Biaxially oriented polyester film

Abstract

To provide a biaxially oriented polyester film which has an extremely low antimony content, excellent hygienic properties, contains less foreign matters, has excellent transparency and heat resistance as well as good printability, processability and productivity.SOLUTION: There is provided a biaxially oriented polyester film which satisfies the following requirements (1) to (5) and is used for packaging or labels. (1) The content of antimony in the film is 10 ppm or less. (2) The content of phosphorus in the film is 25 ppm or more and 75 ppm or less. (3) The intrinsic viscosity of the film is 0.51 dl / g or more and 0.70 dl / g or less. (4) The number of defects of 1 mm or larger per 1000 square meters of the film is 1.0 or less. (5) The film contains 80 mol% or more of ethylene glycol in 100 mol% of the total glycol content in the polyester resin constituting the film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyester film that is excellent in hygiene, printability, processability and productivity. [Background technology]

[0002] Polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), which are thermoplastic resins with excellent heat resistance and mechanical properties, are used in a wide variety of fields, including plastic films, electronics, energy, packaging materials, and automobiles. Among plastic films, biaxially oriented PET film is widely used in industrial and packaging fields because it offers an excellent balance of mechanical strength, heat resistance, dimensional stability, chemical resistance, optical properties, and cost.

[0003] In the field of industrial films, PET films have excellent transparency and can be used as functional films for flat panel displays (FPDs) such as liquid crystal displays and plasma displays. PET films with hydrolysis resistance are also used as backsheets for solar cells, and are used for a variety of purposes as functional films and base films.

[0004] In the field of packaging films, they are used for food packaging and as gas barrier films. In particular, films with excellent gas barrier properties are used as packaging materials for foods, medicines, electronic components, etc. that require airtightness, or as gas blocking materials, and demand has been increasing in recent years.

[0005] However, since packaging films come into direct contact with food, it is desirable for the polyester film to have as few foreign matter as possible from a hygienic standpoint. Also, since the antimony catalyst used in the process of producing (polymerizing) the raw material for polyester is potentially carcinogenic, it is desirable for the polyester film to contain as little antimony as possible or none at all.

[0006] Conventionally, there are polyester raw materials that do not use antimony catalysts, as described in, for example, Patent Documents 1 and 2. However, there is no description of a method for reducing the number of foreign matters in the film or of the desired film properties. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3461175 [Patent Document 2] Patent No. 3506236 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a biaxially oriented polyester film that has an extremely low antimony content, little foreign matter, excellent transparency and heat resistance, and also has excellent printability and print appearance, and a method for producing a film roll obtained by winding up this film. [Means for solving the problem]

[0009] The present invention, which has solved the above problems, comprises the following components. 1. A biaxially oriented polyester film that satisfies the following requirements (1) to (4): (1) The antimony content in the film is 10 ppm or less (2) The phosphorus content in the film is 25 ppm or more and 75 ppm or less. (3) The intrinsic viscosity of the film is 0.51 dl / g or more and 0.70 dl / g or less. (4) The number of defects of 1 mm or more per 1,000 square meters of film is 1.0 or less. 2. The polyester film according to 1., which is made from a polyester raw material containing at least one aluminum compound and at least one phosphorus compound as a polymerization catalyst in the polyester resin. 3. The polyester film according to either 1. or 2., wherein the haze of the film is 1% or more and 8% or less. 4. The polyester film according to any one of 1. to 3., characterized in that the heat shrinkage in the longitudinal direction measured under conditions of 150°C for 15 minutes is 0.8% or more and 3% or less. 5. A polyester film according to any one of 1. to 4., characterized in that the thickness unevenness in both the longitudinal and transverse directions measured over a length of 1 m using a continuous contact thickness meter is 1% or more and 10% or less. 6. A packaging bag comprising one or more layers of the biaxially oriented polyester film according to any one of 1. to 5. 7. A label comprising one or more layers of the biaxially oriented polyester film described in any one of 1. to 5. 8. A method for producing a biaxially oriented polyester film according to any one of 1. to 5., characterized in that a raw polyester resin is melt-extruded so that the difference in intrinsic viscosity between the raw polyester resin and the polyester film is 0.06 dl / g or less, and then cooled and solidified to obtain an unstretched film, which is then biaxially stretched and then heat-set. [Effects of the Invention]

[0010] The present invention provides a biaxially oriented polyester film that has an extremely low antimony content, little foreign matter, excellent transparency and heat resistance, and is also excellent in printability and print appearance, and a method for producing a film roll obtained by winding up this film. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes embodiments of the present invention, but the present invention should not be construed as being limited to the embodiments including the following examples, and various modifications are naturally possible within the scope of achieving the object of the invention and not departing from the gist of the invention.

[0012] (raw polyester resin) The biaxially stretched polyester film of the present invention is composed of a polyethylene terephthalate resin. The polyethylene terephthalate resin contains an ethylene glycol-derived component and a terephthalic acid-derived component as its main components. The term "main components" refers to 80 mol % or more of terephthalic acid out of 100 mol % of all dicarboxylic acid components constituting the polyester, and 80 mol % or more of ethylene glycol out of 100 mol % of all glycol components.

[0013] Other dicarboxylic acid components and glycol components may be copolymerized within a range that does not impair the object of the present invention. The copolymerization amount of the other dicarboxylic acid components and glycol components is less than 20 mol %, preferably 10 mol % or less, and particularly preferably 5 mol % or less, based on the total dicarboxylic acid components or the total glycol components, respectively. Examples of the other dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4'-dicarboxybiphenyl, and 5-sodium sulfoisophthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 2,5-norbornenedicarboxylic acid, and tetrahydrophthalic acid; and aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, octadecanedioic acid, fumaric acid, maleic acid, itaconic acid, mesaconic acid, citraconic acid, and dimer acid.

[0014] Examples of the other glycol components include aliphatic glycols such as 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 1,10-decanediol, dimethyloltricyclodecane, diethylene glycol, and triethylene glycol; bisphenol A, bisphenol S, bisphenol C, bisphenol B; Examples of the ethylene oxide adduct or propylene oxide adduct of phenol Z, bisphenol AP, 4,4'-biphenol, alicyclic glycols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol, polyethylene glycol, and polypropylene glycol are listed.

[0015] As a polymerization method for such a polyethylene terephthalate-based resin, any production method can be used, such as a direct polymerization method in which terephthalic acid and ethylene glycol, and, if necessary, other dicarboxylic acid components and glycol components, are directly reacted, or a transesterification method in which a dimethyl ester of terephthalic acid (containing a methyl ester of another dicarboxylic acid if necessary) and ethylene glycol (containing another glycol component if necessary) are subjected to a transesterification reaction, followed by a polycondensation reaction.

[0016] As the polyester resin, recycled resin made from recycled PET bottles and polyester resin containing a monomer component derived from biomass can also be used.

[0017] The biaxially oriented polyester film of the present invention may contain other resins such as polyamide, polystyrene, polyolefin, and polyesters other than those mentioned above as constituent components. However, in terms of the mechanical properties and heat resistance of the biaxially oriented polyester film, the content of other resins is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less, of the total resin components of the polyester film, and most preferably 0% by mass (all resin components constituting the polyester film are essentially polyethylene terephthalate-based resins).

[0018] The intrinsic viscosity of the polyethylene terephthalate resin is preferably in the range of 0.57 to 0.76 dL / g, more preferably 0.60 to 0.73 dL / g, and even more preferably 0.63 to 0.7 dL / g. If the intrinsic viscosity is lower than 0.57 dL / g, the polyester film is likely to tear (resulting in breakage) during production, while if it is higher than 0.76 dL / g, the filtration pressure increases significantly, making high-precision filtration difficult and making it difficult to extrude the resin through the filter. The intrinsic viscosity of the resin of the polyester film is preferably in the range of 0.51 to 0.70 dL / g, more preferably 0.56 to 0.68 dL / g, and even more preferably 0.59 to 0.65 dL / g. If the intrinsic viscosity is lower than 0.51 dL / g, the polyester film is prone to tearing during processing steps such as printing, while if the intrinsic viscosity is higher than 0.76 dL / g, the effect of improving mechanical properties is likely to become saturated.

[0019] (polymerization catalyst) Next, the polymerization catalyst used in producing the raw material polyester resin used in the present invention will be described. The polymerization catalyst used in the present invention is characterized by its ability to promote esterification. In the present invention, as described below, it is preferable to avoid the use of conventionally used polymerization catalysts containing antimony compounds such as antimony trioxide, as much as possible. As such a polymerization catalyst, a polymerization catalyst containing at least one selected from aluminum compounds and at least one selected from phosphorus-based compounds is preferred.

[0020] When synthesizing the raw material polyester resin used in the present invention, any known aluminum compound can be used as the aluminum compound constituting the polymerization catalyst used without any limitation.

[0021] Specific examples of aluminum compounds include organic aluminum compounds such as aluminum acetate, basic aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, aluminum acetylacetonate, and aluminum oxalate, as well as partial hydrolysates thereof. Of these, carboxylates, inorganic acid salts, and chelate compounds are preferred, and among these, aluminum acetate, basic aluminum acetate, aluminum lactate, aluminum chloride, aluminum hydroxide, aluminum hydroxide chloride, and aluminum acetylacetonate are more preferred, aluminum acetate, basic aluminum acetate, aluminum chloride, aluminum hydroxide, and aluminum hydroxide chloride are even more preferred, and aluminum acetate and basic aluminum acetate are most preferred.

[0022] The amount of the aluminum compound used in the polymerization catalyst according to the present invention is preferably 1 to 80 ppm, more preferably 2 to 60 ppm, still more preferably 3 to 50 ppm, particularly preferably 5 to 40 ppm, and most preferably 10 to 30 ppm, in terms of aluminum atoms remaining relative to the total mass of the resulting polyester resin. If the content is lower than the above range, the catalytic activity may be poor, and if the content is higher than the above range, aluminum-based foreign matter may be generated. Even when the aluminum compound is placed in a reduced pressure environment during polyester polymerization, almost 100% of the amount used remains, so it can be considered that the amount used is the residual amount.

[0023] The phosphorus compound used in the polymerization catalyst is not particularly limited, but the use of phosphonic acid compounds and phosphinic acid compounds is preferable because they have a significant effect of improving catalytic activity, and among these, the use of phosphonic acid compounds is particularly preferable because they have a particularly significant effect of improving catalytic activity.

[0024] Among these phosphorus compounds, phosphorus compounds having a phenol moiety in the same molecule are preferred. Although there are no particular limitations on the phosphorus compound as long as it has a phenol structure, the use of one or more compounds selected from the group consisting of phosphonic acid compounds and phosphinic acid compounds having a phenol moiety in the same molecule is preferred because it has a significant effect of improving catalytic activity. Among these, the use of one or more phosphonic acid compounds having a phenol moiety in the same molecule is particularly preferred because it has a particularly significant effect of improving catalytic activity.

[0025] Furthermore, examples of phosphorus compounds having a phenol moiety in the same molecule include compounds represented by the following general formulas (Chemical Formula 1) and (Chemical Formula 2).

[0026] [ka]

[0027] [ka]

[0028] (In formulas (chemical formula 1) to (chemical formula 2), R 1 R represents a hydrocarbon group having 1 to 50 carbon atoms and containing a phenol moiety, or a hydrocarbon group having 1 to 50 carbon atoms and a substituent such as a hydroxyl group, a halogen group, an alkoxyl group, or an amino group and containing a phenol moiety. 4 represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, or a hydrocarbon group having 1 to 50 carbon atoms containing a substituent such as a hydroxyl group, a halogen group, an alkoxyl group, or an amino group. 2 , R 3 R each independently represents hydrogen, a hydrocarbon group having 1 to 50 carbon atoms, or a hydrocarbon group having 1 to 50 carbon atoms containing a substituent such as a hydroxyl group or an alkoxyl group. However, the hydrocarbon group may contain a branched structure, an alicyclic structure such as cyclohexyl, or an aromatic ring structure such as phenyl or naphthyl. 2 and R 4 The ends of may be bonded together.)

[0029] Examples of the phosphorus compound having a phenol moiety in the same molecule include p-hydroxyphenylphosphonic acid, dimethyl p-hydroxyphenylphosphonate, diethyl p-hydroxyphenylphosphonate, diphenyl p-hydroxyphenylphosphonate, bis(p-hydroxyphenyl)phosphinic acid, methyl bis(p-hydroxyphenyl)phosphinate, phenyl bis(p-hydroxyphenyl)phosphinate, p-hydroxyphenylphenylphosphinic acid, methyl p-hydroxyphenylphenylphosphinate, phenyl p-hydroxyphenylphenylphosphinate, p-hydroxyphenylphosphinic acid, methyl p-hydroxyphenylphosphinate, phenyl p-hydroxyphenylphosphinate, etc. Other examples include phosphorus compounds represented by the following general formula (Chemical Formula 3):

[0030] [ka]

[0031] In the formula (Chemical Formula 3), X1 and X2 each represent hydrogen, an alkyl group having 1 to 4 carbon atoms, or a monovalent or higher metal. In addition, X1 may be a metal with a valence of 2 or more, and X2 may not be present. Furthermore, an anion corresponding to the excess valence of the metal may be placed relative to the phosphorus compound. The metal is preferably Li, Na, K, Ca, Mg, or Al.

[0032] By adding these phosphorus compounds having a phenol moiety in the same molecule during polyester polymerization, the catalytic activity of the aluminum compound is improved, and the thermal stability of the polymerized copolymer polyester resin is also improved.

[0033] Among the above, the phosphorus compound preferably used as the polycondensation catalyst is at least one phosphorus compound selected from the compounds represented by chemical formula (4) and chemical formula (5).

[0034] [ka]

[0035] [ka]

[0036] Irganox 1222 (manufactured by BASF) is a commercially available compound represented by the above chemical formula (Chemical Formula 4). Irganox 1425 (manufactured by BASF) is a commercially available compound represented by the above chemical formula (Chemical Formula 5), ​​and these compounds are also usable.

[0037] The amount of the phosphorus compound used in the polymerization catalyst according to the present invention is preferably such that 10 to 100 ppm, more preferably 15 to 90 ppm, still more preferably 20 to 80 ppm, particularly preferably 25 to 70 ppm, and most preferably 30 to 60 ppm remain in the resulting raw material polyester resin as phosphorus atoms relative to the total mass of the resulting raw material polyester resin. If phosphorus atoms remain in an amount exceeding the upper or lower limit, the polymerization activity may decrease. When a phosphorus compound is placed in a reduced pressure environment during polyester polymerization, approximately 10 to 30% of the amount used is removed from the system depending on the conditions. Therefore, in practice, it is necessary to conduct several trial experiments to determine the percentage of phosphorus compound remaining in the polyester before deciding on the amount to be used.

[0038] Furthermore, the use of the above phosphorus compounds can improve the heat resistance of the resin. Although the reason for this is not clear, it is thought that the hindered phenol moiety in the phosphorus compounds improves the heat resistance of the polyester resin.

[0039] If the residual amount of the phosphorus compound is less than 10 ppm, the effect of improving the heat resistance described above will be weakened, and as a result, the heat resistance and coloration improving effects of the polyester resin of the present invention may not be observed.

[0040] In order to further improve the catalytic activity, metal-containing polycondensation catalysts such as antimony compounds, titanium compounds, tin compounds, and germanium compounds may be used in combination, provided that the effects of the present invention are not impaired. In this case, the antimony compounds are preferably present in an amount of 10 ppm or less in terms of antimony atoms relative to the mass of the resulting copolymerized polyester resin, the germanium compounds are preferably present in an amount of 10 ppm or less in terms of germanium atoms relative to the mass of the resulting polyester resin, the titanium compounds are preferably present in an amount of 3 ppm or less in terms of titanium atoms relative to the mass of the resulting polyester resin, and the tin compounds are preferably present in an amount of 3 ppm or less in terms of tin atoms relative to the mass of the resulting polyester resin. From the perspective of the present invention, it is preferable to avoid the use of metal-containing polycondensation catalysts such as antimony compounds, titanium compounds, tin compounds, and germanium compounds as much as possible.

[0041] In the present invention, in addition to the aluminum compound, a small amount of at least one selected from alkali metals, alkaline earth metals, and compounds thereof may be present as a second metal-containing component. The coexistence of such a second metal-containing component in the catalyst system not only suppresses the production of diethylene glycol but also enhances catalytic activity, thereby obtaining a catalyst component with a higher reaction rate, which is effective in improving productivity. When alkali metals, alkaline earth metals, or compounds thereof are added in combination, the amount used (mol%) is preferably 1×10 based on the number of moles of the dicarboxylic acid component constituting the polyester resin. -5 Even when alkali metals, alkaline earth metals, or compounds thereof are placed in a reduced pressure environment during polyester polymerization, almost 100% of the amount used remains, so the amount used can be considered to be the residual amount.

[0042] The polymerization catalyst according to the present invention has catalytic activity not only in polycondensation reactions but also in esterification reactions and transesterification reactions. Transesterification reactions between alkyl esters of dicarboxylic acids such as dimethyl terephthalate and glycols such as ethylene glycol are usually carried out in the presence of a transesterification catalyst such as zinc, but the catalyst according to the present invention can be used instead of these catalysts. Furthermore, the polymerization catalyst according to the present invention has catalytic activity not only in melt polymerization but also in solid-phase polymerization and solution polymerization.

[0043] The polymerization catalyst for the polyester used in the present invention can be added to the reaction system at any stage of the polymerization reaction. For example, it can be added to the reaction system before the start of the esterification reaction or the transesterification reaction or at any stage during the reaction, just before the start of the polycondensation reaction, or at any stage during the polycondensation reaction. In particular, it is preferable to add the aluminum compound and the phosphorus compound according to the present invention just before the start of the polycondensation reaction.

[0044] (Preferred method for producing biaxially oriented polyester film) The biaxially stretched polyester film of the present invention may have a laminate structure of one layer, two layers, three layers, or four or more layers. In the case of a two or more layer structure, each layer contains the polyethylene terephthalate resin, inorganic particles, and a resin other than the polyethylene terephthalate resin as constituent components as described above, but it is preferable that the type or content of any of the constituent components of adjacent layers is different. In the case of a single layer structure consisting of Layer A, Layer A in the present invention corresponds to the entire biaxially stretched polyester film. In the case of a two-layer structure including Layer A, Layer A in the present invention refers to either one or both layers. In the case of a three-layer structure including Layer A, Layer A in the present invention refers to either one layer or both outer layers.

[0045] In particular, in the case of a three-layer structure, even if there are no inorganic particles in the inner layer, the surface roughness of the film can be controlled by controlling the amount of particles added only to the surface layer, and the content of inorganic particles in the film can be reduced, which is preferable because it also improves the problem of odor components escaping through voids (air gaps) that form at the boundary between the inorganic particles and the polyester resin, resulting in a decrease in aroma retention. Furthermore, it is easy to use recycled raw materials obtained by trimming the edges generated during the film-making process or recycled raw materials from other film-making processes in the inner layer, as long as it does not adversely affect the properties of the film surface, which is also advantageous in terms of cost.

[0046] Examples of inorganic particles that can be used include silica, alumina, titanium dioxide, calcium carbonate, kaolin, and barium sulfate. The average particle size of the inorganic particles is preferably within the range of 0.05 to 3.0 μm when measured using a Coulter counter. The lower limit of the inorganic particle content in the film is preferably 0.01 wt %, more preferably 0.015 wt %, and even more preferably 0.02 wt %. If the content is less than 0.01 wt %, the slipperiness may decrease. The upper limit is preferably 1 wt %, more preferably 0.2 wt %, and even more preferably 0.1 wt %. If the content exceeds 1 wt %, the transparency may decrease, which is not preferable.

[0047] As a method for incorporating inorganic particles into polyester, for example, inorganic particles are dispersed in a predetermined ratio in the form of a slurry in ethylene glycol, which is a diol component, and this ethylene glycol slurry is added at an arbitrary stage before the completion of polyester polymerization. When adding particles, it is preferable to add the aqueous sol or alcohol sol obtained during particle synthesis without first drying it, as this will result in good particle dispersibility and prevent the generation of coarse protrusions. It is also effective to directly mix the water slurry of particles with the desired polyester pellets, feed the mixture to a vented twin-screw kneading extruder, and knead the mixture into the polyester.

[0048] In the present invention, it is preferable to extrude the resin at a temperature in the extruder that is at least 2°C above the melting point of the resin and not more than 6°C above the melting point of the resin. If the extrusion temperature is less than 2°C above the melting point, the resin will not melt and an unmelted material will be extruded, which will become foreign matter, which is undesirable. Also, if the extrusion temperature is higher than 6°C above the melting point, the resin will thermally deteriorate, which will cause foreign matter to be generated, which is undesirable.

[0049] The extruded sheet-like molten resin is then extruded through a T-die and quenched to obtain an unstretched film. As a method for quenching the molten resin, a method in which the molten resin is cast from the T-die onto a rotating drum and rapidly cooled and solidified to obtain a substantially unoriented resin sheet can be preferably employed. Furthermore, sublimates of the molten resin (oligomers, etc.) tend to adhere to the T-die, and if these adhered materials fall off, they will stick to the unstretched sheet and become undesirable foreign matter in the film. For this reason, it is advisable to attach an adhesive sheet to the T-die beforehand to prevent the sublimates from falling off, and to clean the cooling roll with a cleaner while it is in operation so that any foreign matter that adheres to it is not transferred to the unstretched sheet.

[0050] The unstretched film is then biaxially stretched, followed by heat setting and heat relaxation. By appropriately combining the following film-forming conditions, such as the longitudinal and transverse stretching conditions, heat setting conditions, and heat relaxation conditions, it is possible to achieve the desired film properties described below. These are explained in detail below.

[0051] The stretching method can be either simultaneous biaxial stretching or sequential biaxial stretching, but sequential biaxial stretching is preferred from the viewpoint of fast film production speed and high productivity. In the following, a sequential biaxial stretching method by longitudinal stretching-transverse stretching in which longitudinal stretching is carried out first and then transverse stretching is carried out will be described, but the order may be reversed, i.e., transverse stretching-longitudinal stretching.

[0052] The stretching temperature in the longitudinal (machine) direction (hereinafter sometimes abbreviated as MD) is preferably (Tg + 15) to (Tg + 55)°C, and the stretching ratio is preferably 3.3 to 4.7 times, in order to reduce bowing. If the stretching temperature is higher than (Tg + 55)°C or lower than 3.3 times, bowing is reduced, but the molecular orientation in the width direction becomes too great compared to the longitudinal direction, which is undesirable as it disrupts the orientation balance. Furthermore, the flatness of the resulting biaxially stretched polyester film is also undesirable. On the other hand, if the stretching temperature is lower than (Tg + 15)°C or higher than 4.7 times, shrinkage stress increases, which increases bowing, which is undesirable.

[0053] Furthermore, in the longitudinal stretching, instead of a single-stage stretching method, a method of stretching in multiple stages between multiple rolls allows gradual stretching in the longitudinal direction while controlling the stretching speed, thereby reducing the difference in physical properties in the width direction of the film. Two-stage to five-stage stretching is preferred from the viewpoints of effectiveness, equipment, and cost.

[0054] When stretching in the width (transverse) direction (hereinafter sometimes abbreviated as TD), the unstretched film is introduced into a tenter device that can heat the film by holding both ends of the film with clips, and the film is heated to a predetermined temperature with hot air.The film is then stretched in the width direction by widening the distance between the clips while transporting it in the longitudinal direction. Furthermore, if the width direction stretching temperature is less than Tg+5°C, breakage is likely to occur during stretching, which is undesirable. Furthermore, if the temperature is higher than Tg+40°C, uniform width direction stretching is not possible, and thickness unevenness in the width direction increases, which is undesirable because the hardness of the film roll varies greatly. The temperature is more preferably Tg+8°C or higher and Tg+37°C or lower, and even more preferably Tg+11°C or higher and Tg+34°C or lower. The stretching ratio in the width direction is not particularly limited, but is preferably 2 to 6 times. If the stretching ratio is less than 2 times, it is difficult to obtain a high yield in terms of material balance, and the mechanical strength decreases. In addition, uneven thickness in the width direction causes variations in the hardness of the film roll, which is undesirable. Furthermore, if the stretching ratio exceeds 6 times, the film is prone to breakage during stretching and is undesirable.

[0055] The heat setting temperature (heat treatment temperature) after TD stretching is preferably 220 to 245°C. Heat setting temperatures higher than 245°C are undesirable because bowing increases. On the other hand, temperatures lower than 220°C are undesirable because the heat shrinkage increases in both the longitudinal and transverse directions, deteriorating the thermal dimensional stability during vapor deposition processing. Furthermore, heat setting temperatures higher than 245°C after TD stretching are undesirable because bowing increases.

[0056] During the heat relaxation treatment process, the restraining force in the width direction of the film is reduced until it shrinks due to heat relaxation, causing it to sag under its own weight. Furthermore, the film may expand due to accompanying airflow, making it prone to vertical fluctuations. Therefore, during this heat relaxation process, the orientation angle and the difference in oblique heat shrinkage rate of the resulting biaxially oriented polyester film vary greatly depending on the film transport state. One way to mitigate this is to appropriately adjust the air speeds blown from the upper and lower nozzles to keep the film parallel. The heat relaxation rate in the width direction is preferably 4 to 8%. A heat relaxation rate of less than 4% is undesirable because the heat shrinkage rate in the width direction of the resulting biaxially oriented polyester film increases, resulting in poor dimensional stability during vapor deposition processing. On the other hand, a heat relaxation rate of more than 8% is undesirable because it increases bowing and sagging, resulting in greater thickness unevenness in the width direction and therefore greater variation in the hardness of the film roll.

[0057] The film stretched and formed by the above method is wound up by a winder to produce a master roll, which is then slit to a desired width in the subsequent slitting process while applying tension in the film longitudinal direction and pressure (hereinafter referred to as surface pressure) from a contact roll from above the roll, and wound up as a product film roll.

[0058] (Structure and properties of biaxially oriented polyester film) The biaxially stretched polyester film of the present invention preferably has an antimony content of 10 ppm or less. Since antimony is a substance of concern as a carcinogen, the lower the amount, the better, with 5 ppm being preferred and 0 ppm being more preferred. Although the antimony content of the raw material resin used in the present invention is preferably 0 ppm, there is a possibility that antimony may be mixed in during production, so the content is set to 10 ppm or less.

[0059] The biaxially stretched polyester film of the present invention preferably has one or less defects of 1 mm or more per 1000 square meters (for example, per 500 mm film width and 2000 m film roll length). 2 By reducing the number of defects of 1 mm or more per large area to one or less, printability becomes very good. If the number of defects due to foreign matter is large, ink loss occurs during printing, which is undesirable. The fewer the number of defects of 1 mm or more, the better, with 0.5 or less being more preferable, 0.3 or less being even more preferable, 0.1 or less being particularly preferable, and 0 being the most preferable. In the present invention, the limit of one or less is set because there is a possibility of foreign matter being mixed in during unexpected problems.

[0060] In the biaxially stretched polyester film of the present invention, the difference between the intrinsic viscosity of the polyester resin and that of the polyester film is preferably 0.06 dL / g or less. The difference in intrinsic viscosity serves as an indicator of the degree of deterioration during melt extrusion of the polyester resin. A difference in intrinsic viscosity higher than 0.06 dL / g is undesirable because the resin deteriorates in the extruder, causing foreign matter. Furthermore, the difference in intrinsic viscosity is preferably 0 dL / g, but since the film is essentially melted, achieving 0 dL / g is difficult. A difference of 0.05 dL / g or less is preferred, and a difference of 0.04 dL / g or less is more preferred. In order to control the difference in intrinsic viscosity as described above, in the present invention, it is preferable to extrude the resin at a temperature in the extruder that is at least 2°C above the melting point of the resin and not more than 6°C above the melting point of the resin. If the extrusion temperature is less than 2°C above the melting point, the resin will not melt and an unmelted material will be extruded, which will become foreign matter, which is not preferable. Also, if the extrusion temperature is higher than 6°C above the melting point, the resin will thermally deteriorate and become foreign matter, which is not preferable.

[0061] The biaxially stretched polyester film of the present invention preferably has a haze of 1% or more and 8% or less. A haze higher than 8% is undesirable because it impairs the transparency of the film. A low haze is preferable, but in the present invention, the lower limit of haze is set to 1% in order to impart slipperiness. A haze of 7% or less is preferable, and 6% or less is even more preferable.

[0062] The biaxially oriented polyester film of the present invention preferably has a longitudinal heat shrinkage of 0.8% to 3% measured at 150°C for 15 minutes. A longitudinal heat shrinkage of more than 3% is undesirable because the film shrinks during drying in the post-printing process, resulting in misalignment of the printed pattern. While there are no problems with a heat shrinkage of less than 0.8%, the production method of the present invention sets the lower limit at 0.8%, so the upper limit for the longitudinal heat shrinkage is preferably 2.5% or less, and more preferably 2% or less. Heat shrinkage rate = (film length before heat shrinkage - film length after heat shrinkage) ÷ film length before heat shrinkage Film length x 100 (%) Formula (1)

[0063] When the biaxially stretched polyester film of the present invention is measured over a 1 m length, the thickness unevenness in both the longitudinal and transverse directions of the film is preferably 1% to 10%. A thickness unevenness greater than 10% is undesirable because it can cause print omissions and meandering due to wrinkles during processing such as printing. While lower thickness unevenness in the longitudinal and transverse directions of the film is preferable, the lower limit of thickness unevenness in the present invention is about 1%. It is more preferable that the thickness unevenness in the longitudinal and transverse directions be 8% or less, and even more preferably 6% or less.

[0064] The thickness of the biaxially oriented polyester film of the present invention is not particularly limited, but is preferably 2 μm or more and 300 μm or less. A thickness of less than 2 μm is undesirable because the film lacks stiffness, making it prone to wrinkles during processing such as printing, and the lack of stiffness can easily cause problems during the process of making bags or labels. While a thicker film is not a problem, from the perspective of environmental and cost considerations, a thickness greater than 300 μm is undesirable because it goes against the volume reduction achieved by thinning the film. The thickness is more preferably 4 μm or more and 250 μm or less, and even more preferably 6 μm or more and 200 μm or less.

[0065] The width of the product roll of the biaxially oriented polyester film of the present invention is not particularly limited, but is preferably 300 mm or more and 5000 mm or less. A width less than 300 mm is not preferred because it reduces the efficiency of printing and processing. A wider width is not a problem, but if it is too wide, handling becomes complicated during the printing and processing steps, so a width longer than 5000 mm is not preferred. The width of the film roll is more preferably 400 mm or more and 4500 mm or less, and even more preferably 500 mm or more and 4000 mm or less. [Example]

[0066] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the embodiments of these examples and can be modified as appropriate within the scope of the present invention. The compositions of raw materials used in the examples and comparative examples, the film stretching methods and production conditions in the examples and comparative examples are shown in the tables.

[0067] The film was evaluated as follows. [Tg (glass transition temperature), Tm (melting temperature)] Using a differential scanning calorimeter (DSC220, manufactured by Seiko Instruments Inc.), 5 mg of unstretched film was placed in a sample pan, the pan was covered, and the temperature was increased from -40°C to 300°C at a rate of 10°C / min under a nitrogen gas atmosphere. Tg (°C) and Tm (°C) were determined in accordance with JIS-K7121-1987.

[0068] [Intrinsic viscosity (IV)] 0.2 g of polyester was dissolved in 50 ml of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (60 / 40 (weight ratio)), and the viscosity was measured using an Ostwald viscometer at 30° C. The unit is dl / g.

[0069] [Content of various atoms in polyester film] The quantity was determined by the following method.

[0070] (a) Antimony atom 1 g of sample was wet decomposed in a mixture of sulfuric acid and hydrogen peroxide. Sodium nitrite was then added to decompose the Sb atoms. 5+ Brilliant Green was added to form a blue complex with Sb. After extracting this complex with toluene, the absorbance at a wavelength of 625 nm was measured using an absorptiometer (Shimadzu Corporation, UV-150-02). The amount of Sb atoms in the sample was colorimetrically determined using a calibration curve prepared in advance.

[0071] (b) Phosphorus atom One gram of sample was converted to orthophosphoric acid by dry ashing in the presence of sodium carbonate, or by wet decomposition in a mixture of sulfuric acid, nitric acid, and perchloric acid, or a mixture of sulfuric acid and hydrogen peroxide. Molybdate was then reacted in a 1 mol / L sulfuric acid solution to form phosphomolybdic acid, which was then reduced with hydrazine sulfate to form heteropoly blue. The absorbance at a wavelength of 830 nm was measured using a Shimadzu UV-150-02 spectrophotometer. The amount of phosphorus atoms in the sample was quantified using a previously prepared calibration curve.

[0072] (c) Aluminum atom 0.1 g of the sample was dissolved in 6 M hydrochloric acid solution, left to stand for one day, and then diluted with pure water to make a 1.2 M hydrochloric acid measurement solution. The prepared solution sample was analyzed by high-frequency plasma emission spectroscopy.

[0073] [Number of defects] A film roll with a width of 800 mm and a length of 10,000 m (8,000 square meters) was rewound using a rewinding machine. During rewinding, the number of defects was checked using a FUTEC defect detector (model F MAX MR). The number of defects 1 mm or larger in either the vertical or horizontal direction was counted. The total number of defects was used to calculate the number of defects per 1,000 square meters using formula (1). Number of defects per 1000 square meters = total number of defects ÷ 8 (Equation 1)

[0074] [printing] The 800 mm film roll with a roll length of 10,000 m (8,000 square meters) that had been inspected for defects was gravure printed at 5% dot density using a gravure printing machine (Azumaya Iron Works) at a speed of 100 m / min. The ink used was gravure printing ink (Finestar R92 ink, manufactured by Toyo Ink Co., Ltd.) mixed with dilution solvent (SL302, manufactured by Toyo Ink Co., Ltd.) in a ratio of 77:23. The resulting printed sample was rewound using a rewinder. During rewinding, the number of missing prints was counted using a FUTEC defect detector (model F MAX MR). The number of missing prints of 1 mm or larger in either the longitudinal or transverse direction was counted. The total number of missing prints was used to calculate the number of defects per 1,000 square meters using equation (2). Number of printing defects per 1000 square meters = total number of defects ÷ 8 (Equation 2)

[0075] [Heat shrinkage rate] A sample measuring 10 mm wide in the transverse direction and 220 mm long in the longitudinal direction was taken, and benchmark lines were marked at 200 mm intervals in the longitudinal direction. The interval between the benchmark lines was measured (L 0). The film was then sandwiched between papers and placed in a hot air oven controlled at a temperature of 150°C. After 30 minutes of treatment, the film was removed and the interval between the benchmark lines was measured (L) and the thermal shrinkage was calculated using equation (3). The rest of the test was carried out in accordance with JIS-C-2318. Heat shrinkage rate (%) = {(L0-L) / L0} × 100 (Equation 3)

[0076] [Hayes] Measurement was carried out at 23° C. in accordance with JIS K 7105. Measurement was carried out using a haze meter (300A, manufactured by Nippon Denshoku Industries Co., Ltd.) The measurement was carried out twice, and the average value was calculated.

[0077] [Thickness unevenness] The film was sampled into a strip of 1 m in the measurement direction and 40 mm in the width direction, and the thickness of the film sample was continuously measured at a speed of 5 m / min using a continuous contact thickness meter manufactured by Micron Measuring Instruments Co., Ltd. The film thickness unevenness was calculated using the following formula 4. Thickness unevenness = (maximum thickness - minimum thickness) ÷ average thickness × 100 (%) (Equation 4)

[0078] <Preparation of polymerization catalyst solution> (Ethylene glycol solution of phosphorus compounds) A flask equipped with a nitrogen inlet tube and a condenser was charged with 2.0 L of ethylene glycol at room temperature and atmospheric pressure. Then, while stirring at 200 rpm under a nitrogen atmosphere, 200 g of Irganox 1222 (manufactured by BASF) was added as a phosphorus compound, as shown in chemical formula (4). After adding another 2.0 L of ethylene glycol, the jacket temperature was changed to 196°C and the temperature was increased. Once the internal temperature reached 185°C or higher, the mixture was stirred under reflux for 60 minutes. The heating was then stopped, and the solution was immediately removed from the heat source. The mixture was then cooled to 120°C or below within 30 minutes while still under a nitrogen atmosphere.

[0079] (Ethylene glycol solution of aluminum compounds) 5.0 L of pure water was added to a flask equipped with a condenser at room temperature and atmospheric pressure, and then 200 g of basic aluminum acetate (hydroxyaluminum diacetate) was added as a slurry with pure water while stirring at 200 rpm. Further, pure water was added to bring the total volume to 10.0 L, and the mixture was stirred at room temperature and atmospheric pressure for 12 hours. The jacket temperature was then set to 100.5°C, and the mixture was heated. Once the internal temperature reached 95°C or higher, the mixture was stirred under reflux for 3 hours. The stirring was stopped, and the mixture was allowed to cool to room temperature. If undissolved particles were observed, the solution was filtered through a glass filter (3G) to obtain an aqueous solution of the aluminum compound. Next, 2.0 L of the aqueous solution of the aluminum compound and 2.0 L of ethylene glycol were charged into a flask equipped with a distillation apparatus at room temperature and atmospheric pressure, and after stirring at 200 rpm for 30 minutes, a uniform water / ethylene glycol mixed solution was obtained. Next, the jacket temperature setting was changed to 110°C and the temperature was raised, and water was distilled off from the solution. When the amount of distilled water reached 2.0 L, heating was stopped and the solution was allowed to cool to room temperature, yielding an ethylene glycol solution of the aluminum compound.

[0080] In the following, "parts" means "parts by mass." A reactor equipped with a stirrer, thermometer, and distillation cooler was charged with 2130 parts of terephthalic acid, 1955 parts of ethylene glycol, and 0.7 parts of triethylamine, and the temperature was gradually increased from 220°C to 250°C under a pressure of 0.35 MPa. An esterification reaction was then carried out while removing the distilled water from the system. The polymerization catalyst solution was then added to the ethylene glycol solution of a phosphorus compound and the ethylene glycol mixed solution of an aluminum compound so that the phosphorus atoms accounted for 0.047 mol% and the aluminum atoms accounted for 0.021 mol% of the dicarboxylic acid components in the polyester resin. Initial polymerization was then carried out under reduced pressure down to 1.3 kPa over 1 hour, the pressure was then increased to 270°C, and final polymerization was carried out at 0.13 kPa or less to obtain Polyester 1.

[0081] The above-mentioned method for producing polyester 1 was partially modified as follows to produce polyesters 2 and 3. The composition and physical properties of each polyester are shown in Table 1. The polyesters used in the examples and comparative examples are as follows: Polyester 1: Polyethylene terephthalate (IV 0.73 dl / g) Polyester 2: Polyethylene terephthalate (IV 0.73 dl / g) to which SiO2 (Silisia 266 manufactured by Fuji Silysia Corporation) was added as a lubricant in a ratio of 8,000 ppm to the polyester during the production of Polyester 1. Polyester 3: In the production of Polyester 1, antimony catalyst was added instead of aluminum to give a concentration of 0.084 mol% (IV 0.73 dl / g).

[0082] [Table 1]

[0083] Example 1 The above-mentioned polyester 1 and polyester 2 were mixed in a weight ratio of 97:3 and fed into an extruder. The mixed resin was then melted at 270°C, cooled to 260°C, extruded through a T-die, and rapidly cooled by being wound around a rotating metal roll cooled to a surface temperature of 30°C to obtain an unstretched film with a thickness of 220 μm. The take-up speed of the unstretched film (the rotation speed of the metal roll) was approximately 80 m / min. The Tg and Tm of the unstretched film were 75°C and 256°C, respectively. An adhesive sheet made of high-melting-point polyimide was attached to the T-die to prevent volatiles from the molten resin from falling. A UV-irradiation cleaner was used to remove any foreign matter that had fallen onto the cooling roll. The resulting unstretched sheet was heated to 115°C and stretched in the longitudinal direction at a total stretch ratio of 4.5x using a three-stage stretching method: 1.24x in the first stage, 1.4x in the second stage, and 2.6x in the third stage. Subsequently, the sheet was stretched in the width direction at a temperature of 140°C and a stretch ratio of 4.3x, heat-set at 243°C, and subjected to a 5% heat relaxation treatment in the width direction. After the stretching, both ends of the film were cut and removed, followed by a corona discharge treatment and winding into a roll on a winder to produce a master roll of biaxially oriented polyester film 12µm thick and 8m wide. The properties of the obtained film were evaluated using the methods described above. The number of defects was also evaluated using the same method on a roll obtained by slitting the film to a width of 800 mm and a length of 10,000 m. The film manufacturing method is shown in Table 2, and the evaluation results are shown in Table 3. The antimony content was low enough to ensure hygiene, and the film was of good quality with few defects and excellent print appearance.

[0084] Example 2 A biaxially stretched polyester film roll was obtained in the same manner as in Example 1, except that Polyester 1 and Polyester 2 were mixed in a weight ratio of 99.5:0.5 and fed into the extruder. The film production method is shown in Table 2, and the evaluation results are shown in Table 3. The film was of good quality and had better transparency than Example 1. There were also few missing prints, which was good.

[0085] Example 3 A biaxially stretched polyester film roll was obtained in the same manner as in Example 1, except that Polyester 1, Polyester 2, and Polyester 3 were mixed in a weight ratio of 96.5:3:0.5 and fed into the extruder. The film manufacturing method is shown in Table 2, and the evaluation results are shown in Table 3. Although the amount of antimony was slightly higher than in Example 1 and the number of defects increased slightly, the number of defects was still sufficiently small, and the film was of good quality.

[0086] Comparative Example 1 Polyester 3 and polyester 2 were mixed in a weight ratio of 97:3 and fed into an extruder. A biaxially oriented polyester film roll was obtained using the same method as in Example 1 except for the above. The film manufacturing method is shown in Table 2, and the evaluation results are shown in Table 3. The antimony content was higher than in Example 1, resulting in an increased number of defects and an inferior film quality. Furthermore, there were more missing prints than in Example 1, resulting in an inferior result.

[0087] Comparative Example 2 Polyester 1, polyester 2, and polyester 3 were mixed in a weight ratio of 48.5:3:48.5 and charged into an extruder. The mixed resin was then melted at 280°C, cooled to 270°C, and extruded through a T-die, but a biaxially oriented polyester film was obtained in the same manner as in Example 1. The properties of the obtained film were evaluated in the same manner as in Example 1. The film manufacturing method is shown in Table 2, and the evaluation results are shown in Table 3. The evaluation results showed that the biaxially oriented polyester film had a large decrease in intrinsic viscosity, an increased number of defects, and was of poor quality.

[0088] [Table 2]

[0089] [Table 3] [Industrial Applicability]

[0090] The biaxially oriented polyester film of the present invention contains an extremely small amount of antimony and has good printability, processability and productivity, making it suitable for use in food packaging bags and labels with excellent hygiene.

Claims

1. A biaxially oriented polyethylene terephthalate film characterized by satisfying the following requirements (1) to (5) and being used for packaging or labels. (1) The antimony content in the film is 10 ppm or less (2) The phosphorus content in the film is 25 ppm or more and 75 ppm or less. (3) The intrinsic viscosity of the film is 0.51 dl / g or more and 0.70 dl / g or less. (4) The number of defects of 1 mm or more per 1,000 square meters of film is 1.0 or less. (5) The polyester resin constituting the film contains 80 mol % or more of ethylene glycol out of 100 mol % of all glycol components.

2. The polyethylene terephthalate film according to claim 1, which is produced using a polyethylene terephthalate-based raw material characterized in that at least one selected from aluminum compounds and at least one selected from phosphorus compounds are contained in the polyethylene terephthalate-based resin as a polymerization catalyst.

3. 3. The polyethylene terephthalate film according to claim 1, wherein the haze of the film is 1% or more and 8% or less.

4. 4. The polyethylene terephthalate film according to claim 1, wherein the heat shrinkage rate in the longitudinal direction measured under conditions of 150° C. for 15 minutes is 0.8% or more and 3% or less.

5. A polyethylene terephthalate film according to any one of claims 1 to 4, characterized in that the thickness unevenness in both the longitudinal and transverse directions measured over a length of 1 m using a continuous contact thickness meter is 1% or more and 10% or less.

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