JPH0747650B2 - Biaxially oriented polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film, and more specifically, it contains spherical silica particles having different average particle diameters, and is flat and has excellent slipperiness and abrasion resistance. It relates to an excellent biaxially oriented polyester film.

[Prior Art] Due to its excellent properties, biaxially stretched polyester film is widely used in many applications such as magnetic tape, electricity, photography, metallization, and packaging. In particular, because of its characteristics such as 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 recent years, demands for high-density recording and high quality have been increasing in these fields of use, and along with this, the demand for a flat surface on the polyester film which is the base is increasing. However, when the surface becomes flat, there is a problem in that the winding shape of the film in the process of winding the film into a roll is significantly deteriorated, and it is difficult to obtain a film roll having a good winding shape.

The winding defects of the film roll include bump-shaped projections on the roll, wrinkles in the film vertical direction, and misaligned end faces. Prevents bump-shaped projections when the film has poor slipperiness. When a flat film is wound up for the purpose of increasing the tension, it tends to occur when the escape of the air layer generated between the films becomes poor when the flat film is wound up.

Therefore, the polyester film as the base is required to have excellent smoothness and air escape in order to obtain a good film winding shape as well as flatness.

Conventionally, a method of adding inorganic particles such as silicon oxide and calcium carbonate to polyester as a method for improving the slipperiness of a film, or a method of precipitating fine particles containing calcium, lithium or phosphorus in the polymerization system during the synthesis of polyester Proposed. In either method, when the polyester is formed into a film, protrusions are formed on the film surface due to the fine particles to improve the slipperiness of the film.

However, in the method for improving the slipperiness of the film by the projections by the fine particles as described above, the slipperiness is usually improved as the film surface is roughened, but on the other hand, due to the roughening, for example, magnetic recording is performed. In media applications, the surface after application of the magnetic paint tends to be rough, and electromagnetic conversion characteristics tend to deteriorate.

As one of the measures to solve these contradictory flatness and slipperiness, there have been proposed a number of means using composite inorganic fine particles in which large-sized particles and small-sized particles coexist. However, these means also have problems, and it is difficult to meet the demands for high-grade magnetic recording media such as high density and high quality. The reason for this is that the size of the large-sized particles used for the composite inorganic particles is coarse with respect to the required quality for high-grade grading, and the larger the particles, the higher the protrusions on the film surface. The electromagnetic conversion characteristics of magnetic recording media are deteriorated, and the larger the particles, the higher the projections on the film surface and the larger the voids surrounding the particles. In the cleaning process or the calendar processing process, the high protrusions are scraped off, which causes dropout (a missing part of information that occurs during recording and reproduction). This causes dirt on the dust fabric, greatly impairing the characteristics of the magnetic recording medium.

[Object of the Invention] The present inventor has solved the above-mentioned problems, has both flatness applicable to high-quality magnetic recording applications and a good film winding shape, and has good abrasion resistance. As a result of intensive research to develop a film, the shape of the protrusions on the film surface was made sharp, and if the large particles and the small particles were made into a specific combination, slipperiness, air escape and abrasion resistance were achieved even if the film surface was flat. In order to sharply improve the shape of the protrusion, it is most preferable that the particles present in the film are spherical, and there are many near spherical particles such as glass beads. It is difficult to obtain a film satisfying the surface characteristics especially for video tapes, but when a specific spherical silica particle is used in combination with large particles and small particles, a film satisfying the above characteristics is obtained. The inventors have found that what is obtained and have reached the present invention.

Therefore, an object of the present invention is to provide a biaxially oriented polyester film which is excellent in slipperiness, abrasion resistance and the like while maintaining flatness capable of coping with high density recording and high quality of magnetic recording media. It is in.

[Structure / Effect of Invention] According to the present invention, the object of the present invention is that the average particle size of the first component in the polyester is 0.12 μm to less than 0.6 μm, and the particle size ratio (major axis / minor axis) is 1.0. 0.01 to 2.0% by weight of spherical silica particles having a relative standard deviation of 0.3 or less represented by the following formula I is contained, and the average particle diameter of the second component is 0.1 μm or more smaller than that of the first component and 0.02 μm.
Within the above range and less than 0.5 μm, particle size ratio (major axis / minor axis)
Of 1.0 to 1.2 and a relative standard deviation of 0.3 or less represented by the following formula I is contained in an amount of 0.005 to 1.8% by weight and less than that of the first component, and Centerline average roughness (Ra) is 0.002 to 0.012
μm, and the center line average roughness (Ra) and the film surface
10-point average roughness (R _ZD ) is the following formula II And the 10-point average roughness (R _ZD ) and the film-film static friction coefficient (μs) satisfy the following formula III 0.015 ≦ R _ZD × μs ≦ 0.05 (III) Achieved by oriented polyester film.

Where Di: area circle equivalent diameter of each particle (μm): average of area circle equivalent diameter n: represents the number of particles.

The 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 polyesters are substantially linear and have film forming properties, especially film formation by melt casting. 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 glycols include alkylene glycols 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 polyester, for example, one having alkylene terephthalate and / or alkylene naphthalate 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 is A copolymer having 80 mol% or more of ethylene glycol is preferable. At that time, 20 of all acid components
Dicarboxylic acids up to mol% are terephthalic and / or 2.6
-The above-mentioned aromatic dicarboxylic acids other than naphthalene dicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, sebacic acid, etc .; cyclohexane-1,4
It can be an alicyclic dicarboxylic acid such as a dicarboxylic acid. In addition, 20 mol% or less of the total glycol component,
It can be any of the above glycols other than ethylene glycol, or for example hydroquinone, resorcin, 2,2
-Aromatic diols such as bis (4-hydroxyphenyl) propane; Aliphatic diols containing an aromatic ring such as 1,4-dihydroxymethylbenzene; Polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol It can also be (polyoxyalkylene glycol) or the like.

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

Further, in the polyester of the present invention, a polycarboxylic acid or polyhydroxy compound having a functionality of 3 or more, such as trimellitic acid or penta, is used in an amount in a substantially linear range, for example, an amount of 2 mol% or less based on all acid components. A copolymer of erythritol and the like is also included.

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

As the polyester, the intrinsic viscosity obtained by measuring at 35 ° C. as a solution in o-chlorophenol is about 0.4 to about
0.8 is preferable.

The biaxially oriented polyester film of the present invention has a large number of fine projections on the surface of the film.

The large number of fine projections derives from the large number of spherical silica particles contained according to the invention dispersed in the polyester.

The polyester containing the spherical silica particles dispersed therein is usually used at any time during the reaction for forming the polyester, for example, during the transesterification reaction or the polycondensation reaction in the case of the transesterification method, or in the case of the direct polymerization method. It can be produced by adding spherical silica particles (preferably as a slurry in glycol) to the reaction system at a certain time. Preferably, the spherical silica particles are added to the reaction system at the initial stage of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3.

In the present invention, the spherical silica particles dispersedly contained in the polyester have a particle size ratio (major axis / minor axis) of 1.0 to 1.2, preferably 1.0 to 1.1, and more preferably 1.0 to 1.05. The spherical silica particles have a spherical shape that is extremely close to a true sphere, and silica particles that have been known as lubricants are ultra-fine aggregate particles of about 10 μm or aggregates of about 0.5 μm. It is characterized in that it is remarkably different from that of forming a substance (aggregated particles). If the particle size ratio becomes too large, the void ratio becomes too large, which may deteriorate the machinability, which is not preferable. The spherical silica particles have an average particle size of 0.12 to less than 0.6 μm as the first component,
Preferably 0.2 to 0.54 μm, more preferably 0.25 to 0.49 μm
m, particularly preferably 0.38 to 0.48 μm, and the second component having an average particle size of 0.02 μm to less than 0.5 μm, preferably 0.06 μm to less than 0.4 μm, more preferably 0.08 to 0.3
μm, particularly preferably 0.10 to 0.25 μm. If the average particle size of the spherical silica particles as the first component becomes too small, the effect of improving the slipperiness becomes insufficient, which is not preferable.

The difference in average particle size between the first and second components is 0.1 μm
Or more, preferably 0.15 μm or more, more preferably 0.20
μm or more, particularly preferably 0.30 μm or more. If the difference in the average particle size between the first component and the second component is too small, the air escape property is deteriorated, the end face shift is likely to occur during film winding, and the film winding appearance is deteriorated, which is not preferable.

Here, the major axis, the minor axis, and the equivalent circle diameter of the spherical silica particles are, for example, 1 with an electron microscope after depositing a metal on the particle surface.
The average particle size and the particle size ratio are calculated by the following formulas, using the image magnified 10,000 to 30,000 times.

Average particle size = sum of area equivalent circle diameters of measured particles / number of measured particles Particle size ratio = average major axis of silica particles / average minor axis of the minor axis Further, spherical silica particles may have a sharp particle size distribution. Preferably, the relative standard deviation indicating the steepness of the distribution is 0.3.
It is below, and particularly preferably 0.12 or below.

This relative standard deviation is expressed by the following equation.

Where Di: area circle equivalent diameter of each particle (μm): average value of area circle equivalent diameter n: represents the number of particles measured.

If the relative standard deviation uses spherical silica particles of 0.3 or less,
Since the particles are spherical and the particle size distribution is extremely steep, the distribution of the protrusions formed on the film surface is extremely uniform, and a polyester film having uniform protrusion height and excellent slipperiness can be obtained. . Further, in this case, the average particle diameter of the first component and the average particle diameter of the second component are at least 0.1.
Due to the difference of μm, the particle size distributions of the first component and the second component do not substantially overlap with each other. The spherical silica particles are not limited to the production method and the like as long as the above-mentioned conditions are satisfied. For example, spherical silica particles can be obtained by hydrolyzing ethyl orthosilicate [Si (OC ₂ H ₅ ) ₄ ] into hydrous silica [Si
(OH) ₄ ] monodisperse spheres are produced, and the hydrous silica monodisperse spheres are dehydrated to grow silica bonds [≡Si-O-Si≡] three-dimensionally. '81, No. 9, P. 1503).

Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH ≡Si-OH + HO-Si≡ → ≡Si-O-Si≡ + H ₂ O Spherical silica as the first component in the present invention The amount of particles added is 0.01 to 2.0% by weight with respect to polyester,
Preferably 0.01-0.8% by weight, more preferably 0.01-0.2
%, Particularly preferably 0.02 to 0.10% by weight. The addition amount of the spherical silica particles as the second component is 0.005 to 18% by weight, preferably 0.005 to 1.6% by weight based on the polyester.
% By weight, more preferably 0.005 to 0.15% by weight, particularly preferably 0.01 to 0.09% by weight and not more than the amount of the first component. If the addition amount of the first component is less than 0.01% by weight and the addition amount of the second component is less than 0.005% by weight, the effect of improving slipperiness and abrasion resistance is insufficient. The total amount of the first and second components added is 0.015 to 3.0% by weight, preferably 0.02 to 2.0% by weight, more preferably 0.04 to 0.8% by weight, and particularly preferably 0.05 to 0.15% by weight. If the total addition amount exceeds 3.0% by weight, the surface flatness is deteriorated, which is not preferable.

In the polyester of the present invention, an ester product of a polyol having 3 or more hydroxyl groups and a fatty acid monocarboxylic acid having 8 or more carbon atoms is added to the polyester for the purpose of further improving the slipperiness of the film. 5% by weight
Below, preferably 0.05 to 2% by weight, particularly preferably 0.1
It is preferable to disperse the powder in an amount of about 0.9% by weight. It should be noted that when the amount of the ester product is too large, film blocking is likely to occur.

The polyol used as a raw material for the above ester product must have three or more hydroxyl groups. Although the reason for using an alcohol having two or less hydroxyl groups is not clear, even if the produced ester product is dispersed in polyester, the slipperiness of the film cannot be improved. Particularly, a polyol having 3 to 6 hydroxyl groups is preferable from the viewpoint of easy availability. Examples of the polyol having three or more hydroxyl groups include, but are not limited to, glycerin, erythritol, trait, pentaerythritol, arabite, xymerit, adnit, talit, sorbit, mannite, and id.

Further, as the fatty acid monocarboxylic acid to be reacted with the above-mentioned polyol, it is necessary to use one having 8 or more carbon atoms. If a fatty acid monocarboxylic acid having less than 8 carbon atoms is used, the heat resistance of the obtained ester product is insufficient,
It is easily decomposed under heating conditions when it is dispersed in polyester, and is not suitable as a substance dispersed in polyester.
Particularly, a fatty acid monocarboxylic acid having 8 to 25 carbon atoms is preferable because it is easily available. Examples of the fatty acid monocarboxylic acid having 8 or more carbon atoms include berargonic acid, capric acid, undecyl acid, lauric acid, tridecylic acid, myristic acid, pentadecyl acid, palmitic acid, heptadecyl acid, stearic acid, nonadecanoic acid, arachidic acid, behen. Examples thereof include acids, lignoceric acid, and cerotic acid.

When the above-mentioned polyol is reacted with a fatty acid monocarboxylic acid, usually mono, di and triesters are produced. All of these ester products are effective in improving the slipperiness, but are particularly preferable from the viewpoint of heat resistance when the triester is dispersed in the polyester.

Since the manifestation of the effect of the ester product also changes depending on the surface property of the film, the addition amount thereof is preferably selected according to the surface roughness.

Any method may be adopted to disperse the ester product in the polyester, for example, a method of adding and dispersing during the polycondensation reaction or a method of kneading with an extruder may be used, and a high-concentration master polymer may be used in advance. It is also possible to use a method in which the above is prepared and diluted with an unadded polyester.

The biaxially oriented polyester film of the present invention can be produced in accordance with the conventionally accumulated biaxially oriented film production method, but in order to obtain the film characteristics described below, the transverse stretching is performed by the method described below. Is preferred. For example, a polyester containing a predetermined amount of spherical silica particles is melt-cast into an amorphous unstretched film, and then the unstretched film is biaxially stretched, heat set, and if necessary, a relaxation heat treatment. By doing so, a biaxially oriented film can be manufactured. At that time, the film surface characteristics vary depending on the particle size, amount, etc. of the spherical silica particles and the stretching conditions, so it is preferable to appropriately select from the following stretching conditions.
In addition, the density, heat shrinkage ratio, etc. can be adjusted by stretching, heat treatment temperature, magnification,
Since it changes depending on the speed, etc., the conditions for simultaneously satisfying these characteristics are determined. To further explain, for example, the draw ratio is 2.5 or more, particularly 3 or more, in the uniaxial direction.
Also, it is preferable to select from the range where the area draw ratio is 8 times or more, and particularly 10 times or more.

The stretching temperature is the longitudinal stretching temperature: T ₁ is (Tg-10) to (Tg
g + 45) ° C range (Tg: glass transition temperature of polyester), and transverse stretching temperature is (Tg + 20) to (Tg +
It is recommended to select from the range of 100) ℃. Furthermore, the heat setting temperature may be selected from the range of 180 to 250 ° C, more preferably 200 to 230 ° C.

The transverse stretching is preferably carried out in several stages. In that case, the transverse draw ratio in each stage is preferably 1.2 times or more, and particularly preferably 1.3 times or more. Further, the difference in the stretching temperature in each stage of the transverse stretching is preferably 10 ° C. or more, particularly preferably 20 ° C. or more.

By adopting such a multi-stage stretching method, the center line average roughness (Ra) of the film surface is not changed so much, and the friction coefficient can be lowered. The reason for this is not clear,
It is considered that when the transverse stretching is carried out in multiple stages, "waviness" is caused on the film surface substantially by repeating stretching-relaxation-stretching, and the coefficient of friction of the film is lowered.

The biaxially oriented polyester film of the present invention preferably has a center line average roughness (Ra) of 0.002 to 0.012 μm on the surface thereof. If this center line average roughness (Ra) is too large, it is difficult to maintain the electromagnetic exchange characteristics required for a magnetic recording medium for high image quality, and if it is too small, the slipperiness deteriorates and the film is handled. Property and roll-up windability deteriorate. The center line average roughness (Ra) is preferably 0.
The thickness is 003 to 0.008 μm, more preferably 0.003 to 0.005 μm.

Further, the biaxially oriented polyester film in the present invention has the above-mentioned center line average roughness (Ra) and 10-point average roughness (R _ZD ).
And the following formula Have a relationship to satisfy.

If R _ZD / Ra becomes too large, the film surface roughness (R
Although a) is small, the number of high protrusions is too large, which deteriorates the electromagnetic conversion characteristics (especially in the low frequency range), which is not preferable. Normally, when the film is wound into a roll, the air accompanying the film is entrained together with the film.
If R _ZD / Ra is a moderate size, the associated air immediately passes through the film-film layer and is wound into a roll with a normal winding shape, but if R _ZD / Ra becomes too small, the associated air The air escaping becomes worse, and it gets caught in the roll together, and because the air gradually escapes, the winding appearance changes with the passage of time after winding the roll, and wrinkles occur,
Not preferable. From these points, R _ZD / Ra is more preferably 10 or more and 16 or less, and particularly preferably 12 or more and 16 or less.

Further, in the biaxially oriented polyester film of the present invention, the 10-point average surface (R _ZD ) and the film-film static friction coefficient (μs) have a relationship satisfying the following formula 0.015 ≦ R _ZD × μs ≦ 0.050. If the value of R _ZD × μs is too small, air may not escape easily between the film layers when the film is wound into a roll, the film may meander, and the end faces may be easily displaced. On the other hand, if it is too large, pimples (hump-shaped protrusions) occur when wound on a roll, workability and handleability are poor, and wrinkles often occur in the process. From these points, the value of R _ZD × μs preferably satisfies 0.020 to 0.050, and more preferably 0.025 to 0.040.

The biaxially oriented polyester film according to the present invention has a flat surface, but has extremely good slipperiness and air escape property, and windability when wound into a roll, as compared with conventional ones. It also has the characteristic that the winding appearance of the roll after winding is minimal.

The biaxially oriented polyester film of the present invention can be widely used for various applications by utilizing such characteristics. For example, it is useful for stamping foils, packaging films, vapor deposition of gold and silver threads, OHP, pulling in, and the like, and is particularly useful as a base film for magnetic recording media, particularly high-density magnetic recording media.

[Examples] Hereinafter, the present invention will be further described with reference to Examples. Various physical properties and characteristics in the present invention are measured as follows.

(1) Particle size of spherical silica particles The particle size can be measured in the following states.

1) When determining the average particle size, particle size ratio, etc. from the powder 2) When determining the average particle size, particle size ratio, etc. of the particles in the film.

(I) From powder Scatter the powder on the electron microscope sample stand so that the individual particles do not overlap as much as possible, and form a gold thin film deposition layer with a thickness of 200Å to 300Å on this surface with a gold sputtering device. , Observing with a scanning electron microscope at a magnification of 10,000 to 30,000 times,
Determine the major axis (Dli), the minor axis (Dsi) and the area equivalent circle diameter (Di) of at least 100 particles with Luzex 500 manufactured by Nippon Regulator Co., Ltd. Then, using the number average value represented by the following equation, the major axis (D
l), minor axis (Ds), average particle size ().

(Ii) Particles in the film A small piece of the sample film is fixed on a sample stand for a scanning electron microscope, and a sputtering device (JFC-110 manufactured by JEOL Ltd.) is used.
The film surface is subjected to an ion etching treatment under the following conditions using a 0 type ion sputtering device). The condition is that the sample is placed in a bell jar, 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 with the same device, and the film is observed with a scanning electron microscope at a magnification of 10,000 to 30,000, for example, and manufactured by Nippon Regulator Co., Ltd.
Determine the major axis (Dli), the minor axis (Dsi), and the area equivalent circle diameter (Di) of at least 100 particles with Luzex 500. Thereafter, the same procedure as (i) above is performed.

(2) Center line average roughness (Ra) of film surface It is a value defined by JIS-B0601, and in the present invention, a stylus type surface roughness diameter (SURFCORDERSE-30C) of Kosaka Laboratory Ltd. is used. taking measurement. The measurement conditions are as follows.

(A) Stylus tip radius: 2 μm (b) Measuring pressure: 30 mg (c) Cut-off: 0.25 mm (d) Measuring length: 1.0 mm (e): How to compile data Larger value is 1
Exclude one and display the average of the remaining four data.

(3) 10-point average surface roughness (R _ZD ) of the film surface In the above (2) measurement, the highest peak and the lowest valley of each section equally divided into 1/5 of the roughness profile with a measurement length of 1 mm R _ZD is displayed as the average value of the differences R _Z1 , R _Z2 , ..., R _Z5 .

(4) Static friction coefficient (μs) A fixed glass plate is placed under the two laminated films, and the film under the laminated films (the film in contact with the glass plates) is pulled by a low-speed roll. Bird (15
cm / min), fix the detector to one end of the upper film (the end opposite to the take-up direction of the lower film) and detect the film / film pulling force. The thread used at that time has a weight of 1 kg and a lower area of 70 cm.

(5) Winding property In the manufacturing process of biaxially oriented polyester film, the film is wound up on a roll having a width of 800 m and a length of 5000 m at a speed of 250 m / min, and the appearance of the winding roll is inspected in detail to class 1 to 5 To rate.

The end face displacement is graded as follows according to the distance of the end face widthwise displacement.

For bump-shaped projections, count the number of bump-shaped projections with a major axis of 2 mm or more and rank them as follows.

Furthermore, the rolls wound up above were stored at 40 ° C. × 80% RH for 10 days, and the occurrence of vertical wrinkles and horizontal wrinkles was examined by observing the surface and inner layer of the roll.

Example 1 Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and a spherical agent having a mean particle size of 0.48 μm and a particle size ratio of 1.04 as a lubricant. Using silica and spherical silica having an average particle size of 0.20 μm and a particle size ratio of 1.04, polymerization was carried out by an ordinary method to obtain an intrinsic viscosity (orthochlorophenol, 35
C.) 0.62 polyethylene terephthalate was obtained.

170 ℃ of this polyethylene terephthalate pellets,
After drying for 3 hours, supply to the extruder hopper and melt temperature 280 ~ 3
Melt at 00 ° C, extrude this molten polymer through a 1 mm slit die onto a rotating cooling drum with a surface temperature of 20 ° C,
An unstretched film was obtained.

The unstretched film thus obtained is preheated at 76 ° C, further heated by an IR heater having a surface temperature of 890 ° C from 15 mm above between low-speed and high-speed rolls, stretched to 3.6 times, and rapidly cooled. Then, it is fed to a stenter and stretched to 2.9 at 98 ° C as the first stage of transverse stretching, and then to the second stage as 1st stage.
It was stretched at 32 ° C. so that the final transverse stretching ratio was 3.9 times. Then, the obtained biaxially oriented film is 208
It was heat-set at ℃ for 4 seconds.

On the other hand, needle-like α-FeOOH containing 5% of cobalt is heated and hydrogen-reduced to obtain Fe ₂ O ₃ , which is further heated in air to obtain ferromagnetic iron powder having an average needle-like length of 0.2 μm. Obtained.

100 parts by weight of the above ferromagnetic iron powder (hereinafter simply referred to as "part") and the following composition were kneaded and dispersed in a ball mill for 12 hours.

Polyester polyurethane 12 parts Vinyl chloride-vinyl acetate-maleic anhydride copolymer 10 parts α-alumina 5 parts Carbon black 1 part Butyl acetate 70 parts Methyl ethyl ketone 35 parts Cyclohexanone 100 parts After dispersion, further fatty acid oleic acid 1 part Palmitic acid 1 part 1 part of a fatty acid ester (amyl stearate) was added and kneaded for 15 to 30 minutes, then 7 parts of a 25% ethyl acetate solution of a triisocyanate compound was added, and high-speed shear dispersion was carried out for 1 hour to prepare a magnetic coating solution.

After the obtained coating, it was coated on the heat-set biaxially oriented film so that the dry film thickness was 3 μm. Then, after orientation treatment in a direct current magnetic field, it was dried at 100 ° C. After drying, calendering treatment was applied to obtain a magnetic tape for video which was slit to a 1/2 inch width.

The film thus obtained has a good winding property, and even when it is wound at a high speed, there is little occurrence of end face deviation, and there are few bump-like projections.
Further, the winding shape after aging was also good, and the electromagnetic conversion characteristics of the tape after being made into a magnetic tape were also good. The characteristics of this film are shown in Table 1.

Comparative Examples 1 and 2 Biaxially oriented in the same manner as in Example 1 except that spherical particles having different average particle diameters are used and that transverse stretching in film formation is performed at 110 ° C. and 3.9 times in one step. Film and magnetic tape were made.

The properties of this biaxially oriented film are shown in Table-1. In Comparative Example 1, the end surface displacement was good when wound at high speed, but bump-like protrusions were generated, and in Comparative Example 2 When rolled up at a high speed, the end face was likely to be displaced, which was not a good characteristic.

Example 2 A biaxially oriented polyester film was prepared in the same manner as in Example 1 except that spherical silica particles having different average particle diameters were used and 0.3% by weight of pentaerythritol tristearate was added to the polyester. And magnetic tape was created.

This film had good winding properties, and in particular, it had few bump-like projections and had good properties. The film characteristics are shown in Table 1.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area B29L 7:00

Claims (3)

[Claims] 1. A polyester having an average particle size of 0.12 μm to less than 0.6 μm as a first component, a particle size ratio (major axis / minor axis) of 1.0 to 1.2, and a relative standard deviation represented by the following formula I. 0.01 to 2.0% by weight of spherical silica particles having a particle diameter of 0.3 or less, and an average particle diameter of the second component is 0.1 μm or more smaller than that of the first component and is 0.02 μm or more and less than 0.5 μm. / Minor diameter) is 1.0 to 1.2, and the relative standard deviation represented by the following formula I is 0.3 or less, spherical silica particles are contained in an amount of 0.005 to 1.8% by weight and less than the first component, The centerline average roughness (Ra) of the film surface is 0.002 to 0.012 μm, and the centerline average roughness (Ra) and the 10-point average roughness (R _ZD ) of the film surface are represented by the following formula II. And the 10-point average roughness (R _ZD ) and the film-film static friction coefficient (μs) satisfy the following formula III 0.015 ≦ R _ZD × μs ≦ 0.05 (III) Oriented polyester film. Where Di: area circle equivalent diameter of each particle (μm): average of area circle equivalent diameter n: represents the number of particles. 2. The biaxially oriented polyester film according to claim 1, wherein the average particle size of the second component is smaller than the average particle size of the first component by 0.2 μm or more. 3. Center line average roughness (Ra) and 10-point average roughness (R)
_ZD ) is the following formula II ′ The 10-point average roughness (R _ZD ) and the film-film static friction coefficient (μs) satisfy the following formula III ′ 0.025 ≦ R _ZD × μs ≦ 0.040 (III ′). Biaxially oriented polyester film.