JP5298564B2 - Biaxially oriented polyester film and metallized polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film and a metal vapor deposited polyester film, which have a cupping, especially a cupping required as a support for magnetic recording medium. <P>SOLUTION: The biaxially oriented polyester film has a layer composition of two or more layers and is characterized in that; both WA and WB are 0-5 wt.% and WB-WA is 0.1-3.0 wt.%, wherein WA represents content of a heat-resistant thermoplastic resin contained in a portion from center in thickness direction to the side of one surface A, and WB represents content of the heat-resistant thermoplastic resin contained in a portion B from center in thickness direction to the side of the other surface B. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention is useful when used as a magnetic recording material, electronic material, plate-making film, sublimation ribbon, packaging material, metal vapor deposition, and particularly useful as a support for a high-capacity magnetic recording medium. The present invention relates to an oriented polyester film and a metal-deposited polyester film.

  In recent years, magnetic recording media for data storage and digital video tape have been increasing in density and capacity. For example, linear recording magnetic recording media such as LTO (Linear Tape Open) and SDLT (Super Digital Linear Tape) have been developed that have a high capacity of 500 GB or more per volume.

  To increase the capacity, many studies have been made so far, such as increasing the strength of the base film by increasing the draw ratio, optimizing the temperature expansion coefficient and humidity expansion coefficient in the tape width direction, and reducing the diameter of the additive particles. However, even if these techniques are used, sufficient characteristics cannot be obtained for a magnetic recording medium having a high capacity of 500 GB or more per roll.

In these magnetic recording media, the surface of the magnetic recording is controlled by heat-treating the film (Patent Document 1) or controlling the components of the magnetic layer and the back-back coat layer (Patent Document 2) so that the surface of the medium can easily hit the head. It is generally performed to control the convexity. However, when heat-treating the film, the number of steps increases, so the yield may decrease due to wrinkles and the like, and when controlling the constituent components, there is a problem that cupping changes depending on the thickness of the constituent components.
JP 2001-325723 A JP 2005-259287 A

  An object of the present invention is to provide a biaxially oriented polyester film and a metal-deposited polyester film having cupping, particularly cupping necessary as a support for a magnetic recording medium.

The present invention for achieving the above object has a layer structure of two or more layers, and the content of the heat-resistant thermoplastic resin contained in a portion from the center in the thickness direction to one surface A side is defined as WA. When the content of the heat-resistant thermoplastic resin contained in the portion from the center in the direction to the other surface B side is WB, both WA and WB are 0 to 5 wt%, and the value of WB-WA is 0 .1～1.1Wt% der is, wherein the heat-resistant thermoplastic resin is a biaxially oriented polyester film that has a higher Tg than the glass transition temperature (Tg) of the polyester used.

  According to the present invention, it is possible to provide a biaxially oriented polyester film and a metal-deposited polyester film having cupping, particularly cupping necessary as a support for a magnetic recording medium.

  The biaxially oriented polyester film of the present invention has a layer structure including at least two layers containing polyester. Further, in the thickness direction of the film, the content of the heat-resistant thermoplastic resin contained in the portion from the center (center position) to the one surface A side is WA, and the other surface B (surface A When the content of the heat-resistant thermoplastic resin contained in the portion up to the opposite surface) is WB, both WA and WB are 0 to 5 wt%, and WB-WA is 0.1 to 3. 0 wt%.

  The WA is preferably 0 to 4 wt%, more preferably 0 to 3 wt%. WB is preferably 0.2 to 4.5 wt%, more preferably 0.5 to 4.0 wt%. When WA and WB are larger than 5 wt%, the film forming property tends to be unstable. Moreover, WB-WA is preferably 0.2 to 2.5 wt%, more preferably 0.5 to 2.0 wt%. If WB-WA is less than 0.1 wt%, the effect of cupping is difficult to obtain, and if it exceeds 3.0 wt%, the cupping tends to be too large and the head contact tends to be uneven.

  The polyester that can be used in the present invention is not particularly limited as long as it becomes a high-strength film by molecular orientation, but polyethylene terephthalate or polyethylene-2,6-naphthalate is preferably a constituent. Examples of polyester copolymer components other than ethylene terephthalate include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, and 1,4-cyclohexanedimethanol, adipic acid, sebacic acid, and phthalate. Dicarboxylic components such as acid, isophthalic acid and 5-sodiumsulfoisophthalic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, p-oxyethoxybenzoic acid and the like can be used.

  The heat-resistant thermoplastic resin in the present invention means a thermoplastic resin having a Tg higher than the glass transition temperature (Tg) of the polyester used, and may be a thermoplastic resin having melt moldability and compatibility with the polyester. Can be used. Specifically, for example, polyimide resin (including polyetherimide), polysulfone, polyethersulfone, polyamideimide, polyetheretherketone, and polyarylate are exemplified. Among these, from the viewpoints of affinity with polyester and melt moldability, polyimide resins, particularly polyetherimide, are preferable.

  As described above, the biaxially oriented polyester film of the present invention has a laminated structure of two or more layers. This is indispensable for cupping control, and when used as a support for a magnetic recording medium, smoothness for obtaining excellent electromagnetic conversion characteristics is obtained on one surface, and film formation / This is because it becomes easy to achieve an appropriate roughness for imparting excellent transportability in the processing step.

  When the surface A is used as a support for a magnetic recording medium, the surface on the side where the magnetic layer is provided is preferably used, and the surface B on the opposite side is preferably the surface on the running surface side where the backcoat layer is provided.

  When providing a magnetic layer on the surface A side, the polyester film preferably has a surface roughness SRa of 0.5 to 10 nm. When SRa of surface A is smaller than 0.5 nm, a friction coefficient with a conveyance roll etc. becomes large in film production, a processing process, etc., and may cause a process trouble. When SRa is larger than 10 nm, electromagnetic conversion characteristics may be deteriorated when used as a magnetic tape for high-density recording. When the magnetic layer is provided on the surface A side, the lower limit of SRa is more preferably 1 nm, still more preferably 2 nm, and the upper limit is 9 nm, more preferably 8 nm. A more preferable range is 1 to 9 nm, and a further preferable range is 2 to 8 nm.

  On the other hand, when the back coat layer is provided on the surface B side, the surface roughness SRa is preferably 2 to 30 nm. When SRa on the surface B is smaller than 2 nm, the friction coefficient with the transport roll or the like becomes large, which may cause a process trouble. On the other hand, when SRa is larger than 30 nm, the surface protrusion may be transferred to the opposite surface when stored as a film roll or pancake, and electromagnetic conversion characteristics may deteriorate. When the back coat layer is provided on the surface B side, the lower limit of SRa is more preferably 3 nm, still more preferably 4 nm, and the upper limit is 20 nm, more preferably 15 nm. A more preferable range is 3 to 20 nm, and a further preferable range is 4 to 15 nm.

  In order to make SRa within the above range, it is preferable to add inert particles in the layer. In the present invention, when the inert particles I are used in the layer A constituting the surface A, the average particle diameter dI is preferably Is 0.04 to 0.30 μm, more preferably 0.05 to 0.15 μm, and the content is preferably 0.001 to 0.30 mass%, more preferably 0.01 to 0.25 mass%. is there. In the magnetic recording medium support, use of particles having an average particle size larger than 0.30 μm may deteriorate the electromagnetic conversion characteristics. In general, the smaller the average particle size and the added amount, the smaller the SRa, and the larger the average particle size and the added amount, the larger the SRa.

  When the layer B constituting the surface B contains particles, the particles may be one type or two or more types. When the inert particle II having the largest particle diameter to be contained in the layer B is defined as the inert particle II, the average particle diameter dII is preferably 0.1 to 1.0 μm, more preferably 0.4 to 0.9 μm, The content is preferably 0.002 to 0.10% by mass, more preferably 0.005 to 0.05% by mass, and when the inert particles III are further included, the average particle size dIII is smaller than dII. , DIII is preferably 0.05 to 0.5 μm, more preferably 0.2 to 0.4 μm, and the content is preferably 0.1 to 1.0% by mass, more preferably 0.2. It is -0.4 mass%.

  As described above, the layer A and the layer B are the outermost layers constituting the surface A and the surface B, respectively. However, even if the layer A or the layer B has a layer C or a layer D between the two layers, Good.

  The inert particles contained in the biaxially oriented polyester film of the present invention include inorganic particles such as spherical silica, aluminum silicate, titanium dioxide, calcium carbonate, and other organic polymer particles such as crosslinked polystyrene resin particles and crosslinked silicone. Resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, melamine resin particles, and the like are preferable. These 1 type (s) or 2 or more types can be selected and used.

  The inert particles preferably have a uniform particle shape and particle distribution, and the volume shape factor is preferably f = 0.3 to π / 6, more preferably f = 0.4 to π / 6. The volume shape factor f is expressed by the following equation.

f = V / Dm ³
Here, V is the particle volume (μm ³ ), and Dm is the maximum diameter (μm) on the projection plane of the particles.

  The volume shape factor f is the maximum π / 6 (= 0.52) when the particle is a sphere. In order to remove coarse particles and inclusions as necessary, filtration or the like is preferably performed. Among them, spherical silica is preferable because it is excellent in monodispersity, can easily control the formation of protrusions, and the effects of the present invention become better. If necessary, α-type alumina, γ-type alumina, δ-type alumina, θ-type alumina, zirconia having a primary particle size of 0.005 to 0.10 μm, preferably 0.01 to 0.05 μm from the viewpoint of reinforcing the background. In addition, inert particles selected from silica, titanium particles and the like may be contained within a range that does not affect the formation of surface protrusions.

  The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the longitudinal direction and the width direction of 4 to 13 GPa. When the Young's modulus in the longitudinal direction is less than 4 GPa, the film extends in the longitudinal direction due to the tension in the longitudinal direction in the tape drive, and contracts in the width direction due to this elongation deformation, and recording track deviation is likely to occur. The lower limit of the Young's modulus in the longitudinal direction is more preferably 4.3 GPa, still more preferably 4.5 GPa. On the other hand, when the Young's modulus in the longitudinal direction is greater than 13 GPa, a sufficient Young's modulus in the width direction cannot be obtained, which is likely to cause edge damage. The upper limit of the Young's modulus in the longitudinal direction is more preferably 10 GPa, still more preferably 8 GPa. A more preferable range is 4.3 to 10 GPa, and a further preferable range is 4.5 to 8 GPa.

  The biaxially oriented polyester film of the present invention preferably has a Young's modulus in the width direction of 4 to 13 GPa. If the Young's modulus in the width direction is less than 4 GPa, edge damage may be caused. The lower limit of the Young's modulus in the width direction is more preferably 5 GPa, and even more preferably 6 GPa. On the other hand, when the Young's modulus in the width direction is larger than 13 GPa, it is difficult to obtain a sufficient Young's modulus in the longitudinal direction. The upper limit of the Young's modulus in the width direction is more preferably 11 GPa, still more preferably 10 GPa. A more preferable range is 5 to 11 GPa, and a more preferable range is 6 to 10 GPa.

  In addition, in this invention, a longitudinal direction is a direction generally called MD direction, Comprising: The same direction as the longitudinal direction at the time of a polyester film manufacturing process is pointed out, and the width direction is a direction generally called a TD direction. And the same direction (direction orthogonal to MD direction) as the width direction at the time of a polyester film manufacturing process is pointed out.

  Moreover, it is preferable that the thickness of the biaxially oriented polyester film of this invention is 2-10 micrometers. When this thickness is smaller than 2 μm, it is difficult to obtain the necessary strain as a support for a magnetic recording medium. The lower limit of the thickness of the polyester film is more preferably 3 μm, and even more preferably 4 μm. On the other hand, when the thickness of the polyester film is larger than 10 μm, the tape length per one tape is shortened, so that it may be difficult to reduce the size and increase the capacity of the magnetic tape. The upper limit of the thickness of the polyester film is more preferably 8 μm, and even more preferably 6 μm. A more preferable range is 3 to 8 μm, and a further preferable range is 4 to 6 μm.

  In order to provide strength and dimensional stability required for the magnetic recording medium, metal vapor deposition such as aluminum oxide may be performed on at least one surface of the above-described biaxially oriented polyester film. In a vapor deposition film, it is common that cupping occurs due to a difference in expansion and contraction of the vapor deposition film when it is deposited and when it is cooled after vapor deposition. In addition, when an oxide such as aluminum oxide is deposited, the deposited film may change in dimensions due to an oxidation reaction or a hydroxylation reaction that proceeds after the deposition, thereby causing cupping. Furthermore, when oxide vapor deposition is performed on both sides, it is necessary to control the film thickness and the degree of oxidation on the front and back sides. The polyester film of the present invention is also useful for correcting cupping of such metal-deposited polyester film.

  The biaxially oriented polyester film of the present invention as described above is produced, for example, as follows. Hereinafter, examples in which polyethylene terephthalate (PET) is used as the polyester and polyetherimide is used as the heat-resistant thermoplastic resin will be described as representative examples, but the present invention is not particularly limited thereto.

  As a method of incorporating the inert particles into the polyester, for example, the inert particles I are dispersed in the form of a slurry at a predetermined ratio in ethylene glycol, which is a diol component, and this ethylene glycol slurry is added at an arbitrary stage before the completion of polyester polymerization. To do. Here, when adding the particles, for example, when the water sol or alcohol sol obtained at the time of synthesis is added without drying, the dispersibility of the particles is good, and both the slipping property and the electromagnetic conversion property are good. It can be. Also effective for the effect of the present invention is a method in which an aqueous slurry of particles is directly mixed with predetermined polyester pellets, supplied to a vent type twin-screw kneading extruder and kneaded into polyester.

  Polyester pellets substantially free of particles and polyetherimide pellets are mixed at a predetermined ratio, supplied to a vent type twin-screw kneading extruder heated at 270 to 300 ° C., melt-extruded, and pellets Get.

  The thus prepared particles-containing pellets, polyetherimide-containing pellets, and pellets substantially free of particles are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder to produce a polymer. Is filtered through a filter.

Also, in high-density magnetic recording medium applications where a very thin magnetic layer is applied, very small foreign matter can cause DO (dropout), which is a magnetic recording defect. It is effective to use a high-precision fiber sintered stainless filter that collects 95% or more. Subsequently, the sheet is extruded from a slit-shaped slit die and cooled and solidified on a casting roll to obtain an unstretched film. That is, a necessary number of layers are laminated using a plurality of extruders, a plurality of manifolds or a merge block (for example, a merge block having a rectangular merge portion), the sheet is extruded from a die, and cooled by a casting roll to form an unstretched film. create. In this case, a method of installing a static mixer and a gear pump in the polymer flow channel is effective from the viewpoint of stabilization of back pressure and suppression of thickness fluctuation.
Subsequently, the unstretched film is stretched biaxially in the longitudinal direction and the width direction and then heat treated. Although an extending process is not specifically limited, It is preferable to divide into two or more steps in each direction. That is, the method of performing re-longitudinal and re-lateral stretching is preferable because a high-strength film optimum for a magnetic tape for high-density recording can be easily obtained.

  The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching. Since simultaneous biaxial stretching does not involve stretching by a roll, local heating of the film surface does not occur, and surface properties are easy to control, so that it is more preferable as a stretching method. In simultaneous biaxial stretching, an unstretched film is first stretched simultaneously in the longitudinal and width directions at a stretching temperature of, for example, 80 to 160 ° C, preferably 85 to 130 ° C, more preferably 90 to 110 ° C. When the stretching temperature is lower than 80 ° C., the film tends to break, and when the stretching temperature is higher than 160 ° C., it may be difficult to obtain sufficient strength when used as a magnetic recording medium. Further, from the viewpoint of preventing stretching unevenness, the total stretching ratio in the longitudinal direction and the transverse direction is, for example, 8 to 30 times, preferably 9 to 25 times, and more preferably 10 to 20 times. When the draw ratio is less than 8, it is difficult to obtain the necessary and sufficient strength for the high-density magnetic recording medium targeted by the present invention. On the other hand, if the magnification is larger than 30 times, the film may be torn and it may be difficult to manufacture. In order to obtain the strength required for the high-density magnetic recording medium, the temperature is preferably 140 to 210 ° C., more preferably 160 to 200 ° C., preferably 1.05 to 1.8, more preferably, as necessary. Is preferably 1.2 to 1.6 times and stretched in the longitudinal and / or width direction again. If it is less than 1.05, sufficient strength may not be obtained, and if it is more than 1.8 times, the film may be broken and production may be difficult. Thereafter, heat setting is performed at, for example, 180 to 235 ° C., preferably 190 to 220 ° C., for example, for 0.5 to 20 seconds, and preferably for 1 to 15 seconds. If the heat setting temperature is lower than 180 ° C., the crystallization of the film does not proceed and the structure is difficult to stabilize. On the other hand, if the temperature is higher than 235 ° C., the relaxation of the polyester amorphous chain portion proceeds and the Young's modulus decreases, so that it is difficult to obtain sufficient strength for magnetic recording medium applications. Thereafter, a relaxation treatment of 0.5 to 7.0% is performed in the longitudinal and / or width direction.

  Since the biaxially oriented polyester film of the present invention has a difference in heat resistance between the front and back surfaces, the glass transition point of the layer containing a large amount of the heat-resistant thermoplastic resin is high, and it is apparently stretched at a low temperature. Crystal chains tend to be tense. For this reason, in a relaxation process, the layer which contains many heat-resistant thermoplastic resins shrinks more, and as a result, the film which has cupping can be obtained. When used as a support for a magnetic recording medium, it is preferable that the surface A side, that is, the side on which the magnetic layer is provided, is convex in order to ensure head contact, in which case the surface B side contains a heat-resistant thermoplastic resin. It is effective to make the amount larger than the surface A side. When the method of the present invention is used, the required cupping amount can be easily controlled by adjusting the difference in the contents of the heat-resistant thermoplastic resins on the front and back sides. Cupping is evaluated as-(minus) when the A-side is convex, and + (plus) when the B-side is convex. When used as a magnetic recording medium, both positive and negative are too large. , Head hitting tends to be bad. The cupping in the magnetic recording medium support is preferably 0 to -5 mm, more preferably 0 to -3 mm.

  When using the film of the present invention, it is possible to easily produce a polyester film having cupping using a normal polyester film production facility, so that it is possible to omit the step of providing cupping again after providing the magnetic layer. It becomes possible. Accordingly, it is possible to improve the production efficiency of the magnetic recording medium.

  The biaxial polyester film of the present invention is useful when used as a magnetic recording material, an electronic material, a plate-making film, a sublimation ribbon, a packaging material, or a metal deposition, and particularly has a high capacity of 500 GB or more per roll. This is useful when used as a support.

(Methods for measuring physical properties and methods for evaluating effects)
The characteristic value measurement method and effect evaluation method in the present invention are as follows.

(1) Heat-resistant thermoplastic resin concentration WA and WB evaluation method Heat-resistant thermoplastic resin concentrations WA and WB are determined by mass average values according to the following formula. Although the case of a two-layer structure is described, the same applies to the case of multilayer lamination such as three layers, four layers.

  The thicknesses of the A and B layers are TA and TB, and the heat-resistant thermoplastic resin concentrations in the A and B layers are CA and CB. When the thickness of the A layer is the same as or larger than the thickness of the B layer (TA ≧ T / 2 ≧ TB), if the total thickness of the polyester film is T,

  When the thickness of the B layer is larger than the thickness of the A layer (TB> T / 2> TA),

It is.

  In addition, the evaluation method of CA and CB is performed as follows after ashing and removing an unnecessary layer by the plasma low-temperature ashing method.

Pretreatment: Freeze crushing, drying under reduced pressure (room temperature, 2 hours)
Measuring method: Total nitrogen analysis by oxidative decomposition and reduced pressure chemiluminescence method
Vaporized and oxidized in a reaction furnace, and the generated nitric oxide is measured by the chemiluminescence method.

              The concentration is calculated using a calibration curve prepared in advance. Measure three times and calculate from the average value.

In addition, when quantification by total nitrogen analysis is difficult, quantification can be performed by NMR (nuclear magnetic resonance method) of ¹ H nucleus.

(2) Cupping Samples were stored for 24 hours or more under the following conditions, and a strip having a width direction of 50 mm and a longitudinal direction of 300 mm was cut out. As shown in FIG. 1, the distance between a line connecting both ends having a width of 50 mm and a center portion (a portion 25 mm from both ends) was evaluated as cupping with no tension and vertically held vertically. The case where the A side was convex was evaluated as-(minus), and the case where the B side was convex was evaluated as + (plus).

Storage / measurement environment: temperature 23 ° C, humidity 65% RH
Number of measurements: Measured 5 times and calculated from the average value.

×: Less than −5.0 mm ○: −5.0 mm or more and less than −3.0 mm ○○: −3.0 mm or more and less than 0.0 mm ×: 0.0 mm or more (3) Three-dimensional surface roughness Three-dimensional surface roughness SRa (central surface average roughness) was measured using a three-dimensional fine shape measuring instrument (model ET-350K) and a three-dimensional surface roughness analysis system (model TDA-22) of Kosaka Laboratory. The conditions were as follows, and the average value of five measurements was taken as the value.

-Stylus diameter: 2 μm
-Load of stylus: 0.04 mN
・ Vertical magnification: 50,000 times ・ Cutoff: 0.08mm
・ Feeding pitch: 5μm
・ Measurement length: 0.5mm
Measurement area: 0.2 mm ²
Measurement speed: 0.1 mm / second (4) Evaluation of Young's modulus Measured according to JIS-K7161 (1994). Instron type tensile tester is used and the conditions are as follows. The average value of the five measurement results is defined as the Young's modulus in the present invention.

Sample size: width 10mm x test length 100mm
Tensile speed: 200 mm / min Measurement environment: temperature 23 ° C., humidity 65% RH
Number of measurements: Measured 5 times and calculated from the average value.

(5) Average particle diameter of particles The polymer was removed from the polyester film by a plasma low-temperature ashing treatment method to expose the particles. The treatment conditions were selected such that the polymer was ashed but the particles were not damaged as much as possible. The particles were observed with a scanning electron microscope (SEM), and the particle images were processed with an image analyzer. The magnification of SEM was 20,000 times, and the volume average diameter d was obtained from the particle size and its volume fraction from the number of particles of 100 or more by changing the observation location by the following formula. When two or more kinds of particles having different particle diameters were contained, the same measurement was performed for each particle to obtain the particle diameter.

d = Σ (di · Nvi)
Here, di is the particle size, and Nvi is the volume fraction. When the particles were significantly damaged by the plasma low-temperature ashing method, the film cross section was observed with a transmission electron microscope (TEM) at a magnification of 20,000 times. The section thickness of TEM was about 100 nm, the number of particles was measured by changing the observation location, and the volume average diameter d was determined from the above formula.

(6) Volumetric shape factor of particles With a scanning electron microscope, 10 views of the particles were photographed at a magnification of 20,000. Furthermore, the maximum diameter of the projection plane and the average volume of the particles were calculated using an image analysis processing apparatus, and a volume shape factor was obtained by the following formula.

f = V / Dm ³
Here, V is the average volume (μm ³ ) of the particles, and Dm is the maximum diameter (μm) of the projection surface.

(7) Film Lamination Thickness The film cross section was observed at 20,000 times using a transmission electron microscope (TEM). The section thickness of TEM was about 100 nm, and the thickness of each layer was evaluated from the observation results of the interface based on the contained particle diameter and particle concentration. Moreover, when observation by the above is difficult, it can also evaluate using SIMS (secondary ion mass spectrometer). While etching from the surface, the depth profile of the element concentration caused by the particles or the heat-resistant thermoplastic resin is measured, and the thickness of each layer is evaluated.

(8) Evaluation of film formation stability The stability during film formation was evaluated according to the following criteria. Film breakage is preferably 2 times or less per 24 hours under product collection conditions, and the practical level is 1 time or less. Here, the film breakage means that a hole is formed or the film is cut, and it becomes necessary to pass the film again through the film forming apparatus, and the product cannot be removed continuously.

◯: No tearing in 24 hours ○: One to two tears in 24 hours ×: Three or more tears in 24 hours An embodiment of the present invention will be described based on the following examples.

  In the present invention / examples, wt% means mass%.

Example 1
Polyethylene terephthalate pellets (50 wt%) substantially free of particles and “Ultem” 1010 (hereinafter abbreviated as PEI) (50 wt%) manufactured by General Electric (GE), heated to 290 ° C., bent type Pellets containing 50 wt% PEI were prepared by feeding to a biaxial kneading extruder.

  Polyethylene terephthalate containing spherical silica particles having an average particle size of 0.10 μm and a volume shape factor f = 0.51 and polyethylene terephthalate containing substantially no particles so that the content of spherical silica particles is 0.2% by mass. Thermoplastic resin A was prepared by mixing seed pellets.

  Further, polyethylene terephthalate containing divinylbenzene / styrene copolymer crosslinked particles having an average particle size of 0.3 μm and a volume shape factor f = 0.52, and divinyl having an average particle size of 0.8 μm and a volume shape factor f = 0.52 A polyethylene terephthalate containing benzene / styrene copolymer crosslinked particles, a pellet containing 50 wt% PEI, and a polyethylene terephthalate pellet containing substantially no particles, the particle content of 0.3 μm is 0.26% by mass, 0.8 μm. A thermoplastic resin B was prepared by mixing so that the content of the particles was 0.01% by mass and the amount of PEI was 3 wt%. These thermoplastic resins were each dried under reduced pressure at 160 ° C. for 8 hours, then supplied to separate extruders, melt-extruded at 275 ° C. and filtered with high precision, and then merged and laminated with a rectangular two-layer merge block. Layer lamination was used. Thereafter, the film was wound around a casting drum having a surface temperature of 25 ° C. by using an electrostatic application casting method on a cooling roll through a slit die kept at 295 ° C., and solidified by cooling to obtain an unstretched laminated film. This unstretched laminated film was stretched 3.5 times in the longitudinal and width directions at 95 ° C and 12.3 times in total by a linear motor type simultaneous biaxial stretching machine, and then 1.2 times in the longitudinal direction again at 190 ° C. The film was stretched 1.4 times in the width direction and heat treated at 205 ° C. for 3 seconds under a constant length. Thereafter, a relaxation treatment of 2% in the width direction was performed to obtain a biaxially oriented polyester film having a total thickness of 4.3 μm, a thickness of layer B of 0.5 μm, WA = 0%, and WB = 0.7 wt%. The Young's modulus in the longitudinal direction was 5 GPa, the Young's modulus in the width direction was 7 GPa, and the surface roughness SRa was 6 nm on the layer A side and 11 nm on the layer B side.

  The characteristics are as shown in Table 1. The film was not broken and the film forming property was good.

(Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the thicknesses of the layers A and B and the addition amount of the heat-resistant thermoplastic resin to each layer were changed.

( Reference Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the thicknesses of Layer A and Layer B were changed.

(Comparative Example 1)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the amount of the heat-resistant thermoplastic resin added to the layers A and B was changed.

(Comparative Example 2)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the amount of the heat-resistant thermoplastic resin added to the layers A and B was changed.

(Comparative Example 3)
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the thicknesses of the layers A and B and the addition amount of the heat-resistant thermoplastic resin to the layer B were changed.

It is the schematic of cupping evaluation.

Explanation of symbols

1 sample 2 samples

Claims (5)

It has a layer structure of two or more layers, and the content of the heat-resistant thermoplastic resin contained in the portion from the center in the thickness direction to the one surface A side is WA, and from the center in the thickness direction to the other surface B side when the content of the heat-resistant thermoplastic resin contained in the portion and a WB, WA and WB are both 0-5 wt%, and the value of WB-WA is Ri 0.1～1.1Wt% der, the heat-resistant thermoplastic resins that have a higher Tg than the glass transition temperature (Tg) of the polyester used biaxially oriented polyester film. The biaxially oriented polyester film according to claim 1, wherein the heat-resistant thermoplastic resin is a polyimide resin (including polyetherimide), polysulfone, polyethersulfone, polyamideimide, polyetheretherketone, or polyarylate. The biaxially oriented polyester film according to claim 2 , wherein the heat-resistant thermoplastic resin is a polyetherimide. The biaxially oriented polyester film according to any one of claims 1 to 3 , which is used as a support for a magnetic recording medium. The metal vapor deposition polyester film which gave metal vapor deposition to the at least single side | surface of the biaxially-oriented polyester film in any one of Claims 1-4 .

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