JPH03209619A - Base film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve scratching resistance, dubbing resistance and drop-out characteristics by specifying the thickness of a biaxially oriented polyester film, the relation between the diameter of particles and the thickness of the film, the content of the particles, etc. CONSTITUTION:The base film for magnetic recording media consists of the biaxially oriented polyester film formed by laminating a film essentially consisting of the polyester A and the particles on a film essentially consisting of the polyester B. The thickness of the laminated film of the polyester A is 0.005 to 3mum, the average grain size of the particles contained in the laminated film is 0.1 to 10 times the thickness of the laminated film and the content in the laminated film is 2 to 50wt.%. Further, the content of low molecular component in the entire part of a biaxially oriented polyester film is <=1%. The improvement in the scratching resistance, dubbing resistance and drop-out characteristic is not possible if these ranges are exceeded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a base film for a magnetic recording medium made of a biaxially oriented polyester film, and in particular, as a base film for a magnetic recording medium, it is possible to improve the surface characteristics as well as the characteristics of the film as a whole. This invention relates to a film with a laminated structure that is improved.

[Prior Art] As a biaxially oriented polyester film for use as a base film for magnetic recording media with improved surface characteristics, a film is known in which polyester contains substantially spherical silica particles derived from colloidal silica. (For example, Japanese Patent Laid-Open No. 171623/1983).

In such a biaxially oriented polyester film,
The contained silica particles form protrusions on the film surface, lowering the coefficient of friction on the surface and improving handling and running properties, as well as improving the adhesion of the magnetic layer in magnetic recording media applications. It is possible.

On the other hand, although the film does not contain particles as described above, in order to improve the dropout characteristics of magnetic tape, the precipitation of low molecular weight substances on the film surface of a biaxially oriented polyester film is A technique is known that suppresses this by preparing the
27980).

[Problems to be Solved by the Invention] However, in the biaxially oriented polyester film disclosed in JP-A-59-171623, the contained silica particles are randomly distributed over the entire thickness direction of the film. There is a limit to the increase in the density of protrusions on the surface due to particles contained therein, and the height of the protrusions also varies considerably at random. Recently, problems have started to be pointed out due to the non-uniform height of the protrusions and the low density of the protrusions.

If the height of the protrusions on the film surface is uneven, the high protrusions are likely to be scraped, and as the processing speed of the film increases, such as the magnetic layer coating and calendering process in magnetic recording media applications, Recently, the disadvantage that the film surface is scratched by the contacting rolls has been improved.
This is becoming a problem.

In addition, magnetic recording media, especially video tapes, have recently been often used for software (recording and fixing produced video works on packaged media, copying and increasing them), but 1. In this case, with the conventional film-based videotape mentioned above, when dubbing (copying) from a master tape at high speed in the process of recording a video work,
A problem has also arisen in which the decrease in N (signal/'noise ratio, a parameter of image quality) is large, resulting in poor image quality.

Furthermore, if the protrusion density on the film surface is low, the effect of improving the slipperiness of the film surface will be low, and the expected effects of improving handling and running properties will not be obtained.

On the other hand, in the film disclosed in Japanese Patent Publication No. 62-27980, although precipitation of intrinsic viscosity on the film surface is suppressed to some extent, the film surface morphology is not appropriate;
The dropout reduction effect when suppressing the precipitation of low molecular weight substances is insufficient, and the characteristics of preventing scratches on the film surface and suppressing the decrease in S/'N during dubbing are insufficient. Basically not.

In view of the limitations of conventional films as described above, the present invention forms protrusions of high density and uniform height on the surface of a biaxially oriented polyester film to improve the surface scratch resistance (hereinafter referred to as scratch resistance). The aim is to improve image quality (S/'N) and prevent deterioration of image quality (S/'N> due to dubbing in magnetic recording media applications (hereinafter referred to as dubbing resistance). At the same time, it also suppresses the precipitation of low molecular weight substances on the film surface and suppresses the precipitation of small amounts of precipitation. The purpose of this invention is to improve dropout characteristics in magnetic recording media applications by allowing precipitates to exist in the irregularities of the unique surface morphology even when substances are present on the surface.

[Means for Solving the Problems] The base film for a magnetic recording medium of the present invention which meets this objective is obtained by laminating a film mainly composed of polyester A and particles on at least one side of a film mainly composed of polyester B. Consisting of biaxially oriented polyester film,
The thickness of the polyester A laminated film is 0.005
~3 μm1 The average particle size of the particles contained in the laminated film is 9.1 to 10 times the thickness of the laminated film, the content of the particles in the laminated film is 2 to 50% by weight, and The axially oriented polyester film has a total low molecular weight content of 1.0% or less.

In addition, the above object is achieved by the following (2), (3), and (4) according to the present invention.
)(5)(6)(7)(8) This can also be achieved by the base film for magnetic recording media.

(2) Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, the surface of the polyester A laminated film formed by the particles is The average height of the protrusions is 1/4 of the average particle size of the particles.
A base film for a magnetic recording medium having the above properties and characterized in that the content of low molecular weight substances in the entire biaxially oriented polyester film is 1.0% or less.

(3) Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, the surface of the laminated film of polyester A formed by the particles is Regarding the protrusions, the number of protrusions with a height of 1/3 or less of the average particle diameter of the particles is 70% or less of the total number of protrusions, and the low molecular weight substance content of the entire biaxially oriented polyester film is 1.0%. A base film for magnetic recording media characterized by the following:

(4) Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, the surface of the laminated film of polyester A formed by the particles is A base film for a magnetic recording medium, characterized in that the relative standard deviation of the height distribution of protrusions is 0.6 or less, and the content of low molecular weight substances in the entire biaxially oriented polyester film is 1.0% or less. .

(5) Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, and the thickness of the laminated film of polyester A is 0.00.
5 to 3 μm, the average particle size of the particles contained in the laminated film is 0.1 to 10 times the thickness of the laminated film, and the content of the particles in the laminated film is 2 to 50% by weight, and , the intrinsic viscosity of the entire biaxially oriented polyester film is 0.
．． 7 (1!/7 or more).

(6) Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, the surface of the laminated film of polyester A formed by the particles is The average height of the protrusions is 1/4 of the average particle size of the particles.
A base film for a magnetic recording medium having the above characteristics and having an inherent viscosity of the entire biaxially oriented polyester film of 0.7 d1/g or more.

(7) Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, the surface of the polyester A laminated film formed by the particles is Regarding the protrusions, the number of protrusions with a height of 1/3 or less of the average particle diameter of the particles is 70% or less of the total number of protrusions, and the intrinsic viscosity of the entire biaxially oriented polyester film is 0.
A base film for a magnetic recording medium, characterized in that it has a resistance of 7 dA/'J or more.

(8) Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B, the surface of the laminated film of polyester A formed by the particles is A base film for a magnetic recording medium, characterized in that the relative standard deviation of the height distribution of protrusions is 0.6 or less, and the inherent viscosity of the biaxially oriented polyester film as a whole is 0.7 dA/g or more.

In base films for magnetic recording media made of these biaxially oriented polyester films, protrusions with high density and uniform height are formed on the surface by particles containing the polyester film A layer, which improves scratch resistance and magnetic tape applications. By keeping the low molecular weight substance content or intrinsic viscosity of the entire biaxially oriented polyester film within the above specified range, the dubbing resistance of the biaxially oriented polyester film can be improved to prevent precipitation of low molecular weight substances from the base film when used as a magnetic recording medium. Dropout characteristics are improved.

The polyester A used in the present invention is not particularly limited, but in particular, ethylene terephthalate, ethylene α
, β-dis(2-chlorophenoxy)ethane-4,4°
- When the main constituent is at least one structural unit selected from dicarboxylate and ethylene 2,6 naphthalate units, the formation of surface protrusions, scratch resistance, and dubbing resistance in magnetic tape applications are improved. This is desirable because it gives good results. Further, it is extremely desirable that the polyester constituting the present invention be crystalline, since this provides even better scratch resistance and dubbing resistance.

Crystallinity here indicates that it is not so-called amorphous, and quantitatively, the cold crystallization temperature TCC in the crystallization parameter is detected, and the crystallization parameter △
Tcg is 150°C or less.

Further, it is extremely desirable that the crystallinity is 7.5 cal/g or more (change in enthalpy of fusion) as measured by a differential scanning calorimeter because transparency and scratch resistance will be even better. In addition, polyester containing ethylene terephthalate as a main component is particularly desirable because it provides better scratch resistance on the film surface and better dubbing resistance in magnetic tape applications. Note that two or more types of polyesters may be mixed or a copolymer may be used within a range that does not impede the present invention.

The shape of the particles in the polyester A of the present invention is not particularly limited, but the particle size ratio in the film (particle length/breadth axis)
In the case of particles with a diameter of 1.0 to 1.3, especially spherical particles, the height of the protrusions formed on the surface can be easily made uniform and the density can be increased easily, so that scratch resistance and dubbing resistance are improved. can be greatly increased.

Further, when the particles in the polyester A of the present invention have a single particle index in the film of 0.7 or more, preferably 0.9 or more, protrusions of uniform height are likely to be formed, and the film surface is This is particularly desirable since it provides even better scratch resistance and dubbing resistance.

The type of particles in the polyester A of the present invention is not particularly limited, but in order to satisfy the above-mentioned preferable particle characteristics, preferred particles include substantially spherical silica particles derived from colloidal silica, particles made of crosslinked polymers (e.g. cross-linked polystyrene). In particular, crosslinked polymer particles with a high degree of crosslinking until the temperature at 10% weight loss (measured in nitrogen using a thermogravimetric analyzer Shimadzu TG-30M, heating rate 20°C/min) is 380°C or higher. is particularly desirable. In the case of spherical silica derived from colloidal silica, substantially spherical silica with a low sodium content produced by an alkoxide method is particularly desirable. However, other particles, such as particles of calcium carbonate, titanium dioxide, alumina, etc., can also be used satisfactorily with proper control of film thickness and average particle size.

The thickness of the film layer mainly composed of polyester A of the present invention is 0.005 to 3 μm, preferably 0.01 to 1 μm.
, more preferably 0.03 to 0.5 m.

If the film thickness is smaller than the above range, the durability and scratch resistance of the laminated film layer cannot be ensured.
On the other hand, if it is too large, it becomes difficult to form surface protrusions of appropriate height at a high density due to the relationship with the contained particles.

Furthermore, regarding the size of the particles in the present invention, the average particle size in the laminated film containing the particles is 0.1 to 10 times, preferably 0.5 to 5 times, more preferably 0.5 to 5 times the thickness of the laminated film. The range is 1.1 to 3 times.

If the average particle size/laminated film thickness ratio is smaller than the above range, the height of the protrusions formed on the surface will be uneven, resulting in poor scratch resistance and dubbing resistance; This is not preferable because the formed surface protrusions are likely to be scraped off, resulting in poor scratch resistance.

Further, the average particle size (diameter) of the particles in polyester A in the film is 0.005 to 3 μm, preferably 0.02 μm.
Scratch resistance in the range of ~0.45 μm;
This is desirable because the dubbing resistance becomes even better.

Such particles are contained in the polyester A film in an amount of 2 to 50% by weight, preferably 3 to 30% by weight, more preferably 3 to 20% by weight.

If it is smaller than this, the film surface protrusion formation density will be too low, making it impossible to obtain good scratch resistance and dubbing resistance.On the other hand, if it is too high, the proportion of particles will be too high, and the laminated film layer itself will become brittle. If it becomes too much, the dropout characteristics will be poor, which is not preferable.

Further, the average height of the protrusions on the surface of the polyester A laminated film layer formed by the particles is 1/4 or more of the average particle diameter of the particles. Surface protrusions having such an average height can be obtained by appropriately selecting and setting the average particle size of the contained particles with respect to the thickness of the laminated film from the above-mentioned range.

Alternatively, regarding the protrusions on the surface of the polyester A laminated film formed by the particles, the number of protrusions having a height of 1/3 or less of the average particle diameter of the particles is suppressed to 70% or less of the total number of protrusions. In other words, the number of protrusions that are too low in height, in other words, protrusions that have a low effect of improving scratch resistance and dubbing resistance, can be prevented from becoming too large.

Furthermore, polyester A formed by the above particles
The relative standard deviation of the height distribution of protrusions on the surface of the laminated film is 0.6 or less, preferably 0.55 or less, and more preferably 0.5 or less. In other words, by forming protrusions of uniform height, scratch resistance and dubbing resistance are effectively improved.

That is, the laminated film layer of the biaxially oriented polyester film in the present invention contains particles having an average particle diameter near or larger than the thickness of the film layer. In other words, the ultra-thin laminated film contains microparticles with an average particle size close to or larger than the thickness of the film. Once this is done, particles can be distributed in the thickness direction of the entire biaxially oriented polyester film, concentrating substantially only on the laminated film layer. As a result, the density of particles applied to the laminated film can be easily increased, and the density of protrusions on the film surface formed by the particles can also be easily increased.

Furthermore, by containing the particles in the laminated film, the positions of the particles are regulated in the thickness direction of the entire biaxially oriented polyester film, and the thickness and average particle diameter of the laminated film are different from those mentioned above. Because of this relationship, the height of the surface protrusions formed by the particles becomes extremely uniform. Therefore, the scratch resistance of the surface of this laminated film is maintained high, and the dubbing resistance in magnetic tape applications is improved.

A film containing such polyester A and particles as main components is laminated onto a film containing polyester B as main components.

Polyester B is made of the same material as polyester A described above, and polyester B and polyester A may be of the same type or different.

The polyester A film layer is laminated on both sides or one side of the polyester B film layer. In other words,
This is the case when the laminated structure is A y' B / A, A /' B, but of course, it is also possible to use Δ/' B / C, where a 0 layer with a different surface state from A is provided on the opposite side of A, or even more. It may also have a multilayer structure. (Here, A, B
, C may be of the same type or different types.

Further, at least one surface needs to be the A layer. When providing a magnetic layer, it is preferable to provide it on the B layer in the case of an A/B configuration, or on the smooth side in the case of the A/'B/C configuration. ) Polyester B is also preferably a crystalline polymer, especially crystallinity parameter △Tcg or 20~
When the temperature is in the range of 100°C, the scratch resistance etc. of the film surface of the polyester B become even better, so it is desirable. Specific examples include ethylene terephthalate, ethylene α, β-bis(2-chlorophenoxy)ethane-4,
It is desirable to use at least one type of structural unit selected from 4'-dicarboxylate and ethylene 2,6-naphthalate units as the main constituent because the scratch resistance is particularly good. However, within the scope that does not impede the present invention,
The crystal component may be copolymerized within a range that does not impair the desired crystallinity, preferably within 5 mol%.

Polyester B of the present invention may also be blended with other types of polymers within the range that does not impede the purpose of the present invention, and may also contain organic additives such as antioxidants, heat stabilizers, lubricants, and ultraviolet absorbers. It may be added to the extent that it is normally added.

It is not particularly necessary to contain particles in the film mainly composed of polyester B, but when this film layer forms one side of the base film, the average particle size is 0.007~
2t1m, especially 0.02-0.45 μm particles or very small amounts, e.g. 0.001-0.2% by weight, especially 0.00
If the content is 5 to 0.15% by weight, or even 0.005 to 0.12% by weight, it will cause problems in processing and use.
This is extremely desirable because it not only improves the friction coefficient and scratch resistance but also improves the winding appearance of the film. As for the types of particles contained, it is desirable to use those preferably used for polyester A. The types and sizes of particles contained in polyesters A and B may be the same or different.

Polyester A containing the above particles and polyester B are laminated by coextrusion, formed into a sheet, and then biaxially stretched to obtain a biaxially oriented polyester film. Lamination by coextrusion in the present invention refers to extruding polyester A containing particles and polyester B using different extrusion devices, and laminating them before extruding laminated sheet i from a die. This lamination is
Forming and dispensing one sheet into a single sheet may be carried out in the nozzle (for example, a manifold), but since the laminated film layer is extremely thin as shown in (a) above, it should be carried out within the polymer tube before introducing it into the nozzle. Or preferable. In particular, it is particularly preferable to form the laminated portion within the polymer tube into a rectangular shape, since this allows uniform lamination in the width direction. The molten polymer laminated in the rectangular lamination section inside the polymer tube is expanded to a predetermined width in the sheet width direction in the manifold in the nozzle, and then discharged from the nozzle in the form of a sheet.
Biaxially stretched. Therefore, even if the laminated film layer after biaxial orientation is extremely thin, the particle-containing polyester polymer will be laminated to a considerable thickness in the rectangular laminated section inside the polymer tube, making it easy and precise to laminate the layer. can.

In the base film for magnetic recording media made of the biaxially oriented polyester film of the present invention having a laminated structure as described above, the content of low molecular weight substances (for example, nanatsuma, oligomer) in the entire film is 1.0% or less, Preferably it is 0.8% or less.

By keeping the low molecular weight content low in this way,
When used as a magnetic recording medium, the amount of low molecular weight substances that tend to precipitate from the base film side to the magnetic surface side is suppressed to an extremely low level from the beginning, and dropout reduction is suppressed. In the film of the present invention, as mentioned above, a thin polyester A layer is laminated on the eight polyester layers, and this polyester A layer contains particles in a concentrated manner and has a dense structure. , polyester A
The layer itself plays a role in preventing the precipitation of low-molecular weight substances from inside the film, thereby suppressing the dropout of the layer.

Further, in the base film for magnetic recording media of the present invention, the inherent viscosity of the entire film is 0°7d/'9
Above, preferably 0.75 to 0.96 ρ/'9. By having such a high intrinsic viscosity, the entire film has a dense structure, and even if some low molecular weight substances are contained inside the film, the low molecular weight substances migrate to the film surface. It becomes difficult to precipitate,
Dropout reduction in magnetic recording media applications can be suppressed.

Furthermore, by increasing the intrinsic viscosity, the film becomes less likely to tear during biaxial stretching, and the stability of film formation is greatly improved.

In addition, in the base film for magnetic recording media made of the biaxially oriented polyester film of the present invention, the particle concentration ratio of the particles in the surface layer on the side of the laminated film containing particles is 0.1.
It is preferable that it is below.

As shown in the measurement method described below, this surface layer particle concentration ratio indicates how much the particles forming the film surface protrusions are covered with a thin film of polyester A on the film surface, and the particles are substantially on the film surface. The higher the degree of direct exposure, the higher the surface layer particle concentration ratio, and the higher the degree to which surface protrusions are formed, but the surface layer particles are covered with a thin film of polyester A, the lower the surface layer particle concentration ratio. Because the particles forming the protrusions are covered with a thin film of polyester A, even if the particles are distributed at a high density in the ultra-thin laminated film layer, the particles will be covered with a thin film of polyester B.
It will be firmly held by the base film layer. Therefore, by controlling the surface layer particle concentration ratio to the above value or less, particles are prevented from falling off, and the scratch resistance and dubbing resistance of the film surface are maintained at high levels. Such surface particles I! This ratio can be achieved by laminating by coextrusion. Incidentally, also by the coating method, a resin layer is coated with an extremely thin thickness on a film having surface protrusions with a density similar to that of the present invention, that is, polyester B, and particles are contained in the resin layer. Although this is possible, the surface layer particle concentration ratio becomes extremely high (that is, the degree to which the particles are substantially directly exposed to the surface becomes extremely high), and only a film with an extremely brittle surface is obtained compared to the film of the present invention.

Next, a method for manufacturing the base film for magnetic recording media of the present invention will be explained.

First, as a method for incorporating particles into polyester A, it is possible to incorporate particles into the polymer after, during, or before polymerization, but the method of kneading particles into the polymer using a vent-type twin-screw presser is the method within the scope of the present invention. It is effective to obtain a film of

In addition, a method for adjusting the particle content is to prepare a high-concentration master using the above method, and then dilute it with polyester that does not substantially contain particles during film formation to adjust the particle content. This is effective in obtaining a film having a surface morphology within the range of the present invention. Furthermore, a method in which the melt viscosity, copolymerization components, etc. of this particle-high concentration master polymer are adjusted so that its crystallization parameter ΔTC9 is in the range of 30 to 80°C does not cause stretching breakage, and the surface morphology within the scope of the present invention can be obtained. Must be effective for obtaining film.

After the pellet A containing particles is sufficiently dried, it is supplied to a known melt extruder and melted at a temperature above the melting point of the polyester and below the decomposition point, and the other polyester B (type (which may be the same as or different from the polyester containing the particles) is fed to the laminating apparatus as described above, extruded from a slit die into a sheet, cooled and solidified on a casting roll, and then cooled and solidified on a casting roll. Make stretched film. i.e. 2 or 3
These polyester polymers are laminated using a stand extruder, 2 or 3 merging block or die.

When using the confluence block method, the laminated portion should be rectangular as described above, and the difference in melt viscosity (absolute value) of both polyesters should be in the range of O to 2000 poise, preferably O to 1000 poise. It is effective for industrially producing films with a surface morphology within a range of stability and without unevenness in the width direction.

Next, this multilayer unstretched film is biaxially stretched and biaxially oriented. The biaxial stretching method may be either a simultaneous biaxial stretching method or a sequential biaxial stretching method, but in the case of a sequential biaxial stretching method in which the film is stretched in the longitudinal direction and then in the width direction, the film having the surface morphology within the range of the present invention is stabilized. Therefore, it is effective for industrial production without unevenness in the width direction. In the case of sequential biaxial stretching, the stretching in the longitudinal direction is divided into three stages, especially four or more stages, and the stretching is carried out in a range of 40 to 150'.
C and a stretching speed of 1,000 to 50,000%/min and stretching 3 to 6 times is effective for obtaining a film having a surface morphology within the range of the present invention. The stretching temperature and speed in the width direction are 80-170'C11000-2000
A range of 0%/min is suitable. The stretching ratio is preferably 3 to 10 times. Further, if necessary, the film may be further stretched in at least one direction of the longitudinal direction and the width direction.

In any case, the key point of the present invention is to provide an extremely thin layer containing particles and then stretch the layer to an area stretching ratio (longitudinal magnification x width direction magnification) of 9 times or more. Next, this stretched film is heat treated. In this case, the heat treatment conditions are 140 to 280' C1, preferably 16
A heating time of 0.5 to 60 seconds in the range of 0 to 220° C. is suitable, or it is desirable to use microwave heating in combination with the heat treatment because it becomes easier to obtain a film having a surface morphology within the range of the present invention.

The manufacturing method of the film of the present invention is characterized by using a highly concentrated particle polymer having a specific range of thermal properties prepared by a special method.
It is a method of biaxially stretching a film after providing an extremely thin layer containing particles, and a method in which the film is uniaxially stretched during the film forming process, then coated, etc. and further stretched, or a biaxially stretched film] The performance of the laminated film produced by the above-mentioned method is not far superior to that of the film of the present invention, and the film of the present invention is also superior in terms of cost.

[Method of Measuring Physical Properties and Evaluating Effects] The methods of measuring the characteristic values and evaluating the effects of the present invention are as follows.

(1) Average Particle Size of Particles Polyester is removed from the film surface using a plasma low-temperature ashing process (for example, Model PR-503 manufactured by Yamato Scientific Co., Ltd.) to expose the particles. The processing conditions are selected so that the polyester is incinerated but the particles are not damaged. This was observed with a SEM (scanning electron microscope), and an image of the particles (
The shading of light created by particles) is measured using an image analyzer (for example, the Cambridge Instrument 0-cho M90).
0 ), measure the number of particles, change the observation location, perform the following numerical processing when the number of particles is 5000 or more, and use the average diameter determined thereby as the average particle diameter.

D-ΣDi,’N Here, Di is the circular diameter of the particle, and N is the number of particles.

(2) Particle content A solvent is selected that dissolves the polyester but does not dissolve the particles, centrifuges the particles from the polyester, and defines the particle content as the ratio (% by weight) to the total weight of the particles. In some cases, infrared spectroscopy may also be effective.

(3) Glass transition point Tg, cold crystallization temperature TCC1 crystallization parameter ΔTCg, melting point Measured using a DSC (differential scanning calorimeter) model 2 manufactured by Perxielmer. The DSC measurement conditions are as follows. That is, the sample 1101r1 is set in a DSC device, melted at a temperature of 300° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. This rapidly cooled sample is heated at a rate of 10° C./min, and the glass transition point Tg is detected. Continuing to gradually raise the temperature, the temperature reaches the cold crystallization temperature Tc when the exothermic peak temperature of crystallization from the glass state is reached.
c. The temperature was continued to rise gradually, and the melting peak temperature was taken as the melting point. Further, the difference between Tcc and Tg (TCC-Tg) is defined as a crystallization parameter Δcg.

(4) Average height of surface protrusions, relative standard deviation of height distribution 2-detector power type scanning electron microscope [ESM-3200,
The height of the flat surface of the film was measured using O
The measured height of the protrusion when scanned as
Reconstruct the film surface projection image on an image processing device.

Next, the circular diameter is determined from the area of each protrusion obtained by binarizing the protrusion portion using this surface protrusion image, and this is taken as the average diameter of the protrusion. Furthermore, the highest value among the binarized individual protrusion portions is determined as the height of the protrusion, and this value is determined for each protrusion. Change this measurement location to 500
The number of protrusions was determined by repeating the test several times, and the average height of all the measured protrusions was taken as the average height. Furthermore, the standard deviation of the height distribution was determined based on the height data of each protrusion. The value obtained by dividing the obtained standard deviation by the average value of the heights was defined as the relative standard deviation. Also, the magnification of the scanning electron microscope is i
oo.

Select a value between ~8000 times. In some cases, the height information obtained using a high-precision optical interferometry three-dimensional surface analyzer (TOPO-3D manufactured by WYKO, objective lens: 40 to 200 times, effective to use a high-resolution camera) may be used in the above-mentioned SEM. It may be used instead of the value of .

(5) Using surface layer particle concentration ratio secondary ion mass spectrum (SIMS), the concentration ratio of the highest concentration element among the elements caused by particles in the film and the carbon element of the polyester is defined as the particle concentration,
Perform analysis in the thickness direction.

The ratio of the particle concentration A at the outermost layer particle concentration (point at depth O) measured by SIMS to the maximum concentration B obtained by further analysis in the depth direction, A i' B, was defined as the surface layer particle concentration ratio. . The measuring device and conditions are as follows.

■ Measuring device Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOHIKA, West Germany ■
Measurement conditions Primary ion species = 02+ Primary ion acceleration voltage: 12V Primary ion current: 200nA Raster area: 400μm mouth analysis area 2 gates 30% Measurement vacuum degree: 6. OXIO' TorrE-GU
N: 0.5KV-3, OA (6) A cross section of the single particle index film is photographed and observed using a transmission electron microscope (TEM>) to detect particles.If the observation magnification is set to about 100,000 times, it can be further divided. One particle that cannot be observed can be observed.If the total area occupied by the particles is A, and the area occupied by the aggregate where two or more particles are aggregated is B, then (A-B)/A is , is a single particle index.TE
The M conditions are as follows: 1 visual field area: 2μTrL2
Change the measurement location and measure 500 visual fields.

・Equipment 2 JEM-1200EX ・Observation magnification:
1oooooo times Section thickness: Approximately 1000 angstroms (7) Particle size ratio In the measurement of (1) above, the average value of the major diameter of each particle /
It is the ratio of the average value of the short axis.

That is, it can be obtained using the following formula.

Major axis = ΣD1i/N Minor axis = ΣD2i/N Dli and D2i are the major axis (R major axis) and minor axis (shortest axis) of each particle, respectively, and N is the total number of particles.

(8) Thickness of the polyester A layer in the laminated film Using a secondary ion mass spectrometer (SIMS), the concentration of elements originating from the particles with the highest concentration among the particles in the film and the carbon element of the polyester The ratio (M'/'C') is taken as the particle concentration, and analysis is performed in the depth (thickness) direction from the surface of the polyester A layer. In the surface layer, the particle 9 degree is low because of the interface called the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film of the present invention, the particle concentration once reached a maximum value at depth [I] begins to decrease again. Based on this g-degree distribution curve, the depth at which the maximum particle concentration becomes 1/2 [■
] (where n>I) was taken as the lamination thickness.

The conditions are the same as in measurement method (5).

In addition, if the particles contained in the film are organic polymer particles, it is difficult to measure by SIMS, so while etching from the surface, XPS (X-ray photoelectron spectroscopy),
The depth profile of the particle concentration may be measured using IR (infrared spectroscopy) or a confocal microscope, and the layer thickness may be determined using the same method as described above.

(9) Intrinsic viscosity [η] (Units: dI, 'g) A value calculated from the following formula from the solution viscosity measured at 25°C in orthochlorophenol is used.

That is, ηsp/C=[η]+K[η]2 ・With a smile, η5p−
(Solution viscosity/solvent viscosity) -1, C is the weight of dissolved polymer per 100yal of solvent (g/100Trt1, usually 1.
2>, K is Huggins constant (assumed to be 0,343). Also,
Solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

(10) The sample film containing low molecular weight substances is crushed and extracted using a Nexhlet extractor under reflux for 24 hours using chloroform as a solvent. The ratio (wt%) of the weight of the extract obtained by evaporating chloroform to the weight of the original sample was defined as the low molecular component content.

(11) Using a tape running tester, a scratch-resistant film slit into a 1/2 inch wide tape was run on a guide pin (surface roughness: Ra, 10,100 nm (running speed: 10
00TrL/min, 10 passes, wrapping angle: 60
°, running crab 20g>. At this time, the scratches in the film were observed under a microscope, and less than 2 scratches with a width of 2.5 μm or more per tape width were determined to be good, 2 or more and less than 10 scratches were determined to be good, and 10 or more scratches were determined to be poor. Excellent is desirable, but good is still usable for practical purposes.

(12) A magnetic paint having the following composition is applied to the dubbing-resistant film using a gravure roll, magnetically oriented, and dried. Roughly, using a small test calender device (steel roll/'nylon roll, 5 stages), temperature near 0℃, linear pressure: 200 K9/'
1 trigram calendered with cllll, cured for 148 hours at 70'C. The above-mentioned original tape was slit into 1×2 inch pieces to create pancakes.

A length of 250 m from this pancake was assembled into a VTR cassette to make a VTR cassette tape.

(Composition of magnetic paint) -Co-containing iron oxide (8ET1 straight 50/Z 2y"j)
: 100 parts by weight ・S-LEC A (Hinyl chloride/vinyl acetate copolymer manufactured by Sekisui Chemical) = 10 parts by weight Niraporan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane): 10 parts by weight ・Cotonay 1-L (polyisocyanate manufactured by Nippon Polyurethane): 5 parts by weight lecithin
: 1 part by weight ・Methyl ethyl ketone
Nia 5 parts by weight Methyl isobutyl ketone Nia 5 parts Toluene Nia 5 parts by weight Carbon black: 2 parts by weight Lauric acid: 1.5 parts by weight This tape was used to generate a Shibaku TV test waveform using a home VTR. A 100% chroma signal was recorded using an instrument (TG7/'U706), and the chroma S and 'N were measured from the reproduced signal using a Shibaku color video noise measuring instrument (925D/1) and designated as A. In addition, the same sample tape (unrecorded ) The chroma S y'N of the tape after dubbing it onto pancakes was measured in the same manner as above and designated as B. The reduction in chroma S/N due to this dubbing (if A-8> is less than 3 dB, the dubbing resistance is excellent, and the dubbing resistance is 3 dB or more and 5 d
A value of less than 5 dB was determined to be good, and a value of 5 dB or more was determined to be poor. Excellent is desirable, but good is still usable for practical purposes.

(13) Set the dropout video tape in the VTR, record the signal from the TV test signal generator (Shibaku TG-7/1 model), and then perform 100 passes (120 minutes x
ioo pass) was run. Using this tape, a dropout counter was used to pick out those with a dropout width of 5 .mu.sec or more and a reproduced signal attenuation of -16 db or more, which were designated as dropouts. Measurement is 1
0 rolls, if the number of dropouts converted per minute is less than 10, the dropout is good, 10g
Cases of 1 or more were considered defective.

[Example] The present invention will be explained based on examples.

Examples 1 to 8, Comparative Examples 1 to 7 Ethylene glycol slurry containing crosslinked polystyrene particles with different average particle sizes and spherical silica particles derived from colloidal silica was prepared, and this ethylene glycol slurry was heated at 190°C for 1.5 hours. After heat treatment, the mixture was transesterified with dimethyl terephthalate and polycondensed to produce pellets of polyethylene terephthalate (hereinafter abbreviated as PET) containing 0.3 to 55% by weight of the particles. Polyester A is prepared using the pellets, and PET substantially free of particles is produced by a conventional method,
Polyester B was used. 18 of each of these polymers
Dry under reduced pressure (3 Torr) at 0° C. for 3 hours.

Polyester A was fed to extruder 1 and melted at 310°C,
Roughly, polyester B was fed to extruder 2, melted at 280°C, these polymers were combined and laminated in a combined block equipped with a rectangular lamination section, and the surface temperature was increased to 1930°C using the electrostatic application method. It was wound around a casting drum and cooled and solidified to produce a two-layer unstretched film having a polyester A layer on one side. At this time, the total thickness and the thickness of the polyester A layer were adjusted by adjusting the discharge amount of each extruder.

(However, Comparative Example 7 is a single layer A layer). This unstretched film was stretched 4.5 times in the longitudinal direction at a temperature of 80°C.

This stretching was carried out in four stages with a difference in peripheral speed between two sets of rolls. This -axially stretched film was stretched 4°0 times in the width direction at 100°C at a stretching rate of 2000%/min using a stenter, and then heat-treated at 200°C for 5 seconds at a constant length to give a total thickness of 15
A biaxially oriented laminated film having a polyester A layer thickness of 0.08 to 4 μm was obtained. Polyester A of this film
The scratch resistance of the layer side was evaluated.

Next, dubbing resistance and dropout when these films were used as magnetic tapes were evaluated.

Each parameter as a base film is as shown in Table 1, and when these are within the range of the present invention, scratch resistance, dubbing resistance, and dropout have good values as shown in Table 1. However, otherwise it would not be possible to combine these characteristics.

[Effects of the Invention] As explained above, when using the base film for magnetic recording media of the present invention, protrusions of uniform height are formed at high density on the surface of the polyester A layer containing particles, and two Since the content of low molecular weight substances in the entire axially oriented film is kept low below a certain value, or the intrinsic viscosity is set to a high value above a certain value, it is possible to obtain excellent scratch resistance due to uniform protrusion formation. When used for magnetic recording media, it is possible to obtain excellent dubbing resistance, and furthermore, while suppressing the precipitation of low molecular weight substances from the magnetic recording media base film onto the film surface, small amounts of precipitates can be It is possible to obtain excellent dropout characteristics because it is incorporated into the rough surface.

In addition, the biaxially oriented polyester film as the base film for magnetic recording media of the present invention is a film made by direct composite lamination by coextrusion without any operations such as coating during the film forming process. Compared to a laminated film made by intermediate or subsequent coating, the molecules in the outermost layer are also biaxially oriented, so properties other than those mentioned above, such as surface abrasion resistance, are much lower, and cost and quality issues are also affected. This is advantageous in terms of stability, etc.

Claims (1)

[Claims] 1. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
The thickness of the polyester A laminated film is 0.005
~3 μm, the average particle size of the particles contained in the laminated film is 0.1 to 10 times the thickness of the laminated film, and the content of the particles in the laminated film is 2 to 50% by weight, and A base film for a magnetic recording medium, characterized in that the content of low molecular weight substances in the entire biaxially oriented polyester film is 1.0% or less. 2. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
The average height of the protrusions on the surface of the polyester A laminated film formed by the particles is 1/4 or more of the average particle diameter of the particles, and the low molecular weight substance content of the entire biaxially oriented polyester film is 1. A base film for a magnetic recording medium, characterized in that the content is 0% or less. 3. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
Regarding the protrusions on the surface of the polyester A laminated film formed by the particles, the number of protrusions with a height of 1/3 or less of the average particle diameter of the particles is 70% or less of the total number of protrusions, and,
A base film for a magnetic recording medium, characterized in that the content of low molecular weight substances in the entire biaxially oriented polyester film is 1.0% or less. 4. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
The relative standard deviation of the height distribution of protrusions on the surface of the polyester A laminated film formed by the particles is 0.6 or less, and the low molecular weight content of the entire biaxially oriented polyester film is 1.0% or less A base film for magnetic recording media characterized by: 5. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
The thickness of the polyester A laminated film is 0.005
~3 μm, the average particle size of the particles contained in the laminated film is 0.1 to 10 times the thickness of the laminated film, and the content of the particles in the laminated film is 2 to 50% by weight, and The intrinsic viscosity of the entire biaxially oriented polyester film is 0.
A base film for a magnetic recording medium, characterized in that it has a film density of 7 dl/g or more. 6. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
The average height of the protrusions on the surface of the polyester A laminated film formed by the particles is 1/4 or more of the average particle diameter of the particles, and the inherent viscosity of the entire biaxially oriented polyester film is 0.7 dl/g. A base film for magnetic recording media characterized by the above. 7. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
Regarding the protrusions on the surface of the polyester A laminated film formed by the particles, the number of protrusions with a height of 1/3 or less of the average particle diameter of the particles is 70% or less of the total number of protrusions, and,
The inherent viscosity of the entire biaxially oriented polyester film is 0.7
1. A base film for a magnetic recording medium, characterized in that it has a dl/g or more. 8. Consisting of a biaxially oriented polyester film in which a film mainly composed of polyester A and particles is laminated on at least one side of a film mainly composed of polyester B,
The relative standard deviation of the height distribution of the protrusions on the surface of the polyester A laminated film formed by the particles is 0.6 or less, and the intrinsic viscosity of the entire biaxially oriented polyester film is 0.7 dl/g or more. A base film for magnetic recording media characterized by: