JP2017171729A - Copolymer polybutylene terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PTMG copolymer suitable for manufacturing a molded article having improved tensile break induced strain, impact resistance, less in crack or breakage when used in a molded article for an application used without adding a glass fiber, a filler or the like and non-reinforcement and hardly being broken.SOLUTION: There is provided polytetramethylene glycol copolymer polybutylene telephthalate consisting of a dicarboxylic acid component mainly containing terephthalic acid and a diol component containing 1,4-butanediol and polytetramethylene glycol and having α represented by the following formula of 1.5 to 3.5. α=tanδ(10rad/s)/tanδ(10rad/s), where tanδ(10rad/s) represents loss tangent at frequency of 10rad/s in a melting elasticity measurement at 240°C and tanδ(10rad/s) represents loss tangent at frequency of 10rad/s in the measurement.SELECTED DRAWING: None

Description

  The present invention relates to polybutylene terephthalate with improved tensile fracture nominal strain and impact resistance.

  Polyester resins occupy an important industrial position due to their excellent mechanical and chemical properties. For example, aromatic polyester resins such as polyethylene terephthalate and polybutylene terephthalate (hereinafter sometimes referred to as PBT) are resins having excellent heat resistance and chemical resistance. Widely used in fields such as extrusion, injection, etc., such as sheets, bottles, electrical and electronic parts, automotive parts, precision equipment parts. However, in recent years, there has been a demand for a polyester having new functions such as flexibility, low-temperature characteristics, and impact resistance while maintaining the basic characteristics of the polyester, and further, it is hoped that such a polyester can be efficiently produced. It is rare.

In PBT, many studies have been made so far for improving the physical properties, but the cases leading to practical use have been extremely limited. This is because the copolymer component is likely to be randomly incorporated into the PBT chain, causing a decrease in the melting point of the PBT and a decrease in the crystallization rate, and acting in a direction to counteract the advantages of the PBT such as heat resistance and moldability.
When the copolymer component is incorporated into the PBT chain in a long-chain block, the melting point drop corresponding to the introduced weight is small, so that physical property modification can be performed without reducing the heat resistance of the PBT. A typical example of such a copolymerization component is polytetramethylene ether glycol (hereinafter sometimes referred to as PTMG) (Patent Document 1).

  A copolymer obtained by copolymerizing PTMG, which is a soft segment, with PBT crystalline polyester as a hard segment, is called PTMG copolymerized PBT, and can give flexibility to PBT. It is used. Although PTMG copolymerized PBT has improved impact resistance, further improvements have been desired.

JP-A-49-31795

  An object of the present invention is to provide a PTMG copolymer PBT excellent in tensile fracture nominal strain and impact resistance.

As a result of intensive studies on the above-mentioned problems, the present inventors have found that the loss tangent (tan δ) in the dynamic viscoelastic behavior in the molten state of the PTMG copolymerized PBT is within a specific range. Has been found to be improved, leading to the present invention.
That is, the gist of the present invention is as follows.
(1) It consists of a dicarboxylic acid component containing terephthalic acid as a main component and a diol component containing 1,4-butanediol and polytetramethylene glycol, and α represented by the following formula is 1.5 or more and 3.5 or less. A polytetramethylene glycol copolymer polybutylene terephthalate.

α = tan δ (10 ¹ rad / s) / tan δ (10 ² rad / s)
(Where tan δ (10 ¹ rad / s) represents a loss tangent at a frequency of 10 ¹ rad / s in melt viscoelasticity measurement at 240 ° C., and tan δ (10 ² rad / s) is (It represents the loss tangent at a frequency of 10 ² rad / s.)
(2) The polytetramethylene glycol copolymer polybutylene terephthalate according to (1), wherein the polytetramethylene glycol has a number average molecular weight of 500 to 6000.
(3) The polytetramethylene glycol copolymerized polybutylene terephthalate according to (2), wherein the polytetramethylene glycol content relative to the polytetramethylene glycol copolymerized polybutylene terephthalate is 5 to 35% by mass.
(4) The polytetramethylene glycol copolymer polybutylene terephthalate according to (3), wherein the ratio of polytetramethylene glycol having a molecular weight of 17,000 or more in the polytetramethylene glycol is 0.5% by mass or less.
(5) The polytetramethylene glycol copolymer polybutylene terephthalate according to (3), wherein the ratio of polytetramethylene glycol having a molecular weight of 20000 or more in the polytetramethylene glycol is 0.5% by mass or less.

  The PTMG copolymerized PBT in the present invention is a concept including a PBT homopolymer product and a PTMG copolymer PBT compound product, or a compound obtained by compounding two or more types of PTMG copolymer PBTs having different PTMG copolymerization amounts.

  Since the PTMG copolymer PBT of the present invention has improved tensile strain nominal strain and impact resistance, cracks and cracks may occur when used for non-reinforced molded products that do not contain glass fibers or fillers. There is an advantage that it becomes a molded product that is less likely to be damaged.

It is a conceptual diagram of the molecular weight distribution of PTMG used as the raw material of the Example of this invention, and the raw material of a comparative example. It is the figure which plotted Example 5 and Comparative Example 1 of this invention on FIG. 1 (the curve showing the boundary of phase separation) of patent document 1. FIG.

  Embodiments of the present invention will be described in detail below. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not specified by these contents. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. Moreover, the lower limit value or the upper limit value in this specification means a range including the value of the lower limit value or the upper limit value. Further, in the present specification, “main component” means occupying 70 mol% or more of the component. For example, the “dicarboxylic acid component containing terephthalic acid as a main component” means that 70 mol% or more of the total acid components constituting the polyester are terephthalic acid components. In the present specification, a step of performing an esterification reaction and / or a transesterification reaction is referred to as an esterification reaction step.

[1] Raw material of PTMG copolymerized PBT The PTMG copolymerized PBT in the present invention comprises a dicarboxylic acid component mainly composed of terephthalic acid and 1,4-butanediol (hereinafter sometimes referred to as 1,4-BG). It is obtained by subjecting a diol component containing PTMG as a main component to an esterification reaction and / or a transesterification reaction, followed by a polycondensation reaction. In the esterification reaction and / or transesterification reaction and polycondensation reaction, a reaction catalyst can be used.

(Dicarboxylic acid component)
In the present invention, examples of the dicarboxylic acid component include terephthalic acid and dicarboxylic acid components described below. From the viewpoints of mechanical strength, heat resistance, fragrance retention, and the like of the polyester obtained, terephthalic acid is the main component. It is preferable. The dicarboxylic acid component used in the present invention is a dicarboxylic acid and / or an ester-forming derivative thereof produced by a petrochemical method and / or a production method having a fermentation process derived from biomass resources. As ester-forming derivatives of dicarboxylic acids, ester-forming derivatives such as acid anhydrides and acid chlorides are preferred in addition to lower alcohol esters of dicarboxylic acids. Here, the lower alcohol usually refers to a linear or branched alcohol having 1 to 4 carbon atoms.

(Terephthalic acid component)
In the present invention, the content of the terephthalic acid component in the total dicarboxylic acid component is preferably 80 mol% or more, and more preferably 90 mol% or more. When the proportion of the terephthalic acid component is equal to or higher than the above lower limit value, it is easy to crystallize when forming into an electrical component or the like, and from the point of orientation crystallization of molecular chains by stretching when forming into a film, fiber, etc. Mechanical strength, heat resistance, fragrance retention, etc. as a body tend to be good.

(Dicarboxylic acid components other than terephthalic acid components)
The dicarboxylic acid component used in the present invention may contain a dicarboxylic acid component other than the terephthalic acid component.
Specific examples of the dicarboxylic acid component other than the terephthalic acid component used in the present invention include oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecadicarboxylic acid, and dodecane. Aliphatic chain dicarboxylic acids such as dicarboxylic acids and ester-forming derivatives thereof;
Alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid and ester-forming derivatives thereof;
Phthalic acid, isophthalic acid, dibromoisophthalic acid, sodium sulfoisophthalate, phenylenedioxydicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenylether dicarboxylic acid, 4,4'-diphenylketone dicarboxylic acid, 4 , 4′-diphenoxyethanedicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, 2,6-naphthalenedicarboxylic acid and other aromatic dicarboxylic acids and ester-forming derivatives thereof.

The ester-forming derivative is preferably an anhydride such as succinic anhydride or adipic anhydride or a lower alcohol ester.
Among these, from the viewpoint of the physical properties of the obtained polyester, other dicarboxylic acid components include aromatic dicarboxylic acid components such as isophthalic acid and naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid. Ingredients are preferred. These dicarboxylic acid components can be used alone or in admixture of two or more.

(Diol component)
Examples of the diol component in the present invention include 1,4-BG and PTMG as main components.
In the present invention, examples of diol components other than 1,4-BG and PTMG include the following.

Ethylene glycol, diethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, polypropylene glycol, dibutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8 A linear aliphatic diol such as octanediol; 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, 1,
Cycloaliphatic diols such as 4-cyclohexanedimethylol; aromatics such as xylylene glycol, 4,4′-dihydroxybiphenyl, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone Diols: Diols derived from plant materials such as isosorbide, isomannide, isoidet, erythritan and the like. Ethylene glycol, 1,3-propanediol, 1,4-butanediol and the like can also be derived from biomass resources. Of these, ethylene glycol, 1,3-propanediol, and 1,4-cyclohexanedimethylol are preferable from the viewpoint of the physical properties of the polyester obtained. These diol components can be used alone or as a mixture of two or more.

(PTMG copolymerization amount)
In the PTMG copolymerized PBT of the present invention, the lower limit of the copolymerization amount of the PTMG component is 5% by mass, preferably 10% by mass, more preferably 15% by mass with respect to the PTMG copolymerized PBT (total). The upper limit is 35 mass%, preferably 30 mass%, more preferably 25 mass%.

  Here, the copolymerization amount (content) of PTMG is the ratio of the PTMG unit as the diol component in the PTMG copolymer PBT, that is, the amount of the PTMG copolymer obtained by subtracting the water molecule due to ester bond formation from PTMG. The ratio with respect to PBT is expressed by mass%. When the copolymerization ratio of PTMG is within this range, a copolymerized PBT having a good balance between flexibility and impact strength can be obtained. The amount of PTMG copolymerization can be controlled by the amount of PTMG charged when the copolymerized PBT is produced.

(PTMG molecular weight)
In the present invention, the number average molecular weight of PTMG is 500 to 6000, preferably 500 to 3000, more preferably 700 to 2000, and further preferably 800 to 1500. When the molecular weight is within this range, the reactivity during copolymer production is good, the degree of melting point drop due to copolymerization is small, and a copolymerized PBT with good mechanical properties and the like is obtained.

The molecular weight of PTMG is controlled by the reaction temperature, reaction time, catalyst amount, etc. during the production of PTMG.
Moreover, it is preferable that the ratio of molecular weight 17000 or more in PTMG in this invention is 0.5 mass% or less, More preferably, it is 0.2 mass% or less. When the ratio of PTMG having a molecular weight of 17000 or more is within this range, a transparent PTMG copolymer PBT can be obtained at the time of melting, and a transparent film can be easily obtained when formed into a film. In addition, the tensile fracture nominal strain and impact resistance of the molded product are improved.

  Moreover, it is preferable that the ratio of molecular weight 20000 or more in PTMG in this invention is 0.5 mass% or less, More preferably, it is 0.2 mass% or less, More preferably, it is 0.1 mass% or less. When the ratio of PTMG having a molecular weight of 20000 or more is within this range, a transparent PTMG copolymer PBT can be obtained at the time of melting, and a transparent film can be easily obtained when formed into a film. Moreover, the tensile fracture nominal strain and impact resistance of the molded product are also improved.

  Moreover, it is preferable that the ratio of molecular weight 17000 or more in PTMG in the present invention is 0.5 mass% or less, and the ratio of molecular weight 20000 or more is 0.2 mass% or less. When the ratio of PTMG having a molecular weight of 17000 or more and 20000 or more is within this range, a transparent PTMG copolymerized PBT can be obtained at the time of melting, and a transparent film is easily obtained when formed into a film. Moreover, the tensile fracture nominal strain and impact resistance of the molded product are improved.

Further, the ratio of the cyclic PTMG oligomer in the PTMG in the present invention is preferably 1.5 to 4.0% by mass, more preferably 2.0% to 3.5% by mass. A PTMG copolymerized PBT with good transparency can be obtained from time to time, and when it is formed into a film, a more transparent film is easily obtained. In addition, the tensile fracture nominal strain and impact strength of the molded product are also improved.

  In the present invention, the number average molecular weight of PTMG is a monodispersed polystyrene equivalent molecular weight obtained by SEC measurement (size exclusion chromatography method). Further, the ratio of PTMG having a molecular weight of 20000 or more or 17000 or more is obtained as a value obtained by subtracting the mass% of molecules less than 20000 or the mass% of molecules less than 17000 in the integral curve of molecular weight and contained mass% in SEC measurement. It is done.

  PTMG having a molecular weight of 20000 or more in the proportion of PTMG of 0.5% by mass or less and a cyclic PTMG oligomer in the range of 1.5 to 4.0% by mass can be obtained, for example, by the following method. In the production of PTMG, PTMG having a narrow molecular weight distribution is obtained by narrowing the reaction time distribution by adopting a batch method or making the reaction catalyst homogeneous. Further, a part having a molecular weight of 17000 or 20000 or more of PTMG can be obtained by a method such as separation by a solvent precipitation method, a centrifugal separation method, or the like. The methods for measuring the molecular weight distribution of the PTMG component in the PTMG copolymerized PBT, the ratio of the molecular weight component having a molecular weight of 17000 or 20000 or more, and the ratio of the cyclic PTMG oligomer are described in detail in the Examples.

<Other copolymerizable components>
In the present invention, in addition to the diol component and the dicarboxylic acid component, other copolymerizable components may be used as a raw material for the polyester. Other copolymerizable components that can be used in the present invention include glycolic acid, p-hydroxybenzoic acid, hydroxycarboxylic acid such as p-β-hydroxyethoxybenzoic acid and alkoxycarboxylic acid; stearyl alcohol, heneicosanol, octacosanol, Monofunctional carboxylic acids such as benzyl alcohol, stearic acid, behenic acid, benzoic acid, t-butylbenzoic acid, benzoylbenzoic acid; tricarbaric acid, trimellitic acid, trimesic acid, pyromellitic acid, naphthalenetetracarboxylic acid, gallic acid And trifunctional or higher polyfunctional carboxylic acids such as trimethylolethane, trimethylolpropane, glycerol, pentaerythritol, sugar ester, and the like. These other copolymerizable components can be used alone or in admixture of two or more.

<Catalyst and additive>
(Esterification reaction or transesterification catalyst)
Examples of the esterification reaction or transesterification reaction catalyst used in the production of PTMG copolymerized PBT in the present invention include antimony compounds such as antimony trioxide; germanium compounds such as germanium dioxide and germanium tetroxide; tetramethyl titanate. , Titanium alcohols such as tetraisopropyl titanate and tetrabutyl titanate, titanium compounds such as titanium phenolate such as tetraphenyl titanate; dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexahexyldistin oxide, Didodecyltin oxide, triethyltin hydroxide, triphenyltin hydroxide, triisobutyltin acetate, dibutyltin diacete Tin compounds such as magnesium acetate; magnesium compounds such as magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, and magnesium hydrogen phosphate; and calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide In addition to Group 2A metal compounds of the periodic table such as calcium compounds such as side and calcium hydrogen phosphate, manganese compounds, zinc compounds and the like can be mentioned. In the present invention, the Group 2 metal of the periodic table (Nomenclature of Inorganic Chemistry IUPAC Recommendations)
2005) is a Group 2 element of the long-period periodic table. Of these, titanium compounds and tin compounds are preferable, and tetrabutyl titanate is particularly preferable. These catalysts can be used alone or in admixture of two or more.

In this invention, it is preferable to add so that the metal concentration derived from this reaction catalyst contained in PTMG copolymerization PBT may be in the following range.
In the case of an esterification reaction, the lower limit of the metal concentration is usually 1 ppm by mass or more, preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, particularly preferably 20 ppm by mass or more, and most preferably 30 ppm by mass or more. It is. On the other hand, the upper limit of the metal concentration is usually 300 ppm by mass or less, preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less, still more preferably 100 ppm by mass or less, particularly preferably 90 ppm by mass or less, most preferably. It is 60 mass ppm or less. When the metal concentration is less than or equal to the above upper limit value, it is difficult to cause foreign matters, and there is a tendency that deterioration reaction and gas generation at the time of thermal residence of the obtained PTMG copolymerized PBT do not easily occur. , Side reactions tend not to occur easily.

  In the case of transesterification, the lower limit of the metal concentration is usually 1 ppm by mass or more, preferably 5 ppm by mass or more, more preferably 10 ppm by mass or more, particularly preferably 20 ppm by mass or more, and most preferably 25 ppm by mass or more. It is. On the other hand, the upper limit of the metal concentration is usually 300 ppm by mass or less, preferably 250 ppm by mass or less, more preferably 225 ppm by mass or less, still more preferably 200 ppm by mass or less, particularly preferably 175 ppm by mass or less, most preferably. It is 150 mass ppm or less.

(Polycondensation reaction catalyst)
In the present invention, as a polycondensation reaction catalyst used in producing PTMG copolymerized PBT, a catalyst for esterification reaction or transesterification reaction may be used as it is as a polycondensation reaction catalyst, or the catalyst may be further added. May be. The polycondensation reaction catalyst is not particularly limited, but is preferably added so that the metal concentration derived from the polycondensation reaction catalyst contained in the obtained PTMG copolymerized PBT falls within the following range.

  In the case of polycondensation following the esterification reaction, the lower limit of the metal concentration is usually 0.5 mass ppm or more, preferably 1 mass ppm or more, more preferably 3 for the same reason as the catalyst for the esterification reaction. It is at least ppm by mass, particularly preferably at least 5 ppm by mass, and most preferably at least 10 ppm by mass. The upper limit of the metal concentration is usually 300 ppm by mass or less, preferably 200 ppm by mass or less, more preferably 100 ppm by mass or less, particularly preferably 50 ppm by mass or less, and most preferably 30 ppm by mass or less.

  In the case of polycondensation after the transesterification reaction, the lower limit of the metal concentration is usually 5 ppm by mass or more, preferably 10 ppm by mass or more, more preferably 15 ppm by mass for the same reason as the catalyst for the transesterification reaction. As described above, it is particularly preferably 20 ppm by mass or more, and most preferably 30 ppm by mass or more. The upper limit of the metal concentration is usually 300 ppm by mass or less, preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less, particularly preferably 100 ppm by mass or less, and most preferably 50 ppm by mass or less.

Moreover, when using a titanium compound as an esterification reaction catalyst, from the viewpoint of foreign matter suppression, the metal concentration of titanium contained in the finally obtained PTMG copolymerized PBT is preferably 250 ppm by mass or less, More preferably, it is 100 mass ppm or less, Most preferably, it is 60 mass ppm or less, Most preferably, it is 50 mass ppm or less.
The metal concentration (mass) in the PTMG-copolymerized PBT is determined by recovering the metal contained in the PTMG-copolymerized PBT by a method such as wet ashing, and then performing atomic emission, Induced Coupled Pla
It can be measured using the sma (ICP) method or the like.

(Reaction aid)
In the esterification reaction, transesterification reaction and polycondensation reaction described later, in addition to the above catalyst, phosphorus compounds such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid and esters and metal salts thereof; sodium acetate and benzoic acid Reaction aids such as sodium compounds such as sodium, compounds of group 1A metal elements of the periodic table such as potassium compounds such as lithium acetate and potassium acetate; compounds of group 2A metal elements of the periodic table such as magnesium acetate and calcium acetate Can be added as

(Other additives)
In the esterification reaction, transesterification reaction, and polycondensation reaction described later, 2,6-di-t-butyl-4-octylphenol, pentaerythrityl-tetrakis [3- (3 ′, 5′-t-butyl- 4′-hydroxyphenyl) propionate]; thioether compounds such as dilauryl-3,3′-thiodipropionate, pentaerythrityl-tetrakis (3-laurylthiodipropionate); triphenyl phosphite, tris Antioxidants such as phosphorus compounds such as (nonylphenyl) phosphite and tris (2,4-di-t-butylphenyl) phosphite; representative of paraffin wax, microcrystalline wax, polyethylene wax, montanic acid and montanic acid ester Long chain fatty acids and esters thereof; A release agent such as Ile can also be used.

[2] Method for Producing PTMG Copolymerized PBT The PTMG copolymerized PBT of the present invention is a known method for producing PBT except that specific PTMG is used as a part of the diol component, that is, terephthalic acid or an ester-forming derivative thereof. The esterification step in which esterification reaction and / or transesterification reaction of a dicarboxylic acid component as the main component and a diol component containing PTMG as the main component and 1,4BG is performed, and the oligomer obtained by the esterification step are combined. It can carry out by the method of obtaining polyester through the polycondensation process which carries out a condensation reaction.

“Specific PTMG” refers to PTMG whose number average molecular weight is in a specific numerical range, or whose specific high molecular weight component content is in a specific numerical range, as described above. Further, it refers to PTMG in which the amount of cyclic PTMG oligomer is in a specific numerical range.
The PTMG copolymerized PBT can be produced mainly by a so-called direct polymerization method in which terephthalic acid is used as a main raw material and a transesterification method in which a dialkyl ester of terephthalic acid is used as a main raw material. Although it is different, it is not particularly limited.

The reaction conditions for the esterification step are arbitrary as long as the esterification reaction and / or transesterification reaction can proceed, and the reaction temperature is 120 ° C. or higher, preferably 150 ° C. or higher, while 245 ° C. or lower, preferably Is 230 ° C. or lower. The reaction time is 2 to 8 hours, preferably 2 to 6 hours, and more preferably 2 to 4 hours.
The esterification step produces an oligomer in which a diol having 1,4BG as a main component and a dicarboxylic acid component having terephthalic acid or its ester-forming derivative as a main component are reacted. And in the polycondensation process mentioned later, this oligomer polycondensation reaction is performed.

The polycondensation reaction is usually performed by a melt polycondensation reaction. The conditions in the polycondensation step are arbitrary as long as the polycondensation reaction can proceed. The reaction temperature during the polycondensation reaction is preferably 245 ° C. or lower, more preferably 240 ° C. or lower, and preferably 230 ° C. or higher, more preferably 235 ° C. or higher. When the reaction temperature is at most the upper limit value, the thermal decomposition reaction during production tends to be suppressed and the color tone tends to be improved. If the reaction temperature is equal to or higher than the lower limit, the polycondensation reaction is likely to proceed efficiently.

  The lower the pressure in the reaction tank during the polycondensation reaction, the easier the reaction proceeds, but usually it is 27 kPa or less, preferably 20 kPa or less, more preferably 13 kPa or less, and at least one polycondensation reaction tank preferably has a state of 2 kPa or less. It is preferable to take. The time required for the polycondensation reaction is adjusted so as to make the range constant by measuring the melt viscosity and intrinsic viscosity of the obtained PBT, but is usually 2 to 12 hours, preferably 2 to 10 hours. When the polycondensation reaction is carried out continuously, the average residence time in the polycondensation reaction tank is regarded as the time required for the polycondensation reaction.

In the present invention, the timing for adding PTMG to the reaction system is from the start of the esterification reaction and / or the transesterification reaction to the end of the polycondensation reaction. By adding during this period, the block property as a copolymerization component is easily maintained, and a PTMG copolymerized PBT with a low melting point reduction is obtained. Preferably, the addition timing is preferably after completion of the esterification reaction and / or transesterification or before the start of the polycondensation reaction in terms of the addition operation and securing the block property.
After completion of the polycondensation reaction, it is extracted in a strand form from the reaction vessel and cut into water or pellets by cutting after water cooling. The pellet can be further solid-phase polycondensed as necessary to further increase the viscosity, or to reduce impurities such as THF contained in the pellet.

[3] PTMG copolymer PBT MVR at 245 ° C. of PTMG copolymer PBT properties present invention (melt volume flow rate ^Unit: cm 3 / 10min) is preferably from 10 to 100, more preferably from 25 to 75. When the MVR is within this range, a copolymerized PBT having good moldability and good physical properties when formed into a molded product can be obtained.
The terminal carboxyl group amount (equivalent / ton) of the PTMG copolymerized PBT of the present invention is preferably 3 to 50, more preferably 3 to 35. When the amount of the terminal carboxyl group is within this range, a copolymerized PBT having good heat resistance and hydrolysis resistance can be obtained.

(Tan δ ratio α)
Α represented by the following formula of the PTMG copolymerized PBT of the present invention is 1.5 or more and 3.5 or less.
α = tan δ (10 ¹ rad / s) / tan δ (10 ² rad / s)
(Where tan δ (10 ¹ rad / s) represents a loss tangent at a frequency of 10 ¹ rad / s in melt viscoelasticity measurement at 240 ° C., and tan δ (10 ² rad / s) is (It represents the loss tangent at a frequency of 10 ² rad / s.)
The α is preferably 2 or more, and more preferably 3 or more.
When α is in this range, the nominal tensile strain, impact strength, etc. are improved. Α in the present invention is controlled by the molecular length, amount, flexibility and the like of PTMG which is a copolymerization component. In addition, α tends to be low when uniformity cannot be maintained, for example, a part of the components undergo phase separation at 240 ° C.

[4] Composition The PTMG copolymer PBT of the present invention can be blended with various additives such as stabilizers, fillers, flame retardants, PBT and other resins, if necessary, to obtain a polyester composition. . Moreover, it can be set as a molded object using this resin composition.

(Formulation method)
The method of blending the various additives and resins is not particularly limited, but a method of using a uniaxial or biaxial extruder having equipment capable of devolatilization from the vent port as a kneader is preferable. Each component including the additional components can be supplied to the kneader in a lump or can be supplied sequentially. In addition, two or more kinds of components selected from each component, including additional components, can be mixed in advance.

(Molding method)
The PTMG copolymer PBT and the composition thereof of the present invention can be formed into a molded body by a molding method generally used for thermoplastic resins, that is, a molding method such as injection molding, hollow molding, extrusion molding or press molding. .

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example at all unless the summary is exceeded. In addition, the measurement method of the physical property and evaluation item which were employ | adopted in the following examples is as follows.
<PTMG number average molecular weight, ratio of molecular weight 20000 or 17000 or more SEC measurement> SEC measurement of PTMG molecular weight was performed using a high-speed GPC apparatus HLC-8120 GPC manufactured by Tosoh Corporation.

The sample was dissolved in a reagent primary THF (containing an antioxidant dibutylhydroxytoluene) as a mobile phase solution, and filtered through a 0.45 μm PTFE filter for measurement.
The number average molecular weight (Mn) was calculated from the measured data using a high-speed GPC apparatus Tosoh GPC-8020 model II manufactured by Tosoh Corporation and calculated as a polystyrene equivalent value.
Similarly, the amount of polytetramethylene glycol having a molecular weight of 20000 or 17,000 or more in terms of polystyrene is analyzed using Tosoh GPC-8020 model II manufactured by Tosoh Corporation and from 100% (total amount) of the integrated molecular weight distribution curve. The molecular weight was calculated by reducing the ratio of 20000 or less or the ratio (%) of 17000 or less.

The SEC conditions are shown below.
High-speed GPC device: HLC-8120 GPC (manufactured by Tosoh Corporation)
Analysis software: GPC-8020 modelII (manufactured by Tosoh Corporation)
Detector: RI (built-in device)
Mobile phase: Reagent grade 1 THF (containing antioxidant dibutylhydroxytoluene)
Flow rate: 0.6ml / min Injection: 0.1wt% x 20μL
Column: TSKgel SuperHM-L (6.0mm ID x 15cmL x 2) (manufactured by Tosoh Corporation)
Column temperature: 40 ° C
Calibration sample: monodisperse polystyrene Calibration method: polystyrene conversion Calibration curve approximation formula: cubic formula.

<Number average molecular weight of PTMG component in PTMG copolymerized PBT, ratio of molecular weight 20000 or 17000 or more, SEC measurement>
To about 10 g of PTMG copolymerized PBT pulverized into a fine powder, 50 ml of a 20% by mass aqueous sodium hydroxide solution is added and heated to reflux until dissolved in a reflux apparatus with a Dimroth condenser. Thereafter, the mixture is cooled, and excess sodium hydroxide is neutralized with terephthalic acid. The solution is filtered. The filtrate contains PTMG that has formed a copolymer. The filtrate was analyzed and calculated by the method described in <PTMG number average molecular weight, ratio of molecular weight 20000 or 17000 or more SEC measurement>, and the ratio of molecular weight 20000 or less or 17000 or less (%) was calculated.

<Melt viscoelasticity tan δ, α>
The melt viscoelasticity was measured using ARES-G2 (TA Instruments) by the following method.
The pellets were vacuum dried at 120 ° C. for 8 hours and pressed at 240 ° C. to prepare a sheet. Thereafter, a circular sample piece having a diameter of 25 mm was prepared by a punching machine. The measurement conditions are as follows.

Measuring device: ARES-G2 (TA Instruments)
Measuring jig: Cone Plate 25mm. 0.02rad Gap thickness 0.5mm
Measurement conditions: Oscillation Frequency
Temperature 240 ℃
Test Parameters Strain 10%
Logarithmic sweep, Angular frequency 1.0 to 600rad / S
Points per decade 10
Tan δ at angular velocities of 101 rad / s and 102 rad / s was determined and the ratio was α.

^{<MVR Melt volume flow rate (cm} 3/10 minutes)>
Prior to measurement, the pellets were vacuum dried at 120 ° C. for 8 hours.
MVR was measured at 245 ° C. under a load of 2.16 kg using a melt indexer model L242-4431 manufactured by Tateyama Kagaku in accordance with the test method described in ISO1133. Specifically, 6 g of the sample is put in a cylinder of a melt indexer set at 245 ° C., a piston is set, a 2.16 kg load is applied to the resin heated to 245 ° C., and the orifice passes through 2.095 mm, It was determined in terms and MVR ^(cm 3/10 min) from the capacitance of time flowing resin in volume flowing out in 10 minutes.

<Charpy impact strength (kJ / m ² )>
Digital impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd. Model: Using DG-UB, ISO
The test was conducted at 179-1 under the following conditions. The notch was cut using a notching tool model A-3 manufactured by Toyo Seiki Seisakusho Co., Ltd.
Hammer capacity: 2J, 7.5J
Specimen type: ISO179 / 1eA (r = 0.25 ± 0.05, width = 8.0 ± 0.2)
Notch: Cutting processing Note that the larger the Charpy impact strength, the better.

<Tensile fracture nominal strain (%)>
The pellet was dried with an air dryer at 120 ° C. for 8 hours, and a molded piece (test piece: ISO-1A) was injection molded under the following conditions using FE80S12ASE manufactured by Nissei Plastic Industry.
Molding temperature: 250 ° C (cylinder setting)
Mold temperature: 80 ℃ (surface temperature)
Injection speed: 200mm ± 100mm / s (injection time about 2 seconds)
Holding pressure time: 20 seconds Cooling time: 10 seconds About the test piece obtained Stroke AP model manufactured by Toyo Seiki Seisakusho Co., Ltd .: APII was used to perform a tensile test by the method of ISO527-1,2 and tensile fracture The nominal strain was measured.
Test piece: ISO-1A
Test speed: 50mm / min
Test speed: 50mm / min
In addition, it is preferable that the tensile fracture nominal strain is large.

<Terminal carboxyl group concentration AV (equivalent / ton)>
After pulverizing the pellets, the sample was dried at 140 ° C. for 15 minutes in a hot air drier, cooled to room temperature in a desiccator, 0.1 g was accurately weighed and collected in a test tube, and 3 ml of benzyl alcohol was added. The solution was dissolved at 195 ° C. for 3 minutes while blowing dry nitrogen gas, and then 5 ml of chloroform was gradually added and cooled to room temperature. One to two drops of phenol red indicator were added to this solution, and titrated with a 0.1N sodium hydroxide benzyl alcohol solution with stirring while blowing dry nitrogen gas, and the procedure was terminated when the color changed from yellow to red. Moreover, the same operation was implemented as the blank, without dissolving the said sample, and the amount of terminal carboxyl groups (acid value) was computed by the following formula | equation.

Terminal carboxyl content (equivalent / ton) = (ab) × 0.1 × f / w
(Where a is the amount of benzyl alcohol solution of 0.1N sodium hydroxide required for titration (μl), b is the amount of benzyl alcohol solution of 0.1N sodium hydroxide required for titration without sample. (Amount (μl), w is the amount (g) of the sample, and f is the titer of a benzyl alcohol solution of 0.1 N sodium hydroxide.)

<Amount of cyclic PTMG oligomer in PTMG (% by mass)>
In the measurement of the amount of cyclic PTMG oligomer in PTMG, the amount of cyclic PTMG oligomer was identified by the following GC / MS, and diethylene glycol dibutyl ether was calculated as an internal standard by GC / FID under the same conditions as GC / MS.

GC / MS analyzer: Agilent Technologies 6890 (manufactured by Agilent Technologies)
Mass spectrometer: Water GCT Premier
Column: GL Science InertCap1 15m × 0.25mmI.D. Film thickness 0.25μm
Temperature rising condition: 60 ℃ ⇒10 ℃ / min⇒300 ℃ (10min)
Inlet temperature: 280 ℃
Carrier gas: He 1ml / min
Split ratio: 1/20
Ionization method: EI, CI
Measurement mass range: EI m / z = 20-500 CI m / z = 70-500
CI reaction gas: Isobutane Injection volume: 1 μL

GC / FID analyzer: Agilent Technologies 6890 (manufactured by Agilent Technologies)
Column: GL Science InertCap1 15m × 0.25mmI.D. Film thickness 0.25μm
Temperature rising condition: 60 ℃ ⇒10 ℃ / min⇒300 ℃ (10min)
Inlet temperature: 280 ℃
Carrier gas: He 1ml / min
Split ratio: 1/20
Detector temperature: 320 ° C
Injection volume: 1 μL

Analysis sample: The analysis sample was prepared by the following procedure.
A 50 wtppm acetone solution of diethylene glycol dibutyl ether was prepared. (Liquid A)
After pulverizing the pellets, the sample was dried at 140 ° C. for 15 minutes in a hot air dryer, cooled to room temperature in a desiccator, 0.1 g of the sample was precisely weighed into a 10 ml volumetric flask, and the volume was increased with the solution A. . This solution was measured as an analytical sample.

<Amount of cyclic PTMG oligomer in polymer (% by mass)>
After pulverizing the pellets, the sample was dried at 140 ° C. for 15 minutes in a hot air dryer and cooled to room temperature in a desiccator, and 0.2 g of the sample was precisely weighed, and hexafluoroisopropanol / chloroform = 2/3 (vol. 3 ml) is completely dissolved. 20 ml of chloroform is added to the solution, and 10 ml of methanol is added dropwise with stirring to reprecipitate the polymer. After standing for 3 hours, the supernatant is filtered with a 0.45 μm PTFE (polytetrafluoroethylene) filter, and the filtrate is evaporated to dryness with an evaporator. Dissolve in 1 ml dimethylformamide and filter through a 0.45 μm PTFE filter. Using diethylene glycol dibutyl ether as an internal standard, the cyclic PTMG concentration in the resin was calculated using the following apparatus.

LC equipment: Agilent 1200 series (manufactured by Agilent Technologies)
Column: CAPCELLPAK C18 MG (4.6mmI.D. × 75mm × 3μm)
Eluent A: 0.1% formic acid aqueous solution Eluent B: Acetonitrile Gradiene program (A%): 50% → 10 min → 0% (5 min)
Gradien program (B%): 50% → 10min → 100% (5min)
Flow rate: 1000 μL / min Column bath temperature: 40 ° C.
Injection volume: 10 μL
Detector: DAD (UV = 210 nm)
MS equipment: Agilent LC / MS 6130 (manufactured by Agilent Technologies)
Ion source: ESI (Positive); AJS
Fragmentor Voltage: 40-100V
Capillaly Voltage: 2000-4500V
Drying Gas, Sheath Gas: 12ml / min, 300 ℃
Nebulizer Pressure: 60psi
Nozzle Voltage: 1000-2000V
Detector: MS (ESI-Pos, Scan; m / z 100-2000)
[Example 1]

  In a transesterification reaction tank equipped with a stirrer, a nitrogen inlet, a heating device, a thermometer, and a distillation tube, 71.8 parts by mass of dimethyl terephthalate, 39.3 parts by mass of 1,4-BG, a number average molecular weight of 1000 and a molecular weight of 20000 0.05 mass% of the above components, 0.10 mass% of the component having a molecular weight of 17,000 or more, 20.4 mass parts of PTMG having a cyclic PTMG oligomer amount of 2.6 mass%, and tetrabutyl titanate as a catalyst in terms of titanium metal. Then, it was added as a 1,4-BG solution so as to be 33 mass ppm with respect to the polymer to be produced (PTMG copolymerized PBT). Subsequently, after the liquid temperature in the tank was held at 150 ° C. for 60 minutes, the temperature was raised to 210 ° C. over 90 minutes and held at 210 ° C. for 30 minutes. During this time, the ester exchange reaction was carried out for 180 minutes in total while distilling the produced methanol.

  15 minutes before the end of the transesterification reaction, magnesium acetate tetrahydrate is dissolved in 1,4-BG so as to be 48 mass ppm with respect to the polymer produced as magnesium metal, and further produced polymer Hindered phenol antioxidant (Ciba Geigy Co., Ltd., Irganox 1010: tetrakis [methylene-3 (3,5-di-tert-butyl-4-hydroxy-phenyl)) Propionate] Methane was added in a slurry state of 1,4-BG, and subsequently, an amount of 25 ppm by mass as titanium metal was added as a solution of 1,4-BG to a polymer that produces tetrabutyl titanate, followed by stirring. Transfer to a polycondensation reaction tank equipped with equipment, nitrogen inlet, heating device, thermometer, distilling tube, and vacuum outlet, and apply reduced pressure. , It was carried out polycondensation reaction.

The polycondensation reaction was gradually reduced from normal pressure to 0.4 KPa over 85 minutes, and continued at 0.4 KPa or less. The reaction temperature was maintained at 210 ° C. for 15 minutes from the start of depressurization, and then increased to 240 ° C. over 45 minutes and maintained at this temperature. The reaction was terminated when a predetermined stirring torque was reached (MVR at 245 ° C. corresponds to 65 cm 3/10 min). The time required for the polycondensation reaction was 150 minutes. (The polycondensation reaction time was defined as the time from the start of pressure reduction to the return pressure with nitrogen.)

Next, the inside of the tank was decompressed with nitrogen from the depressurized state, and then pressurized for extracting the polymer. The heat medium temperature of the die at the time of extraction was set to 235 ° C., the polymer was extruded from the die in the form of a strand, and then the strand was cooled in a cooling water tank, and then cut with a strand cutter and pelletized. The proportion of PTMG in the polymer is 20% by weight. The melt viscoelasticity at 240 ° C. of the obtained polymer was measured to determine tan δ. As a result, tan δ (10 ¹ rad / s) = 26.3, an δ (10 ² rad / s) = 11.0, and α was 2.4. The amount of cyclic PTMG oligomer in the polymer was 0.52% by mass, the nominal tensile fracture strain was 530%, and the Charpy impact strength was 23.1 kJ / m ² .
[Example 2]

In Example 1, PTMG to be copolymerized was PTMG having a number average molecular weight of 1000, a component amount of 0.05% having a molecular weight of 20000 or more, a component amount of 0.14% having a molecular weight of 17000 or more, and a cyclic PTMG oligomer amount of 3.0% by mass. Polymerization was conducted in the same manner as in Example 1 except that the PTMG copolymerized PBT was obtained. The physical property values of the obtained polymer are summarized in Table 1-1.
[Example 3]

In Example 1, PTMG to be copolymerized has a number average molecular weight of 1000, a component amount of 0.01% having a molecular weight of 20000 or more, a component amount of 0.03% having a molecular weight of 17000 or more, and a cyclic PTMG oligomer amount of 2.6% by mass. Polymerization was conducted in the same manner as in Example 1 except that the PTMG copolymerized PBT was obtained. The physical property values of the obtained polymer are summarized in Table 1-1.
[Example 4]

  In Example 1, 63.7 parts by mass of dimethyl terephthalate, 34.6 parts by mass of 1,4-BG, 0.05% component amount having a molecular weight of 20000 or more with a number average molecular weight of 1000, and 0 component amount having a molecular weight of 17,000 or more. Polymerization was carried out in the same manner as in Example 1 except that PTMG was changed to 30.5 parts by mass of 10% and the amount of cyclic PTMG oligomer was 2.7% by mass to obtain PTMG copolymerized PBT (A).

Separately, polymerization was carried out in the same manner as in Example 1 except that 88.2 parts by mass of dimethyl terephthalate and 49.1 parts by mass of BG were used to obtain a PTMG amount of 0, to obtain PBT (B). Subsequently, 66.7 parts by mass of copolymerized PBT (A) pellets and 33.3 parts by mass of PBT (B) pellets were mixed and melt-kneaded with an extruder to form pellets. The physical properties of the obtained composition are shown in Table 1-1.
[Comparative Example 1]

In Example 1, PTMG to be copolymerized was PTMG having a number average molecular weight of 1000, a component amount of 0.89% having a molecular weight of 20000 or more, a component amount of 1.48% having a molecular weight of 17000 or more, and a cyclic PTMG oligomer amount of 6.0% by mass. Polymerization was conducted in the same manner as in Example 1 except that the PTMG copolymerized PBT was obtained. The physical property values of the obtained polymer are summarized in Table 1-1.
[Example 5]

In Example 1, 80.0 parts by mass of dimethyl terephthalate, 44.2 parts by mass of 1,4-BG, 0.05% of a component having a number average molecular weight of 1000 and a molecular weight of 20000 or more, and a component of 0 having a molecular weight of 17,000 or more. Polymerization was carried out in the same manner as in Example 1 except that the amount of cyclic PTMG oligomer was changed to 10.2 parts by mass of PTMG of 2.6% by mass to obtain PTMG copolymerized PBT. The physical properties of the obtained polymer are shown in Table 1-2.
[Example 6]

In Example 5, PTMG to be copolymerized is PTMG having a number average molecular weight of 1000, a component amount of 0.05% having a molecular weight of 20000 or more, a component amount of 0.14% having a molecular weight of 17000 or more, and a cyclic PTMG oligomer amount of 3.0% by mass. Polymerization was carried out in the same manner as in Example 5 except that the PTMG copolymerization was obtained. The physical properties of the obtained polymer are shown in Table 1-2.
[Example 7]

In Example 5, PTMG to be copolymerized has a number average molecular weight of 1,000, a component amount of 0.01% having a molecular weight of 20000 or more, a component amount of 0.03% having a molecular weight of 17,000 or more, and a cyclic PTMG oligomer amount of 2.6% by mass. Polymerization was conducted in the same manner as in Example 5 except that the PTMG copolymerized PBT was obtained. The physical properties of the obtained polymer are shown in Table 1-2.
[Example 8]

In Example 1, PTMG to be copolymerized was PTMG having a number average molecular weight of 1000, a component amount of 0.07% having a molecular weight of 20000 or more, a component amount of 0.23% having a molecular weight of 17000 or more, and a cyclic PTMG oligomer amount of 1.2% by mass. Polymerization was carried out in the same manner as in Example 1 except that the PTMG copolymerized PBT was obtained. The physical property values of the obtained polymer are shown in Table 1-1.
[Comparative Example 2]

In Example 5, PTMG to be copolymerized was PTMG having a number average molecular weight of 1000, a component amount of 0.89% having a molecular weight of 20000 or more, a component amount of 1.48% having a molecular weight of 17,000 or more, and a cyclic PTMG oligomer amount of 6.0% by mass. Polymerization was conducted in the same manner as in Example 5 except that the PTMG copolymerized PBT was obtained. The physical properties of the obtained polymer are shown in Table 1-2.
[Example 9]

In Example 1, 67.8 parts by mass of dimethyl terephthalate, 36.9 parts by mass of 1,4-BG, 0.05% component amount having a molecular weight of 20000 or more with a number average molecular weight of 1000, and 0 component component having a molecular weight of 17000 or more Polymerization was carried out in the same manner as in Example 1 except that PTMG was changed to 25.5 parts by mass of 10% and cyclic PTMG oligomer amount of 2.6% by mass to obtain PTMG copolymerized PBT. The physical properties of the obtained polymer are shown in Table 1-3.
[Comparative Example 3]

In Example 9, PTMG to be copolymerized has a number average molecular weight of 1,000, a component amount of 0.89% having a molecular weight of 20000 or more, a component amount of 1.48% having a molecular weight of 17,000 or more, and a cyclic PTMG oligomer amount of 6.0% by mass. Polymerization was carried out in the same manner as in Example 9 except that the PTMG copolymerized PBT was obtained. The physical properties of the obtained polymer are shown in Table 1-3.
[Example 10]

In Example 1, 59.6 parts by mass of dimethyl terephthalate, 32.2 parts by mass of 1,4-BG, 0.05% of a component having a number average molecular weight of 1000 and a molecular weight of 20000 or more, and a component of 0 having a molecular weight of 17,000 or more. Polymerization was conducted in the same manner as in Example 1 except that PTMG was 35.6 parts by mass with 10% and cyclic PTMG oligomer amount of 2.6% by mass to obtain PTMG copolymerized PBT. The physical properties of the obtained polymer are shown in Table 1-3.
[Comparative Example 4]

  In Example 10, PTMG to be copolymerized has a number average molecular weight of 1000, a molecular weight of 0.89% or more, a molecular weight of 18,000 or more, a component weight of 1.48%, and a cyclic PTMG oligomer amount of 6.0% by weight. Polymerization was carried out in the same manner as in Example 10 except that the PTMG copolymerized PBT was obtained. The physical properties of the obtained polymer are shown in Table 1-3.

<Discussion>
When the PTMG contents are compared and compared, it can be seen that when α is in the range of 1.5 to 3.5, the Charpy impact strength and the tensile fracture nominal strain are improved. Further, as is clear from the difference in the visual state of the molten polymer in the examples and comparative examples, the above-mentioned specific high molecular weight component content and the amount of cyclic PTMG oligomer are within a predetermined range, so that the molten polymer is transparent. PTMG copolymer PBT having good properties can be obtained. This degree of transparency provides a measure of knowing that the nominal tensile strain and Charpy impact strength have been improved.

<Discussion on Difference between PTMG Copolymer PBT described in Patent Document 1 and PTMG Copolymer PBT of the Present Invention>
Patent Document 1 discloses PTMG copolymerized PBT. Regarding PTMG used as a raw material, there is no disclosure or suggestion regarding molecular weight distribution, but since the filing date is very old as Showa 47, PTMG used at that time has insufficient molecular structure control, It is presumed that the molecular weight distribution was very wide (see FIG. 1 (b)). On the other hand, PTMG used in the present invention has a narrow molecular weight distribution (see FIG. 1 (a)).

Further, the fact that the PTMG disclosed in Patent Document 1 is different in molecular structure from the PTMG used in the present invention is supported by the data of the experimental examples (Example 5 and Comparative Example 1) described above. FIG. 2 is a plot of the data of Example 5 and Comparative Example 1 of the present invention on the phase diagram described in FIG. 1 of Patent Document 1 (a diagram showing the presence or absence of phase separation).
In FIG. 1 of Patent Document 1, Example 5 of the present invention is “transparent” in a region that is “cloudy”. This fact suggests that PTMG is different in molecular structure from that used in the present invention.

  The PTMG copolymerized PBT of the present invention is improved in the tensile fracture nominal strain and impact resistance of the PBT molded product, and is applied to a wider range of applications.

Claims (5)

Polytetrafluoroethylene comprising a dicarboxylic acid component containing terephthalic acid as a main component and a diol component containing 1,4-butanediol and polytetramethylene glycol, and α represented by the following formula is 1.5 or more and 3.5 or less Methylene glycol copolymer polybutylene terephthalate.
α = tan δ (10 ¹ rad / s) / tan δ (10 ² rad / s)
(Where tan δ (10 ¹ rad / s) represents a loss tangent at a frequency of 10 ¹ rad / s in melt viscoelasticity measurement at 240 ° C., and tan δ (10 ² rad / s) is (It represents the loss tangent at a frequency of 10 ² rad / s.)   The polytetramethylene glycol copolymer polybutylene terephthalate according to claim 1, wherein the polytetramethylene glycol has a number average molecular weight of 500 to 6,000.   The polytetramethylene glycol copolymer polybutylene terephthalate according to claim 2, wherein the content of polytetramethylene glycol is 5 to 35 mass% with respect to the polytetramethylene glycol copolymer polybutylene terephthalate.   The polytetramethylene glycol copolymer polybutylene terephthalate according to claim 3, wherein the proportion of polytetramethylene glycol having a molecular weight of 17,000 or more in the polytetramethylene glycol is 0.5% by mass or less.   The polytetramethylene glycol copolymer polybutylene terephthalate according to claim 3, wherein the ratio of polytetramethylene glycol having a molecular weight of 20000 or more in the polytetramethylene glycol is 0.5% by mass or less.

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