JPH08124150A - Polyester film for magnetic tape - Google Patents

Abstract

PURPOSE: To obtain a polyester film for a magnetic tape excellent in scraping resistance, windability and electromagnetic transducing characteristics. CONSTITUTION: This polyester film has 600-1,500kg/mm<2> Young's modulus in the longitudinal direction and contains 0.01-2.0wt.% inert fine particles of 0.6-5.0μm average particle diameter. The surface roughness Ra of this film is 20-50nm and the coefft. of compression of protrusions is 0.2-0.8.

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 magnetic tape, and more particularly to a polyester film for magnetic tape which is excellent in abrasion resistance, winding property and electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art Biaxially oriented polyester films are used in many applications such as magnetic tapes, electricity, photography, metallization and packaging due to their excellent properties. In particular, due to its high strength and elastic modulus, it is widely used as a base film for magnetic recording media such as video tapes, audio tapes, computer tapes and floppy disks.

In these base films, the abrasion resistance is a major factor affecting the workability of the manufacturing process of the base film and the working process in each application, as well as the product quality. Especially when used as a base film for magnetic tape, if the abrasion resistance is insufficient, shavings are generated in the calendering process after coating the magnetic layer, which may cause dropout of magnetic recording. .

In these fields, the demands for higher density recording and higher quality have been increasing in recent years, and the polyester film which is the base has been required to keep abrasion resistance and running property and to have a surface. The requirement for flatness is becoming increasingly stronger.

However, when the film becomes flat, the winding shape in the step of winding the film and the step of winding the pancake in the magnetic tape manufacturing process is significantly deteriorated.

Therefore, the polyester film as the base is required to have flatness and windability.

As a method for improving the running property and abrasion resistance of a film, it has been proposed in the past to incorporate inorganic fine particles or organic fine particles into a polyester as a single component or as a two component. For example, Japanese Patent Publication No. 6-21172
In the publication, a biaxially oriented polyester film containing specific inorganic fine particles in the polyester and having a specific film protrusion softness coefficient is proposed, but this method does not necessarily improve abrasion resistance and winding property. The effect is not enough.

[0008]

As a result of extensive studies on such problems, the present inventor has found that the film has a specific Young's modulus in the longitudinal direction (longitudinal direction) and has a specific surface on the film surface due to the inert fine particles. The inventors have found that forming projections having roughness and a specific compression coefficient can improve the abrasion resistance of the film, and have reached the present invention.

Accordingly, it is an object of the present invention to provide a polyester film for magnetic tape which is excellent in abrasion resistance, winding property and electromagnetic conversion characteristics.

[0010]

The object of the present invention is, according to the present invention, that the Young's modulus in the longitudinal direction of the film is 600 to 15.
00 kg / mm ² , with an average particle size of 0.6 in the film
0.01 to 2.0% by weight of inert particles of ˜5.0 μm, film surface roughness (Ra) of 20 to 50 nm, and protrusion compression coefficient of 0.2 to 0.8. Is achieved by a polyester film for magnetic tape.

In the present invention, as the polyester constituting the film, those having alkylene terephthalate and / or alkylene naphthalate as a main constituent are preferably used.

Among such polyesters, not only polyethylene terephthalate and polyethylene-2,6-naphthalate but also, for example, 8 of all dicarboxylic acid components are used.
A copolymer in which 0% or more is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid and 80 mol% or more of all glycol components is ethylene glycol is preferable. At that time, 20 mol% or less of the total acid content of the dicarboxylic acid is an aromatic dicarboxylic acid other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, for example, isophthalic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylethanedicarboxylic acid, It may be diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid or the like, and may be aliphatic dicarboxylic acid such as adipic acid, sebacic acid or the like, alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid or the like. . The glycol of 20 mol% or less of the total glycol component may be a glycol other than ethylene glycol, such as trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, etc., and cyclohexanedimethanol. Alicyclic glycol, hydroquinone,
It may also be an aliphatic diol containing an aromatic ring such as resorcin, 2,2-bis (4-dihydroxymethylbenzene), a polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polytetramethylene glycol and the like.

Further, the polyester in the present invention includes
For example, those in which a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid is copolymerized or bonded with 20 mol% or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component are also included.

Further, in the polyester of the present invention, the tricarboxylic or polyfunctional polycarboxylic acid or polyhydroxy compound, such as trimellitate, is contained in a substantially linear range, for example, in an amount of 2 mol% or less based on the total acid components. Also included are those obtained by copolymerizing acid, pentaerythritol and the like.

The above polyester is known per se and can be produced by a method known per se.

The above polyester preferably has an intrinsic viscosity of 0.4 to 0.8 obtained by measuring it as a solution in o-chlorophenol at 35 ° C., and 0.5 to 0.7.
Those of 0.55 to 0.65 are particularly preferable.

Polyester for magnetic tape in the present invention
The film has a Young's modulus in the longitudinal direction of 600 to 1500K.
g / mm²And preferably 650 to 1200 Kg /
mm ², And more preferably 700 to 1000 kg / mm
²Is. This is due to the inert microparticles according to the invention
Fine protrusions are used in the magnetic tape manufacturing calender process
Of the protrusion due to the pressure of the film, and from the inside of the film
To prevent shavings caused by the release of fine particles of
Of. Young's modulus in the longitudinal direction is 700 kg / mm²Not yet
If it is full, it will be filled by the pressure during the calendering process.
The projections on the film surface are compressed and deformed, but at this time, the film
If the Young's modulus in the longitudinal direction is insufficient, the protrusions can easily come off,
Particles inside the film jump out, resulting in magnetic recording
It is not preferable because it may drop out. one
On the other hand, this Young's modulus is 1500 Kg / mm²Be super
Since rupture is likely to occur during film formation and productivity will decrease.
Not preferable. Also, the width direction (horizontal direction) at this time
The length ratio is not specified, but in the longitudinal direction
It is preferably lower than the Young's modulus, and its range is preferable.
400 to 800 kg / mm²Is.

The polyester film for magnetic tape according to the present invention has a surface roughness (Ra) of 20 to 50 nm, preferably 23 to 40 nm. Surface roughness (R
If the value of a) is less than 20 nm, the shape of the pancake is unfavorably deteriorated when the pancake is wound in the magnetic tape manufacturing process. On the other hand, if the surface roughness (Ra) is more than 50 nm, the flatness of the film surface becomes insufficient and, as a result, the electromagnetic conversion characteristics are deteriorated, which is not preferable.

The average particle size of the inert fine particles contained in the polyester film for magnetic tape of the present invention is 0.
It is 6 to 5.0 μm. If the average particle size is less than 0.6 μm, there will be many winding defects during pancake winding in the magnetic tape manufacturing process, which is not preferable. On the other hand, if the average particle size exceeds 5.0 μm, the abrasion resistance is poor and the electromagnetic conversion characteristics are poor, which is not preferable.

The amount of the inert fine particles contained in the polyester film for magnetic tape of the present invention is 0.01-.
It is 2.0% by weight. 0.2% by weight of inert particles
When it is less than the above range, the number of winding defects during pancake winding in the magnetic tape manufacturing process increases, which is not preferable. On the other hand, 2.
If it exceeds 0% by weight, abrasion resistance is poor and electromagnetic conversion characteristics are poor, which is not preferable.

The polyester film for magnetic tape according to the present invention has a projection compression coefficient of 0.2 to 0.8. When this coefficient is less than 0.2, the projections on the film surface are in a hard state and the deformation of the projections is small, the pressure cannot be absorbed in the calendering process of magnetic tape production, and the projections easily drop off or the particles inside the film pop out. As a result, magnetic recording may be lost (drop out), which is not preferable. On the other hand, when the coefficient is more than 0.8, the protrusions on the film surface are in a soft state, the protrusion deformation is large, the protrusions are not easily crushed by the pressure of the calendering process, and the protrusions are not restored. It is not preferable because the winding appearance in the step of winding the pancake in the step is significantly deteriorated.

The polyester film having the above-mentioned projection compression coefficient in the present invention is preferably a compression-deformable inert fine particle, and a powder of the inert fine particle, which is a polyester produced by an extruder in a polyester film forming step. This can be achieved by adding the powder as it is just before the pellet melting step. The cause of this is not clear, but the affinity between the polyester and the inert fine particles to be added is improved as compared with the case where the inert fine particles are added as a slurry to the conventionally known reaction system of polyester, and the fine surface projections of the polyester film are improved. It is considered that the voids around the particles in the film forming the film become small, and the projection compression coefficient in the specific range according to the present invention is obtained by the synergistic effect with the specific inert particles.

In the present invention, the inert fine particles contained in the above polyester are preferably 1. As inert inorganic fine particles, 1) silicon dioxide (including hydrate, diatomaceous earth, silica sand, quartz, etc.); 2) Ca and Ba sulfates; 3) Li, Na, and K benzoates; 4) Ca, B
terephthalate of a, Zn, and Mn; 5) Mg, Ca,
Ba, Zn, Cd, Pb, Sr, Mn, Fe, Co and Ni titanates; 6) Ba and Pb chromates; 7)
Carbon (eg carbon black, graphite, etc.); 8)
1. Ca and Mg carbonates; 9) fluorspar; 10) zeolite and the like; As inert organic fine particles, 1) crosslinked silicone resin particles; 2) polystyrene or crosslinked polystyrene particles; 3) styrene / acrylic and acrylic crosslinked particles; 4) styrene / methacrylic and methacrylic crosslinked vinyl particles Particles; 5) Benzanamin-formaldehyde particles; 6) Polytetrafluoroethylene particles;
7) Polyphenyl ester particles; 8) phenyl resin particles and the like. More preferably, silicon dioxide (aggregated silica, spherical silica, etc.), silicic acid anhydride, hydrous silicic acid, barium sulfate, lithium benzoate, clay (including kaolin, bentonite, clay etc.), talc, diatomaceous earth, calcium carbonate, Examples include crosslinked silicone resin particles and crosslinked polystyrene particles. Particularly preferred are silicon dioxide (aggregated silica, spherical silica, etc.), calcium carbonate, crosslinked silicone resin particles, and crosslinked polystyrene particles.

It is preferable that the inert fine particles are directly added to the polyester pellets in the form of powder just before the melting step by the extruder. However, as long as the object of the present invention is not impaired, the inert fine particles may be added at the reaction stage of the polyester, for example, from the initial stage of the esterification reaction or transesterification reaction to the end of the polycondensation reaction. When it is added to the reaction system of polyester, it may be added as a powder, but it is preferable to add it as a glycol slurry using the glycol component of the reaction system.

The polyester film of the present invention can be produced according to a conventionally known method for producing a biaxially stretched film. For example, a polyester film containing inert fine particles is melted to form an amorphous unstretched film, and then the unstretched film is biaxially stretched, heat-fixed, and if necessary, subjected to relaxation heat treatment. To be done.

At that time, the film surface characteristics vary depending on the particle size and the amount of the inert fine particles in the polyester and the stretching conditions, and are appropriately selected from the conventional stretching conditions.

The Young's modulus, voids, density, heat shrinkage, etc. in the longitudinal direction of the film also change depending on the temperature, magnification, speed, etc. during stretching and heat treatment, so conditions for simultaneously satisfying these characteristics are determined. For example, polyester is melted and extruded at a temperature of melting point (Tm: ° C.) to (Tm + 70) ° C. to obtain an unstretched film having an intrinsic viscosity of 0.35 to 0.9 dl / g, and the unstretched film is uniaxially (longitudinal direction). Or transversely) at a temperature of (Tg-10) ° C to (Tg + 70) ° C (however, Tg: glass transition temperature of polyester) at a draw ratio of 2.5 to 6.0, and then in the above-mentioned stretching direction. Stretching is performed at a temperature of Tg (° C.) to (Tg + 70) ° C. at a ratio of 2.5 to 5.0 times in the orthogonal direction (when the first stage stretching is the longitudinal direction, the second stage stretching is the transverse direction). It can be manufactured. In this case, the area draw ratio is 9 to 22 times, and further 1
It is preferably 2 to 22 times. The stretching means may be simultaneous biaxial stretching or sequential biaxial stretching.

Further, the biaxially oriented film has (Tg + 7
It is preferable to heat-set at a temperature of 0) ° C. to Tm (° C.). For example, for polyethylene terephthalate, 19
It is preferable to heat-fix at 0 to 230 ° C. The heat setting temperature is, for example, 1 to 60 seconds.

The polyester film for magnetic tape of the present invention has a Young's modulus in the longitudinal direction of the film in a specific range, a surface roughness of the film in a specific range, and a specific average particle size in the polyester in a specific amount. Since it has inert fine particles contained therein and the protrusion compression coefficient of the film is within a specific range, it exhibits excellent abrasion resistance, winding property, and electromagnetic conversion characteristics.

Although the cause of this is not clear, the fine surface protrusions on the film surface are compressed by the calender roll pressure in the calendering process in the magnetic tape manufacturing process, and at this time, the fine surface protrusions are deformed. It is considered that the abrasion resistance is improved by the synergistic effect of the flexibility of the protrusions in the direction perpendicular to the base film surface and the Young's modulus in the longitudinal direction of the base film.

Various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Young's modulus The film is cut into a sample having a width of 10 mm and a length of 15 cm, the gap between the chucks is 100 mm, and the film is pulled at a pulling speed of 10 mm / min and a chart speed of 5000 mm / min with an Instron type universal pulling tester. The Young's modulus is calculated from the tangent line of the rising portion of the obtained load-elongation curve. The measurement is N =
Conduct 5 times and use the average.

(2) Film surface roughness (Ra) It is a value defined by JIS-B0601 as the center line average roughness (Ra), and is a stylus surface roughness meter (SURFCORDER SE) of Kosaka Laboratory Ltd. -30C). The measurement conditions are as follows. (A) Stylus tip radius: 2 μm (b) Measurement pressure: 30 mg (c) Cutoff: 0.25 mm (d) Measurement length: 2.5 mm (e) Data compilation method The same sample was repeatedly measured 5 times, The largest value is 1
Except for one, the average value of the remaining four data is rounded off to the fourth decimal place and displayed up to the third decimal place.

(3) Average Particle Size (DP) CP-50 Model Centrifugal Particle Size Analyzer (Centrifugal Particle S) manufactured by Shimadzu Corporation
ize Analyzer). The particle diameter corresponding to 50 mass% is read from the integrated curve of the particles of each particle diameter calculated based on the obtained centrifugal sedimentation curve and the abundance thereof, and this value is taken as the above average particle diameter (Book Technology ”Nikkan Kogyo Shimbun, 1975, pp. 242-247).

(4) Protrusion compression coefficient The film is cut into a 1/2 inch width to obtain a sample piece.
Micro Topograph manufactured by Toyo Seiki Co., Ltd.
pograph), set the above test piece on the plane prism of the device, put opal glass on it, pressurize,
A physical quantity Rp (Printing Roughness) proportional to the average depth of the depressions on the surface of the test piece pressed onto the flat prism surface is measured (N = 10 times average). Pressurization at this time is 1.5K
gf / cm ² and 7.5 Kgf / cm ² are measured, respectively. These measured values are Rp1.5 and Rp, respectively.
The projection compression coefficient is calculated by the following formula assuming 7.5.

[0036]

[Formula 1] Protrusion compression coefficient = Rp7.5 / Rp1.5

(5) Calender Scraping (Scraping Resistance) Scraping of the running surface of the base film is evaluated using a three-stage mini super calender (made by Yuri Roll). The calender is a three-stage calender with a mirror tex roll and a steel roll, the processing temperature is 70 ° C, the linear pressure applied to the film is 300 kg / cm, and the film speed is 10 m.
Run at a speed of / minutes. When the running film was run for a total length of 2000 m, the abrasion resistance of the base film was evaluated by the stains attached to the mirrortex roll of the calendar. ⊙: Mirrortex roll is not stained. ○ ... Although the gloss of Mirrortex roll is slightly reduced,
No adhesion of shavings is observed. Δ: Scraped powder is adhering to the Mirrortex roll. × ... A large amount of shavings was found on the Mirrortex roll.

(6) Electromagnetic conversion characteristics Using a fully automatic taste analyzer AA-501 manufactured by Tektronix, frequencies 315 Hz and 10
The input sensitivity and S / N ratio (signal-noise) are measured at KHz, and the in-house standard tapes are compared and evaluated as follows. A: Output sensitivity is not lower than input sensitivity. O: Output sensitivity is slightly lower than input sensitivity, but at a good level. △: Output sensitivity is lower than input sensitivity,
There is no problem in practical use. ×: Output sensitivity is lower than input sensitivity and cannot be used.

(7) Pancake winding form The raw fabric after coating the magnetic layer was wound on a pancake using a shear air type slitter (RT type manufactured by Nishimura Seisakusho Co., Ltd.) to make microslits with a width of 3/20 inch. , Visually observe the pancake roll. ◎… The end face of the pancake is flat and the winding shape is good. ○… The winding form is good although there is a slight misalignment on the end face of the pancake. △… The misalignment is seen on the end face of the pancake, but there is no practical problem and the yield is almost reduced. No ×: The end face of the pancake is greatly misaligned, the roll is collapsed, etc., and the production yield is significantly reduced.

[0040]

EXAMPLES The present invention will be further described below with reference to examples.

[Examples 1 to 8] Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, and phosphorous acid as a stabilizer were reacted by a conventional method to give a unique reaction. Polyethylene terephthalate having a viscosity of 0.62 was obtained.

After drying the polyethylene terephthalate pellets at 170 ° C. for 3 hours, the polyethylene terephthalate pellets were fed to a kneader together with the additive particles shown in Table 1 as a lubricant, and the pellets and the additive particles were kneaded and then fed to an extruder hopper for melting. Temperature 28
It is melted at 0 to 300 ° C., the molten polymer is extruded through a 1 mm slit die onto a rotary cooling drum having a surface finish of about 0.3 s and a surface temperature of 20 ° C., and rapidly cooled to a thickness of 1
An unstretched film of 50 μm was obtained.

The unstretched film thus obtained is preheated to 55 ° C., and further 10 mm between low speed and high speed rolls.
The film was heated from above by an IR heater having a surface temperature of 800 ° C., stretched 4.5 times, rapidly cooled, then supplied to a stenter, and stretched 3.5 times in the transverse direction at 90 ° C. The obtained biaxially oriented polyester film was heat set at a temperature of 205 ° C. for 5 seconds to obtain a heat set biaxially oriented polyester film having a thickness of 7 μm.

The film thus obtained has 70
A paint consisting of weight percent γ-Fe ₂ O ₂ and 30 weight percent binder was applied. This binder is 5% by weight of urethane rubber, 3.5% by weight of nitrocellulose, 1.5% by weight of vinyl chloride resin, 90% by weight of methyl ethyl ketone, and 15% by weight of an isocyanate resin compound as a curing agent to the resin. It was added. After coating, calendering was further performed to obtain a magnetic layer-coated raw fabric having a width of 600 mm.

This coated raw material was micro-slit of 3/20 inch using a shear type slitter,
A magnetic tape having a thickness of 12 μm was obtained.

The characteristics of the biaxially oriented polyester film and magnetic tape thus obtained are shown in Table 1.

Comparative Example 1 Dimethyl terephthalate and ethylene glycol were used, manganese acetate was used as a transesterification catalyst, antimony trioxide was used as a polymerization catalyst, phosphorous acid was used as a stabilizer, and Table 2 (Comparative Example 1) was used as a lubricant.
The additive particles shown in (1) were added and reacted by a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity of 0.62.

The polyethylene terephthalate pellets were dried at 170 ° C. for 3 hours, then fed to an extruder hopper and melted at a melting temperature of 280 to 300 ° C. The molten polymer was surface-finished through a 1 mm slit die to a surface finish of 0.1.
The film was extruded onto a rotary cooling drum having a surface temperature of 20 ° C. for about 3 s and rapidly cooled to obtain an unstretched film having a thickness of 200 μm.

The unstretched film thus obtained is preheated to 75 ° C., and further 10 mm between low speed and high speed rolls.
The film was heated from above by an IR heater having a surface temperature of 900 ° C., stretched 3.3 times, rapidly cooled, then supplied to a stenter, and stretched 3.5 times in the transverse direction at 105 ° C. The obtained biaxially oriented polyester film was heated at 215 ° C for 5
After heat setting for 2 seconds, a heat setting biaxially oriented polyester film having a thickness of 15 μm was obtained.

The film thus obtained was mixed with 70
A paint consisting of weight percent γ-Fe ₂ O ₂ and 30 weight percent binder was applied. This binder is 5% by weight of urethane rubber, 3.5% by weight of nitrocellulose, 1.5% by weight of vinyl chloride resin, 90% by weight of methyl ethyl ketone, and 15% by weight of an isocyanate compound as a curing agent to the resin. It was done. After coating, calendering was further performed to obtain a magnetic layer-coated raw fabric having a width of 600 mm.

This coated raw material was micro-slit of 3/20 inch using a shear type slitter,
A magnetic tape having a thickness of 19 μm was obtained.

The properties of the biaxially oriented polyester film and magnetic tape thus obtained are shown in Table 2.

Comparative Example 2 0.05% by weight of siloid (aggregated silica) having an average particle size of 1.7 μm was used in place of the added inactive particles in Comparative Example 1, and the method of adding the siloid of Example 1 was used. A film and a tape were obtained in the same manner as in Comparative Example 1 except that the polyester pellets were kneaded with the siloid as a powder and then melt-extruded. The properties of the biaxially oriented polyester film and magnetic tape thus obtained are shown in Table 2.
Shown in

[Comparative Examples 3 to 8] Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, and phosphorous acid as a stabilizer were polymerized by a conventional method to obtain an intrinsic viscosity. 0.62 of polyethylene terephthalate was obtained.

After drying the polyethylene terephthalate pellets at 170 ° C. for 3 hours, the particles were added to the kneader together with the additive particles shown in Table 2 as a lubricant, and the pellets and the additive particles were kneaded and then supplied to the extruder hopper. , Melt at a melting temperature of 280 to 300 ° C.,
The film was extruded onto a rotary cooling drum having a surface finish of about 0.3 s and a surface temperature of 20 ° C. through the slit die and rapidly cooled to obtain an unstretched film having a thickness of 150 μm.

The unstretched film thus obtained is preheated to 55 ° C., and further 10 mm between low speed and high speed rolls.
The film was heated from above by an IR heater having a surface temperature of 800 ° C., stretched 4.5 times, rapidly cooled, then supplied to a stenter, and stretched 3.5 times in the transverse direction at 90 ° C. The obtained biaxially oriented polyester film was heat set at a temperature of 205 ° C. for 5 seconds to obtain a heat set biaxially oriented polyester film having a thickness of 7 μm.

To the film thus obtained, 70
A paint consisting of weight percent .gamma.-FO2 O2 and 30 weight percent binder was applied. This binder is 5% by weight urethane rubber, 3.5% by weight nitrocellulose, 1.5% by weight vinyl chloride resin, 90% by weight methyl ethyl ketone, and 15% by weight of an isocyanate compound as a curing agent to the resin. It was done. After coating, calendering was further performed to obtain a magnetic layer-coated raw fabric having a width of 600 mm.

This coated raw material was microslit of 3/20 inch using a shear type slitter,
A 12 μm magnetic tape was obtained.

The characteristics of the biaxially oriented polyester film and magnetic tape thus obtained are shown in Table 2.

[Comparative Example 9] In place of the added inert particles in Comparative Example 3, 0.1% by weight of crosslinked silicone resin particles having an average particle size of 1.0 μm was used. A film and a tape were obtained in the same manner as in Comparative Example 3 except that the same procedure as in Example 1 was performed and the polyester reaction system was added.

The characteristics of the biaxially oriented polyester film and magnetic tape thus obtained are shown in Table 2.

[0062]

[Table 1]

[0063]

[Table 2]

As is clear from these tables, the one according to the present invention is excellent in abrasion resistance, is excellent in windability, and is excellent in electromagnetic conversion characteristics. On the other hand, those outside the scope of the present invention could not satisfy all of the abrasion resistance, the winding property, and the electromagnetic conversion characteristics at the same time.

[0065]

According to the present invention, the Young's modulus in the longitudinal direction of the film is in a specific range, the surface roughness of the film is in a specific range, and the polyester contains a specific average particle size in a specific amount. It is possible to provide a polyester film for magnetic tape, which has excellent abrasion resistance, winding property, and electromagnetic conversion characteristics, because it has inert fine particles that meet the requirements and the protrusion compression coefficient of the film is in a specific range. it can.

Claims (2)

[Claims] 1. A Young's modulus in the longitudinal direction of the film is 600 to.
1500 kg / mm ²And the average particle size in the film
Inert fine particles of 0.6 to 5.0 μm in an amount of 0.01 to 2.0
% By weight, and the film surface roughness (Ra) is 20 to 50.
nm, and the protrusion compression coefficient is 0.2 to 0.8.
Polyester film for magnetic tape characterized by
M 2. The polyester film for a magnetic tape according to claim 1, wherein the inert fine particles are at least one selected from aggregated silica, spherical silica, calcium carbonate, crosslinked silicone resin particles and crosslinked polystyrene particles.