Polyester film roll

Abstract

The objective is to obtain a polyester film roll that reduces distortion after inorganic layer lamination processing, in response to the recent advancements in quality standards. [Solution] A polyester film roll made by winding a biaxially oriented polyester film, wherein the biaxially oriented polyester film has a film thickness unevenness of 0.5% or more and 1.4% or less across its entire width.

Description

Technical Field

[0001] The present invention relates to a biaxially oriented polyester film roll that can reduce the distortion of a laminated film after laminating an inorganic layer or the like and improve the yield in a customer process by controlling the thickness unevenness in the width direction of the polyester film.

Background Art

[0002] Polyester films are used in a variety of industrial material applications from the viewpoints of mechanical properties, thermal properties, stiffness, and cost. Especially recently, as process papers related to electronic components, they are used for release films for molding green sheets of multilayer ceramic capacitors, liquid crystal polarizer release films, base materials for dry film resists, and the like.

[0003] However, with the recent sophistication of various applications, polyester films are required to have no fine defects that have not been a problem so far and to have a more uniform quality than ever.

[0004] Patent Document 1 discloses a release polyester film with few fine defects on the film surface by reducing the number of depression defects and controlling the surface roughness.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in applications where inorganic layers are laminated onto polyester film, the demands for density and precision are accelerating, making it difficult to adequately address the current challenges. Therefore, the objective of this invention is to provide a polyester film roll that can reduce distortion of the laminated film after the inorganic layer is laminated, in order to meet the increasingly sophisticated quality requirements of recent years. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have found that the above problem can be solved by providing a polyester film roll made by winding a biaxially oriented polyester film, wherein the biaxially oriented polyester film has a film thickness unevenness of 0.5% to 1.4% over its entire width. A preferred embodiment of the present invention has the following configuration. (1) A polyester film roll made by winding a biaxially oriented polyester film, wherein the biaxially oriented polyester film has a film thickness unevenness of 0.5% or more and 1.4% or less over its entire width. (2) The polyester film roll according to (1), wherein the thickness of the biaxially oriented polyester film is 15 μm or more and 35 μm or less. (3) The polyester film roll according to (1) or (2), wherein the film width of the biaxially oriented polyester film is 1500 mm or more and 2200 mm or less. (4) A polyester film roll according to any one of (1) to (3), wherein the average center surface roughness SRa of the biaxially oriented polyester film is 20 nm or more and 40 nm or less, the thermal shrinkage rate in the longitudinal direction of the film after heat treatment at 100°C for 30 minutes is 0.1% or more and 1.0% or less, and the thermal shrinkage rate in the width direction of the film after heat treatment at 100°C for 30 minutes is 0.1% or more and 0.5% or less. (5) The polyester film roll according to any one of (1) to (4), wherein the biaxially oriented polyester film has an average value of 0.5% or more and 1.2% or less of film thickness irregularities in each section divided at 450 mm intervals in the film width direction. (6) The polyester film roll according to (5), wherein the film width of the biaxially oriented polyester film is 1500 mm or more and 2200 mm or less. (7) The biaxially oriented polyester film is a polyester film roll according to any one of (1) to (6), containing 25% by mass or more of post-consumer raw materials. (8) The polyester film roll according to any one of (1) to (7), wherein the biaxially oriented polyester film is used for laminating a ceramic layer on the film. (9) A polyester film roll according to any one of (1) to (8) wherein the biaxially oriented polyester film is used for laminating materials for an all-solid-state battery on the film. [Effects of the Invention]

[0008] This invention provides a polyester film roll that can reduce distortion of the laminated film after inorganic layer lamination, in response to the recent advancements in quality control. Furthermore, this makes it possible to improve yield in customer processes to an even greater extent than before. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the strain evaluation after ceramic layer lamination. [Modes for carrying out the invention]

[0010] The following describes typical embodiments of the polyester film and polyester film roll of the present invention. However, the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the present invention.

[0011] The polyester film of the present invention may be a single-layer film or a laminated structure of two or more layers. When two layers are laminated, it consists of a polyester A layer and a polyester B layer, and when three layers are laminated, it is a laminated film consisting of three layers: polyester A layer, polyester B layer and polyester C layer, or polyester A layer, polyester B layer and polyester A layer. A structure of three or more layers is preferable because, in layers without a surface layer (inner layers), recovered raw materials from edge portions generated in the film-making process, or recycled raw materials from other film-making processes, can be mixed in as appropriate, within a range that does not adversely affect the properties of the film surface, thereby reducing the consumption of petroleum resources and providing cost advantages.

[0012] The polyester in the polyester film of the present invention comprises a dicarboxylic acid component and a diol component. In this specification, a component refers to the smallest unit that can be obtained by hydrolyzing polyester. As the dicarboxylic acid component constituting the polyester, it is preferable to use terephthalic acid at a concentration of 30 mol% or more relative to the total dicarboxylic acid component in order to carry out the present invention. Other dicarboxylic acid components besides terephthalic acid include, but are not limited to, aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedionic acid, dimer acid, eicosanedionic acid, pimelic acid, azelaic acid, methylmalonic acid, and ethylmalonic acid; alicyclic dicarboxylic acids such as adamantanedicarboxylic acid, norbornenedicarboxylic acid, cyclohexanedicarboxylic acid, and decalindicarboxylic acid; and dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 5-sodium sulfoisophthalic acid, phenylendanedicarboxylic acid, anthracenedicarboxylic acid, phenantradiocarboxylic acid, and aromatic dicarboxylic acids such as 9,9'-bis(4-carboxyphenyl)fluorenic acid, or their ester derivatives.

[0013] Furthermore, examples of diol components constituting such polyesters include, but are not limited to, aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, and 1,3-butanediol; alicyclic diols such as cyclohexanedimethanol, spiroglycol, and isosorbide; diols such as bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis(4-hydroxyphenyl)fluorene, and aromatic diols; and diols formed by the linking of multiple diols mentioned above.

[0014] The polyester of the present invention can be produced by known methods. Specifically, the esterification step can be carried out using one or more esterification reactors under stirring. For example, when using a single esterification reactor, the reaction temperature is usually 240-280°C, the relative pressure to atmospheric pressure is usually 0-400 kPa, and the reaction time is usually 1-10 hours. The esterification reaction rate of the esterification reaction product obtained in the esterification step is usually 95% or more.

[0015] It is preferable to proceed to a melt polycondensation step after the esterification reaction. The melt polycondensation step can usually be carried out in a continuous or batch manner using one or more polycondensation reactors, and can be carried out while gradually reducing the pressure from atmospheric pressure and distilling the generated ethylene glycol out of the system under heating and stirring. For example, in the case of a batch manner using a single polycondensation reactor, the reaction temperature is usually 250 to 290°C, the final absolute pressure obtained by gradually reducing the pressure from atmospheric pressure is usually 0.013 to 1.3 kPa (0.1 to 10 Torr), and the reaction time is usually 1 to 20 hours. Furthermore, from the viewpoint of improving the electrostatic casting properties during polyester film molding, compounds containing sulfur, phosphorus, calcium, magnesium, and manganese elements can be added during the polycondensation reaction.

[0016] The intrinsic viscosity of polyester resin can be determined by the stirring torque of the polymer at the end of polymerization. When the stirring torque is high, the melt viscosity of the polymer is high, and the intrinsic viscosity (IV) is also high. The stirring torque for determining the end of polymerization should be set so that the target intrinsic viscosity is achieved. In this invention, it is preferable to set the stirring torque for determining the end of polymerization so that the IV of the film is between 0.50 dL / g and 0.70 dL / g. This range makes it easy to control surface roughness and is preferable from the viewpoint of thermal shrinkage characteristics and puncture strength. The obtained polymerized polyester resin can be discharged in strand form from the bottom of the polymerization apparatus and cut with a cutter while being water-cooled. Since the chip shape can be controlled by cutting, polyester chips with a desirable bulk density can be obtained in this invention.

[0017] In the present invention, one or more of the following polycondensation reaction catalysts can be used: antimony trioxide, antimony pentoxide, antimony acetate, antimony glycolate, germanium dioxide, and organotitanium compounds. Among these, antimony trioxide is preferred in terms of the transparency and availability of the resulting polyester.

[0018] A preferred embodiment of the polyester film roll of the present invention has film thickness unevenness in the full width of 0.5% or more and 1.4% or less, more preferably 0.7% or more and 1.2% or less. The film thickness unevenness shall be determined by the method described in the examples. By setting it within the above range, the distortion of the laminated film after the inorganic layer lamination process in the customer process can be reduced. When the film thickness unevenness exceeds 1.4%, uneven heat deformation corresponding to the thickness unevenness in the plane of the biaxially oriented polyester film occurs due to the heat applied in the inorganic layer lamination process, which may cause large distortion in the laminated film and reduce the yield in the customer process. Also, when the film thickness unevenness is less than 0.5%, excessive air escapes when the biaxially oriented polyester film is wound, resulting in stronger blocking, and there is a tendency for peeling electrification to increase and foreign matter adhesion to increase during use by the customer. As a method for adjusting the film thickness unevenness of the biaxially oriented polyester film to satisfy the above range, there is a method of adjusting the temperature distribution in the oven during the stretching process of the biaxially oriented polyester film. When the temperature distribution is large, stretching unevenness occurs and the film thickness unevenness tends to increase. By reducing the temperature distribution, a biaxially oriented polyester film satisfying the above range can be obtained.

[0019] In the biaxially oriented polyester film of the present invention, it is preferable that the film thickness unevenness in each section divided at intervals of 450 mm in the width direction is all 0.5% or more and 1.2% or less. More preferably, the thickness unevenness in each section is 0.7% or more and 1.0% or less. By adopting such a configuration, excellent thickness uniformity can be maintained even when supplied as a slit product. By setting the thickness unevenness of each section to 1.2% or less, it is possible to prevent the occurrence of uneven heat deformation corresponding to the thickness unevenness due to the heat applied in the inorganic layer lamination process in the slit product cut out from the section, which may cause large distortion in the laminated film and improve the yield in the customer process. On the other hand, by setting the thickness unevenness to 0.5% or more, it is possible to prevent the deterioration of blocking and the increase of peeling charge due to excessive air bleeding during winding. As a method of adjusting the thickness unevenness of each section to meet the above range, a method of adjusting the temperature distribution in the oven during the stretching process of the biaxially oriented polyester film can be mentioned. In particular, it is preferable to control the temperature difference in the width direction inside the oven in the width direction stretching process within ±3% in order to make the thickness unevenness in the width direction good and the thickness unevenness in each 450 mm section within a suitable range. When the temperature distribution is large, stretching unevenness occurs, and the thickness unevenness tends to increase. By reducing the temperature distribution, a biaxially oriented polyester film that meets the above range can be obtained.

[0020] The thickness of the biaxially oriented polyester film of the present invention is preferably from 10 μm to 35 μm, more preferably from 15 μm to 25 μm, and still more preferably from 16 μm to 20 μm. When the thickness of the biaxially oriented polyester film is less than 10 μm, breakage is likely to occur during film formation, which may reduce productivity. In addition, when tension is applied to the film, it is likely to deform, and the process suitability during ceramic layer lamination tends to be greatly impaired. On the other hand, when the thickness exceeds 35 μm, the price of the biaxially oriented polyester film may increase from the perspective of increasing the amount of raw materials used, and it may become unfavorable from the perspectives of transportation costs and the amount of CO2 generated during transportation.

[0021] The film width of the biaxially oriented polyester film of the present invention is preferably 1500 mm or more and 2200 mm or less. If it is less than 1500 mm, it may significantly reduce the production efficiency at the customer's end. If it exceeds 2200 mm, it tends to be difficult to uniformly coat the entire effective width of the ceramic layer lamination, which may be undesirable.

[0022] The average center surface roughness (SRa) of the biaxially oriented polyester film of the present invention is 20 nm to 40 nm, more preferably 25 nm to 35 nm. If the average center surface roughness (SRa) is less than 20 nm, the film's slipperiness deteriorates, and friction with the conveyor roll may easily cause abrasive scratches. On the other hand, if the average center surface roughness (SRa) exceeds 40 nm, protrusions on the film may transfer to the film when it is wound up.

[0023] The biaxially oriented polyester film of the present invention preferably has a thermal shrinkage rate of 0.1% or more and 1.0% or less in the longitudinal direction of the film after heat treatment at 100°C for 30 minutes, and a thermal shrinkage rate of 0.1% or more and 0.5% or less in the width direction of the film. If the thermal shrinkage rate exceeds the upper limit, wrinkles may occur due to film shrinkage when the ceramic layer is laminated. If the thermal shrinkage rate falls below the lower limit, it may become difficult to achieve a suitable thickness and unevenness in the film, and the biaxially oriented polyester film of the present invention may not be obtainable.

[0024] The biaxially oriented polyester film of the present invention preferably contains 25% by mass or more of post-consumer raw materials in the entire biaxially oriented polyester film. Post-consumer raw materials refer to polyester films that would otherwise be discarded after being fed into customer processes, such as for release film applications, and have been processed again for use as raw materials for making biaxially oriented polyester films. By including post-consumer raw materials, it becomes possible to realize a resource recycling cycle.

[0025] The biaxially oriented polyester film of the present invention is preferably used in applications involving the lamination of a ceramic layer on the film, particularly in solid-state batteries. A release layer can also be provided between the film and the ceramic layer.

[0026] Next, the method for manufacturing the polyester film and film roll of the present invention will be described, but the present invention is not limited to such examples. (Step 1) Using terephthalic acid or dimethyl terephthalate and ethylene glycol as raw materials, a low polymer such as BHT (bishydroxyethyl terephthalate) is obtained by reactions such as esterification and transesterification. Then, terephthalic acid and ethylene glycol, as well as compounds containing sulfur, phosphorus, calcium, magnesium, and manganese elements are added, and a polyester resin is obtained by polycondensation reaction. (Step 2) A process to obtain an unstretched polyester film with a thickness of 180 to 1400 μm by melt-extruding polyester resin into a sheet, and then contacting the melt-extruded polyester resin into a sheet on a casting roll at 18 to 50°C for 1 to 15 seconds to cool and solidify it. (Step 3) A step in which the unstretched polyester film obtained in (Step 2) is stretched in the longitudinal direction at a stretching ratio of 2.5 to 5.0 times, and then cooled to obtain a uniaxially oriented polyester film. (Step 4) The uniaxially oriented polyester film obtained in (Step 3) is stretched at a stretching ratio of 3.0 to 6.0 times in the width direction, and the stretching ratio in the width direction is higher than the stretching ratio in the longitudinal direction, and then cooled to obtain a biaxially oriented polyester film. (Step 5) A step in which the polyester film obtained in Step 4 is wound up to obtain an intermediate film roll. (Step 6) A step in which the intermediate film roll obtained in Step 5 is slit to an appropriate width to obtain a polyester film roll.

[0027] The following provides a detailed explanation of each step.

[0028] (Process 1) Manufacturing of polyester resin A slurry consisting of terephthalic acid and ethylene glycol is gradually added to an esterification reactor containing BHT (bishydroxyethyl terephthalate) dissolved at 250°C, and the esterification reaction proceeds while water is distilled off. The temperature in the reaction system is controlled to 245-250°C, and the esterification reaction is terminated when the reaction rate reaches 95%, and the resulting esterified product is charged in molten state into a polymerization apparatus equipped with a distillation device.

[0029] Antimony trioxide and a compound containing sulfur and phosphorus are added as an ethylene glycol solution. Subsequently, the pressure in the polymerization reactor is gradually reduced to below 0.13 kPa in 35 minutes, and at the same time, the temperature is gradually increased to 279°C to carry out the polymerization reaction and obtain a polyester resin.

[0030] (Step 2) Preparation of unstretched film The polyester resin is dried as needed, supplied to an extruder, and melt-extruded. In the production of the polyester film and film roll of the present invention, a single-screw or twin-screw extruder can be used. In addition, to eliminate the pellet drying process, a vented extruder equipped with a vacuum line can be used. Furthermore, in the case of a multilayer film, a so-called tandem extruder can be used for the intermediate layer, where the extrusion volume is greatest, with each extruder responsible for melting the pellets and maintaining the molten pellets at a constant temperature. In order to achieve the intrinsic viscosity of the film within the above range, the average intrinsic viscosity of the polyester resin supplied to the extruder is preferably 0.55 to 0.64 dL / g, and more preferably 0.55 to 0.62 dL / g.

[0031] Next, the polyester resin extruded by the extruder is filtered. Since even small foreign matter can cause defects in the film, it is effective to use a high-precision filter that can capture 95% or more of foreign matter larger than 5 μm. The molten polyester resin undergoes thermal decomposition and hydrolysis, which breaks its molecular chains and reduces its intrinsic viscosity. For stable melt extrusion, the temperature and moisture content of the polyester resin during melt extrusion are preferably 5 to 40°C above the melting point of the polyester resin and 300 ppm or less.

[0032] Next, the polyester resin is formed into a sheet using a T-shaped die or the like, and the sheet-shaped polyester resin is cooled and solidified on a casting roll to obtain an unstretched film. In the case of a three-layer laminated film, the film is laminated in three layers using three extruders and three manifolds or confluence blocks (for example, confluence blocks with a rectangular confluence section), and the sheet is extruded from the die. At this time, it is desirable that the gap between the die can be automatically adjusted by a heater. Furthermore, it is even more desirable to be able to feed back the film thickness after stretching into the gap between the die in order to suppress thickness unevenness. Also, if the film thickness is made uniform in the width direction of the polyester film, or if the gap between the die is adjusted so that the center of the film in the width direction is slightly thicker, it becomes easier to control the thickness unevenness of the polyester film roll to satisfy a desirable range. In addition, surface treatment of the die with tungsten carbide is preferable from the viewpoint of suppressing die streaks, as it provides excellent scratch and abrasion resistance during cleaning and maintenance of the die. Die streaks occur at a fixed thickness location, resulting in thickness unevenness. The sheet extruded from the die is cooled on a casting roll to create an unstretched film. In this case, installing a static mixer and a gear pump in the polymer flow path is an effective means of suppressing thickness unevenness in the present invention, from the viewpoint of stabilizing back pressure and suppressing thickness fluctuations. The gear pump has the function of blocking pressure fluctuations in the extrusion process, and is necessary for uniform thickness control. By keeping the rotation speed of the gear built into the gear pump constant, thickness unevenness can be kept to a minimum. In the present invention, it is also effective to control the rotation speed of the gear pump by feeding back the thickness of the wound intermediate product in terms of weight, because the discharge decreases as the filter pressure increases.

[0033] Furthermore, the temperature of the casting roll is preferably 18-50°C, and the cooling time during which the sheet-formed polyester resin contacts the casting roll is preferably 1-15 seconds. If the temperature of the casting roll is below 18°C, condensation is likely to occur on the casting drum, which may worsen the film-forming properties. If the temperature of the casting roll exceeds 50°C, the cooling rate slows down, causing microcrystals to form in the unstretched film, which accelerates crystal orientation in the subsequent stretching process and worsens the orientation angle. Similarly, if the cooling time during contact with the casting roll is less than 1 second, insufficient cooling time leads to uneven cooling and stretching, making it difficult to achieve the aforementioned ranges for film thickness and surface roughness. The cooling time by the casting roll can be increased by increasing the diameter of the casting roll or lowering the line speed, but considering equipment space and productivity, the upper limit is 15 seconds. More preferably, the temperature of the casting roll is 20-30°C, and the cooling time during which the sheet-formed polyester resin contacts the casting roll is 3-12 seconds.

[0034] Furthermore, the thickness of the unstretched film obtained in step 2 is preferably 180 to 1400 μm. If the thickness of the unstretched film is less than 180 μm, the film thickness is insufficient to stretch it so that the orientation angle and thermal shrinkage rate are within the desired range, and film tearing may occur during stretching. On the other hand, if the thickness of the unstretched film exceeds 1400 μm, when the polyester resin sheet is cooled and solidified on the casting roll, uneven cooling may occur in the thickness direction, making it difficult to obtain a uniform polyester film. In addition, the final thickness of the biaxially oriented polyester film may fall outside the above range.

[0035] One method for incorporating inert particles into polyester is to disperse inert particles in a predetermined proportion in the form of a slurry in ethylene glycol, which is a diol component, and add this ethylene glycol slurry at any stage before the completion of polyester polymerization. When adding the particles, it is preferable to add the aqueous sol or alcohol sol obtained during synthesis without drying it first, as this improves particle dispersibility and suppresses the generation of coarse protrusions. Alternatively, a method of directly mixing the aqueous slurry of particles with a predetermined polyester pellet and supplying it to a vented twin-screw compounding extruder to knead it into the polyester is also effective for producing the polyester film of the present invention.

[0036] (Step 3) Preparation of uniaxially oriented film A uniaxially oriented polyester film is obtained by stretching the unstretched film obtained in step 2 above at a stretching ratio of 2.5 to 5.0 times in the longitudinal direction and then cooling it. Stretching in the longitudinal direction is preferably performed in one or multiple stages at a stretching temperature of 90 to 130°C. From the viewpoint of suppressing thickness unevenness in the longitudinal direction, a stretching temperature of 100 to 120°C and a stretching ratio of 3 to 4 times are more preferable, and from the viewpoint of preventing stretching unevenness and scratches, stretching is preferably performed in two or more stages. If the stretching temperature and stretching ratio exceed the above range, it becomes difficult to keep the thermal shrinkage rate and thickness irregularities within the above range. Furthermore, stretching in the longitudinal direction causes shrinkage in the width direction, but it is preferable that the width reduction of the film from this stretching process to the cooling process be 15% or less. If the width reduction of the film exceeds 15%, it may lead to meandering and width fluctuations in the film, as well as the risk of film breakage. The shrinkage of the film width can be controlled by adjusting the thickness profile of the film edge before longitudinal stretching, or by adjusting the stretching tension with a nip roll or similar device.

[0037] The film width reduction shown here is calculated by dividing the difference between the film width immediately before the longitudinal stretching process and the film width after stretching and cooling by the film width immediately before the longitudinal stretching process. A film temperature of 25-45°C during the cooling process in (Step 3) is preferable for stable stretching in the width direction in the following (Step 4).

[0038] (Step 4) Preparation of biaxially oriented film The uniaxially oriented polyester film obtained in step 3 is stretched at a stretching ratio of 3.0 to 6.0 times in the width direction, and at a stretching ratio higher in the width direction than in the longitudinal direction. This transverse stretching machine uses self-circulation in each oven chamber to blow hot air onto the film, thereby raising the film temperature and performing stretching and heat fixing. At this time, in order to prevent oligomers precipitated from the heat-treated film in the oven from cooling and adhering to the oven, it is preferable to replace the air by supplying and exhausting air in the oven. At this time, if the temperature of the air supplied to the oven remains close to that of the outside air when it merges with the circulating air, temperature unevenness may occur in the air after the merger, which may worsen the thickness unevenness in the longitudinal and width directions. Therefore, it is preferable to heat the supplied air to the same temperature as the circulating air, or to a temperature that matches the capacity of the heat exchanger that heats the circulating air.

[0039] Furthermore, when adjusting the intake and exhaust volume of air in the oven, it is preferable that the direction of the air flowing above and below the conveyed film is the same. In each chamber of the oven, in addition to the self-circulating air, there is an accompanying airflow flowing from upstream in the same direction as the film conveying direction, and intake or exhaust of air from outside the oven, causing the airflow inside the stent (STN) to change in a complex manner. In this case, due to the pressure difference between chambers, the airflow between chambers may change, for example, from flowing from upstream to downstream to flowing from downstream to upstream. If the air temperature differs between chambers, the airflow between chambers may lead to uneven expansion and contraction of the film. For this reason, the intake and exhaust conditions of the oven can be adjusted so that the exhaust volume is greater than the intake volume to induce airflow in the same direction. When a film obtained using such an intake and exhaust system is used, it is preferable to stretch it in the width direction at a stretching temperature of 90 to 130°C. When the stretching temperature is lower than 90°C and the stretching ratio is higher than 6.0 times, the strength of the film tends to increase, but the film becomes more prone to tearing and may worsen thermal shrinkage. A stretching temperature of 100-120°C and a stretching ratio of 4.0-5.0 times are more preferable. Furthermore, in order to reduce distortion after lamination of the ceramic layer, it is preferable that the stretching ratio in the width direction is higher than the stretching ratio in the longitudinal direction. When the stretching ratio in the width direction is higher than the stretching ratio in the longitudinal direction, the molecular orientation within the film becomes more isotropic, which helps to suppress differences in physical properties in the width direction, and consequently leads to a reduction in distortion after lamination of the ceramic layer. In addition, controlling the temperature difference in the width direction inside the oven to within ±3% is preferable in order to ensure good thickness uniformity in the width direction and to keep the thickness irregularities within a suitable range.

[0040] The polyester film of the present invention may be further re-stretched one or more times in each direction, or it may be re-stretched simultaneously in two axes. In this case, the film may be heated at a temperature of 80°C to 100°C on the conveying rolls before re-stretching in the longitudinal direction, or it may be conveyed using rolls that have not been heated. Furthermore, the re-stretching process may be passed without applying a stretching ratio. After re-stretching, transverse stretching is performed, and the film is heat-treated after stretching. This heat treatment can be performed in an oven, on heated rolls, or any other conventionally known method. The heat treatment temperature can usually be any temperature between 150°C and 245°C, and the heat treatment time is usually preferably between 1 second and 60 seconds. The heat treatment may be performed while relaxing the film in its longitudinal and / or width directions. After the heat treatment, it is preferable to relax the film in the width direction by 0% to 10% at a temperature lower than the heat treatment temperature, between 0°C and 150°C.

[0041] (Step 5) Step to obtain an intermediate film roll The biaxially oriented polyester film obtained in step 4 is cut at the edges and then wound up using a winding device to become an intermediate biaxially oriented film roll.

[0042] (Step 6) Step to obtain a biaxially oriented polyester film roll. The intermediate biaxially oriented film roll obtained in step 5 is slit to an appropriate width and length in a slitting step and wound up to obtain the polyester film roll of the present invention.

[0043] The biaxially oriented polyester film roll and biaxially oriented polyester film obtained by the above method can suppress distortion after lamination of the ceramic layer, and are therefore preferably used in applications where a ceramic layer is laminated on a biaxially oriented polyester film, particularly as a molding component for all-solid-state batteries and multilayer ceramic capacitors. [Examples]

[0044] The methods for measuring and evaluating characteristic values ​​in the examples and comparative examples are as follows.

[0045] (1) Thickness irregularities of biaxially oriented polyester film roll The entire width of a film roll was continuously measured over 1,000 m using the FiDiCa film thickness distribution analyzer manufactured by JFE Techno Research Corporation, at intervals of 1.5 mm in the width direction and 10 mm in the length direction. The thickness measurement data from each measurement point in the width direction was averaged in the length direction, and the maximum, minimum, and average values ​​(in-plane average thickness) were calculated from the averaged thicknesses at each point in the width direction. The film thickness irregularity was calculated as (maximum value - minimum value) / in-plane average thickness × 100 (%).

[0046] (2) Film thickness irregularities in each section divided at 450 mm intervals in the film width direction Using the FiDiCa film thickness distribution analyzer manufactured by JFE Techno Research Corporation, thickness data was continuously measured over 1,000 m of the entire width of a film roll at 1.5 mm intervals in the width direction and 10 mm intervals in the length direction. The film was divided into sections at 450 mm intervals in the width direction, starting from the center of the film width and moving towards both ends. Within each section, the thickness measurement data was averaged in the length direction, and the maximum, minimum, and average values ​​(average thickness within the section) were calculated from the averaged thickness at each point in the width direction. Note that any remaining sections less than 450 mm at the film ends that occur when the film width is not divisible by 450 mm were excluded from the measurement. For each section, the film thickness irregularity was calculated using (maximum value - minimum value) / average thickness within the section × 100 (%), and the average of the obtained values ​​for each section was taken as the film thickness irregularity in each section divided at 450 mm intervals in the film width direction of that roll.

[0047] (3) Width of biaxially oriented polyester film The film cut from the surface of the film roll was placed on a flat measuring table, and the length in the width direction was measured using a Class 1 metal ruler conforming to JIS B 7516, which was defined as the film width.

[0048] (4) Thickness of biaxially oriented polyester film A sample was taken from the entire width of the polyester film, and 10 of these samples were stacked together. The thickness was measured using a Mitutoyo micrometer, and the result was divided by 10 to obtain the thickness of each individual sample. Ten sampling points were evenly spaced along the width, and the average value was taken to determine the average thickness.

[0049] (5) Center surface average roughness SRa The surface profile curve was measured using a three-dimensional micro-surface shape measuring instrument (ET-350K, manufactured by Kosaka Laboratory). From the resulting surface profile curve, the average center surface roughness SRa, a three-dimensional extension of the concept according to JIS-B0601 (2001), was determined. The measurement conditions are as follows. X-direction measurement length: 0.5 mm, X-direction feed rate: 0.1 mm / sec Y-direction feed pitch: 5 μm, Y-direction line count: 40 lines Cutoff: 0.25mm Touch pressure: 0.02 mN Magnification in height (Z direction): 50,000 times.

[0050] (6) Thermal shrinkage Two lines were drawn on the film surface, each 10 mm wide and approximately 100 mm long. The distance between these two lines was measured at 23°C and defined as L0. This film sample was then placed in a 100°C oven for 30 minutes under a 1.5 g load. The distance between the two lines was measured again at 23°C and defined as L1. The thermal shrinkage rate was then calculated using the following formula. Thermal shrinkage rate (%) = {(L0-L1) / L0} × 100 Measurements were taken at three points along the length and width of the film, and the average value was calculated.

[0051] (7) Evaluation of strain after ceramic layer lamination treatment A single-sheet sample measuring 400 mm in width and 400 mm in length was cut from a biaxially oriented polyester film roll at three equal points along the width of the film roll. A 300 mm line was drawn parallel to the width direction in the longitudinal center of each sample, and then a ceramic layer was laminated onto the biaxially oriented polyester film using the method described below. The deformation of the line after the ceramic layer was laminated was measured using a Keyence IM-7030 image dimension measuring instrument, and the degree of distortion after ceramic lamination was evaluated in three stages: ◎, ○, and ×. The appearance in Example 1 was ◎, and ◎ is a level that does not pose a practical problem. The degree of distortion was calculated using the parameter Z calculated from the maximum values ​​of the vertical displacements X (mm) and Y (mm) from the straight line connecting the ends of the line after ceramic lamination, using the formula (Xmax-Ymax) / 300 mm × 100 (Figure 1). ◎: Z≦0.05 ○: 0.05 <Z≦0.09 ×: 0.09 <Z (8) Lamination of ceramic layers 100 parts by mass of barium titanate (product name HPBT-1, manufactured by Fuji Titanium Industries Co., Ltd.), 10 parts by mass of polyvinyl butyral (product name BL-1, manufactured by Sekisui Chemical Co., Ltd.), 5 parts by mass of dibutyl phthalate, and 60 parts by mass of toluene-ethanol (mass ratio 30:30) were mixed with glass beads having a number average particle size of 2 mm. The mixture was then mixed and dispersed in a jet mill for 20 hours, and then filtered to prepare a paste-like ceramic slurry. The obtained ceramic slurry was cut to 200 mm x 300 mm, lines were drawn on it, and then, while applying a constant tension in the longitudinal direction, it was coated onto a biaxially oriented film using a bar coater to a dry thickness of 0.5 μm. It was dried at 120°C to obtain a laminated film with a ceramic layer.

[0052] (Example 1) A slurry consisting of 86 parts by mass of terephthalic acid and 37 parts by mass of ethylene glycol (1.15 times the molar amount of terephthalic acid) was gradually added to an esterification reactor containing 105 parts by mass of BHT (bishydroxyethyl terephthalate) dissolved at 250°C, and the esterification reaction was carried out while distilling off water. The temperature in the reaction system was controlled to 245-250°C, and the esterification reaction was terminated when the reaction rate reached 95%, and the resulting 105 parts by mass of esterified product (equivalent to 100 parts by mass of PET (polyethylene terephthalate)) was charged in molten state into a polymerization apparatus equipped with a distillation device.

[0053] 0.0084 parts by mass of antimony trioxide and 0.0175 parts by mass of tetrabutylphosphonium p-toluenesulfonate were added as an ethylene glycol solution. Subsequently, the pressure in the polymerization reactor was gradually reduced to 0.13 kPa or less over 35 minutes, and at the same time, the temperature was gradually increased to 279°C. The polymerization reaction was carried out until the intrinsic viscosity of the polyester resin composition reached 0.625 dL / g. After that, the polycondensation reactor was returned to atmospheric pressure with nitrogen gas, and the mixture was discharged in strand form into cold water from a nozzle. The mixture was then pelletized into cylindrical shapes using an extruder to obtain the polyester resin composition.

[0054] Furthermore, a water slurry of divinylbenzene / styrene copolymer crosslinked particles with a volume-average particle size of 1.0 μm and a volume-shape coefficient of f=0.51, obtained by adsorbing monomers, was incorporated into the above-mentioned polyester resin composition pellets using a vented twin-screw kneader to obtain a master pellet containing 1 part by mass of divinylbenzene / styrene copolymer crosslinked particles with a volume-average particle size of 1.0 μm per 99 parts by mass of the polyester resin composition. The volume shape coefficient f is expressed by the following formula. f = V / Dm 3 Here, V is the particle volume (μm). 3 ), where Dm is the maximum diameter (μm) of the particle on the projection plane. The volume shape coefficient f takes its maximum value of π / 6 when the particle is spherical.

[0055] These polyesters were each dried under reduced pressure at 160°C for 8 hours to achieve a moisture content of 100 ppm. They were then fed into separate extruders and melt-extruded at 275°C. After filtration through a high-precision filter with a collection efficiency of 95% and particles larger than 5 μm, the layers were combined and laminated using a rectangular three-layer confluence block to form a three-layer laminate consisting of polyester layer B, polyester layer A, and polyester layer B'. The above-mentioned master pellets were used for polyester layer B and polyester layer B', and the above-mentioned polyester resin composition was used for polyester layer A.

[0056] Subsequently, the film was cooled and solidified for 7 seconds on a casting roll with a surface temperature of 25°C using an electrostatic casting method via a slit die maintained at 285°C, yielding an unstretched film with a thickness of 540 μm. This unstretched film was first stretched 3.8 times in the longitudinal direction using a roll heated to 103°C and a radiation heater. The width reduction at this time was 14%. Next, it was stretched 4.3 times in the width direction at 110°C using a tenter. After that, the film was cooled to a temperature of 35°C at a width reduction rate of 18% / min during the cooling process. A roll method was used for this cooling process, with the roll temperature set to 30°C and the cooling process time set to 15 seconds. Then, heat treatment was performed at 195°C to wind up a three-layer biaxially oriented polyester film to obtain an intermediate product roll. The obtained intermediate product roll was slit using a slitter to obtain a polyester film roll with a thickness of 19 μm, a film lamination thickness of polyester layer B / polyester layer A / polyester layer B' = 1.0 μm / 17 μm / 1.0 μm, a film width of 1800 mm, and a longitudinal length of 15000 m. The film thickness irregularity was 1.1%, and the thickness irregularity in the 450 mm section was 0.9%.

[0057] Table 1 lists the evaluation results for other examples and comparative examples.

[0058] (Example 2) A film roll was manufactured under the same conditions as in Example 1, except that the automatic adjustment time for the nozzle gap using a heater was shortened compared to Example 1, and the oven temperature was adjusted by the output of the circulating fan inside the oven. The thickness unevenness of the film was 1.4%, and the thickness unevenness in the 450 mm section was 1.2%.

[0059] (Example 3) The film formation conditions were adjusted so that the thickness was 25 μm while the resin extrusion amount was constant, and the post-consumer raw materials and polyester resin composition were mixed into polyester layer A so that the post-consumer raw materials accounted for 30% of the total weight of the film. The procedure was carried out in the same manner as in Example 1. The film thickness was 0.9%, and the thickness irregularity in the 450 mm section was 0.8%.

[0060] (Example 4) A film roll was manufactured under the same conditions as in Example 1, except that the automatic adjustment time for the nozzle gap using a heater was made longer than in Example 1, and the oven temperature was adjusted by the output of the circulating fan inside the oven. The thickness unevenness of the film was 1.4%, and the thickness unevenness in the 450 mm section was 0.7%.

[0061] (Comparative Example 1) A film roll was prepared under the same conditions as in Example 1, except that the gap between the end caps was adjusted so that the central part in the film width direction was thinner, and the oven temperature was adjusted by the output of the circulating fan inside the oven. The thickness unevenness of the film was 2.0%, and the thickness unevenness in the 450 mm section was 1.5%.

[0062] [Table 1]

Claims

1. A polyester film roll formed by winding a biaxially oriented polyester film, wherein the biaxially oriented polyester film has a film thickness unevenness of 0.5% or more and 1.4% or less across its entire width. The film thickness and unevenness shall be determined by the following measurement method. (Measurement method) Using the FiDiCa film thickness distribution analyzer manufactured by JFE Techno Research Corporation, the entire width of the film roll was continuously measured for 1,000 m at intervals of 1.5 mm in the width direction and 10 mm in the length direction. The thickness measurement data from each measurement point in the width direction was averaged in the length direction, and the maximum, minimum, and average values ​​(in-plane average thickness) were calculated from the averaged thickness at each point in the width direction. The film thickness irregularity was calculated as (maximum value - minimum value) / in-plane average thickness × 100 (%).

2. The polyester film roll according to claim 1, wherein the thickness of the biaxially oriented polyester film is 15 μm or more and 35 μm or less.

3. The polyester film roll according to claim 1, wherein the film width of the biaxially oriented polyester film is 1500 mm or more and 2200 mm or less.

4. The polyester film roll according to claim 1, wherein the average center surface roughness SRa of the biaxially oriented polyester film is 20 nm or more and 40 nm or less, the thermal shrinkage rate in the longitudinal direction of the film after heat treatment at 100°C for 30 minutes is 0.1% or more and 1.0% or less, and the thermal shrinkage rate in the width direction of the film after heat treatment at 100°C for 30 minutes is 0.1% or more and 0.5% or less.

5. The polyester film roll according to claim 1, wherein the biaxially oriented polyester film has an average value of 0.5% or more and 1.2% or less for each section divided at 450 mm intervals in the film width direction. The film thickness irregularities in each section, which is divided at 450 mm intervals in the film width direction, shall be determined by the following measurement method. (Measurement method) Using the FiDiCa film thickness distribution measuring device manufactured by JFE Techno Research Corporation, thickness data is continuously measured over 1,000 m of the entire width of the film roll at intervals of 1.5 mm in the width direction and 10 mm in the length direction. The film width is divided into sections at 450 mm intervals from the center of the film's total width toward both ends. Within each section, the thickness measurement data is averaged in the length direction, and the maximum, minimum, and average values ​​(average thickness within the section) are calculated from the averaged thickness at each point in the width direction. Note that any remaining sections less than 450 mm at the film ends that occur when the total film width is not divisible by 450 mm are excluded from the measurement. For each section, the film thickness irregularity is calculated using (maximum value - minimum value) / average thickness within the section × 100 (%), and the average of the obtained values ​​for each section is taken as the film thickness irregularity in each section divided at 450 mm intervals in the film width direction of that roll.

6. The polyester film roll according to claim 5, wherein the film width of the biaxially oriented polyester film is 1500 mm or more and 2200 mm or less.

7. The polyester film roll according to claim 1, wherein the biaxially oriented polyester film contains 25% by mass or more of post-consumer raw materials.

8. The polyester film roll according to any one of claims 1 to 7, wherein the biaxially oriented polyester film is used for laminating a ceramic layer on the film.

9. The polyester film roll according to any one of claims 1 to 7, wherein the biaxially oriented polyester film is used for laminating materials for an all-solid-state battery onto the film.

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