JPH054412B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a biaxially oriented polyester film, and more specifically, a biaxially oriented polyester film that contains spherical silica particles with different average particle diameters and is flat and has excellent slip properties, abrasion resistance, etc. Regarding. [Prior Art] Due to its excellent properties, biaxially stretched polyester films are widely used in many applications such as magnetic tapes, electricity, photography, metallization, and packaging. In particular, due to its properties such as high strength and elastic modulus, magnetic recording media, such as video tapes,
Widely used as a base film for audio tapes, computer tapes, floppy disks, etc. In recent years, demands for higher density recording and higher quality have been increasing in these application fields, and with this, there has been an increasing demand for the base polyester film to have a flat surface. However, when the surface becomes flat, the winding appearance of the film in the process of winding the film into a roll deteriorates significantly, and there is a problem that it is difficult to obtain a film roll with a good winding appearance. A defect in the winding appearance of a film roll is that bump-like protrusions occur on the roll. If there are wrinkles in the longitudinal direction of the film, or the edges of the film are misaligned, or the film has poor slipperiness, it may be necessary to wind the film with high tension to prevent bump-like protrusions. In the above cases, when the escape of the air layer between the films becomes difficult, these problems tend to occur. Therefore, the base polyester film is required to have not only flatness but also excellent slipperiness and air escape properties in order to obtain a good film winding appearance. Conventionally, methods for improving the slipperiness of films include adding inorganic particles such as silicon oxide or calcium carbonate to polyester, or precipitating fine particles containing calcium, lithium, or phosphorus in the polymerization system during polyester synthesis. Proposed. In either method, when polyester is formed into a film, projections are formed on the surface of the film due to fine particles, thereby improving the slipperiness of the film. However, in the above-mentioned method of improving the slipperiness of a film using protrusions made of fine particles, the slipperiness usually improves as the film surface becomes rougher, but on the other hand, due to the roughening, e.g. When used as a magnetic recording medium, the surface after applying the magnetic paint tends to become rough and the electromagnetic conversion characteristics tend to deteriorate. As one of the measures to solve these contradictory problems of flatness and slipperiness, many methods have been proposed that utilize composite inorganic fine particles in which large-sized particles and small-sized particles coexist. However, these means also have problems, and as they are, it is difficult to meet the demands for higher grades of magnetic recording media, such as higher density and higher quality. The reason for this is that the size of the large particles used in composite inorganic particles is too large for the quality required for high-grade grades, and the larger the particles, the higher the protrusions on the film surface. In addition, the larger the particles, the higher the protrusions on the film surface and the larger the voids surrounding the particles. During the cleaning process or calendar processing process, tall protrusions are scraped off, causing dropouts (missing information that occurs during recording and playback), and furthermore, calendar stains during the processing process and dust fumes used to clean the base film surface are removed. This causes abrasive contamination, which greatly impairs the properties of the magnetic recording medium. [Object of the Invention] The present inventor has solved the above-mentioned problems, and has created a film that has both flatness and good film winding appearance that can be applied to high-quality magnetic recording applications, and also has good abrasion resistance. As a result of intensive research to develop the film, the shape of the protrusions on the film surface was sharpened,
Furthermore, if a specific combination of large particles and small particles is used, the slip properties, air escape properties, and abrasion resistance can be greatly improved even if the film surface is flat. The particles that exist are most preferably spherical, and there are many particles that are close to spherical, including glass beads, but it is difficult to obtain a film that satisfies the surface characteristics especially for video tapes from these particles. However, the inventors have discovered that a film satisfying the above characteristics can be obtained by using specific spherical silica particles in combination of large particles and small particles, and has thus arrived at the present invention. Therefore, an object of the present invention is to provide a biaxially oriented polyester film that has excellent slip properties, abrasion resistance, etc. while maintaining flatness that can meet the demands for higher density recording and higher quality magnetic recording media. There is a particular thing. [Configuration/Effects of the Invention] The object of the present invention is to provide polyester with an average particle size of 0.05 μm to 0.5 μm as a first component, a particle size ratio (major axis/breadth axis) of 1.0 to 1.2, and a polyester having the following formula: The second component contains 0.01 to 2.5% by weight of spherical silica particles with a relative standard deviation of 0.5 or less, and has an average particle size larger than the first component by 0.1 μm or more.
Spherical silica particles in the range of 0.15 μm or more and less than 0.6 μm, a particle size ratio (major axis / minor axis) of 1.0 to 1.2, and a relative standard deviation expressed by the following formula of 0.5 or less are used in an amount of 0.005 to 2.0% by weight. This is achieved by a biaxially oriented polyester film containing the same or less amount of the first component within the range. Here, Di: Area circle equivalent diameter of each particle (μm): Average value of area circle equivalent diameter {=( _o 〓 ⁱ⁼¹ Di)/n} (μm) n: Represents the number of particles. The polyester in the present invention is a polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyester is substantially linear;
It also has film-forming properties, particularly film-forming properties by melt molding. Examples of aromatic dicarboxylic acids include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, and anthracene. Dicarboxylic acids and the like can be mentioned. Examples of 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 diols such as cyclohexanedimethanol. etc. can be mentioned. In the present invention, polyesters containing, for example, alkylene terephthalate and/or alkylene naphthalate as main constituents are preferably used. Among such polyesters, for example, not only polyethylene terephthalate and polyethylene-2,6-naphthalate, but also terephthalic acid and/or 2,6-naphthalene dicarboxylic acid account for 80 mol% or more of the total dicarboxylic acid component, and the total glycol component A copolymer in which 80 mol% or more of ethylene glycol is ethylene glycol is preferred. At that time, the total acid component
Up to 20 mol% of the dicarboxylic acid can be the aromatic dicarboxylic acids mentioned above other than terephthalic acid and/or 2,6-naphthalene dicarboxylic acid, and also aliphatic dicarboxylic acids such as adipic acid, sebacic acid, etc.; cyclohexane- It can be an alicyclic dicarboxylic acid such as 1,4-dicarboxylic acid. In addition, up to 20 mol% of the total glycol component can be the above-mentioned glycols other than ethylene glycol, or aromatic glycols such as hydroquinone, resorcinol, 2,2-bis(4-hydroxyphenyl)propane, etc. Diol;
Aliphatic diols containing an aromatic ring such as 1,4-dihydroxymethylbenzene; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc. can also be used. In addition, the polyester used in the present invention includes, for example, an aromatic oxyacid such as hydroxybenzoic acid;
Also included are those in which a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as -hydroxycaproic acid is copolymerized or combined in an amount of 20 mol % or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component. Furthermore, the polyester in the present invention has a substantially linear amount, e.g.
Also included are those copolymerized with a trifunctional or higher functional polycarboxylic acid or polyhydroxy compound, such as trimellitic acid, pentaerinlitol, etc., in an amount of mol % or less. The above polyester is known per se, and can be produced by a method known per se. The polyester preferably has an intrinsic viscosity of about 0.4 to about 0.8 as measured as a solution in o-chlorophenol at 35°C. The biaxially oriented polyester film of the present invention has many fine protrusions on its surface. According to the invention, these large numbers of fine protrusions originate from a large number of spherical silica particles dispersed and contained in the polyester. Polyesters containing dispersed spherical silica particles are usually used during the reaction to form polyesters.
For example, spherical silica particles (preferably as a slurry in glycol) are added to the reaction system at any time during the transesterification reaction or polycondensation reaction when using the transesterification method, or at any time during the polycondensation reaction when using the direct polymerization method. It can be produced by adding it to. Preferably, spherical silica particles are added to the reaction system at the beginning of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3. In the present invention, the spherical silica particles dispersed in polyester have a particle size ratio (major axis/minor axis) of 1.0.
-1.2, preferably 1.0-1.1, more preferably 1.0
~1.05. These spherical silica particles have individual shapes that are extremely close to true spheres, and are silica particles that have been traditionally known as lubricants.
It is distinctive in that it is significantly different from ultrafine lumpy particles of about 10 mμm or aggregates (agglomerated particles) of about 0.5 μm by agglomerating these particles. If the particle size ratio becomes too large, the void ratio becomes large;
Perhaps for this reason, it is undesirable because the machinability deteriorates.
The spherical silica particles have an average particle diameter of 0.05 to 0.5 μm, preferably 0.05 to 0.4 μm, as a first component.
More preferably, the second component has an average particle size of 0.15 μm or more and less than 0.6 μm, preferably 0.2 μm or more and less than 0.6 μm, and even more preferably 0.3 μm or more and less than 0.6 μm.
0.5 μm, particularly preferably 0.4-0.5 μm
It is a seed. If the average particle size of the spherical silica particles as the first component becomes too small, the effect of improving slipperiness will be insufficient, which is undesirable. If it becomes too large, the difference in average particle size from the second component will become small, resulting in poor air escape properties. This is undesirable because the effect of improving the film winding appearance (edge misalignment) becomes insufficient. Also, the difference in average particle size between the first component and the second component is
It is 0.1 μm or more, preferably 0.15 μm or more, and more preferably 0.20 μm or more. . If the difference in average particle size between the first component and the second component is too small, air escape performance will be poor, end face deviation will easily occur during film winding, and the film winding appearance will be poor, which is not preferable. Here, the major axis, minor axis, and area-circle-equivalent diameter of spherical silica particles are determined from an image magnified, for example, 10,000 to 30,000 times with an electron microscope after metal is deposited on the particle surface, and the average particle diameter and particle diameter are The ratio is calculated using the following formula. Average particle size = Sum of area circle equivalent diameters of measured particles / Number of measured particles Particle size ratio = Average major axis of silica particles / Average minor axis of the particles In addition, the spherical silica particles need to have a sharp particle size distribution. The relative standard deviation, which represents the steepness of the distribution, must be 0.5 or less, more preferably 0.3 or less, and particularly preferably 0.12 or less. This relative standard difference is expressed by the following formula. Here, Di: Area circle equivalent diameter of each particle (μm): Average value of area circle equivalent diameter {=( _o 〓 ⁱ⁼¹ Di)/n} (μm) n: Represents the measured number of particles. When spherical silica particles with a relative standard deviation of 0.5 or less are used, the particles are truly spherical and have an extremely steep particle size distribution, so the distribution of protrusions formed on the film surface is extremely uniform, and the height of the protrusions is A polyester film with a uniform shape and excellent slip properties can be obtained. Furthermore, in this case, since there is a difference of at least 0.1 μm between the average particle size of the first component and the average particle size of the second component, the particle size distributions of the first component and the second component do not substantially overlap with each other. As long as the spherical silica particles satisfy the above-mentioned conditions, there are no limitations on the manufacturing method or the like. For example, spherical silica particles are produced by hydrolyzing ethyl orthosilicate [Si(OC ₂ H ₅ ) ₄ ] to create monodisperse hydrated silica [Si(OH) ₄ ] spheres, and then dehydrating these monodisperse hydrated silica spheres. It can be manufactured by growing silica bonds [≡Si-O-Si≡] three-dimensionally (Journal of the Chemical Society of Japan '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 2.5 to polyester
% by weight, preferably 0.05 to 2.0% by weight, more preferably 0.05 to 1.0% by weight, particularly preferably
It is 0.1-0.5% by weight. In addition, the amount of spherical silica particles added as the second component is
0.005-2.0% by weight, preferably 0.01-1.5% by weight,
The amount is more preferably 0.02 to 1.0% by weight, particularly preferably 0.04 to 0.4% by weight, and is the same as or less than the amount of the first component. Of these, the amount is preferably equal to or less than that of the first component. Addition amount of the first component is 0.01% by weight
If the amount of the second component added is less than 0.005% by weight, the effect of improving slipperiness and abrasion resistance will be insufficient. The total amount of the first component and second component added is 0.015 to 3.0% by weight, preferably 0.02 to 2.0% by weight, more preferably 0.04 to 1.0% by weight, particularly preferably 0.06 to 0.3% by weight. If the total amount added exceeds 3.0% by weight, the surface flatness will decrease,
Undesirable. The biaxially oriented polyester film of the present invention can be produced in accordance with conventional methods for producing biaxially oriented films. For example, polyester containing a predetermined amount of spherical silica particles is melt-formed to form an amorphous unstretched film, then the unstretched film is stretched biaxially, heat-set, and if necessary, subjected to relaxation treatment. Manufactured by At this time, the film surface characteristics vary depending on the particle size, amount, etc. of the spherical silica particles, and also depending on the stretching conditions, so they are appropriately selected from conventional stretching conditions. Furthermore, since the density, thermal shrinkage rate, etc. change depending on the temperature, magnification, speed, etc. during stretching and heat treatment, conditions are determined to satisfy these characteristics at the same time. For example, the stretching temperature is such that the first stage stretching temperature (e.g. longitudinal stretching temperature: T ₁ ) is (Tg-
10) - (Tg + 45) °C (however, Tg: glass transition temperature of polyester), the second-stage stretching temperature (for example, transverse direction stretching temperature: T ₂ ) is (T ₁ + 5) -
It is recommended to select from the range of (T ₁ +40)°C. Also,
The stretching ratio is preferably selected from a range in which the uniaxial stretching ratio is 2.5 times or more, particularly 3 times or more, and the area magnification is 8 times or more, especially 10 times or more. Furthermore, the heat setting temperature is preferably selected from the range of 180 to 250°C, more preferably 200 to 230°C. The biaxially oriented polyester film of the present invention is characterized by extremely small voids compared to conventional films. The reason why the voids around the spherical silica particles are small is that the particles have a good affinity for polyester, and the particles themselves are very close to true spheres, so the stress around the lubricant propagates evenly during stretching, and the polyester This is presumed to be due to the fact that stress is not concentrated on a part of the particle interface. In the present invention, by adding spherical silica particles whose particle size distribution is extremely sharp, the distribution of protrusions formed on the surface of the polyester film is extremely uniform, and the heights of the large and small protrusions are uniform. A film is obtained. The biaxially oriented polyester film of the present invention has uniform uneven surface characteristics, excellent slipperiness, and excellent abrasion resistance, and is characterized by significantly less generation of scratches, white powder, and the like. This biaxially oriented polyester film can be widely used in various applications by taking advantage of these characteristics. For example, when used as a base film for magnetic recording such as video, audio, and computers,
Excellent electromagnetic conversion characteristics, slipperiness, running durability, etc. can be obtained. Furthermore, when used in capacitor applications, low coefficient of friction, excellent windability, low crushing load, high transparency, etc. can be obtained. As mentioned above, this biaxially oriented polyester film is preferably used as a base film for magnetic recording media, particularly as a base film for magnetic tapes, but is not limited thereto, and can be used for electrical applications, packaging applications, films for vapor deposition, etc. It can be widely applied to other fields as well. Furthermore,
One or both sides of the film may be subjected to an adhesion treatment, for example, an adhesion layer coating, a corona treatment, or other surface treatment. The film also contains antistatic agents,
A third component such as an ultraviolet absorber or a coloring agent may be included. [Examples] The present invention will be further explained below with reference to Examples.
Note that various physical property values and characteristics in the present invention were measured as follows. (1) Particle size of spherical silica particles There are the following conditions for measuring particle size. (1) When calculating the average particle size, particle size ratio, etc. from powder (2) When calculating the average particle size, particle size ratio, etc. of particles in a film. (i) From powder The powder is scattered on an electron microscope sample stage so that the individual particles do not overlap as much as possible, and a thin gold film is deposited on the surface using a gold sputtering device to a thickness of 200 Å to 300 Å.
For example, 1
Observe at a magnification of 10,000 to 30,000 times and use the Japanese Regulator.
Determine the major axis (Dli), minor axis (Dsi), and area equivalent diameter (Di) of at least 100 particles using Luzetx 500 manufactured by Co., Ltd. The major axis (Dl), minor axis (Ds), and average particle diameter ( ) of the silica particles are expressed by the number average value expressed by the following formula. Dl＝( _o 〓 ⁱ⁼¹ Dli) / n, Ds = ( _o 〓 ⁱ⁼¹ Dsi) / n, = ( _o 〓 ⁱ⁼¹ Di) / n (ii) For particles in a film A small piece of the sample film The film was fixed on a sample stage for a scanning electron microscope, and the surface of the film was subjected to ion etching using a JEOL sputtering device (JFC-1100 type ion sputtering device) under the following conditions. The conditions were to place the sample in a bell gear, raise the vacuum level to approximately 10 ^-3 Torr, and
Perform ion etching for approximately 10 minutes at a voltage of 0.25 KV and a current of 12.5 mA. Furthermore, gold sputtering is applied to the surface of the film using the same equipment, and the film is observed with a scanning electron microscope at a magnification of, for example, 10,000 to 30,000 times, and the major diameter of at least 100 particles (Dli ), short axis (Dsi), and area circle equivalent diameter (Di). The following steps are performed in the same manner as in (i) above. (2) Particle size, etc. of particles other than silica particles (1) Average particle size Measured using Shimadzu's CP-50 Centrifugal Particle Size Analyzer, based on the obtained centrifugal sedimentation curve. From the calculated integrated curve of particles of each particle size and their abundance, 50
Read the particle size corresponding to the mass percent and use this value as the above average particle size (Book ``Particle Size Measurement Technology''
Published by Nikkan Kogyo Shimbun, 1975, pp. 242-247). (2) Particle size ratio Fixed molding of small film pieces with epoxy resin,
Create ultra-thin sections (cut in the direction of film flow) approximately 600 Å thick using a microtome. This sample was examined using a transmission electron microscope (manufactured by Hitachi: H-
800 model) to observe the cross-sectional shape of the lubricant (particles) in the film, and express it as the ratio of the long axis to the short axis of the lubricant. (3) Relative standard deviation value Measurement is carried out in the same manner as for silica particles.For particles other than spherical, the volume is calculated from the particle size ratio in the film thickness direction, and the particle size is calculated using the diameter of an equivalent sphere. diameter, and calculate the relative standard deviation value. (3) Film surface roughness (Ra) This is the value defined in JIS-B0601 as the centerline average roughness (Ra). SE-30C). The measurement conditions are as follows. (a) Stylus tip radius: 2μm (b) Measurement pressure: 30mg (c) Cutoff: 0.25mm (d) Measurement length: 0.5mm (e) How to summarize data Measure the same sample 5 times and find the largest value Exclude one, round off the average value of the remaining four data to the fourth decimal place, and display up to the third decimal place. (4) Coefficient of friction of film (μk) A film cut into 1/2 inch width was fixed to a rod (surface roughness 0.3μm) in an environment of 20℃ and 60% humidity.
It is brought into contact with the object at an angle θ = (152/180) π radians (152°) and moved (friction) at a speed of 200 cm/min.
When the tension controller is adjusted so that the inlet tension T ₁ is 50 g, the exit tension (T ₂ : g) is detected by the exit tension detector after the film has traveled 90 m, and the running friction coefficient μk is calculated using the following formula. calculate. μk = (2.303/θ) log (T ₂ / T ₁ ) = 0.868 log (T ₂ /50) (5) Abrasion resistance The abrasion resistance of the running surface of the base film is evaluated using a 5-stage mini super calendar. . The calendar is a 5-stage calendar with nylon rolls and steel rolls, the processing temperature is 80℃, the linear pressure applied to the film is 200Kg/cm, and the film speed is 50
Run at m/min. The total length of the running film is 2000m.
The abrasion resistance of the base film is evaluated based on the dirt that adheres to the top roller of the calendar during running. <Four-level judgment> ◎: No stains on the nylon roll ○: Almost no stains on the nylon roll ×: Stain on the nylon roll ××: Severe stain on the nylon roll (6) Electromagnetic conversion characteristics (Chroma S/N) Commercially available Using a home VTR, record a signal in which a 100% chroma level signal is superimposed on a 50% white level signal (a 100% white level signal has a peak-to-peak voltage of 0.714 volts), and then record the reproduced signal. Measurement is performed using Shibasoku Noise Meter Type 952R. The definition of chroma S/N is as follows according to Shibasoku's definition. Chroma S/N (dB) = 20log ES (p-p) / EN (rms) Here, ES (p-p) is the peak:to:peak voltage level (p-p) of the reproduced signal of the white level signal. . ES (p-p) = 0.714V (p-p) EN (rms) is the square root value of the peak voltage of the reproduced signal of the chroma level signal. EN (rma) = AM noise effective value voltage (t) (7) Dropout Count the dropout of 5μCsec x 10dB using a commercially available dropout counter (for example, Shibasoku VH01BZ type) and calculate the number of dropouts per minute. (8) Scratch Judgment Slit the base film into 1/2 inch width, and at the same time as measuring the friction coefficient in (4) above, wrap the film on a fixed rod up to an angle of 152°, run it for 10 meters at a film speed of 20 cm/sec, and then 1/2 after repeating 50 times
The thickness, depth, and number of scratches on the surface of the inch-wide base film are evaluated according to the following five criteria. <5-level judgment> ◎ No scratches observed on the 1/2 inch wide base film ○ Almost no scratches observed on the 1/2 inch wide base film △ Scratches observed on the 1/2 inch wide base film (no scratches observed on the 1/2 inch wide base film) × Several thick scratches are observed on the 1/2-inch wide base film × × Many thick and deep scratches are observed all over the 1/2-inch wide base film (9) Winding state Film is 500 mm wide and long. The material is wound onto a roll with a length of 5,000 m at a speed of 100 m/min, and the appearance of the rolled up roll is inspected in detail and graded from grade 1 to grade 5. The end face misalignment is graded as follows based on the distance of the end face misalignment in the width direction. Regarding lump-like protrusions, count the number of lump-like protrusions with a major diameter of 2 mm or more and grade them as follows.

[Table] Example 1 Dimethyl terephthalate and ethylene glycol were transesterified using manganese acetate as a catalyst,
Antimony trioxide was used as a polymerization catalyst, phosphorous acid was used as a stabilizer, and an average particle size of 0.14 μm was used as a lubricant.
Spherical silica particles with a particle size ratio of 1.03 and an average particle size of 0.42 μm,
Polyethylene terephthalate with an intrinsic viscosity (orthochlorophenol, 35° C.) of 0.62 was obtained by polymerization using a conventional method using spherical silica particles with a particle size ratio of 1.05. This polyethylene terephthalate pellet
After drying at 170℃ for 3 hours, feed it to the extruder hopper.
The polymer was melted at a melting temperature of 250 to 300°C, and the molten polymer was extruded through a 1 mm slit die onto a rotating cooling drum with a surface temperature of 20°C to obtain an unstretched film. The unstretched film thus obtained was heated at 80°C.
The film was further heated between low speed and high speed rolls using an IR heater with a surface temperature of 850°C from 15 mm above, stretched to 3.6 times, rapidly cooled, and then fed to a stenter at 105°C in the transverse direction. It was stretched 3.8 times. The obtained biaxially oriented film was heat set at a temperature of 510° C. for 5 seconds to obtain a heat set biaxially oriented film with a thickness of 15 μm. Furthermore, on this film, 100 parts by weight of Co-containing iron oxide powder with the following composition Eslec A (vinyl chloride-vinyl acetate copolymer manufactured by Sekisui Chemical) 10 Nitsuporan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane) 10 Coronate L (manufactured by Nippon Polyurethane) Polyisocyanate) 5 Lecithin 1 Methyl ethyl ketone 75 Methyl isobutyl ketone 75 Toluene 75 Additives (lubricant, silicone resin) 0.15 Magnetic paint was applied using a gravure roll, and the magnetic paint layer was smoothed using a doctor knife. While the magnetic paint is still dry, it is magnetically oriented using a conventional method, then brought into the open, dried and cured, and then calendered to make the coated surface uniform and slit to form a magnetic layer with a thickness of approximately 4μ. A 1/2 inch wide magnetic tape was prepared. The first characteristic of this film and magnetic tape is
Shown in the table. The film thus obtained had a low surface roughness Ra, a low coefficient of friction, a good winding appearance when wound into a roll, and good calender abrasion properties. Further, after processing into a magnetic tape, the electromagnetic conversion characteristics, dropout (D/O), and other characteristics were also good. Example 2 A film and tape were prepared in the same manner as in Example 1, except that the average particle diameter of the spherical silica particles used and the amount added were changed as shown in Table 1. The properties were good as shown in Table 1. Comparative Examples 1 to 4 Films and tapes were produced in the same manner as in Example 1 except that kaolin and calcium carbonate were used as particles.
The properties are shown in Table 1, but none of them were good.

[Table] Example 3 The average particle diameter and amount of spherical silica used were
Films and tapes were prepared in the same manner as in Example 1 except for the changes shown in the table. Its properties were particularly excellent as shown in Table 2.

【table】

【table】

Claims (1)

[Claims] 1. As the first component in the polyester, the average particle size is
The particle size ratio (major axis/minor axis) is 0.05μm to 0.5μm.
1.0 to 1.2 and the relative standard deviation expressed by the following formula is 0.01 to 2.5.
% by weight, and as a second component, the average particle diameter is in the range of 0.15 μm or more and less than 0.6 μm, which is 0.1 μm or more larger than the first component, and the particle size ratio (major axis / short axis) is 1.0 ~
1.2 and having a relative standard deviation of 0.5 or less expressed by the following formula, in an amount within the range of 0.005 to 2.0% by weight, which is the same as or less than the first component. Axially oriented polyester film. Here, Di: Area circle equivalent diameter of each particle (μm): Average value of area circle equivalent diameter {=( _o 〓 ⁱ⁼¹ Di)/n} (μm) n: Represents the number of particles.