration in the color of the resulting PBT and corrosion of the equipment.

In particular, PBT using BDO produced by the butadiene process has residual terminal acetyl groups, which cause the problem of generating acetic acid due to the heat generated during kneading and molding. In addition, problems due to acetic acid occur in the recovery process of tetrahydrofuran (hereinafter sometimes abbreviated as "THF"), a by-product produced during the production of PBT. Problems due to acetic acid here are similar to problems due to terminal acetyl groups resulting from acetic acid mixed in terephthalic acid, which will be described later, and include, for example, the need for distillation equipment made of high-quality materials that can withstand acetic acid and the need for neutralization equipment to neutralize the acetic acid in the wastewater after THF recovery.

Although BDO produced by the Reppe process does not have such a problem, it still has the problem of deterioration in color tone of the resulting PBT due to specific impurities.
For example, Patent Document 1 discloses a method for producing polybutylene terephthalate by esterifying and polycondensing a glycol mainly composed of 1,4-butylene glycol (=BDO) containing 2-(4'-hydroxybutoxy)tetrahydrofuran and a dicarboxylic acid mainly composed of terephthalic acid (=TPA) containing acetic acid, but does not disclose any features or problems of the present invention.

Furthermore, in PBT produced by the esterification reaction of terephthalic acid and BDO, terminal acetyl groups are formed due to acetic acid mixed in terephthalic acid. These terminal groups are hydrolyzed by heat during kneading or molding, for example, to generate acetic acid. The generated acetic acid causes deterioration of metal polymerization equipment, molding equipment, vacuum-related equipment, and the like.
Similarly, when the PBT is molded into a product, the terminal acetyl group of the PBT generates acetic acid through thermal decomposition and hydrolysis. When the PBT is used for electrical and electronic components, the generated acetic acid corrodes metal contacts and causes malfunctions.

For these reasons, there is a demand for PBT that has excellent color tone and suppresses the generation of acetic acid.

JP 2001-48968 A

The object of the present invention is to provide PBT and its manufacturing method, which has a favorable polymer color tone, i.e., has little yellow or blue tinge and generates little acetic acid when heated, a PBT composition containing this PBT and its manufacturing method, and a molded article using this PBT composition and its manufacturing method.

As a result of intensive research by the present inventors to solve the above problems, it was discovered that these problems could be solved by using PBT having specific amounts of terminal acetyl groups, terminal butyraldehyde groups, and structural units derived from 2-methyl-1,4-butanediol (hereinafter sometimes abbreviated as "2Me1,4-BDO"), and this led to the completion of the present invention. This can be achieved to a higher degree by using PBT having specific amounts of terminal benzaldehyde groups and terminal methylphenyl groups at the same time. The inventors have found that this can be achieved by using 1,4-butanediol containing specific amounts of 2Me1,4-BDO and 2-(4-hydroxybutyloxy)tetrahydrofuran (hereinafter, sometimes abbreviated as "BGTF") as the diol raw material for PBT, and further, that this can be achieved to a higher degree by using terephthalic acid containing specific amounts of 4-carboxybenzaldehyde (hereinafter, sometimes abbreviated as "4CBA") and p-toluic acid (hereinafter, sometimes abbreviated as "p-TA") as the dicarboxylic acid raw material.
The present invention was completed based on these findings, and the gist of the present invention is as follows.

[1] The terminal acetyl group concentration is less than 0.1 equivalents/ton, and the terminal butyl aldehyde group concentration is 0.05 to 0.13 equivalents/ton;
A polybutylene terephthalate characterized in that a ratio of structural units derived from 2-methyl-1,4-butanediol (hereinafter, sometimes referred to as "2-methyl-1,4-butanediol") to all structural units derived from a diol component is 0.020 to 0.080 mol %.

[2] Polybutylene terephthalate according to [1], characterized in that the terminal benzaldehyde group concentration is 0.03 to 0.07 equivalents/ton and the terminal methylphenyl group concentration is 0.3 to 0.8 equivalents/ton.

[3] A method for producing polybutylene terephthalate according to [1] or [2], characterized in that in the method for producing polybutylene terephthalate by reacting a terephthalic acid component with 1,4-butanediol, 1,4-butanediol containing 250 to 1000 ppm by mass of 2-methyl-1,4-butanediol and 10 to 1500 ppm by mass of 2-(4-hydroxybutyloxy)tetrahydrofuran is used as the 1,4-butanediol.

[4] The method for producing polybutylene terephthalate according to [3], characterized in that the molar consumption ratio of 1,4-butanediol to terephthalic acid components is 1.15 or more and less than 2.00, and polybutylene terephthalate containing 35 to 90 ppm of Ti is produced.

[5] The method for producing polybutylene terephthalate according to [3] or [4], characterized in that the terephthalic acid component used is terephthalic acid having a 4-carboxybenzaldehyde content of 5 to 25 ppm and a p-toluic acid content of 85 to 185 ppm.

[6] A polybutylene terephthalate composition comprising the polybutylene terephthalate described in [1] or [2] and an additive.

[7] A method for producing the polybutylene terephthalate composition described in [6], characterized in that the polybutylene terephthalate and additives are kneaded using an extruder at a kneading resin temperature of 320°C or less.

[8] A molded article made of the polybutylene terephthalate composition described in [6].

[9] A method for producing a molded article according to [8], characterized in that the polybutylene terephthalate composition is molded using a molding machine at a molten resin temperature of 280°C or less.

The PBT of the present invention has a favorable polymer color tone, i.e., it is less yellowish or blueish, and generates little acetic acid when heated, so the compound and molded products obtained using it have good color tone and high commercial value, and generate little acetic acid, which corrodes metals. Therefore, the molded products obtained can be used for various purposes, such as electrical and electronic parts, automobile parts, films, sheets, filaments, etc.

The present invention will be described in detail below. However, the following explanations of the constituent elements are representative examples of the embodiments of the present invention, and the present invention is not limited to these contents.
In the present invention, the "main component" of the dicarboxylic acid component refers to a component that is contained in the dicarboxylic acid component in an amount of 50 mol % or more. The same applies to the "main component" of the diol component.
Further, the structural unit derived from 2-methyl-1,4-butanediol refers to a structural unit derived from 2-methyl-1,4-butanediol used as a raw material for producing PBT and incorporated into PBT. Hereinafter, the "structural unit derived from 2-methyl-1,4-butanediol" may be simply referred to as a "2-methyl-1,4-butanediol unit."
Additionally, "ppm" refers to "ppm by mass."

<PBT>
(Dicarboxylic acid component, diol component, copolymer component)
In the present invention, PBT refers to a polymer having a structure in which a terephthalic acid component and a 1,4-butanediol (BDO) component are ester-bonded, in which 50 mol % or more of the dicarboxylic acid component is composed of a terephthalic acid component, and 50 mol % or more of the diol component is composed 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, and particularly preferably 95 mol % or more, and the proportion of BDO in all diol components is preferably 70 mol % or more, more preferably 80 mol % or more, and even more preferably 95 mol % or more. If the terephthalic acid component or BDO is less than 50 mol %, the crystallization rate of PBT decreases, leading to deterioration of moldability.

The PBT of the present invention further incorporates 2-methyl-1,4-butanediol as a copolymerization component into the PBT, and contains a specified ratio of 2-methyl-1,4-butanediol units.

In the present invention, the dicarboxylic acid other than terephthalic acid is not particularly limited, and examples thereof include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid, alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid, and aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These dicarboxylic acid components other than terephthalic acid may be used alone or in combination of two or more.

In the present invention, the diol component other than BDO is not particularly limited, and examples thereof include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 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-cyclohexanedimethylol, and 1,4-cyclohexanedimethylol; and aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone.
As for these diol components other than BDO, one type may be used alone, or two or more types may be used in combination.

In the present invention, one or more of the following may be used as copolymerization components: hydroxycarboxylic acids such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, and p-β-hydroxyethoxybenzoic acid; monofunctional components such as alkoxycarboxylic acids, stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, and benzoylbenzoic acid; and polyfunctional components having three or more functional groups such as tricarballylic acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, trimethylolethane, trimethylolpropane, glycerol, and pentaerythritol.

(Amount of copolymerization of copolymerization components)
The PBT of the present invention is characterized in that the amount of 2-methyl-1,4-butanediol copolymerized, which is the ratio of 2-methyl-1,4-butanediol units to all structural units derived from the diol component, is 0.020 to 0.080 mol %.
When the amount of 2-methyl-1,4-butanediol copolymerized exceeds the upper limit of the above range, the physical properties of PBT, such as melting point, color tone, solution haze, and fish eyes of the obtained molded product, become unfavorable, and the object of the present invention cannot be achieved.
In order to make the amount of 2-methyl-1,4-butanediol copolymerized less than 0.020 mol %, it is necessary to use BDO produced by the butadiene process, and the resulting PBT has residual terminal acetyl groups, which causes the problem of the generation of acetic acid as described above.

The amount of 2-methyl-1,4-butanediol copolymerized in the copolymer PBT of the present invention is 0.020 mol% or more, and preferably 0.030 mol% or more. The upper limit of the amount of 2-methyl-1,4-butanediol copolymerized is 0.080 mol% or less, preferably 0.070 mol% or less, more preferably 0.060 mol% or less, and even more preferably 0.050 mol% or less.

The amount of 2-methyl-1,4-butanediol copolymerized in PBT can be determined by the method described in the Examples section below.

(End group of PBT)
The terminal acetyl group concentration of the PBT of the present invention is less than 0.1 equivalent/ton. If the terminal acetyl group concentration is less than 0.1 equivalent/ton, the generation of acetic acid during heating can be suppressed, and contact failure of electric and electronic parts can be prevented.

The terminal butyl aldehyde group concentration of the PBT of the present invention is 0.13 equivalents/ton or less. If the terminal butyl aldehyde group concentration is 0.13 equivalents/ton or less, the color tone of the PBT will be good. The lower limit of the terminal butyl aldehyde group concentration is usually 0.05 equivalents/ton, since the production of the terminal butyl aldehyde group is an unavoidable impurity in the manufacturing process of the raw material BDO. Therefore, the terminal butyl aldehyde group concentration of the PBT of the present invention is 0.05 to 0.13 equivalents/ton, preferably 0.07 to 0.12 equivalents/ton, and more preferably 0.08 to 0.11 equivalents/ton.

In addition, the terminal acetyl group of the PBT of the present invention is sometimes referred to as a terminal acetyl group derived from 1-acetoxy-4-hydroxybutane (hereinafter, sometimes abbreviated as "1,4-HAB") in the PBT raw material because of its production method, but it is specified by a measurement method described later and is not limited to being derived from 1,4-HAB.
In addition, the terminal butyl aldehyde group of the PBT of the present invention is sometimes referred to as a terminal aldehyde group derived from 4-hydroxybutanal in the PBT raw material because of its production method, but it is specified by a measurement method described later and is not limited to being derived from 4-hydroxybutanal.

When terminal benzaldehyde groups, for example terminal benzaldehyde groups derived from 4CBA resulting from relatively inexpensive terephthalic acid, are present in PBT, the color tone of the PBT tends to deteriorate, i.e., the yellowish or blueish tinge tends to become stronger; however, when a specific amount of terminal methylphenyl groups, for example terminal methyl groups derived from p-toluic acid, are present, such color defects tend to be reduced, although the reason for this is unclear. The effect of the presence of specific amounts of terminal benzaldehyde groups and terminal methylphenyl groups in PBT to suppress the appearance of such yellowish or blueish tinges is an effect that has not been previously discovered.

The terminal benzaldehyde group concentration of the PBT of the present invention is preferably 0.03 to 0.07 equivalents/ton, more preferably 0.04 to 0.07 equivalents/ton, and even more preferably 0.05 to 0.06 equivalents/ton. The terminal methylphenyl group concentration of the PBT of the present invention is preferably 0.3 to 0.8 equivalents/ton, more preferably 0.4 to 0.7 equivalents/ton, and even more preferably 0.5 to 0.6 equivalents/ton.

The terminal benzaldehyde group of the PBT of the present invention is sometimes referred to as a terminal aldehyde group derived from 4CBA in the PBT raw material because of its manufacturing method, but it is identified by the measurement method described below and is not limited to being derived from 4CBA. Similarly, the terminal methylphenyl group of the PBT of the present invention is sometimes referred to as a terminal methyl group derived from p-toluic acid in the PBT raw material because of its manufacturing method, but it is identified by the measurement method described below and is not limited to being derived from p-toluic acid.

The terminal carboxyl group concentration of the PBT of the present invention is usually 0.1 to 50 equivalents/ton, preferably 1 to 40 equivalents/ton, more preferably 5 to 30 equivalents/ton, particularly preferably 7 to 25 equivalents/ton, and most preferably 10 to 19 equivalents/ton. If the terminal carboxyl group concentration is too high, hydrolysis resistance may deteriorate. In order to make this value less than 0.1 equivalents/ton, it is necessary to adopt economically disadvantageous conditions, such as an extremely small production scale, which is not realistic.

The terminal hydroxyl group concentration of the PBT of the present invention is usually 43 to 120 equivalents/ton, preferably 50 to 110 equivalents/ton, more preferably 55 to 100 equivalents/ton, and particularly preferably 60 to 90 equivalents/ton. If the terminal hydroxyl group concentration is too high, a large amount of THF will be generated due to decomposition of the terminal hydroxyl groups during melting such as molding. For example, THF will be generated during molding, and the molded product will have a poor appearance due to THF, such as silver, which is not preferable. If the terminal hydroxyl group concentration is equal to or higher than the above lower limit, PBT can be easily manufactured.

The terminal vinyl group concentration of the PBT of the present invention is usually 0.1 to 13 equivalents/ton, preferably 0.5 to 12 equivalents/ton, and more preferably 1 to 11 equivalents/ton. If the terminal vinyl group concentration is too high, it will cause deterioration in color tone. The terminal vinyl group concentration tends to increase further due to the thermal history during molding, so if the molding temperature is high or if the manufacturing method includes a recycling process, the color tone will deteriorate even more significantly. If the terminal vinyl group concentration is equal to or higher than the above lower limit, PBT can be easily manufactured.

The terminal acetyl group concentration, terminal butylaldehyde group concentration, terminal benzaldehyde group concentration, terminal methylphenyl group concentration, terminal carboxyl group concentration, terminal hydroxyl group concentration, and terminal vinyl group concentration of PBT can be determined by the method described in the Examples section below.

(Cobalt/Manganese content)
The PBT of the present invention may contain cobalt and manganese derived from the catalyst used in the production of terephthalic acid. From the viewpoint of color tone and thermal stability, the amount of cobalt and manganese in the PBT of the present invention is preferably 0.20 ppm or less, more preferably 0.15 ppm or less. Each of these values is more preferably 0.10 ppm or less, particularly preferably 0.07 ppm or less, and most preferably 0.05 ppm or less. Incidentally, the presence of 0.01 ppm of cobalt and manganese does not substantially cause any problems.

<Method of manufacturing PBT>
In terms of ease of obtaining the PBT of the present invention, it is preferable to use 1,4-butanediol (BDO) described below as a diol component in the method for producing the PBT of the present invention. For example, PBT can be produced through a process in which a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of BDO are mixed under stirring in a predetermined ratio to obtain a raw material slurry, followed by a process in which the raw material slurry is heated under normal or reduced pressure to cause an esterification reaction to obtain a PBT low polymer (oligomer), followed by a melt polycondensation process in which the obtained oligomer is gradually reduced in pressure and heated to cause a melt polycondensation reaction to obtain PBT.

An example of the process for producing oligomers is a method in which an esterification reaction is carried out using a single esterification reaction tank or a multi-stage reaction apparatus in which multiple esterification reaction tanks are connected in series, with or without a catalyst, under normal or reduced pressure, while removing water produced in the reaction and excess diol components from the system, until the esterification reaction rate (the proportion of all carboxyl groups in the raw dicarboxylic acid components that have reacted with the diol components and been esterified) reaches 90% or more.

In general, the temperature of the esterification reaction is preferably 212 to 233° C., more preferably 220 to 230° C., and even more preferably 223 to 228° C. If the esterification reaction temperature is low, the esterification reaction tends to be delayed, whereas if the esterification reaction temperature is high, the amount of THF increases, and the molar consumption ratio of the raw material tends to increase.
The pressure for the esterification reaction is preferably about 10 to 133 kPa, and the residence time is preferably about 1 to 4 hours.

An example of the melt polycondensation process is a method in which a single melt polycondensation tank or multiple melt polycondensation tanks are connected in series, and a multi-stage reaction apparatus is used, for example, with the first stage being a complete mixing type reactor equipped with an agitator, and the second and third stages being horizontal plug-flow type reactors equipped with agitators, in which the diol produced is distilled out of the system while being heated under reduced pressure in the presence of a catalyst.

The polycondensation reaction is usually carried out at a temperature of 210 to 280°C, preferably about 220 to 250°C, under reduced pressure of 27 kPa or less, preferably 13 kPa or less. The reaction tank may be a single tank or multiple tanks, but in order to prevent discoloration and deterioration and to suppress an increase in terminal groups such as vinyl groups, it is recommended that at least one reaction tank be carried out under a high vacuum of usually 1.3 kPa or less, preferably 0.3 kPa or less. To increase the reaction rate, it is recommended to adopt conditions such as increasing the degree of reduced pressure, accelerating the rate of temperature rise, and increasing the rate of renewal of the reaction liquid surface.

The PBT obtained by the polycondensation reaction is usually extracted in the form of a strand or sheet from an outlet provided at the bottom of the polycondensation reaction tank, and then cut with a cutter while being cooled with water or after being cooled with water to form pellets, chips, or other granular material (e.g., about 3 to 10 mm in length).

(Raw material 1,4-butanediol (BDO))
As the BDO which is the main component of the diol component for producing the PBT of the present invention, the BDO obtained by the following Reppe process is preferably used.
Acetylene and formaldehyde are reacted to produce 1,4-butynediol, which is then hydrogenated to produce 1,4-butenediol. The resulting 1,4-butenediol is then hydrogenated to produce BDO (BDO composition). In the purification process, this BDO composition can be further purified by precision distillation according to the required quality of the BDO product.

For the BDO used as the raw material for the PBT of the present invention, the content of 2-methyl-1,4-butanediol and 2-(4-hydroxybutyloxy)tetrahydrofuran is adjusted by strengthening precision distillation or blending.

The 2-methyl-1,4-butanediol content in the raw material BDO used in the production of the PBT of the present invention is usually 250 to 1000 ppm by mass, preferably 300 to 800 ppm by mass, and more preferably 350 to 700 ppm by mass.
In the esterification reaction, a portion of 2Me1,4-BDO reacts and is incorporated into oligomers, and a portion of the 2Me1,4-BDO is cyclized by dehydration during the esterification reaction to become 3-methyltetrahydrofuran (hereinafter, sometimes abbreviated as "3MTHF"), which is distilled out of the system as an esterification distillate.
If the 2Me1,4-BDO content in the raw material BDO exceeds the upper limit, the amount of 2Me1,4-BDO copolymerized increases, which is undesirable since it lowers the melting point of the resulting PBT, deteriorates the color tone b value, deteriorates the solution haze, and increases the number of fish eyes in the resulting molded product.Furthermore, 2Me1,4-BDO undergoes dehydration and cyclization, which increases the amount of 3M THF distilled off in the esterification reaction, making it difficult to separate it from THF by distillation, which is undesirable from the viewpoint of purifying and recovering THF.
On the other hand, BDO having a 2Me1,4-BDO content less than the above lower limit is BDO produced by the butadiene process, and the resulting PBT has residual terminal acetyl groups, which causes problems due to the generation of acetic acid, as described above.

In addition, 2-(4-hydroxybutyloxy)tetrahydrofuran (hereinafter sometimes abbreviated as "BGTF") in the raw material BDO generates 2-hydroxytetrahydrofuran by hydrolysis, which becomes 4-hydroxybutanal through an acetal reaction during the esterification reaction and is incorporated into PBT. If the BGTF content in the raw material BDO is too high, the resulting PBT will have a high terminal butyl aldehyde content and an undesirable color tone. The upper limit of the BGTF content in the raw material BDO is 1500 ppm by mass or less, preferably 1200 ppm by mass or less, and more preferably 950 ppm by mass or less, and the lower limit is 10 ppm by mass or more, preferably 100 ppm by mass or more, more preferably 150 ppm by mass or more, and even more preferably 500 ppm by mass or more.

(Raw material terephthalic acid (TPA))
The raw material dicarboxylic acid component for obtaining the PBT of the present invention is not particularly limited, and a commonly known terephthalic acid can be used. Preferably, terephthalic acid containing specific amounts of 4CBA and p-toluic acid is used. That is, terephthalic acid having a 4CBA content of 5 to 25 ppm, preferably 6 to 20 ppm, and a p-toluic acid content of 85 to 185 ppm, preferably 105 to 180 ppm, more preferably 142 to 175 ppm is used. When the contents of 4CBA and p-toluic acid are out of the above ranges, the obtained PBT tends to have a stronger yellowish or bluish tinge.

In addition, the raw material terephthalic acid preferably has an acetic acid content of 200 ppm or less, more preferably 150 ppm or less, and even more preferably 130 ppm or less. When PBT is produced using terephthalic acid having an acetic acid content of the above upper limit or less, the amount of acetic acid generated from the produced PBT is reduced, which is preferable. The lower limit of the acetic acid content of the raw material terephthalic acid is usually preferably less than about 10 ppm.
Terephthalic acid having the above-mentioned contents of 4CBA, p-toluic acid, and further acetic acid can be obtained by adjusting the purification conditions in the production process of terephthalic acid.

The raw material terephthalic acid used in the production of the PBT of the present invention may contain cobalt and manganese, which are residual catalysts during the production of terephthalic acid. From the viewpoint of the color tone and thermal stability of the resulting PBT, the amount of cobalt and manganese in the raw material terephthalic acid is preferably 0.20 ppm or less, more preferably 0.15 ppm or less, even more preferably 0.10 ppm or less, and most preferably 0.07 ppm or less. The presence of 0.01 ppm each of cobalt and manganese in terephthalic acid does not substantially impair the product.

(Polycondensation catalyst)
When the oligomer obtained by the esterification reaction between the diol component and the dicarboxylic acid component is polycondensed, a titanium compound and preferably a compound of a metal of Group 2A of the Periodic Table are usually used as a catalyst.
These catalyst components may be used in the esterification reaction and then the polycondensation reaction may be carried out as is, or may not be used in the esterification reaction, or may be used only with the titanium catalyst and the remaining catalyst components added at the polycondensation stage. Furthermore, a part of the catalyst amount finally used may be used in the esterification reaction and then appropriately added as the polycondensation reaction proceeds. In any case, in the present invention, titanium and preferably a metal of Group 2A of the Periodic Table are inevitably contained in the PBT finally obtained, and the amount thereof will be described later.

Specific examples of titanium compounds 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, etc. These may be used alone or in combination of two or more.
Of these, tetraalkyl titanates are preferred, and of these, tetrabutyl titanate is preferred.

In order to adjust the terminal acetyl concentration, terminal butyl aldehyde concentration, and amount of 2-methyl-1,4-butanediol copolymerization of the resulting PBT to the ranges specified by the present invention, the content of the titanium (Ti) catalyst is preferably 35 to 90 ppm by mass ratio of titanium (Ti) atoms to PBT. The Ti content of PBT is more preferably 45 to 69 ppm, and even more preferably 52 to 68 ppm. If the Ti content is higher than this range, the amount of 2-methyl-1,4-butanediol and terminal butyl aldehyde copolymerized increases, the melting point decreases, and the color tone becomes undesirable. Furthermore, if the Ti content is too high, the hydrolysis resistance and solution haze of the resulting PBT deteriorate, and the number of fish eyes in the resulting molded product increases. On the other hand, if the Ti content is less than the above range, the amount of 2-methyl-1,4-butanediol copolymerized and the amount of terminal butyl aldehyde decrease, and in particular, the decrease in the amount of 2-methyl-1,4-butanediol copolymerized causes dehydration and cyclization, and the amount of 3M THF distilled in the esterification reaction increases. As a result, it becomes difficult to separate it from THF by distillation, which is undesirable in terms of purifying and recovering THF. In addition, the polymerizability deteriorates.

Specific examples of the periodic table Group 2A metal compound in the present invention include various compounds of beryllium, magnesium, calcium, strontium, and barium, but from the viewpoints of ease of handling and availability, and catalytic effect, magnesium compounds and/or calcium compounds are preferred, and magnesium compounds with excellent catalytic effect are particularly 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 periodic table Group 2A metal compounds may be used alone or in combination of two or more.
Of these, magnesium acetate is preferred.

The content of the Group 2A metal in the PBT of the present invention is not particularly limited, but is preferably 3 to 150 ppm by mass ratio of the metal atom of Group 2A to the PBT. This amount is more preferably 5 ppm or more, and even more preferably 10 ppm or more. This amount is more preferably 50 ppm or less, even more preferably 40 ppm or less, particularly preferably 30 ppm or less, and most preferably 15 ppm or less. If the content of the Group 2A metal is too high, the color tone and hydrolysis resistance are deteriorated, and if it is too low, the polymerizability is deteriorated. When an acetate of a Group 2A metal is used, since an acetic acid source enters the reaction system, the amount of the Group 2A metal in the PBT is preferably 15 ppm or less.

The molar ratio of titanium atoms to Group 2A metal atoms in the periodic table (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 even more preferably 0.3 to 1.5.

The content of metals such as titanium atoms in PBT can be measured using methods such as atomic emission, atomic absorption, and inductively coupled plasma (ICP) after recovering the metals in the polymer using a method such as wet ashing.

In the production of the PBT of the present invention, in addition to the titanium compounds and periodic table Group 2A metal compounds, antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, phosphorus compounds such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, their esters and metal salts, sodium hydroxide, sodium benzoate, and other reaction aids may be used.

(BDO/TPA Consumption Molar Ratio)
In order to adjust the amount of 2-methyl-1,4-butanediol copolymerized, the terminal acetyl group concentration, and the terminal butyl aldehyde concentration of the obtained PBT to the ranges specified in the present invention, in the production process of PBT, the contents of 2-methyl-1,4-butanediol and 2-(4-hydroxybutyloxy)tetrahydrofuran in BDO are set to preferred ranges, and the molar ratio of 1,4-butanediol and terephthalic acid consumed ([BDO (moles)]/[TPA (moles)], hereinafter sometimes referred to as the "BDO/TPA consumed molar ratio") is preferably 1.15 or more and less than 2.00, and this molar ratio is more preferably 1.18 or more and 1.90 or less, and even more preferably 1.20 or more and 1.80 or less. If this molar ratio is less than 1.15, there is a tendency for the esterification reactivity to decrease and the catalyst to be deactivated, and if it is 2.00 or more, there is a tendency for the thermal efficiency to decrease and for by-products such as tetrahydrofuran to increase. This molar ratio can be controlled by the BDO/TPA molar ratio, the amount of Ti catalyst, and the esterification reaction temperature, which act in a complex manner on the BDO/TPA molar ratio consumed.
The above "BDO/TPA consumption molar ratio in the system during the esterification reaction" refers to the total of BDO entering the reaction tank from outside the reaction tank, including BDO supplied together with terephthalic acid as a raw material slurry, BDO supplied independently from these, BDO used as a catalyst solvent, etc. If the BDO/TPA consumption molar ratio is smaller than the BDO/TPA molar ratio added to the esterification reaction tank, the excess BDO will be recycled.

<Physical properties of PBT>
(Intrinsic Viscosity)
When the PBT of the present invention is used for compounding or injection molding, the intrinsic viscosity of the PBT is preferably 0.6 to 1.3 dL/g. If the intrinsic viscosity is less than 0.6 dL/g, the mechanical strength of the molded product tends to be insufficient, and if 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.

When the PBT pellets of the present invention are used for extrusion of films, sheets, or filaments, the intrinsic viscosity of the PBT is usually 1.00 to 1.60 dL/g, preferably 1.03 to 1.50 dL/g, more preferably 1.05 to 1.45 dL/g, particularly preferably 1.10 to 1.40 dL/g, and particularly preferably 1.15 to 1.35 dL/g. If the intrinsic viscosity is less than 1.00 dL/g, the extrusion moldability is deteriorated, leading to drawdown of the resin and molding loss, resulting in insufficient mechanical strength of extrusion molded products such as films, or the melt viscosity is low and the fluidity is too high, resulting in poor extrusion moldability. On the other hand, if the intrinsic viscosity exceeds 1.60 dL/g, the melt viscosity is high, the fluidity is deteriorated, and the extrusion moldability tends to be deteriorated.

The intrinsic viscosity of PBT can be determined by the method described in the Examples section below.

(Melting Point)
The melting point of the PBT of the present invention is usually 224.0 to 225.0° C. If the melting point is lower than this range, the heat resistance is inferior, which is not preferred. The higher the melting point, the higher the heat resistance, which is preferred.
The melting point of PBT can be determined by the method described in the Examples section below.

(Crystallization temperature)
The crystallization temperature of the PBT of the present invention is usually 160 to 200°C, preferably 170 to 195°C, and more preferably 175 to 190°C.
The cooling crystallization temperature in the present invention is the temperature of the exothermic peak due to crystallization that appears when the resin is cooled from a molten state at a temperature drop rate of 20°C/min using a differential scanning calorimeter. The cooling crystallization temperature corresponds to the crystallization rate, and the higher the cooling crystallization temperature, the faster the crystallization rate, so that the cooling time during injection molding can be shortened and productivity can be increased. If the cooling crystallization temperature is low, it takes a long time for crystallization during injection molding, and the cooling time after injection molding must be extended, which tends to lengthen the molding cycle and reduce productivity.
The temperature-lowering crystallization temperature of PBT can be determined by the method described in the Examples section below.

(Solution Haze)
The solution haze of the PBT of the present invention is not particularly limited, but is usually 10% or less, preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. When the solution haze is high, the amount of foreign matter also tends to increase, significantly lowering the commercial value. The solution haze tends to increase when the titanium catalyst is largely deactivated.
The solution haze of PBT can be determined by the method described in the Examples section below.

<Compounding>
The PBT of the present invention can be made into a compound product by adding various additives or compounding materials as required during or after the production of the PBT.

For example, antioxidants may include phenolic compounds such as 2,6-di-t-butyl-4-octylphenol and pentaerythrityl-tetrakis [3-(3',5'-t-butyl-4'-hydroxyphenyl)propionate], thioether compounds such as dilauryl-3,3'-thiodipropionate and pentaerythrityl-tetrakis (3-laurylthiodipropionate), and phosphorus compounds such as triphenyl phosphite, tris (nonylphenyl) phosphite, and tris (2,4-di-t-butylphenyl) phosphite. Release agents may include paraffin wax, microcrystalline wax, polyethylene wax, long-chain fatty acids and their esters, such as montanic acid and montanic acid esters, and silicone oil.

In addition, the PBT of the present invention can be blended with a reinforcing filler. The reinforcing filler is not particularly limited, but examples include inorganic fibers such as glass fiber, carbon fiber, silica-alumina fiber, zirconia fiber, boron fiber, boron nitride fiber, potassium silicon nitride titanate fiber, and metal fiber, and organic fibers such as aromatic polyamide fiber and fluororesin fiber. Two or more of these reinforcing fillers can also be used in combination. Of the above reinforcing fillers, inorganic fillers, especially glass fiber, are preferably used.

When the reinforcing filler is an inorganic or organic fiber, the average fiber diameter is not particularly limited, but is usually 1 to 100 μm, preferably 2 to 50 μm, more preferably 3 to 30 μm, and particularly preferably 5 to 20 μm. The average fiber length is not particularly limited, but is usually 0.1 to 20 mm, and preferably 1 to 10 mm.

In order to improve the interfacial adhesion with PBT, it is preferable to use the reinforcing filler after surface treatment with a converging agent or surface treatment agent. Examples of converging agents or surface treatment agents include functional compounds such as epoxy compounds, acrylic compounds, isocyanate compounds, silane compounds, and titanate compounds. The reinforcing filler can be surface-treated in advance with a converging agent or surface treatment agent, or the reinforcing filler can be surface-treated by adding a converging agent or surface treatment agent when preparing the PBT composition. The amount of reinforcing filler added is usually 150 parts by mass or less, preferably 5 to 100 parts by mass, per 100 parts by mass of PBT.

The PBT of the present invention can be blended with other fillers together with the reinforcing filler. Examples of the other fillers that can be blended include plate-shaped inorganic fillers, ceramic beads, asbestos, wollastonite, talc, clay, mica, zeolite, kaolin, potassium titanate, barium sulfate, titanium oxide, silicon oxide, aluminum oxide, magnesium hydroxide, and the like. These can also be used in combination of two or more. By blending plate-shaped inorganic fillers, the anisotropy and warpage of the resulting molded product can be reduced. Examples of plate-shaped inorganic fillers include glass flakes, mica, and metal foil. Of these, glass flakes are preferably used.

In addition, a flame retardant can be blended into the PBT of the present invention to impart flame retardancy. The flame retardant is not particularly limited, and examples thereof include organic halogen compounds, antimony compounds, phosphorus compounds, other organic flame retardants, and inorganic flame retardants. Examples of organic halogen compounds include brominated polycarbonate, brominated epoxy resin, brominated phenoxy resin, brominated polyphenylene ether resin, brominated polystyrene resin, brominated bisphenol A, and polypentabromobenzyl acrylate. Examples of antimony compounds include antimony trioxide, antimony pentoxide, and sodium antimonate. Examples of phosphorus compounds include phosphate esters, polyphosphoric acid, ammonium polyphosphate, and red phosphorus. Examples of other organic flame retardants include nitrogen compounds such as melamine and cyanuric acid. Examples of other inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, silicon compounds, and boron compounds. These can also be used in combination of two or more.

The PBT of the present invention can be blended with other conventional additives as necessary. Such additives are not particularly limited, and examples include stabilizers such as antioxidants and heat stabilizers, as well as lubricants, release agents, catalyst deactivators, crystal nucleating agents, and crystallization promoters. These additives can be added during or after polymerization. Furthermore, in order to impart desired performance to the PBT, stabilizers such as ultraviolet absorbers and weathering stabilizers, colorants such as dyes and pigments, antistatic agents, foaming agents, plasticizers, impact modifiers, and the like can be blended.

The PBT of the present invention can be blended with thermoplastic resins such as polyethylene, polypropylene, polystyrene, polyacrylonitrile, polymethacrylic acid ester, ABS resin, polycarbonate, polyamide, polyphenylene sulfide, polyethylene terephthalate, liquid crystal polyester, polyacetal, polyphenylene oxide, and thermosetting resins such as phenolic resin, melamine resin, silicone resin, and epoxy resin, as necessary. Two or more of these thermoplastic resins and thermosetting resins can also be used in combination.

The method of compounding the various additives and additional components such as resins is not particularly limited, but a method of melt-kneading the PBT pellets using a single-screw or twin-screw extruder equipped with a vent port for volatilization is preferred. Each component, including the additional components, can be fed to the kneader all at once, or they can be fed sequentially. Also, two or more components selected from each component, including the additional components, can be mixed in advance.

When the PBT of the present invention is used as at least a part of the raw material and melt-kneaded in an extruder as described above to produce a compound product, it is preferable that the kneading resin temperature in the extruder is 320°C or lower. If the kneading resin temperature is 320°C or lower, thermal decomposition tends to be suppressed. From this viewpoint, it is more preferable that the kneading resin temperature in the extruder is 310°C or lower, and even more preferable that it is 300°C or lower. On the other hand, from the viewpoint of ensuring uniform melting, it is preferable that the kneading resin temperature in the extruder is 240°C or higher, and particularly 250°C or higher.

<Molding method>
The method for molding the PBT of the present invention and the compound product containing the PBT of the present invention is not particularly limited, and molding methods generally used for thermoplastic resins, i.e., molding methods such as injection molding, blow molding, extrusion molding, and press molding, can be applied.
In any molding method, it is preferable that the molten resin temperature during molding is 280° C. or lower from the viewpoints of suppressing thermal decomposition of PBT, color tone, and other aspects.

(Injection Molding)
Of the above molding methods, it is preferable to use an injection molding machine when used for automobile parts and electric/electronic parts.
The molten resin temperature during injection molding is preferably 280° C. or lower. If the molten resin temperature is 280° C. or lower, this is preferable in that thermal decomposition is suppressed. From this viewpoint, the molten resin temperature during injection molding is more preferably 275° C. or lower, and further preferably 270° C. or lower. On the other hand, from the viewpoint of ensuring uniform melting, the molten resin temperature during injection molding is preferably 240° C. or higher, particularly preferably 250° C. or higher.

(Extrusion molding)
The PBT of the present invention is less colored and has excellent transparency, particularly in the case of thin products, and therefore has a remarkable improving effect in applications such as sheets, films, and monofilaments (including fibers) produced by extrusion molding.

The molding temperature for films, sheets, and filaments using the PBT of the present invention is not particularly limited, but since a high molding temperature, i.e., a high molten resin temperature, leads to deterioration in color tone, an increase in the concentration of terminal carboxyl groups, and ultimately deterioration in hydrolysis resistance, the molding temperature is usually 280° C. or less, preferably 265° C. or less, and more preferably 260° C. or less. Since the molded products (films, sheets, filaments) using the PBT of the present invention do not contain high-viscosity substances that cause fisheyes in the raw material PBT pellets, even when molded at such low temperatures as described above, the occurrence of fisheyes is minimal, and it is possible to achieve both reduction in fisheyes and prevention of thermal degradation during molding, which have been difficult to achieve up until now.
However, from the viewpoint of ensuring uniform melting, the molten resin temperature is preferably 240° C. or higher, particularly preferably 250° C. or higher.

<Use of recycled materials>
When molding the PBT of the present invention or the above-mentioned compound product, recycled raw materials may be used as at least a part of the molding material from the viewpoint of reducing waste, reducing costs, and obtaining the improved effect of the present invention. Even in this case, as long as the ratio of recycled raw materials used is equal to or less than a predetermined value, the deterioration of physical properties is within an acceptable range, which is preferable.

Here, examples of recycled raw materials include raw materials and ingredients such as parts other than the molded product produced when molding using the PBT pellets of the present invention, and parts that have no commercial value produced during production, such as film ends or sheet ends. In this case, runners, spools, film ends, sheet ends, etc. may be recycled in their original form, or if they cause inconvenience to production, such as adversely affecting the feeder of the raw material or the ability to bite into the screw of the molding machine, they may be processed by granulation, cutting, crushing, etc.

The ratio of recycled raw materials to the total raw materials or materials, where A is the mass of all raw materials or materials including recycled raw materials and C is the mass of recycled raw materials, preferably satisfies the following formula (1). It is particularly recommended to satisfy the following formula (2), and in particular the following formula (3).
0.01 ≦ C/A ≦ 0.5 (1)
0.05 ≦ C/A ≦ 0.4 (2)
0.10≦C/A≦0.3 (3)

If the ratio of recycled materials is high, it can lead to a deterioration in color tone, an increase in foreign matter, and an increase in the concentration of terminal carboxyl groups, while if the ratio of recycled materials is low, sufficient effects cannot be achieved in terms of reducing waste and costs.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples in any way as long as the gist of the present invention is not exceeded.
The methods for measuring the physical properties and evaluation items used in the following examples are as follows.

(1) Intrinsic viscosity (IV)
The viscosity was measured using an Ubbelohde viscometer in the following manner: A mixed solvent of phenol/tetrachloroethane (mass ratio 1/1) was used, and a polymer solution having a concentration of 1.0 g/dL and the solvent alone were mixed at 30° C. The number of seconds it took to fall was measured and calculated using the following formula.
IV=((1+4K _H η _sp ) ^0.5 -1)/(2K _H・C)
(Here, η _sp =η ₀ -1, η is the number of seconds it takes for the polymer solution to fall, η ₀ is the number of seconds it takes for the solvent to fall, C is the polymer solution concentration (g/dL), and K _H is Huggins' constant. , 0.33 was adopted.)

(2) Titanium Concentration PBT was wet decomposed with high-purity sulfuric acid and nitric acid for the electronics industry, and the titanium concentration was measured using a high-resolution ICP (Inductively Coupled Plasma)-MS (Mass Spectrometer) (manufactured by Thermoquest).

(3) 2Me1,4-BDO copolymerization amount, terminal acetyl group concentration, terminal butylaldehyde group concentration, terminal vinyl group concentration, terminal hydroxyl group concentration, terminal benzaldehyde group concentration, and terminal methylphenyl group concentration 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 ¹ H NMR spectrum was measured using an AVANCE NEO spectrometer (manufactured by Bruker). The chemical shift reference was set to 0.00 ppm for the signal of tetramethylsilane.

(4) Terminal Carboxyl Group Concentration 0.5 g of PBT or oligomer was dissolved in 25 mL of benzyl alcohol, and the solution was titrated with a 0.01 mol/L benzyl alcohol solution of sodium hydroxide to determine the terminal carboxyl group concentration.

(5) Melting point (Tm) and cooling crystallization temperature Using a PerkinElmer differential scanning calorimeter (Model DSC7), the temperature was raised from room temperature to 300°C at a heating rate of 20°C/min, and then lowered to 30°C at a heating rate of 20°C/min, and the temperature at the exothermic peak was taken as the cooling crystallization temperature. The higher the cooling crystallization temperature, the faster the crystallization rate and the shorter the molding cycle.
Subsequently, the temperature was raised again from room temperature to 300° C. at a heating rate of 20° C./min, and the endothermic peak temperature during the heating was recorded as the melting point.

(6) Color Tone: Using a color difference meter "Z-300A" manufactured by Nippon Denshoku Co., Ltd., evaluation was performed in the L, a, b color system. The lower the b value, the less yellowish the color is, which is preferable. However, when the b value is lower than -2.2, the color tone is unfavorable because the color tone is less yellowish but more blueish.
The b value is preferably in the range of -2.2 to 1.5, more preferably -2.1 to 1.3, and further preferably -2.0 to 1.2.

(7) Amount of acetic acid generated PBT pellets vacuum dried at 120° C. for 8 hours were loaded into a melt indexer at 270° C., melted for 10 minutes, extruded, and cooled. Immediately after, the pellets were placed in an aluminum moisture-proof bag and sealed to prevent the components generated during melting from volatilizing out.
A thermal desorption tube (TDU tube, manufactured by Gestell) and a transport adapter for the TDU were dried in a dryer at 200° C. for 30 minutes in advance, and acetic acid was measured by the following method.
50 (±2) mg of the melt-heat-treated sample was precisely weighed and inserted into a TDU tube. This TDU tube was introduced into a thermal desorption apparatus ("TDU" manufactured by Gestell) at 40°C, and then the inside of the tube was replaced with helium, and the temperature was raised to 250°C at a rate of 12°C/sec. for 10 minutes for thermal extraction. During this thermal extraction, the volatile components generated from the sample were collected by cooling a GC injection port ("CIS4" manufactured by Gestell) filled with quartz wool to -150°C. Here, an empty TDU tube without a sample inserted was treated in the same manner as above to serve as a blank. The components collected by cooling at the GC injection port were vaporized by rapidly heating the collection portion to 250°C, and introduced into a GC column, where they were measured by GC/MS ("7890GC" manufactured by Agilent/"5977MSD" manufactured by Agilent) to confirm the amount of acetic acid. The lower the amount of acetic acid generated, the more preferable the result.

(8) Acetic acid concentration in distillation wastewater 1 to 20 g of a sample was dissolved in water, and titration was carried out to the end point using an automatic titrator with a 0.1 N KOH solution as the titrant. The acetic acid in the measurement solution was calculated from the titration amount from the start to the end point.

(9) Cobalt (Co) and Manganese (Mn) Content 1.0 g of a terephthalic acid or PBT sample was weighed into a platinum crucible, 5 mL of high-purity sulfuric acid for electronics industry was added, and then the mixture was heated to generate a carbide. The addition of sulfuric acid was repeated until the carbide was completely generated. The generated carbide was incinerated at 800°C and then diluted with 2 mL of high-purity nitric acid for electronics industry. The metal elements in this solution were quantified using a graphite furnace atomic absorption spectrophotometer ("GF-AAS" manufactured by Varian Technologies Japan Limited) and converted into the amount (ppm) per terephthalic acid or PBT.

(10) Content of 4CBA and p-TA in Terephthalic Acid A sample was dissolved in a 2N aqueous ammonia solution, diluted to a predetermined concentration with ultrapure water, and then measured by high performance liquid chromatography equipped with an ODS column.

(11) Acetic acid content in terephthalic acid A sample was dissolved in a 2N potassium hydroxide aqueous solution, precipitated with an aqueous phosphoric acid solution, and filtered through a filter paper. The acetic acid content in the filtrate was quantified using a gas chromatograph equipped with a DB-FFAP capillary column. An aqueous propionic acid solution was used as the internal standard.

(12) Contents of 2Me1,4-BDO, 1,4HAB, and BGTF in 1,4-butanediol Using a gas chromatograph (Shimadzu GC-2025) and a polar column (J&W DB-WAX), the contents of the components of each peak contained in BDO were determined by the modified area percentage method calculated from the effective carbon coefficient. The details of the GC conditions are as follows.
Conditions (polar column)
Analytical column: J&W DB-WAX, 60 m x 0.320 mmid, df = 0.5 μm
Column flow rate: 1 mL/min
Split ratio: 1/90
Oven temperature: 70°C (15 min) → 10°C/min → 170°C (45 min)
Sample chamber and detector temperature: 240°C
Injection volume: 1 mL
・Carrier gas: Nitrogen

(13) 3M THF Concentration in Esterification Distillate Using a gas chromatograph (Shimadzu GC-2025) and a non-polar column (J&W DB-1), the content of each peak component contained in BDO was determined by the modified area percentage method calculated from the effective carbon coefficient.
Conditions (non-polar column)
Column: J&WDB-1, 60m x 0.25mmid, df = 1μm
Column temperature: 50° C. (7 min) → 10° C./min → 250° C. (20 min)
Split ratio: 1/100
Sample chamber and detector temperature: 240°C
Injection volume: 0.8 μL
Carrier gas: Nitrogen The moisture content of the sample was measured by the following method, and the moisture concentration was subtracted from 100%. The remaining components were calculated by dividing proportionately the concentrations of each component calculated by gas chromatography.
That is,
Gas chromatograph component concentration + water concentration = 100% by mass
It was decided.
The 3M THF concentration is preferably 500 ppm or less.

(14) Water concentration in esterified distillate The water concentration was measured by the Karl Fischer method using a Dia Instruments Model: CA-200. Aquamicron dehydrating solvent GEX and 3 mg of Aquamicron titrant SS-Z were used as the water content measurement reagent. 10 μL of the esterified distillate was injected into the device using a microsyringe, and the water concentration was measured.

(15) Acetic acid concentration in distillation wastewater 1 to 20 g of a sample was dissolved in water, and titration was carried out to the end point using an automatic titrator with 0.1 N KOH solution as the titrant. The acetic acid in the measurement solution was calculated from the titration amount from the start to the end point.
The concentration of acetic acid in the distillation wastewater is preferably 300 ppm or less from the viewpoints of neutralization and corrosion of equipment.

(16) Solution Haze
2.70 g of PBT was dissolved in 20 mL of a mixed solvent of phenol/tetrachloroethane = 3/2 (mass ratio) at 110 ° C for 30 minutes, and then cooled in a thermostatic water bath at 30 ° C for 15 minutes, and the turbidity was measured using a turbidity meter "NDH-300A" manufactured by Nippon Denshoku Co., Ltd. with a cell length of 10 mm. The lower the value, the better the transparency.

(17) Measurement of fisheye count PBT was dried at 140°C for 4 hours under a nitrogen atmosphere, and a film was formed under the following conditions using a continuous extrusion film forming apparatus ("ME-20/26V2&CR-7&FS-5" manufactured by OCS Corporation), and the number of fisheyes (number/ ^m2 ) was measured. The number of fisheyes was measured by automatically counting the number of fisheyes with a major axis of 16 µm or more present in an area of 1 ^m2 using a CCD camera attached to the apparatus while the film was being formed. The smaller this value, the more excellent the molded appearance. It is preferable that the number of fisheyes is 1,000 or less per ^m2 .
・Cylinder temperature (temperature at four points between the nozzle and the bottom of the hopper):
250℃-250℃-250℃-250℃
Screw rotation speed: 100 rpm
Resin pressure: 75 MPa
Chill roll temperature: 50°C
Film thickness: 50 μm

[Terephthalic acid]
Terephthalic acid (hereinafter abbreviated as "TPA") used as a raw material for producing PBT in the following Examples and Comparative Examples was produced through a process in which p-xylene was oxidized in an acetic acid solvent in the presence of a catalyst containing cobalt and manganese, and then purified by hydrogenation, and during this process, certain amounts of cobalt, manganese, 4CBA, p-TA, and acetic acid may be contained. The contents of these vary depending on the production conditions, but in the present invention, these terephthalic acids were used alone or in blends so as to obtain the values in Table 1.
The terephthalic acid used in the blend includes terephthalic acid that has not been subjected to a hydrogenation reaction.

[1,4-butanediol]
The BDO used as a raw material for producing PBT in the following Examples and Comparative Examples was produced as follows.
(1) Reppe process: Acetylene and formaldehyde are reacted to produce 1,4-butynediol, which is then hydrogenated to produce 1,4-butenediol. The resulting 1,4-butenediol is then hydrogenated to produce BDO, and in this process, a certain amount of 2-methyl-1,4-butanediol (2Me1,4-BDO) and 2-(4-hydroxybutyloxy)tetrahydrofuran (BGTF) may be contained. The content of these compounds varies depending on the production conditions, but in the present invention, they were used by strengthening purification through additional distillation or blending to obtain the specified content, so as to obtain the values in Table 1.

(2) Butadiene process Butadiene was acetoxylated to obtain 1,4-diacetoxybutene, which was then hydrogenated to obtain 1,4-diacetoxybutane, which was then hydrolyzed to obtain 1-acetoxy-4-hydroxybutane, and the BDO composition obtained by further hydrolysis was adjusted in the hydrolysis step of the acetoxylated product. Thereafter, high boiling points and low boiling points were distilled from the crude BDO, and the crude BDO containing 1-acetoxy-4-hydroxybutane (1,4-HAB) and 2-(4-hydroxybutyloxy)tetrahydrofuran (BGTF) was distilled from the top of the column together with 1,4-HAB and BGTF together with a portion of the BDO, and a BDO composition with an adjusted 1,4-HAB content and BGTF content was obtained from the bottom of the column. Even after this process, a certain amount of 1,4-HAB and BGTF may still be contained. The contents of 1,4-HAB and BGTF vary depending on the hydrolysis conditions and distillation conditions, but in the present invention, these BDOs were used alone or in combination so as to obtain the values shown in Table 1.

[Example 1]
The PBT was prepared as follows.
A slurry was continuously fed to an esterification reaction tank (abbreviated as "Es" in Table 1) having a screw-type agitator filled with a PBT oligomer having an esterification rate of 99%, and an esterification reaction was carried out. A BDO solution containing a tetrabutyl titanate catalyst in an amount such that titanium was 55 ppm relative to PBT was fed to the esterification reaction tank. Additional BDO was fed to the esterification tank so that the molar ratio of BDO to terephthalic acid was 2.6. The temperature of the reaction tank was 226°C, the pressure was 60 kPa, and the average residence time was 180 minutes.

The PBT oligomer with an esterification rate of 96.5% was then continuously transferred to the first polycondensation reaction tank. In the first polycondensation reaction tank, the polycondensation reaction was carried out continuously. The reaction temperature was 230°C, the pressure was 3.9 kPa, and the average residence time was 120 minutes. This product was then transferred to the second polycondensation reaction tank, where the polycondensation reaction was carried out continuously. The reaction temperature was 240°C, the pressure was 130 Pa, and the average residence time was 80 minutes.

The resulting polymer was passed through a discharge line by a gear pump, and was continuously discharged in the form of strands from a die head through a filter, and cut with a rotary cutter to obtain PBT pellets (major axis approximately 3 mm, minor axis approximately 2 mm, length approximately 4 mm).

The resulting PBT had an intrinsic viscosity (IV) of 0.85 dL/g, a terminal acetyl group concentration of less than 0.1 equivalent/ton, a terminal butylaldehyde group concentration of 0.06 equivalent/ton, and a copolymerization amount of 2-methyl-1,4-butanediol of 0.030 mol %.
The melting point of this PBT was 224.9° C. When the color tone (b value) of this PBT was measured, it was found to be good at −0.8, and the amount of acetic acid generated after heat treatment at 270° C. for 10 minutes was small at less than 1 ppm.

In addition, a distillation operation was performed in a distillation column to recover THF from the distillate from the esterification reaction tank. When the esterification distillate was analyzed, the 3M THF content was 200 ppm. From the viewpoint of the size, reflux ratio, and throughput of an industrial distillation column, it is preferable that the 3M THF content is 500 ppm or less as an impurity.
A composition liquid containing THF as the main component was obtained on the low boiling point side (top) of the distillation column, and an acetic acid-containing composition liquid containing water as the main component was obtained on the high boiling point side (bottom). The acetic acid concentration in this mixed liquid (this mixed liquid is called "distillation wastewater") was less than 10 ppm. From the viewpoint of corrosion of the material of the distillation column and the cost of treating the wastewater, it is preferable that it is 300 ppm or less. The molar ratio of BDO and TPA consumed was 1.26.
The evaluation results of the obtained PBT are summarized in Table 2.

[Example 2]
In Example 1, terephthalic acid and BDO shown in Table 1 were used, and PBT was obtained in the same manner as in Example 1, except that the conditions were as shown in Table 1. The evaluation was performed in the same manner, and the results are shown in Table 2. These were favorable, as in Example 1.

[Comparative Examples 1 to 4]
PBT was obtained in the same manner as in Example 1 except that terephthalic acid and BDO shown in Table 1 were used and the conditions shown in Table 1 were followed. PBT was evaluated in the same manner, and the results are shown in Table 2.

As shown in Tables 1 and 2, the PBT of Examples 1 and 2, which met the requirements of the present invention, had good color tone, generated little acetic acid, and was high quality PBT.
On the other hand, the PBTs of Comparative Examples 1 to 4, which do not satisfy the requirements of the present invention, were undesirable in any one of the following points: low melting point, poor color tone, high fish eye, high solution haze, etc.
In addition, there was also PBT in which the ester distillate (crude THF) contained a large amount of 3M THF, making it difficult to recover THF by distillation.

Claims (8)

The terminal acetyl group concentration is less than 0.1 equivalents/ton, and the terminal butyl aldehyde group concentration is 0.05 to 0.11 equivalents/ton;
a terminal benzaldehyde group concentration of 0.03 to 0.07 equivalents/ton and a terminal methylphenyl group concentration of 0.3 to 0.8 equivalents/ton;
A polybutylene terephthalate, characterized in that the proportion of structural units derived from 2-methyl-1,4-butanediol in all structural units derived from a diol component is 0.020 to 0.060 mol %. A method for producing polybutylene terephthalate by reacting a terephthalic acid component with 1,4-butanediol,
The method for producing polybutylene terephthalate according to claim 1 , characterized in that the 1,4-butanediol used contains 250 to 1000 ppm by mass of 2-methyl-1,4-butanediol and 10 to 1500 ppm by mass of 2-(4-hydroxybutyloxy)tetrahydrofuran. The consumption molar ratio of 1,4-butanediol to terephthalic acid components is set to 1.15 or more and less than 2.00,
The method for producing polybutylene terephthalate according to claim 2, characterized in that polybutylene terephthalate containing 35 to 90 ppm of Ti is produced. The method for producing polybutylene terephthalate according to claim 2 or 3, characterized in that terephthalic acid having a 4-carboxybenzaldehyde content of 5 to 25 ppm and a p-toluic acid content of 85 to 185 ppm is used as the terephthalic acid component. A polybutylene terephthalate composition comprising the polybutylene terephthalate of claim 1 and an additive. 6. The method for producing a polybutylene terephthalate composition according to claim 5 , wherein the polybutylene terephthalate and the additive are kneaded at a kneading resin temperature of 320° C. or less using an extruder. A molded article comprising the polybutylene terephthalate composition according to claim 5 . The method for producing a molded article according to claim 7 , characterized in that the polybutylene terephthalate composition is molded using a molding machine at a molten resin temperature of 280°C or less.