JPS62284741A - Base film for magnetic record medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention <Industrial Application Field> The present invention relates to a base film for magnetic recording media, and more specifically to a base film for a magnetic recording medium, and more specifically, a flat metal thin film with excellent running properties and capable of long-term recording. II! This invention relates to a polyester base film for magnetic recording media.

<Prior Art> In recent years, as high-density magnetic recording media, a ferromagnetic metal thin film is formed 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 Patent Application Laid-open No. 147010/1983), a perpendicularly magnetized film made of a Co--Cr alloy (Japanese Patent Application Laid-open No. 134706/1983), and the like have been proposed.

A metal thin 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, U.S. Pat. No. 3,787.327 is based on the idea that static characteristics such as coercive force 11C1 or magnetic characteristics such as the squareness ratio of the hysteresis loop do not depend much on the surface condition of the non-magnetic support used. An example of a Co--Cr multilayer structure by vacuum@deposition as disclosed in No. However, the metal thin film formed is thin, and the surface condition (surface irregularities) of the nonmagnetic support directly manifests as irregularities on the magnetic film, which is considered to be a cause of 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 point of view of handling such as taking up and unwinding two films, if the film surface is flat, the film-to-film slipperiness will be poor, and a blocking phenomenon will occur, making it impossible to use as a product. is required to be coarse.

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 temperature of the vehicle, and it has the drawback of particularly poor running performance at high temperatures and high humidity. Furthermore, when recording for a long time, the difference between the head's output waveform (hereinafter referred to as the envelope) from the initial stage becomes significantly large, and the output decreases.
It had drawbacks such as difficulty in long-term recording.

<Object of the Invention> An object of the present invention is to provide a polyester base film for a metal thin film magnetic recording medium, which is capable of forming a flat metal thin film with excellent running properties and capable of long-time recording.

<Configuration/Effects of the Invention> According to the present invention, the purpose of the present invention is to achieve the following characteristics (a) to K.
) on one side of a biaxially oriented polyester film that satisfies (a) Young's modulus in the longitudinal direction of 500 kg/mm2
Less than (Ω) Lateral Young's modulus 850kg/m
m2 or more (c) Heat shrinkage rate at 150℃ in the lateral direction 1
~5% (d) Center line average roughness (Ra) 0.001 on the surface
~0.003 u rhinoceros) Height (h) is 0.27~0.54
The number of protrusions of μ is 0.2 or less/mm2.It is made of a composition whose main components are polyurethane, acrylic resin, low molecular weight polyolefin wax, and a roughening substance with an average particle size of 0.15μ or less, and the surface center line average By forming a thin film having a roughness Ra of 0.002 to 0.01 μ on the surface and having no mountain-like irregularities on the surface, and using the polyester film surface on which the thin film is not formed as the surface on which the metal thin film is formed, a base film for a magnetic recording medium is used. achieved.

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 650kg/m
m2 or more (c) Heat shrinkage rate at 150'C in the lateral direction
1-5%) Surface centerline average roughness (Ra) 0.001
~0.003 a (e) Protrusion height (h) is 0.27~0
．． Number of 54μ protrusions: 0.2 pieces/mm2 or less This biaxially oriented polyester film is made based on the method of melt extruding polyester, rapidly cooling it to make an unstretched film, and then sequentially biaxially stretching the unstretched film. Can be done. 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 forming the unstretched film. The film is produced by successive biaxial stretching and heat treatment. At that time, the film forming conditions are adjusted to a longitudinal stretching ratio of 3.0 to 3.8 so that the film has the above characteristics.
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. Further, the Young's modulus in the lateral direction is preferably 700 kg/mm2 or more, and 15 in the lateral direction.
The heat shrinkage rate at 0°C is preferably 2 to 4%, the center line average roughness Ra of the surface is preferably 0.0015 to 0.0025μ, and the protrusion height (h) on the surface is 0.27 to 0.
The number of 54μ protrusions is preferably O pieces/mm2.

The centerline average roughness Ra and the number of protrusions on the surface can be controlled by a lubricant that is normally dispersed and contained in the polyester. Which lubricant has an average particle size of 20 to 100 mμ, especially 30 mμ?
-80 mμ silicon oxide is preferably mentioned, and the silicon oxide contains 0.005 to 0.1% by weight, especially o, ooa
It is preferable to disperse and contain it in the polyester in a proportion of 0.05% by weight. It is preferable that the lubricant does not contain coarse particles such as agglomerated particles. For example, when silicon oxide is added in the polyester manufacturing process, the silicon oxide is obtained by replacing condensate in a -H water dispersion sol with glycol (e.g. ethylene glycol). It is preferable to use it as a glycol dispersion. 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.
When oomμ is exceeded, the protrusions on the film surface become larger;
This is not preferable because the output as an electromagnetic conversion characteristic is greatly reduced. Furthermore, if the content of the lubricant is too small, the film surface will become too flat, while if it is too large, the protrusions on the film surface will become too small, which is not preferable.

In the present invention, polyurethane is used on one side of a biaxially oriented polyester film that satisfies the above characteristics.

It consists of a composition mainly consisting of an acrylic resin, a low molecular weight polyolefin wax, and a roughening substance with an average particle size of 0.15 μm or less, and the center line average roughness of the surface Ra is 0.002
~0.01μ, and forms a film that does not have mountain-like irregularities as shown in Figure 1, but has a surface state of minute irregularities as shown in Figure 2.

The coating solution that forms a thin film on the surface of this polyester film is preferably an aqueous coating solution, and the polyurethane in the coating solution is preferably an aqueous polyurethane, which is a water-based coating solution that is formed by a carboxylic acid salt base, a sulfonic acid base, or a sulfuric acid half ester base. It is a polyurethane with increased affinity, and such water affinity-imparting groups are usually introduced during or after polyurethane synthesis.

The amount of bases such as carboxylate bases, sulfonate bases, and sulfuric acid half-ester bases is preferably 0.5 to 15% by weight. If the proportion of the base is too small, the water affinity of the polyurethane will be insufficient, making it difficult to prepare a coating solution, and if it is too large, the original properties of the polyurethane will be impaired, which is not preferable. Such aqueous polyurethane forms a stable aqueous dispersion or aqueous solution using a dispersion aid if desired.

Examples of polyhuman [1xy compounds used in the synthesis of polyurethane include polyethylene glycol.

Polypropylene glycol, polyethylene propylene glycol, polytetramethylene glycol, hexamethylene glycol, tetramethylene glycol, 1.5
-bentanediol, diethylene glycol, triethylene glycol, polycaprolactone, polyhexamethylene adipate.

Polyhexamethylene sebacate, polytetramethylene adipate, polytetramethylene sebacate.

Trimethylolpropane, trimethylolethane.

Examples include pentaerythritol and glycerin. Examples of the polyisocyanate compound include hequinamethylene diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, isophorone diisocyanate, an adduct of tolylene diisocyanate and trimethylolpropane, an adduct of hexyrimethylene diisocyanate and trimethylol ethane, and the like. can. Examples of carboxylic acid-containing polyols include dimethylolpropionic acid and dimethylolacetic acid.

Examples include dimethylolvaleric acid and trimellitic acid bis(ethylene glycol) ester. Examples of the amino group-containing carboxylic acid include β-aminopropionic acid, T-amino M, and P-aminobenzoic acid. As the hydroxyl group-containing carbonic acid, for example, 3
-Hydroxypropionic acid, γ-hydroxybutyric acid 1. P-
Examples include (2-hydroxyethyl)benzoic acid and malic acid. Examples of compounds having an amine group or a hydroxyl group and a sulfonic group include aminomethane sulfonic acid,
Examples include 2-aminoethanesulfonic acid, 2-amino-5-methylbenzene-2-sulfonic acid, sodium β-hydroxyethanesulfonate, propane sultone and butane sultone addition products of aliphatic diprimary amine compounds, etc. Preferred examples include propane sultone adducts of aliphatic diprimary amine compounds. Furthermore, an amine group or a hydroxyl group and 5Ar! Examples of the compound containing an i-half ester group include aminoethanol sulfuric acid, ethylenediamine ethanol sulfuric acid, aminobutanol sulfuric acid, hydroxyethanol sulfuric acid, γ-hydroxypropanol sulfuric acid, α-hydroxybutanol sulfuric acid, and the like.

Polyurethane can be synthesized using these compounds by conventionally well-known methods.

The acrylic resin as a thin film forming component in the present invention includes:
The methyl methacrylate component is 40 to 80 mol%,
20 to 6 other vinyl monomer components copolymerizable with this
Preferably, it is a water-based acrylic resin having a content of 0%. Methyl methacrylate component in acrylic resin is 40 mol%
If it is less than that, the coating film tends to decrease in strength and become soft, and the handling property deteriorates due to deterioration in blocking resistance.
Preferred G). On the other hand, the methyl methacrylate component is 8
If it exceeds 0 mol %, the coating film tends to harden, the coating film becomes brittle, the adhesion to the substrate decreases, the film forming property is poor, and so on, which is not preferable.

Examples of other vinyl heptamers copolymerizable with the above-mentioned methyl methacrylate include alkyl acrylate (alkyl groups include methyl group, ethyl group, n-propyl group,
isopropyl group, n-butyl group, isobutyl L t-butyl group, 2-ethylhexyl group, cyclohexyl group, benzyl group, phenylethyl group, etc.); alkyl methacrylate (as an alkyl group, an alkyl group other than the methyl group of the above-mentioned alkyl acrylate, etc.) ); 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,
Hydroxy-containing uppers such as 2-hydroxypropyl acrylate and 2-hydroxypropyl methacrylate;
Acrylamide, methacrylamide, N-methylmethacrylamide.

N-methylacrylamide, N-methylol acrylamide, N-methylol methacrylamide.

Amide group-containing monomers such as N,N-dimethylolallylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-phenylacrylamide; N,N-diethylaminoethyl acrylate;
Amino group-containing monomers such as N,N-diethylaminoethyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether; styrene sulfonic acid, vinyl sulfonic acid and their salts (sodium salt, potassium salt,
Sulfones such as ammonium salts etc.) : heptamer containing L group or its salt; crotonic acid.

Itaconic acid, acrylic acid, maleic acid, fumaric acid and their salts (sodium salt, potassium salt).

Monomers containing carboxyl groups or their salts such as ammonium salts, etc.; monomers containing acid anhydrides such as fomaleic anhydride and itaconic anhydride; vinyl isocyanate, 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.

Examples include vinylidene chloride, vinyl acetate, vinyl chloride, and the like.

The above-mentioned hexamers copolymerized with methyl methacrylate are freely selected singly or in combination of two or more, or
From the viewpoints of imparting hydrophilicity to the acrylic resin, dispersion stability of aqueous liquids, and adhesion to polyester films, hydroxyl groups, amide groups, carboxyl groups, or their salts (sodium salts, potassium salts) are recommended.

Those having a functional group such as ammonium salt (ammonium salt, etc.) are preferred. In addition, thermosetting type is suitable for improving the heat resistance 2 strength, water resistance, etc. of the coating film, for example, epoxy group-containing monomer and amino group, acid anhydride group.

Combination with a hexamer containing a carboxyl group, hydroxyl group or N-methylol group; Combination of a hexamer containing an N-methylol or N-methylol ether group and a hexamer containing a carboxyl group or an amino group In addition, examples include monomers that have thermosetting properties even when used alone, such as carboxylic acid base yamethylol group. One type or a combination of two or more of these reactive groups can be optionally introduced into one type of acrylic resin or two or more types of acrylic resins. It may be a combination of resins. It is also possible to add one or more low molecular weight substances (for example, alkylolated melamine, etc.) having groups that react with the reactive groups in the acrylic resin and react with each other when heated.

The aqueous liquid of acrylic resin can be produced by any known method. At that time, if necessary, use molecular weight regulators (mercaptans) and dispersion aids (polymer protective colloids such as polyvinyl alcohol and hydroxymethylcellulose).
etc. may be added.

In addition, the application of low molecular weight surfactants, high molecular weight surfactants, dual-reactive surfactants, etc., and the production method using so-called soap-free polymerization, which does not contain surfactants, may also be adopted.

The low-molecular-weight polyolefin wax used as a thin film-forming component in the present invention refers to a low-molecular-weight polyolefin wax that has physical and chemical properties similar to high-molecular-weight polyolefin resins, but has extremely low melt viscosity, , microcrystalline wax.

It has a higher melting point than carnauba wax, -E silane wax, etc. In particular, low molecular weight polypropylene has a high melting point of 150'C.

These polyolefin waxes can be made water-based by known manufacturing methods such as mixing molten polyolefin and hot water containing an emulsifier (surfactant, etc.) to form an O/W emulsion, or by oxidizing the wax into molecules. Polyolefins containing carboxyl groups are easier to emulsify with water. Among these low molecular weight polyolefins, polyethylene wax is preferable, and among them, the average molecular weight is 00
0 to 10,000, density 0.91 to 0.97 ((]/
d) Melt viscosity (14
Polyethylene waxes having a 0° C., cps) in the range of about 20 to about 700 are preferred. Furthermore, the molecular weight is 200
Those in the range of 0 to 4,000 are preferred because they are easily water-based and satisfy the properties such as Wj properties as a polyethylene wax. In addition, high molecular weight polyethylene (molecular weight 20,000)
Since the melt viscosity is extremely high at approximately 80 million cps, it is extremely difficult to make it water-based.

In the present invention, the surface roughening substances to be mixed with the aqueous liquid (aqueous solution, dispersion, or emulsion) of the polyurethane, acrylic resin, and low molecular weight polyolefin wax include polystyrene, polymethyl methacrylate, methyl methacrylate copolymer, polytetra Fine organic powders such as fluoroethylene, polyvinylidene fluoride or polyacrylonitrile, benzoguanamine resin, etc., or silica, alumina, titanium dioxide, chlorine, talc, graphite, calcium carbonate.

Inorganic fine powders such as feldspar, molybdenum disulfide, carbon black, or barium sulfate may be used, and these may be made into an aqueous dispersion using an emulsifier or the like. , an aqueous acrylic resin liquid, and a low molecular weight omega polyolefin wax aqueous liquid.

This surface roughening substance is fine particles with an average particle size of 0.15 μm or less, preferably 0.01 to 0.1 μm. Furthermore, these water-insoluble solid substances are preferably ultrafine particles with a specific gravity not exceeding 3 in order to avoid settling in the aqueous dispersion. If the average particle size is larger than 0.15 μm, the surface of the thin film becomes too rough, which is not preferable.

The surface roughening substance has the effect of promoting the uniform formation of microprotrusions on the thin film itself, and the reinforcing effect of the thin film with the fine powder n-form, and also provides anti-blocking properties to the thin film of acrylic resin and low molecular weight polyolefin wax.

Coupled with the effect of reducing frictional force and the effect of contributing to the scratch resistance of the thin film due to the synergistic effect of both, it imparts an excellent slipperiness effect to the polyester film.

The main components of the thin film are polyurethane (A) and acrylic resin (
8) The mixing ratio of the low molecular weight polyolefin wax (C) and the roughening substance (D) is usually [(A)±(8)
+(C)]/([)) =98/2 to 40/60. [
(A) + (B) J/(C) =98/2~40/60
．． And (^) /(B) =90/10~10/90
(solid content equivalent double weight%) is preferably within the range of
Furthermore, [(^)+(B)+(C)]/(D)=9
515-60/40. [(A)±(B)]/(C)
=9515~80/40. (A) /(B) =80
It is preferably in the range of /20 to 20/80 (weight ratio). If the mixing ratio of acrylic resin, low molecular weight polio, and reflex wax is too small, the frictional force will increase and the handling property will be deteriorated, while if it is too large, the adhesion between the thin film and the polyester film will be reduced or the thin film will become brittle. change to I
G, and the slipperiness of the film decreases. Furthermore, if the mixing ratio of the surface roughening substance is too small, the effect of the added surface roughening substance as a substance for forming fine projections in the thin film will decrease, and the fine powder itself will have a reinforcing effect on the thin film. If this ratio is too high, the ratio of surface roughening substances will increase, reducing the adhesion between the thin film and the polyester film, making the thin film brittle, etc. , the minute protrusions are destroyed by the abrasive force applied to the film during use, and the thin film is worn away, which impairs the sustainability of the smoothing effect.

The polyurethane, acrylic resin, and low molecular weight polyolefin wax (C) may be mixed with the surface roughening substance (0) after each is in the state of an aqueous dispersion, and (A)
, (B) or (C), or (A).

(B) and (C) A powdered surface roughening substance may be added to the entire aqueous dispersion, and if necessary, an emulsifier may be added and dispersed by stirring.

The thin film on the polyester film in the present invention is preferably formed by applying the above-mentioned coating liquid to the surface of the polyester film before the oriented crystallization process is completed. At that time, in order to ensure that the coating film can be coated smoothly, corona discharge treatment is applied to the film surface as a preliminary treatment, or
Alternatively, it is preferable to use a chemically inert surfactant together with the thin film forming composition.

The surfactant is a substance that promotes wetting of the polyester film so that the surface tension of the coating liquid can be lowered to 40 dyne/Cm or less, and includes, for example, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, etc. , glycerin fatty acid esters, fatty acid metal soaps, alkyl sulfates, alkyl sulfonates, alkyl sulfosuccinates, and other anionic and nonionic surfactants. Further, additives such as antistatic agents, ultraviolet absorbers, lubricants, etc. can be mixed within a range that does not eliminate the effects of the present invention.

Here, the polyester film before the above-mentioned crystal orientation is completed includes an unstretched film, a film stretched in the −axial direction, a film stretched in the biaxial direction, but at least one of which has a predetermined stretching orientation. Examples include films that do not have a degree of orientation.

The solid content concentration of the coating liquid is usually 30 mm by weight or less, and 15
It is preferable that the weight is ω% or less. The appropriate viscosity is 100 Cps or less, preferably 20 Cps or less. The amount of five coated films is preferably about 0.5 to 20 g, more preferably 1 to 10 g per 17 Ff of the running film. In other words, in the biaxially stretched film finally obtained, 1TI is applied to one surface of the film.
Approximately 0.001 to 1 g per i, more preferably approximately 0.01 to 0.3
(A solid content of 1 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.

The above coating solution is preferably applied to a film that has been subjected to longitudinal to axial stretching, and then the film is preferably introduced into a tenter for transverse stretching and heat setting. As the film is stretched in this state, its area is expanded and heated to volatilize water and firmly adhere to the surface of the biaxially stretched film.

The above-mentioned coating liquid in the present invention is converted into a solid coating film having a large number of microprojections, as described above, by the substrate stretching process and the heat treatment process. This heating is preferably about 100
The temperature is about 240'C for about 1 to about 20 seconds.

The thin film thus formed on one side of the polyester film has a surface center line average roughness of 0.002 to 0.01μ and has no mountain-like irregularities on the surface (see Figure 1).
It has uniform minute irregularities.

According to the present invention, it is possible to provide a biaxially oriented polyester film for metal thin film magnetic recording media that has a flat film surface and can form a gold a thin film surface with excellent running properties, and in particular, noise is dramatically reduced. It is possible to provide a biaxially oriented polyester film that is useful for producing a metal thin film magnetic recording medium that has a significantly superior noise level, excellent running properties on the metal thin film surface, and excellent running durability in the case of long-term recording.

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 made by Koita Research Institute, the needle radius is 2 μm,
Measurement load 30mg, magnification 200,000 times, cutoff o,
Hold a chip under the condition of oamm, cut off a part of measurement length L from the film surface roughness curve in the direction of its center line, and set the center line of this handled part on the X axis and vertical magnification. When the roughness curve is expressed as Y=f(x) with the direction of YINl, the value given by the following equation 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. Carl 2ei
ss (manufactured by JEN^ Co., Ltd.) at 100 times magnification, the number of projections corresponding to the height of the projections in each photograph is determined and converted to 1 mm2. At this time, the field of view of the 10 photographs is 1.55111 m2.

3. Electromagnetic conversion characteristics (recording density characteristics) 10 S/N (d8) ratio during K8Pl recording and reproduction and 10
The high-density recording characteristics, especially the noise level, are evaluated based on the rate of decrease in the output during 50KBPI recording and reproducing relative to the output during 8Pr recording and reproducing.

4. Long-term durability Repeat recording and playback using a commercially available VIIS system VTR, and evaluate the playback screen after 100 repeated runs using the following criteria.

O: The running is smooth and there is no fluctuation in the playback screen. X: There is some fluctuation in the playback screen.
The distance between each chuck was 100 mm, and the pulling speed was 10 mm/min.

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

6.30 in a hot air circulation furnace (gear aging tester) with a heat shrinkage rate of 150℃
It is calculated using the following formula after free heat shrinkage for a minute.

Original fabric - Shrinkage Double reaction heat shrinkage rate = xloo (%) Original fabric
A length of 300 mm is used as the long original fabric.

Examples 1 to 3 and Comparative Examples 1 to 3 1 part of 1001 ff of dimethyl terephthalate and 70 parts by weight of ethylene glycol and 0.02 parts of zinc acetate as a catalyst.
Mietakebe (added 0,020 mol% to dimedimethyl terephthalate, carried out transesterification reaction while distilling methanol off at 150 to 240°C for 4 hours, then added stabilizer (glycol solution of phosphorus compound) in terms of trimethyl phosphate) 0.014 parts by weight was added, and then 0.014 parts by weight was added as a polycondensation catalyst.
044 weight of antimony trioxide was added, and roughly Table-1
By adding a predetermined amount of silicon oxide having the average particle size described in 1.
A polycondensation reaction is carried out for 4 hours in a high vacuum of mmt 1 g or less,
Polyethylene terephthalate having an intrinsic viscosity (η: O-chlorophenol solvent, measured at 25° 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
The film was sequentially biaxially stretched 3.4 times at 00'C and 4.3 times in the transverse direction at 120'C, and further heat-set at 225°C for 30 seconds to obtain biaxially oriented films each having a thickness of 10μ. that time,
Immediately before the uniaxially stretched film, which had undergone longitudinal stretching, entered the tenter, the coating solution prepared below was uniformly coated on one side of the film by a kiss coating method. The average coating amount at this time was about 40 wetts per meter of the above-mentioned -axially stretched film (this amount corresponds to about 0.02 g per butt of the biaxially stretched film described below). Next, the uniaxially oriented film coated on one side was heat-set, and a biaxially oriented polyester film was formed.

<Coating liquid> Aqueous polyurethane dispersion containing carboxylic acid amine base [
Manufactured by Toyo Polymer ■: Product name Merci 585,128 parts by weight (as non-volatile ingredients), acrylic resin emulsion [
Methyl methacrylate/ethyl acrylate/acrylamide = 49/43/8 (mol%)] 28 parts by weight, polyethylene wax emulsion (melting point 105°C) 7 parts by weight, colloidal silica aqueous dispersion (average particle size 40-50 mμ
) 27 parts by weight and polyoxyethylene nonylphenyl ether [manufactured by NOF ■: trade name NS-208,5]
Dilute and dissolve 10 parts by weight with ion-exchanged water to obtain a solid concentration of 2.
Weight% coating! 5 liquids were prepared.

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

The characteristics of the film surface (I> and ([)) 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 1,000 mm.Then, the film was cut into 1/4" width in the machine direction, and a metal film magnetic recording tape was cut into 1/4" width. and 0.3μ
9.5 cm / using a ring head with a gap length of m
Recording and reproduction were performed at a speed of 1.2 seconds, and electromagnetic conversion characteristics (digital recording density characteristics) were evaluated.

The results are shown in Table-1.

From these results, it is understood that the magnetic recording medium based on the film of the present invention has a large S/N ratio, a significantly superior noise level, and excellent long-term durability.

Examples 4 to 6 and Comparative Examples 4 to 5 Using the same polymer as in Example 2, an unstretched film was prepared and subjected to the film forming conditions listed in Table 2 (however, those not listed in the table were 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 ([).

A cobalt-nickel alloy thin film was formed on the surface (I) of this polyester film by vacuum evaporation to a thickness of 1000 mm. Subsequently, the film was cut into 1/4" width in the machine direction to obtain a metal thin film magnetic recording tape, and recorded and reproduced at a speed of 9.5 cm/sec using a ring head with a gap length of 0.3 μm to determine the electromagnetic conversion characteristics. (digital recording density characteristics) was evaluated.

Furthermore, long-term running durability was evaluated. These results are shown in Table-2.

It can be seen from Table 2 that Examples 4 to 6 have excellent long-term running durability, a large S/N ratio, and a significantly excellent noise level.

[Brief explanation of the drawing]

Figure 11 and Figure 2 are differential interference micrographs of the film surface. Procedure amendment writing method) September 1986, these 2 days

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 transverse direction: 1 to 5% (d) Surface centerline average roughness (Ra) 0.001 to 0.003 μ (e) Number of protrusions with a height (h) of 0.27 to 0.54μ: 0.2 pieces/mm^2 or less (2) Polyurethane, acrylic resin, low molecular weight polyolefin wax, and roughened surface with an average particle size of 0.15μ or less A thin film is formed from a composition whose main component is a substance, the center line average roughness Ra of the surface is 0.002 to 0.01μ, and there is no mountain-like unevenness on the surface, and the thin film is formed. A base film for magnetic recording media in which the metal thin film is formed on the polyester film surface. 2. Biaxially oriented polyester film has an average particle size of 20 to 1
The base film for a magnetic recording medium according to claim 1, containing 0.005 to 0.1% by weight of silicon oxide having a particle diameter of 0.00 mμ.