JPH0768726A - Biaxially oriented polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a biaxially oriented polyester film for a magnetic recording medium having excellent feeding stability, electromagnetic conversion characteristics and excellent high speed dubbing characteristics. CONSTITUTION:A polyester has at least two laminated layers by coextrusion in such a manner that a layer for forming at least one surface layer (polyester A layer) contains particles of 0.5-2.0wt.% and that, when totally integrated volume of the particles each having a particle size of 0.2mum or more is 100, the particles exist at a ratio that an integrated volume of the particles each having a particle size of 0.5-1.0mum is 50-90 and an integrated volume of the particles each having a particle size exceeding 1.0mum is 10 or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film for a magnetic recording medium, which has excellent running stability and electromagnetic conversion characteristics and is excellent in high speed dubbing.

[0002]

2. Description of the Related Art Conventionally, VTR tapes are recorded exclusively in a video recorder such as recording a TV program on a home VTR deck or photographing a person or a landscape with a handy VTR camera. It was mostly done in. In this case, the tape speed during recording (similarly during playback) is 3.335 cm / sec in the VHS system and 1.4 in the 8 mm video system.
The tape speed was 345 cm / sec, and even at the time of high-speed search (fast-forwarding / rewinding in the reproducing state), the tape speed was at most several times that.

However, in recent years, a recording method using a high-speed dubbing machine has been widely used in order to reduce the price of recorded video soft tapes. This high-speed dubbing machine currently uses a thermo-magnetic transfer recording method using a laser beam or a method of reversing a magnetic field by applying a bias magnetic field, but a recording speed (tape speed) of 4 is common to these. ~ 5m / sec, normal home VT
It is to be 100 times faster than the tape speed of the R deck. As a result, the price of recorded video soft tapes can be significantly reduced compared to the case of performing constant-speed dubbing.

At the time of this high-speed dubbing, due to the high tape speed, various problems that do not occur during constant-speed dubbing or during normal recording / playback on a home VTR occur. For example, when the tape runs on the transfer drum or the guide pin of the high-speed dubbing machine, it is necessary to sufficiently discharge the air existing between them and run the tape while completely adhering the air. If the air is not exhausted sufficiently, the tape travels in a floating state, and a phenomenon (abbreviated as tape meandering) in which the traveling position is not constant and the tape moves in an unstable manner can be seen. In a severe case, the traveling position largely moves and the end of the tape comes into contact with a transfer drum or a component that supports the guide pin, and the like, which often causes damage (abbreviated as tape edge damage).
Also, during the loading process of rewinding the high speed dubbed video pancake into a cassette, the tape speed is around 10 m / sec. In this case, the exhaustion of air existing between the VTR tapes becomes a problem, but this is insufficient. And the end faces of the rolls wound in the cassette become uneven (abbreviated as high-speed winding disorder), and in severe cases, tape edge damage may occur.

In order to solve such a problem, it is known that a magnetic recording medium based on a polyester film having a laminated structure is excellent in high-speed dubbing property (for example, Japanese Patent Laid-Open No. 2-77431). However, the main aim is to improve dubbing resistance to prevent a decrease in S / N ratio during dubbing and scratch resistance to prevent scratching of the tape during high-speed running, and to prevent tape meandering and tape edge damage, No solution was found. On the other hand, Japanese Examined Patent Publication (Kokoku) No. 4-68144 discloses that a laminated film having a high strength (F ₅ ) is preferable for preventing tape edge damage. Even if it was sufficient, the effect was insufficient with a high-speed dubbing machine with a tape speed of 4 m / sec or more.

[0006]

As a result of various studies, the present inventors have found that a biaxially oriented polyester film for a magnetic recording medium having a certain specific structure can solve the above problems. That is, the gist of the present invention is a polyester film in which at least two layers are laminated by coextrusion, and the layer (polyester A layer) constituting at least one surface layer thereof has a thickness of 0.5 to 2.0.
% Of particles, and 0.2 μm of the particles
When the total cumulative volume of particles having the above particle diameter is 100, the cumulative volume of particles having a particle diameter of 0.5 to 1.0 μm is 50 to 90, and the cumulative volume of particles having a particle diameter of more than 1.0 μm is It exists in a biaxially oriented polyester film for a magnetic recording medium, characterized in that it is present in a ratio such that the cumulative volume is 10 or less.

The present invention will be described in detail below. The biaxially oriented polyester film for magnetic recording media of the present invention has a structure in which at least two layers are laminated by coextrusion, and it is necessary that all the layers are uniformly biaxially oriented. Furthermore, it is necessary that at least one of the layers constituting the surface layer is a polyester A layer described later, and a layer adjacent thereto (hereinafter referred to as polyester B layer) is required. In this case, the laminated structure of the polyester film may be a two-layer structure of A / B, or an A / B in which an arbitrary C layer is provided as a layer constituting the surface opposite to the A layer.
It may be a laminated body of / C. Further, it may be an A / B / A in which the same composition as the A layer is laminated on both surfaces with the same thickness, or a laminate having a structure of A / B / A ′ in which only the thickness is different on the front and back sides.

The polyester constituting the layers A and B is preferably polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), but if it is 5 mol% or less, a third component such as terephthalic acid or isophthalic acid is used. , Phthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, aromatic dicarboxylic acid such as biphenyldicarboxylic acid, triethylene glycol, diethylene glycol, neopentyl glycol, glycol such as cyclohexanedimethanol, p-hydroxy A polyester obtained by copolymerizing an aromatic hydroxycarboxylic acid such as benzoic acid may be used.

The intrinsic viscosity of the polyester constituting the A layer and the B layer is 0.55 or more in consideration of continuity during film formation,
Further, it is preferably 0.60 or more. In particular, the polyester A layer has a higher intrinsic viscosity, which is more advantageous in terms of abrasion resistance, and is preferably 0.65 or more, and more preferably 0.70 or more.

The biaxially oriented polyester film for magnetic recording media of the present invention has a polyester A layer of 0.5 to 2.0.
% Of particles, and 0.2 μm of the particles
When the total cumulative volume of particles having the above particle diameter is 100, the cumulative volume of particles having a particle diameter of 0.5 to 1.0 μm is 50 to 90, and the cumulative volume of particles having a particle diameter of more than 1.0 μm is It is necessary that the total volume be 10 or less. The cumulative volume referred to here is that particles of 0.2 μm or more existing in the polyester A layer are classified by 0.1 μm according to the particle size, and one particle having the particle size is included in the number of particles in each classification. It is defined as the sum of the values multiplied by the volume of. That is, it is expressed by the following equation.

Σ {N _i · (4/3) · π (r _i / 2) ³ } (1) In the above equation, N _i is the number of particles counted for each classification, r _i
Indicates the median value of the particle diameter for each classification. At this time, in order to classify the particles by 0.1 μm according to the particle diameter, the average value of the short diameter and the long diameter of the particles is defined as the particle diameter.

In the present invention, the particles having a particle size of 0.2 μm or more present in the polyester A layer are not preferably monodisperse particles having a uniform particle size, and the particle size has a certain value. Need to have a distribution. That is, when the total cumulative volume of particles having a particle diameter of 0.2 μm or more is 100, the cumulative volume of particles having a particle diameter of 0.5 to 1.0 μm is 50 to 90, and preferably 60 to The cumulative volume of particles having a particle size of 80 or more than 1.0 μm is 10 or less, preferably 5 or less. Particles having a particle diameter of 0.5 to 1.0 μm existing in the polyester A layer are generated between the tape and the transfer drum or the guide pin, or between the VTR tape when the VTR tape is prepared with the polyester A layer as the running surface. It was found that the effect of discharging the existing air is very high, the tape meandering and the high-speed winding disturbance are less likely to occur, and moreover, the electromagnetic conversion characteristics are less likely to be deteriorated. Therefore, it is necessary to set a high proportion of particles having this particle size range, and it is necessary that the cumulative volume does not fall below 50. 1.0 μm
Particles having a particle diameter exceeding 10 are already saturated in the air discharging effect and tend to deteriorate the electromagnetic conversion characteristics, so that the existing ratio is 10 or less. Furthermore, 0.2-
Particles having a particle size of 0.5 μm have the property of forming many fine projections on the film surface, and these projections are mainly effective for improving the running property in a normal VTR deck, not during high-speed dubbing. Therefore, when the total cumulative volume of particles having a particle diameter of 0.2 μm or more is 100, it is preferable that the cumulative volume is about 10 to 50.

As the type of particles having a particle diameter of 0.2 μm or more in the polyester A layer, those conventionally known for blending base films can be used. That is, calcium carbonate, calcium phosphate, barium sulfate, titanium oxide, kaolin, talc, silica,
Examples thereof include crosslinked organic particles such as crosslinked polystyrene resin and crosslinked acrylic resin. Particularly, spherical or ellipsoidal particles are preferable because they are excellent in running property and electromagnetic conversion characteristics. Further, only one kind of these particles can be selected and used, but two or more kinds may be mixed and used. As the particles present in the polyester A layer, in addition to the particles having a particle diameter of 0.2 μm or more, particles having a particle diameter of less than 0.2 μm may be present. Particularly, the average primary particle size is 0.001 to 0.09 μm
The presence of at least one kind of particles selected from the group consisting of γ-alumina, δ-alumina, and θ-alumina in the range of 10 to 100% of the surface of the polyester A layer during high-speed dubbing or repeated reproduction of recorded soft tape. It is extremely preferable because it can improve abrasion and scratches.

In the polyester A layer of the biaxially oriented polyester film for magnetic recording media of the present invention, 0.5 to 2.
There should be 0% by weight of particles. This concentration is equal to that of particles having a particle diameter of 0.2 μm or more as described above.
Refers to the sum of particles having a particle size of less than μm. As a ratio of these particles, particles having a particle diameter of 0.2 μm or more are usually 0.5 to 1.9% by weight, preferably 0.5.
% To 1.2% by weight, usually 0.1 to 0.6% by weight of particles having a particle size of less than 0.2 μm, preferably 0.2 to
It is selected from the range of 0.5% by weight. Polyester A
When the amount of particles in the layer is less than 0.5% by weight, the effect of discharging the air existing between the polyester A surface and the transfer drum or guide pin or between the VTR tapes is small, and the tape meandering or high-speed winding disturbance is caused. Is likely to occur and, at the same time, the running performance in a normal VTR deck begins to deteriorate, which is not preferable. On the contrary, when the amount of particles in the polyester A layer exceeds 2.0% by weight, the effect of exhausting air is sufficient, but the deterioration of electromagnetic conversion characteristics becomes conspicuous.
After all it is not preferable.

The thickness of the polyester A layer of the biaxially oriented polyester film for magnetic recording media of the present invention is 0.5 to 3.
When the thickness is in the range of 0 μm, and more preferably in the range of 0.7 to 2.0 μm, the effect of the present invention is exhibited well, which is preferable. Polyester A
If the layer thickness is less than 0.5 μm, the particles added during high-speed dubbing will fall off, and the dropout tends to increase. Conversely, the thickness of the polyester A layer is 3.0 μm
If it exceeds, the effect of effectively discharging air and preventing the tape meandering may be reduced. When the laminated structure of the polyester film is A / B / A ′ described above, the thickness of the A ′ layer is not limited to this, and an arbitrary thickness can be adopted as long as it is thinner than the A layer.

The biaxially oriented polyester film for magnetic recording media of the present invention is required to have a polyester A layer satisfying the above-mentioned constitutional requirements laminated on at least one surface thereof. The surface to be treated preferably has the following characteristics. That is, when the surface of the polyester A layer is measured with a stylus type two-dimensional roughness meter, the center line average roughness Ra ^A is 7 to 25 nm, further 10 to 20 nm, and the ten-point average roughness Rz ^A is 180 to 330.
nm, further 200 to 300 nm, and 0.
Large protrusions having a height of 2 μm or more are preferably present at the following frequencies.

[0016]

[Table 1] Large protrusion height classification Frequency 0.2 to 0.3 μm 15 to 70 pcs / 25 mm 0.3 to 0.4 μm 3 to 20 pcs / 25 mm 0.4 to 0.5 μm 0 to 10 pcs / 25 mm 0 0.5 to 0.6 μm 0 to 5 mm / 25 mm 0.6 μm or more 0 mm / 25 mm

The frequency of the large protrusions is particularly important during high-speed dubbing where the tape speed is 4 to 5 m / sec and during the loading process where the tape speed is around 10 m / sec. These protrusions are too high protrusions from the viewpoint of conventional electromagnetic conversion characteristics, but since they are rare in existence as they are first found when observing the film surface over a wide area, the electromagnetic conversion characteristics are It is possible to effectively discharge the air without lowering it, and as a result, it is considered that the tape meandering and the high-speed winding disturbance can be prevented.

In the biaxially oriented polyester film for a magnetic recording medium of the present invention, polyester containing substantially no particles may be used in the polyester B layer, but the same particles as those present in the polyester A layer are diluted. It is also possible to use polyesters which are present in the specified form. Especially in the latter case, it is necessary to recycle the scraps generated in the film forming process, for example, the ears held by the tenter clips and the off-speech products as the raw material for the B layer, in order to reduce the cost of the film, or It is also a very preferable method from the viewpoint of reducing industrial waste. In addition, particles different from the polyester A layer can be present in the polyester B layer,
In any case, the amount of particles present in the polyester B layer is 1/3 or less, more preferably 1/5 or less of that of the polyester A layer, so that the electromagnetic conversion characteristics are not deteriorated, and tape meandering and high-speed winding disorder are caused. It is preferable in that

Further, the thickness of the layer B is preferably 1/2 or more of the total thickness of the polyester film from the viewpoint that the electromagnetic conversion characteristics are not deteriorated and that the tape meandering and the high speed winding disorder are prevented. The biaxially oriented polyester film for magnetic recording media of the present invention has a difference Δn between the refractive index in the width direction (n _TD ) and the refractive index in the longitudinal direction (n _MD ).
When (birefringence, n _TD −n _MD ) is 0.020 or more,
In particular, it has excellent cutting properties and is suitable as a base film for magnetic tape. The cuttability is a characteristic when the magnetic tape is slit by a shear cutter or the like, and when the cuttability is poor, the cut end may be curled up in a streak shape, or a whisker or powder may be generated from the cut end. When such a phenomenon occurs, white powder adheres to the VTR tape, deteriorating the electromagnetic conversion characteristics and inducing dropout. Δ above
n is preferably 0.030 or more, particularly preferably 0.
035 or more, and conversely, when Δn is extremely large,
The upper limit for Δn is 0.0
It is preferably 55.

The biaxially oriented polyester film for a magnetic recording medium of the present invention is preferable because the effect is most exerted when the polyester A surface is used as a running surface and a magnetic layer is provided on the opposite surface. When the polyester A layer is provided on both the front and back sides, the magnetic layer may be provided on either one of them. In the magnetic layer used for the magnetic recording medium, the main magnetic substance is preferably Co-containing γ-iron oxide or metallic iron, and these are preferably dispersed in the resin binder of the magnetic layer. Composition of resin binder and coating method thereof,
As the calendering method, known methods can be adopted.

On the surface of the film on which the magnetic layer is provided,
An undercoat layer may be provided for the purpose of enhancing the adhesiveness with the magnetic layer. For the undercoat layer, a polymer such as polyurethane, polyester, or acrylic is used as an aqueous dispersion, which is applied to a polyester film that has been longitudinally stretched, and then laterally stretched by a tenter. It is effective to apply by so-called in-line coating, in which drying and heat curing are simultaneously performed.

Next, the method for forming the polyester film which is the base material of the present invention will be described. The polyester A layer resin and the polyester B layer resin are separately dried as required, and then extruded by separate extruders and laminated by a feed block type coextrusion device before the die or a multi-manifold Using a co-extrusion device of the type, they are laminated in a spinneret to form an integral composite, and then melt-extruded into a sheet shape and cooled and solidified on a casting drum to form an unstretched film. At this time, it is preferable to perform cooling and solidification by using an electrostatic contact method in order to obtain the flatness of the film. For the extruder for layer A, use #
# 60 for B layer extruder with 1200 mesh or more
It is preferable to attach a filter corresponding to 0 mesh or more, and to extrude while performing filtration because coarse projections can be reduced and dropout can be reduced. Furthermore, it is preferable to install a static mixer and a metering pump in each melt line in order to obtain uniform film and film thickness.

The unstretched film thus obtained is biaxially stretched to be biaxially oriented. A so-called sequential biaxial stretching method in which longitudinal stretching and then transverse stretching are performed for stretching is preferable. For the longitudinal stretching, the stretching temperature is 50 to 180 ° C. and the stretching ratio is 2.
The conditions suitable for the composition of the polyester are selected from the range of 0 to 9.0 times. This stretching can be performed in one stage, but if the stretching temperature and the ratio are within the above ranges, the stretching may be performed in two or more stages so that the alumina particles in the polyester A layer are loosened in a good dispersion state. Is possible and preferable. At this time, the stretching temperature may be the same or different in each stage. The stretching speed for longitudinal stretching is 5000 to 500
The range of 000% / min is preferable in order to obtain a uniform film thickness. In addition, the in-line coating described above can be performed at the stage of the longitudinal stretching. As a stretching method in the width direction, a method using a tenter is preferable. For stretching in the width direction, a stretching temperature of 80 to 170 ° C., a stretching ratio of 3.0 to 6.0 times, a stretching ratio of 100 to 70,000.
A stretching rate of% / min is preferred.

Further, re-stretching can be carried out if necessary. This re-stretching can be carried out in any of the machine direction, the transverse direction and the machine direction, and can be selected from the range of the re-stretching ratio of 1.01 to 1.50 at a stretching temperature of 100 to 220 ° C. In particular, in order to improve the cutting property described above, when Δn is set to 0.020 to 0.055, achieving this by re-transverse stretching does not significantly change the projection shape on the film surface. This is preferable because it can be performed. Next, this stretched film is heat-set. In this case, the heat setting temperature is 170 to 250 ° C., preferably 180.
The heat shrinkage is preferably in the range of up to 230 ° C. and the heat setting time is in the range of 1 to 60 seconds. The heat shrinkage due to the heat treatment at 100 ° C. for 30 minutes is 1.0% or less in both the vertical and horizontal directions, and further 0 It is preferable to carry out so as to be 0.5% or less.

[0025]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. The methods for measuring the physical properties of the film in Examples and Comparative Examples are as follows.

Cumulative Volume of Particles The surface of the polyester A layer was treated with a plasma etching apparatus (Yamato Scientific Co., Ltd. Plasma Reactor PR-41 type).
Was used to perform etching in an argon atmosphere to expose the particles in the polyester A layer. This film was observed with a scanning electron microscope to find that it was 3000 to 10000.
The size of the particles was measured one by one by taking a photograph at a magnification of 2 times. The average value of the short diameter and the long diameter of the particles is selected as the particle diameter, and 500 or more particles having the particle diameter of 0.2 μm or more are selected and classified by 0.1 μm according to the particle diameter, and the number N _i of the particles in each classification is I counted. Further, using the median value r _i of the particle diameter of each classification, the integrated volume was calculated by the following formula.

Σ {N _i · (4/3) · π · (r _i / 2) ³ } (1) The cumulative volume of each particle size range is that of all particles of 0.2 μm or more observed. The ratio is shown when the total cumulative volume is 100.

Surface roughness (center line average roughness Ra, ten-point average roughness Rz) The surface roughness was measured according to the method described in JIS B0601-1976. For measurement, a surface roughness meter SE-3F made by Kosaka Laboratory Ltd.
Was used. The center line average roughness and the ten-point average roughness were determined under the conditions of a stylus diameter of 2 μm, a stylus load of 30 mg, a cutoff value of 0.08 mm, and a measurement length of 2.5 mm. This was performed at 12 measurement points, the maximum value and the minimum value were cut, respectively, and the average value of 10 points was calculated and set as Ra and Rz.

Large protrusion frequency The same device as that used for measuring the surface roughness, the measurement conditions were a stylus diameter of 2 μm, a stylus load of 30 mg, a cutoff value of 0.08 mm, and a measurement length of 25 mm. The number of protrusions having a height of 0.2 μm or more was recorded and classified from the chart, and the number was counted. This measurement was performed 10 times for each sample, and the average value was calculated for each classification to create a histogram. Thickness composition of each laminated part Embedded in resin so that the cross section in the thickness direction of the polyester film can be observed and fixed, a 100-nm-thick section is cut out using a microtome, Hitachi, Ltd. transmission electron The thickness composition of each laminated part was measured by observing with a microscope H-9000 (magnification: 10,000 to 20,000 times, accelerating voltage: 100 kV).

Birefringence (Δn) The refractive index in the width direction (n _TD ) and the refractive index in the longitudinal direction (n _MD ) of the film were measured using an Abbe refractometer manufactured by Atago Optical Co., Ltd., and the difference Δn (Birefringence, n _TD −n _MD ) was determined. Scratch resistance Hard chrome plated metal pin (diameter 6mm, surface roughness 0.2S) fixed on the diamagnetic layer surface (A surface) of the VTR tape
And was rubbed once with a tension of 50 g, a winding angle of 135 °, and a tape speed of 4 m / sec. Aluminum was vapor-deposited on the rubbed surface of this sample tape to a thickness of 1000 Å, the amount of scratches was visually determined, and evaluated according to the following five-stage criteria. 1. Extremely large number of scratches 2. A lot of scratches 3. The amount of scratches is 2. And 4. Intermediate 4. Small amount of scratches 5. Not scratched

Electromagnetic conversion characteristics On one polyester A surface of a film sample, a magnetic coating composition having the following composition was mixed and dispersed by a ball mill for 24 hours and then applied by a gravure roll.

[Table 2] Co-containing iron oxide (BET 50 m ² / g): 100 (parts by weight) Polyurethane resin: 10 Nitrocellulose: 5 Vinyl chloride / vinyl acetate copolymer: 10 Lecithin: 2 Polyisocyanate: 5 Carbon black: 2 Methyl ethyl ketone: 75 Methyl butyl ketone: 75 Toluene: 75

Before the paint was sufficiently dried and solidified, it was magnetically oriented and then dried to form a magnetic layer. Further, this coated film was subjected to a spar calendering treatment at a temperature of 70 ° C., a linear pressure of 200 Kg / cm, and a number of steps of 5 and then wound up at 70 ° C.,
Curing was performed for 48 hours. The thickness of the magnetic layer at this time was 5 μm. Slit this 1/2 inch wide,
A video pancake wound on a reel with a length of 5000 m, and cut into a length of 250 m and then incorporated into a case to prepare a VTR cassette. VTR deck (Matsushita Electric Industrial Co., Ltd. NV-820)
0) and color video noise meter (Shibasoku Co., Ltd.)
CS / N was measured. The evaluation is based on the relative value (d
It is represented by B).

A high-speed dubbing machine (SO
It was incorporated into NY Co., Ltd. HSP5000C), the test signal was mirror-inverted and the mirror mother tape recorded and set so that the magnetic layers were aligned, and high-speed dubbing was performed at a tape speed of 4.5 m / sec. At this time, the tape running position on the transfer drum and the guide pin was observed to check whether or not the tape moved. The evaluation used the following criteria. Rank A The traveling position does not move at all, and it travels at a fixed position from the beginning to the end Rank B An intermediate position between Rank A and Rank C A movement of the traveling position can be seen, but the range of movement is small Rank D Rank C Intermediate rank of E E The traveling position is large and moves in an unstable manner.

The video pancake produced by the high-speed winding disorder in the loading process is transferred to the high-speed video tape winding device (SONY XENON loader TL).
-1215 VC) was used to wind up on the cassette reel. At this time, 3 hours of VHS 2 hours tape (about 250 m)
The winding speed was 0 second, and the uniformity of the end surface of the VTR tape wound on the reel was evaluated according to the following criteria. Rank A End faces are extremely evenly aligned. Rank B End face is partially uneven. Rank C End face is often uneven and uneven. Rank D End face is uneven and not at all. Rank E End face is uneven and not at all. Not aligned, some edges of the tape are frilled Intrinsic viscosity 1 g of polymer is phenol / tetrachloroethane = 50
Dissolve in 100 ml of 50/50 (weight ratio) mixed solvent,
It was measured at ° C.

Examples 1 to 3 and Comparative Examples 1 to 3 <Production of Polyester Resin> 100 parts of dimethyl terephthalate, 65 parts of ethylene glycol and 0.09 part of magnesium acetate are placed in a reactor, heated and heated, and methanol is distilled off. While carrying out the transesterification reaction.
It took about 4 hours after the start of the reaction and the temperature was raised to 230 ° C. to substantially end the transesterification reaction. Here below Table-1
The particles shown in 2 and 2 were treated with ethylene glycol slurry.
Ethyl acid phosphate 0.4
Parts, and 0.04 parts of antimony trioxide were added, and then the temperature of the reaction system was gradually reduced from atmospheric pressure to finally set the temperature to 1 mmHg. After 4 hours, the system was returned to normal pressure and the intrinsic viscosity was 0.7.
5 polyester resin was obtained. Further, as a polyester resin for dilution, a resin which was polymerized in the same manner as above except that ethylene glycol slurry of particles was not added in the above resin production was also prepared (intrinsic viscosity 0.6
2).

<Production of Polyester Film> As a raw material for the polyester A layer, a resin containing each particle shown in Tables 1 and 2 was used, and as a raw material for the polyester B layer,
Pelletized film scraps and diluting resin are mixed, and the particle concentration is 1/1 of that of polyester A layer.
The one set to 0 was used. Each of these resins was separately dried at 180 ° C. for 4 hours, and then subjected to a three-layer coextrusion device, and melt-extruded at an extrusion temperature of 290 ° C. At this time, for the layer A, a B mesh equivalent to # 2000 mesh is used.
For layers, it is filtered with a filter equivalent to # 1200 mesh, and then A / B /
They were combined and laminated so that the laminated structure of A was obtained. Further, it was extruded in a sheet form from a die and cooled and solidified on a casting roll at 30 ° C. while using the electrostatic adhesion method to obtain an unstretched sheet having a three-layer structure. At this time, the discharge rate of each extruder was adjusted so that the layer A had the thicknesses shown in Tables 1 and 2.

Next, this unstretched sheet was stretched at 113 ° C. in the length direction by 2.9 times, and further stretched at 102 ° C. by 1.1 times. A roll stretching method was used for this stretching. Here, a coating solution in which sulfonylisophthalic acid-modified polyethylene terephthalate was dispersed in water was coated on one side A so as to have a thickness of 0.05 μm by drying after biaxial stretching. The film is then introduced into a tenter and 4.1 at 108 ° C.
The film was stretched in the widthwise direction, the film temperature was once lowered to 60 ° C., and then stretched again at 140 ° C. in the widthwise direction 1.05 times. After that, heat setting was performed at 215 ° C. for 15 seconds to obtain a biaxially oriented film having a total thickness of 15 μm. The birefringence of the obtained film was 0.040. The characteristics of these films when used as a magnetic recording medium are shown in Tables 3 and 4 below.

[0037]

[Table 3]

[0038]

[Table 4] Table-2

[0039]

[Table 5]

[0040]

[Table 6]

In Examples 1 to 3, since the cumulative volume of particles having a particle diameter of 0.5 to 1.0 μm in the polyester A layer exceeded 50 in any case, meandering and loading during high speed dubbing were performed. A magnetic recording medium has been obtained which has less disturbance of high-speed winding in the process and has excellent electromagnetic conversion characteristics. In Comparative Example 1, since the cumulative volume of the particles having the particle diameter of 0.5 to 1.0 μm is less than 50, the electromagnetic conversion characteristics are good, but the meandering during the high speed dubbing and the high speed winding disturbance in the loading process occur. It will be easy. In Comparative Example 2, although the cumulative volume of the particles having the particle diameter of 0.5 to 1.0 μm exceeds 50, 1.
The cumulative volume of particles having a particle size of more than 0 μm exceeds 10, and electromagnetic conversion characteristics are deteriorated. Comparative Example 3
In the same manner as in Comparative Example 1, since the cumulative volume of the particles having the particle diameter of 0.5 to 1.0 μm is less than 50, the electromagnetic conversion characteristics are good, but the meandering speed during high-speed dubbing and the high speed in the loading process are high. It becomes easy to cause winding disorder.

[0042]

In the biaxially oriented polyester film for magnetic recording media of the present invention, the frequency of the large protrusions formed on the surface layer is in a preferable range by setting the particle size distribution of the particles existing on the surface layer within a certain range. It is what As a result, when a VTR tape is produced using the polyester film of the present invention, it has a feature that it is possible to effectively reduce the meandering / rapid winding disturbance in the high-speed dubbing and loading process without deteriorating the electromagnetic conversion characteristics. is doing. Therefore, it is possible to supply a very useful base film not only for the unrecorded blank VTR tape but also for the recorded VTR tape for software, and its industrial value is high.

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Claims (2)

[Claims] 1. A polyester film in which at least two layers are laminated by coextrusion, and the layer (polyester A layer) constituting at least one surface layer of the polyester film is 0.1.
The total cumulative volume of particles containing 5 to 2.0% by weight and having a particle diameter of 0.2 μm or more is 1
00, the cumulative volume of particles having a particle diameter of 0.5 to 1.0 μm is 50 to 90, and the cumulative volume of particles having a particle diameter of more than 1.0 μm is 10 or less. A biaxially oriented polyester film for a magnetic recording medium, which is characterized by: 2. The average primary particle size of 0.001 to 0.6% by weight of the particles present in the polyester A layer is 0.001.
The biaxial orientation for a magnetic recording medium according to claim 1, wherein the particles are at least one kind of particles selected from the group of γ-alumina, δ-alumina, and θ-alumina in the range of 0.09 μm to 0.09 μm. Polyester film.