JP2746786B2 - Polyester film for magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium, and more particularly to a polyester film useful for producing a magnetic recording medium having excellent running properties, electromagnetic conversion characteristics, storage durability and the like.

[0002]

2. Description of the Related Art As a high-density magnetic recording medium, a ferromagnetic metal thin film magnetic recording medium in which a ferromagnetic metal thin film is formed on a nonmagnetic support by a physical deposition method such as vacuum evaporation or sputtering or a plating method is known. . For example, a magnetic tape on which Co is deposited (Japanese Patent Laid-Open No. 54-147010), Co-
Perpendicular magnetic recording media using a Cr alloy
No. 4706) is known. The metal thin film formed by such thin film forming means as vapor deposition, sputtering or ion plating has a very small thickness of 1.5 μm or less, and in spite of that, the thickness of the magnetic recording layer is 3 μm or more. There is an advantage that performance equal to or higher than that of a magnetic recording medium (a magnetic recording medium obtained by mixing a magnetic substance powder into an organic polymer binder and coating it on a nonmagnetic support) can be obtained.

[0003] By the way, it is considered that the magnetic characteristics such as the coercive force Hc or the squareness ratio of the hysteresis loop, which are the static characteristics of the magnetic recording medium, do not depend much on the surface condition of the non-magnetic support used. As an example based on this idea, U.S. Pat. No. 3,787,327 discloses a multilayer structure of Co--Cr by vacuum evaporation.

However, in a metal thin-film type magnetic recording medium, the thickness of the metal thin film formed on the surface of the non-magnetic support is small, and the surface condition (surface unevenness) of the non-magnetic support is not changed on the surface of the magnetic recording layer. As a drawback that it causes noise.

[0005] From the viewpoint of noise, it is preferable that the surface state of the nonmagnetic support is as smooth as possible. On the other hand, from the viewpoint of handling such as winding and unwinding of the base film, if the film surface is smooth, the sliding property between the film and the film is poor, and a blocking phenomenon occurs.
It cannot be a product and therefore requires a rough base film surface. As described above, the surface of the non-magnetic support is required to be smooth from the viewpoint of electromagnetic conversion characteristics, and is required to be rough from the viewpoint of handling properties. Therefore, it is necessary to simultaneously satisfy these two conflicting properties.

Further, a serious problem of the metal thin film magnetic recording medium when it is actually used is the running property of the metal thin film surface. In the case of a coating type magnetic recording medium in which a conventional magnetic powder is mixed with an organic polymer binder and applied to a base film, a lubricant is dispersed in the binder to improve the runnability of the magnetic surface. However, in the case of a metal thin-film magnetic recording medium, such measures cannot be taken, and it is very difficult to maintain a stable running property.
In particular, it has disadvantages such as poor running performance at high temperature and high humidity.

For the purpose of improving this drawback, Japanese Patent Publication No. Sho 62
Japanese Patent No. 30105 proposes forming fine projections on the film surface using fine particles, a water-soluble resin and a silane coupling agent. In addition, Japanese Patent Publication 62-30
No. 106 and JP-A-59-229316 propose to form fine projections on the film surface using fine particles and a water-soluble resin. However, all of them have fine particles present in the trapezoidal protrusions of the water-soluble resin, and do not have fine particles uniformly present on the film surface. Japanese Patent Publication No. 34456/1989 proposes that a discontinuous film of a water-soluble polymer and fine particles forming higher projections are independently adhered to the film surface. However, this is inferior in uniformity on the film surface because the projections are discontinuous films and are due to fine particles that are not uniformly dispersed.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the drawbacks of the prior art and to provide a magnetic recording medium having excellent running properties and electromagnetic conversion characteristics, particularly a polyester film useful for producing a metal thin film magnetic recording medium. Is to provide.

[0009]

The present invention has the following arrangement to attain the object.

The surface of the polyester film is coated with a primer for a magnetic layer consisting of a continuous thin film, and the continuous thin film has fine protrusions (A) having fine particles having an average particle diameter of 0.1 μm or less as nuclei and resin as a binder. ) And microprojections (B) made only of the resin. The height of the microprojections (A) is 13 nm or less, and is 1.0 × 10 ^{4 to} 1.0 × 10 ⁸ / mm ² . Present in a small proportion, and the fine protrusions (B) were 4.0 ×
10 ⁶ / mm ² present in the following proportions, micro surface roughness Ra ^s of the continuous thin film portion by only the resin is not more than 1.10 nm, and a surface roughness Ra of the continuous film is 1~10n
m, a polyester film for a magnetic recording medium.

The polyester constituting the film of the present invention is a linear saturated polyester synthesized from an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof. Preferred specific examples of such a polyester include polyethylene terephthalate,
Examples thereof include polyethylene isophthalate, polytetramethylene terephthalate, poly (1,4-cyclohexylene dimethylene terephthalate), polyethylene-2,6-naphthalenedicarboxylate, and the like, and copolymers of these or other resins with a small proportion thereof And the like.

[0012] Such a polyester can be produced by a conventionally known method. For example, polyethylene terephthalate can be produced by an esterification reaction of terephthalic acid and ethylene glycol or a transesterification reaction of dimethyl terephthalate and ethylene glycol, followed by polycondensation of the reaction product.
In that case, a known catalyst can be used, but it is preferable to use an organic titanium compound as a catalyst for the polycondensation reaction from the viewpoint of film characteristics.

As the organic titanium compound, there can be mentioned, for example, those described in JP-A-63-278927. To further explain, an alcoholate or an organic acid salt of titanium, a reaction product of a tetraalkyl titanate with an aromatic polycarboxylic acid or an anhydride thereof and the like can be exemplified, and titanium tetrabutoxide as a preferred specific example,
Examples include titanium isopropoxide, titanium oxalate, titanium acetate, titanium benzoate, titanium trimellitate, and a reaction product of tetrabutyl titanate with trimellitic anhydride. The amount of the organic titanium compound used is preferably such that the titanium atom accounts for 3 to 10 mg atom% based on the acid component constituting the polyester.

In the polyester, a surface roughening material well-known in the art, such as calcium carbonate, kaolinite, titanium dioxide, silica, alumina, and other additives may be added to the polyester within a range not to impair the purpose of the present invention. An agent can be contained.

The above polyester is melt-extruded by a conventional method, stretched and oriented biaxially, and heat-set to form a film. Biaxial stretching can be performed by a biaxial stretching method such as a sequential biaxial stretching method or a simultaneous biaxial stretching method. This biaxially oriented polyester film usually has a crystal orientation characteristic in which the heat of fusion obtained at a heating rate of 10 ° C./min in a nitrogen atmosphere using a differential scanning calorimeter is 4 cal / g or more. The film thickness after stretch orientation is generally 3 to 100 μm.
m, preferably in the range of 4 to 50 μm.

In the present invention, a continuous thin film is applied on the surface of the polyester film as a primer for the magnetic layer. Then, a magnetic layer, in particular, a ferromagnetic metal thin film layer is formed on this thin film. On the surface of this continuous thin film, microprojections (A) having fine particles having an average particle diameter of 0.1 μm or less, preferably 0.05 μm or less as nuclei and a resin as a binder were used.
0 × 10 ^{4 to} 1.0 × 10 ⁸ pieces / mm ² , preferably 1.
It is present at a rate of 0 × 10 ^{5 to} 8.0 × 10 ⁷ pieces / mm ² . The height of the microprojections (A) is 13 nm or less, preferably 12 nm or less. Further, on the surface of the continuous thin film, there are no more than 4.0 × 10 ⁶ microprotrusions (B) / mm ² , preferably 8.0 × 10 ⁶ , of the background made of only the binder resin.
⁵ / mm ² present in the following proportions, micro surface roughness Ra ^s of the continuous thin film portion by only the resin (background portion) is 1.10nm
Or less, preferably 1.00 nm or less. And, the surface roughness (whole surface roughness) Ra of the continuous thin film is 1 to 1
0 nm (0.001 to 0.010 μm), preferably 1
７7 nm (0.001 to 0.007 μm).

The fine particles include organic fine particles such as polystyrene, polymethyl methacrylate, methyl methacrylate copolymer, cross-linked methyl methacrylate copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, and benzoguanamine resin; silica; Alumina, titanium dioxide, kaolin,
Any of inorganic fine particles such as talc, graphite, calcium carbonate, feldspar, molybdenum disulfide, carbon black, and barium sulfate may be used. These may be in the form of an aqueous dispersion using an emulsifier or the like, or may be in the form of a fine powder that can be added to the aqueous liquid.

Examples of the resin (binder) for binding the fine particles to the polyester film surface include an alkyd resin,
Examples thereof include unsaturated polyester resins, saturated polyester resins, phenol resins, epoxy resins, amino resins, polyurethane resins, vinyl acetate resins, vinyl chloride-vinyl acetate copolymer resins, acrylic resins, and acrylic-polyester resins. These resins may be a homopolymer, a copolymer, or a mixture.

The acrylic resin may be, for example, an acrylate ester (alcohol residues include methyl, ethyl, n-propyl, isopropyl, n-butyl,
Isobutyl group, t-butyl group, 2-ethylhexyl group,
Examples thereof include a cyclohexyl group, a phenyl group, a benzyl group and a phenylethyl group); methacrylic acid esters (alcohol residues are the same as described above); 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate,
Hydroxy-containing monomers such as -hydroxypropyl acrylate, 2-hydroxypropyl methacrylate; acrylamide, methacrylamide, N-methylmethacrylamide, N-methylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N, N-dimethylol Amide group-containing monomers such as acrylamide, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-phenylacrylamide; amino group-containing monomers such as N, N-diethylaminoethyl acrylate and N, N-diethylaminoethyl methacrylate; Epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether; styrene sulfonic acid, vinyl sulfo Monomers containing sulfonic acid groups or salts thereof, such as acids and salts thereof (eg, sodium salts, potassium salts, ammonium salts, etc.); crotonic acid, itaconic acid, acrylic acid, maleic acid, fumaric acid, and Monomers containing a carboxyl group or a salt thereof such as a salt (eg, sodium salt, potassium salt, ammonium salt, etc.); monomers containing an anhydride such as maleic anhydride or itaconic anhydride; other vinyl isocyanate, allyl isocyanate, styrene , Vinyl methyl ether, vinyl ethyl ether, vinyl trisalkoxysilane, alkyl maleic acid monoester,
Alkyl fumaric acid monoester, acrylonitrile,
(Meth) acrylic monomers such as acrylic acid derivatives and methacrylic acid derivatives, which are made from a combination of monomers such as methacrylonitrile, alkyl itaconic acid monoester, vinylidene chloride, vinyl acetate and vinyl chloride Is preferably contained in an amount of 50 mol% or more, particularly preferably a component containing a methyl methacrylate component.

Such an acrylic resin can be self-crosslinked with a functional group in the molecule, or can be crosslinked with a crosslinking agent such as a melamine resin or an epoxy compound.

The acid components constituting the polyester resin include, for example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-cyclohexanedicarboxylic acid, 2,6-
Naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, succinic acid, 5-sodium sulfoisophthalic acid, 2
—Polyvalent carboxylic acids such as potassium sulfoterephthalic acid, trimellitic acid, trimesic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, and monopotassium trimellitic acid salt. Examples of the hydroxy compound component include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol,
-Xylylene glycol, ethylene oxide adduct of bisphenol A, diethylene glycol, triethylene glycol, polyethylene oxide glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, dimethylolpropionic acid Examples include polyvalent hydroxy compounds such as potassium. A polyester resin can be prepared from these compounds by a conventional method. When making an aqueous coating liquid, 5
-It is preferable to use a polyester resin containing a sodium sulfoisophthalic acid component or a carboxylate group.
Such a polyester resin can be a self-crosslinking type having a functional group in the molecule, or can be crosslinked using a curing agent such as a melamine resin or an epoxy resin.

Further, the acryl-polyester resin is used to mean an acryl-modified polyester resin and a polyester-modified acryl resin. The acryl-polyester resin is one in which an acryl resin component and a polyester resin component are bonded to each other. Type, block type, etc. Acrylic-polyester resin, for example, adds a radical initiator to both ends of the polyester resin to polymerize the acrylic monomer, or attaches a radical initiator to the side chain of the polyester resin to polymerize the acrylic monomer. Alternatively, it can be produced by attaching a hydroxyl group to the side chain of the acrylic resin and reacting it with a polyester having an isocyanate group or a carboxyl group at a terminal to obtain a comb polymer.

As a method for forming fine projections having fine particles as cores and a resin as a binder on the surface of a polyester film, a resin coating solution containing fine particles, preferably an aqueous coating solution, is used during the production process of the polyester film. A method of applying and drying and solidifying the surface, or a method of applying and drying and solidifying a resin coating solution containing fine particles on a biaxially oriented polyester film can be employed, but the former is more preferable. Inclusion of a surfactant for facilitating application in these coating solutions is inevitable.

The ratio between the fine particles and the resin (binder) is preferably determined by the above-mentioned design of the surface properties. The total amount of the fine particles is 1 to 40% by weight, and the resin as the binder is 20 to 40% by weight. Preferably it is 95% by weight. If the amount of the fine particles is too small, a predetermined amount of projections cannot be uniformly provided on the coating film. On the other hand, if the amount is too large, the dispersibility deteriorates and it is difficult to uniformly provide the predetermined amount of projections. If the amount of the resin serving as the binder is too small, the adhesion of the coating film to the polyester film decreases, while if the amount is too large, the blocking resistance decreases.

As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brushing method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method, or the like may be applied alone or in combination.

When a magnetic layer, particularly a metal thin film magnetic layer, is provided on the continuous thin film formed in this manner, noise is drastically reduced, the noise level is excellent in each step, and the running and storage of the metal thin film surface are improved. Excellent durability can be obtained.

In the present invention, it is preferable to coat a continuous thin film for forming a smooth surface on the other surface of the polyester film, that is, the surface opposite to the surface on which the continuous thin film serving as a primer of the magnetic layer is provided. This thin film has a cellulosic resin and an average particle diameter of 0.15 μm or less, preferably 0.05 μm or less.
Containing fine particles of 1 to 0.1 μm and having a surface roughness Ra
Is 2 to 10 nm (0.002 to 0.01 μm), preferably 3 to 9 nm (0.003 to 0.009 μm).

Examples of the cellulose resin include ethyl cellulose, methyl cellulose, acetyl cellulose, acetoacetyl cellulose, nitrocellulose, carboxylated cellulose, carboxymethyl cellulose, and cellulose acetate butyrate.
By using this cellulosic resin, many minute folds can be formed on the surface of the coating film.

The fine particles include polystyrene,
Organic fine particles such as polymethyl methacrylate, methyl methacrylate copolymer, methyl methacrylate copolymer crosslinked product, polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, benzoguanamine resin, silica, alumina, titanium dioxide, kaolin, talc, graphite Any of inorganic fine particles such as calcium carbonate, feldspar, molybdenum disulfide, carbon black, barium sulfate and the like may be used. These may be in the form of an aqueous dispersion using an emulsifier or the like,
Further, those which can be added to the aqueous liquid in the form of fine powder may be used.

The cellulosic resin and the fine particles have an effect of promoting uniform formation of fine projections on the coating film itself and a function of reinforcing the coating film by the fine particles themselves. Combined with the effect on the reduction and the like, and the improvement of the scratch resistance due to the synergistic action of the two, it gives the film excellent slipperiness.

The resin forming the thin film having a smooth surface is preferably a resin excellent in blocking resistance, frictional force reducing property and the like, and preferably includes acrylic resin, polyester resin and acryl-polyester resin. In the description of these resins, the description of the acrylic resin, polyester resin, and acrylic-polyester resin described above as the resin used for forming the magnetic layer primer can be used as it is.

The mixing ratio of the components forming the smooth surface, that is, the thin film forming resin (component a), the cellulose resin (component b) and the fine particles (component c) is preferably determined by designing the surface characteristics. Component a is 30 to 80% by weight, component b is 1 to 50% by weight, component c is 5 to 40% by weight
It is preferred that If the amount of the component a is too small, the adhesion of the coating film to the polyester film is reduced. On the other hand, if the amount is too large, the blocking resistance and the slipperiness are reduced. When the amount of the component b is too small, the folds of the coating film are reduced and workability is deteriorated. On the other hand, when the amount is too large, the surface is too rough. If the amount of the component c is too small, the lubricity is reduced, while if it is too large, the particles are liable to fall off from the coating film.

The formation of the coating film in the present invention may be carried out after the production of the polyester film or during the production of the polyester film, but is preferably carried out during the production of the polyester film. For example, it is preferable to apply an aqueous coating solution to the surface of the polyester film before the completion of the crystal orientation.

Here, the polyester film before the completion of the crystal orientation means an unstretched film obtained by melting and extruding a polyester into a film as it is, and the unstretched film is oriented in either the longitudinal direction or the transverse direction. The stretched uniaxially stretched film, and further stretched in the biaxial direction,
At least one direction is a low-magnification stretching, and a biaxially stretched film which requires stretching orientation in the direction (finally in the longitudinal direction and / or
Or a biaxially stretched film before re-stretching in the transverse direction to complete the oriented crystallization.

The film of the present invention is preferably prepared by applying an aqueous coating liquid having the above composition to a film that has not been stretched or has been stretched at least in a uniaxial direction before completion of the crystal orientation,
Next, it is manufactured by a so-called in-line coating method in which longitudinal stretching and / or transverse stretching and heat setting are performed. At that time, in order to smoothly apply the coating film on the surface of the polyester film before the completion of the oriented crystal, a corona discharge treatment is performed on the film surface as a preliminary treatment, or together with the coating composition, It is preferable to use a chemically inert surfactant in combination. Such a surfactant can lower the surface tension of the aqueous coating solution to 40 dyne / cm or less, and promotes wetting of the polyester film. Examples of the surfactant include polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, Examples of the surfactant include anionic and nonionic surfactants such as glycerin fatty acid ester, fatty acid metal soap, alkyl sulfate, alkyl sulfonate, and alkyl sulfosuccinate. Further, other additives such as, for example, an antistatic agent, an ultraviolet absorber, and a lubricant can be mixed within a range in which the effects of the present invention are not lost.

In the present invention, the solid content of the coating liquid, especially the aqueous coating liquid, is usually 30% by weight or less, preferably 15% by weight or less. This viscosity is usually 100 centipoise (cp
s) or less, preferably 20 cps or less. The amount of coating is preferably about 0.5 to 20 g, and more preferably about 1 to 10 g per m ² of the running film. In other words, in the finally obtained biaxially oriented film, about 0.001 to 1 g per 1 m ² , and more preferably about 0.005 to 1
Preferably, the solid content is 0.3 g.

As a coating method, any known coating method can be applied. For example, a roll coating method, a gravure coating method, a roll brushing method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method, or the like may be applied alone or in combination.

According to a preferred production method of the present invention,
The aqueous coating liquid is applied to the film immediately after the longitudinal uniaxial stretching, and the film is guided to a tenter for transverse stretching and heat setting. At that time, the coated material is expanded in the state of an unsolidified coating film as the film is stretched, and the area thereof is expanded and heated to evaporate water, and a thin solid continuous coating layer is formed on the surface of the biaxially stretched film. The film is converted and firmly fixed to the biaxially stretched film surface. The above stretching and heat treatment are preferably performed at a temperature from about 80C to about 240C. The heat treatment is usually performed for about 1 to about 20 seconds.

Conditions for oriented crystallization of the polyester film,
For example, stretching, heat setting, and the like can be performed under conditions conventionally accumulated in the art.

The production of a metal thin-film magnetic recording medium using the polyester film of the present invention can be performed by a method known per se,
For example, JP-A-54-147010, JP-A-52-147010
The method can be performed by the method described in 134706, specifically, a vacuum deposition method, an ion plating method,
A sputtering method can be preferably used.

The polyester film of the present invention can form a magnetic layer which is smooth and excellent in running property and storage durability, in particular, a metal thin-film magnetic layer, greatly reduces noise, has a remarkably excellent noise level, and has a magnetic surface. In particular, it is useful for manufacturing a magnetic recording medium having excellent running properties on a metal thin film surface, particularly, a metal thin film magnetic recording medium.

The various properties herein are measured as follows.

(1) Intrinsic viscosity [η] It is determined from the value measured at 35 ° C. in an orthochlorophenol solvent.

(2) Average particle diameter The average particle diameter is represented by the “equivalent spherical diameter” of the particles at 50% by weight of the total particles determined by the light transmission centrifugal sedimentation method.

(3) Number of protrusions The number of protrusions on the film surface is measured by a scanning electron microscope. That is, a microprojection having fine particles as a nucleus has a magnification of 20,000 to 50,000 times, and a microprojection made of resin alone has a magnification of 10,000 to 20,000 times.
Evaluate by 10,000 times.

(4) Height of Microprojections The height of the microprojections on the film surface is measured by a three-dimensional roughness meter (scanning tunnel microscope) using a tunnel current. That is, using a sample in which gold having a thickness of 200 Å was uniformly deposited on the film surface, the voltage applied between the surface to be measured and the metal probe was 0.8 V, and the set tunnel current was 0.5 nA. The height of each microprojection is measured by measuring a range of 2 μm × 2 μm in the atmosphere, and the average value of 10 microprojections is defined as the height of the microprojections.

[0047] (5) Measurement length in the direction of the micro surface roughness Ra ^s above its center line by selecting a portion having no microprotrusions from the film surface roughness curve in the range of 2 microns × 2 microns as measured on the same sample When the roughness curve is represented by Y = f (x) with the center line of the extracted portion taken as the X axis and the direction of the vertical magnification as the Y axis, the value given by the following equation is obtained. Expressed in nm.

[0048]

(Equation 1)

In practice, this measurement is based on a value obtained for a length of 0.4 to 1.2 μm in a portion having no microprojections, and
And times, and small surface roughness Ra ^s with a mean value of 10 measurements.

(6) Surface Roughness Ra (Center Line Average) According to JIS B0601, using a high-precision surface roughness meter SE-3FAT manufactured by Kosaka Laboratory Co., Ltd. Radius 2μ
m, load 30mg, magnification 200,000, cut off 0.0
Under the condition of 8 mm, the chart is drawn, a portion of the measured length L is extracted from the film surface roughness curve in the direction of the center line, the center line of the extracted portion is set as the X axis, and the direction of the vertical magnification is set as the Y axis. When the roughness curve is represented by Y = f (x),
The value given by the following equation is expressed in μm.

[0051]

(Equation 2) This measurement was performed for four pieces with the reference length set to 1.25 mm, and the average value was shown.

(7) Coefficient of friction (film slippery) The coefficient of static friction (μs) is measured using a slippery measuring device manufactured by Toyo Tester Co. according to ASTM D1894-63. However, the thread plate is a glass plate and the load is 1
kg. The film slippery is determined based on the following criteria: ：: good (less than μs 0.6) Δ: slightly poor (μs 0.6 to 0.8) ×: bad (μs 0.8 or more) )

(8) Running Durability FIG. 1 is a schematic view of an apparatus for evaluating film running properties. In the drawing, 1 is a payout reel, 2 is a tension controller, 3, 5, 6, 8, 9, and 11 are free rollers, 4 is a tension detector (entrance), 7 is a chrome-plated fixing pin (5 mmφ), and 10 is tension. A detector (outlet), 12 is a guide roller, and 13 is a take-up reel.

As shown in FIG. 1, under a 20 ° C., 60% RH atmosphere, the film was attached to a fixed pin having an outer diameter of 5 mm at an angle θ = (15
(2/180) π radian (152 °), and move and rub at a speed of 3.3 cm per second. The tension controller 2 is adjusted so that the entrance tension (T ₁ ) becomes 30 g, the vehicle is run for 10 m, rewinded, and the running is repeated again. This reciprocation is one time.

1) Sharpness Observe whether there is any substance deposited on the fixed pin after running 30 times repeatedly, and evaluate at the following level: ○: Deposit hardly recognized △: Some with traces of adhesion ×: Many

2) Scratch resistance Observation of the friction state (degree of occurrence of scratches) on the film surface after running 30 times was repeated and evaluated at the following levels: ○: Scratch hardly recognized X: Significant occurrence What you do

(9) Electromagnetic conversion characteristics S / N (dB) ratio at 10 KBPI recording / reproducing and 10K
The high-density recording characteristics, particularly the magnitude of the noise level, are evaluated based on the reduction rate of the output at the time of 50 KBPI recording / reproduction with respect to the output at the time of BPI recording / reproduction. Less than output decrease rate A = (Output at 10 KBPI recording / reproduction) / (Output at 50 KBPI recording / reproduction) ：: A is less than 10 ×: A is 10 or more

(10) Tape running property A commercially available 8 mm VT under two conditions of normal temperature, normal humidity, and high temperature and high humidity
Using R, the screen fluctuation due to disturbance in tape running when recording and reproduction were repeated was observed. The evaluation criteria are as follows: ○: Running smoothly, no fluctuation in reproduction evaluation ×: Driving slows down in some places, causing fluctuation in reproduction screen

(11) Scratch resistance (adhesion) The scratch resistance was observed on the tape thin film after running 100 times under normal temperature, normal humidity and high temperature and high humidity conditions. The evaluation criteria are as follows: ：: almost no scratches are observed on the tape thin film surface ○: extremely weak scratches are slightly observed on the tape thin film surface ×: tape thin film surface Severe scratches occur on the upper surface. The normal temperature and normal humidity are conditions of 25 ° C. and 60% RH, and the high temperature and high humidity conditions are 40 ° C. and 80% RH.

[0060]

The present invention will be further described below with reference to examples. The “parts” in the examples are parts by weight.

[0061]

Example 1 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, manganese acetate tetrahydrate 0.019
Parts and 0.013 part of sodium acetate trihydrate were charged into a reactor, and transesterification was carried out while gradually increasing the internal temperature from 145 ° C. When the transesterification rate reaches 95%, 0.044 part of a glycol solution of a phosphorus compound obtained by previously reacting 25 parts of trimethyl phosphate and 75 parts of ethylene glycol is added as a stabilizer, and ethylene glycol 2 is used as a polymerization catalyst. 0.8 parts trimellitic anhydride and 0.6 parts tetrabutyl titanate in 5 parts
Liquid with 5 parts reacted (titanium content 11% by weight)
0.011 part was added. Next, the reaction product was transferred to a polymerization reactor and subjected to a polycondensation reaction under a high-temperature vacuum (final internal temperature: 290 ° C.) to obtain polyethylene terephthalate having an intrinsic viscosity of 0.60.

The polyethylene terephthalate was melt-extruded according to a conventional method, quenched to prepare a 131 μm-thick unstretched film, and then the unstretched film was vertically stretched by 9 mm.
Sequential biaxial stretching was performed 3.6 times at 0 ° C. and 3.7 times at 105 ° C. in the horizontal direction, and heat setting was further performed at 230 ° C. for 30 seconds to prepare a biaxially oriented film having a thickness of 9.8 μm. .

At this time, a coating solution having the following composition was applied to the uniaxially stretched film before the transverse stretching by a roll coating method to obtain the surface (A) of the film.
And (B). The surface (A) is the surface on the side on which the magnetic layer is formed, and the surface (B) forms a smooth surface.

Composition of the coating liquid applied to the film surface (A): 83.5 parts of a 1.5 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Oil & Fats Co., Ltd.), polymethyl methacrylate fine particles (Nippon Shokubai Chemical Co., Ltd.) 1.5 parts by weight of a 1.5 wt% solution of Eposter MA (manufactured by Kogyo Co., Ltd.) (however, the average particle size of the fine particles is 0.03 μm), and polyoxyethylene nonylphenyl ether (NS208. 15 parts of a 1.5 wt% solution of 5). The coating amount is 2.7 g / m ² on a wet basis.

Composition of coating liquid applied to film surface (B): 54.7 parts of a 2.1 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), a cellulose resin (Shin-Etsu Chemical Co., Ltd.) 23.1 parts of a 2.1 wt% solution of methyl cellulose SM-15 manufactured by Nippon Shokubai Co., Ltd .; 9.0 parts of a 2.1 wt% solution of polymethyl methacrylate fine particles (Eposter MA manufactured by Nippon Shokubai Chemical Industry Co., Ltd.) The average particle size is 0.03 μm), and a 1 wt% solution of polyoxyethylene nonyl phenyl ether (NS208.5 manufactured by NOF Corporation) of 12.0%
Department. The coating amount is 4.0 g / m ² on a wet basis.

Using a vacuum deposition apparatus, place the polyester film along a cylindrical can having a diameter of 1 m along with a 5 × 10
^-5 (Torr) oxygen at a minimum incident angle of 43 degrees with Co-N
i (containing 20 wt% of Ni) was obliquely deposited so as to have a film thickness of about 1500 angstroms, and then slit into a width of 8 mm to obtain a magnetic tape.

Table 1 shows the characteristics of the polyester film and the magnetic recording medium provided with a magnetic layer on the surface (A) side of the film.

[0068]

Example 2 In Example 1, when the internal temperature during the transesterification reaction reached 190 ° C., an ethylene glycol slurry of silicon dioxide having an average particle size of 0.10 μm (10 wt% of silicon dioxide / ethylene glycol slurry) was used. 3
A polyester film and a magnetic recording medium were obtained in exactly the same manner as in Example 1 except that 0 part was added and the coating liquid applied to the film surface (A) was changed as follows. Table 1 shows these characteristics.

Composition of coating liquid applied to film surface (A): Polyester resin (Pluscoat Z-, manufactured by Ryo Kagaku Co., Ltd.)
461), 55.0 parts of a 0.7 wt% solution of polymethyl methacrylate fine particles (Nippon Shokubai Kagaku Kogyo Co., Ltd. Eposter MA) 30.0 wt% solution
Parts (however, the average particle diameter of the fine particles is 0.03 μm), and 15.0 parts of a 0.7 wt% solution of polyoxyethylene nonyl phenyl ether (NS240 manufactured by NOF Corporation). The coating amount is 2.7 g / m ² on a wet basis.

[0070]

Example 3 0.021 part of manganese salicylate and 0.005 part of potassium acetate were added to a mixture of 100 parts of dimethyl 2,6-naphthalenedicarboxylate and 60 parts of ethylene glycol, and 0.007 part of titanium oxalate was further added. , 1
The transesterification reaction was performed while gradually raising the temperature from 50 ° C to 240 ° C. When the transesterification reaction rate reaches 93%, trimethyl phosphate 2
0.032 parts of a mixture obtained by reacting 5 parts with 75 parts of ethylene glycol was added at a liquid temperature of 140 ° C., and 0.130 parts of an ethylene glycol slurry (10 wt%) of silicon dioxide having an average particle diameter of 0.010 μm was further added. Was added. Next, the reaction product was transferred to a polymerization reactor, and a polycondensation reaction was carried out under a high-temperature vacuum (final internal temperature: 280 ° C.) to give an intrinsic viscosity of 0.57.
Of polyethylene-2,6-naphthalate.

This polyethylene-2,6-naphthalate was melt-extruded according to a conventional method, quenched to prepare an unstretched film having a thickness of 78 μm, and then the unstretched film was stretched 4.0 times in the longitudinal direction at 135 ° C. The film was successively biaxially stretched at 145 ° C. in the direction of 5.0 times and further heat-set at 200 ° C. for 30 seconds to prepare a biaxially oriented film having a thickness of 4.0 μm.

At this time, a coating solution having the following composition was applied to the uniaxially stretched film before the transverse stretching by the roll coating method to obtain the surface (A) of the film.
And (B). The surface (A) is the surface on the side on which the magnetic layer is formed, and the surface (B) forms a smooth surface.

Composition of coating liquid applied to film surface (A): 30.0 parts of a 0.7 wt% solution of polyester resin (Polyester WR961 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), acryl-polyester resin (Takamatsu Oil 35.0 parts of a 0.7 wt% solution of Pesresin SH551A manufactured by Co., Ltd.), colloidal silica (Cataloid-SN manufactured by Catalysis Kasei Co., Ltd.)
5.0 parts by weight of a 0.7% by weight solution, and 30.0 parts by weight of a 0.7% by weight solution of a polyoxyethylene nonylphenyl ether (NS240 manufactured by NOF Corporation). The coating amount is 3.8 g / m ² on a wet basis.

Composition of the coating liquid applied to the film surface (B): 54.7 parts of a 2.0 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), a cellulose resin (Shin-Etsu Chemical Co., Ltd.) 24.3 parts of a 2.0 wt% solution of methylcellulose SM-15 manufactured by Catalysis-SI-Cataloid-SI-
350), 2.0 wt% solution of polyoxyethylene nonyl phenyl ether (NS208.5, manufactured by NOF Corporation) 10.0 wt% solution
Department. The coating amount is 5.6 g / m ² on a wet basis.

Table 1 shows the characteristics of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the surface (A) side of this film in the same manner as in Example 1.

[0076]

Example 4 A mixture of 100 parts of terephthalic acid bis-β-hydroxyethyl ester, 65 parts of terephthalic acid and 29 parts of ethylene glycol was subjected to an esterification reaction at a temperature of 210 to 230 ° C. The reaction was terminated when the amount of distilled water produced by the reaction reached 13 parts, and the reaction product 1
0.0067 parts of titanium acetate was added per 00 parts. Next, the reaction product was transferred to a polymerization reactor, and a polycondensation reaction was carried out under a high-temperature vacuum (final internal temperature: 285 ° C.) to give an intrinsic viscosity of 0.6.
0 was obtained.

This polyethylene terephthalate was melt-extruded according to a conventional method and rapidly cooled to prepare a 131 μm-thick unstretched film.
The film was subjected to sequential biaxial stretching at 3.6 ° C. and 3.7 times at 105 ° C. in the transverse direction, and further heat-set at 230 ° C. for 30 seconds to prepare a 9.8 μm thick biaxially oriented film.

At this time, the coating solution having the following composition was applied to the uniaxially stretched film before the transverse stretching by the roll coating method to obtain the surface (A) of the film.
And (B). The surface (A) is the surface on the side on which the magnetic layer is formed, and the surface (B) forms a smooth surface.

Composition of coating liquid applied to film surface (A): 69.9 parts of a 1.5 wt% solution of acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), polymethyl methacrylate fine particles (Nippon Shokubai Chemical Co., Ltd.) 0.1 parts of a 1.5 wt% solution of Eposter MA (manufactured by Kogyo Co., Ltd.) (however, the average particle size of the fine particles is 0.03 μm), polyoxyethylene nonyl phenyl ether (NS240 manufactured by NOF Corporation) 30.0 parts of a 1.5 wt% solution of The coating amount is 1.9 g / m ² on a wet basis.

Composition of the coating liquid applied to the film surface (B): 56.7 parts of a 3.0 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), a cellulose resin (Shin-Etsu Chemical Co., Ltd.) 24.3 parts of a 3.0% by weight solution of methyl cellulose SM-15 manufactured by Nippon Shokubai Co., Ltd .; 9.0 parts of a 3.0% by weight solution of polymethyl methacrylate fine particles (Eposter MA manufactured by Nippon Shokubai Chemical Industry Co., Ltd.) The average particle size is 0.035 μm), and a 3.0 wt% solution of polyoxyethylene nonyl phenyl ether (NS208.5 manufactured by NOF Corporation) 10.0
Department. The coating amount is 4.0 g / m ² on a wet basis.

Table 1 shows the properties of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the surface (A) side of this film in the same manner as in Example 1.

[0082]

Example 5 A polyester film was obtained in exactly the same manner as in Example 1 except that the coating solution applied to the film surface (A) was changed as follows.

Table 1 shows the properties of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the film surface (A) side in the same manner as in Example 1.

Composition of coating liquid applied to film surface (A): 83.5 parts of a 6.0 wt% solution of polyester resin (Polyester WR961 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), polymethyl methacrylate fine particles (Nippon Shokubai) 1.5 parts of a 6.0 wt% solution of Epcot MA (manufactured by Chemical Industry Co., Ltd.) (however, the average particle size of the fine particles is 0.06 μm); polyoxyethylene nonylphenyl ether (NS240 manufactured by NOF Corporation) ) Of 16.0 parts by weight of a 6.0 wt% solution. The coating amount is 4.0 g / m ² on a wet basis.

[0085]

Comparative Example 1 A polyester film was obtained in exactly the same manner as in Example 1 except that the coating liquid applied to the film surface (A) was changed as follows.

Table 1 shows the properties of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the film surface (A) side in the same manner as in Example 1.

Composition of coating liquid applied to film surface (A): 83.5 parts of a 1.5 wt% solution of acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), polymethyl methacrylate fine particles (Nippon Shokubai Kagaku) 1.5 parts by weight of a 1.5 wt% solution of Eposter MA (manufactured by Kogyo Co., Ltd.) (however, the average particle size of the fine particles is 0.06 μm), polyoxyethylene nonyl phenyl ether (NS240 manufactured by NOF Corporation) 15.0 parts of a 1.5 wt% solution of The coating amount is 2.7 g / m ² on a wet basis.

[0088]

Comparative Example 2 A polyester film was obtained in exactly the same manner as in Example 1, except that the coating solution applied to the film surface (A) was changed as follows.

Table 1 shows the characteristics of the obtained polyester film and the magnetic recording medium having a magnetic layer provided on the film surface (A) side in the same manner as in Example 1.

Composition of coating liquid applied to film surface (A): 83.5 parts of a 4.7 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), 83.5 parts of polymethyl methacrylate fine particles (Nippon Shokubai Kagaku) 1.5 parts of 4.7 wt% solution of Eposter MA (manufactured by Kogyo Co., Ltd.) (however, the average particle size of the fine particles is 0.03 μm), polyoxyethylene nonylphenyl ether (NS240 manufactured by NOF Corporation) 15.0 parts of a 4.7 wt% solution of The coating amount is 2.7 g / m ² on a wet basis.

[0091]

Comparative Example 3 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, manganese acetate tetrahydrate 0.019
Parts and 0.013 part of sodium acetate trihydrate were charged into a reactor, and transesterification was carried out while gradually increasing the internal temperature from 145 ° C. When the transesterification rate reaches 95%, 0.044 part of a glycol solution of a phosphorus compound obtained by previously reacting 25 parts of trimethyl phosphate and 75 parts of ethylene glycol is added as a stabilizer, and ethylene glycol 2 is used as a polymerization catalyst. 0.8 parts trimellitic anhydride and 0.6 parts tetrabutyl titanate in 5 parts
Liquid with 5 parts reacted (titanium content 11% by weight)
0.011 part was added. Next, the reaction product was transferred to a polymerization reactor, and a polycondensation reaction was performed under a high-temperature vacuum (final internal temperature: 290 ° C.) to obtain polyethylene terephthalate having an intrinsic viscosity of 0.60.

The polyethylene terephthalate was melt-extruded according to a conventional method and quenched to prepare a 131 μm-thick unstretched film.
The film was successively biaxially stretched at 3.6 ° C. and 3.7 times at 105 ° C. in the transverse direction, and heat-set at 200 ° C. for 30 seconds to prepare a 9.8 μm thick biaxially oriented film.

At this time, the coating solution having the following composition was applied to the uniaxially stretched film before the transverse stretching by the roll coating method to obtain the film surface (A).
And (B). The surface (A) is the surface on the side on which the magnetic layer is formed, and the surface (B) forms a smooth surface.

Composition of coating liquid applied to film surface (A): 83.0 parts of a 1.3 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), polymethyl methacrylate fine particles (Nippon Shokubai Chemical Co., Ltd.) 2.0 parts of 1.3 wt% solution of Eposter MA (manufactured by Kogyo Co., Ltd.) (however, the average particle size of the fine particles is 0.03 μm), polyoxyethylene nonylphenyl ether (NS208. 15 parts of a 1.3 wt% solution of 5). The coating amount is 2.7 g / m ² on a wet basis.

Composition of the coating liquid applied to the film surface (B): 54.7 parts of a 2.1 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), a cellulose resin (Shin-Etsu Chemical Co., Ltd.) 23.1 parts of a 2.1 wt% solution of methyl cellulose SM-15 manufactured by Nippon Shokubai Co., Ltd .; 9.0 parts of a 2.1 wt% solution of polymethyl methacrylate fine particles (Eposter MA manufactured by Nippon Shokubai Chemical Industry Co., Ltd.) The average particle size is 0.03 μm), and a 1 wt% solution of polyoxyethylene nonyl phenyl ether (NS208.5 manufactured by NOF Corporation) of 12.0%
Department. The coating amount is 4.0 g / m ² on a wet basis.

Table 1 shows the characteristics of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the surface (A) side of this film in the same manner as in Example 1.

[0097]

Comparative Example 4 A polyester film was obtained in exactly the same manner as in Example 2, except that the coating solution applied to the film surface (A) was changed as follows.

Table 1 shows the characteristics of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the film surface (A) side in the same manner as in Example 1.

Composition of coating liquid applied to film surface (A): acrylic resin (Primal AC manufactured by Rohm and Haas Co.)
8604 parts of a 1.5 wt% solution of -604) 5.0 parts of a 1.5 wt% solution of polymethyl methacrylate fine particles (Nippon Shokubai Kagaku Kogyo Co., Ltd. eposter MA) 0.03 μm), 10.0 parts of a 1.5 wt% solution of polyoxyethylene nonyl phenyl ether (NS240 manufactured by NOF Corporation). The coating amount is 2.7 g / m ² on a wet basis.

[0100]

Comparative Example 5 A polyester film was obtained in exactly the same manner as in Example 2, except that the coating solution applied to the film surface (A) was changed as follows.

Table 1 shows the properties of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the film surface (A) side in the same manner as in Example 1.

Composition of coating liquid applied to film surface (A): 5.0 parts of a 0.7 wt% solution of an acrylic-polyester resin (Pesthresin SH551A manufactured by Takamatsu Yushi Co., Ltd.), an acrylic resin (Primal manufactured by Rohm and Haas Co.) AC
-64) 10.0 parts by weight of a 0.7 wt% solution of polymethyl methacrylate fine particles (Nippon Shokubai Chemical Industry Co., Ltd. Eposter MA) 70.0%
Parts (however, the average particle diameter of the fine particles is 0.03 μm), a 15.0% by weight solution of a polyoxyethylene nonylphenyl ether (NS208.5 manufactured by NOF Corporation) of 15.0% by weight.
Department. The coating amount is 2.7 g / m ² on a wet basis.

[0103]

Comparative Example 6 The average particle size of 0.10 added when the internal temperature during the transesterification reaction reached 190 ° C. in Example 2.
0.30 parts of an ethylene glycol slurry of silicon dioxide having a thickness of 10 μm (10 wt% of silicon dioxide / ethylene glycol slurry) was subjected to transesterification at an internal temperature of 200.
° C, an ethylene glycol slurry of calcium carbonate having an average particle size of 0.75 μm (calcium carbonate 1)
A polyester film was obtained in exactly the same manner as in Example 2 except that the amount was changed to 1.2 parts (0 wt% / ethylene glycol slurry).

Table 1 shows the characteristics of the obtained polyester film and the magnetic recording medium having a magnetic layer provided on the film surface (A) side in the same manner as in Example 1.

[0105]

Comparative Example 7 In Example 1, trimellitic anhydride was added in 2.5 parts of ethylene glycol added as a catalyst.
Polyester was prepared in exactly the same manner as in Example 1 except that 0.011 part of a liquid obtained by reacting 8 parts with 0.65 part of tetrabutyl titanate (titanium content: 11% by weight) was changed to 0.090 part of antimony trioxide. I got a film.

Table 1 shows the characteristics of the obtained polyester film and the magnetic recording medium having a magnetic layer provided on the film surface (A) side in the same manner as in Example 1.

[0107]

Comparative Example 8 A polyester film was obtained in the same manner as in Example 1 except that the coating was not performed on the film surface (A).

Table 1 shows the properties of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the film surface (A) side in the same manner as in Example 1.

[0109]

Comparative Example 9 A polyester film was obtained in exactly the same manner as in Example 1 except that the coating liquid applied to the film surface (A) was changed as follows.

Composition of coating liquid applied to film surface (A): 85.0 parts of a 1.5 wt% solution of acrylic-polyester resin (Pesthresin SH551A, manufactured by Takamatsu Oil & Fats Co., Ltd.), polyoxyethylene nonyl phenyl ether (Nippon Oil & Fats) 1.5 wt% solution of NS208.5) (15.0)
Department. The coating amount is 2.7 g / m ² on a wet basis.

Table 1 shows the properties of the obtained polyester film and the magnetic recording medium provided with a magnetic layer on the film surface (A) side in the same manner as in Example 1.

[0112]

[Table 1]

[0113]

According to the polyester film of the present invention, a magnetic layer having a smooth and excellent running property, in particular, a metal thin film magnetic layer can be formed, the noise is remarkably reduced, and a magnetic recording medium excellent in each level of the noise level can be obtained. It can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus for measuring a coefficient of dynamic friction in order to evaluate a film running property.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Feeding reel 2 Tension controller 3,5,6,8,9,11 Free roller 4 Tension detector (entrance) 7 Fixing pin 10 Tension detector (exit) 12 Guide roller 13 Take-up reel

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B32B 23/08 B32B 23/08 (72) Inventor Satomi Miura 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture Teijin Limited Sagamihara Research Inside the center (56) References JP-A-4-144473 (JP, A) JP-A-5-194772 (JP, A)

Claims (4)

(57) [Claims] A polyester film is coated on its surface with a primer for a magnetic layer consisting of a continuous thin film, and the continuous thin film has fine projections having fine particles having an average particle size of 0.1 μm or less as nuclei and a resin as a binder. (A) and minute projections (B) made of only the resin are formed, and the minute projections (A) have a height of 13 nm or less and are 1.0 × 10 ^{4 to} 1.0 × 10 ^8.
Particles / mm ² , and the fine projections (B) are 4.0
× present in a proportion of 10 ⁶ / mm ² or less, fine surface roughness Ra ^s of the continuous thin film portion by only the resin is not more than 1.10 nm, and a surface roughness Ra of the continuous film is 1 to 10
A polyester film for a magnetic recording medium, characterized in that the 2. A continuous thin film for forming a smooth surface is coated on another surface of the polyester film, the continuous thin film contains a cellulose resin and fine particles having an average particle diameter of 0.15 μm or less, The polyester film for a magnetic recording medium according to claim 1, wherein the roughness Ra is 2 to 10 nm. 3. The polyester film for a magnetic recording medium according to claim 1, wherein the polyester is a polyester produced using an organic titanium compound as a polymerization catalyst. 4. The polyester film for a magnetic recording medium according to claim 1, wherein the binder of the fine particles is at least one resin selected from an acrylic resin, a polyester resin, and an acryl-polyester resin.