JPH02208039A - Base film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a flat base film excellent in running properties and withstanding long-time recording by forming a membrane composed of a predetermined composition to the single surface of a biaxillary stretched polyester film having predetermined characteristics and setting the surface having no membrane formed thereto to a metal membrane forming surface. CONSTITUTION:A membrane, wherein the center line mean roughness Ra of the surface of a surface roughening substance having a mean particle size of 0.15mum or less is 0.002-0.01mum, consisting of at least one kind of a resin selected from an acrylic resin, a polyester resin and an acrylic/polyester resin and a cellulosic resin is formed to the single surface of a biaxially stretched polyester film satisfying properties such that the Young's modulus in the longitudinal direction thereof is 500kg/mm<2> or less, the Young's modulus in the lateral direction thereof is 650kg/mm<2> or more, the heat-shrinkage factor in the lateral direction thereof at 150 deg.C is 5.1-10%, surface center line mean roughness (Pa) is 0.0008-0.005mum and the number of projections having a height (h) of 0.27-0.54mum are 0.2/mm<2> or less and the surface having no membrane formed thereto of the polyester film is set to a metal membrane forming surface.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a base film for magnetic recording media, and more specifically, a polyester base film for metal thin film magnetic recording media that is flat, has excellent running properties, and is capable of long-term recording. Regarding.

<Prior art> In recent years, high-density magnetic recording media have been developed by forming a ferromagnetic metal thin film as a magnetic recording layer on a nonmagnetic support by a vacuum deposition method such as vacuum evaporation or sputtering, or a plating method without using a binder. A thin film magnetic recording material using this ferromagnetic metal has been proposed. For example, a CO vapor-deposited tape (Japanese Unexamined Patent Publication No. 54-147010), a perpendicularly magnetized film made of a Co--Cr alloy (Japanese Unexamined Patent Publication No. 52-134706), and the like have been proposed.

A metal film formed by such a thin film forming means such as vapor deposition, sputtering, or ion blating is expected to have performance equivalent to or better than that of a conventional coated recording medium having a thickness of 3 μm or more.

By the way, US Pat. No. 3,787. An example is a vacuum-deposited Co--Cr multilayer structure as disclosed in No. 327. However, the formed metal thin film is thin, and the surface condition of the nonmagnetic support (surface unevenness)
The drawback was that this directly appeared as unevenness in the magnetic film, which caused noise. Therefore, from the viewpoint of noise, it is preferable that the surface condition of the nonmagnetic support is as smooth as possible.

On the other hand, from the viewpoint of handling such as winding and unwinding the film, if the film surface is flat, the film
The films cannot be used as a product due to poor mutual sliding properties and blocking phenomenon, and the surface of the base film is required to be rough.

Furthermore, from the viewpoint of electromagnetic conversion characteristics, the surface of the nonmagnetic support is required to be flat, while from the viewpoint of handling properties, it is required to be rough.

A base film is required to simultaneously satisfy these two contradictory properties.

Furthermore, when a metal thin film magnetic recording medium is actually used, a serious problem is the runnability of the metal thin film surface. In the case of conventional coated magnetic recording media, a lubricant can be added to the organic binder of the magnetic powder to improve the running properties of the magnetic surface, but in the case of metal thin film magnetic recording media, the running properties cannot be stabilized. It is very difficult to maintain the head's output waveform (hereinafter referred to as the envelope), and the running performance in high temperature and high humidity is poor.When recording for a long time, the difference between the initial output waveform (hereinafter referred to as envelope) of the head is extremely large, and the output decreases and becomes long. It had drawbacks such as difficulty in recording time. When playing a magnetic recording tape made of ferromagnetic metal powder (so-called metal tape) with a head running a magnetic recording tape made of a rough metal thin film, there should be no abnormality in the envelope (hereinafter referred to as compatibility with metal tape). gender)
is required.

Furthermore, the temperature is high during vacuum deposition, and if the lateral heat shrinkage rate of the base film is too low, the tape will curl, while if it is too high, wrinkles will occur, causing problems in the processing process.

<Purpose of the Invention> The present invention is capable of forming a thin metal film that is flat, has excellent running properties, enables long-time recording, has good compatibility with metal tapes, and is easy to process and does not curl. An object of the present invention is to provide a polyester base film for metal thin film magnetic recording media.

<Configuration/Effects of the Invention> According to the present invention, an object of the present invention is to achieve the following characteristics (a) to (
One side of a biaxially oriented polyester film that satisfies (e): (a) Young's modulus in the longitudinal direction: 500 kg/mm2 or less (0) Young's modulus in the transverse direction: 650 kg/mm2 or more (c) Heat shrinkage at 150°C in the transverse direction Rate 5.1-10% (
-) Surface center line average roughness (Ra) o, oooa~0.005μ (e) Number of protrusions with height (h) of 0.27~0.54μ 0.2 pieces/mm2 or less ) at least one resin selected from acrylic resins, polyester resins, and acrylic-polyester resins (g) cellulose resins (h) with an average particle size of 0.15 μm or less A base film for a magnetic recording medium, in which a thin film having a center line average roughness Ra of 0.002 to 0.01 μm is formed on the surface of a roughened material, and the surface of a polyester film on which the thin film is not formed is a surface on which a metal thin film is formed. achieved by

In the present invention, polyester is a linear saturated polyester synthesized from an aromatic dibasic acid or its ester-forming derivative and a diol or its ester-forming derivative. Specific examples of such polyesters include polyethylene terephthalate, polyethylene isophthalate,
Polybutylene terephthalate, poly(1,4-cyclohexylene dimethylene terephthalate), polyethylene-
Examples include 2゜6-naphthalene dicarboxylate,
Copolymers of these or blends of these with small proportions of other resins are also included.

The biaxially oriented polyester film of the present invention has the following properties (
This is a film that satisfies (a) to (e).

(a) Young's modulus in the longitudinal direction 500 kg/mm2
Below (0) Lateral Young's modulus 650klJ/
111112 or more (I\) Heat shrinkage rate at 150°C in the lateral direction 5.1 to 10% (-1-) Surface center line average roughness (Ra) 0.0008 to 0.005 μ (e) Protrusion height Number of protrusions with a length (h) of 0.27 to 0.54 μ: 0.2 pieces/a
m2 or less This biaxially oriented polyester film can be produced based on a method in which polyester is melt-extruded, rapidly cooled to form an unstretched film, and then the unstretched film is successively stretched in two wheels. For example, a biaxially oriented polyethylene terephthalate film that satisfies the above properties (a) to (e) can be obtained by melt-extruding polyethylene terephthalate containing a lubricant through a die, rapidly cooling it on a casting drum to form an unstretched film, and then producing an unstretched film. The film is produced by sequentially stretching in the two-wheel direction and heat-treating it. At that time, the film forming conditions are set at a longitudinal stretching ratio of 3. G~3.8
8 times, lateral stretching ratio 3.5 to 4.5 times, stretching temperature 8 times each
Select from a range of 0 to 120°C and a heat setting temperature of 150 to 240°C. Further, the heat shrinkage rate in the lateral direction can be set to a desired value by relaxing or tensioning the material in the lateral direction.

Biaxially oriented polyester film is 4-15μ, even 5μ
A thickness of ~13μ is preferred. If it is less than 4μ, the tape will be thin and have poor durability, and if it exceeds 15μ, it will have poor long-term recording characteristics. Young's modulus in the longitudinal direction is 500 K
MIIm2 or less and Young's modulus in the lateral direction is 650 K
9/1112 or more is required. Outside this range,
The VTR's held touch deteriorates, and the electromagnetic conversion characteristics deteriorate. The preferred transverse Young's modulus is 700 KMam2
That's all. Thermal shrinkage rate at 150℃ in the lateral direction is 5.1~
Must be between 10%.

If the heat shrinkage rate in the transverse direction at 150° C. is less than 5.1%, the tape will curl during the vapor deposition process, and if it exceeds 10%, the base will shrink significantly during the same process, resulting in wrinkles. A preferable heat shrinkage rate at 150° C. in the transverse direction is 6 to 9%.

The center line average roughness Ra of the surface is o, oooa~o, oo
It needs to be sμ. If it is less than o or oooaμ, the surface of the base film becomes too flat and the repeated running durability is poor. On the other hand, if it exceeds o, oosμ, the surface of the base film will become too rough and the electromagnetic conversion characteristics will deteriorate.

The centerline average roughness Ra of the surface is preferably 0.0010 to 0.
, 0025μ.

The number of protrusions with a protrusion height (h) of 0.27 to 0.54 μ on the surface must be 0.2/1lIII2 or less.

If it exceeds 0.2/111+112, the surface of the base film will become rough and the electromagnetic conversion characteristics will deteriorate. The number of protrusions having a protrusion height (h) of 0.27 to 0.54 μ on a preferable surface is 0 10III12.

The center line average roughness Ra of the surface and the number of protrusions can be controlled by a lubricant that is usually dispersed and contained in the polyester. This lubricant has an average particle size of 20 to ioomμ, especially 30
Silicon oxide of ~80 rsμ is preferably mentioned, the silicon oxide containing from 0.005 to 0.1% by weight, especially o, oo
a to 0.05% by weight in polyester. It is preferable to disperse and contain it. It is preferable that the lubricant does not contain coarse particles such as aggregated particles. For example, when silicon oxide is added in the polyester manufacturing process, the silicon oxide is -H
It is preferable to substitute a model made into an aqueous dispersion sol with glycol (for example, ethylene glycol) to prepare a glycol dispersion before use. It is not preferable to directly disperse silicon oxide in glycol because agglomeration occurs upon addition, resulting in the formation of coarse protrusions on the film surface.

If the average particle size of the lubricant, especially silicon oxide, is less than 20 mμ, the film surface will become completely flat, resulting in poor running durability.On the other hand, if it exceeds ioomμ, the protrusions on the film surface will become large, resulting in a decrease in output as an electromagnetic conversion characteristic. is large and undesirable. On the other hand, if the content of the lubricant is too small, the film surface will become too flat, and if the content is too low, the protrusions on the film surface will become too high, which is not preferable.

In the present invention, the coating film formed on one side of the biaxially oriented polyester film that satisfies the above characteristics is (f) at least one resin selected from acrylic resin, polyester resin, and acrylic-polyester resin; It is obtained by a composition whose main components are (g) a cellulose resin and (h) a roughening substance with an average particle size of 0.15 μm or less.

The surface roughness of this coating film is the center line average roughness (Ra) of 0.0
It is in the range of 0.02 to 0.01 μlll. Despite this excellent surface flatness, the film of the present invention has excellent slip properties.

The acrylic resin may be, for example, an acrylic ester (alcohol residues include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group). group, phenyl group.

Examples include benzyl group, phenylethyl group, etc.): Methacrylic acid ester (alcohol residue is the same as above):
2-Hydroxyethyl acrylate.

Hydroxy-containing acrylamides such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, methacrylamide, N-methylmethacrylamide, N-methylacrylamide, N-methylolacrylamide, N-methylolmethacrylate Amide, N,N-dimethylolacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide.

Amide group-containing monomers such as N-phenylacrylamide: N,N-diethylaminoethyl acrylate, N
, N-diethylaminoethyl methacrylate and the like: glycidyl acrylate, glycidyl methacrylate.

Epoxy group-containing monomers such as allyl glycidyl ether: styrene sulfonic acid, vinyl sulfonic acid, and their salts (eg, sodium salts).

Monomers containing sulfonic acid groups or their salts, such as potassium salts, ammonium salts, etc.: crotonic acid, itaconic acid, acrylic acid, maleic acid, fumaric acid, and their salts (eg, sodium salts).

Monomers containing carboxyl groups or their salts such as potassium salts, ammonium salts, etc.: maleic anhydride,
Seven polymers containing acid anhydrides such as itaconic anhydride; and other vinyl isocyanates.

Allyl isocyanate, styrene, vinyl methyl ether, vinyl ethyl ether, vinyl tris alkoxysilane, alkyl maleic acid monoester, alkyl fumaric acid monoester, acrylonitrile, methacrylonitrile, alkyl itaconic acid monoester, vinylidene chloride, vinyl acetate, vinyl chloride However, those containing 50 mol% or more of (meth)acrylic monomers such as acrylic acid derivatives, methacrylic acid derivatives, etc. are preferable. Those containing a component of methyl methacrylate are preferred.

Such acrylic resins can be self-crosslinked using functional groups within the molecule, or can be crosslinked using a crosslinking agent such as a melamine resin or an epoxy compound.

In addition, the acid components constituting the polyester resin include terephthalic acid, isophthalic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, 9,2,8 naphthalenedicarboxylic acid, 4,4°-diphenyldicarboxylic acid, adipic acid, Sebacic acid, dodecanedicarboxylic acid, succinic acid, 5
-Na sulfoisophthalic acid, 2-sulfoterephthalic acid, trimellitic acid.

trimesic acid, trimellitic anhydride, phthalic anhydride, p
Examples include polyhydric carboxylic acids such as -hydroxybenzoic acid and monopotassium trimellitic acid salt.

In addition, hydroxy compound components include ethylene glycol, propylene glycol, 1,3-propanediol, 1.4-butanediol, 1.6-hexanediol, neopentyl glycol, 1.4 cyclohexane dimetatool, p-xylylene Glycol, bisphenol 8-ethylene oxide adduct, diethylene glycol,
Examples of polyhydric hydroxy compounds include triethylene glycol, polyethylene oxide glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, and potassium dimethylolpropionate. Polyester resins can be produced from these compounds by conventional methods. When preparing an aqueous coating liquid, it is preferable to use a polyester resin containing a 5-Ha sulfoisophthalic acid component or a carboxylic acid group.

Such a polyester resin can be a self-crosslinking type having a functional group in its molecule, or can be crosslinked using a curing agent such as a melamine resin or an epoxy resin.

In addition, the acrylic-polyester resin is used to include acrylic-modified polyester resin and polyester-modified acrylic resin, and does not mean that the acrylic resin component and the polyester resin component are bonded to each other in some way. Yes, there are graft types, block types, etc.

For example, a radical initiator is added to both ends of a polyester resin to polymerize an acrylic monomer; a radical initiator is added to the side chain of a polyester resin to polymerize an acrylic monomer. Alternatively, a comb-shaped polymer can be produced by attaching hydroxyl groups to the side chains of an acrylic resin and reacting it with a polyester having an isocyanate group or carboxyl group at the end.

These can be used alone or in combination of two or more.

In general, examples of the cellulose resin include ethyl cellulose, methyl cellulose, acetyl cellulose, acetoacetyl cellulose, nitrocellulose, carboxylated cellulose, carboxymethyl cellulose, cellulose acetate butyrate, and the like. By using this cellulose resin, it is possible to form a large number of minute folds in the coating film.

Further, as the surface roughening substance, for example, polystyrene, polymethyl methacrylate, methyl methacrylate copolymer, crosslinked methyl methacrylate copolymer, polytetrafluoroethylene, polyvinylidene fluoride,
Organic fine powder such as polyacrylonitrile, benzoguanamine resin, etc., or silica, alumina, titanium dioxide, kaolin, talc, graphite, calcium carbonate,
Inorganic fine powders such as feldspar, molybdenum disulfide, carbon black, barium sulfate, etc. may be used, and these may be made into an aqueous dispersion using an emulsifier or the like. It may be something that can be added.

This surface roughening substance is fine particles with an average particle diameter of 0.15 μm or less, preferably 0.01 to 0.1 μm. Also,
In order to avoid these water-insoluble solid substances from settling in the aqueous dispersion, it is preferable to select ultrafine particles whose specific gravity does not exceed 3.

Such surface roughening substances have the effect of promoting the uniform formation of minute protrusions on the coating film itself and the reinforcing effect of the coating film due to the fine powder itself, and also improve the blocking resistance and friction of the resin (to) the coating film. The effect on force reduction, etc., and the synergistic effect of both improve the scratch resistance of the coating film, giving the polyester film excellent slipperiness.

In the present invention, the main components for forming a coating film, namely, component (F), component (T), and component (although the blending ratio of the component (sword) can be freely selected, the amount of component (F) is 30 to 80% by weight per total solid content). %
, component (g) is 1 to 50% by weight, component (h) is 5 to 40%
Preferably, it is % by weight. If the amount of component (f) is too small, the adhesion of the coating film to the base (polyester film) will be reduced, while if it is too large, blocking resistance and slip properties will be reduced. If the amount of component (g) is too small, the wrinkles and unevenness of the coating film will be reduced, resulting in poor workability, while if it is too large, the surface will be too rough. Ingredients (If there are too few ingredients, the slipperiness will decrease; if there are too many ingredients, particles will easily fall off from the coating.

There are no particular restrictions on the mixing of these components, but they may preferably be mixed in the form of an aqueous dispersion, such as an aqueous dispersion of component (N) or component (g), or a mixture of component (g) and component (g). The powdered surface roughening substance (H) and, if necessary, an emulsifier may be added to the liquid and dispersed by stirring.

The coating film in the present invention is preferably formed by applying a coating liquid during the polyester film manufacturing process. For example, it is preferable to apply an aqueous coating liquid to the surface of the polyester film before the oriented crystallization process is completed.

Here, the polyester film before crystal orientation is completed refers to an unstretched film obtained by thermally melting the polymer and forming it into a film as it is; an unstretched film that is oriented in either the longitudinal direction or the lateral direction. Uniaxially stretched film:
Furthermore, it includes those that have been stretched and oriented at low magnification in two directions, the machine direction and the transverse direction (two-wheel stretched films before being finally re-stretched in the machine direction or the transverse direction to complete oriented crystallization).

The film of the present invention can be produced by applying a coating solution of the above composition to a film that is preferably unstretched or stretched in at least one direction before crystal orientation is completed, and subjected to longitudinal stretching and/or transverse stretching and heat setting as it is. It is manufactured using the so-called in-line coating method. At that time, in order to ensure that the coating film can be smoothly applied to the surface of the polyester film before the oriented crystallization process is completed, the film surface is subjected to corona discharge treatment as a preliminary treatment, or together with the coating composition. It is preferable to use this together with a chemically inert surfactant. Such a surfactant is one that promotes wetting to a polyester film such that the surface tension of the aqueous composition can be lowered to 40 dyne/cm or less, and includes, for example, polyoxyethylene alkylphenyl ether, polyoxyethylene-fatty acid ester, etc. , sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal soap.

Examples include anionic and nonionic surfactants such as alkyl sulfates, alkyl sulfonates, and alkyl sulfosuccinates. Furthermore, within the range that does not eliminate the effects of the present invention, for example, antistatic agents, ultraviolet absorbers,
Other additives such as lubricants can be mixed.

In the present invention, the solid content concentration of the coating liquid, particularly the aqueous coating liquid, is usually 30% by weight or less, preferably 15% by weight or less. Viscosity is less than ioo cps, preferably 20 cps
S or less is appropriate. "Coating" is the running film 1.
Approximately 0.5 to 20 g/m, preferably 1 to iog/m. In other words, in the final two-wheel stretched film, approximately 0.001 to 1 per Td is applied to one surface of the film.
A solids content of about 0.01 to 0.30 (7) is preferred.

Any known coating method can be used as the coating method.

For example, a roll coating method, a gravure coating method, a roll plush method, a spray coating, an air knife coating, an impregnation method, a curtain coating method, etc. may be applied alone or in combination.

According to a preferred production method of the present invention, the aqueous liquid is preferably applied to the film immediately after being subjected to longitudinal-axial stretching, and then led to a tenter for transverse stretching and heat setting. At that time, the area of the coated material is expanded as the film is stretched in an unsolidified state, and the area is heated to volatilize water, forming a large number of minute folds and minute protrusions on the surface of the two-wheel stretched film. It is converted into a thin solid coating layer with a strong adhesion to the two-wheel stretched film surface.

According to the present invention, the aqueous liquid is converted into a solid coating film having a large number of microfolds and microprotrusions, as described above, by stretching and heat treating the substrate.

This heating is preferably carried out at a temperature of about 100 to about 240°C for about 1 to about 20 seconds.

In the present invention, the surface of the biaxially oriented polyester film on which the thin film made of the composition containing the above (f) to (h) as main components is not formed is the surface on which the metal thin film is formed. As a method for forming a metal thin film on this surface, conventionally known methods such as a vapor deposition method, a sputtering method, an ion blating method, etc. can be used. The metal used in this thin film forming method is not particularly limited as long as it can form a ferromagnetic thin film, such as Fe,
Ni, Co, Co-Cr, etc. can be mentioned.

According to the present invention, it is possible to provide a biaxially oriented polyester base film for metal thin film magnetic recording media, which has a flat film surface and can form a metal thin film surface with excellent running properties.
In particular, a metal thin film magnetic recording medium that dramatically reduces noise, has a significantly superior noise level, has excellent running properties on the metal thin film surface, has excellent running durability during long-term recording, and has good compatibility with metal tapes. A biaxially oriented polyester film useful for manufacturing can be provided.

<Example> The present invention will be further explained below with reference to Examples.

In addition, the physical properties of the film were measured by the following method.

1. Center line average roughness Ra According to JIS 80601, using a high-precision surface roughness meter 5E-3FAT manufactured by Koita Research Institute, the needle radius is 2 μm,
Measurement tube 13011g, magnification 200,000 times, cutoff o
, Hang the chart under the conditions of oamm, and handle a part of measurement length L from the film surface roughness curve in the direction of its center line.The center line of this handled part is the X axis, and the direction of vertical magnification is the Y axis. When the roughness curve is expressed as Y = f (X) as an axis, the value given by the following formula is expressed in μm.

In this measurement, four measurements were made with a measurement length of 1.25 mm, and the average value is expressed.

2. Number of surface protrusions: Vacuum-deposit aluminum uniformly on the film surface to a thickness of 400 to 500 or less, paste collodion on the opposite non-evaporated surface (film surface), and after drying, visible monochromatic light multiple interference Reflection microscope (e.g. cart Zei
ss manufactured by JENA) at 100 times magnification, the number of projections corresponding to the height of the projections in each photograph is determined and converted to 11III112. Photo 1 at this time
The field of view for 0 images is 1.55nlll12.

3. Electromagnetic conversion characteristics (recording density characteristics) 10. S/N (dB) ratio and l0K during BPI recording and reproduction
The high-density recording characteristics, especially the noise level, are evaluated based on the reduction rate of the output during BPI recording and reproducing to 50% relative to the output during BPI recording and reproducing.

4. Long-term durability: Repeat recording and playback using a commercially available Bmm system VTR.
The following criteria will be used to evaluate the playback screen after running 100 times.

Q: Additional hits are smooth and there is no fluctuation in the playback screen. The following criteria will be used to evaluate the output waveform.

0: The output waveform is unchanged from the initial state, and there is no decrease in output.

X: The difference in the output waveform from the initial stage is extremely large, and the output decreases. 6. Cut the Young's modulus film into a sample width of 10 mm and length of 150 ml, set the chuck spacing to 1G01111, and pull at a tensile speed of 10 m.
m/min.

Tensile in an Instron type universal tensile tester at a chart speed of 500 mm/min. Young's modulus is calculated from the tangent to the rising part of the obtained load-elongation curve.

7.30 in a hot air circulation furnace (gear aging tester) with a heat shrinkage rate of 150℃
Free heat shrink for a minute and sieve using the following formula.

Original length - Length heat shrinkage rate after shrinkage = X100 (%) Original
300 mm is used as the long length.

Examples 1 to 3 and Comparative Examples 1 to 3 1001 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol, and 0°023 parts by weight of zinc acetate as a catalyst.
Part by weight (0,020 mol %) of dimedimethyl terephthalate was added, transesterification was carried out at 150 to 240°C for 4 hours while methanol was distilled off, and then a stabilizer (a glycol solution of a phosphorus compound) was added to 0% in terms of trimethyl phosphate.
．． 0.014 parts by weight was added, and then 0.0 parts as a polycondensation catalyst was added.
Adding 4 layers of antimony trioxide and adding a predetermined amount of silicon oxide with the average particle size roughly listed in Table 1,
A polycondensation reaction is carried out for 4 hours in a high vacuum of 11 mHg or less,
Polyethylene terephthalate having an intrinsic viscosity (η: 0-chlorophenol solvent, measured at 35° C.) of 0.65 was obtained.

These polyethylene terephthalates were melt-extruded and rapidly cooled according to a conventional method to form an unstretched film, and then 1
3.4 times at 00℃, 4.3 times at 120℃ laterally 2
Axial stretching was performed, and further heat setting was performed at 225°C for 30 seconds.
Biaxially oriented films of 10μ each were obtained. At this time, the coating solution prepared below was uniformly coated on one side of the uniaxially stretched film, which had been subjected to longitudinal stretching, by a kiss coating method at a position immediately before entering the tenter. The average coating amount at this time was about 4 g wet per yd of the above-mentioned -axially stretched film (this amount was 1 yd for the two-wheel stretched film described below).
(equivalent to approximately 0.029 per go). Next, the uniaxially stretched film coated on one side was heat-set to obtain a biaxially oriented polyester film.

<1! Cloth liquid〉 Modified acrylic water dispersion “Bess Resin 5H-9J (manufactured by Takamatsu Yushi ■) 57 parts by weight, methylcellulose 21 parts by weight,
11 parts by weight of aqueous silicon oxide dispersion with an average particle size of 0.03μ and polyoxyethylene nonylphenyl ether rNS
11 parts by weight of 208.5 J was diluted and dissolved in ion-exchanged water to prepare a coating solution with a solid content concentration of 4% by weight.

The film thus obtained had good slipperiness, no blocking occurred, and could be wound up well.

The characteristics of the film surfaces (I) and (n) are summarized in Table 1.

A cobalt-nickel alloy thin film was formed on the surface (I) of this polyester film by vacuum deposition to a thickness of 1000 mm.The film was then cut into a width of B m/m in the machine direction to obtain a metal thin film magnetic recording tape. Recording and reproduction were performed at a speed of 9.5 cm 2 /sec using a ring head with a gap length of 0.3 μm, and electromagnetic conversion characteristics (digital recording density characteristics) were evaluated.

Furthermore, compatibility with the metal tape was evaluated based on the output waveform when the metal tape was played back with a head running this metal thin film magnetic recording tape. We also evaluated the tape processing characteristics during vacuum evaporation.

The results are shown in Table-1.

These results show that the magnetic recording media based on the films of Examples 1 to 3 have large S/N ratios, extremely high noise levels, excellent long-term durability, and It is clear that the compatibility is excellent, and furthermore, the tape processing characteristics are excellent. On the other hand, in the film of Comparative Example 1, the center line average roughness of the film surface (I) was Ra O,0004μ-, and the film surface was so flat that the tape stuck to the head, the vapor deposited layer was peeled off from the film, and the electromagnetic Conversion characteristics could not be measured.

Furthermore, since the film of Comparative Example 2 had a flat film surface (I), the running durability of the tape was poor.

Also, the film of Comparative Example 3 satisfied long-term durability and compatibility with metal tape, and had no problems such as curling or wrinkles during processing, but the film surface (I) was rough and had difficulty in electromagnetic conversion. It didn't have enough characteristics.

Examples 4 to 6 and Comparative Examples 4 to 6 Using the same polymer as in Example 2, an unstretched film was prepared and the film forming conditions listed in Table 2 were applied. Same conditions as Example 2)1
A 0 μm film was prepared, and a coating liquid having the same composition as in Example 2 was applied to the film surface (n).

A cobalt-nickel alloy thin film was formed on the surface (I) of this polyester film by vacuum deposition to a thickness of 1000 mm.Then, the film was cut into a width of 8111III in the machine direction to form a metal thin film magnetic recording tape with a thickness of 0.3 μm. 9.5CIll/using a ring head with a gap length of
Recording and reproduction were performed at SeC speed, and electromagnetic conversion characteristics (digital recording density characteristics) were evaluated.

We also evaluated long-term running durability and compatibility with metal tape. These results are shown in Table-2.

These results show that the magnetic recording media based on the films of Examples 4 to 6 have large S/N ratios, extremely high noise levels, and excellent long-term durability.
It is clear that it has excellent compatibility with metal tapes and has excellent tape processing characteristics. On the other hand, the film of Comparative Example 4 has long-term durability and does not curl during processing.

Although there were no problems such as wrinkles, the balance of Young's modulus in the vertical and horizontal directions was poor, and compatibility with metal tape was poor. Furthermore, since the film of Comparative Example 5 had a low heat shrinkage rate at 150° C. in the transverse direction, the tape curled during vacuum deposition. Furthermore, the film of Comparative Example 6 was heated at 150°C in the lateral direction.
Because of its high heat shrinkage rate, the film shrinks significantly during vacuum deposition, resulting in wrinkles and could not be made into a tape.

Claims (1)

[Claims] 1. (1) On one side of a biaxially oriented polyester film that satisfies the following properties (a) to (e), (a) Young's modulus in the longitudinal direction is 500 kg/mm^2 or less (b) Lateral Young's modulus in the direction 650 kg/mm^2 or more (c) Heat shrinkage rate at 150°C in the lateral direction 5.1 to 10% (d) Surface center line average roughness (Ra) 0.0008 to 0.005 μ ( E) Number of protrusions with a height (h) of 0.27 to 0.54 μ: 0.2 pieces/mm^2 or less (2) Composed of the following (F) to (H) as main components (F) Acrylic (g) Cellulose resin (h) Center line average roughness Ra of the surface of the roughened material with an average particle diameter of 0.15 μm or less (3) A base film for a magnetic recording medium, wherein a thin film having a thickness of 0.002 to 0.01 μm is formed, and (3) the surface of the polyester film on which the thin film is not formed is the surface on which the metal thin film is formed. 2. Biaxially oriented polyester film has an average particle size of 20 to 1
2. The base film for a magnetic recording medium according to claim 1, containing 0.1% by weight or less of silicon oxide having a particle diameter of 0.00 mμ.