JPH05209063A - Biaxially oriented polyester film - Google Patents

Abstract

(57) [Summary] [Object] To provide a biaxially oriented polyester film having excellent surface properties, abrasion resistance and running properties. [Structure] The average particle size is 0.05 to 1.5 μm, and the spherical ratio defined by the major axis / minor axis is 1.0 to 2.0,
Spherical or elliptic spherical vaterite-type calcium carbonate particles having a particle size distribution value of 2.00 or less defined by the following formula,
Particles obtained by surface-treating with a copolymer containing a polyalkylene glycol unit and a polyacrylic acid unit and / or a polyacrylic acid derivative unit and then surface-treating with a polyacrylic acid salt are 0. Biaxially oriented polyester film containing 001 to 5% by weight. Particle size distribution value = d ₂₅ / d ₇₅ [In the above formula, d ₂₅ and d ₇₅ are measured by measuring the cumulative volume of the particle group from the large particle side, and the particle diameter corresponding to 25% and 75% of the total volume (μm )]]

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a biaxially oriented polyester film having excellent surface properties, abrasion resistance and running properties.

[0002]

BACKGROUND OF THE INVENTION Polyester films are widely used as industrial materials, but in recent years, high-grade orientation has become remarkable in various applications,
It has been strongly desired that the film surface is more uniform than ever. In addition, the abrasion characteristics represented by abrasion of the film and abrasion of the surface layer and falling of particles are not always sufficient, and improvement in this respect is also desired. Especially in magnetic recording medium applications where strict quality is required, it is necessary to satisfy these points to a high degree. Conventionally, as a means for improving the running property and abrasion resistance of a polyester film, the presence of inert fine particles in the film,
A method for appropriately roughening the film surface is known,
Although some improvements have been made, sufficient results have not always been obtained.

For example, in the case of using so-called precipitated particles from the catalyst residue at the time of polyester production as fine particles,
Since the precipitated particles are easily broken by stretching, the running property and wear resistance are poor, and it is also difficult to recycle and use the precipitated particles.
On the other hand, when inert inorganic compound particles are added to polyesters such as silicon oxide, barium sulfate, titanium dioxide, and calcium phosphate, the particles are not broken or deformed by stretching, and relatively sharp protrusions may be given. You can
Although the runnability is improved, the particles generally have a wide particle size distribution and particles easily fall off, so that when they are used for magnetic recording media, for example, they often cause deterioration of electromagnetic conversion characteristics and frequent occurrence of dropouts. I will end up.

In recent years, in order to overcome these problems, sharp
It has been proposed to use inorganic or organic particles having a narrow particle size distribution. For example, JP-A-62-207356
JP-A-59-217755 and JP-A-59-217755 respectively disclose monodisperse silicon oxide and crosslinked organic particles produced by an emulsion polymerization method. However, when the silicon oxide particles are used, the hardness thereof is high, so that the base material with which the film comes into contact is easily scratched, and when the crosslinked organic particles are used, heat resistance is difficult and the stretching There is a drawback that the particles are easily deformed. As described above, the actual situation is that a polyester film satisfying the surface uniformity, running property and abrasion resistance of the film at a high level has not been obtained so far.

[0005]

Means for Solving the Problems As a result of intensive studies made by the present inventors in view of the above problems, as a result, particles of vaterite-type calcium carbonate having a specific shape, which were surface-treated with a specific compound, were selected. It was found that the film containing the film has excellent properties, and the present invention has been completed.

That is, the gist of the present invention is that the average particle size is 0.05 to 1.5 μm, and the spherical ratio defined by the major axis / minor axis is 1.0 to 2.0. A copolymer containing polyalkylene glycol units and polyacrylic acid units and / or polyacrylic acid derivative units in spherical or elliptic spherical vaterite-type calcium carbonate particles having a particle size distribution value of 2.00 or less. A biaxially oriented polyester film is characterized by containing 0.001 to 5% by weight of particles obtained by performing a surface treatment with a polyacrylate after the surface treatment. Particle size distribution value = d ₂₅ / d ₇₅ [In the above formula, d ₂₅ and d ₇₅ are measured by measuring the cumulative volume of the particle group from the large particle side, and the particle diameter corresponding to 25% and 75% of the total volume (μm )]]

The present invention will be described in detail below. The important gist of the present invention is monodisperse or near monodisperse, spherical or elliptic spherical vaterite-type calcium carbonate,
This is to include particles whose surface is treated with a specific compound in a polyester film.

Conventionally, as a method for producing calcium carbonate particles, in addition to a method of pulverizing and classifying natural calcium carbonate, as disclosed in, for example, JP-A-59-69425, a calcium hydroxide solution contains carbon dioxide. Precipitable calcium carbonate particles by a so-called synthetic method, in which a gas is injected and reacted, are known. In this case, it is known that calcite-type calcium carbonate particles having a relatively uniform particle size can be obtained. However, since such particles cannot reach the desired particle size distribution, even if the particles are contained, it is highly possible. Films with good properties at various levels cannot be obtained. The present inventors have adopted a carbonation reaction in which carbon dioxide is blown in an alcohol medium, in which methanol is a typical example, in such a synthesis method, and the hydrogen ion concentration, reaction rate, reaction temperature in the system are adopted. It was found that vaterite-type calcium carbonate particles having an extremely sharp particle size distribution can be produced by appropriately selecting production conditions such as.

In the present invention, among such vaterite-type calcium carbonate particles, spherical particles or ellipsoidal particles having a relatively spherical shape are used. The spherical ratio of such particles is 1.0 to 2.0 when the spherical ratio is defined by the value of the major axis / minor axis of the particles, preferably 1.0 to 1.5, and more preferably 1.0 to 1.2. When a polyester film having a spherical ratio of more than 2.0 is blended, it is not suitable because a polyester film satisfying a high level of running property cannot be obtained. Further, in the present invention, the particle size distribution value of such vaterite-type calcium carbonate particles is 2.00 or less, preferably 1.80 or less, more preferably 1.50 or less. When the particle size distribution value exceeds 2.00, the surface roughness of the finally obtained film becomes uneven, which is not suitable. Furthermore, the average particle size of the calcium carbonate particles used in the present invention is 0.05 to
It is 1.5 μm, and preferably 0.10 to 1.0 μm. If the average particle size is less than 0.05 μm, the running property and wear resistance are hardly improved and it is unsuitable. On the other hand, when the average particle size exceeds 1.5 μm, the surface roughness of the film becomes too high, which is not suitable.

The calcium carbonate particles used in the present invention are
It is essential to carry out a surface treatment with a specific compound before including it in the polyester film. That is, the particles are first surface-treated with a copolymer containing a polyalkylene glycol unit and a polyacrylic acid unit and / or a polyacrylic acid derivative unit, and subsequently surface-treated with a polyacrylic acid salt. If the surface treatment is not performed with a copolymer containing a polyalkylene glycol unit and a polyacrylic acid unit and / or a polyacrylic acid derivative unit, the affinity between the calcium carbonate particles and the polyester film is insufficient. The particles fall off the surface of the film, resulting in poor runnability and abrasion resistance of the film. In addition, voids called voids are formed around the particles, resulting in poor transparency of the film, which is not preferable.

The copolymer used as the surface treating agent in the present invention includes, for example, a copolymer of polyacrylic acid and polyethylene glycol monomethacrylate, polyacrylic acid, methoxy polyethylene glycol and polypropylene glycol. -Copolymer of monomethacrylic acid or a polyacrylic acid partially neutralized with ammonia, or a polyacrylic acid soda replaced with, but not limited to these Absent. The amount of these copolymers used is not particularly limited, but is preferably 0.1 to 5% by weight per particle. 0.1% by weight
If it is less than 5% by weight, the surface treatment effect tends to be insufficient, and if it exceeds 5% by weight, the particles may aggregate or the surface treating agent itself may aggregate.

Further in the present invention, the particles are subsequently surface-treated with a polyacrylate. If this treatment is not carried out, the dispersibility of the particles in the polyester film becomes insufficient and the surface uniformity of the film deteriorates, which is not preferable. Examples of such polyacrylic acid salts include, but are not limited to, sodium polyacrylate and ammonium polyacrylate. The amount of these polyacrylic acid salts used is not particularly limited, but is preferably 0.5 to 5% by weight per particle. 0.5% by weight
If the amount is less than 5%, the aggregation of the particles tends to be remarkable, and if it exceeds 5% by weight, the aggregation of the particles may similarly occur. The surface treatment is performed by adding these surface treatment agents to a slurry in which vaterite-type calcium carbonate particles are dispersed in water, alcohol, ethylene glycol or the like, and further dispersing and mixing.

The amount of the surface-treated vaterite-type calcium carbonate particles added to the film is 0.001-5.
Weight% If the blending amount is less than 0.001% by weight, the running property and abrasion resistance of the obtained polyester film are insufficient, and if the blending amount exceeds 5% by weight, the surface roughness of the film becomes too high. Therefore, it is inappropriate.
The biaxially oriented polyester film referred to in the present invention is a film obtained by stretching a polyester having 80% or more of repeating structural units having ethylene terephthalate units or ethylene-2,6-naphthalate units in the machine direction and the transverse direction. Refers to. In recent years, there has been a tendency for video tapes based on polyester films to last for a long time.
There is a demand for thinner polyester films with higher strength. Such high strength is mainly achieved by changing the film forming conditions of the film, and specifically, the following film forming method can be adopted. That is, a substantially non-oriented unstretched sheet is 3.0 to 6.0 times in the machine direction at 80 ° C. to 140 ° C. and then 3.0 to 6.0 in the transverse direction.
This is a method in which it is stretched twice and heat-treated at 170 to 240 ° C. As a matter of course, after the biaxial stretching in the longitudinal and transverse directions or the simultaneous biaxial stretching is performed, the longitudinal direction is 1.
It is also possible to adopt a method of heat-treating after performing 05-2.5 times re-stretching. At this time, a method such as heat setting before re-longitudinal stretching, longitudinal relaxation after re-longitudinal stretching, or before or after re-longitudinal stretching and fine stretching in the longitudinal direction can be appropriately adopted. Further, re-stretching may be performed in the transverse direction as well.

Usually, when strongly stretched to have such high strength, particles easily fall off from the surface layer of the film and wear resistance deteriorates. However, when the particles of the present invention are used, such falling phenomenon occurs. Is extremely small, and as a result, the abrasion resistance of the film is extremely excellent. By the way, in the present invention, it is possible to improve the running property, abrasion resistance, scratch resistance and the like of the film by using one or more kinds of other particles in combination within the range not exceeding the gist thereof. Specific examples of the other particles here include kaolin, talc, carbon black, molybdenum sulfide, gypsum, aluminum oxide, barium sulfate, lithium fluoride, calcium fluoride, zeolite, calcium phosphate, silicon dioxide, titanium dioxide. Etc. can be mentioned. In particular, in order to improve the scratch resistance required of the magnetic recording base film, it is preferable to use aluminum oxide together. In this case, delta type or gamma type aluminum oxide particles having an average particle diameter of 0.5 μm or less are particularly preferable.

In addition to these inorganic particles, heat-resistant polymer fine powder can be used. As a typical example in this case, a monovinyl compound having only one aliphatic unsaturated bond in a molecule, as described in JP-B-59-5216, and a divinyl compound in the molecule as a cross-linking agent. Although it is possible to exemplify a copolymer with a compound having one or more aliphatic unsaturated bonds, the present invention is not limited thereto, and examples thereof include a thermosetting epoxy resin, a thermosetting phenol resin, and a thermosetting resin. It is also possible to use a fine powder of a curable urea resin, a benzoguanamine resin, or a fluororesin such as polytetrafluoroethylene. In the production of the polyester containing the vaterite-type calcium carbonate particles used in the present invention, the particles and the additive particles used in combination are preferably added during the polyester synthesis reaction. Particularly, it is preferably added after the completion of the transesterification reaction or the esterification reaction and before the start of the polycondensation reaction. The particles to be added are usually added as a slurry of ethylene glycol. The concentration of particles in the ethylene glycol slurry to be added is 5 to 50% by weight, preferably 10 to 40%. If the particle concentration of the slurry is less than 5% by weight, the amount of ethylene glycol used increases and the basic unit of ethylene glycol tends to increase. Also, the particle concentration is 50
Addition of a slurry in excess of weight% may deteriorate the dispersibility of particles.

The film of the present invention is a video tape base.
In addition to being used as a film, it is also effective when used as an audio film. Further, if necessary, it can be used for a dielectric of a capacitor, for packaging, for plate making, and for other purposes.

[0017]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. The measuring methods and definitions of various physical properties and characteristics in the examples are as follows. In the examples and comparative examples, “part” means “part by weight”. (1) Average particle size and particle size distribution Shimadzu Corporation centrifugal sedimentation type particle size distribution measuring device (SA-CP
Equivalent spherical distribution measured by type 3) 5
The average particle size was 0%. At the same time, the diameter of the point with a weight fraction of 25% and the weight fraction of 75% are added up from the large particle side.
The ratio [γ] of the diameters of the points was used as an index of the particle size distribution. (2) Spherical ratio It was calculated by measuring the major axis and minor axis of the particles from the scanning electron micrograph of the particles.

(3) Average Roughness of Film Surface and Uniformity of Roughness According to the method described in Japanese Industrial Standard JIS B0601, Kosaka Laboratory Ltd. surface roughness measuring machine (SE-
3F) was used to determine the centerline average roughness (Ra) and maximum height (Rt). The smaller Rt / Ra, the more uniform the surface. (4) Runnability The sliding property of the film was evaluated. Sliding property is 53 g (T ₂ ) when the film is wound around a fixed hard chrome-plated metal roll (diameter 6 mm) at a winding angle (θ) of 135 °.
The load was applied to one end, and this was run at a speed of 1 m / mim, the resistance force (T ₁ , g) at the other end was measured, and the friction coefficient (μd) during running was determined by the following formula. μd = (180 / πθ) ln (T ₁ / T ₂ ) = 0.424
_{· Ln (T 1/53)} (5) was evaluated wear properties than white powder generation amount shown in wear resistance below. <White powder generation amount> A film is wound around a fixed pin made of hard chrome with a diameter of 6 mm and brought into contact with the fixed pin at an angle of 135 °, and the film is 1000 m at a speed of 10 m / min and a tension of 200 g.
The amount of wear white powder adhering to the pins was visually evaluated, and evaluated according to the ranks shown below. Rank A: Not attached at all Rank B: Attached in a small amount Rank C: Attached in a small amount (more than Rank B) Rank D: Attached extremely

(6) Magnetic tape characteristics First, a magnetic tape was manufactured. That is, the magnetic fine powder 20
0 parts, polyurethane resin 30 parts, nitrocellulose 10
Parts, vinyl chloride-cellulose acetate copolymer 10 parts, lecithin 5 parts, cyclohexanone 100 parts, methyl isobutyl ketone 100 parts, and methyl ethyl ketone 300 parts are mixed and dispersed in a ball mill for 48 hours, and then 5 parts of a polyisocyanate compound is added to the magnetic coating. After applying this to a polyester film, it was magnetically oriented before the paint was sufficiently dried and solidified, and then dried to form a magnetic layer having a thickness of 2 μm. <Calendar stain> Next, it is composed of a mirror-finished metal roll and a polyester-based composite resin roll.
Using a multi-stage super calender, magnetic tape 5000 m was repeatedly run 7 times under the conditions of roll temperature 85 ° C., linear pressure 250 kg / cm and running speed 80 m / min, and adhered to the resin roll. The amount of white powder was visually evaluated and evaluated according to the ranks shown below. ○: Almost no adhesion of white powder is observed on the resin roll. Δ: Very slight adhesion of white powder is observed. × ... Adhesion of white powder is clearly observed. Then, after slitting the tape to a 1/2 inch width. The following magnetic tape characteristics were evaluated at a constant speed using an NV-3700 type video deck manufactured by Matsushita Electric.

<VTR head output (S / N)> With a synchroscope, the measured frequency is V at 4 MHz.
Measure the TR head output and set the blank to 0 dB (d
The relative value is shown in decibels as B). <Number of Dropouts> A video tape on which a signal of 4.4 MHz was recorded was reproduced, and the number of dropouts was measured with a dropout counter of Okura Industry Co., Ltd. for about 20 minutes and converted into the number of dropouts per minute. (7) Scratch resistance A magnetic tape slit to a width of 1/2 inch has a diameter of 6 mm.
Wrap the film around the hard chrome plated metal pin (Finishing 3S) of 135 °, traveling speed 4m / min, tension 5
The base film surface of the magnetic tape was rubbed once with 0 g. Next, aluminum was vacuum-deposited on the abraded surface to a thickness of about 1000Å, and the amount of scratches was visually observed, and the following judgment was made. Rank 1: Extremely large amount of scratches Rank 2: Large amount of scratches Rank 3: Intermediate amount of scratches 2, 4 Rank 4: Small amount of scratches Rank 5: No scratches

Example 1 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol and 0.09 part of magnesium acetate tetrahydrate were placed in a reactor, heated and heated, and methanol was distilled off to carry out a transesterification reaction. The temperature was raised to 230 ° C. over 4 hours, and the transesterification reaction was substantially completed. Next, the average particle size is 0.25 μm, and the particle size distribution value is 1.
50 parts of approximately spherical (spherical ratio = 1.1) vaterite-type calcium carbonate was added as ethylene glycol slurry. In this case, a copolymer of soda polyacrylate, methoxypolyethylene glycol and polypropylene glycol monomethacrylate as a surface treatment agent is preliminarily used in an amount of 3.0% by weight based on the particles. It was added to the ethylene glycol slurry of the particles, and was added by T.K. K. After stirring and mixing with a homomixer, the polyacrylic acid soda was further added to the particles in an amount of 3.0.
After adding so as to be in a weight%, the slurry was further stirred and mixed, and the surface-treated slurry was used. After adding the slurry, 0.03 parts of phosphoric acid and 0.03 of antimony trioxide are added.
Add 4 parts and carry out polycondensation reaction for 4 hours to obtain an intrinsic viscosity of 0.6.
A polyethylene terephthalate of 5 was obtained. Then, the polyester is dried and melt-extruded at 290 ° C. to obtain an amorphous sheet, and the obtained amorphous sheet is 3.5 times at 93 ° C. in the sheet flow direction (longitudinal direction) and 110 ° C. in the lateral direction. Was stretched 3.5 times and heat-treated at 220 ° C. for 3 seconds to obtain a film having a thickness of 15 μm. A magnetic layer was applied to the obtained film to obtain a magnetic tape, and its characteristics were measured.

Comparative Example 1 Polyethylene terephthalate was used in the same manner as in Example 1 except that as the surface treatment agent, 3.0 wt% of polyacrylic acid soda was added to the particles and the surface treatment was performed on the vaterite type calcium carbonate. A tarte film was obtained and its characteristics were evaluated. Comparative Example 2 Only a copolymer of soda polyacrylate, methoxypolyethylene glycol and polypropylene glycol monomethacrylate as a surface treatment agent was treated so as to be 3.0% by weight based on the particles. A polyethylene terephthalate film was obtained in the same manner as in Example 1 except that the vaterite-type calcium carbonate was used, and its characteristics were evaluated.

Example 2 A film was obtained in the same manner as in Example 1 except that an ellipsoidal (spherical ratio = 1.7) vaterite type calcium carbonate having an average particle size of 0.25 μm and a particle size distribution value of 1.50 was used. , Its characteristics were evaluated. Comparative Example 3 A polyethylene terephthalate film was obtained in the same manner as in Example 1 using the agglomerated calcite-type calcium carbonate obtained by the synthesis method having an average particle size of 0.25 μm and a particle size distribution value of 2.05. evaluated. Comparative Example 4 A film was obtained in the same manner as in Example 1 using flattened (spherical ratio = 2.5) vaterite-type calcium carbonate having an average particle size of 0.25 μm and a particle size distribution value of 1.60, and its characteristics were obtained. Was evaluated.

Example 3 With the vaterite-type calcium carbonate used in Example 1,
A film was obtained in the same manner as in Example 1 to determine whether or not a delta type aluminum oxide having a primary particle size of 0.03 μm was used in combination, and the characteristics thereof were evaluated. Example 4 With the vaterite-type calcium carbonate used in Example 2,
A film was obtained in the same manner as in Example 1 to determine whether or not a delta type aluminum oxide having a primary particle size of 0.03 μm was used in combination, and the characteristics thereof were evaluated. Example 5 In the production of the polyester of Example 1, a transesterification reaction was carried out in the same manner as in Example 1 except that dimethyl-2,6-dimethylnaphthalate was used instead of dimethyl terephthalate. Next, 0.5 part of the vaterite-type calcium carbonate used in Example 1 was added as ethylene glycol slurry, 0.03 part of phosphoric acid and 0.04 part of antimony trioxide were added, and polycondensation reaction was carried out by a conventional method. Then, polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.51 was obtained. The obtained polymer is 0.3 mmHg, 2
Solid phase polymerization was carried out at 35 ° C. for 8 hours to obtain polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.65. The polymer is 2
Sheets were extruded from the extruder at 95 ° C., and an amorphous sheet having a thickness of 100 μm was obtained by using an electrostatic applied cooling method. Next, after stretching 4.2 times in the longitudinal direction at 140 ° C. and 3.9 times in the transverse direction with a tenter, heat treatment is performed at 220 ° C. for 5 seconds,
A polyethylene-2,6-naphthalate film having a thickness of 9 μm was obtained and its characteristics were evaluated.

Example 6 A film was prepared in the same manner as in Example 5 except that an ellipsoidal (spherical ratio = 1.7) vaterite type calcium carbonate having an average particle size of 0.25 μm and a particle size distribution value of 1.50 was used. The obtained characteristics were evaluated. The results obtained above are summarized in Table 1 below.
~ 4.

[0026]

Table 1 Example 1 Comparative Example 1 Comparative Example 2 ──────────────────────────────────── < Blended particles> Type Vaterite type Vaterite type Vaterite type Calcium carbonate Calcium carbonate Calcium carbonate Average particle size (μm) 0.25 0.25 0.25 Spherical ratio 1.1 1.1 1.1 1.1 Particle size distribution value 1.5 1. 5 1.5 Particle content 0.50 0.50 0.50 (wt%) <Film property> Ra (μm) 0.013 0.013 0.020 Rt / Ra 8 8 24 Sliding property 0.23 0. 26 0.35 Abrasion resistance White powder generation A CA <Magnetic tape characteristics> Calendar dirt 〇 × 〇 S / N (dB) +0.5 -1.5 -2.0 Dropout (pieces / minute) 4 25 25 Scratch resistance 3 2 2

[0027]

Table 2 Example 2 Comparative Example 3 Comparative Example 4 ──────────────────────────────────── < Blended particles> Type Vaterite type Calcite type Vaterite type Calcium carbonate Calcium carbonate Calcium carbonate Average particle size (μm) 0.25 0.25 0.25 Spherical ratio 1.7-2.5 Particle size distribution value 1.5 2.05 1.6 Particle content (wt%) 0.50 0.50 0.50 <Film characteristics> Ra (μm) 0.013 0.016 0.012 Rt / Ra 5 26 5 Sliding property 0.28 0.30 0.36 Abrasion resistance White powder generation A A B <Magnetic tape characteristics> Calendar dirt ○ ○ △ S / N (dB) + 1.5-1.5 +1.0 Dropout (pieces / minute) 18 10 Scratch resistance 3 2 2

[0028]

Table 3 Example 3 Example 4 ──────────────────────────────────── <Blended particles> [First particles] Type Vaterite type Vaterite type Calcium carbonate Calcium carbonate Average particle size (μm) 0.25 0.25 Spherical ratio 1.1 1.7 Particle size distribution value 1.5 1.5 Particle content (wt%) ) 0.50 0.50 [Second particles] Type Al ₂ O ₃ Al ₂ O ₃ Average particle diameter (μm) 0.03 0.03 Particle content (wt%) 0.30 0.30 <Film characteristics > Ra (μm) 0.013 0.013 Rt / Ra 8 4 Sliding property 0.23 0.28 Abrasion resistance White powder generation amount A A <Magnetic tape characteristics> Calendar stain 〇 〇 S / N (dB) +0.8 +1.7 Dropout (pieces / minute) 2 1 Scratch resistance 5 5

[0029]

Table 4 Example 5 Example 6 ──────────────────────────────────── <Blended particles> Type Vaterite type Vaterite type Calcium carbonate Calcium carbonate Average particle size (μm) 0.25 0.25 Spherical ratio 1.1 1.7 Particle size distribution value 1.5 1.5 Particle content (wt%) 0.50 0. 50 <Film property> Ra (μm) 0.013 0.012 Rt / Ra 8 5 Sliding property 0.25 0.29 Abrasion resistance White powder generation amount A A <Magnetic tape property> Calendar stain 〇 〇 S / N (dB) +0.8 +1.5 Dropout (pieces / min) 3 1 Scratch resistance 3 3

[0030]

The film of the present invention has a uniform and fine surface structure, and is particularly excellent in abrasion resistance and running property,
It is useful as an industrial material such as a base film for a magnetic recording medium and has a high industrial value.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // B29K 67:00 B29L 7:00 4F C08L 67:00

Claims (1)

[Claims] 1. The average particle size is 0.05 to 1.5 μm, the spherical ratio defined by the major axis / minor axis is 1.0 to 2.0, and the particle size distribution value defined by the following formula is 2. After surface treatment of spherical or elliptic spherical vaterite-type calcium carbonate particles of 0.000 or less with a copolymer containing a polyalkylene glycol unit and a polyacrylic acid unit and / or a polyacrylic acid derivative unit , 0.001 to 5% by weight of particles obtained by surface treatment with polyacrylate
A biaxially oriented polyester film characterized by containing. Particle size distribution value = d ₂₅ / d ₇₅ [In the above formula, d ₂₅ and d ₇₅ are measured by measuring the cumulative volume of the particle group from the large particle side, and the particle diameter corresponding to 25% and 75% of the total volume (μm )]]