Polyester resin and polyester film

Abstract

The present invention aims to provide a polyester resin in which the amount of foreign matter is reduced and the increase in volume resistivity (ρV) is suppressed. The present invention relates to a polyester resin made using raw materials obtained by chemical recycling, wherein the total content of Na, Ca, and Zn is 1 ppm by mass or more and 50 ppm by mass or less.

Description

[Technical Field]

[0001] This invention relates to polyester resin and polyester film. [Background technology]

[0002] Polyester resins occupy an important industrial position due to their excellent mechanical and chemical properties. They possess superior thermal and mechanical properties, as well as excellent chemical resistance, scratch resistance, and transparency. As a result, they are widely used in various molded products such as fibers, films, sheets, and bottles in fields such as industrial parts, electrical and electronic components, automotive parts, food packaging, and medical packaging.

[0003] In recent years, due to growing environmental concerns and the need for resource conservation, the recycling of used PET bottles, PET films, and other PET molded products has been increasing, and methods for utilizing them are attracting attention. For example, Patent Documents 1 to 3 disclose polyester resin compositions containing recycled raw materials derived from PET bottles, and disclose mechanically recycled polyester resin and / or chemically recycled polyester resin as recycled raw materials. Furthermore, Patent Document 4 discloses a chemically recycled polyethylene terephthalate resin containing aluminum atoms and phosphorus atoms, with a particle count of 2000 particles / ml or less for foreign matter with a particle size of 0.50 to 0.69 μm as measured by a particle counter. Patent Document 5 discloses a biaxially oriented polyester film containing alkaline earth metal compounds and phosphorus compounds, and discloses a biaxially oriented polyester film in which the ratio of the mass of alkaline earth metal atoms to the mass of phosphorus atoms is 1.0 or more and 5.0 or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-56047 [Patent Document 2] Japanese Patent Publication No. 2023-35545 [Patent Document 3] Japanese Patent Publication No. 2023-36069 [Patent Document 4] Japanese Patent Publication No. 2024-28087 [Patent Document 5] Japanese Patent Publication No. 2024-18209 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, recycled PET raw materials derived from PET molded products tend to contain more impurities compared to petroleum-derived PET raw materials (virgin PET raw materials). Furthermore, in order to achieve good properties in polyester films, there is a demand to keep the volume resistivity (ρV) low. However, adding metal-containing catalysts to lower the volume resistivity (ρV) can cause impurities, and it has been particularly difficult to control the volume resistivity (ρV) when using recycled raw materials.

[0006] Therefore, in order to solve the problems of the conventional technology, the inventors of this invention proceeded with research with the aim of providing a polyester resin in which the amount of foreign matter is reduced and the increase in volume resistivity (ρV) is suppressed. [Means for solving the problem]

[0007] Examples of specific embodiments of the present invention are shown below.

[0008] [1] A polyester resin made from raw materials obtained by chemical recycling, A polyester resin having a total content of Na, Ca, and Zn of 1 ppm by mass or more and 50 ppm by mass or less. [2] The polyester resin according to [1], wherein the raw material obtained by chemical recycling contains dimethyl terephthalate. [3] The polyester resin according to [2], wherein the raw material obtained by chemical recycling contains 50% by mass or more of dimethyl terephthalate. [4] The polyester resin according to any one of [1] to [3], wherein the total content of Na, Ca, and Zn in the raw material obtained by chemical recycling is 1 ppm by mass or more and 50 ppm by mass or less. [5] A polyester resin according to any one of [1] to [4], wherein the content of structural units derived from monomers obtained by chemical recycling contained in the polyester resin is 10 mol% or more. [6] A polyester resin according to any one of [1] to [5], wherein the total content of Na and Ca is 1 ppm by mass or more and 50 ppm by mass or less. [7] A polyester resin according to any one of [1] to [6], wherein the Na content is 0.1 ppm by mass or more and 50 ppm by mass or less. [8] A polyester resin according to any one of [1] to [7], wherein the Ca content is 0.1 ppm by mass or more and 50 ppm by mass or less. [9] A polyester resin according to any one of [1] to [8], wherein the Zn content is 0.01 ppm by mass or more and 10 ppm by mass or less.

[10] Volume resistivity (ρV) is 5.0 × 10 7 A polyester resin as described in any of [1] to [9], having a value of Ω·cm or less.

[11] The polyester resin according to any one of [1] to

[10] , wherein the content of structural units derived from diethylene glycol is 1.5 mol% or less relative to 100 mol% of the total diol components in the polyester resin.

[12] A polyester resin according to any of [1] to

[11] , for use in the manufacture of polyester film.

[13] A polyester film formed from the polyester resin described in any of [1] to

[12] . [Effects of the Invention]

[0009] According to the present invention, a polyester resin can be obtained in which the amount of foreign matter is reduced and the increase in volume resistivity (ρV) is suppressed. [Modes for carrying out the invention]

[0010] Hereinafter, the present invention will be described in detail. The following description may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it means "X or more and Y or less", and also includes the meaning of "preferably greater than X" or "preferably less than Y". Further, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the intention of "preferably greater than X" or "preferably less than Y". In the following description, the "film" and "sheet" are not clearly distinguished, and when referred to as "film", it includes "sheet", and when referred to as "sheet", it includes "film".

[0011] (Polyester resin) This embodiment relates to a polyester resin using a raw material obtained by chemical recycling, and the total content of Na (sodium), Ca (calcium), and Zn (zinc) is 1 mass ppm or more and 50 mass ppm or less (hereinafter also referred to as this polyester resin).

[0012] In this embodiment, the total content of Na, Ca, and Zn in the polyester resin is preferably 1 mass ppm or more, more preferably 1.5 mass ppm or more, further preferably 2.0 mass ppm or more, still more preferably 2.5 mass ppm or more, and particularly preferably 3.0 mass ppm or more. Also, the total content of Na, Ca, and Zn in the polyester resin is preferably 50 mass ppm or less, more preferably 30 mass ppm or less, further preferably 20 mass ppm or less, still more preferably 15 mass ppm or less, and particularly preferably 10 mass ppm or less.

[0013] To calculate the total content of Na, Ca, and Zn in polyester resin, 2.5 g of polyester resin is heated with hydrogen peroxide in the presence of sulfuric acid, decomposed completely, and then diluted to 50 ml with distilled water. The total content of Na, Ca, and Zn is then quantified using a plasma emission spectrometer (JOBIN YVON ICP-AES "JY46P"). These total contents are then converted to mass ppm in the polyester resin.

[0014] Because the polyester resin of this embodiment has the above-described structure, the amount of foreign matter is reduced and the increase in volume resistivity (ρV) is suppressed. More preferably, the polyester resin of this embodiment uses raw materials of polyester resin obtained by chemical recycling, and the raw materials of polyester resin obtained by chemical recycling contain a predetermined amount of Na, Ca and / or Zn. This makes it easier to reduce the amount of foreign matter while keeping the volume resistivity (ρV) of the polyester resin low. A polyester resin with a low amount of foreign matter and a low volume resistivity (ρV) has good processability, such as film-forming properties. Such a polyester resin is suitable for various applications such as polyester films and polyester containers. In particular, this polyester resin is suitable for the manufacture of polyester films, and is especially preferred for the manufacture of polyester films for optical applications.

[0015] In this embodiment, it is believed that the carboxylic acid terminus of the polyester resin and metal ions of Na, Ca, and / or Zn form a salt. Therefore, by keeping the total content of Na, Ca, and Zn in the polyester resin within a predetermined range, the amount of ionic bonding can be controlled to an appropriate range, and it is expected that the volume resistivity inside the polyester resin will decrease as the ionic bonding sites are dispersed within the polyester.

[0016] The total content of Na and Ca in this polyester resin is preferably 1 ppm by mass or more, more preferably 1.5 ppm by mass or more, even more preferably 2.0 ppm by mass or more, even more preferably 2.5 ppm by mass or more, and particularly preferably 3.0 ppm by mass or more. Furthermore, the total content of Na and Ca in the polyester resin is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even more preferably 20 ppm by mass or less, even more preferably 10 ppm by mass or less, and particularly preferably 8 ppm by mass or less.

[0017] The Na content in this polyester resin is preferably 0.1 ppm by mass or more, more preferably 0.5 ppm by mass or more, even more preferably 1.0 ppm by mass or more, and particularly preferably 1.5 ppm by mass or more. Furthermore, the Na content in this polyester resin is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even more preferably 20 ppm by mass or less, even more preferably 10 ppm by mass or less, and particularly preferably 8 ppm by mass or less. By setting the Na content to be above the lower limit, the volume resistivity (ρV) of the polyester resin can be effectively suppressed. Furthermore, by setting the Na content to be below the upper limit, the amount of foreign matter in the polyester resin can be more effectively suppressed.

[0018] The Ca content in this polyester resin is preferably 0.1 ppm by mass or more, more preferably 0.3 ppm by mass or more, and even more preferably 0.5 ppm by mass or more. Furthermore, the Ca content in this polyester resin is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even more preferably 20 ppm by mass or less, even more preferably 10 ppm by mass or less, even more preferably 8 ppm by mass or less, even more preferably 5 ppm by mass or less, and particularly preferably 3 ppm by mass or less. By keeping the Ca content within the above range, the volume resistivity (ρV) of the polyester resin can be reduced without increasing the amount of foreign matter. In addition, Ca forms salts with the carboxylic acid ends of polyester and causes foreign matter, so by keeping the Ca content within the above specific range, the volume resistivity (ρV) can be effectively reduced without increasing the amount of foreign matter.

[0019] The Zn content in this polyester resin is preferably 0.00 ppm by mass or more, more preferably 0.01 ppm by mass or more, more preferably 0.05 ppm by mass or more, even more preferably 0.1 ppm by mass or more, and particularly preferably 0.3 ppm by mass or more. Furthermore, the Zn content in this polyester resin is preferably 10 ppm by mass or less, more preferably 8 ppm by mass or less, even more preferably 5 ppm by mass or less, and particularly preferably 3 ppm by mass or less. By setting the Zn content to be above the lower limit, the volume resistivity (ρV) of the polyester resin can be effectively suppressed. Furthermore, by setting the Zn content to be below the upper limit, the amount of foreign matter in the polyester resin can be more effectively suppressed.

[0020] In order to keep the Na, Ca, and / or Zn content in this polyester resin within the above range, it is preferable to use a raw material containing a predetermined amount of Na, Ca, and / or Zn, and more preferably to use a raw material obtained by chemical recycling containing a predetermined amount of Na, Ca, and / or Zn. For example, raw materials obtained by chemical recycling may contain specific metals as catalysts during manufacturing, such as during depolymerization, and the raw material obtained by chemical recycling can be obtained by appropriately adjusting the metal content during purification. Using chemically recycled raw materials is preferable from the viewpoint of resource recycling, and chemical recycling is also preferable because the amount of metal can be adjusted in processes such as depolymerization.

[0021] When using petroleum-derived raw materials, magnesium catalysts are often added in larger quantities or phosphorus catalysts are reduced to lower the ρV. However, this can lead to reduced thermal stability and increased impurities in the resulting polyester resin. In this embodiment, by using raw materials obtained through chemical recycling containing predetermined amounts of Na, Ca, and / or Zn, a polyester resin with a low ρV can be obtained without controlling the amount of catalyst added. Furthermore, by using raw materials obtained through chemical recycling containing predetermined amounts of Na, Ca, and / or Zn, catalyst addition becomes unnecessary, thus reducing the amount of impurities.

[0022] The intrinsic viscosity of this polyester resin is preferably 0.45 dL / g or higher, more preferably 0.50 dL / g or higher, even more preferably 0.53 dL / g or higher, and particularly preferably 0.55 dL / g or higher. Furthermore, the viscosity of this polyester resin is preferably 0.80 dL / g or lower, more preferably 0.75 dL / g or lower, and even more preferably 0.70 dL / g or lower. Setting the intrinsic viscosity of the polyester resin to be above the lower limit above improves stability during film formation. On the other hand, setting the intrinsic viscosity to be below the upper limit above is preferable because it has the advantage of making it easier to suppress excessive pressure increase in the film-forming extruder. The intrinsic viscosity of the polyester resin is measured at 30°C using a viscosity(IV) measuring device after accurately weighing 1 g of polyester resin, dissolving it in 100 mL of a phenol / tetrachloroethane = 50 / 50 (mass ratio) mixed solvent.

[0023] The acid value (number of terminal carboxyl groups: AV) of this polyester resin is preferably 20 eq / T or higher, more preferably 22 eq / T or higher, and even more preferably 24 eq / T or higher. Furthermore, the acid value (AV) of this polyester resin is preferably 30 eq / T or lower. If the acid value of the polyester resin is above the lower limit, the heat resistance of the polyester resin is improved, and its processability is enhanced. Furthermore, if the acid value of the polyester resin is below the upper limit, the moisture resistance of the polyester resin is improved, and it becomes less susceptible to the effects of the usage environment.

[0024] The acid value (number of terminal carboxyl groups: AV) of polyester resin is calculated using the following formula. Terminal carboxyl group weight (eq / T) = (AB) × 0.01 × f × 1000 / W Here, A is the volume (ml) of 0.01N sodium hydroxide benzyl alcohol solution required for titration, B is the volume (ml) of 0.01N sodium hydroxide benzyl alcohol solution required for blank titration, W is the volume (g) of the resin sample, and f is the titer of the 0.01N sodium hydroxide benzyl alcohol solution.

[0025] The volume resistivity (ρV) of this polyester resin is preferably 5.0×10 7 Ω·cm or less, more preferably 4.5×10 7 Ω·cm or less, still more preferably 4.0×10 7 Ω·cm or less, even more preferably 3.5×10 7 Ω·cm or less, still even more preferably 3.0×10 7 Ω·cm or less, yet still even more preferably 2.5×10 7 Ω·cm or less, particularly preferably. The lower limit of the volume resistivity (ρV) of this polyester resin is not particularly limited, but the volume resistivity (ρV) is preferably 1.0×10 6 Ω·cm or more. When the volume resistivity is within this range, the adhesion to the cooling drum by the electrostatic printing adhesion method during film formation can be improved, the film formation speed can be increased, and the productivity can be improved. By setting the volume resistivity to be not more than the above upper limit value, the film-forming property of the film can be enhanced.

[0026] The volume resistivity of the polyester resin is measured by the following method. First, put the polyester resin (resin sample) into a test tube with branches, fully replace the inside of the tube with nitrogen, then immerse it in an oil bath at 160°C, and vacuum dry the inside of the tube to 1 Torr or less for 4 hours with a vacuum pump. Next, raise the temperature of the oil bath to 295°C to melt the resin sample, then repeatedly perform nitrogen repressurization and depressurization to remove the mixed air bubbles, and insert two stainless steel electrode plates with an area of 1 cm 2 parallel to each other at an interval of 5 mm (the non-opposite back surface is coated with an insulator) into the melt. After the temperature stabilizes, apply a DC voltage of 100 V between the electrodes with a resistance meter, and obtain the volume resistivity (Ω·cm) from the resistance value at that time.

[0027] When a film with a thickness of 50 μm is produced from this polyester resin, the number of foreign matters with a particle size of 25 μm or more per 1 m 2 of the film is preferably 5000 or less, more preferably 3000 or less. By setting the number of foreign matters within the above range, the smoothness of the film can be enhanced, and the productivity during film production can be improved.

[0028] The number of foreign particles in the polyester resin is measured by the following method. First, 10 kg of the resin sample is crystallized and dried in a hot air dryer at 160°C for 4 hours to reduce the moisture content to 100 ppm or less. Then, it is melt-extruded in a 20 mm diameter uniscrew extruder at a resin temperature of 285°C and an extrusion speed of 8 kg / hour to obtain a film with a thickness of 50 μm and a width of 100 mm from a 150 mm T-die. Next, the film thickness range is confirmed by focusing on the front and back surfaces of the film. Then, using an image processing device (OCS Corporation, FS-5 FILM SCAN), images are acquired by focusing and scanning from the front to the back surface in grayscale image accumulation input mode. The maximum value of the straight-line distance between two points on the periphery of the particles recognized by the image processing device is defined as the maximum diameter, and the number of particles with a maximum diameter of 25 μm or more is counted. This operation is repeated three times in different fields of view, and the average value of the number is calculated as 1 m 2 Convert to a per unit of film area.

[0029] The content of structural units derived from diethylene glycol relative to 100 mol% of all diol components in this polyester resin is preferably 1.5 mol% or less, more preferably 1.4 mol% or less, and even more preferably 1.3 mol% or less. When the content of structural units derived from diethylene glycol relative to 100 mol% of all diol components in the polyester resin is within the above range, the decrease in the glass transition temperature (Tg) and melting point (Tm) of the polyester resin can be suppressed, and a polyester resin with excellent heat resistance and durability can be obtained. Furthermore, in this embodiment, by setting the total content of Na, Ca, and Zn within a specific range, the amount of free carboxylic acid terminals during polyester resin polymerization can be adjusted, the by-production of diethylene glycol can be suppressed, and consequently the content of structural units derived from diethylene glycol in the resulting polyester resin can be reduced.

[0030] <Polyester resin raw materials> Polyester resin is a polycondensate of aromatic or aliphatic dicarboxylic acid and diol. Typical polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), with polyethylene terephthalate (PET) being preferred. In the production of polyester resin, one type each of dicarboxylic acid and diol may be selected and produced under normal polycondensation conditions, or two or more types may be appropriately combined and produced.

[0031] Examples of dicarboxylic acid raw materials constituting this polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfondicarboxylic acid, and their ester derivatives; and aliphatic dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedionic acid, cyclohexanedicarboxylic acid, and their ester derivatives. Among these, terephthalic acid or dimethyl terephthalate is preferred as the dicarboxylic acid raw material.

[0032] In this embodiment, the polyester resin is made from raw materials obtained by chemical recycling, and it is preferable to use dicarboxylic acid obtained by chemical recycling or biomass-derived dicarboxylic acid as the dicarboxylic acid raw material. In particular, it is preferable that the dicarboxylic acid raw material mainly contains dicarboxylic acid obtained by chemical recycling, more preferably mainly contains terephthalic acid or dimethyl terephthalate obtained by chemical recycling, and especially preferably mainly contains dimethyl terephthalate.

[0033] The dimethyl terephthalate content in the raw materials obtained by chemical recycling is preferably 50% by mass or more, more preferably 65% ​​by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0034] The diol raw materials constituting this polyester resin preferably include, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-hexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, spiroglycol, etc.

[0035] In this embodiment, biomass-derived diols or diols obtained by chemical recycling may be used as diol raw materials. In this case, the raw material obtained by chemical recycling may contain ethylene glycol obtained by chemical recycling.

[0036] When the polyester resin is made of homopolyester, it is preferable that the polyester resin contains structural units derived from aromatic dicarboxylic acid components and structural units derived from aliphatic glycols. In this case, examples of aromatic dicarboxylic acids include terephthalic acid, dimethyl terephthalate, and 2,6-naphthalenedicarboxylic acid, and examples of aliphatic glycols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Typical polyesters include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN), and it is preferable that the polyester is PET. Furthermore, as the polyester resin, polyethylene terephthalate, which contains 80 mol% or more, preferably 90 mol% or more, of ethylene terephthalate units, or polyethylene-2,6-naphthalate, which contains ethylene-2,6-naphthalate units, may also be used.

[0037] On the other hand, if the polyester resin is a copolymerized polyester, it is preferable that it is a copolymer containing 30 mol% or less of a third component. The third component is a component other than the compound that is the main component of the dicarboxylic acid component constituting the polyester and the compound that is the main component of the diol component. For example, in polyethylene terephthalate, it is a component other than terephthalic acid and ethylene glycol. Examples of dicarboxylic acid components of copolymerized polyester include one or more of isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid. Examples of glycol components of copolymerized polyester include one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol.

[0038] The polyester resin preferably contains structural units derived from monomers obtained by chemical recycling. In this case, the content of structural units derived from monomers obtained by chemical recycling in the polyester resin is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more. Furthermore, all monomers constituting the polyester may be monomers obtained by chemical recycling, and the content of structural units derived from monomers obtained by chemical recycling in the polyester resin may be 100 mol%.

[0039] In this embodiment, it is preferable that the raw material obtained by chemical recycling contains at least one selected from the group consisting of Na, Ca, and Zn. In this case, the total content of Na, Ca, and Zn in the raw material obtained by chemical recycling is preferably 1 ppm by mass or more, more preferably 1.5 ppm by mass or more, even more preferably 1.8 ppm by mass or more, even more preferably 2.0 ppm by mass or more, and particularly preferably 2.5 ppm by mass or more. Furthermore, the total content of alkali metals and alkaline earth metals in the raw material obtained by chemical recycling is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even more preferably 20 ppm by mass or less, even more preferably 15 ppm by mass or less, even more preferably 10 ppm by mass or less, and particularly preferably 8 ppm by mass or less. By setting the total content of Na, Ca, and Zn to be above the lower limit, the volume resistivity (ρV) of the polyester resin can be effectively suppressed. Furthermore, by setting the total content of Na, Ca, and Zn to be below the upper limit, the amount of foreign matter in the polyester resin can be more effectively suppressed.

[0040] In this embodiment, the total content of Na and Ca in the raw material obtained by chemical recycling is preferably 1 ppm by mass or more, more preferably 1.5 ppm by mass or more, even more preferably 1.8 ppm by mass or more, even more preferably 2.0 ppm by mass or more, and particularly preferably 2.5 ppm by mass or more. Furthermore, the total content of Na and Ca in the raw material obtained by chemical recycling is preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, even more preferably 10 ppm by mass or less, even more preferably 8 ppm by mass or less, and particularly preferably 5 ppm by mass or less. By setting the total content of Na and Ca to be above the lower limit, the volume resistivity (ρV) of the polyester resin can be effectively suppressed. Furthermore, by setting the total content of Na and Ca to be below the upper limit, the amount of foreign matter in the polyester resin can be more effectively suppressed.

[0041] In this embodiment, the Na content in the raw material obtained by chemical recycling is preferably 0.1 ppm by mass or more, more preferably 0.5 ppm by mass or more, even more preferably 1.0 ppm by mass or more, and particularly preferably 1.5 ppm by mass or more. Furthermore, the Na content in the raw material obtained by chemical recycling is preferably 50 ppm by mass or less, more preferably 25 ppm by mass or less, even more preferably 10 ppm by mass or less, even more preferably 8 ppm by mass or less, and particularly preferably 5 ppm by mass or less. By setting the Na content to be above the lower limit, the volume resistivity (ρV) of the polyester resin can be effectively suppressed. Furthermore, by setting the Na content to be below the upper limit, the amount of foreign matter in the polyester resin can be more effectively suppressed.

[0042] In this embodiment, the Ca content in the raw material obtained by chemical recycling is preferably 0.1 ppm by mass or more, more preferably 0.3 ppm by mass or more, and even more preferably 0.5 ppm by mass or more. Furthermore, the Ca content in the raw material obtained by chemical recycling is preferably 50 ppm by mass or less, more preferably 30 ppm by mass or less, even more preferably 20 ppm by mass or less, even more preferably 10 ppm by mass or less, even more preferably 8 ppm by mass or less, even more preferably 5 ppm by mass or less, and particularly preferably 3 ppm by mass or less. By keeping the Ca content within the above range, the volume resistivity (ρV) of the polyester resin can be reduced without increasing the amount of foreign matter. In addition, Ca forms salts with the carboxylic acid termini of polyester and causes foreign matter, so by keeping the Ca content within the above specific range, the volume resistivity (ρV) can be effectively reduced without increasing the amount of foreign matter.

[0043] In this embodiment, the Zn content in the raw material obtained by chemical recycling is 0.00 ppm by mass or more, preferably 0.01 ppm by mass or more, more preferably 0.05 ppm by mass or more, even more preferably 0.1 ppm by mass or more, and particularly preferably 0.3 ppm by mass or more. Furthermore, the Zn content in the raw material obtained by chemical recycling is preferably 10 ppm by mass or less, more preferably 8 ppm by mass or less, even more preferably 5 ppm by mass or less, and particularly preferably 3 ppm by mass or less. By setting the Zn content to be above the lower limit, the volume resistivity (ρV) of the polyester resin can be effectively suppressed. Furthermore, by setting the Zn content to be below the upper limit, the amount of foreign matter in the polyester resin can be more effectively suppressed.

[0044] Furthermore, in this embodiment, biomass-derived raw materials may be used in the production of the polyester resin. In this case, it is preferable that the diol component of the polyester is derived from biomass. For example, biomass-derived ethylene glycol can be obtained by producing ethylene glycol via ethylene oxide from ethanol (biomass ethanol) produced from biomass as a raw material using a conventionally known method. Alternatively, commercially available biomass ethylene glycol may be used.

[0045] <Chemical Recycling> One method of chemical recycling involves sorting, crushing, and washing collected PET bottles and polyester films to remove foreign matter, followed by depolymerization to break them down into raw materials or intermediate raw materials for polyester resin, and then purifying them.

[0046] Depolymerization methods include decomposing polyethylene terephthalate with methanol under pressure to produce dimethyl terephthalate (DMT) and ethylene glycol (EG), then separating the DMT and EG by crystallization to obtain recycled DMT; and decomposing polyethylene terephthalate into bishydroxyethyl terephthalate (BHET), an intermediate raw material in resin production, by adding glycol (e.g., ethylene glycol (EG)) in the presence of a catalyst, and further decomposing it into dimethyl terephthalate (DMT).

[0047] The process of depolymerizing a polyester product to obtain dimethyl terephthalate (DMT) includes, for example, the following steps: (1) Process of crushing the recovered polyester product (2) Process to remove polymer components and foreign matter that are different from polyester. (3) A step to obtain dimethyl terephthalate (DMT) by adding pulverized polyester to methanol containing a depolymerization catalyst and carrying out depolymerization. (4) Solid-liquid separation, concentration and / or purification process of dimethyl terephthalate (DMT)

[0048] In step (1) above, the recovered polyester product is washed as necessary, then crushed into flakes. The crushing may be done underwater, and the washing and crushing steps may be performed simultaneously. The washing step may involve alkaline washing or neutral washing.

[0049] In step (2) above, polymer components other than polyester (e.g., nylon, polyethylene, polypropylene, polyvinyl chloride, etc.) contained in the pulverized material are removed. Methods such as air separation, flotation separation, and centrifugal separation can be used to remove these polymers. Furthermore, a foreign matter removal step using physical or chemical separation methods may be provided before or after these steps. In addition, a decolorization step may be provided before or after these steps.

[0050] In step (3) above, it is preferable to add 0.1 to 50 parts by mass of methanol relative to the total mass of the pulverized polyester. The reaction is preferably carried out at, for example, 150 to 280°C and a pressure of 2 to 4 MPa. For polyester resins with many impurities, it is more preferable to carry out the reaction at a pressure of 0.3 to 0.6 MPa.

[0051] In step (4) above, a solid-liquid separation step, a concentration step, and / or a purification step of dimethyl terephthalate (DMT) are performed. In the solid-liquid separation step, concentration step, and / or purification step, ethylene glycol and excess methanol components are removed from crude DMT to obtain concentrated DMT. After the depolymerization reaction, the mixed solution of crude DMT and crude ethylene glycol / methanol can be cooled and filtered to remove solid impurities. Further adsorption and ion exchange treatment may be performed to remove colorants and dissolved ions. After the solid-liquid separation step, it is preferable to distill and evaporate the mixed solution of crude DMT and crude ethylene glycol / methanol to separate and distill off ethylene glycol and methanol to obtain concentrated DMT. Alternatively, the mixed solution may be cooled to 10°C or below to crystallize the DMT, and then concentrated DMT may be obtained by solid-liquid separation of ethylene glycol / methanol and DMT. Purified dimethyl terephthalate can be obtained by vacuum evaporating this concentrated DMT under predetermined conditions. High-purity purified DMT can be obtained as described above. Note that the purified DMT may also contain oligomers in addition to DMT.

[0052] Examples of depolymerization catalysts include sodium carbonate, sodium carboxylate salts, manganese acetate, and zinc acetate. The amount of catalyst added for depolymerization is not particularly limited, but it is preferably 0.01 to 10% by mass relative to the total mass of the recycled material.

[0053] Depolymerization may be carried out in the presence of an alkali compound. Examples of alkali compounds include tetraethylammonium hydroxide (EAH), potassium hydroxide (KOH), calcium hydroxide, and sodium hydroxide. Among these, tetraethylammonium hydroxide is preferred. By adding an alkali compound together with glycol in the depolymerization step, the formation of by-products such as diethylene glycol (DEG) in the depolymerization reaction can be suppressed. This reduces the DEG content in the polymer polymerized using the low polymer obtained by depolymerization, thereby improving polymer quality.

[0054] Similarly, recycled DMT can be obtained by adding glycol (e.g., ethylene glycol (EG)) and, in the presence of a catalyst, decomposing it into bishydroxyethyl terephthalate (BHET), an intermediate raw material in resin production, and then further decomposing it into dimethyl terephthalate (DMT).

[0055] <Optional ingredients> In addition to the polyester resin, this polyester resin may optionally contain conventionally known fillers such as organic particles and inorganic particles, various additives such as nucleating agents, antioxidants, heat stabilizers, lubricants, antistatic agents, flame retardants, flame retardant aids, antiblocking agents, viscosity modifiers, and color inhibitors.

[0056] This polyester resin may contain a polycondensation catalyst used in the production of recycled polyester. Examples of metal components included in the polycondensation catalyst include antimony, phosphorus, manganese, calcium, magnesium, cobalt, tin, germanium, zinc, aluminum, and titanium. In particular, it is preferable that the metal component be at least one selected from the group consisting of antimony, germanium, aluminum, and titanium.

[0057] The method of blending the aforementioned optional components is not particularly limited. For example, methods such as directly blending the additive with polyester chips, or the so-called masterbatch method in which a masterbatch chip containing a high concentration of the additive is obtained in advance and then blended back into the polyester, can be employed.

[0058] (Method of manufacturing polyester resin) The method for producing this polyester resin includes a step of charging dimethyl terephthalate (DMT) and ethylene glycol into a molten polycondensation reactor and carrying out a polycondensation reaction. In this embodiment, it is preferable that the dimethyl terephthalate (DMT) is a monomer obtained by chemical recycling, and the polyester resin can be obtained by charging dimethyl terephthalate (DMT) and ethylene glycol into a molten polycondensation reactor and carrying out a polycondensation reaction.

[0059] Examples of polycondensation catalysts used in the polycondensation process include antimony compounds, germanium compounds, aluminum compounds, titanium compounds, phosphorus compounds, and magnesium compounds. Among these, it is preferable to use at least one selected from antimony compounds, titanium compounds, magnesium compounds, and phosphorus compounds, more preferably antimony compounds or titanium compounds, and even more preferably titanium compounds. By using the above-mentioned compounds, particularly titanium compounds, as the polycondensation catalyst, it is possible to reduce the amount of polycondensation catalyst added, thereby making it easier to suppress the generation of foreign matter originating from the polycondensation catalyst.

[0060] The polycondensation reaction between dimethyl terephthalate (DMT) and ethylene glycol is preferably carried out, for example, at 200-300°C and under a pressure of 0.01-0.5 MPa.

[0061] After the polycondensation reaction is complete, the resulting polymer is removed from the reaction vessel in strand form, cooled in water, or cut after water cooling to form pellets. The pellets can be further polymerized to a higher degree by solid-phase polycondensation as needed.

[0062] Solid-phase polycondensation reactions are carried out under an inert gas atmosphere such as nitrogen, under reduced pressure, or under an inert gas flow. The reaction temperature for solid-phase polycondensation is usually 150°C or higher, preferably 200°C or higher, while it is usually 270°C or lower, preferably 220°C or lower. The solid-phase polycondensation reaction is carried out for a relatively long time until the desired intrinsic viscosity is reached. The reaction time for solid-phase polycondensation is usually 100 hours or less, preferably 6 to 80 hours. Solid-phase polycondensation can be carried out in batch or continuous manner.

[0063] (Polyester film) This polyester resin is preferably used for the manufacture of polyester films. Furthermore, this embodiment may also relate to a polyester film formed from the above-described polyester resin. By using this polyester resin, a polyester film with fewer impurities can be obtained. In addition, since the volume resistivity (ρV) of the polyester resin in this embodiment is controlled to be low, the film-forming properties of the polyester film can be improved.

[0064] The polyester film may be a single layer or a laminated structure of two or more layers. If the polyester film is a laminated structure, it may be a multilayer structure of four or more layers, in addition to a two-layer or three-layer structure.

[0065] The polyester film may be an unoriented film (sheet) or an oriented film, but it is preferably an oriented film, and more preferably a biaxially oriented film.

[0066] The thickness of the polyester film is not particularly limited as long as it is within the range that allows it to be formed as a film, but from the viewpoint of mechanical strength, handling, and productivity, it is preferably in the range of 5 to 300 μm, more preferably 10 to 125 μm.

[0067] <Method for manufacturing polyester film> A method for manufacturing a polyester film preferably includes the step of extruding dried polyester resin pellets from a die as a molten sheet using an extruder, and then cooling and solidifying it with a cooling roll to obtain an unstretched sheet. In this case, it is preferable to improve the adhesion between the sheet and the rotating cooling drum in order to improve the flatness of the sheet, and electrostatic application adhesion and / or liquid coating adhesion methods are preferably employed.

[0068] Next, the obtained unstretched sheet is stretched in one direction using a roll or tenter type stretcher. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3 to 6 times. Then, it is stretched in a direction perpendicular to the first stretching direction, usually at 70 to 170°C, with a stretching ratio of usually 2.5 to 7 times, preferably 3 to 6 times. Subsequently, heat treatment is performed at a temperature of 180 to 270°C under tension or under relaxation of 30% or less to obtain a biaxially oriented film. In the above stretching, a method can also be adopted in which stretching in one direction is performed in two or more stages. In that case, it is preferable that the final stretching ratios in both directions are within the above ranges.

[0069] Furthermore, simultaneous biaxial stretching can also be used for the production of polyester film. Simultaneous biaxial stretching is a method in which an unstretched sheet is simultaneously stretched and oriented in the machine direction and width direction under temperature control, usually at 70 to 120°C, preferably 80 to 110°C, with a stretching ratio of usually 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in area ratio. Subsequently, heat treatment is performed at a temperature of 170 to 270°C under tension or under relaxation of 30% or less to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching apparatus employing the above stretching method, conventionally known stretching methods such as screw type, pantograph type, and linear drive type can be used. [Examples]

[0070] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0071] (Example 1) 301 parts by mass of Mitsubishi Chemical's polyethylene terephthalate film "Diafoil T369" (thickness 25 μm) and 2700 parts by mass of methanol were placed in a separable flask. 0.71 parts by mass of sodium carbonate, a transesterification catalyst, were added, and depolymerization was carried out at atmospheric pressure and 200°C for 5 hours to obtain an ethylene glycol / methanol solution containing dimethyl terephthalate (DMT). This solution was cooled to 55°C and filtered through a 1 μm membrane filter to obtain 2954 parts by mass of filtrate. This solution was cooled to 3°C to obtain an ethylene glycol / methanol-containing liquid solid mainly composed of dimethyl terephthalate (DMT). The ethylene glycol / methanol-containing liquid solid was washed with water at 3°C ​​to obtain 302 parts by mass of aqueous solid. This aqueous solid was dissolved in water at 85°C to a solid content of 20% by mass, and filtered through a 1 μm membrane filter to obtain 1508 parts by mass of aqueous solution. This solution was cooled to 20°C, the resulting solid was filtered, and the water was dried to obtain 253 parts by mass of a depolymerization composition containing dimethyl terephthalate (DMT).

[0072] 100 parts by mass of dimethyl terephthalate and 64 parts by mass of ethylene glycol, obtained by the chemical recycling described above, were charged into an esterification reactor equipped with a stirrer, a heating device, and a distillate separation column, and heated to 150°C to melt the dimethyl terephthalate. Subsequently, an ethylene glycol solution of magnesium acetate tetrahydrate was added so that the amount of magnesium added was 0.009 parts by mass per 100 parts by mass of polyethylene terephthalate obtained (resulting in a magnesium content of 10 ppm from the catalyst relative to polyethylene terephthalate). The reaction vessel was heated to 225°C over 3 hours under atmospheric pressure, and then the transesterification reaction was carried out while stirring and methanol was removed by distillation for 1 hour, thereby substantially completing the transesterification reaction and obtaining the oligomer. Next, to the oligomer transferred to the polycondensation reactor, an ethylene glycol solution of ethyl acid phosphate was added as a heat stabilizer in an amount of 0.020 parts by mass per 100 parts by mass of polyethylene terephthalate. At the same time, an ethylene glycol solution of antimony trioxide was added as a polycondensation catalyst in an amount of 0.013 parts by mass. Then, the pressure was reduced from atmospheric pressure to 0.05 kPa, the temperature was raised from 225°C to 280°C, and the reaction was carried out by holding at 280°C for 2 hours to obtain polyethylene terephthalate with an intrinsic viscosity of 0.602 dL / g.

[0073] (Comparative Example 1) Polyethylene terephthalate pellets were obtained in the same manner as in Example 1, except that dimethyl terephthalate derived from petroleum raw materials was used instead of dimethyl terephthalate obtained by the chemical recycling described above.

[0074] (Measurement and evaluation) <Metal atom content (mass ppm) in dimethyl terephthalate raw material> Approximately 0.5 g of dimethyl terephthalate (chemically recycled DMT) obtained through chemical recycling or dimethyl terephthalate derived from petroleum raw materials was placed in a platinum crucible, and 0.5-1 ml of sulfuric acid was added. The platinum crucible was heated on a ceramic heater to carbonize it, then heated with a burner, and heated in an electric furnace at 650°C for 1 hour. After cooling, 1 ml of 5% hydrofluoric acid and pure water were added. After confirming dissolution, 1.2 ml of 28% aqueous ammonia was added, and the volume was finalized to 50 ml with pure water. The obtained sample was quantified using ICP-AES (Thermo Fisher Scientific, iCAP7600Duo.) and converted to mass ppm in the chemically recycled DMT. If the content of each metal was below the detection limit, the content was considered to be 0.

[0075] <Metal atom content in polyester resin (mass ppm)> Approximately 0.5 g of polyester resin was placed in a platinum crucible, and 0.5-1 ml of sulfuric acid was added. The platinum crucible was heated on a ceramic heater to carbonize it, then heated with a burner, and heated in an electric furnace at 650°C for 1 hour. After cooling, 1 ml of 5% hydrofluoric acid and pure water were added. After confirming dissolution, 1.2 ml of 28% aqueous ammonia was added, and the volume was finalized to 50 ml with pure water. The obtained sample was quantified using ICP-AES (Thermo Fisher Scientific, iCAP7600Duo.) and converted to mass ppm in the polyester resin. If the content of each metal was below the detection limit, the content was considered to be 0.

[0076] <Intrinsic viscosity (IV)> The intrinsic viscosity of the polyester resin was measured by the following method. Approximately 0.25 g of the sample was dissolved in approximately 25 mL of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (mass ratio 1 / 1) to a concentration of 1.00 g / dL, and then cooled to 30°C. At 30°C, the number of seconds for dropping the sample solution and the solvent alone was measured using a fully automated solution viscometer (Sentec Co., Ltd., "DT553"), and the intrinsic viscosity (IV) was calculated using the following formula. IV = ((1 + 4K H η sp ) 0.5-1) / (2K H C) Here, η sp =η / η0-1, where η is the number of seconds the sample solution falls, η0 is the number of seconds the solvent alone falls, C is the concentration of the sample solution (g / dL), and K H K is Huggins' constant. H A value of 0.33 was adopted. The sample was dissolved at 110°C for 30 minutes.

[0077] <Acid value (AV): Amount of terminal carboxyl groups> The acid value (number of terminal carboxyl groups: AV) of the polyester resin was calculated using the following formula. Terminal carboxyl group weight (eq / T) = (AB) × 0.01 × f × 1000 / W Here, A is the volume (ml) of 0.01N sodium hydroxide benzyl alcohol solution required for titration, B is the volume (ml) of 0.01N sodium hydroxide benzyl alcohol solution required for blank titration, W is the volume (g) of the resin sample, and f is the titer of the 0.01N sodium hydroxide benzyl alcohol solution.

[0078] <Diethylene glycol content> 5 g of polyester resin was dissolved in 50 ml of a 4 mol / L KOH methanol solution under reflux at 220°C for 70 minutes. After cooling in a water bath, 50 g of terephthalic acid was added and shaken. The solution was filtered by suction using glass fiber, and the filtrate was measured by gas chromatography. A wax column was used, and a FID detector was employed.

[0079] <Measurement of the number of foreign particles in resin> 10 kg of polyester resin was crystallized and dried in a hot air dryer at 160°C for 4 hours to reduce the moisture content to 100 ppm or less. Then, it was melt-extruded in a 20 mm diameter uniscrew extruder at a resin temperature of 285°C and an extrusion speed of 8 kg / hour, obtaining a film with a thickness of 50 μm and a width of 100 mm from a 150 mm T-die. Next, the film thickness range was confirmed by focusing on the front and back surfaces of the film. Then, using an image processing device (OCS Corporation, FS-5 FILM SCAN), images were captured by focusing and scanning from the front to the back surface in grayscale image accumulation input mode. The maximum value of the straight-line distance between two points on the periphery of particles recognized by the image processing device was defined as the maximum diameter, and the number of particles with a maximum diameter of 25 μm or more was counted. This operation was repeated three times in different fields of view, and the average value of the count was calculated per 1 m². 2 This was converted to a per-film area ratio.

[0080] <Volume resistivity (ρV)> 23g of resin sample was placed in a branched test tube with an inner diameter of 20mm and a length of 180mm. After thoroughly purging the inside of the tube with nitrogen, it was immersed in an oil bath at 160°C and vacuum-dried for 4 hours with a vacuum pump to a pressure of less than 1 Torr inside the tube. Next, the oil bath temperature was raised to 285°C to melt the resin sample, and then the mixed air bubbles were removed by repeatedly restoring nitrogen pressure and depressurizing. In this molten material, an area of ​​1cm² was added. 2 Two stainless steel electrode plates 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 between the electrodes using a resistance meter (Hewlett-Packard "MODEL HP4339B"), and the volume resistivity (Ω·cm) was determined from the resulting resistance.

[0081] [Table 1]

[0082] The polyester resin obtained in Example 1 had a low content of impurities and a low volume resistivity (ρV). Such polyester resins have good film-forming properties. In addition, the polyester resin obtained in Example 1 had a low content of structural units derived from diethylene glycol.

Claims

1. This polyester resin is made using raw materials obtained through chemical recycling. The total content of Na, Ca, and Zn is 1 ppm by mass or more and 50 ppm by mass or less. The Na content is 0.1 ppm by mass or more and 30 ppm by mass or less. The Ca content is 0.1 ppm by mass or more and 30 ppm by mass or less. A polyester resin having a Zn content of 0.01 ppm by mass or more and 10 ppm by mass or less.

2. The polyester resin according to claim 1, wherein the raw material obtained by the aforementioned chemical recycling contains dimethyl terephthalate.

3. The polyester resin according to claim 2, wherein the raw material obtained by the chemical recycling contains 50% by mass or more of dimethyl terephthalate.

4. The polyester resin according to claim 1, wherein the total content of Na, Ca, and Zn in the raw material obtained by the chemical recycling is 1 ppm by mass or more and 50 ppm by mass or less.

5. The polyester resin according to claim 1, wherein the polyester resin contains 10 mol% or more of structural units derived from monomers obtained by chemical recycling.

6. The polyester resin according to claim 1, wherein the total content of Na and Ca is 1 ppm by mass or more and 50 ppm by mass or less.

7. The volume resistivity (ρV) is 5.0 × 10⁻⁶. ７ The polyester resin according to claim 1, wherein the density is Ω·cm or less.

8. The polyester resin according to claim 1, wherein the content of structural units derived from diethylene glycol is 1.5 mol% or less relative to 100 mol% of the total diol components in the polyester resin.

9. The polyester resin according to claim 1, for use in manufacturing polyester film.

10. A polyester film formed from the polyester resin according to any one of claims 1 to 9.

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