Biaxially oriented polyester film roll

Abstract

To provide a polyester film roll having excellent printability and processability.SOLUTION: A film roll is made by winding a biaxially oriented polyester film having an antimony content of 10 ppm or less and a phosphorus content of 25 ppm or more and 75 ppm or less, and having an arithmetic mean roughness of the film surface of 0.02 μm or more and 0.05 μm or less, and satisfies the following requirements (1) to (6). (1) The winding length is 8,000 m or more and 80,000 m or less. (2) The width is 500 mm or more and 4,000 mm or les. (3) The average hardness of the outermost layer of the film roll is in the range of 500 or more and 700 or less. (4) The hardness variation of the outermost layer of the film roll is 10% or more and 20% or less. (5) The thickness is 5 μm or more and 40 μm or less. (6) In the thickness unevenness in the film width direction in the surface layer, there are places where the thickness pattern is a recess, and the thickness unevenness of the maximum recess calculated from the maximum thickness difference in the recess with the largest thickness difference (the largest recess) and the average thickness of the film is 10% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially stretched polyester film roll that is excellent in hygiene. More specifically, the present invention relates to a biaxially stretched polyester film roll that does not develop wrinkles or other defects even after long-term storage after film formation, and that does not cause problems in processing steps such as printing and bag making, and is therefore suitable for use in food packaging bags and labels. [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. To impart barrier properties, vapor deposition processing is generally performed using film rolls.

[0005] In recent years, the processing of vapor-deposited polyester film has been accelerated and the width and length of the film rolls used as the substrate have been increased in order to improve productivity. As the rolls become wider and longer, problems such as poor running performance and the tendency for wrinkles, misalignment, and spoken wrinkles to occur have arisen, resulting in localized unevenness and voids in the vapor-deposited thin film, which can deteriorate the gas barrier properties. Wrinkles can also occur during winding after vapor deposition, resulting in poor appearance and making the film unusable as a product. Furthermore, packaging bags are often ultimately discarded as waste, and thus thinner thickness is required to address environmental concerns. As the thickness decreases, the film loses its stiffness, resulting in poor appearance and defects during storage after slitting. This can cause problems when printing or processing the film roll. In particular, areas where slack occurs have poor flatness, and areas where slack occurs in the width direction of the film roll can result in missing prints, resulting in wastage. With thinner films, faster printing speeds, and more colors being used, these problems caused by slack and changes in appearance due to storage are becoming more apparent. The present inventors have newly discovered that film rolls with slack within a range that was previously acceptable and not a problem are difficult to apply.

[0006] To solve this problem, a film roll winding method has been proposed in which the surface pressure applied by the contact roll is increased on the surface layer compared to the surface pressure on the core (Patent Document 1). However, although Patent Document 1 describes the winding hardness, winding surface pressure, and winding tension required to prevent wrinkles on the surface layer, wrinkles on the core, and winding misalignment, it does not describe any changes in the appearance of the film roll due to long-term storage.

[0007] Furthermore, food packaging films come into direct contact with food, so from a hygienic standpoint, it is desirable for the polyester film to contain as little foreign matter as possible. Furthermore, because the antimony catalyst used in the process of producing (polymerizing) polyester raw materials is potentially carcinogenic, it is desirable for the polyester film to contain as little antimony as possible, or none at all. Conventionally, there are polyester raw materials that do not use antimony catalysts, as described in Patent Documents 2 and 3, for example. However, there is no description of methods for reducing film foreign matter or the desired film properties. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 63-252853 [Patent Document 2] Patent No. 3461175 [Patent Document 3] Patent No. 3506236 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-151907 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a biaxially oriented polyester film roll which has an extremely low antimony content, little foreign matter, excellent transparency and heat resistance, and is not prone to loosening of the film roll immediately after film formation, and is also not prone to loosening of the film roll over time even when stored for a long period of time, and is less likely to cause defects during printing processing. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have discovered that, in a slitting process in which a polyester film having a desired surface roughness is slit to a desired width from a master roll without using antimony to produce a product roll, the hardness of the roll can be controlled within the above-mentioned range by controlling the winding tension after slitting and the contact pressure of the contact roll, and that the film roll is less likely to sag after long-term storage, thereby completing the present invention. The present invention comprises the following configurations.

[0011] 1. A biaxially oriented polyester film roll comprising a biaxially oriented polyester film wound up, the biaxially oriented polyester film having an antimony content of 10 ppm or less, a phosphorus content of 25 ppm or more and 75 ppm or less, and an arithmetic mean roughness of the film surface of 0.02 μm or more and 0.05 μm or less, wherein the biaxially oriented polyester film and the film roll satisfy the following requirements (1) to (6): (1) The film roll length is 8,000 m or more and 80,000 m or less (2) Film roll width is 500 mm or more and 4000 mm or less (3) The hardness of the outermost layer of the film roll is measured at intervals of 50 mm in the width direction of the film, and the average hardness is in the range of 500 to 700. (4) The hardness of the outermost layer of the film roll is measured at intervals of 50 mm in the width direction of the film, and the variation in hardness is 10% or more and 20% or less. (5) Film thickness is 5 μm or more and 40 μm or less (6) In the thickness unevenness in the film width direction on the surface layer of the film roll, the thickness pattern has a recessed portion, and at the recess with the largest thickness difference (maximum recess), the thickness unevenness of the maximum recess calculated from the maximum thickness difference at the maximum recess and the average thickness of the film is less than 10%. 2. A biaxially stretched polyester film roll according to 1., wherein the thickness unevenness in the width direction of the film of each sample sampled at 1000 m intervals along the winding length from the surface of the film roll is 10% or less for all samples, calculated from the maximum thickness difference at the largest recess and the average thickness of the film. 3. The biaxially stretched polyester film roll according to any one of 1. to 2., wherein the absolute value of the difference in refractive index in the width direction between the maximum recess and either of the maximum thickness points at both ends of the recess is 0.010 or less. 4. A biaxially oriented polyester film roll according to any one of 1. to 3., characterized in that the number of defects of 1 mm or more per 10,000 square meters of film is 1.0 or less. 5. The biaxially stretched polyester film roll according to any one of 1. to 4., wherein the static friction coefficient and the dynamic friction coefficient between the outer surface and the inner surface of the film roll are both 0.1 or more and 0.8 or less. 6. The biaxially stretched polyester film roll according to any one of 1. to 5., wherein the intrinsic viscosity of the film is 0.51 dl / g or more and 0.70 dl / g or less. 7. A method for producing a biaxially oriented polyester film roll according to any one of 1. to 6., 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 heat-set.The biaxially oriented film is then wound up as a master roll, and the master roll is then slit and wound up into a roll. [Effects of the Invention]

[0012] The present invention can provide a biaxially oriented polyester fill roll that has an extremely low antimony content, little foreign matter, excellent transparency and heat resistance, and is not prone to loosening of the film roll immediately after film formation, and is also not prone to loosening over time even when stored for a long period of time, making it less likely to cause defects during printing processing. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing the maximum recess in the thickness unevenness in the width direction of the film of the present invention. [Figure 2]FIG. 2 is a diagram showing an example of a film transverse stretching (TD) step of the present invention. [Figure 3] FIG. 2 is a diagram showing an example of a cooling step in the film transverse stretching (TD) step of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] (raw polyester resin) The biaxially stretched polyester film of the present invention comprises a polyethylene terephthalate resin as a constituent component. Here, the polyethylene terephthalate resin contains an ethylene glycol-derived component and a terephthalic acid-derived component as main constituent components. The "main constituent components" mean that terephthalic acid accounts for 80 mol% or more of 100 mol% of all dicarboxylic acid components, and ethylene glycol accounts for 80 mol% or more of 100 mol% of all glycol components.

[0016] 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.

[0017] 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; alicyclic glycols such as bisphenol A, bisphenol S, bisphenol C, bisphenol Z, bisphenol AP, ethylene oxide adducts or propylene oxide adducts of 4,4'-biphenol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol; polyethylene glycol; and polypropylene glycol.

[0018] 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.

[0019] As the polyester resin, recycled resins made from recycled PET bottles and polyester resins containing monomer components derived from biomass can also be used.

[0020] 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).

[0021] 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 0.70 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.

[0022] (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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] [ka]

[0030] [ka]

[0031] (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. 4represents 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.)

[0032] 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):

[0033] [ka]

[0034] 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.

[0035] 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.

[0036] 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).

[0037] [ka]

[0038] [ka]

[0039] 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.

[0040] 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.

[0041] 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 believed that the hindered phenol moiety in the phosphorus compounds improves the heat resistance of the copolymer polyester resin.

[0042] 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 copolymer polyester resin of the present invention may not be observed.

[0043] To further improve 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 copolymerized 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 copolymerized 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.

[0044] 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. -5Even 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.

[0045] 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.

[0046] 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.

[0047] (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, layer A in the present invention refers to either one layer or both outer layers.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The stretching method can be either simultaneous biaxial stretching or sequential biaxial stretching, but sequential biaxial stretching is preferred in terms 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 explained. It may also be stretched longitudinally.

[0055] The stretching temperature in the longitudinal (machine) direction (hereinafter sometimes abbreviated as MD) is preferably (Tg + 5) to (Tg + 55)°C, and the stretching ratio is preferably 3 to 5 times, in order to reduce bowing. If the stretching temperature is higher than (Tg + 55)°C or lower than 3 times, although bowing is reduced, orientation in the longitudinal direction becomes insufficient, resulting in increased thickness unevenness in the longitudinal direction, which is undesirable. Furthermore, the flatness of the resulting biaxially stretched polyester film is also undesirable, which is undesirable. On the other hand, if the stretching temperature is lower than (Tg + 5)°C or higher than 5 times, shrinkage stress increases, which increases bowing, which is undesirable.

[0056] 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.

[0057] 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 stretching temperature in the width direction is less than Tg+5°C, breakage is likely to occur during stretching, which is undesirable. Furthermore, if the temperature is higher than Tg+70°C, uniform width-direction stretching becomes impossible, resulting in large thickness variations in the width direction, which is undesirable because of large variations in hardness of the film roll. The temperature is more preferably Tg+10°C or higher and Tg+65°C or lower, and even more preferably Tg+15°C or higher and Tg+60°C or lower. The stretching ratio in the width direction is not particularly limited, but is preferably 3 times or more and 7 times or less. A stretching ratio of less than 3 times results in poor productivity, and the orientation in the width direction is insufficient, resulting in thickness unevenness in the width direction and unevenness in the hardness of the film roll in the width direction, which is undesirable. A stretching ratio of more than 7 times is also undesirable because the film is prone to breakage during stretching. Multi-stage stretching, such as two or three stages, is also preferable because it improves thickness unevenness in the width direction.

[0058] The heat setting temperature (heat treatment temperature) after TD stretching is preferably 230 to 255°C. Heat setting temperatures higher than 255°C are undesirable because they approach the melting point of the polyester resin, causing the film to melt and break. Furthermore, the film surface becomes rough and white due to melting, resulting in a loss of transparency, which is also undesirable. On the other hand, temperatures lower than 230°C are undesirable because the heat shrinkage rate increases in both the longitudinal and transverse directions, resulting in poor thermal dimensional stability during vapor deposition processing.

[0059] 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.

[0060] Furthermore, when the heat-treated film is cooled in the TD, oligomers are generated. If oligomers adhere to the film, they become defects and cause printing defects, which is undesirable. Therefore, it is preferable to remove the oligomers within the TD or at the TD exit using an adhesive roll or similar. A specific example of oligomer removal is the method shown in Figure 3. Simply blowing cooling air onto the film will generate oligomers, which will then float around in the zone and adhere to the film. Therefore, by installing a plenum duct to suck in the oligomers after blowing cooling air, the amount of oligomers floating around in the zone is reduced, making it more difficult for the oligomers to adhere to the film.

[0061] The film stretched and formed by the above method is wound up by a winder device to produce a master roll. It is then slit to a specified width and length using a slitter and wound onto a winding core to obtain a biaxially stretched polyester film roll. The winding core can typically be a plastic core, metal core, or cardboard core of 3 inches, 6 inches, or 8 inches. The preferred winding length and width of the film roll are as described above. In addition, it is preferable to reduce slack that occurs during slitting by adopting the following slitting conditions.

[0062] Specific slitting conditions include an initial tension of 70 to 160 N / m, preferably 80 to 150 N / m, and an initial surface pressure of 200 to 400 N / m, preferably 250 to 350 N / m, at which slitting begins. An initial tension higher than 160 N / m is undesirable because the uneven thickness of the recessed portions is slightly stretched by the tension during slitting, causing slack. An initial tension of 70 N / m or less is undesirable because the tension is insufficient when the film is slit and wound, resulting in uneven edges of the film roll (so-called edge misalignment). It is also desirable to reduce the tension after the winding length reaches 500 m. Specifically, it is desirable to reduce the tension consistently in correlation with the winding length so that the tension 300 m before the end of slitting is 50 to 80%, preferably 60 to 70%, of the initial tension. It is also preferable to keep the surface pressure as constant as possible throughout the entire winding length. The initial surface pressure is preferably ±5% or less over the entire winding length, and more preferably ±3% or less.

[0063] In general, in industrially produced film rolls, a continuously produced film is continuously wound up. If the film-forming conditions are constant, the degree of thickness unevenness in the film width direction is approximately constant throughout the entire winding length. However, slight variations in each process during film formation can cause slight variations throughout the entire winding length. It is preferable that thickness unevenness in the film width direction be controlled throughout the entire winding length. Whether thickness unevenness is controlled throughout the entire winding length can be confirmed, for example, by taking samples from the surface layer of the film roll at regular intervals along the winding length and measuring the thickness unevenness of each sample. In the film roll of the present invention, thickness unevenness can be measured by taking samples from the surface layer of the film roll and using them as a representative value for the film roll. In the present invention, as described in the Examples below, samples are taken from a portion 5 m removed from the surface layer of the film roll and measured to use as a representative value. The preferred range of thickness unevenness in the film width direction (thickness unevenness at the maximum recess and the entire width direction) on the surface layer of the film roll is as described above. In a preferred embodiment of the present invention, samples are collected and measured every 1000 m of the roll length, and the thickness unevenness (thickness unevenness at the largest recess and across the entire width direction) for all samples falls within a predetermined range. The preferred range of thickness unevenness in the film width direction (thickness unevenness at the largest recess and across the entire width direction) over the entire length of the film roll is as described above.

[0064] (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.

[0065] In the biaxially oriented 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. This difference in intrinsic viscosity serves as an indicator of the degree of degradation during melt extrusion of the polyester resin. A difference higher than 0.06 dL / g is undesirable because the resin deteriorates in the extruder, causing foreign matter. The intrinsic viscosity difference is preferably 0 dL / g, but achieving 0 dL / g is difficult because the resin essentially melts. A difference of 0.05 dL / g or less is preferred, and 0.04 dL / g or less is even more preferred. To control the difference in intrinsic viscosity as described above, the present invention preferably extrudes 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. An extrusion temperature lower than 2°C above the melting point is undesirable because the resin does not melt and unmelted material is extruded, which becomes foreign matter. Furthermore, extrusion at a temperature higher than 6°C above the melting point is undesirable because the resin thermally deteriorates and becomes foreign matter.

[0066] The biaxially oriented polyester film of the present invention preferably has one or less defects of 1 mm or larger per 10,000 square meters. By reducing the number of defects of 1 mm or larger per 1,000 square meters to one or less, printability is significantly improved. A large number of defects due to foreign matter is undesirable because it can cause ink loss during printing. The fewer the number of defects of 1 mm or larger, the better; 0.5 or less is more preferable, 0.3 or less is even more preferable, 0.1 or less is particularly preferable, and 0 is most preferable. In the present invention, the limit of one or less is set to reflect the possibility of foreign matter being mixed in during unexpected problems.

[0067] The arithmetic mean roughness of the surface of the biaxially stretched polyester film of the present invention is preferably 0.02 μm or more and 0.05 μm or less. If it is less than 0.02 μm, blocking (adhesion of the film within the film roll) occurs, which is undesirable, resulting in noise (the sound of the adhered film peeling off) or film breakage during unwinding, which is undesirable. On the other hand, if it exceeds 0.05 μm, it is undesirable because the vapor-deposited thin film is likely to come off during processing steps such as vapor deposition, which deteriorates the gas barrier properties.

[0068] The thickness of the biaxially oriented polyester film of the present invention is preferably 5 μm or more and 40 μm or less. The upper limit of the film thickness is more preferably 35 μm or less, and even more preferably 30 μm or less. Since thicknesses up to 5 μm were confirmed in the present invention, the lower limit of the thickness was set to 5 μm or more. Furthermore, a thicker film tends to be more stiff and less prone to sagging, so a thicker film is not a problem, but it would be counter to environmental concerns by reducing the thickness. Since thinner films are more prone to sagging, a thinner film thickness is more difficult in the present invention.

[0069] Furthermore, the static and dynamic friction coefficients between the outer and inner film surfaces of the biaxially oriented polyester film of the present invention are preferably 0.1 to 0.8. If the coefficient is lower than 0.1, the film may slip too much, causing misalignment of the end surfaces. If the coefficient is higher than 0.8, the amount of air entrapment during slitting increases, which is undesirable because air escapes from the recesses of the film roll, making it prone to slack and wrinkles. The coefficients are preferably 0.13 to 0.77, and more preferably 0.16 to 0.74.

[0070] (Characteristics of biaxially oriented polyester film roll) The winding length of the biaxially oriented polyester film roll of the present invention is preferably 8,000 m or more and 80,000 m or less. In processes such as printing and vapor deposition, a longer winding length reduces the frequency of roll replacement and improves work efficiency. It is preferably 10,000 m or more, more preferably 12,000 m or more, and particularly preferably 14,000 m or more. There is no particular upper limit, and a longer winding length is preferable, but the inventors have only confirmed a winding length up to 80,000 m, so a winding length of 80,000 m was set as the upper limit. Note that as the winding length of the film roll increases, the area of ​​the film increases, increasing the chance of slack defects occurring. Therefore, in the present embodiment, a longer winding length of the film roll is more difficult.

[0071] The width of the biaxially oriented polyester film roll of the present invention is preferably 500 mm or more and 4000 mm or less. There is no particular upper limit; a wider film roll is preferable because it reduces loss during the printing process. However, the inventors have only confirmed widths up to 4000 mm, so the upper limit was set at 4000 mm. Furthermore, as described above, a wider film roll is preferable because it improves the efficiency of processing, such as printing. A preferred width is 700 mm or more, more preferably 900 mm or more, and particularly preferably 1100 mm or more. As the width of the film roll increases, the area of ​​the film increases, increasing the chance of sagging defects occurring. Therefore, a longer film roll width in this embodiment of the present invention is more difficult.

[0072] Furthermore, the biaxially stretched polyester film roll of the present invention has portions where the thickness pattern is recessed in the thickness unevenness in the width direction of the film roll, and at the recess with the largest thickness difference (maximum recess), the thickness unevenness at the maximum recess, calculated from the maximum thickness difference at the maximum recess and the average film thickness using the following formula 1, is preferably 10% or less (an example is shown in Figure 1). Uneven thickness of recessed portion = (maximum height thickness of recessed portion - minimum height thickness of recessed portion) ÷ average thickness ×100(%) ···Formula 1

[0073] In the present invention, a recess refers to a thickness pattern consisting of a peak, a valley, and a peak, where the peak is a point at which the thickness decreases in both directions across the film width measured using a continuous contact thickness meter as described below, and the valley is a point at which the thickness increases in both directions across the film width measured using a continuous contact thickness meter as described below. Films that do not have such a thickness pattern, i.e., films that do not have recesses, are not included in the present invention. For two peaks and one valley in a recess, the greater of the thickness differences between the peaks and the valleys (or both values ​​if they are the same) is referred to as the maximum thickness difference in the recess.

[0074] If the thickness variation at the maximum recess is greater than 10%, air may be trapped and trapped when the film is slit at the recess and wound into a film roll. This can lead to air loss during subsequent storage of the film roll, resulting in wrinkles and sagging. Furthermore, because the recess is thinner than other areas in the width direction, it is stretched longitudinally by the tension applied when the film is slit and wound into a film roll. As a result, the longitudinal length of the recess in the film roll becomes longer than other areas in the width direction, resulting in sagging at that area. Research by the present inventors has revealed that this problem is particularly pronounced when the thickness difference between the recess and both ends is large. The preferred thickness variation at the maximum recess is 9% or less, and more preferably 8% or less. A lower thickness variation at the maximum recess is preferable; in the inventors' tests, 3% was the lowest.

[0075] The thickness unevenness of the recesses as described above should be measured using a continuous contact thickness meter as shown in the following examples. For example, as shown in Patent Document 4, if the thickness is measured at intervals of 30 mm to 500 mm in the measurement direction, the maximum thickness difference in the recesses may be at an unmeasured position, making it difficult to accurately determine the thickness difference in the recesses. The thickness unevenness in this invention refers to that measured using a continuous contact thickness meter.

[0076] Furthermore, it is preferable that the thickness unevenness in the width direction of the film of each sample sampled at 1000 m intervals along the winding length from the surface layer of the biaxially oriented polyester film of the present invention, calculated from the maximum thickness difference at the maximum recess and the average thickness of the film, is 10% or less for all samples.

[0077] As mentioned above, if the maximum thickness variation of the recesses is greater than 10%, air may be trapped and trapped when the film is slit at the recesses and wound into a film roll. This can lead to air loss during subsequent storage of the film roll, resulting in wrinkles and sagging, which is undesirable. Furthermore, because the recesses are thinner than other areas in the width direction, they are stretched longitudinally by the tension generated during slitting. As a result, the longitudinal length of the recesses in the film roll becomes longer than other areas in the width direction, resulting in sagging at those areas. Research by the present inventors has revealed that this problem is particularly pronounced when the thickness difference between the recesses and their opposite ends (the difference in thickness between the valleys and peaks) is large. Therefore, the thickness variation of the recesses in the width direction of the roll is important. A preferred thickness variation of the recesses is 9% or less, and more preferably 8% or less.

[0078] Furthermore, in the maximum recess in the width-direction thickness pattern of the polyester film roll of the present invention, the absolute value of the difference in width-direction refractive index between the maximum thickness point (the thicker of the two peaks) at either end of the recess and the minimum thickness point (the valley) of the recess is preferably 0.01 or less. If the absolute value of the difference in width-direction refractive index between the maximum thickness point at either end of the recess and the minimum thickness point of the recess is greater than 0.01, the minimum thickness point and the maximum thickness point of the recess will differ in longitudinal elongation, resulting in a difference in longitudinal elongation due to tension during slitting. This increases the longitudinal length of the film roll, causing slack at that point. The absolute value of the width-direction refractive index difference is preferably 0.008 or less, more preferably 0.006 or less. The lower the absolute value of the width-direction refractive index difference, the lowest value found in the inventors' tests was 0.0003.

[0079] The hardness of the outermost layer of the polyester film roll of the present invention, measured at 50 mm intervals in the width direction of the film, is preferably in the range of 500 to 700 on average, with a hardness variation of 10% to 20%. The "outermost layer" of a film roll refers to the surface of the roll after unwinding the film from the roll and removing 5 m from the longitudinal end. The hardness is measured using a Parotestor 2 hardness tester manufactured by Proseo GmbH, Switzerland. A winding hardness of the film roll surface layer less than 500 is undesirable, because air trapped during slitting escapes and the film roll becomes loose when the film roll is stored in a warehouse for six months, for example. A winding hardness of the film roll surface layer higher than 700 is undesirable, because the film roll becomes too hard and the aforementioned recesses are compressed, causing loosening. The winding hardness of the film roll surface layer is preferably 530 to 670, and more preferably 560 to 640. Furthermore, the variation in hardness measured across the width of the film roll is preferably 10% or more and 20% or less. A variation higher than 20% is undesirable, as it indicates, for example, uneven thickness across the film width after half a year of storage in a warehouse, or tension differences across the width in slitting equipment, making slack more likely to occur after storage. Furthermore, a variation of less than 10% is preferable, and in the present invention, 10% was the lower limit, so it was set to 10%. The upper limit of the variation in winding hardness across the width is preferably 19% or less, and more preferably 18% or less. [Example]

[0080] 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.

[0081] 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.

[0082] [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.

[0083] [Content of various atoms in polyester film] The quantity was determined by the following method.

[0084] (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.

[0085] (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.

[0086] (c) Aluminum atom 0.1 g of the sample was dissolved in 6 M hydrochloric acid solution, left 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.

[0087] [SRa (arithmetic mean roughness) of film surface] The surface roughness of the film was measured by the following method. Equipment: Scanning confocal laser microscope (Olympus LEXT) Laser type: 405nm semiconductor laser Objective lens: 50x Shooting mode: High precision Confocal images of the measurement surface were captured using the above equipment and conditions. Surface Roughness Analysis Measurement range: 256μm x 256μm Analysis software: OLS4100 No cutoff Surface roughness analysis was performed under the above conditions, and the arithmetic mean roughness (SRa) was measured. Measurements were performed 10 times at different measurement positions, and the average value was calculated. However, if partial abnormalities such as scratches were clearly visible in the image, they were not included in the measurement, and the measurement was repeated, avoiding the abnormal areas.

[0088] [Thickness unevenness across the entire width] The roll was placed on a slitter. Five meters of the roll surface was then removed, and the film roll was sampled across the entire width and 40 mm in the longitudinal direction. The thickness in the width direction was measured continuously at 5 m / s using a continuous contact thickness meter manufactured by Micron Measurement Instruments. The maximum thickness during measurement was defined as Tmax., the minimum thickness as Tmin., and the average thickness as Tave. The thickness unevenness in the film width direction was calculated using the following formula (1): Thickness unevenness = {(Tmax. - Tmin.) / Tave.} × 100 (%) Formula (1)

[0089] [Thickness variation in recesses] The continuous contact thickness in the width direction was determined as described above, and the location of the maximum recess was found as shown in Figure 1. The thickness unevenness of the maximum recess was calculated using the following formula (2). When the heights at both ends of the maximum recess were different, the higher value was selected. Thickness unevenness of maximum recess = (maximum height thickness of maximum recess - minimum height thickness of maximum recess) ÷ average thickness × 100 (%) Formula (2)

[0090] [Thickness unevenness at the maximum concave part in the roll width direction over the roll length] The roll was placed on a slitter. Five meters of the roll surface was then removed, and the thickness unevenness at the largest recess in the roll width direction was measured using the method described above. After the measurement, the roll was rewound 1,000 meters on the slitter, and the thickness unevenness at the largest recess in the roll width direction was measured using the method described above. After rewinding 1,000 meters, the thickness unevenness at the largest recess in the roll width direction was repeatedly measured.

[0091] [Difference in refractive index between the maximum concave portion and both ends of the maximum concave portion] The refractive index in the width direction of the film at the maximum recess and at the position where the thickness is greater at both ends of the maximum recess was measured using an Abbe refractometer. The difference was calculated using the following formula (3) and taken as the absolute value. Difference in refractive index between the maximum recess and both ends of the maximum recess = |Refractive index in the width direction of the maximum recess - Refractive index in the width direction at the higher position of both ends of the maximum recess| Equation (3)

[0092] [Coefficient of friction] In accordance with JIS K-7125, a tensile tester (ORIENTEC Tensilon) was used to measure the static and dynamic coefficients of friction when the front and back surfaces of the film were joined together in an environment of 23°C and 65% RH. The weight of the sled (weight) around which the upper film was wrapped was 1.5 kg, and the dimensions of the base area of ​​the sled were 63 mm long and 63 mm wide. The tensile speed during friction measurement was 200 mm / min.

[0093] [Evaluation of slack] A sample was taken from the film roll across the entire width and between 4m and 6m in the longitudinal direction and placed on a flat table. If a continuous strip-like area in the longitudinal direction was visually observed where the flatness was even slightly worse than the other areas, this was considered to be slack. The evaluation was carried out as follows. The same evaluation was also carried out after storing the film in a warehouse at a temperature of 23°C for one year. No looseness: ○ Looseness in one or more places: ×

[0094] [Evaluation of winding hardness] Measurements were taken across the width of the roll at 50 mm intervals from the end using a Parotester 2 hardness tester manufactured by Proseo GmbH, Switzerland. The average of the values ​​measured across the width of the roll was used as the measured value. The hardness variation was calculated using equation (4). (Maximum value of winding hardness in the width direction - Minimum value of winding hardness in the width direction) ÷ Average winding hardness × 100 (%) Formula (4)

[0095] Wrinkle evaluation of film rolls The polyester film rolls were visually evaluated for wrinkles on the surface of the rolls immediately after production and after storage for one year in a warehouse at 23°C according to the following criteria. A rating of ◯ or △ was considered acceptable. ○: No wrinkles △: There are slight wrinkles, but the wrinkles disappear when a tension of about 20 N / m is applied to the pulled-out film. ×: There are strong wrinkles, and the wrinkles do not disappear even when a tension of about 20 N / m is applied to the pulled-out film.

[0096] [Number of defects] The obtained film roll was rewound using a rewinding machine. During rewinding, the number of defects was checked using a defect detector (model F MAX MR) manufactured by FUTEC. The number of defects 1 mm or larger in size in either the vertical or horizontal direction was counted. The number of defects per 10,000 square meters was calculated using equation (5) from the total number of defects. Number of defects = total number of defects ÷ {film roll width (m) × film roll length (10,000 m)} Formula (5)

[0097] [printing] Immediately after production, and after one year of storage in a warehouse at 23°C, the film rolls were gravure printed using a gravure printing machine (Azumaya Iron Works) at a speed of 300 m / min with a 5% halftone dot density. 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 77:23 ratio. The resulting printed samples were 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 missing prints per 10,000 square meters using Equation (6). Number of missing prints = total number of missing prints ÷ {film roll width (m) × film roll length (10,000 m)} (Formula 6)

[0098] <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.

[0099] (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.

[0100] 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. Subsequently, the polymerization catalyst solution was 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 a polyester resin.

[0101] 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 (spherical silica with an average particle size of 2 μm) was added as a lubricant in the production of Polyester 1 above at a ratio of 7,500 ppm to the polyester.

[0102] [Table 1]

[0103] Example 1 The above-mentioned polyester 1 and polyester 2 were mixed in a weight ratio of 96:4 and charged 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 (rotational 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. A laser cleaner was installed on the cooling metal roll to prevent adhesion of foreign matter. The resulting unstretched sheet was heated to 110°C and stretched in the longitudinal direction using two stretching stages: 1.5x in the first stage and 3x in the second stage, for a total stretch ratio of 4.5x. Subsequently, in a transverse stretching process (hereinafter referred to as the tenter) at a temperature of 130°C, the sheet was stretched in the width direction using two stretching stages: 2x in the first stage and 2.3x in the second stage, for a total stretch ratio of 4.6x (see Figure 2). After stretching in the width direction at 4.6x, the sheet was heat-set at 243°C and heat-relaxed by 5% in the width direction. The heat-relaxed film was cooled to below 50°C in the tenter, and the oligomer was removed across the entire width of the film at the exit of the tenter using the exhaust device shown in Figure 3. Next, both ends of the stretched 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 with a thickness of 12 μm, a width of 8 m, and a roll length of 85,000 m. The biaxially stretched film obtained above was slit with a slitter into widths of 4000 mm, 2000 mm, and 1000 mm so as to have a roll length of 80000 m. A 6-inch metal core was used.

[0104] Specific slitting conditions were as follows: slitting began with an initial tension of 150 N / m and an initial surface pressure of 330 N / m. As the winding length increased from 1,000 m to 79,000 m, the tension was reduced at a constant rate from 150 to 80 N / m. Slitting was also carried out with a constant surface pressure of 330 N / m. The film production process conditions and slitting conditions are shown in Table 2. The properties of the obtained film were evaluated using the methods described above. The evaluation results are shown in Tables 3 and 4. A film with the target properties was obtained, and the slack was good. In addition to the results in Table 3 (surface layer of the film roll), all samples every 1000 m were evaluated for slack, and all samples from the above three film rolls were rated ○ (no slack).

[0105] 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 94:6 and fed into the extruder. The film-forming process conditions and slitting conditions are shown in Table 2, and the evaluation results are shown in Tables 3 and 4. The film was of good quality.

[0106] Example 3 A biaxially stretched polyester film roll was obtained in the same manner as in Example 1, except that the film thickness was changed to 6 μm and the roll length was changed to 30,000 m. The film-forming process conditions and slitting conditions are shown in Table 2, and the evaluation results are shown in Tables 3 and 4. The film was of good quality.

[0107] Comparative Example 1 Slitting was started under the following conditions: initial tension of 120 N / m, initial surface pressure of 280 N / m. The tension was reduced at a constant rate from 120 to 50 N / m as the winding length increased from 1,000 m to 79,000 m. Slitting was also carried out with a constant surface pressure of 280 N / m. Other than the slitting conditions, the film was produced under the same conditions as in Example 1. The film-forming process conditions and slitting conditions are shown in Table 2, and the evaluation results are shown in Tables 3 and 4. The winding hardness was low, and the appearance of the film roll after storage in the warehouse and the film slack were poor. Furthermore, there was a large number of missing prints after long-term storage.

[0108] Comparative Example 2 An unstretched sheet obtained in the same manner as in Example 1 was heated to 110°C and stretched in the longitudinal direction by two stages: 1.5x in the first stage and 2x in the second stage, for a total stretch ratio of 3x. Subsequently, in a transverse stretching process (hereinafter referred to as the tenter), the sheet was stretched in the width direction by 2x in the first stage at a temperature of 140°C and 2.3-stage stretching at a temperature of 170°C, for a total stretch ratio of 4.6x. After stretching in the width direction at 4.6x, the sheet was heat-set at 243°C and heat-relaxed by 5% in the width direction. The heat-relaxed film was cooled to below 50°C in the tenter, and the oligomer was sucked in the width direction at the exit of the tenter using the exhaust device shown in Figure 3. Next, both ends of the stretched film were cut and removed, followed by corona discharge treatment and winding into a roll on a winder to produce a master roll of biaxially oriented polyester film with a thickness of 12 μm, a width of 8 m, and a roll length of 35,000 m. Specific slitting conditions included starting with an initial tension of 150 N / m and an initial surface pressure of 330 N / m. As the winding length increased from 1,000 m to 29,000 m, the tension was reduced at a constant rate from 150 to 80 N / m. Slitting was performed with a constant surface pressure of 330 N / m, resulting in a film roll with a winding length of 30,000 m. The film-forming process conditions and slitting conditions are shown in Table 2, and the evaluation results are shown in Tables 3 and 4. The thickness was uneven in the width direction, the winding hardness varied widely, and the appearance and slack of the film roll were poor, resulting in a polyester film roll of inferior quality.

[0109] [Table 2]

[0110] [Table 3]

[0111] [Table 4] [Industrial Applicability]

[0112] The biaxially oriented polyester film roll of the present invention has good slack as described above, and therefore can be suitably used in processing such as printing.

Claims

1. A biaxially oriented polyester film roll for packaging is formed by winding up a biaxially oriented polyester film for packaging, the film being made of a polyethylene terephthalate composition which may contain 5% by mass or less of a resin component other than polyester, the film having an antimony content of 10 ppm or less, a phosphorus content of 25 ppm to 75 ppm, no titanium, containing 1% by mass or less of inorganic particles in the film, and having an arithmetic mean roughness of the film surface of 0.02 μm to 0.05 μm, wherein the biaxially oriented polyester film and the film roll satisfy the following requirements (1) to (6): (1) The film roll length is 8,000 m or more and 80,000 m or less. (2) Film roll width is 500 mm or more and 4000 mm or less (3) The hardness of the outermost layer of the film roll is measured at intervals of 50 mm in the width direction of the film, and the average hardness is in the range of 500 to 700. (4) The hardness of the outermost layer of the film roll is measured at intervals of 50 mm in the width direction of the film, and the variation in hardness is 10% or more and 20% or less. (5) Film thickness is 5 μm or more and 40 μm or less (6) In the thickness unevenness in the film width direction on the surface layer of the film roll, the thickness pattern has a recessed portion, and at the recess with the largest thickness difference (maximum recess), the thickness unevenness of the maximum recess calculated from the maximum thickness difference at the maximum recess and the average thickness of the film is less than 10%.

2. 2. The biaxially stretched polyester film roll for packaging according to claim 1, wherein the thickness unevenness in the width direction of the film of each sample sampled at intervals of 1000 m along the winding length from the surface layer of the film roll is 10% or less for all samples, as calculated from the maximum thickness difference at the largest recess and the average thickness of the film.

3. 3. The biaxially stretched polyester film roll for packaging according to claim 1, wherein the absolute value of the difference in the width direction refractive index between the maximum recess and either of the maximum thickness points at both ends of the recess is 0.010 or less.

4. 4. The biaxially oriented polyester film roll for packaging according to claim 1, wherein the number of defects of 1 mm or more per 10,000 square meters of film is 1.0 or less.

5. 5. The biaxially stretched polyester film roll for packaging according to claim 1, wherein the static friction coefficient and the dynamic friction coefficient of the outer surface and the inner surface of the film roll are both 0.1 or more and 0.8 or less.

6. 6. The biaxially stretched polyester film roll for packaging according to claim 1, wherein the intrinsic viscosity of the film is 0.51 dl / g or more and 0.70 dl / g or less.

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