JPH0768373B2 - Biaxially oriented polyester film for magnetic recording media - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film for a magnetic recording medium,
More specifically, the present invention relates to a biaxially oriented polyester film for magnetic recording media, which contains silicon resin fine particles having different average particle diameters and is particularly improved in slipperiness, abrasion resistance and scratch resistance.

[Prior Art] Biaxially oriented polyester films typified by polyethylene terephthalate films are widely used as base films for magnetic recording media such as magnetic tapes because of their excellent physical and chemical properties.

In the biaxially oriented polyester film, its slipperiness and abrasion resistance are major factors affecting the workability of the film manufacturing process and the processing process in each application, and further the quality of the product. If these are insufficient, for example, when a magnetic layer is applied to the surface of a biaxially oriented polyester film and used as a magnetic tape, friction between the coating roll and the film surface during application of the magnetic layer is severe, and the abrasion of the film surface due to this is also caused. It is severe, and in extreme cases, wrinkles such as scratches on the film surface occur.

Generally, in order to improve the slipperiness of the film, a method of reducing the contact area with the guide roll or the like by giving unevenness to the film surface is adopted, and it is roughly classified into (i)
A method of precipitating inactive fine particles from a catalyst residue of polyester used as a film raw material and a method of (ii) adding inactive inorganic fine particles are used. The larger the size of the fine particles in these raw polyesters,
Generally, the effect of improving the slipperiness is great, but in precision applications such as magnetic tapes, especially for video, the large particles themselves can cause defects such as dropouts. The unevenness of the film surface needs to be as fine as possible, and under the present circumstances, there is a demand for satisfying these contradictory properties at the same time.

Conventionally, as a method for improving the slipperiness of a film, a method of adding inorganic particles such as silicon oxide, titanium dioxide, calcium carbonate, talc, clay and calcined kaolin to an aromatic polyester which is a film substrate (for example, JP-A-54). −
57562) or a method of precipitating fine particles containing calcium, lithium or phosphorus in a polymerization system for producing an aromatic polyester (Japanese Patent Publication No. S52-52).
-32914 gazette). When formed into a film, the fine particles which are inactive to the aromatic polyester form projections on the film surface, and the projections improve the slipperiness of the film.

However, the method of improving the slipperiness of the film by the projections of the fine particles has an essential problem that the projections hinder the flatness of the film surface on the one hand.

As an attempt to solve these contradictory flatness and slipperiness, means for utilizing a composite fine particle system of relatively large particle diameter and relatively small particle diameter has been proposed.

U.S. Pat. No. 3,821,156 discloses a combination of 0.5 to 30 .mu.m calcium carbonate microparticles 0.02 to 0.1% by weight with 0.01 to 1.0 .mu.m silica or hydrated alumina silicate 0.01 to 0.5% by weight.

U.S. Pat.No. 3,884,870 describes about 0.5 to 30 μm of calcium carbonate, calcined aluminum silicate, hydrous aluminum silicate, magnesium silicate, calcium silicate, calcium phosphate, silica, alumina, barium sulfate, mica, diatomaceous earth, etc. Inert fine particles About 0.002-0.018% by weight
Of about 0.01 to about 1.0 μm of silica, calcium carbonate, calcined calcium silicate, hydrated calcium silicate, calcium phosphate, alumina, barium sulfate, magnesium sulfate, diatomaceous earth, etc. The combination is disclosed.

US Pat. No. 3,980,611 has a particle size of 1.0 μm or less, 1 to
It is disclosed that calcium phosphate fine particles of three particle size grades of 2.5 μm and 2.5 μm or more are combined and added to the aromatic polyester in a total amount of 5000 ppm or less.

JP-B-55-41648 (JP-A-53-71154) is 1.
A combination of 0.22 to 1.0% by weight of fine particles of 2 to 2.5 μm and 0.003 to 0.25% by weight of fine particles of 1.8 to 10 μm, wherein the fine particles are oxides or inorganics of elements of groups II, III and IV of the periodic table. Proposes to be salt.

Japanese Patent Publication No. 55-40929 (Japanese Patent Publication No. 52-11908),
Inert inorganic fine particles of 3 to 6 μm 0.01 to 0.08% by weight and 1 to
In combination with 2.5 μm of inert inorganic fine particles of 0.08 to 0.3% by weight, the total amount of these fine particles having different particle diameters is 0.1 to
Disclosed is a mixed particle of 0.4% by weight and a ratio of large particle size to small particle size of 0.1 to 0.7.

JP-A-52-78953 discloses 10 to 1,000 mμ of inert particles 0.0
1 to 0.5 wt% and 0.5 to 15 μm calcium carbonate 0.11 to 0.5
A biaxially oriented polyester film containing wt% is disclosed. In JP-A-52-78953, various inorganic substances other than calcium carbonate are listed in the general description as 10 to 1000 mμ inactive particles. However, this publication only discloses a specific example using silica or clay, which is usually available as fine particles of 10 to 1000 mμ, as an inorganic substance.

However, means for utilizing these composite fine particle systems are also
From the viewpoint of further improving the quality of the magnetic recording medium, there are many problems to be solved. For example, it cannot be said that these composite fine particles have a sufficient affinity with polyester, and voids are usually formed around the fine particles in the film, so that it cannot be said that the abrasion resistance is sufficient.

Japanese Patent Laid-Open No. 63-191838 discloses the use of silicon resin fine particles as a fine particle having no voids or a very small proportion thereof, and further, a composite of the silicon resin fine particles and an inert fine particle having a smaller particle diameter. The use of fine particles is suggested. This improves the abrasion resistance.

Recently, in manufacturing a magnetic recording medium, particularly a magnetic tape, an increase in speed of a production line has been pursued in order to reduce costs, and a base film suitable for this increase in speed is required. For example, not only wear with conventional coating rolls,
There is a demand for a base film that can withstand the abrasion of the coated magnetic layer due to the smoothing bar.

However, according to the research results of the present inventor, it is difficult to develop a base film capable of responding to the above-mentioned speed increase in the conventional composite fine particle system, and in particular, composite fine particles of silicon resin fine particles and inert fine particles having improved abrasion resistance are sufficient. It became clear that it cannot be said.

[Object of the Invention] An object of the present invention is to provide a biaxially oriented polyester film for a magnetic recording medium, which is capable of coping with recent speeding up of the magnetic recording medium manufacturing process and which is excellent in slipperiness, abrasion resistance and scratch resistance. To provide.

Other objects and advantages of the invention will be apparent from the following description.

According to the present invention, the above objects and advantages of the present invention are as follows.
In addition, (I) aromatic polyester, (II) (a) the following formula (A) R _x SiO _{2-(x / 2)} (A) where R is a hydrocarbon group having 1 to 7 carbon atoms. And x is a number from 1 to 1.2. (B) The following formula (B) f = v / D ³ (B) where v is the average per particle Volume (μm ³ ),
And D is the average maximum particle size (μm) of the particles, the volumetric shape factor (f) is greater than 0.4 and π / 6 or less, and (c) the average particle size is 0.005-0.5 μm 0.05 to 2% by weight of silicon resin fine particles (P ₁ ) (based on aromatic polyester), and (III) (a) mainly composed of the composition represented by the above formula (A), (b) the above formula (B) The defined volumetric shape factor (f) is
0.005 to 1.5% by weight of silicon resin fine particles (P ₂ ) having an average particle size larger than 0.4 and π / 6 or less, and (c) larger than the above silicon resin fine particles (P ₁ ) and 0.3 to 2.0 μm (P ₂ ). Is achieved by a biaxially oriented polyester film for magnetic recording media formed from an intimately mixed composition (for aromatic polyester).

The aromatic polyester in the present invention is a polyester having an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such aromatic polyesters are substantially linear and have film-forming properties, especially film-forming properties by melt molding. Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid and anthracenedicarboxylic acid. You can Examples of the aliphatic glycol include polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, and alicyclic compounds such as cyclohexanedimethanol. Examples thereof include diols.

In the present invention, as the aromatic polyester, for example, one having alkylene terephthalate and / or alkylenaphthalate as a main constituent component is preferably used.

Among such polyesters, for example, polyethylene terephthalate, polyethylene-2,6-naphthalate, of course, for example, 80 mol% or more of the total dicarboxylic acid component is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and the total glycol component. A copolymer having 80 mol% or more of ethylene glycol is preferable. 20 mol% or less of the total acid component can be the above aromatic dicarboxylic acids other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid. An alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid, etc .; Also, 20 mol% or less of the total glycol component can be the above glycols other than ethylene glycol,
Alternatively, for example, aromatic diols such as hydroquinone, resorcin, and 2,2-bis (4-hydroxyphenyl) propane; aliphatic diols having an aromatic ring such as 1,4-dihydroxydimethylbenzene; polyethylene glycol, polypropylene glycol, polytetra It can also be a polyalkylene glycol (polyoxyalkylene glycol) such as methylene glycol.

In the aromatic polyester in the present invention, a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid and an aliphatic oxyacid such as ω-hydroxycaproic acid, a dicarboxylic acid component and an oxycarboxylic acid. Those which are copolymerized or bonded at 20 mol% or less based on the total amount of the components are also included.

Further, the aromatic polyester in the present invention has a substantially linear amount, for example, an amount of 2 mol% or less based on the total acid component, of a trifunctional or higher polycarboxylic acid or polyhydroxy compound such as trimellitic acid. And a copolymer of pentaerythritol and the like are also included.

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

The aromatic polyester has an intrinsic viscosity of about 0, measured at 35 ° C. as a solution in o-chlorophenol.
Those of 4 to about 0.9 are preferred.

The biaxially oriented polyester film of the present invention has a large number of fine projections on the film surface, as will be apparent from the following description of Ra which defines the flatness of the film surface.

The large number of fine projections originates from the large number of substantially inert silicone resin particles contained in the aromatic polyester dispersed therein according to the present invention.

In the present invention, the silicone resin fine particles (P ₁ ) and (P ₂ )
Is the following formula (A) R _x SiO _{2-(x / 2)} (A) where R is a hydrocarbon group having 1 to 7 carbon atoms, and x is a number of 1 to 1.2. It has the composition represented.

R in the above formula (A) is a hydrocarbon group having 1 to 7 carbon atoms, and for example, an alkyl group having 1 to 7 carbon atoms, a phenyl group or a tolyl group is preferable. The alkyl group having 1 to 7 carbon atoms may be linear or branched, and examples thereof include methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n. -Pentyl, n-
Examples include heptyl and the like.

Among these, methyl and phenyl are preferable as R, and methyl is particularly preferable.

X in the above formula (A) is a number from 1 to 1.2. When x is 1 in the above formula (A), the following formula (A) can be represented by the following formula (A1 RSiO _1.5 ... (A1) where R is the same as above.

The above formula (the composition of A is the following structural portion in the three-dimensional polymer chain structure of the silicone resin; It is derived from.

Further, when the above formula (A) x is 1.2, the formula (A) wherein the following formula _{(A2 R 1.2 SiO 1.4 ...... (} A2, the definition of R can be expressed in the same above .

The composition of the above formula (A2 is 0.8 mol of the structure of the above (A1) and the following formula (A) ′ R ₂ SiO (A) ′ where R is 0.2 mol of the structure represented by Can be understood to consist of.

The above formula (A) ′ represents the following structural portion in the three-dimensional polymer chain of the silicone resin; Derived from.

As will be understood from the above description, the composition of the above formula (A) of the present invention substantially consists of, for example, only the structure of the above formula (A1), or the composition of the above formula (A1 and the above formula (A2). It can be seen that the structure is composed of coexisting structures in a state where they are randomly bonded at an appropriate ratio.

The silicone resin fine particles (P ₁ ) and (P ₂ ) in the present invention are
Preferably, in the above formula (A), x has a value between 1 and 1.1.

Further, the silicone resin fine particles (P ₁ ) in the present invention,
(P ₂ ) is the following formula (B) f = v / D ³ (B) where v is the average volume (μm ³ ) per particle,
D is the average maximum particle size (μm) of the particles, and the volume shape factor (f) defined by is greater than 0.4 and not more than π / 6.

In the above definition, the average particle size of the particles of D should be understood to mean the distance having the maximum length of the distance between any two points where any straight line across the particle intersects the perimeter of the particle.

Preferred f value of the silicone resin fine particles in the present invention is 0.
It is 44 to π / 6, and a more preferable value of f is 0.48 to π / 6. A particle whose f value is π / 6 is a true sphere. The use of silicon resin fine particles having an f value smaller than the lower limit makes it extremely difficult to control various film surface characteristics.

It is important that the fine particles in the present invention have two kinds of average particle sizes, large and small. That is, the silicon resin fine particles (P ₁ ) have an average particle size of 0.005 to 0.5 μm, and the silicon resin fine particles (P ₂ ) have an average particle size larger than the average particle size of the fine particles (P ₁ ) and 0.3 to 2.0 μm. It is essential that there be. The preferable average particle diameter of the fine particles (P ₁ ) is 0.01 to 0.5 μm, and the preferable average particle diameter of the fine particles (P ₂ ) is 0.5 to 2.0 μm. The difference in average particle size between the small particle (P ₁ ) and the large particle (P ₂ ) is preferably 0.1 μm or more, and more preferably 0.2 μm or more.

The average particle diameter referred to here is the diameter at the point of 50% integration of the equivalent spherical particle size distribution calculated based on the Stokes equation.

Further, the content of the silicone resin fine particles (P ₁ ) is 0.05 to 2% by weight, preferably 0.05, with respect to the aromatic polyester.
The content of the silicone resin fine particles (P ₂ ) is 0.005 to 1.5% by weight, preferably 0.005 to 0.5% by weight, based on the aromatic polyester.

Silicone resin fine particles: average particle diameter of (P ₁ small particles) 0.005
If it is less than μm, the projections on the film surface become extremely small, and the effect of improving the slipperiness between the films cannot be obtained, and if it is more than 0.5 μm, the silicone resin fine particles (P ₂ :
In combination with (large particles), a film having a surface flatness while satisfying slipperiness and abrasion resistance cannot be obtained. If the content of the small particles (P ₁ ) is less than 0.05% by weight, the effect of improving the slipperiness cannot be obtained, and if it is more than 2% by weight, the abrasion resistance is satisfied and the surface is flat. I can't get the film. On the other hand, when the average particle size of the silicon resin fine particles (P ₂ : large-diameter particles) is smaller than 0.3 μm, the slidability, especially the friction coefficient with the guide post in the cassette half, which is important as a magnetic tape, becomes high and the abrasion resistance is increased. If the thickness is larger than 2.0 μm, the flatness of the film surface is deteriorated, which is not desirable. Further, when the content of large particles (P ₂ ) is less than 0.005% by weight, the effect of lowering the friction coefficient of the guide post is insufficient and the content is 1.5% by weight.
If the amount is larger than the above range, the flatness of the film surface is lowered, which is not desirable. Further, if the difference in average particle size between the small particle (P ₁ ) and the large particle (P ₂ ) is too small, the effect of improving scratch resistance while satisfying the sliding property and the abrasion resistance becomes small, which is desirable. Absent. For example, in the case of a magnetic tape, especially a base film for video without a back coat layer, the protrusions added to improve the sliding property of the base film due to friction with the guide posts in the cassette half are avoided during long-term use. Absent. This drop-out protrusion is sandwiched between the guide post and the cassette during use of the cassette, and as a result, it causes the base film surface hard-to-clip clutch. For this, it is effective to make it difficult for the protrusions themselves to fall off and to make the protrusions on the film surface different in size. It is generally easy to fall off due to friction with the guide posts due to high protrusions, that is, particles with a large particle size, but the dropout protrusions have the characteristic of not having defects during the process of being dragged on the film, and In addition, if a protrusion that is not easily damaged by the guide post exists on the film surface, the drop-out protrusion that causes scratches is repelled, and the advantage that scratches do not grow is obtained.

The silicone resin fine particles used in the present invention are disclosed in
It can be produced by the method described in JP-A No. 63-191838 or a method similar thereto.

The silicone resin fine particles (P ₁ ) and (P ₂ ) used in the present invention are γ = D ₂₅ / D ₇₅ (C) where γ is the particle size ratio and D ₂₅ is the total weight of the particles. Is the particle size when it is 25% by weight and D ₇₅ is the particle size when the cumulative weight of the microparticles is 75% of the total weight. However, the cumulative weight ratio shall be measured from the larger particle size.

The particle size ratio (γ) represented by is preferably in the range of 1 to 1.4. This particle size ratio is more preferably 1-1.
It is in the range of 3, and particularly preferably in the range of 1.15.

In the production of the biaxially oriented polyester film of the present invention, the silicon resin fine particles (P ₁ ) and (P ₂ ) are intimately mixed with the aromatic polyester by mixing these fine particles with each other before or after the polymerization of the aromatic polyester. It may be sufficiently kneaded with the aromatic polyester in a polymerization vessel, in an extruder for pelletizing after completion of the polymerization, or in an extruder for melt extrusion into a sheet.

The biaxially oriented polyester film of the present invention is obtained by, for example, melting an aromatic polyester 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. The stretched film is uniaxially (longitudinal or transverse) at a temperature of (Tg-10) to (Tg + 70) ° C (however, Tg:
The glass transition temperature of the aromatic polyester) at a draw ratio of 2.5 to 5.0, and then in the direction perpendicular to the stretching direction (when the first stage stretching is the longitudinal direction, the second stage stretching is the transverse direction).
Can be produced by stretching at a temperature of Tg (° C)-(Tg + 70 ° C) at a draw ratio of 2.5 to 5.0 times. In this case, the area stretching ratio is preferably 9 to 22 times, more preferably 12 to 22 times. The stretching means may be simultaneous biaxial stretching or sequential biaxial stretching.

Further, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) ° C. to Tm (° C.). For example, polyethylene terephthalate film is preferably heat set at 190 to 230 ° C. The heat setting time is, for example, 1 to 60 seconds.

Thus, the winding property during film formation is good, the abrasion resistance in the magnetic tape manufacturing process is extremely good, and the friction coefficient with the running part of the magnetic recording / reproducing device (hardware) is small, and the abrasion is also extremely high. A small amount of biaxially oriented polyester film can be obtained.

As described above, the biaxially oriented polyester film of the present invention is excellent in surface flatness, slipperiness, and abrasion resistance, especially in smoothing bars and calenders in the magnetic tape production process, which are excellent in abrasion resistance and scratch resistance. It can respond to speeding up of the line. Although the reason why the biaxially oriented polyester film of the present invention is excellent in abrasion resistance and scratch resistance in a production line with a higher speed has not yet been clarified, the following reasons are considered.

That is, since the voids are hardly observed at all due to the high affinity between the silicone resin fine particles and the aromatic polyester, the hardness of the fine particles is suitable for high speed, and the protrusions formed on the film surface are appropriate. The two kinds of particles, large and small, are spherical and have a sharp particle size distribution, and the shape of the protrusions formed on the film surface,
According to the complex action that the height is uniform and the smoothing bar and calendar contact are uniform, it is difficult to apply unreasonable force to specific projections, and the separated fine particles are hard to cause scratches. Conceivable.

Due to the above characteristics, the biaxially oriented polyester film of the present invention is extremely useful as a base film of a magnetic recording medium, especially a magnetic tape.

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

(1) Average particle diameter (d) Shimadzu CP-50 type Centrifugal particle size analyzer (Centrifugal Particle Size
Analyser). The particle diameter corresponding to 50 mass% is read from the integrated curve of particles of each particle diameter calculated based on the obtained centrifugal sedimentation curve and its abundance, and this value is taken as the above average particle diameter (Book Technology ", published by Nikkan Kogyo Shimbun, 1975, pp. 242-247).

(2) Particle size distribution ratio (γ) Based on the centrifugal sedimentation curve obtained in the measurement of the average particle size of the particles, an integrated curve of the particles of each particle size and their abundance is calculated and drawn, The cumulative weight of particles accumulated from the larger
Read the particle size corresponding to 25 mass% (D ₂₅ ) and the particle size corresponding to the cumulative mass of particles of 75 mass% (D ₇₅ ) and divide the former value by the latter value (D ₂₅ / D ₇₅ ), And the particle size distribution ratio (γ) of each particle is calculated.

(3) Volumetric shape factor (f) For example, a photograph of particles is taken 10 times at a magnification of 5000 with a scanning electron microscope.
Field-of-view photography, for example, image analysis processor Luzex 500
(Manufactured by Nippon Regulator Co., Ltd.), the average value of the maximum diameters is measured for each field of view, and the average value of 10 fields of view is calculated and designated as D.

The average volume {V = (π / 6) d ³ } of the particles is obtained from the average particle diameter d of the particles obtained in the item (1) of the measuring method, and the shape factor f is calculated by the following equation.

In the formula f = v / D ³ , v represents the average volume (μm ³ ) per particle, and D represents the average maximum particle size (μm) of the particles.

(4) Film running friction coefficient (μk) The film is measured as follows using the apparatus shown in FIG. In FIG. 1, 1 is an unwind reel, 2 is a tension controller, 3,5,6,8,9 and 11 are free rollers, 4 is a tension detector (inlet), and 7 is a stainless steel SUS304 fixed rod ( The outer diameter is 5 mmφ, 10 is a tension detector (outlet), 12 is a guide roller, and 13 is a take-up reel.

At a temperature of 20 ° C and a humidity of 60%, the film cut into 1/2 inch width is attached to 7 fixed rods (surface roughness 0.3 μm) at angle θ =
(152/181) π radian (152 °) contact at 200c / min
Move (rub) at a speed of m. Inlet tension T ₁ is 35g
The exit tension (T ₂ : g) when the tension controller 2 is adjusted so that the film travels for 90 m, is detected by the exit tension detector, and the running friction coefficient μk is calculated by the following formula.

μk = (2.303 / θ) log (T 2 / T 1) = 0.868log (T 2/35) (5) flatness CLA of the film surface (Center Line Average: center line average roughness) of JIS B 0
Measure according to 601. Using a probe type surface roughness meter (SURFCOM 3B) from Tokyo Seimitsu Co., Ltd., the radius of the needle is 2μ and the load is 0.
Draw a chart (film surface roughness curve) under the condition of 07g, extract the measured length L part from the obtained film surface roughness curve in the direction of its center line, and use the center line of this extracted part as the X axis. When the roughness curve Y = f (x) is expressed with the direction of longitudinal magnification as the Y axis, the value (Ra: μm) given by the following equation is defined as the flatness of the film surface.

In the present invention, 8 pieces are measured with a reference length of 0.25 mm, and Ra is expressed as an average value of 5 pieces excluding 3 pieces with the largest value.

(6) Sharpness-A The sharpness of the running surface of the film is evaluated using a 5-stage mini super calendar. The calender is a five-stage calender of nylon and steel rolls, the processing temperature is 80 ℃,
The linear pressure applied to the film is 200 kg / cm, and the film speed is
The abrasion resistance of the base film is evaluated by the dirt attached to the top roller of the calender when the film is run for a total length of 2000 m at 50 m / min.

<Judgment> ◎ Nylon roll is not soiled at all ○ Nylon roll is barely soiled × Nylon roll is soiled × × Nylon roll is heavily soiled.

(7) Scrapability-In the apparatus shown in FIG. 1 used for measuring the running friction coefficient of the B film, a blade for an industrial razor tester made by US GKI was used in place of the fixing rod made of SUS 304 stainless steel in 7 The film is made to hit the blade edge at an angle of 6 degrees, and the blade is run for 100 m under the same conditions as the measurement of running friction, and the sharpness is evaluated by the amount of shavings adhering to the blade edge.

<Judgment> ◎ The width of shavings adhering to the blade edge is less than 0.5 mm ○ The width of shavings adhering to the blade edge is 0.5 mm or more and less than 1.0 mm × The width of shavings adhering to the blade edge is 1.0 mm or more ( 8) Void ratio A sample film piece is fixed on a sample stand for a scanning electron microscope, and a sputtering device manufactured by JEOL Ltd. (JFC-1100) is used.
Type ion sputtering apparatus), the film surface is subjected to ion etching treatment under the following conditions. The sample stage is installed in the venger, and the degree of vacuum is raised to a vacuum state of about 10 ^-3 Torr, and ion etching is performed for about 10 minutes at a voltage of 0.25 kV and a current of 12.5 mA. Further, gold sputtering is applied to the surface of the film by the same apparatus to form a gold thin film layer of about 200 Å, and the measurement is performed using a scanning electron microscope at a magnification of 10,000 to 30,000 times, for example. In addition, the boiling is measured only with a lubricant having a particle size of 0.2 μm or more.

(9) Scratch resistance (10) Intrinsic viscosity [η] A value measured at 35 ° C using o-chlorophenol as a solvent, the unit is 100 cc / g.

[Examples] Hereinafter, the present invention will be further described with reference to Examples.

Examples 1 to 3 and Comparative Examples 1 to 7 Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and addition as shown in Table 1 as a lubricant. The particles were added and polymerized 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 and then fed to the extruder hopper to melt at a temperature of 280-3.
It was melted at 00 ° C., and the molten polymer was 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. to obtain an unstretched film of 200 μm.

The unstretched film thus obtained is preheated at 75 ° C., and further heated by one IR heater having a surface temperature of 900 ° C. from 15 mm above between low speed and high speed rolls and stretched to 3.6 times, It was rapidly cooled, then fed to a stenter and stretched 3.7 times in the transverse direction at 105 ° C. The resulting biaxially oriented film is 2
Heat setting was performed for 5 seconds at a temperature of 05 ° C. to obtain a heat setting biaxially oriented film having a thickness of 15 μm.

The characteristics of this film are shown in Table 1.

As is clear from Table 1, the product according to the present invention has excellent abrasion resistance, running property and scratch resistance, and has extremely excellent properties as a biaxially oriented polyester film for magnetic recording media.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for measuring a friction coefficient (μk) of a film. In FIG. 1, 4 is a tension detector (inlet), and 10 is a tension detector (outlet).

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Claims (3)

[Claims] 1. (I) Aromatic polyester, (II) (a) The following formula (A) R _x SiO _{2-(x / 2)} (A) where R is a carbon atom having 1 to 7 carbon atoms. It is a hydrogen group, and x is mainly a composition represented by a number of 1 to 1.2. (B) The following formula (B) f = v / D ³ (B) where v is one particle Is the average volume (μm ³ ) per
And D is the average maximum particle size (μm) of the particles, the volumetric shape factor (f) is greater than 0.4 and π / 6 or less, and (c) the average particle size is 0.005-0.5 μm 0.05 to 2% by weight of silicon resin fine particles (P ₁ ) (based on aromatic polyester), and (III) (a) mainly composed of the composition represented by the above formula (A), (b) the above formula (B) The defined volumetric shape factor (f) is
0.005 to 1.5% by weight of silicon resin fine particles (P ₂ ) having an average particle size larger than 0.4 and π / 6 or less, and (c) larger than the above silicon resin fine particles (P ₁ ) and 0.3 to 2.0 μm (P ₂ ). A biaxially oriented polyester film for a magnetic recording medium, which is formed from a composition in which (a aromatic polyester) is intimately mixed. 2. Silicon resin fine particles (P ₁ ) and (P ₂ ) are represented by the following formula (C) γ = D ₂₅ / D ₇₅ (C) where D ₂₅ is when the cumulative weight of particles is 25%. Is the average particle size (μm), and D ₇₅ is the average particle size (μm) when the cumulative weight of the particles is 75%. The particle size distribution ratio (γ) is defined as a value between 1 and 1.4. A biaxially oriented polyester film for magnetic recording media according to claim 1. 3. A biaxially oriented polyester film for a magnetic recording medium according to claim 1, wherein the aromatic polyester comprises an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component.