Polyester film

Abstract

To provide a polyester film capable of inhibiting formation of wrinkles and misalignment in processing when subjected to a processing step involving heating at 70°C to 140°C.SOLUTION: Provided is a polyester film whose width-direction dimensional change rate at 70°C to 140°C, relative to its dimension at 30°C, is 0.00% or more to 0.20% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyester film having high dimensional stability when undergoing a processing step involving heating.

Background Art

[0002] Polyester films are widely used for industrial material applications from the viewpoints of mechanical properties, thermal properties, and cost. Among them, in particular, with the spread of smartphones, electric vehicles, and electronic components accompanying the spread of autonomous driving in recent years, especially the demand for multilayer ceramic capacitors (hereinafter sometimes referred to as MLCCs) has expanded, and it is expected that the consumption of polyester films used in their manufacture will also increase. MLCCs are manufactured through the following steps. A dielectric paste is applied and dried on a base film coated with a release layer. After printing the internal electrodes, the solid matter made of the dielectric paste is peeled off from the release film. The obtained dielectric sheets are laminated, pressed, compressed, cut to a predetermined size, fired, and then the external electrodes are plated to complete.

[0003] The properties required for the base film used in the manufacture of MLCCs include thickness uniformity, no defects such as foreign matter or large protrusions, and dimensional stability in the processing temperature range due to heating during the drying of the dielectric paste or the printing of the internal electrodes. In addition, the base film for MLCC manufacture generally has a release layer laminated on one side of a polyester film, and this release layer is laminated through a process of coating a solvent containing a release component on one side of the polyester film and then heating and drying. Therefore, dimensional stability in the processing temperature range is also important in the release layer lamination process. As technologies for providing polyester films with improved dimensional stability, Patent Document 1 discloses a polyester film for thermal transfer ink ribbons that suppresses wrinkle generation when wound as a film roll during the manufacture of the polyester film by defining the surface roughness and crystallinity of the polyester film, and Patent Document 2 discloses a polyester film roll for a transfer material without local slack defects by defining the surface roughness and coefficient of kinetic friction of the polyester film. Also, as polyester films suitable for use as the base material in the manufacturing process of multilayer ceramic capacitors, Patent Document 3 that defines the refractive index in the longitudinal direction and the surface roughness of both sides of the polyester film, and Patent Document 4 that defines the Young's modulus in the longitudinal and width directions of the polyester film and the rate of dimensional change in the longitudinal direction at 80°C to 140°C are disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, with the trend of miniaturization and increased capacitance of MLCCs, the thickness of dielectric sheets has been increasingly thinned. In addition, the use in fields where reliability is particularly important, such as autonomous driving, is also increasing. Therefore, although the influence of conventional base films on the quality of MLCCs was small, thickness defects of dielectric sheets caused by fine wrinkles generated in the base film during processing have also come to have a great impact on the quality and yield of MLCCs. Also, during MLCC manufacturing, the process involves peeling the dielectric sheet printed with internal electrodes from the base film and laminating a large number of them. If the dimensional stability of the base film is low, it can also cause misalignment of the printed internal electrodes after lamination.

[0006] Generally, in the processing steps using polyester films, since no tension is applied in the film width direction, the dimensional stability in the film width direction is particularly important for wrinkles generated during processing and misalignment of electrodes. Also, among the wrinkles generated during processing, for suppressing the generation of wrinkles in the process of applying heat during processing, the dimensional stability in the processing temperature range is important. For example, during MLCC manufacturing, processing steps involving heating are passed through, such as release layer coating, dielectric sheet formation, and internal electrode printing. Examples are shown where heating is performed at 90°C to 140°C during release layer coating, 50°C to 100°C during dielectric sheet formation, and 40°C to 120°C during internal electrode printing. Therefore, improving the dimensional stability of polyester films at temperatures above the glass transition temperature and below 140°C is effective in suppressing the above problems.

[0007] Many polyester films with high dimensional stability defined by the heat shrinkage rate at 150°C or 190°C as in Patent Documents 1 to 3 have been disclosed so far. However, in order to suppress fineness and the like in the MLCC manufacturing process, it is necessary to highly control the dimensional stability, particularly in the width direction, in the temperature range of 140°C or lower.

[0008] An object of the present invention is to provide a polyester film capable of suppressing the generation of wrinkles and processing misalignment when passing through a processing step involving heating at 70°C to 140°C.

Means for Solving the Problems

[0009] As a result of intensive studies in view of the above circumstances, the present inventors have found that a polyester film capable of solving the above problems can be obtained by adopting the following configuration, and thus have arrived at the present invention.

[0010] That is, a preferred embodiment of the present invention has the following configuration. (1) A polyester film having a dimensional change rate in the width direction of 0.00% or more and 0.20% or less at 70°C to 140°C with respect to the dimension at 30°C. (2) The polyester film according to (1), wherein the dimensional change rate in the longitudinal direction of the polyester film at 70°C to 140°C with respect to the dimension at 30°C is -0.10% or more and 0.30% or less. (3) The polyester film according to (1) or (2), wherein the F5 value of the polyester film in the longitudinal direction at 100°C is 48 MPa or more and 80 MPa or less. (4) The polyester film according to any one of (1) to (3), wherein the thickness of the polyester film is 15 μm or more and 500 μm or less. (5) The polyester film according to any one of (1) to (4), having a release layer on one side thereof.

Advantages of the Invention

[0011] According to the present invention, it is possible to obtain a polyester film capable of suppressing the occurrence of wrinkles and processing deviation during a processing step involving heating at 70°C to 140°C.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in more detail.

[0013] The present invention relates to a polyester film having a dimensional change rate in the width direction of 0.00% or more and 0.20% or less at 70°C to 140°C with respect to the dimension at 30°C.

[0014] The polyester in the polyester film of the present invention is a polyester composed of dibasic acids and glycols. As aromatic dibasic acids, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenyletherdicarboxylic acid, diphenylketonedicarboxylic acid, phenylindanedicarboxylic acid, sodium sulfoisophthalic acid, dibromoterephthalic acid, etc. can be used. As alicyclic dibasic acids, oxalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, etc. can be used. As glycols, as aliphatic diols, ethylene glycol, propylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, diethylene glycol, etc. can be used. As aromatic diols, naphthalenediol, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis[4(2-hydroxyethoxy)phenyl]propane, bis(4-hydroxyphenyl)sulfone, hydroquinone, etc. can be used. As alicyclic diols, cyclohexanedimethanol, cyclohexanediol, etc. can be used.

[0015] The above polyester can be produced by a known method, and it is preferable to use those having an intrinsic viscosity with a lower limit of 0.50 and an upper limit of 0.80. More preferably, the lower limit is 0.55 and the upper limit is 0.75. The measurement of the intrinsic viscosity uses the value calculated by the following formula from the solution viscosity measured at 25°C in orthochlorophenol. ηsp / C = [η] + K[η] 2 ·C Here, ηsp = (solution viscosity / solvent viscosity) - 1, C is the weight of the dissolved polymer per 100 ml of the solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (assumed to be 0.343). Also, the solution viscosity and the solvent viscosity are measured using an Ostwald viscometer. The unit is shown in [dl / g].

[0016] The polyester film of the present invention may have a single-layer structure or a laminated structure of two or more layers. In the case of a two-layer structure, it is an A-layer / B-layer laminated structure composed of a polyester A layer and a polyester B layer. In the case of a three-layer structure, it is an A-layer / B-layer / A-layer composed of a polyester A layer and a polyester B layer, or an A-layer / B-layer / C-layer laminated structure using a polyester C layer in addition to the polyester A layer and the polyester B layer. It is also possible to have a structure of four or more layers as needed. By forming irregularities on the surface of the polyester film, lubricity during the film-forming process and processing process of the polyester film can be imparted. As a method of forming irregularities on the surface of the polyester film, it is possible by incorporating particles in the layer constituting the outermost layer, or in the case of a laminated structure of three or more layers, by making the outermost layer particle-free and incorporating particles in the intermediate layer. As the particles to be incorporated, either organic particles, inorganic particles, or both can be used. As the organic particles, crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, and crosslinked polyester particles are preferable. Among the inorganic particles, spherical silica, aluminum oxide, and calcium carbonate are preferable. Regarding the shape and particle size distribution of the particles, those that are uniform are preferable, and particularly, those with a particle shape close to spherical are preferable. The volume shape coefficient is preferably f = 0.3 to π / 6, and more preferably f = 0.4 to π / 6. The volume shape coefficient f is represented by the following formula. f = V / Dm 3 Here, V is the particle volume (μm 3 ), and Dm is the maximum diameter (μm) on the projected surface of the particle. Note that the volume shape coefficient f takes the maximum value of π / 6 (=0.52) when the particle is a sphere. Also, it is preferable to remove aggregated particles and coarse particles by performing filtration or the like as needed.

[0017] The width direction of the polyester film of the present invention refers to the direction perpendicular to the flow of the polyester film during the film-forming process of the polyester film, and the longitudinal direction of the polyester film refers to the direction perpendicular to the width direction.

[0018] The dimensional change rate in the present invention is measured by a thermal expansion and contraction measuring device. The detailed measuring method will be described later. Incidentally, the dimensional change rate takes a positive value when the polyester film expands and a negative value when it contracts.

[0019] The polyester film of the present invention is required to have a dimensional change rate in the width direction with respect to the dimension at 30°C in the range of 0.00% or more and 0.20% or less from 70°C to 140°C. When the polyester film of the present invention is processed through a heating process using it as a base material, generally, no tension is applied in the width direction of the polyester film in the processing process. Therefore, by setting the dimensional change rate in the width direction from 70°C to 140°C with respect to the dimension at 30°C within the above range, the dimensional stability is improved. On the other hand, when the dimensional change rate in the width direction with respect to the dimension at 30°C is less than 0.00% or greater than 0.20% from 70°C to 140°C, shrinkage or elongation in the width direction of the film occurs in the heating process during processing, and wrinkles in the longitudinal direction of the film are likely to occur.

[0020] For example, when the polyester film of the present invention is used as a release film base material for applications where particularly high thickness uniformity is required, such as the dielectric sheet of an MLCC, the thickness unevenness of the dielectric sheet due to fine wrinkles of the release film generated in the heating process also causes capacitance defects in the MLCC. Therefore, it is important to set the dimensional change rate within the above range. The dimensional change rate shall be determined by the method described in the examples.

[0021] In order to set the dimensional change rate in the width direction with respect to the dimension at 30°C in the range from 70°C to 140°C within the above range, it is possible to adjust the draw ratio, temperature, and heat setting temperature in the width direction to the ranges described later, or to provide an intermediate cooling chamber or a slow cooling chamber after heat setting. Also, by performing a relaxation treatment of about 0.5% to 7% in the width direction of the polyester film in the aforementioned intermediate cooling chamber or slow cooling chamber, the dimensional change rate can be set within the above range. In particular, the relaxation treatment when the temperature of the polyester film is from 70°C to 140°C is effective. A more preferable range of the dimensional change rate in the width direction with respect to the dimension at 30°C in the range from 70°C to 140°C is 0.03% or more and 0.17% or less, and an even more preferable range is 0.05% or more and 0.15% or less.

[0022] It is preferable that the dimensional change rate in the longitudinal direction of the polyester film of the present invention at 70°C to 140°C with respect to the dimension at 30°C is -0.10% or more and 0.30% or less. By setting the dimensional change rate in the longitudinal direction at 70°C to 140°C with respect to the dimension at 30°C within the above range, the dimensional stability when the polyester film of the present invention is processed through a heating process using it as a base material is improved. Generally, in the processing process, tension is applied in the longitudinal direction of the polyester film. Therefore, by adjusting this tension, it is possible to suppress a certain degree of wrinkles and deformation. However, when the dimensional change rate in the longitudinal direction at 70°C to 140°C with respect to the dimension at 30°C is less than -0.10%, local wrinkles occur because the shrinking stress of the polyester film exceeds the processing tension, and when the dimensional change rate in the longitudinal direction at 70°C to 140°C is greater than 0.30%, problems such as the occurrence of wrinkles and slack due to the expansion of the polyester film are likely to occur.

[0023] To set the dimensional change rate in the longitudinal direction at 70°C to 140°C with respect to the dimension at 30°C within the above range, it is possible by adjusting the longitudinal draw ratio, temperature, and heat setting temperature to the ranges described later, or by providing an intermediate cooling chamber or a slow cooling chamber after heat setting. Also, by performing a relaxation treatment of about 0.5% to 7% in the longitudinal direction of the polyester film in the aforementioned intermediate cooling chamber or slow cooling chamber, or by adjusting the tension applied in the longitudinal direction during the formation of the polyester film, the dimensional change rate can be set within the above range. When controlling the relaxation treatment and tension, it is particularly effective to perform it when the temperature of the polyester film is 70°C to 140°C. A more preferable range of the dimensional change rate in the longitudinal direction at 70°C to 140°C with respect to the dimension at 30°C is -0.10% or more and 0.20% or less, and an even more preferable range is -0.10% or more and 0.15% or less. Note that the dimensional change rate shall be determined by the method described in the examples.

[0024] The F5 value of the polyester film of the present invention at 100 °C in the longitudinal direction is preferably 48 MPa or more and 80 MPa or less. The F5 value is the stress when the polyester film is stretched by 5% in the tensile test described below. By setting the F5 value at 100 °C in the longitudinal direction within the above range, the dimensional stability of the polyester film of the present invention during processing through a heating step using the polyester film as a base material is improved. When the F5 value at 100 °C in the longitudinal direction is less than 48 MPa, the polyester film is stretched in the longitudinal direction due to the processing tension, and wrinkles and slack in the longitudinal direction of the film are likely to occur. The upper limit of the F5 value at 100 °C in the longitudinal direction is not particularly limited, but 80 MPa is the upper limit from the general manufacturing method of polyester films.

[0025] To set the F5 value at 100 °C in the longitudinal direction within the above range, it is possible by adjusting the draw ratio, temperature, and heat setting temperature in the longitudinal direction to the ranges described below. A more preferable range of the F5 value at 100 °C in the longitudinal direction is 50 MPa or more and 80 MPa or less.

[0026] The polyester film of the present invention preferably has a thickness of 15 μm or more and 500 μm or less. When the thickness is less than 15 μm, the film is too thin, and the film-forming stability may become unstable, or the polyester film may break during the processing step or when used for release applications. On the other hand, when it exceeds 500 μm, when collecting a film roll of the same width and the same weight, the winding length becomes short, the productivity of the processing step deteriorates, and when used for release, since the polyester film of the present invention is discarded after use, it is not preferable from the viewpoint of waste reduction. The thickness of the polyester film is more preferably 15 μm or more and 100 μm or less, and even more preferably 15 μm or more and 50 μm or less.

[0027] Next, the manufacturing method of the polyester film of the present invention will be described using polyethylene terephthalate among polyesters.

[0028] As described above, the polyethylene terephthalate that constitutes the main component of the polyester film of the present invention can contain particles. As a method thereof, for example, particles are dispersed as a slurry in ethylene glycol, which is a diol component, at a predetermined ratio, and this ethylene glycol slurry is added at an arbitrary stage before the completion of polyester polymerization. Here, when adding the particles, for example, it is preferable to add the particles without drying the hydrosol or alcohol sol obtained during synthesis, so that the dispersibility of the particles is improved and the generation of coarse protrusions can be suppressed. Also, a method of directly mixing an aqueous slurry of the particles with a predetermined polyester pellet, feeding it to a vent-type twin-screw kneading extruder, and kneading it into the polyester is also effective.

[0029] The particle-containing masterbatch thus produced is mixed with a particle-free pellet that substantially does not contain particles or the like at a predetermined ratio, dried, and then fed to a known extrusion machine for melt lamination. As the extruder in the production of the polyester film of the present invention, a single-screw or twin-screw extruder can be used. In order to omit the pellet drying step, a vent-type extruder provided with a vacuum drawing line can also be used. Also, for the layer with the largest extrusion amount, a so-called tandem extruder can be used, in which the function of melting the pellet and the function of maintaining the melted pellet at a constant temperature are shared by each extruder.

[0030] The polymer melted and extruded by the extruder is filtered by a filter. Since even a very small foreign object entering the film will result in a coarse protrusion defect, it is effective to use a high-precision filter that can collect 95% or more of foreign objects of, for example, 3 μm or larger. Subsequently, it is extruded into a sheet shape from a slit-shaped die and cooled and solidified on a casting roll to produce an unstretched film. That is, in the case of a single-layer polyester film, the molten polymer extruded from one extruder, in the case of a two-layer polyester film, the molten polymer laminated in two layers using two extruders and a two-layer manifold or a merging block (for example, a merging block having a rectangular merging section), and in the case of a polyester film with a three-layer structure of different types, the molten polymer laminated in three layers using three extruders and a three-layer manifold or a merging block are each extruded from the die into a sheet shape and cooled by a casting roll to produce an unstretched film. Also, from the viewpoints of stabilizing the back pressure and suppressing thickness fluctuations, it is preferable to install a static mixer and a gear pump in the polymer flow path.

[0031] The stretching method may be sequential biaxial stretching or simultaneous biaxial stretching. Since simultaneous biaxial stretching does not involve stretching by rolls, it suppresses local heating spots on the surface of the polyester film, and uniform quality can be obtained. Also, it is preferable in that it can suppress the speed difference at the contact location between the polyester film and the roll associated with roll stretching during stretching and the occurrence of scratches due to the transfer of minute scratches on the roll. Sequential biaxial stretching is preferable in that the characteristics in the longitudinal direction and the width direction can be individually and finely controlled.

[0032] Hereinafter, the stretching method will be described by taking sequential biaxial stretching as an example. The unstretched film obtained as described above is first stretched in the longitudinal direction at a stretching temperature of 1°C or more and 60°C or less above the glass transition temperature of the polyester resin, preferably 1°C or more and 50°C or less above the glass transition temperature, in the longitudinal direction by 2.5 times or more and 5.0 times or less. When the stretching temperature is lower than 1°C above the glass transition temperature, the polyester film is likely to break, and when the stretching temperature is higher than 60°C above the glass transition temperature, sufficient strength tends not to be obtained. The stretching temperature in the width direction is 20°C or more and 80°C or less above the glass transition temperature, preferably 20°C or more and 65°C or less above the glass transition temperature. The stretching ratio in the width direction is preferably 2.5 times or more and 5.0 times or less. Also, the area stretching ratio in the longitudinal and width directions (the product of the stretching ratio in the longitudinal direction and the stretching ratio in the width direction) is preferably 9 times or more and 25 times or less, more preferably 12 times or more and 25 times or less. By setting it within such a range, a polyester film can be stably produced while maintaining sufficient strength. After stretching in the longitudinal and width directions, heat setting is performed at 130°C or more and 170°C or less above the glass transition temperature, preferably 140°C or more and 170°C or less above the glass transition temperature, for 0.5 seconds or more and 20 seconds or less, preferably 1.0 seconds or more and 15 seconds or less. When the heat setting temperature is lower than 130°C above the glass transition temperature, the thermal crystallization of the polyester film does not proceed, so the dimensional change rate and the like tend to be unstable. Also, a temperature difference of 20°C or less, preferably 10°C or less, more preferably 5°C or less between the upper and lower surfaces of the polyester film is preferable in terms of stabilizing the physical properties of the polyester film. When the temperature difference between the upper and lower surfaces of the polyester film is larger than 20°C, it tends to easily cause a slight deterioration in flatness during heat setting. Thereafter, a relaxation treatment of 0.5% or more and 7.0% or less is performed in the longitudinal direction and / or the width direction. Taking polyethylene terephthalate as a specific example, since the glass transition temperature of polyethylene terephthalate is generally 70°C, the stretching temperature in the longitudinal direction is 71°C or more and 130°C or less, the stretching temperature in the width direction is 90°C or more and 150°C or less, and the heat setting temperature is 200°C or more and 240°C or less.Even when stretching is performed step by step, the conditions within the same range are sufficient. Examples of such methods include stretching in the longitudinal direction first, then in the width direction, then again in the longitudinal direction, and if necessary, again in the width direction; or stretching in the longitudinal direction first, then again in the longitudinal direction, and then in the width direction.

[0033] In sequential biaxial stretching, in the stretching process in the longitudinal direction, since the polyester film comes into contact with the roll and scratches are likely to occur due to the speed difference between the peripheral speed of the roll and the speed of the polyester film, a drive method in which the peripheral speed of the roll can be individually set for each roll is preferred. In the stretching process in the longitudinal direction, the material of the conveying roll is selected according to whether the unstretched film is heated above the glass transition temperature before stretching or conveyed to the stretching zone while maintaining a temperature below the glass transition temperature and then heated all at once during stretching. When the unstretched film is heated above the glass transition temperature before stretching, in order to prevent adhesion due to heating, it can be selected from non-sticky silicone rolls, ceramics, and Teflon (registered trademark). Also, for the stretching roll, which is the process where the most load is applied to the film and scratches and stretching marks are likely to occur in this process, the arithmetic mean roughness Ra of the stretching roll is preferably 0.005 μm or more and 1.0 μm or less, and more preferably 0.1 μm or more and 0.6 μm or less. If Ra is greater than 1.0 μm, the unevenness on the roll surface during stretching is transferred to the film surface, which is not preferable. If it is less than 0.005 μm, the roll and the polyester film base adhere, and the polyester film tends to be easily damaged by heat. In order to control the surface roughness, it is effective to appropriately adjust the particle size of the abrasive, the number of polishing times, etc. When the unstretched film is conveyed to the stretching zone while maintaining a temperature below the glass transition temperature and then heated all at once during stretching, the conveying roll in the preheating zone is preferably a metal roll made of hard chromium or tungsten carbide with a surface-treated Ra of 0.2 μm or more and 0.6 μm or less.

[0034] After heat setting, the polyester film can be provided with, for example, an intermediate cooling zone or a slow cooling zone to adjust the dimensional change rate and flatness. In particular, in order to make the dimensional change rate in the width direction with respect to the dimension at 30°C in the range of 0.0% or more and 0.2% or less in the temperature range of 70°C to 140°C, a shielding plate with an angle changing mechanism is provided vertically in the intermediate cooling chamber or the slow cooling chamber so that the high temperature in the heat setting zone does not leak and does not flow back, and it is also effective to relax in the longitudinal direction and / or the transverse direction in the temperature range of 70°C to 140°C. In the case of sequential biaxial stretching and simultaneous biaxial stretching, since both ends in the width direction of the polyester film are gripped by clips or the like in the tenter, the dimensional change rate in the width direction of the polyester film can be adjusted by controlling the distance between the two clips. On the other hand, after the clip is released at the tenter exit, no tension is applied in the width direction of the polyester film, so the dimensional change rate is affected by the natural shrinkage of the polyester film. In order to control the dimensional change rate in the width direction in the temperature range after the clip is released, it is effective to adjust the temperature of the polyester film at the time of clip release.

[0035] After the biaxially stretched polyester film is cooled in the conveying process, the edges are cut and then wound up to obtain the polyester film of the present invention. By adjusting the roll rotation speed in the conveying process, since the longitudinal tension applied to the polyester film after clip release at the tenter exit changes, when the temperature of the polyester film at the time of clip release is 70 °C or higher, the above adjustment is effective for controlling the longitudinal dimensional change rate. Further, in this conveying process, the thickness of the polyester film can be measured, and the data can be fed back to adjust the thickness of the polyester film by adjusting the die thickness or the like, or foreign matter detection can be performed by a defect detector. When cutting the edge, it is preferable to suppress the generation of cutting dust. The edge can be cut using any of a round blade, a shear blade, and a straight blade. However, when using a straight blade, it is preferable not to always make the portion of the blade hitting the polyester film the same because it can suppress the wear of the blade. Further, the blade preferably has a mechanism for oscillation. In addition, it is also effective to provide a suction device at the cutting portion of the polyester film to suck the generated cutting dust and the shaving dust generated by the abrasion of the ends of the polyester film after cutting.

[0036] Further, it is also possible to slit the obtained polyester film of the present invention to an appropriate width and length and wind it up as the polyester film of the present invention.

[0037] Since the occurrence of wrinkles is suppressed when the polyester film of the present invention is processed including a heating process, it can be suitably used as a polyester film for a processing step substrate involving heating at 70 °C to 140 °C, and particularly as a polyester film for a roll-to-roll processing step substrate involving heating at 70 °C to 140 °C. For example, when used as a release film, a uniform release object with suppressed unevenness can be obtained. In particular, when used as a release film for forming a dielectric sheet in the manufacturing process of a multilayer ceramic capacitor, a uniform dielectric sheet without thickness defects or printing misalignment of internal electrodes can be obtained, and the yield of multilayer ceramic capacitor manufacturing can be improved.

Example

[0038] Next, the present invention will be described in more detail with reference to examples, but the present invention should not be construed as being limited to such examples.

[0039] [Method for Evaluating Characteristics] (1) Dimensional change rate in the width direction and longitudinal direction of the polyester film A 40 mm × 5 mm rectangular sample with the longitudinal direction as the measurement direction was cut out from the polyester film, and the expansion and contraction of the film were measured under the following conditions using a thermal expansion and contraction measuring device (TM9300) manufactured by Ikeda Rika Co., Ltd. Heating rate: 10 °C / min Measurement range: 30 to 190 °C Measurement atmosphere: Nitrogen Load: 1 g (when measuring the width direction), 50 g (when measuring the longitudinal direction) Distance between chucks: 20.00 mm Measurement interval: 1 second Assuming the film length at 30 °C is L(30) mm and the film length at temperature T °C is L(T) mm, the dimensional change rate (%) at temperature T °C was determined from the following formula.

[0040] Dimensional change rate (%) = (L(T) - L(30)) ÷ L(30) × 100.

[0041] (2) F5 value at 100 °C in the longitudinal direction of the polyester film A 150 mm × 10 mm rectangular sample was cut out from the polyester film in the longitudinal direction, and a tensile test was conducted under the following conditions using a tensile testing machine (Tensilon UCT - 100 manufactured by Orientec). Tensile speed: 300 mm / min Initial distance between chucks: 50 mm The film sample was set in a thermostatic layer pre-set at 100 °C, and after preheating for 90 seconds, a tensile test was conducted. The load applied to the film when the sample was stretched by 5% (when the distance between the chucks became 52.5 mm) was read, and the value obtained by dividing it by the cross-sectional area of the sample before the test (film thickness × 10 mm) was defined as the stress at 5% elongation (F5). The measurement was performed 5 times for each sample, and the evaluation was carried out using the average value.

[0042] (3) Thickness of the polyester film Using a digital micrometer (μ-mate) manufactured by Sony Corporation, the thicknesses at 10 equally spaced locations in the width direction of a sample with 5 polyester films stacked were measured. The average value was divided by 5 to obtain the thickness per polyester film.

[0043] (4) Evaluation of wrinkles (after the film forming process (room temperature), after the release layer lamination (120 °C, 20 seconds)) Using the polyester film roll wound up in the film forming process of the polyester film and the polyester film roll obtained by unwinding the polyester film and laminating the release layer by the method described below and then winding it up, the evaluation of wrinkles was carried out according to the following procedure. The film was drawn out from the surface layer of the polyester film roll, and a tension of 5 N / m was applied in the drawing direction and held. A straight tube-shaped LED light of 1500 lux was irradiated from the back of the drawn-out polyester film, and a range of 1 m × 1 m was visually observed, and the number of wrinkles generated in the longitudinal direction of the film was counted by the following method. The LED light is projected onto the polyester film as a white line. This white line is straight when no wrinkles are generated in the polyester film, but has a wavy shape when wrinkles are generated in the polyester film. The locations where the white line fluctuates by 1 mm or more in the direction perpendicular to the straight line where the white line should be (the straight line when no wrinkles are generated) were counted as wrinkles. The measurement was performed 5 times in different fields of view, and the average value was used as the number of wrinkles per 1 m 2 For the film width less than 1 m, the wrinkles in 1 m × the full width of the film were observed, and the number of wrinkles was divided by the film width to convert it to the number of wrinkles per 1 m 2 For the number of wrinkles per width. ◎: The number of wrinkles is 0 pieces / m2 〇: Number of wrinkles is 0 pieces / m 2 More than, 1 piece / m 2 Less than △: Number of wrinkles is 1 piece / m 2 More than, 3 pieces / m 2 Less than ×: Number of wrinkles is 3 pieces / m 2 More than that.

[0044] (5) Evaluation of dimensional stability after dielectric sheet formation (dried at 100 °C) and internal electrode printing (dried at 90 °C) Alignment marks were made at intervals of 100 mm in the longitudinal direction at positions 5 mm from both ends of the film on the release film after the release layer was laminated. Before applying the ceramic slurry, the distance (L0) between each alignment mark in the width direction and the longitudinal direction was measured, and after the dielectric sheet formation and internal electrode printing, the distance (L1) between the alignment marks was measured again. The distance at 100 locations in each of the longitudinal direction and the width direction was measured, and the coefficient of variation (CV) obtained by dividing the standard deviation of the difference in alignment marks (L1 - L0) due to processing by the average of L1 was calculated. ◎: Coefficient of variation is 0.0005 or less 〇: Coefficient of variation is greater than 0.0005 and 0.0007 or less △: Coefficient of variation is greater than 0.0007 and 0.001 or less ×: Coefficient of variation is greater than 0.001.

[0045] [Example 1] (1) Preparation of polyester pellets (Preparation of polyester pellet A) 86.5 parts by mass of terephthalic acid and 37.1 parts by mass of ethylene glycol are subjected to an esterification reaction at 255 °C while distilling off water. After completion of the esterification reaction, 0.02 parts by mass of trimethyl phosphate, 0.06 parts by mass of magnesium acetate, 0.01 parts by mass of lithium acetate, and 0.0085 parts by mass of antimony trioxide are added, and then heated to 290 °C under reduced pressure and the temperature is raised to carry out a polycondensation reaction to obtain polyester pellet A having an intrinsic viscosity of 0.63 dl / g.

[0046] (Preparation of polyester pellet B) A water slurry of divinylbenzene / styrene copolymer crosslinked particles (crosslinking degree 80%) with a volume average particle diameter of 0.8 μm and a volume shape factor f = 0.51, consisting of 80% by mass of divinylbenzene, 15% by mass of ethylvinylbenzene, and 5% by mass of styrene by the seed method, was incorporated into the above-mentioned substantially particle-free homopolyester pellets using a vented twin-screw kneader to obtain polyester pellets B containing 2.0% by mass of divinylbenzene / styrene copolymer crosslinked particles with a volume average particle diameter of 0.8 μm based on the polyester.

[0047] (2) Preparation of polyester pellets The polyester pellets supplied to each layer of the extruder are prepared in the following ratios. The ratios described below are mass ratios (unit: mass%) with respect to the total polyester resin constituting each layer. Layer A Polyester pellets A: 92.5 Polyester pellets B: 7.5 Layer B Polyester pellets A: 100.0.

[0048] (3) Production of polyester film The raw materials prepared for each of the above layers were mixed and dried under reduced pressure at 160 °C for 8 hours. Then, the raw materials for layer A were supplied to extruder 1, and the raw materials for layer B were supplied to extruder 2. In extruders 1 and 2, the polyester pellets were melted at 275 °C, and the extruded molten polymer was filtered with high precision through a filter. The molten polymer extruded from extruder 1 was separated into two streams after high-precision filtration and laminated into an A / B / A three-layer structure using a rectangular three-layer confluence block so that layer A was laminated on both sides of layer B. At this time, the amounts of the molten polymer discharged from extruders 1 and 2 were adjusted so that the thickness of layer A in the final film was 2 μm and that of layer B was 26 μm. Then, it was wound around a casting drum with a surface temperature of 25 °C using the electrostatic application casting method through a slit die maintained at 295 °C and cooled and solidified to obtain an unstretched film.

[0049] This unstretched film was stretched 3.5 times in the longitudinal direction at 80 °C using a roll stretching machine that stretches the film using the peripheral speed difference between two sets of rolls. While gripping both ends of the obtained uniaxially stretched film with clips, it was led into a preheating zone at 90 °C in a tenter and then continuously stretched 4.0 times in the width direction perpendicular to the longitudinal direction in a heating zone at 110 °C. The obtained biaxially stretched film was heat-set at 225 °C for 4 seconds, and further relaxation treatment was performed in the width direction by 4.0% in the section where it was cooled from 200 °C to 130 °C. Then, when the film temperature reached 105 °C, it was released from the clips. At this time, the air volume of the supply and exhaust air was adjusted and a shielding plate was installed so that the temperature unevenness in the width direction of the tenter was 2% or less in the stretching and heat-setting processes and 5% or less in the cooling process, and the gases in spaces with different temperatures did not mix. Also, the peripheral speed of the first roll in the conveying process after the tenter was adjusted to be 0.999 times the film conveying speed. Then, the edges of the polyester film were removed, wound around a core, and a polyester film with an overall thickness of 30 μm was obtained. Further, the obtained polyester film was slit to obtain a polyester film roll with a width of 1100 mm. Regarding the polyester film obtained by slitting, the above-mentioned wrinkle evaluation was carried out. The evaluation results are shown in the table.

[0050] (4) Coating of the release layer Next, a coating solution of a crosslinking primer layer (trade name BY24-846 manufactured by Toray Dow Corning Silicone Co., Ltd.) adjusted to a solid content of 1% by mass was applied to the obtained polyester film roll using a gravure coater so that the coating thickness after drying was 0.1 μm, and it was dried and cured at 100 °C for 20 seconds. Then, within 1 hour, a coating solution of 100 parts by mass of an addition reaction type silicone resin (trade name LTC750A manufactured by Toray Dow Corning Silicone Co., Ltd.) and 2 parts by mass of a platinum catalyst (trade name SRX212 manufactured by Toray Dow Corning Silicone Co., Ltd.) adjusted to a solid content of 5% by mass was applied by gravure coating so that the coating thickness after drying was 0.1 μm, dried and cured at 120 °C for 30 seconds, and then wound up to obtain a release film. Regarding the obtained release film, the above-mentioned wrinkle evaluation was carried out. The evaluation results are shown in the table. Further, the release film after the wrinkle evaluation was slit to obtain a release film with a width of 150 mm.

[0051] (5) Coating of the dielectric sheet To 100 parts by mass of barium titanate (trade name HPBT-1 manufactured by Fuji Titanium Industry Co., Ltd.), 10 parts by mass of polyvinyl butyral (trade 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), glass beads with a number average particle diameter of 2 mm were added, and after mixing and dispersing for 20 hours with a jet mill, filtration was performed to adjust a paste-like ceramic slurry. The obtained ceramic slurry was applied onto a release film with a dry thickness of 0.8 μm using a die coater and dried at 100 °C to obtain a wound dielectric sheet.

[0052] (6) Printing of the internal electrodes 44.6 parts by mass of Ni particles, 52 parts by mass of terpineol, 3 parts by mass of ethyl cellulose, and 0.4 parts by mass of benzotriazole were kneaded and slurried to obtain a paint for the internal electrode layer. The paint for the internal electrode layer was applied onto the dielectric sheet in a predetermined pattern by the screen printing method, dried at 90 °C for 5 minutes, and a dielectric sheet having an internal electrode pattern was obtained. Regarding the obtained dielectric sheet, the evaluation of the dimensional stability after the formation of the dielectric sheet and the printing of the internal electrodes described above was carried out. The evaluation results are shown in the table.

[0053] [Example 2] In the production of the polyester film, the longitudinal stretching temperature was 120 °C, the heat setting temperature was 230 °C, the heat setting time was 3.5 seconds, the relaxation treatment in the width direction was 3.0%, and the peripheral speed of the first roll in the conveying process after the tenter was 1.000 times the film conveying speed. Otherwise, it was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0054] [Example 3] In the production of the polyester film, the heat setting temperature was 235 °C, the relaxation treatment in the width direction was 6.0%, the film temperature at the time of clip release was 110 °C, and the peripheral speed of the first roll in the conveying process after the tenter was 1.001 times the film conveying speed. Otherwise, it was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0055] [Example 4] In the production of the polyester film, the longitudinal stretching ratio was 4.0 times, the transverse stretching temperature was 120 °C, the transverse stretching ratio was 5.0 times, the heat setting temperature was 215 °C, the relaxation treatment in the width direction was 3.0%, the film temperature at the time of clip release was 101 °C, and the peripheral speed of the first roll in the conveying process after the tenter was 1.002 times the film conveying speed. Otherwise, it was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0056] [Example 5] In the production of the polyester film, the longitudinal stretching temperature was 85 °C, the longitudinal stretching ratio was 2.8 times, the transverse stretching temperature was 130 °C, the transverse stretching ratio was 4.5 times, the heat setting temperature was 240 °C, the heat setting time was 6 seconds, the relaxation treatment in the width direction was 6.0%, the film temperature at the time of clip release was 101 °C, and the peripheral speed of the first roll in the conveying process after the tenter was 1.003 times the film conveying speed. Otherwise, it was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0057] [Example 6] In the production of the polyester film, the longitudinal stretching ratio was 3.1 times, the transverse stretching temperature was 95 °C, the heat setting temperature was 235 °C, the relaxation treatment in the width direction was 5.0%, the film temperature at the time of clip release was 108 °C, and the peripheral speed of the first roll in the conveying process after the tenter was 0.995 times the film conveying speed. Otherwise, it was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0058] [Example 7] In the production of the polyester film, the longitudinal stretching temperature was 75 °C, the longitudinal stretching ratio was 5.0 times, the transverse stretching temperature was 100 °C, the heat setting temperature was 210 °C, the heat setting time was 3 seconds, the film temperature at the time of clip release was 102 °C, and the peripheral speed of the first roll in the conveying process after the tenter was 0.997 times the film conveying speed. Otherwise, it was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0059] [Example 8] In the production of the polyester film, the longitudinal stretching temperature was 84°C, the longitudinal stretching ratio was 4.5 times, the transverse stretching ratio was 3.5 times, the heat setting temperature was 220°C, the relaxation treatment in the width direction was 5.0%, the film temperature at the time of clip release was 106°C, and the peripheral speed of the first roll in the conveying process after the tenter was 1.004 times the film conveying speed. The rest was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0060] [Example 9] In the production of the polyester film, the amount of the molten polymer discharged from Extruders 1 and 2 was adjusted so that the thickness of the A layer of the final film was 1.5 μm and that of the B layer was 15 μm, and the heat setting time was 3 seconds. The rest was carried out in the same manner as in Example 1, and a polyester film with an overall thickness of 18 μm was obtained. The results of each evaluation are shown in the table.

[0061] [Example 10] In the production of the polyester film, the amount of the molten polymer discharged from Extruders 1 and 2 was adjusted so that the thickness of the A layer of the final film was 3.0 μm and that of the B layer was 94 μm, and the heat setting time was 12 seconds. The rest was carried out in the same manner as in Example 1, and a polyester film with an overall thickness of 100 μm was obtained. The results of each evaluation are shown in the table.

[0062] [Comparative Example 1] In the production of the polyester film, the heat setting temperature was 245°C, the relaxation treatment in the width direction was 8.0%, the film temperature at the time of clip release was 116°C, and the peripheral speed of the first roll in the conveying process after the tenter was 1.003 times the film conveying speed. The rest was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0063] [Comparative Example 2] In the production of the polyester film, the longitudinal stretching ratio was 4.5 times, the transverse stretching ratio was 4.5 times, the heat setting temperature was 230°C, the relaxation treatment in the width direction was 8.0%, the film temperature at the time of clip release was 114°C, and the peripheral speed of the first roll in the conveying process after the tenter was 0.996 times the film conveying speed. The rest was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0064] [Comparative Example 3] In the production of a polyester film, the longitudinal stretching temperature is 79 °C, the transverse stretching temperature is 115 °C, the heat setting temperature is 245 °C, the relaxation treatment in the width direction is 0.1%, the film temperature at the time of clip release is 95 °C, and the peripheral speed of the first roll in the conveying process after the tenter is 1.000 times the film conveying speed, and the rest was carried out in the same manner as in Example 1. The results of each evaluation are shown in the table.

[0065]

Table 1

[0066]

Table 2

Industrial Applicability

[0067] Since the polyester film of the present invention suppresses the occurrence of wrinkles and processing deviation during processing including a heating step, it can be suitably used as a polyester film for a processing step base material involving heating at 70 °C to 140 °C, and particularly as a polyester film for a roll-to-roll processing step base material involving heating at 70 °C to 140 °C. For example, when used as a release film, a uniform release object with suppressed unevenness can be obtained. In particular, by using it as a release film for forming a dielectric sheet in the manufacturing process of a multilayer ceramic capacitor, a uniform dielectric sheet without thickness defects and printing deviation of internal electrodes can be obtained, and the yield of multilayer ceramic capacitor manufacturing can be improved.

Claims

Claim 1 A polyester film having a dimensional change rate in the width direction of 0.00% or more and 0.20% or less at 70°C to 140°C with respect to the dimension at 30°C. Claim 2 The polyester film according to claim 1, wherein the dimensional change rate in the longitudinal direction of the polyester film at 70°C to 140°C with respect to the dimension at 30°C is -0.10% or more and 0.30% or less. Claim 3 The polyester film according to claim 1, wherein the F5 value at 100°C in the longitudinal direction of the polyester film is 48 MPa or more and 80 MPa or less. Claim 4 The polyester film according to claim 1, wherein the thickness of the polyester film is 15 μm or more and 500 μm or less. Claim 5 The polyester film according to claim 1, having a release layer on one side thereof.

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