JP4441324B2 - Biaxially oriented polyester film and magnetic recording medium - Google Patents

Description

  The present invention relates to a biaxially oriented laminated polyester film, and more particularly, a biaxially oriented laminated polyester film excellent in dimensional stability and slit property, and particularly suitable for a base film of a linear track type magnetic recording medium, and the same The present invention relates to a magnetic recording medium.

  Polyester films typified by polyethylene terephthalate films are magnetic recording media that make use of excellent mechanical properties, thermal properties, electrical properties, surface properties, optical properties, and heat and chemical resistance. It is widely used in various applications such as for packaging, condensers and packaging.

  Films used for these applications are usually cut to a width according to the application. Japanese Patent Laid-Open No. 63-251221 is known as a technique for preventing chips from being generated during cutting. As a technique for solving the problem at the time of cutting, a technique such as Japanese Patent Laid-Open No. 63-95933 is known. Further, when cutting the film, it has been dealt with by cutting the temperature around the cutter at a low temperature of 20 ° C. or lower.

  However, in accordance with the needs for higher quality and compactness of products for these applications, the required characteristics for polyester films are becoming increasingly severe. Among the above-mentioned applications, particularly in magnetic recording medium applications, the base film has been thinned to have a thickness of 10 μm or less along with high quality, long-time recording, and downsizing.

  When these films are cut using a shear cutter or the like and wound up, there is a problem that a phenomenon called “high edge” occurs in which the film edge rises along the cut surface. When the film is wound with this high edge generated, only the edge portion of the film is stretched. For example, when a magnetic layer is provided on the surface to form a magnetic tape, the flatness is impaired, and RF The output waveform may be disturbed. In order to solve this problem, the number average molecular weight and intrinsic viscosity of the polyester constituting the film may be set within a specific range, such as JP-A-7-6351 (Patent Document 1) and JP-A-10-214415 ( This is proposed in Patent Document 2).

  By the way, the problem of the high edge is a unique problem that occurs when the rigidity in the width direction is extremely increased as compared with the longitudinal direction, as described in Patent Document 2. For this reason, a film having the same or higher rigidity in the longitudinal direction than the width direction does not have the problem of a high edge and has been used well.

Japanese Unexamined Patent Publication No. 7-6351 Japanese Patent Laid-Open No. 10-214415

  However, in recent years, the recording density has been increased, for example, in the film used for data storage, etc., since the position of the edge portion of the film is used as a reference when reading and writing data, the flatness is reduced at the edge portion of the film. It is not enough that there is no abnormality such as “high edge”, and the shape of the cut surface of the edge part is also required, and the film has the same or higher rigidity in the longitudinal direction compared to the width direction. However, it was becoming impossible to take sufficient measures. Further, Patent Document 2 proposes that the intrinsic viscosity of one layer be 0.55 dl / g or less, but when actually making such a laminated film and cutting it, the shape of the cut portion was determined. However, the edge portion cannot be used as a reference for reading and writing data.

  Therefore, an object of the present invention is to provide a biaxially oriented laminated polyester film that does not cause a problem even when the cut edge portion is used as a reference for data reading and writing when it is cut into a desired width. It is to provide a magnetic recording medium using the same.

Thus, according to the present invention, an object of the present invention is a laminated film consisting of at least two polyester layers, the weight average molecular weight of the polyester constituting the layers is in the range of 2 9 000-36000, a longitudinal elastic modulus 6.0 GPa or more, the elastic modulus in the width direction is 4.0 or more, the elastic modulus in the longitudinal direction is the same as or larger than the elastic modulus in the width direction, and the film thickness is in the range of 2 to 10 μm. Achieving with an axially oriented laminated polyester film, and as a preferred embodiment thereof, the polyester is polyethylene-2,6-naphthalate, one film surface has a center line surface roughness of 10 nm or less, and the other film surface is The center line surface roughness is larger than that of one film surface and is 5 to 30 nm, and the base film of the magnetic recording medium A biaxially oriented laminated polyester film comprising at least one of the films is also provided.

  The present invention also provides a magnetic recording medium in which a magnetic layer is laminated on one side of the biaxially oriented laminated polyester film of the present invention.

As described above, the biaxially oriented polyester film of the present invention is a laminated film composed of at least two polyester layers, the weight average molecular weight of the polyester constituting each layer is in the range of 28000 to 36000, and the elastic modulus in the longitudinal direction is 6 It is 0.0 GPa or more, the elastic modulus in the width direction is 4.0 or more, the elastic modulus in the longitudinal direction is the same as or larger than the elastic modulus in the width direction, and the film thickness is in the range of 3 to 7 μm. For convenience of explanation, “film longitudinal direction” is the film forming direction, longitudinal direction, MD direction or MD, and “direction perpendicular to the film longitudinal direction and thickness direction” is the width direction, lateral direction, TD direction or TD, “elastic modulus” is Young's modulus, “longitudinal modulus” is E _MD , “width modulus” is E _TD , “surface roughness” is Ra, “one surface” is surface A, “ The “other surface” may be referred to as surface B, “surface roughness of one surface” may be referred to as RaA, “surface roughness of the other surface” may be referred to as RaB, and “weight average molecular weight” may be referred to as Mw.

First, if the _EMD is less than the lower limit, the longitudinal strength of the magnetic tape becomes weak, and if a strong force is applied in the longitudinal direction during recording / reproduction, the magnetic tape easily breaks or stretches. On the other hand, if the _ETD is less than the lower limit, when the linear track type magnetic tape is used, the dimensional change in the width direction at the time of temperature / humidity change becomes large, and a recording / playback error due to track deviation occurs. Preferred _{E MD} is more than 7 GPa, it is more 8GPa more. Also preferred _{E TD} is more 5 GPa, is more 6GPa more.

From the viewpoint of reducing the longitudinal stretch when subjected for the magnetic tape of linear track system, E _MD is required to be greater than or equal to the E _TD. E _MD is 1GPa or more than _{E TD,} further 2GPa or more, and particularly greater than 3 GPa, while eliminating the problem of high edge, further the molecular chains were oriented with the longitudinal direction, longitudinal direction, i.e. film formation direction of the slit of Can be improved. _{Incidentally,} the sum of _{E MD} and _{E TD} is, 10～20GPa, further particularly 12～16GPa. If the sum of E _MD and E _TD is less than 10 GPa, the strength of the magnetic tape will be weak, the tape will be easily broken, and the dimensional change during temperature / humidity changes will be large. Is likely to occur. On the other hand, if it exceeds 20 GPa, the stretch ratio becomes high during film formation, the film breaks frequently, and the product yield is remarkably deteriorated.

  Furthermore, if the Mw of each polyester layer constituting the film exceeds the upper limit, although it is a film whose rigidity is not increased in the width direction, abnormalities such as high edges do not occur, but the cut surface is in the width direction of the film. It swells up and becomes insufficient as a standard for reading and writing data. On the other hand, when the Mw is below the lower limit, sufficient mechanical properties cannot be obtained, and film formation becomes difficult. Preferred Mw is in the range of 28000-37000, and more preferably in the range of 29000-36000. In addition, this Mw needs that all the polyester layers are in the range, and it does not have to be satisfied on average as a whole.

  Finally, if the thickness of the film exceeds the upper limit, when the magnetic recording medium is used, the surface area of the magnetic layer of the magnetic recording medium that can be accommodated in the cartridge decreases, and a sufficient recording capacity cannot be obtained. On the other hand, if the thickness of the film is lower than the lower limit, when a strong force is applied in the longitudinal direction when recording / reproducing as a magnetic tape, the film is easily broken or stretched.

According to the present _{invention, E MD} is more than 6 _GPa, biaxially oriented with _{E TD} is equal to or greater than the 4GPa above and _{E MD} is _{E TD,} and Mw of the polyester constituting the film is in the range of from 26,000 to 38,000 By being a polyester film, a biaxially oriented laminated polyester film suitable for a base film of a magnetic recording medium that is excellent in electromagnetic conversion characteristics, transportability, and dimensional stability and also has slitting properties is provided.

  And, when the biaxially oriented polyester film of the present invention is used as a base film for a magnetic recording medium, as a digital data storage tape that does not generate an error rate due to track deviation, has excellent output characteristics and running properties, and can withstand long-term use. A useful magnetic recording medium can be obtained.

Hereinafter, the biaxially oriented polyester film of the present invention and a magnetic recording medium using the same will be described.
<Polyester>
Examples of the polyester in the present invention include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polyethylene-α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate. Etc. These polyesters may be a copolymer in which the repeating unit is changed to another third component or a blend. Among these polyesters, polyethylene terephthalate and polyethylene-2,6-naphthalate (hereinafter sometimes referred to as PEN) are preferable because strength is relatively high and easily expressed, and PEN is particularly preferable from the viewpoint of increasing strength. Most preferred. Of course, PEN as used herein may be used alone, as a copolymer with other polyesters, or as a mixture of two or more polyesters. Specifically, the repeating structural unit is preferably not only ethylene-2,6-naphthalate but also preferably 10 mol% or less, more preferably 5 mol% or less, based on the repeating structural unit. The component PEN copolymer and polymer mixture may be sufficient. Further, polyethylene terephthalate in which strength is improved by adding a functional agent such as polyimide to polyethylene terephthalate is also preferable.

  The polyester is not particularly limited as long as the Mw when formed into a film falls within the above range. Preferably, the polyester Mw before film formation is 28000-56000, further using a polyester film of 30000-52000, Mw 34,000-56000 polyester and Mw 23,000-38000 polyester in combination, For example, the Mw when the polyester is dried and dried to form a film in the subsequent melt-extrusion step is decreased until it falls within the aforementioned range. If the Mw of the polyester before film formation is excessively high, Mw in the film does not decrease to the above-mentioned range without causing excessive thermal decomposition during film formation. If the Mw of the previous polyester is excessively low, the Mw in the film tends to be smaller than the above range due to thermal decomposition during film formation.

  The production method of the polyester used in the present invention is not particularly limited, and a method known per se can be arbitrarily adopted. For example, in the case of polyethylene-2,6-naphthalate, an ester-forming derivative of an acid component, for example, a di-lower alkyl-2,6-naphthalate and ethylene glycol can be produced by a transcondensation reaction and then a polycondensation reaction, Usually, these reactions are carried out in the presence of a catalyst.

  The polyester used in the present invention may contain organic or inorganic inert particles as a lubricant in order to improve the winding property of the film during film formation, the transportability of the film, and the like.

<Polyester film>
In the biaxially oriented laminated polyester film of the present invention, one film surface (surface A) has a centerline surface roughness (RaA) of 10 nm or less, and the other film surface (surface B) has a centerline surface roughness ( RaB) is preferably larger than that of surface A and 5 to 30 nm. When RaA exceeds the upper limit of the surface A, that is, the surface on which the magnetic layer is formed when used as a base film of a magnetic recording medium, the surface of the magnetic layer becomes rough when used as a magnetic tape, and electromagnetic conversion characteristics deteriorate. A preferable RaA is in the range of 0.1 to 7 nm, more preferably 0.5 to 5 nm. Further, the surface B, that is, the surface on the side where the magnetic layer is not formed (non-magnetic layer side) when used as a base film of a magnetic recording medium, is flat during storage in a roll state when RaB exceeds the upper limit. A rough surface shape on the nonmagnetic layer side is transferred to the surface of the magnetic layer, that is, the surface of the magnetic layer is roughened to deteriorate the electromagnetic conversion characteristics, and if it is less than the lower limit, the transportability is lowered and wrinkles are generated. In addition, from the viewpoint of improving electromagnetic conversion characteristics and transportability by changing the roughness of both surfaces of the biaxially oriented polyester film in this way, if RaA and RaB are the same, an improvement effect cannot be obtained, and at least RaB is RaA. Need to be coarser than. In order to combine such RaA and RaB in a biaxially oriented polyester film, it is necessary to laminate at least two polyester layers having different surface shapes. And adjustment of the surface shape obtained can be adjusted with the inert particle contained in the below-mentioned polyester layer. For example, one side of a polyester layer that does not contain inert particles or contains a small amount of inert particles that are small in size, but contains a large number of inert particles or more inert particles. It is sufficient to laminate a polyester layer containing A third polyester layer may be further interposed between the two.

  Such surface roughness can be adjusted by including inactive fine particles in the polyester constituting the film. As the inert particles, for example, inorganic fine particles (for example, kaolin, alumina, titanium oxide, calcium carbonate, silicon dioxide, etc.) containing the elements of Periodic Tables IIA, IIB, IVA, and IVB, silicone resins, crosslinks Examples thereof include fine particles made of a polymer having high heat resistance such as polystyrene. Preferably, the polyester layer A forming the surface A does not contain or contains inert particles, and in the case of containing the inert particles having an average particle size of 0.02 to 0.5 μm, and further 0.03 to 0.4 μm. Based on the weight of the polyester layer A, it is preferable to contain 0.01 to 0.4% by weight (with respect to polymer), and more preferably 0.02 to 0.3% by weight (with respect to polymer). Further, the polyester layer B forming the surface B has an average particle size of 0.03 to 1.0 μm, more preferably 0.04 to 0.8 μm, based on the weight of the polyester layer B. It is preferable to contain -1.0weight% (with respect to a polymer), and also 0.08 to 0.5weight% (with respect to a polymer). At this time, the inert particles to be used are not limited to one type, and two or more types of inert particles having different average particle diameters may be used.

  The biaxially oriented laminated polyester film of the present invention preferably has a humidity expansion coefficient in the width direction (hereinafter sometimes referred to as αh) of 0 to 15 ppm /% RH, and more preferably 3 to 10 ppm /% RH. When αh is out of the above range, a dimensional change due to a change in humidity increases, and a track shift occurs, resulting in an error. Such a humidity expansion coefficient can be adjusted by increasing the elastic modulus in the width direction.

  The biaxially oriented laminated polyester film of the present invention preferably has a temperature expansion coefficient in the width direction (hereinafter sometimes referred to as αt) of −10 to 10 ppm / ° C. When αt is smaller than −10 ppm / ° C. or larger than 10 ppm / ° C., the dimensional change due to the temperature change becomes large, and when the temperature changes, the track shift occurs and an error occurs. Such αt can be adjusted by, for example, imparting thermal dimensional stability by a heat setting process while keeping the Young's modulus within the above range.

<Manufacturing method>
The biaxially oriented laminated polyester film of the present invention can be produced, for example, by the following method. First, prepare at least two polyester pellets with different inert particle sizes and contents, dry them, and then feed them to different extruders, and in the molten state, two layers or more The above layers are stacked. Then, while maintaining the laminated state, it is extruded onto a cooling drum to create a laminated unstretched film. In the case of a polyethylene-2,6-naphthalate film, this unstretched film is stretched in the machine direction at a temperature of 100 to 170 ° C. at a magnification of 5 to 8 times, and then in the direction perpendicular to the stretch direction, that is, in the width direction. Stretch at a magnification of 4 to 7 times at a temperature of 115 to 180 ° C. Alternatively, longitudinal and lateral stretching may be divided into two or more stages as necessary (longitudinal multistage stretching, longitudinal-horizontal-longitudinal three-stage stretching, longitudinal-horizontal-vertical-horizontal four-stage stretching, etc.). . Moreover, you may implement by simultaneous biaxial stretching. Thus, the total draw ratio is preferably 10 to 60 times, more preferably 20 to 50 times as the area draw ratio. Under the present circumstances, in order to express the slit property improvement effect by a polyester film, it is preferable that the value which deducted the draw ratio of the horizontal direction from the draw ratio of the vertical direction is 0.5 times or more. The biaxially oriented film is preferably heat-set at a temperature of 180 to 250 ° C., more preferably 200 to 230 ° C., and the heat setting time is preferably 1 to 60 seconds.

<Magnetic recording medium>
The biaxially oriented laminated polyester film of the present invention has an elastic modulus necessary for dimensional stability, excellent flatness and running property, and also has excellent slit property, so that it is a high-density magnetic recording medium. In particular, it is preferably used as a base film of a digital recording type magnetic machine recording medium.

  The magnetic recording medium of the present invention is obtained by applying a magnetic layer to one side surface (or flat side surface in the case of lamination) of the above-described support of the present invention, or by a method such as vacuum deposition, sputtering, or ion plating. A ferromagnetic metal thin film layer made of chromium or an alloy or oxide containing these as a main component is formed, and a protective layer such as diamond-like carbon (DLC) is formed on the surface, if necessary, fluorine-containing It is formed by sequentially providing a carboxylic acid-based lubricating layer and further providing a backcoat layer on the surface opposite to the magnetic layer.

  Since the magnetic recording medium thus obtained has excellent dimensional stability and slitting properties, in order to realize a high capacity of the tape, the linear recording density is increased, the track density is increased, and the tape length is increased. It can be suitably used for data storage applications that employ linear track systems such as QIC, DLT, higher capacity super DLT, and LTO, which are scaled.

Hereinafter, the present invention will be further described based on examples. The various physical property values and characteristics in the present invention are measured and defined as follows.
(1) Young's modulus Using a tensile tester “Tensilon” manufactured by Toyo Baldwin Co., Ltd., in a room adjusted to a temperature of 20 ° C. and a humidity of 50%, the film was cut into a sample width of 10 mm and a length of 15 cm, and between chucks. The Young's modulus is calculated from the tangent of the rising portion of the load-elongation curve obtained by pulling at 100 mm and pulling at a pulling speed of 10 mm / min and a chart speed of 500 mm / min.

(2) Surface roughness (Ra)
Using a stylus type surface roughness meter (Surfcoder 30C) manufactured by Kosaka Laboratory Co., Ltd., a chart (film surface roughness curve) is applied under the conditions of a needle radius of 2 μm and a stylus 30 mg. From the film surface roughness curve, a portion of the measurement length L is extracted in the direction of the center line, the center line of the extraction portion is taken as the X axis, the direction of the vertical magnification is taken as the Y axis, and the roughness curve is represented by Y = f ( When represented by X), Ra (μm) given by the following formula is defined as the film average roughness.

本発明では、測定長を１．２５ｍｍとし、カットオフ値を０．０８ｍｍとして、５回測定した平均値をＲａとする。

In the present invention, the measurement length is 1.25 mm, the cutoff value is 0.08 mm, and the average value measured five times is Ra.

(3) Average particle diameter of inert particles Measured using a CP-50 type Centrifugal Particle Size Analyzer manufactured by Shimadzu Corporation. The particle size corresponding to 50 mass percent is read from the cumulative curve of the particle size and the abundance of each particle size calculated based on the centrifugal sedimentation curve obtained, and this value is taken as the average particle size. To do.

(4) Temperature expansion coefficient (αt)
A film sample was cut into a length of 15 mm and a width of 5 mm so that the width direction was the measurement direction, set in TMA3000 manufactured by Vacuum Riko, pretreated at 60 ° C. for 30 minutes in a nitrogen atmosphere (0% RH), and then to room temperature. Let the temperature drop. Thereafter, the temperature is raised from 25 ° C. to 70 ° C. at 2 ° C./min, the sample length at each temperature is measured, and the temperature expansion coefficient (αt) is calculated from the following equation. Note that the measurement direction was the longitudinal direction of the sample, 10 measurements were taken, and the average value was used.

ここで、Ｌ_４０：４０℃のときのサンプル長（ｍｍ）
Ｌ_６０：６０℃のときのサンプル長（ｍｍ）
△Ｔ：２０（＝６０−４０）℃
０．５×１０^−６：石英ガラスの温度膨張係数である。

Here, L ₄₀ : sample length at 40 ° C. (mm)
L ₆₀ : sample length at 60 ° C. (mm)
ΔT: 20 (= 60-40) ° C.
0.5 × 10 ⁻⁶ : The temperature expansion coefficient of quartz glass.

(5) Humidity expansion coefficient (αh)
A film sample was cut into a length of 15 mm and a width of 5 mm so that the width direction would be the measurement direction, set in a TMA3000 manufactured by Vacuum Riko, under a nitrogen atmosphere at 30 ° C., a humidity of 30% RH, and a humidity of 70%. RH is kept constant, the length of the sample at that time is measured, and the humidity expansion coefficient is calculated by the following equation. The measurement direction was the longitudinal direction of the sample, and 10 samples were measured. The average value was αh.

ここで、Ｌ_３０：３０％ＲＨのときのサンプル長（ｍｍ）
Ｌ_７０：７０％ＲＨのときのサンプル長（ｍｍ）
△Ｈ：４０（＝７０−３０）％ＲＨである。

Here, sample length (mm) when L ₃₀ : 30% RH
Sample length when L _{70 is} 70% RH (mm)
ΔH: 40 (= 70-30)% RH.

(6) Track deviation (error rate)
Using a LTO1 drive manufactured by Hewlett-Packard Company, recording was performed at 10 ° C. and 10% RH temperature and then played back at 30 ° C. and 80% RH temperature. The track deviation width was measured and evaluated according to the following criteria.
(Double-circle): 800 nm or less (circle): Over 800 nm and 1200 nm or less x: Over 1200 nm.
It shows that it is so favorable that the absolute value of these deviation | shift widths is small.

(7) Thickness of polyester film The thickness of the entire film is measured at 10 points at random using a micrometer, and the average value is used.
As for the thickness of each layer, the layer thickness of the polyester layer having a higher content of inert particles is measured by the method described below, and the layer thickness of the other polyester layer is calculated by subtracting the above-mentioned layer thickness from the total thickness. Ask. That is, using a secondary ion mass spectrometer (SIMS), the metal element (M +) caused by the highest concentration of particles in the film having a depth of 5,000 nm from the surface layer excluding the coating layer The concentration ratio (M + / C +) of hydrocarbon (C +) of polyester is defined as the particle concentration, and analysis in the thickness direction is performed from the surface to a depth of 5,000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the present invention, the particle concentration may once rise to a stable value 1 and then rise to a stable value 2 or may monotonously decrease. Based on this distribution curve, the former has a depth that gives a particle concentration of (stable value 1 + stable value 2) / 2, and the latter has a depth at which the particle concentration is ½ of the stable value 1. The thickness (μm) of the thin polyester layer is defined as the depth (this depth is deeper than the depth that provides the stable value 1).

The measurement conditions are as follows.
(A) Measurement device Secondary ion mass spectrometer (SIMS); manufactured by PERKIN ELMER INC., “6300”
(B) Measurement conditions Primary ion species: O ²⁺
Primary ion acceleration voltage: 12KV
Primary ion current: 200 nA
Raster area: 400 μm
Analysis area: 30% gate
Measurement vacuum: 6.0 × 10 ⁻⁹ Torr
E-GUNN: 0.5KV-3.0A

  In the case where organic polymer particles other than silicone resin are the most abundant particles in the range of 5,000 nm from the surface layer, it is difficult to measure by SIMS, so FT-IR (Fourier transform infrared spectroscopy while etching from the surface) ) Depending on the particle, a concentration distribution curve similar to the above is measured by XPS (X-ray photoelectric spectroscopy) or the like to determine the layer thickness (μm).

(8) Slit property The biaxially oriented polyester film was cut in the film forming direction using a shear cutter, the cut surface was observed with a scanning electron microscope from the film forming direction of the film, and evaluated as follows.
A. Ten heights (H) protruding from the film surface were measured in the thickness direction of the high edge film, and the average value was evaluated according to the following criteria.
A: 0.1 μm or less ○: Over 0.1 μm, 0.2 μm or less X: 0.2 μm or more End face shape In the width direction of the film, the width (p) height protruding from the cutting start point of the film by the shear cutter was measured at 10 points, and the average value was evaluated according to the following criteria.
A: 10% or less with respect to the film thickness (t) B: Over 10% and 15% or less with respect to the film thickness (t) X: Over 15% with respect to the film thickness (t)

(9) Weight average molecular weight Measured by GPC using a mixed solvent of 1,1,1,3,3,3-hexafluoroisopropanol and orthochlorophenol and further using chloroform as a mobile phase.

[Example 1]
Polyethylene-2,6-naphthalate having a weight average molecular weight of 30000 (hereinafter sometimes referred to as PEN) containing 0.1% by weight of spherical silica particles having an average particle diameter of 0.1 μm, and PEN having a weight average molecular weight of 45,000 A resin composition 1 having a weight ratio of 50:50, 0.15% by weight of spherical silica particles having an average particle diameter of 0.3 μm, and 0.10% by weight of spherical silica particles having an average particle diameter of 0.1 μm, A PEN having a weight average molecular weight of 30,000 and a PEN having a weight average molecular weight of 45,000 and a resin composition 2 having a weight ratio of 50:50 were each dried at 180 ° C. for 5 hours, and then supplied to an extruder hopper. The molten resin composition 1 is laminated on the surface A in a molten state at 0 ° C., and the surface composition is laminated so that the resin composition 2 is positioned on the surface B. The film was extruded on a casting drum maintained at a temperature of 0.3S and a surface temperature of 60 ° C., and rapidly solidified to obtain a laminated unstretched film.

  The laminated unstretched film thus obtained was preheated at 120 ° C., and further heated by an infrared heater having a surface temperature of 830 ° C. from above 14 mm between low-speed and high-speed rolls and stretched 5.4 times. Then, it was rapidly cooled, then supplied to a stenter, and stretched 4.8 times in the transverse direction at 125 ° C. Subsequently, the film was heat-fixed at 225 ° C. for 3 seconds to obtain a biaxially oriented laminated film having a thickness of 6.0 μm. The Young's modulus of the obtained film was 8 GPa in the vertical direction and 7 GPa in the horizontal direction, the thickness of the polyester layer forming the surface A was 2.0 μm, and the thickness of the polyester layer forming the surface B was 4.0 μm. In addition, the thickness of the polyester layer which forms the surface A and the surface B was adjusted with the discharge amount.

On the other hand, the composition shown below was put in a ball mill, kneaded and dispersed for 16 hours, and then 5 parts by weight of an isocyanate compound (Desmodur L manufactured by Bayer) was added, and high-speed shear dispersion was performed for 1 hour to obtain a magnetic paint.
Magnetic paint composition:
Needle-like Fe particles 100 parts by weight Vinyl chloride-vinyl acetate copolymer 15 parts by weight (Surek Chemical Co., Ltd. SREC 7A)
Thermoplastic polyurethane resin 5 parts by weight Chromium oxide 5 parts by weight Carbon black 5 parts by weight Lecithin 2 parts by weight Fatty acid ester 1 part by weight Toluene 50 parts by weight Methyl ethyl ketone 50 parts by weight Cyclohexanone 50 parts by weight

  This magnetic coating is applied to the surface A of the above-described biaxially oriented laminated PEN film so that the coating thickness after drying is 0.5 μm, and then subjected to an orientation treatment in a DC magnetic field of 2500 gauss and heated at 100 ° C. After drying, it was rolled up by super calendering (linear pressure 200 kg / cm, temperature 80 ° C.). The wound roll was left in an oven at 55 ° C. for 3 days.

Further, a back coat layer paint having the following composition was applied to the surface B of the biaxially oriented laminated PEN film on which the magnetic layer was formed so that the thickness after drying was 1 μm, dried, and further 6.35 mm (= 1 ′ / 4) to obtain a magnetic tape.
Backcoat layer paint composition:
Carbon black 100 parts by weight Thermoplastic polyurethane resin 60 parts by weight Isocyanate compound 18 parts by weight (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.)
Silicone oil 0.5 parts by weight Methyl ethyl ketone 250 parts by weight Toluene 50 parts by weight Properties of the obtained biaxially oriented laminated polyester film and magnetic tape are shown in Table 1.

[Example 2]
Resin composition 1 is a resin composition 3 having a weight average molecular weight of 45,000 and PEN having a weight average molecular weight of 30000, which contains no inert particles, and a weight ratio of 25:75. Resin composition 2 has an average particle diameter of 0. Weight ratio of PEN having a weight average molecular weight of 45,000 and PEN having a weight average molecular weight of 30,000, containing 0.15% by weight of spherical silica particles having a size of 3 μm and 0.10% by weight of spherical silica particles having an average particle diameter of 0.1 μm The same operation as in Example 1 was repeated except that the resin composition 4 was changed to 25:75 and the thickness and the draw ratio of the polyester layer forming the surface A and the surface B were changed.
Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape.

[Example 3]
The resin composition 1 was changed to a resin composition 5 of PEN having a weight average molecular weight of 45000 containing 0.1% by weight of spherical silica particles having an average particle diameter of 0.1 μm, and the resin composition 2 was changed to an average particle diameter of 0 Weight ratio of PEN having a weight average molecular weight of 45,000 and PEN having a weight average molecular weight of 30,000, containing 0.15% by weight of spherical silica particles having a size of 3 μm and 0.1% by weight of spherical silica particles having an average particle diameter of 0.1 μm When changing to 40:60 resin composition 6 and drying, the same operation as in Example 1 was repeated except that the humidity-conditioned humid air was used and the draw ratio was changed.
Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape.

[Example 4]
Instead of the resin composition 1, a resin composition 7 in which the weight ratio of the PEN having a weight average molecular weight of 45,000 and the PEN having a weight average molecular weight of 30000 of the resin composition 1 is changed to 10:90 is used. Instead, the same operation as in Example 1 was used except that the resin composition 8 in which the weight ratio of the PEN having a weight average molecular weight of 45,000 and the PEN having a weight average molecular weight of 30000 of the resin composition 2 was changed to 10:90 was used. Was repeated.
Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape.

[Comparative Example 1]
Resin composition 9 in which the weight ratio of PEN having a weight average molecular weight of 45,000 and PEN having a weight average molecular weight of 30000 of resin composition 1 was changed to 0:10 was used instead of resin composition 1, and the weight of resin composition 2 Example 1 except that the resin composition 10 in which the weight ratio of PEN having an average molecular weight of 45000 and PEN having a weight average molecular weight of 30000 was changed to 0:10 was used instead of the resin composition 2 and the draw ratio was adjusted. Similar operations were repeated.
Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape.

[Comparative Example 2]
The resin composition 11 in which the weight ratio of the PEN having a weight average molecular weight of 45000 and the PEN having a weight average molecular weight of 30000 of the resin composition 1 is changed to 10: 0 is used instead of the resin composition 1, and the weight of the resin composition 2 is used. Example 1 except that the resin composition 12 in which the weight ratio of PEN having an average molecular weight of 45000 and PEN having a weight average molecular weight of 30000 was changed to 10: 0 was used instead of the resin composition 2 and the draw ratio was adjusted. Similar operations were repeated.
Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape.

[Comparative Example 3]
The same operation as in Example 2 was repeated except that the draw ratio was changed.
Table 1 shows the properties of the obtained biaxially oriented polyester film and magnetic tape.

Claims (5)

A laminated film consisting of at least two polyester layers, there weight average molecular weight of polyester constituting each layer in the range of 2 9 000-36000, in the longitudinal direction of the elastic modulus is more than 6.0 GPa, the width direction of the elastic modulus 4 A biaxially oriented laminated polyester film characterized by having a thickness of 0.0 GPa or more, an elastic modulus in the longitudinal direction equal to or greater than an elastic modulus in the width direction, and a film thickness in the range of 2 to 10 μm.   The biaxially oriented laminated polyester film according to claim 1, wherein the polyester is polyethylene-2,6-naphthalate.   The biaxial film according to claim 1, wherein one film surface has a center line surface roughness of 10 nm or less, and the other film surface has a center line surface roughness larger than that of one film surface and 5 to 30 nm. Oriented laminated polyester film.   The biaxially oriented laminated polyester film according to claim 1, which is used for a base film of a magnetic recording medium.   A magnetic recording medium comprising the biaxially oriented laminated polyester film according to claim 1 and a magnetic layer formed on one side thereof.