Polybutylene terephthalate and polyester film

Abstract

The present invention provides polybutylene terephthalate, which has a sufficiently low volume resistivity at temperatures suitable for film formation and enables high-speed film formation, and a polyester film using this polybutylene terephthalate. [Solution] The volume resistivity at 250°C (ρV(250°C)) is 13 × 10 7 Polybutylene terephthalate with a resistivity of Ω·cm or less. Preferably, the volume resistivity at 285°C (ρV(285°C)) is 10 × 10⁻¹⁰. 7 Polybutylene terephthalate with a resistivity of Ω·cm or less, and a ratio of the volume resistivity at 250°C (ρV(250°C)) to the volume resistivity at 285°C (ρV(285°C)) (ρV(250°C) / ρV(285°C)) of 3.0 or less. A polyester film made by forming a film-forming material containing 50% by mass or more of this polybutylene terephthalate.

Description

[Technical Field]

[0001] This invention relates to polybutylene terephthalate (hereinafter sometimes abbreviated as "PBT"), which enables high-speed film formation, and to polyester films using this polybutylene terephthalate. [Background technology]

[0002] PBT using terephthalic acid (hereinafter sometimes abbreviated as "TPA") as the main component of the dicarboxylic acid and 1,4-butanediol (hereinafter sometimes abbreviated as "BDO") as the main component of the diol has excellent mechanical properties, heat resistance, moldability, and recyclability, as well as high mechanical strength and excellent chemical resistance, and is therefore widely used as a material for industrial molded products such as connectors, relays, and switches for automobiles and electrical and electronic equipment. BPT is also widely used as a molding material for films, sheets, and fibers (filaments), and consequently, there is a demand for high-quality PBT.

[0003] PBT film, in particular, boasts excellent resistance to flexural fatigue, abrasion, and pinholes, as well as superior chemical resistance, similar to polyethylene terephthalate (sometimes abbreviated as "PET"). Furthermore, unlike nylon, it does not absorb moisture and therefore does not undergo dimensional changes due to moisture absorption, which is another desirable characteristic. For these reasons, PBT film, especially biaxially oriented PBT film, has been attracting considerable attention in recent years.

[0004] In film applications, with the recent trend towards high-speed film manufacturing, problems have arisen, such as deterioration of flatness during film melt extrusion and decreased productivity due to film breakage. In film manufacturing methods where an unstretched sheet is obtained by extruding from a T-die and casting onto a cooling roll, and then stretched, it is necessary to improve the adhesion between the extruded sheet-like molten material and the surface of the cooling roll in order to eliminate surface defects in the resulting film and improve thickness uniformity. As a method to improve the adhesion between the sheet-like molten material extruded from the T-die and the surface of the cooling roll, a method (electrostatic adhesion casting method) is effective, in which a wire-shaped electrode is placed between the extrusion die and the cooling roll, a high voltage is applied, and static electricity is generated on the surface of the unsolidified sheet-like molten material, causing the sheet-like molten material to adhere to the surface of the cooling roll and cool rapidly. To effectively perform this electrostatic adhesion casting method, PBT is required that has a low volume resistivity during melting (hereinafter sometimes abbreviated as "ρV") and high adhesion to the cooling roll during film melt extrusion.

[0005] Patent Document 1 states that the volume resistivity value when melted at 285°C is 8 × 10⁻⁶. 7 While polyester resin pellets with a resistivity of Ω·cm or less are disclosed, Patent Document 1 specifically describes only PET as a polyester resin, with no specific disclosure regarding PBT, and certainly no mention or suggestion of the volume resistivity of PBT at 250°C. Since PET does not melt at 250°C, it is not possible to measure its volume resistivity at 250°C.

[0006] Patent Document 2 states that the volume resistivity at 285°C is ρν ≤ 10 × 10 7 Although a biaxially oriented polyester film for back-surface protection of solar cells that satisfies Ω·cm has been disclosed, this Patent Document 2 also specifically mentions only PET as the polyester resin, and there is no specific disclosure regarding PBT, much less any mention or suggestion of the volume resistivity of PBT at 250°C. As mentioned above, PET does not melt at 250°C, so it is not possible to measure its volume resistivity at 250°C.

[0007] Patent Document 3 states that the melting resistivity is 0.10 × 10 8 Ω cm or more, 1.0×10 8 A biaxially oriented polybutylene terephthalate film with a resistivity of Ω·cm or less is disclosed, and the polyester resin composition used therefor has a melting resistivity of 1.0 × 10 at 265°C. 8 Ω·cm or less, preferably 0.5 × 10⁻⁶ 8Ω·cm or less, more preferably 0.25 × 10⁻⁶ 8 Although it is stated to be Ω·cm or less, in the example of Patent Document 3, the volume resistivity at 250°C of the PBT (Mitsubishi Engineering Plastics Novaduran 5020, melting point 220°C) used in the manufacture of the PBT film is 13 × 10⁻¹⁰, as shown in Comparative Example 8 below. 7 It exceeds Ω·cm. Furthermore, Patent Document 3 states that it is preferable to include alkaline earth metal compounds and phosphorus compounds in the film in a mass ratio (M2 / P) of alkaline earth metal atoms (M2) to phosphorus atoms (P) of 1.2 or more and 5.0 or less. It also states that if the M2 / P value exceeds 5.0, the adverse effects such as the promotion of foreign matter formation and discoloration of the film become greater than the effect of reducing the melting resistivity, and are therefore undesirable. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2016-132733 [Patent Document 2] Japanese Patent Publication No. 2014-80609 [Patent Document 3] International Publication No. 2015 / 072163 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] As described above, while studies have been conducted on polyester resins with low volume resistivity to effectively perform electrostatic adhesion casting, PBT with sufficiently low volume resistivity at temperatures suitable for film formation has not been provided. The object of the present invention is to provide a polybutylene terephthalate that has a sufficiently low volume resistivity at temperatures suitable for film formation and enables high-speed film formation, and a polyester film using this polybutylene terephthalate. [Means for solving the problem]

[0010] The inventor of the present invention has found PBT that can solve the above problems and has completed the present invention. That is, the gist of the present invention is as follows.

[0011] [1] Polybutylene terephthalate having a volume resistivity (ρV(250°C)) at 250°C of 13×10 7 Ω·cm or less.

[0012] [2] The polybutylene terephthalate according to [1], having a volume resistivity (ρV(285°C)) at 285°C of 10×10 7 Ω·cm or less.

[0013] [3] The polybutylene terephthalate according to [1] or [2], wherein the ratio (ρV(250°C) / ρV(285°C)) of the volume resistivity (ρV(250°C)) at 250°C to the volume resistivity (ρV(285°C)) at 285°C is 3.0 or less.

[0014] [4] The polybutylene terephthalate according to any one of [1] to [3], having a solution haze measured by the following method of 40% or less. <Measurement method of solution haze> For a solution prepared by dissolving 2.70 g of polybutylene terephthalate in 20 mL of a mixed solvent of phenol / tetrachloroethane = 3 / 2 (mass ratio), measure the solution haze with a cell length of 10 mm.

[0015] [5] The content of titanium atoms (Ti) is 37 to 100 ppm, the content of alkaline earth metal atoms (M2) is 15 ppm or less, the content of phosphorus atoms (P) is 9 ppm or less, and The mass ratio (M2 / P) of alkaline earth metal atoms (M2) to phosphorus atoms (P) is 5.1 or more. The polybutylene terephthalate according to any one of [1] to [4].

[0016] [6] A polyester film obtained by forming a film-forming raw material containing 50% by mass or more of polybutylene terephthalate as described in any of [1] to [5]. [Effects of the Invention]

[0017] The polybutylene terephthalate of the present invention has a low volume resistivity at temperatures suitable for film formation, enabling high-speed film formation and resulting in excellent film productivity. Furthermore, by adjusting the titanium atom content and solution haze of the polybutylene terephthalate to predetermined values, it is possible to obtain higher quality films with fewer fisheye defects. Furthermore, the polybutylene terephthalate of the present invention has a low volume resistivity at temperatures suitable for forming blended films of PET (pellets) and PBT (pellets), enabling high-speed film formation. It also offers excellent productivity in PET and PBT blended films, resulting in high-quality PET / PBT blended films with fewer fisheye defects. Therefore, by using the polybutylene terephthalate of the present invention, polyester films such as PBT films and PBT / PET blend films can be efficiently manufactured with high productivity and yield. [Modes for carrying out the invention]

[0018] The present invention will now be described in detail, but the following description of the constituent elements is representative of embodiments of the present invention, and the present invention is not limited to these.

[0019] <pbt> (Dicarboxylic acid components, diol components, copolymer components) In the present invention, PBT refers to a polymer having a structure in which terephthalic acid (TPA) and 1,4-butanediol (BDO) are ester-bonded, wherein 50 mol% or more of the dicarboxylic acid component consists of the TPA component, and 50 mol% or more of the diol component consists of BDO. The proportion of the TPA component in the total dicarboxylic acid component is preferably 70 mol% or more, more preferably 80 mol% or more, and particularly preferably 95 mol% or more. The proportion of BDO in the total diol component is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 95 mol% or more. If the TPA component or BDO is less than 50 mol%, the crystallization rate of PBT decreases, and the flexural fatigue resistance, abrasion resistance, pinhole resistance, and chemical resistance deteriorate.

[0020] In the present invention, there are no particular restrictions on the dicarboxylic acid components other than terephthalic acid that constitute PBT. Examples 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; aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid; or derivatives thereof. These dicarboxylic acid components other than terephthalic acid may be used individually or in combination of two or more. Regarding the manufacturing method of PBT, there are two main methods: the direct gravure method using terephthalic acid (TPA) as the dicarboxylic acid component, and the DMT method using terephthalic acid esters such as dimethyl terephthalate. However, from the viewpoint of manufacturing cost, it is preferable to use TPA as the dicarboxylic acid component raw material for the PBT of the present invention and to manufacture PBT by the direct gravure method.

[0021] In the present invention, there are no particular restrictions on the diol components other than BDO that constitute PBT. Examples 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; aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. These diol components other than BDO may be used individually or in combination of two or more.

[0022] The PBT of the present invention may further use one or more of the following as copolymerization components: monofunctional components such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, p-β-hydroxyethoxybenzoic acid, hydroxycarboxylic acids, alkoxycarboxylic acids, stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, and benzoylbenzoic acid; and trifunctional or polyfunctional components such as tricarbaryl acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, trimethylolethane, trimethylolpropane, glycerol, and pentaerythritol.

[0023] (Concentration of terminal carboxyl groups, concentration of terminal hydroxyl groups, concentration of terminal vinyl groups) 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. When the terminal carboxyl group concentration is too high, the hydrolysis resistance may deteriorate. In order to make this value less than 0.1 equivalent / ton, economically disadvantageous conditions such as an extremely small production scale must be adopted, which is not realistic.

[0024] The terminal hydroxyl group concentration of the PBT of the present invention is usually 23 to 60 equivalents / ton, preferably 25 to 50 equivalents / ton, more preferably 27 to 45 equivalents / ton, particularly preferably 30 to 40 equivalents / ton. When the terminal hydroxyl group concentration is too high, the amount of tetrahydrofuran (hereinafter sometimes abbreviated as "THF") generated due to the decomposition of the terminal hydroxyl group during melting such as molding increases. For example, THF is generated during film formation, resulting in appearance defects derived from THF, which is not preferable. If the terminal hydroxyl group concentration is above the above lower limit, the production of PBT is easy.

[0025] 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, more preferably 1 to 11 equivalents / ton. When the terminal vinyl group concentration is too high, it causes deterioration of the color tone. Due to the thermal history during molding, the terminal vinyl group concentration tends to further increase. Therefore, in the case of a high molding temperature or a production method having a recycling process, the color tone deterioration becomes more prominent. If the terminal vinyl group concentration is above the above lower limit, the production of PBT is easy.

[0026] The terminal carboxyl group concentration, terminal hydroxyl group concentration, and terminal vinyl group concentration of PBT can be determined by the methods described in the Examples section below.

[0027] <Production method of PBT> The PBT of the present invention is manufactured through a process of mixing a dicarboxylic acid component mainly composed of TPA and a diol component mainly composed of BDO in a predetermined ratio under stirring to form a raw material slurry; then heating the raw material slurry under normal or reduced pressure to cause an esterification reaction to form a low-polymer (oligomer) of PBT; and then gradually reducing the pressure of the obtained oligomer and heating it to cause a melt polycondensation reaction to obtain PBT.

[0028] An example of a process for obtaining an oligomer is to use a single esterification reactor or a multi-stage reactor consisting of multiple esterification reactors connected in series, and carry out the esterification reaction with or without a catalyst, under atmospheric pressure or reduced pressure, while removing the water and excess diol components produced in the reaction from the system, until the esterification reaction rate (the percentage of all carboxyl groups of the starting material dicarboxylic acid that react with the diol component and become esterified) reaches 90% or more, thereby obtaining an oligomer.

[0029] Typically, the temperature for the esterification reaction is preferably 212-233°C, more preferably 220-230°C, and even more preferably 223-228°C. Lower esterification reaction temperatures tend to delay the reaction, while higher esterification reaction temperatures tend to increase the amount of THF produced as a by-product and increase the molar ratio of the raw materials consumed. The pressure for the esterification reaction is preferably around 10 to 133 kPa, and the residence time in the esterification reaction vessel is preferably around 1 to 4 hours.

[0030] An example of a melt polycondensation process is a multi-stage reactor using a single melt polycondensation tank or multiple melt polycondensation tanks connected in series, for example, a fully mixed reactor with a stirring blade in the first stage, and horizontal plug-flow reactors with stirring blades in the second and third stages, in which the diol produced is distilled out of the system while heating under reduced pressure in the presence of a catalyst.

[0031] Generally, the temperature of the polycondensation reaction is 210 to 280°C, preferably about 220 to 250°C, and the pressure is 27 kPa or less, preferably 13 kPa or less under reduced pressure. The reaction tank can be single or multi-stage, but in order to suppress coloring and deterioration and to suppress the increase of end groups such as vinyl groups, in at least one reaction tank, it is preferably carried out under a high vacuum of usually 1.3 kPa or less, preferably 0.3 kPa or less. To increase the reaction rate, conditions such as increasing the degree of vacuum, increasing the heating rate, and increasing the renewal rate of the reaction liquid surface can be adopted.

[0032] The PBT obtained by the polycondensation reaction is usually withdrawn in the form of strands or sheets from the outlet provided at the bottom of the polycondensation reaction tank, and then cut with a cutter into granular forms such as pellets or chips (for example, about 3 to 10 mm in length) while being cooled with water or after being cooled with water.

[0033] <Solid-phase polymerization of PBT> If necessary, the PBT pellets of the present invention can also be obtained by subjecting the PBT obtained by the above melt polycondensation reaction to solid-phase polymerization. Solid-phase polymerization is usually carried out under reduced pressure or under an inert gas stream in order to prevent oxidative degradation of PBT. The temperature is not particularly limited, but if it is too high, coloring tends to increase, and if it is too low, the molecular weight does not increase at a practical rate. Therefore, it is usually 150 to 220°C, preferably 160 to 215°C, more preferably 180 to 213°C, and still more preferably 190 to 210°C. The time for solid-phase polymerization is not particularly limited, but in the case of a copolymer system with a low melting point, conditions of low temperature and long time are selected, and in the case of wanting to increase production efficiency, conditions of high temperature and short time are selected. Generally, as the solid-phase polymerization time after reaching a predetermined temperature, it is usually 2 to 20 hours, preferably 3 to 15 hours, and more preferably 4 to 12 hours.

[0034] <Polycondensation catalyst> When polycondensing the oligomer obtained by the esterification reaction of the diol component and the dicarboxylic acid component, usually a titanium compound is used as the catalyst, and preferably further a compound of a Group 2A metal (alkaline earth metal) of the periodic table is used. These catalyst components may be used in the esterification reaction and then proceed directly to the polycondensation reaction, or they may not be used in the esterification reaction, or only the titanium compound catalyst may be used, with the remaining catalyst components added at the polycondensation stage. Furthermore, a portion of the final amount of catalyst to be used may be used in the esterification reaction, and additional catalysts may be added as appropriate as the polycondensation reaction progresses. In any case, in this invention, the final PBT will necessarily contain titanium and preferably alkaline earth metals which are metals of Group 2A of the periodic table, but the amount will be described later.

[0035] Specific examples of titanium compounds include inorganic titanium compounds such as titanium dioxide and titanium tetrachloride, tetraalkyl titanates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, and tetraaryl titanates such as tetraphenyl titanate. These may be used individually or in combination of two or more. Among these, tetraalkyl titanate is preferred, and among those, tetrabutyl titanate is preferred.

[0036] The amount of titanium (Ti) catalyst used is preferably 37 to 100 ppm by mass ratio as the titanium atom (Ti) content of the resulting PBT, more preferably 38 to 95 ppm, even more preferably 39 to 90 ppm, and particularly preferably 40 to 85 ppm. If the Ti atom content is higher than the above range, there is a tendency for deterioration of the color tone, hydrolysis resistance, and solution haze of the resulting PBT (due to the inevitably larger amount of precipitated Ti), and an increase in fisheyes in the resulting film. On the other hand, if the Ti atom content is lower than the above range, there is a tendency for the amount of BDO converted to THF to increase, or for polymerization reactivity to deteriorate, resulting in a longer time required to obtain PBT of the desired degree of polymerization, or for the desired degree of polymerization not to be reached at all.

[0037] During PBT production, the Ti catalyst reacts with the raw materials TPA and BDO, or by-products generated in the esterification process, during which the Ti functions as a catalyst. This reaction results in the deposition of insoluble components, rendering the catalyst ineffective. In this case, the amount of Ti catalyst decreases, increasing the volume resistivity of the resulting PBT. This means that PBT unsuitable for high-speed film deposition is produced. This is thought to be because the Ti compound becomes metal Ti, no longer contributing to the reduction of volume resistivity. Furthermore, if the Ti catalyst reacts with the raw material TPA, the raw material BDO, or by-products generated in the esterification process, and precipitates as an insoluble component in the reaction system, it is undesirable because it can lead to deterioration of the solution haze.

[0038] One method to suppress the deposition of the Ti catalyst is to adjust the BDO / TPA consumption molar ratio, as described later.

[0039] Specific examples of Group 2A metal (alkaline earth metal) compounds in the present invention include various compounds of beryllium, magnesium, calcium, strontium, and barium. However, magnesium compounds and / or calcium compounds are preferred in terms of ease of handling and availability, as well as catalytic effect, and magnesium compounds, which exhibit excellent catalytic effect, are particularly preferred. Specific examples of magnesium compounds include magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, and magnesium hydrogen phosphate. Specific examples of calcium compounds include calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide, and calcium hydrogen phosphate. These Group 2A metal compounds may be used individually or in combination of two or more. Among these, magnesium acetate is preferred.

[0040] The content of Group 2A metals in the periodic table, i.e., alkaline earth metals, in the PBT of the present invention is not particularly limited, but it is preferably 15 ppm or less in mass ratio to PBT as alkaline earth metal atoms (M2). This amount is more preferably 5 ppm or more, and even more preferably 10 ppm or more. If the content of Group 2A metals in the periodic table is too high, the color tone and hydrolysis resistance will deteriorate, and if it is too low, the polymerization properties will deteriorate.

[0041] The molar ratio (M2 / Ti) of alkaline earth metal (M2) atoms to titanium atoms in the PBT of the present invention is typically 0.01 to 100, preferably 0.05 to 10, more preferably 0.07 to 3, and even more preferably 0.10 to 1.5.

[0042] In the production of PBT according to the present invention, in addition to the titanium compounds and Group 2A metal compounds of the periodic table mentioned above, reaction aids such as antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, sodium hydroxide, and sodium benzoate may also be used.

[0043] In the production of polyester resins, phosphorus compounds are sometimes used as heat stabilization aids. However, while phosphorus compounds contribute to improved heat stability, they also inactivate the Ti catalyst. Therefore, if phosphorus compounds are added during the esterification or polymerization reaction, the reactivity deteriorates, the desired reaction activity cannot be obtained, and the esterification or polymerization reaction may not be completed or may be delayed. Furthermore, phosphorus compounds tend to worsen the hydrolysis resistance of the resulting PBT. For this reason, when using phosphorus compounds, it is preferable to add them so that the phosphorus atom (P) content is 9 ppm or less relative to the resulting PBT, more preferably 7 ppm or less, even more preferably 5 ppm or less, and particularly preferable that it be below the detection limit, i.e., no phosphorus compounds are added.

[0044] Furthermore, the content ratio (mass ratio) (M2 / P) of alkaline earth metal atoms (M2) to phosphorus atoms (P) in the PBT of the present invention is preferably 5.1 or higher, more preferably 7.0 or higher, and even more preferably 8.0 or higher. If this M2 / P mass ratio is 5.1 or higher, the volume resistivity described later can be satisfied. When no phosphorus compound is added, this M2 / P mass ratio is 10.0 or higher, taking into consideration the detection limit of P.

[0045] The metal content of titanium atoms (Ti), alkaline earth metal atoms (M2), and phosphorus atoms (P) in PBT can be measured using methods such as atomic emission, atomic absorption, and inductively coupled plasma (ICP) after recovering the metals from the PBT by methods such as wet ashing.

[0046] In order to adjust the volume resistivity of the obtained PBT to the specified range of the present invention, it is preferable that the molar ratio of BDO and TPA components consumed in the PBT manufacturing process ([BDO (moles)] / [TPA (moles)], hereinafter sometimes referred to as the "BDO / TPA molar ratio") be 1.2 or more and less than 2.0, more preferably 1.4 or more and 1.9 or less, and even more preferably 1.5 or more and 1.8 or less. If the BDO / TPA consumption molar ratio is less than 1.2, it tends to lead to a decrease in esterification reactivity and deactivation of the Ti catalyst, significantly affecting the volume resistivity of the resulting PBT. For example, even with the same Ti content, if the Ti compound used as a catalyst is deactivated, such as in a complex compound with TPA or BOD, the volume resistivity of the resulting PBT will be higher, which is considered undesirable. On the other hand, when the BDO / TPA consumption molar ratio is 2.0 or higher, thermal efficiency tends to decrease, and by-products such as THF tend to increase. ​The molar ratio of BDO / TPA consumed can be controlled by controlling the molar ratio of BDO / TPA for the esterification reaction, the amount of Ti catalyst, and the esterification reaction temperature. These, namely the molar ratio of BDO / TPA for the esterification reaction, the amount of Ti catalyst, and the esterification reaction temperature, act on the molar ratio of BDO / TPA consumed in a complex manner.

[0047] The "molar ratio of BDO / TPA for the esterification reaction" mentioned above refers to the total amount of BDO that enters the reaction tank from outside the reaction tank, such as BDO supplied together with the TPA component as the raw material slurry, BDO supplied independently of these, and BDO used as the solvent for the catalyst. When the molar ratio of BDO / TPA consumed is smaller than the molar ratio of BOD / TPA added to the esterification reaction tank, the excess BDO will be recycled and used.

[0048] <Physical properties of PBT> The physical properties and preferred physical properties of the PBT of the present invention are as follows.

[0049] (Limiting viscosity number) When the PBT pellets of the present invention are used for extrusion applications such as films, sheets or filaments, the limiting viscosity number of PBT is usually 0.85 to 1.60 dL / g, preferably 1.03 to 1.50 dL / g, more preferably 1.05 to 1.55 dL / g, still more preferably 1.10 to 1.50 dL / g, and particularly preferably 1.15 to 1.35 dL / g. When the limiting viscosity number is less than 0.85 dL / g, the extrusion formability deteriorates, leading to resin drawdown and molding defects, and the mechanical strength of extrusion-molded products such as films becomes insufficient, or the melt viscosity becomes low and the fluidity is too high, resulting in deteriorated extrusion formability. On the other hand, when the limiting viscosity number exceeds 1.60 dL / g, the melt viscosity increases, the fluidity deteriorates, and the extrusion formability tends to deteriorate.

[0050] The limiting viscosity number of PBT can be determined by the method described in the section of the examples given below.

[0051] (Solution haze) The solution haze of the PBT of the present invention, as measured by the following method, is not particularly limited, but is usually 40% or less, preferably 10% or less, more preferably 5% or less, even more preferably 3% or less, and most preferably 1% or less. A high solution haze in PBT suggests that a large amount of foreign matter is present due to the deactivation of the titanium catalyst. This phenomenon significantly reduces the commercial value of the product. <Method for measuring solution haze> For a solution prepared by dissolving 2.70 g of polybutylene terephthalate in 20 mL of a phenol / tetrachloroethane mixed solvent (3 / 2 by mass ratio), the solution haze was measured using a cell with a length of 10 mm.

[0052] The PBT solution haze can be determined more specifically by the method described in the Examples section below.

[0053] (Volume resistivity) The PBT of the present invention has a volume resistivity (ρV(250℃)) of 13 × 10⁻¹⁰ at 250℃. 7 It is less than or equal to Ω·cm, and 12 × 10 7 It is preferable that it be Ω·cm or less, and 11 × 10 7 It is more preferable that the value be Ω·cm or less. If ρV (250℃) is higher than the above upper limit, the high-speed film-forming ability of the film tends to decrease.

[0054] When considering the production of blend films of PBT with polyethylene terephthalate (PET), polyethylene naphthalate (hereinafter sometimes abbreviated as "PEN"), or polybutylene naphthalate (hereinafter sometimes abbreviated as "PBN"), film production at a higher temperature of 285°C is required. In this case, the volume resistivity (ρV(285°C)) of the PBT of the present invention at 285°C is 10 × 10⁻¹⁰ 7 It is preferable that it be Ω·cm or less, and 9 × 10 7 It is more preferable that it be Ω·cm or less, and 7 × 10 7 It is even more preferable that the value be less than or equal to Ω·cm.

[0055] Furthermore, for the PBT of the present invention, the ratio (ρV(250°C) / ρV(285°C)) of the volume resistivity value (ρV(250°C)) at 250°C to the volume resistivity value (ρV(285°C)) at 285°C is preferably 3.0 or less, more preferably 2.8 or less, still more preferably 2.5 or less, and particularly preferably 2.0 or less. On the other hand, this ratio (ρV(250°C) / ρV(285°C)) is preferably 0.5 or more, more preferably 0.7 or more, still more preferably 0.8 or more, and particularly preferably 0.9 or more. If ρV(250°C) / ρV(285°C) is within the above range, in either the case of forming a film of PBT alone or a blend film of PBT and another polyester resin such as PET, the high-speed film-forming property is excellent.

[0056] Specifically, the volume resistivity value of PBT can be determined by the method described in the section of Examples below.

[0057] <PBT Composition> To the PBT of the present invention, various particles, additives, and resins other than PBT can be added as necessary to form a PBT composition.

[0058] (Particles) When forming a film of the PBT of the present invention, inorganic particles and / or organic particles can be added to prevent blocking on the film surface. However, when the film requires transparency for optical applications or the like, it is preferable to minimize the addition amount of the particles or not to add them. Examples of the inorganic particles include calcium carbonate, barium sulfate, alumina, silica, talc, titania, kaolin, mica, zeolite, etc., and surface-treated products thereof with a silane coupling agent or a titanate coupling agent. Examples of the organic particles include particles of acrylic resins, styrene resins, crosslinked resins, etc. The particle size of these particles is preferably in the range of 0.05 to 5.0 μm in terms of the average particle size. The amount of these particles added, as a content in the PBT composition, is typically 0.001% by mass at the lower limit, preferably 0.05% by mass, and typically 2.0% by mass at the upper limit, preferably 1.0% by mass, and more preferably 0.5% by mass. These particles can be added during or after the polycondensation reaction of PBT.

[0059] (Additives) The PBT of the present invention may contain other conventional additives as needed. Other additives that can be added to the PBT of the present invention include, for example, antioxidants, ultraviolet absorbers, light stabilizers, antistatic agents, lubricants, antiblocking agents, antifogging agents, nucleating agents, plasticizers, and colorants. These additives may be used individually or in combination of two or more. These additives can be added during or after the polycondensation reaction step of the PBT. The amount of other additives added is usually 5% by mass or less, preferably 0.05 to 2% by mass, as the content in the PBT composition.

[0060] (Blending method) The method for blending the various particles and additives mentioned above is not particularly limited, but it is preferable to use a single-screw or twin-screw extruder equipped with a vent for evaporation as the kneader. Each component, including additional components, can be supplied to the kneader all at once, or they can be supplied sequentially. Alternatively, two or more components selected from each component, including additional components, can be pre-mixed.

[0061] <Polyester film> The PBT of the present invention has a low volume resistivity at temperatures suitable for film formation and excellent high-speed film formation properties, making it suitable for use as a raw material for polyester films.

[0062] In this invention, "film" encompasses "sheet." Generally, a film is a thin, flat product with a thickness that is extremely small compared to its length and width, and whose maximum thickness is arbitrarily limited, and which is usually supplied in roll form (Japanese Industrial Standard JIS K6900:1994). Generally, a sheet, according to the definition in JIS, is a thin, flat product whose thickness is generally small relative to its length and width. However, since the boundary between sheet and film is not clear, in this invention, "film" encompasses "sheet." Therefore, "polyester film" may also be "polyester sheet."

[0063] In polyester films using the PBT of the present invention as a film-forming raw material, it is preferable that the PBT content of the present invention in the film-forming raw material is 50% by mass or more. If the PBT content of the present invention in the film-forming raw material is 50% by mass or more, the effect of high-speed film formation by using the PBT of the present invention, which has a low volume resistivity, can be effectively obtained. The PBT content of the present invention in the film-forming raw material is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 62% by mass or more. The PBT content of the present invention in the film-forming raw material may be 100% by mass.

[0064] The PBT-containing film-forming raw material of the present invention may also be a PBT composition containing the PBT of the present invention as described above. This PBT composition may contain, in addition to the aforementioned particles and other additives, polyester resins other than PBT such as PET, PEN, and PBN, or resins other than polyester resins. Due to its low volume resistivity, the PBT of the present invention can exhibit excellent high-speed film-forming properties not only in PBT-only films but also in blended films of PBT with other polyester resins such as PET, PEN, and PBN.

[0065] The method for forming the polyester film of the present invention using PBT is not particularly limited, and known methods can be used. In particular, conventionally known methods are used for forming biaxially oriented films, such as sequential biaxial stretching, where the PBT pellets of the present invention or a film-making raw material containing them is melt-extruded into a film or sheet, rapidly cooled in a cooling drum to form an unstretched film or sheet, and then, after preheating the unstretched film or sheet, it is stretched in the longitudinal direction and subsequently in the transverse direction, or simultaneous biaxial stretching, where it is stretched biaxially in both the longitudinal and transverse directions simultaneously. The stretching ratio in this case is usually in the range of 2 to 6 times in both the longitudinal and transverse directions, and if necessary, the film is heat-set and / or heat-relaxed after biaxial stretching. The thickness of the biaxially oriented film is usually about 1 to 300 μm.

[0066] The lower limit of the melting temperature for the PBT pellets of the present invention is preferably 200°C, more preferably 210°C. If the melting temperature is below 200°C, unmelted material may be generated or the extrusion may become unstable. The upper limit of the melting temperature is preferably 290°C, more preferably 270°C, and even more preferably 260°C or lower. If the melting temperature exceeds 290°C, resin degradation may occur.

[0067] The method for forming a film when blending the PBT pellets of the present invention with other polyester resin pellets that have a higher melting point than PBT, such as PET pellets, is not particularly limited, and known methods similar to those described above can be used. The lower limit of the melting temperature of the above blend pellets is preferably 200°C, more preferably 210°C. If the melting temperature is below 200°C, unmelted material may be generated or the extrusion may become unstable. The upper limit of the melting temperature is preferably 300°C, more preferably 290°C, and even more preferably 285°C. If the melting temperature exceeds 300°C, resin degradation may occur. [Examples]

[0068] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the essence of the invention.

[0069] [Measurement and Evaluation Methods] The measurement and evaluation methods for PBT in the following examples and comparative examples are as follows.

[0070] (1) Volume resistivity (ρV) 15 g of resin sample was placed in a branched test tube with an inner diameter of 20 mm and a length of 180 mm. After thoroughly purging the inside of the tube with nitrogen, it was immersed in an oil bath at 250°C, and the inside of the tube was vacuum-dried for 20 minutes at a pressure of less than 1 Tor using a vacuum pump. Then, the oil bath temperature was raised to 285°C to melt the sample, and then mixed air bubbles were removed by repeatedly restoring nitrogen pressure and depressurizing. In this molten body, an area of ​​1 cm² was added. 2 Two stainless steel electrodes were inserted parallel to each other with a 5mm gap between them (the non-opposing back surfaces were covered with an insulator). After the temperature stabilized, a DC voltage of 100V was applied using a resistance meter (Hewlett-Packard "MODELHP4339B"), and the resistance values ​​at 250°C or 285°C were measured. The volume resistivity ρV(250°C) and ρV(285°C)(Ω·cm) were then calculated.

[0071] (2) Intrinsic viscosity (IV) The viscosity was determined using an Ubbelohde viscometer in the following manner: Using a phenol / tetrachloroethane mixed solvent (mass ratio 1 / 1), the number of seconds for dropping a 1.0 g / dL PBT solution and the solvent alone was measured at 30°C, and the viscosity was calculated using the following formula. IV = ((1 + 4K H η sp ) 0.5 -1) / (2K H ·C) (However, η sp =η0-1, where η is the number of seconds the PBT solution falls, η0 is the number of seconds the solvent falls, C is the concentration of the PBT solution (g / dL), and K is the concentration of the PBT solution (g / dL). H (This is Huggins' constant, and we adopted 0.33.)

[0072] (3) Titanium atom (Ti) content, alkaline earth metal atom (M2) content, phosphorus atom (P) content PBT was wet-decomposed using high-purity sulfuric acid and nitric acid for the electronics industry, and measured using a high-resolution ICP (Inductively Coupled Plasma)-MS (Mass Spectrometer) (Thermoquest).

[0073] (4) Concentration of terminal hydroxyl groups and terminal vinyl groups PBT was dissolved in a mixed solvent of deuterated chloroform / deuterated hexafluoroisopropanol / deuterated pyridine (21 / 9 / 1 volume ratio) containing trace amounts of tetramethylsilane, and the results were obtained using an AVANCE NEO spectrometer (Bruker). 1 1H NMR spectra were measured. The chemical shift reference was set with the tetramethylsilane signal at 0.00 ppm. In Tables 1 and 2, terminal hydroxyl group concentration is referred to as "terminal OH group concentration".

[0074] (5) Concentration of terminal carboxyl groups The results were obtained by dissolving 0.5 g of PBT or oligomer in 25 mL of benzyl alcohol and titrating with a 0.01 mol / L benzyl alcohol solution of sodium hydroxide. In Tables 1 and 2, the concentration of terminal carboxyl groups is referred to as "concentration of terminal COOH groups".

[0075] (6) Color tone The colors were evaluated using the ZE6000 color difference meter manufactured by Nippon Denshoku Co., Ltd., in the L, a, and b color systems. A lower b value indicates less yellowness, which is preferable. However, when the b value falls below -2.2, although there is less yellowness, the color becomes bluer, resulting in an undesirable hue. The b value is preferably in the range of -2.2 to 1.5, more preferably in the range of -2.1 to 1.3, and even more preferably in the range of -2.0 to 1.2.

[0076] (7) Solution haze 2.70 g of PBT was dissolved in 20 mL of a phenol / tetrachloroethane mixed solvent (3 / 2 by mass ratio) at 110°C for 30 minutes. After cooling in a 30°C constant temperature water bath for 15 minutes, the turbidity was measured using a Nippon Denshoku Corporation NDH-300A turbidimeter with a cell length of 10 mm. A lower value indicates better transparency.

[0077] (8) Electrostatic adhesion Unstretched films were prepared by drying PBT or a blend of PBT and PET at 120°C, melt-extruding it at 250°C, and rapidly cooling and solidifying it on a rotating cooling drum maintained at a surface temperature of 40°C. When winding these unstretched films, electrostatic adhesion was evaluated using the electrostatic pinning method based on the following criteria, considering the small variation in film thickness and the stable winding speed. A score of ○ or ◎ indicated good productivity. ○: Winding speed 30m / min or more ×: Winding speed less than 30m / min

[0078] (9) Measurement of the number of fisheyes PBT or a blend of PBT and PET is dried under a nitrogen atmosphere at 140°C for 4 hours, and film is formed using a continuous extrusion film molding machine (OCS "ME-20 / 26V2&CR-7&FS-5") under the following conditions, resulting in fisheye count (pieces / m²). 2 The fisheye count was measured using the CCD camera attached to the device while the film was being deposited, at 1m. 2 The number of fisheyes with a major axis of 16 μm or larger present in the area was automatically counted and measured. A smaller value indicates better molded appearance. The number of fisheyes is 1,000 per square meter. 2 The following is preferable: • Cylinder temperature (temperature at 4 locations between the nozzle and the bottom of the hopper): If using only PBT = 250℃-250℃-250℃-250℃ In the case of PBT+PET = 285℃-285℃-285℃-285℃ Screw rotation speed: 100 rpm • Resin pressure: 75 MPa • Chill roll temperature: 40°C Film thickness: 50μm

[0079] [Example 1] PBT was manufactured according to the following procedure. A slurry prepared by mixing 1.80 moles of BDO with 1.00 moles of TPA was continuously supplied to an esterification reactor (abbreviated as "Es" in Tables 1 and 2) equipped with a screw-type stirrer packed with PBT oligomers with a 99% esterification rate, and the esterification reaction was carried out. The esterification reactor was supplied with a BDO solution containing tetrabutyl titanate catalyst in an amount that resulted in a titanium content of 40 ppm relative to PBT. Additional BDO was supplied to the esterification reactor so that the molar ratio of BDO to TPA (BDO / TPA molar ratio in Es) was 2.6. The reactor temperature was 226°C, the pressure was 60 kPa, and the average residence time was 180 minutes. Next, the PBT oligomer with an esterification rate of 96.5% was continuously transferred to the first polycondensation reactor. In the first polycondensation reactor, the polycondensation reaction was carried out continuously in the presence of magnesium acetate tetrahydrate catalyst in an amount of 10 ppm relative to PBT. The reaction temperature was 230°C, the pressure was 3.9 kPa, and the average residence time was 120 minutes. Next, this product was transferred to the second polycondensation reactor and 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. Next, the product was continuously supplied to the third polymerization reactor, which was adjusted to a temperature of 238°C and a pressure of 130 Pa, and the polymerization reaction was further carried out with stirring for a residence time of 80 minutes to obtain the polymer.

[0080] The obtained polymer was extracted via an extraction gear pump through an extraction line, filtered, and continuously extracted in strand form from a die head. It was then cut with a rotary cutter to obtain PBT pellets (approximately 3 mm in major diameter, 2 mm in minor diameter, and 4 mm in length). The intrinsic viscosity (IV) of the obtained PBT was 1.20 dL / g. The molar ratio of BDO to TPA consumed was 1.67. The evaluation results of the obtained PBT pellets are summarized in Table 1.

[0081] [Examples 2-4, Comparative Examples 1-3] In Example 1, PBT pellets were obtained in the same manner as in Example 1, except that the Ti content, Mg content, and BDO / TPA consumption molar ratio were as shown in Tables 1 and 2. The evaluation was carried out in the same manner, and the evaluation results are summarized in Tables 1 and 2. Furthermore, in Example 4 and Comparative Example 3, the films were formed and evaluated by blending PET pellets with the following physical properties in the ratios shown in Tables 1 and 2 during film formation.

[0082] [PET pellets] Intrinsic viscosity (IV): 0.82dL / g Ti content: 4ppm Mg content: 6ppm P content: 6ppm Mg / P mass ratio: 1 Volume resistivity at 285°C (ρV(285°C)): 210 × 10⁻¹⁰ 7 Ω·cm

[0083] [Comparative Examples 4-7] In a transesterification reactor equipped with a stirrer, nitrogen inlet, heater, thermometer, and distillation tube, 71.8 parts by mass of dimethyl terephthalate, 39.3 parts by mass of BDO, and tetrabutyl titanate as a catalyst were added as a BDO solution at a concentration of 33 ppm relative to the polymer to be produced (on a titanium atom basis). The temperature of the liquid in the reactor was then maintained at 150°C for 60 minutes, then raised to 210°C over 90 minutes and held at 210°C for 30 minutes. During this time, the methanol produced was distilled off, and the transesterification reaction was carried out for a total of 180 minutes. Fifteen minutes before the end of the transesterification reaction, magnesium acetate tetrahydrate was added in BDO at a concentration of 48 ppm relative to the polymer to be produced as magnesium atoms. Then, 0.15 parts by mass of a hindered phenol antioxidant (BASF Corporation, Irganox 1010: tetrakis (methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate) was added as a BDO slurry relative to the polymer to be produced. Subsequently, tetrabutyl titanate was added as a BOD solution so that the total content of titanium atoms relative to the polymer to be produced was as shown in Table 2. The mixture was then transferred to a polycondensation reactor equipped with a stirrer, nitrogen inlet, heater, thermometer, distillation tube, and vacuum exhaust port, and the polycondensation reaction was carried out under reduced pressure.

[0084] The pressure inside the polycondensation reaction vessel was gradually reduced from atmospheric pressure to 0.4 kPa over 85 minutes, and then maintained at 0.4 kPa or lower. The reaction temperature was maintained at 210°C for 15 minutes from the start of the reduced pressure, and then increased to 240°C over 45 minutes, where it was maintained. The reaction was terminated when the predetermined stirring torque was reached. The time required for the polycondensation reaction (from the start of reduced pressure to restoration with nitrogen) was 150 minutes. Next, the tank was repressurized with nitrogen after being under reduced pressure, and then pressurized for polymer extraction. The heat transfer medium temperature at the nozzle was set to 235°C, and the polymer was extruded from the nozzle in strand form. After cooling the strand in a cooling water tank, it was cut with a strand cutter to obtain PBT pellets.

[0085] The obtained PBT pellets were evaluated in the same manner as in Example 1, and the evaluation results are summarized in Table 2. Comparative Example 7 was evaluated by blending the aforementioned PET pellets with the material described in Table 2 during film formation.

[0086] [Comparative Example 8] A similar evaluation was conducted on commercially available PBT (Mitsubishi Engineering Plastics' "NovaDuran 5020") pellets, and the evaluation results are summarized in Table 2.

[0087] [Table 1]

[0088] [Table 2]

[0089] From these results, it can be seen that the PBT pellets in the examples exhibit excellent electrostatic adhesion when forming films and produce films with fewer fisheyes, meaning they are PBT pellets with excellent high-speed film formation capabilities and film quality. In contrast, the PBT in the comparative examples all had high ρV (250°C) and ρV (285°C), resulting in poor electrostatic adhesion, and some of them had many fisheyes, leading to poor molded appearance. [Industrial applicability]

[0090] The PBT of the present invention has a low volume resistivity at a predetermined temperature, enabling high-speed film formation when manufacturing PBT-only films or blended films of PBT with other polyester resins such as PET. This makes it possible to manufacture high-quality polyester films with high productivity using the PBT of the present invention.< / pbt>

Claims

1. The volume resistivity at 250°C (ρV(250°C)) is 13 × 10⁻¹⁰ ７ Polybutylene terephthalate with a value of Ω·cm or less.

2. The volume resistivity at 285°C (ρV(285°C)) is 10 × 10 ７ The polybutylene terephthalate according to claim 1, wherein the value is Ω·cm or less.

3. The polybutylene terephthalate according to claim 1, wherein the ratio of the volume resistivity at 250°C (ρV(250°C)) to the volume resistivity at 285°C (ρV(285°C)) (ρV(250°C) / ρV(285°C)) is 3.0 or less.

4. The polybutylene terephthalate according to claim 1, wherein the solution haze measured by the following method is 40% or less. <Method for measuring solution haze> For a solution prepared by dissolving 2.70 g of polybutylene terephthalate in 20 mL of a phenol / tetrachloroethane mixed solvent (3 / 2 by mass ratio), the solution haze was measured using a cell with a length of 10 mm.

5. The titanium atom (Ti) content is 37 to 100 ppm, the alkaline earth metal atom (M2) content is 15 ppm or less, and the phosphorus atom (P) content is 9 ppm or less. The polybutylene terephthalate according to claim 1, wherein the mass ratio (M2 / P) of alkaline earth metal atoms (M2) to phosphorus atoms (P) is 5.1 or greater.

6. A polyester film obtained by forming a film-forming raw material containing 50% by mass or more of polybutylene terephthalate as described in any one of claims 1 to 5.

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