JPH0440623A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a traveling property and wear resistance by incorporating specific calcium carbonate particles into the above film nd specifying the refractive index in the thickness direction thereof to a certain specific range. CONSTITUTION:This polyester film contains 0.005 to 2.0wt.% vaterite type calcium carbonate particles having 0.07 to 1.5mum average grain size and %h 1.60 grain size distribution value expressed by equation I. Further, the refractive index in the thickness direction of the film is specified to >= 1.492. In this case, d25, d75 denote the grain sizes (mum) respectively corresponding to 25% and 75% of the total volume when the integrated volume of the particle groups is measured from a large particle size. The traveling property and wear resistance are improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a polyester film for magnetic recording media that has a uniform surface and highly improved running properties and abrasion resistance.

More specifically, the present invention relates to a polyester film containing vaterite-type calcium carbonate particles and having these properties improved by adjusting the refractive index in the thickness direction of the film to a certain range.

(Prior Art and Problems to be Solved by the Invention) Polyester films have excellent physical and chemical properties and are widely used in industry.

In particular, biaxially oriented polyethylene terephthalate film is superior in flatness, mechanical strength, and dimensional stability compared to other films, and is now indispensable as a base material for magnetic recording media.

On the other hand, improvements in magnetic recording media have been made at a rapid pace in recent years, and as a result, requirements for base films have become even more stringent.

For example, in applications requiring high-density recording, such as videotapes, a flatter surface of the base film is required. However, when the film surface becomes flat,
Not only does running performance deteriorate, but friction and wear between the film and the base material increase, causing various problems such as scratches on the film and generation of abrasion powder. This abrasion powder causes a loss of recorded signals, that is, dropout, and significantly reduces the quality of the film.

It is generally known that in order to improve the runnability and abrasion characteristics of a film, it is sufficient to roughen the film surface appropriately.

In order to achieve this, a method has been adopted in which fine particles are present in the raw polyethylene, and although this method has been put into practical use in some cases, it has not necessarily been successful in satisfying these characteristics to a high degree.

For example, when so-called precipitated particles from catalyst residues during polyester production are used as fine particles, the fine particles are easily destroyed by stretching, resulting in poor runnability and abrasion resistance, and it is also difficult to reuse them.

In addition, when inert inorganic compound particles are added to polyester such as kaolin, silicon oxide, titanium dioxide, calcium phosphate, etc., the particles are not destroyed or deformed by stretching, and can be stretched to give relatively steep protrusions. However, since the particle size distribution is generally wide, deterioration of electromagnetic conversion characteristics and frequent dropouts due to coarse protrusions are often observed.

In order to overcome this antinomy phenomenon, it has recently been proposed to use inorganic or organic particles having a sharp particle size distribution. For example, JP-A-62-207356 and JP-A-59-217755 disclose monodisperse silicon oxide and crosslinked organic particles produced by emulsion polymerization, respectively. However, in this case as well, silicon oxide particles have high hardness and are likely to damage the substrate with which the film comes into contact, and crosslinked organic particles have problems in that they are easily deformed by stretching and have poor heat resistance.

As described above, the reality is that no polyester film for magnetic recording has been obtained that highly satisfies running properties and abrasion resistance and also has other necessary properties.

[Means to solve the problem]

In view of the above-mentioned problems, the present inventors have made extensive studies and found that a polyester film containing certain specific calcium carbonate particles and having a refractive index in the thickness direction within a certain range can achieve this. This led to the completion of the present invention.

That is, the gist of the present invention is that the average particle size is 0.07 to 1.5 μm.
Then, vaterite type calcium carbonate particles having a particle size distribution value defined by the following formula of 1.60 or less are 0.005 to 2.0.
% by weight, and the refractive index in the thickness direction of the film is 1°492 or more.

(In the formula, d zs and d qs are the particle diameters (μm) corresponding to 25% and 75% of the total volume, respectively, when the integrated volume of the particle group is measured from the large particle side.) Below, the present invention will be explained in further detail. Explain.

The polyester in the present invention refers to a polyester obtained using terephthalic acid or its ester and ethylene glycol as main starting materials, but it may contain other third components. In this case, as the dicarboxylic acid component,
For example, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, terephthalic acid, adipic acid, sebacic acid,
It is possible to use one or more kinds of oxycarboxylic acid components such as p-oxyethoxybenzoic acid and the like. Glycol components include ethylene glycol,
One or more of propylene glycol, butanediol, 1,4-cyclohexane dimetatool, neopentyl glycol, etc. can be used. In any case, the polyester of the present invention is preferably a polyester in which 80% or more of the repeating structural units have ethylene terephthalate units.

Further, the polyester may contain arbitrary additives such as a heat stabilizer, a bronking inhibitor, an antioxidant, a coloring agent, an antistatic agent, and an ultraviolet absorber.

One of the features of the present invention is the use of specific vaterite-type calcium carbonate particles. Calcium carbonate particles can be produced by a method of pulverizing and classifying natural calcium carbonate, as well as a so-called synthesis method in which a calcium hydroxide solution is reacted with a carbon dioxide-containing gas, as shown in JP-A No. 5,969,425. Precipitated calcium carbonate is known. In this case, calcite-type calcium carbonate particles with a relatively uniform particle size are obtained, and it is known that these particles can be blended into a polyester film as shown in Japanese Patent Publication No. 1-16856, for example. The particles still cannot reach the desired particle size distribution.

The present inventors have discovered that in such a synthesis method, vaterite-type calcium carbonate with an extremely sharp particle size distribution can be produced by selecting production conditions including the hydrogen ion concentration and reaction rate of the system.

A typical example of this is the VAN brand manufactured by Maruo Calcium ■. Although the vaterite-type calcium carbonate can be added to the polyester production process as it is, it is preferably subjected to surface treatment in order to reduce its solubility in the reaction system and improve its dispersibility. As a surface treatment agent that also serves as a dispersant, for example, JP-A-59-
Preferably used are surface treating agents such as those described in JP-A No. 69426 or JP-A-1-256558, particularly high-molecular polycarboxylic acids or their sodium salts and ammonium salts. It is usually effective to add these during the production step of the core particles.

Such vaterite-type calcium carbonate is obtained in the form of a sphere or an ellipsoid, and the ratio of the major axis to the minor axis is usually about 1.8 or less. In the present invention, the particle size distribution value is 1.
60 or less, preferably 1.50 or less, more preferably 1
．． Must be 40 or less. If this value exceeds 1.60, the surface roughness of the final film will be non-uniform and the electromagnetic properties will be impaired.

Further, the average particle size of the particles used in the present invention is 0.07 to 1.
It should be 5 μm, preferably 0.15-1.0 μm. If this value is less than 0.07 .mu.-, there is little improvement in runnability or wear resistance, while if it exceeds 1.5 .mu.-, the roughness is uniform but the absolute value becomes too large and the electromagnetic properties deteriorate.

Further, the amount added to the film is selected from the range of 0.005 to 2.0% by weight, preferably 0.01 to 0.8% by weight. If the amount is less than 0.005% by weight, running properties and wear resistance will not improve, and if it exceeds 2.0% by weight, the electromagnetic properties will deteriorate.

As described above, in the present invention, certain specific calcium carbonate particles are used, but at the same time, in the present invention, it is essential that the refractive index in the thickness direction of the polyester film is 1°492 or more. Refractive index power in the thickness direction of the film, 4
If it is less than 92, even if the particles of the present invention are used, the effect of imparting slipperiness and abrasion resistance is insufficient, so it is not preferable. Note that this value is preferably 1.494 or more and 1.505 or less. A film having such physical properties can be obtained, for example, in the case of longitudinal-transverse sequential biaxial stretching, by setting the longitudinal stretching temperature to about 105-115°C, which is 5-30°C higher than the normal stretching temperature. Alternatively, it can also be obtained by performing significant lateral relaxation after two-wheel stretching and before heat treatment.

When the refractive index in the thickness direction of the film is 1.492 or more, another advantage is that the adhesiveness of the magnetic layer is improved when applied.

In this way, in the present invention, the desired effect can only be obtained by a combination of using a certain vaterite type calcium carbonate particle and setting the refractive index in the thickness direction of the film within a certain range. One or more types of other particles may be used in combination for the purpose of further improving the film properties, etc., without impairing the purpose of the above.

Precipitated particles can be mentioned as one of such particles. The term "precipitated particles" as used herein refers to particles that are precipitated in a reaction system when, for example, a system using an alkali metal or alkaline earth metal compound as a transesterification catalyst is polymerized by a conventional method. Alternatively, precipitation may be carried out by adding terephthalic acid during transesterification or polycondensation reaction.

In these cases, one or more phosphorus compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, tributyl phosphate, acidic ethyl phosphate, phosphorous acid, trimethyl phosphite, triethyl phosphite, and tributyl phosphite are used. It may be left to exist.

Furthermore, even when an esterification step is performed, inert material particles can be precipitated by these methods.

For example, an alkali metal or alkaline earth metal compound is made to exist before or after the completion of the esterification reaction, and the polymerization reaction is carried out in the presence or absence of a phosphorus compound.

In any case, the fine precipitated compounds generated during the polyester production reaction in the present invention include calcium, lithium,
Contains one or more elements such as antimony and phosphorus.

Another example is so-called additive particles. These additive particles refer to particles added externally to the polyester manufacturing process, and specifically include kaolin, talc, carbon, molybdenum sulfide, gypsum, rock salt, aluminum oxide, barium sulfate, sulfur fluoride, calcium fluoride, and zeolite. , calcium phosphate, silicon dioxide,
Examples include titanium dioxide.

Note that heat-resistant polymer fine powder can also be mentioned as an example of such additive particles. A typical example of this case is a monovinyl compound having only one aliphatic unsaturated bond in the molecule and a crosslinking agent as described in Japanese Patent Publication No. 59-5216. Examples include copolymers with compounds having at least 3 aliphatic unsaturated bonds, but are not limited to these, for example, thermosetting phenolic resins, thermosetting epoxy resins, thermosetting It is also possible to use fine powder of a fluororesin such as a polyurea resin, a henzoguanamine resin, or a polytetrafluoroethylene.

Naturally, examples of particles that can be combined with the vaterite-type calcium carbonate particles of the present invention include natural calcium carbonate and calcite-type calcium carbonate produced by synthetic methods.

In addition, in the present invention, when the average particle diameter of the particles used in combination is larger than that of the vaterite-type calcium carbonate of the present invention, the weight is equal to or less than that of the calcium carbonate, preferably 0.
005 to 0.5 times the weight, more preferably 0.01 to 0.00.
It is best to choose from the range of 3 times the weight. On the other hand, when the particle size of the particles used in combination is smaller, the weight can be equal to or more than the weight of the calcium carbonate, for example, 1 to 20 times the weight.

In the present invention, two or more types of such vaterite particles having different average particle sizes may be used.

Incidentally, in recent years, base films for magnetic recording have often been required to have flatness, slipperiness, and abrasion resistance in addition to adhesion.

This is because, for example, when the tape runs at high speed, the tape may be damaged from the contact portion, or the film may be easily damaged by generated abrasion powder. If there are many scratches, not only will the appearance be unfavorable, but it will also cause contamination in the process and an increase in dropouts.

In order to highly improve this scratch resistance, it is particularly preferable to select aluminum oxide as the particles used in combination. In particular, the average particle size is 0.5μ or less, preferably 0.1μ
Delta-type or gamma-type aluminum oxide particles of m or less in size, particularly delta-type aluminum oxide particles, are preferably used. Examples of methods for producing these particles include pyrolysis, that is, flame hydrolysis using anhydrous aluminum chloride as a raw material;
Alternatively, there may be mentioned an ammonium alum thermal decomposition method, that is, a method in which aluminum hydroxide is used as a starting material, reacted with sulfuric acid to produce aluminum sulfate, and then reacted with ammonium sulfate to produce ammonium alum.

The primary particle size of aluminum oxide obtained by these methods is usually in the range 5-40 nm, but often 0.5 nm.
Since it forms aggregates exceeding μm in size, it is desirable to crush them appropriately before use. In this case, the secondary particles may be agglomerated to some extent, but the apparent average particle size is 0.
The thickness is preferably 5 μm or less, preferably 0.1 μ+s or less.

As described above, in the present invention, by combining the vaterite-type calcium carbonate particles and the refractive index in the thickness direction of the film with other particles, such as fine aluminum oxide particles, as necessary, extremely excellent magnetic properties can be achieved. Although it has become possible to obtain a recording polyester film, the effect will be maximized when some of the following requirements in the film forming stage are further added to the combination of the first two.

That is, in the present invention, when the melting specific resistance of the polyester composition containing vaterite-type calcium carbonate used for film formation is within a certain range, a highly valuable film with better flatness can be obtained.

That is, when obtaining the film of the present invention, usually 280
The polyester is extruded into a sheet through the lip part from an extruder at a temperature in the range of ~310"C and heated to 40-70"C.
to obtain a biaxially oriented film, and then to obtain a biaxially oriented film, the sheet material is stretched in the longitudinal and transverse directions to at least 4 times the area magnification.
The heat treatment is carried out at a temperature in the range of 240°C. At this time, in order to obtain an amorphous sheet, a so-called electrostatic application cooling method is adopted, and the specific resistance of the polyester composition when melted is set to 6X10" to 5.X10". It has been found that a film with better flatness can be obtained if the thickness is set to 'Ω-cm.

The electrostatic cooling method is, for example, as described in Japanese Patent Publication No. 37-6142, when obtaining an amorphous sheet from a molten polymer, an electrostatic charge is applied to the sheet and the sheet is electrostatically cooled by rotation. Although pressing strongly against a drum is the best method, cooling is the most effective method, but it can be applied particularly effectively when the melted resistivity of polyester containing vaterite-type calcium carbonate is within this range, and it can further improve the flatness of the resulting film. It can be improved. A more preferable range of specific resistance is 8×1
06~1×108Ω-c! It is 11.

Incidentally, in order to adjust the specific resistance during melting to a desired value, the following method may be adopted.

That is, in order to reduce the specific resistance, it is sufficient to solubilize the metal component in the polyester, and for this purpose, for example, the metal element used as a transesterification reaction catalyst or added after the transesterification or esterification reaction if necessary. It is preferable to add a relatively small amount, for example, an equivalent amount or less of a phosphorus compound to the metal element.

On the other hand, in order to increase the specific resistance, the amount of metal compounds dissolved in the polyester should be reduced.

In the present invention, either a transesterification reaction method or an esterification reaction method can be employed, but the former is preferred,
Specifically, for example, a magnesium catalyst, a manganese catalyst, a calcium catalyst, etc. are used to increase the degree of polymerization of polyester containing core particles in the presence of a phosphorus compound of about 0.3 to 1.0 times equivalent.

The average refractive index (n) of the film of the present invention is 1.59
It is preferable to set it as the range of 8-1.605.

When n is less than 1.598, dimensional stability deteriorates when some heat is applied to the film, leading to a decrease in skew characteristics. On the other hand, when n exceeds 1.605, the film surface becomes brittle and white powder is significantly generated.

The value of n is preferably in the range of 1.600 to 1.603.

In these cases, if aluminum oxide particles are also used as the particles, a higher degree of scratch resistance is imparted to the film, resulting in an even more excellent film.

By the way, when producing polynisnal containing vaterite-type calcium carbonate particles of the present invention, the particles are preferably added during the polyester synthesis reaction. In particular, it is suitable to add it after the end of the transesterification reaction or the esterification reaction and before the start of the polycondensation reaction.

The particles are usually added as a slurry with a particle concentration of 3 to 50% by weight in a solvent such as ethylene glycol.

If the particle concentration of the slurry is less than 3% by weight, the amount of ethylene glycol used increases and the basic unit of ethylene glycol increases, which is undesirable.
Addition of a slurry that has been dissolved often deteriorates the dispersibility of the particles.

In addition, as a polycondensation reaction catalyst for polyester synthesis, S
Commonly used catalysts such as b, Ge, Ti, Sn, and Si compounds are used.

The film of the present invention, which is suitable for use in magnetic recording media, can only be obtained by a combination of specific particles and specific film physical properties, and the surface roughness of the film is usually 0.0 O5 to 0.05 in terms of centerline average roughness. 0.1 μm, preferably O,
OO7~0.08μm, more preferably 0.01~0.
Selected from the range of 0.03 μm.

The film of the present invention is useful as a base film for videotapes, and can also be particularly effective when used as an audio film. In other words, in this field, conventional two-way radio cassette players, component stereos, etc.
As a result of the spread of models equipped with a dubbing function that is more than double the speed, the tape and the base material come into contact at higher speeds during the dubbing process and during fast forwarding and rewinding. The effects of this will be effectively demonstrated.

Furthermore, base films for magnetic disks, especially high-density floppy disks, have strict requirements for reducing coarse protrusions due to their nature, and in combination with the requirements for workability and abrasion resistance, the film of the present invention can be used effectively.

〔Example〕

EXAMPLES The present invention will be explained in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

The various physical properties of the present invention were measured by the following methods.

In the examples, "part J" and "%" each refer to "part by weight".
and "% by weight".

(1) Average particle size and particle size distribution value The particle size was measured by a photographic method using an electron microscope and converted into an equioblate sphere. The particle size distribution was determined by measuring the particle diameters of about 1000 particles, and integrating the volumes from the large particle side. The particle size at 25% of the total volume is defined as aZS, and the particle size at 75% is defined as d7s, and the sharpness of the particle size distribution is indicated by the value of the ratio (d zs/d 75 ). The closer this value is to 1, the sharper the image.

Note that the average particle diameter is expressed as d5° (μm).

(2) Resistivity during melting
Brit, J, App 1. Phya) No. 17
Vol., pp. 1149-1154 (1966). However, in this case, the melting temperature change of the polymer is 295°
C, and the value immediately after applying 1,000 V of DC is the specific resistance at the time of melting.

(3) Refractive index in the film thickness direction and average refractive index Sodium D measured at 23°C using Atsube's refractometer
This is the value for the line. The average refractive index n is given by n=173 (nα+nβ+nr), where nα is the refractive index in the thickness direction, nγ is the refractive index in the main orientation direction, and nβ is the refractive index in the direction perpendicular to the main orientation direction.

(4) Smoothness of the film The film is wound around a fixed hard chrome-plated metal roll (diameter 6N11) using the device shown in Figure 1.
(θ), apply a load of 53 g (Tz) to one end, run it at a speed of 1 m/min, measure the resistance force (T + (g)) at the other end, and calculate the friction during running using the following formula. The count (μd) was determined.

π θ Tz 5 (5) Surface roughness of film Center line average roughness (Ra); (2) Determined as follows using a surface roughness measuring machine (SE-3F) manufactured by Koita Research Institute. That is, a part with a reference length L (2°5 mm) is extracted from the film cross-sectional curve in the direction of its center line, and the roughness curve y=f is created with the center line of this extracted part as the y-axis and the vertical magnification direction as the y-axis. When expressed as (x), the value given by the following formula is expressed in [μm]. The centerline average roughness was determined by determining the cross-sectional curves of zero lines from the surface of the sample film, and was expressed as the average value of the centerline average roughness of the sampled portions determined from these cross-sectional curves. The tip radius of the stylus is 2 μm, the load is 30 mg, and the force and 1-off value are 0.08
It was set as lIm.

Maximum height (Rt); ■A portion of the standard length (2.5 mm) extracted from the cross-sectional curve obtained by a surface roughness measuring machine (SE-3F) manufactured by Koita Research Institute (hereinafter referred to as the extracted portion) When the sampled part is sandwiched between two straight lines parallel to the average line of This is the maximum height of the extracted part. The maximum height was determined by determining 10 cross-sectional curves from the surface of the sample film, and was expressed as the average value of the maximum height of the sampled portion determined from these cross-sectional curves. The radius of the stylus used at this time was 2.0 μm, and the load was 30
The cutoff value at o+g is 0.08 mm. Furthermore, R
The smaller t/Ra is, the more uniform the surface roughness of the film is.

(6) Abrasion-resistant evaluation Using the tape abrasion evaluation machine shown in Figure 2, a polyester film with a width of 10n+m was run over a length of 200m, and a fixing pin (diameter 6mm, material 5U) shown in (1) in the figure was used.
The amount of abrasion powder adhering to S42C)-J2, Finish 0.23) was visually evaluated and divided into four ranks. The running speed of the film was 11.4 m/min, the tension was detected by a tension pickup indicated by (V), and the initial tension was 300 g.
The angle θ of the winding with the film was set to 135°.

Rank A: No adhesion observed at all.

Rank B: Very slight adhesion is observed, but there is no problem in practical use.

Rank C: The amount of adhesion is slightly large and may cause problems if used for a long time.

Rank C: The amount of adhesion is large and it is difficult to use it practically.

(7) Magnetic tape characteristics First, the following magnetic paint was applied to a polyester film to form a magnetic layer so that the film thickness after drying was 2 μm. That is, 200 parts of magnetic fine powder, 30 parts of polyurethane resin, 10 parts of nitrocellulose, 10 parts of salt-vinyl acetate copolymer, 5 parts of lecithin, 100 parts of cyclohexanone, 100 parts of methyl isobutyl ketone, and 300 parts of methyl ethyl ketone were mixed in a ball mill to give 48 parts. After time mixing and dispersion, 5 parts of a polyisocyanate compound was added to form a magnetic paint, which was applied to a polyester film. Before the paint was sufficiently dried and solidified, it was magnetically oriented and then dried. Furthermore, this coated film was surface-treated using a supercalender, and each portion was slit into a 2-inch width to form a videotape. This videotape was recorded using a Matsushita Electric ■ NV-3700 video deck.
The following magnetic tape characteristics were evaluated by a regular customer.

VTR head output: The VTR head output at a measurement frequency of 4 MHz was measured using a synchroscope, and the relative value to the reference sample was expressed in decibels (dB).

Number of dropouts: Play a videotape recording a 44 MHz signal, measure the number of dropouts at 15μsec -20dB5 for about 20 minutes using a dropout counter manufactured by Taishoku Industry ■, and calculate the number of dropouts per minute ( pcs/min).

(8) Abrasion resistance One part of the magnetic tape slit to a width of 2 inches is attached to a hard chrome-plated metal pin (diameter mm, finish 33) under a tension of 50 g.
,! The heath film surface of the magnetic tape is rubbed once at an angle of 135° and a running speed of 3 m/sec.

Next, about 1000 people vacuum-deposited aluminum on the scratched surface.
The amount of damage was visually judged and divided into the following five ranks.

Rank 1: The amount of damage is extremely large.

Rank 2: The amount of damage is large.

Rank 3: The amount of damage is in the middle of 2.4.

Rank 4: The amount of damage is small.

Rank 5: No damage.

Example 1 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol, and 0.09 parts of magnesium acetate tetrahydrate were placed in a reactor, the temperature was raised, methanol was distilled off, and a transesterification reaction was carried out for 4 hours from the start of the reaction. The temperature was raised to 230'C, and the transesterification reaction was substantially completed.

Next, vaterite-type calcium carbonate (AN-030 manufactured by Maruo Calcium ■) 0 which was surface-treated with a high molecular weight polycarboxylic acid having an average particle diameter of 0.25 μm and a particle size distribution value of 1.29.
．． 5 parts of ethylene glycol slurry was added thereto, 0.04 part of ethylene acid phosphate and 0.04 part of antimony trioxide were added, and a polycondensation reaction was carried out for 4 hours to obtain polyethylene terephthalate.

The intrinsic viscosity of the polyester was 0.63, and the specific resistance when melted was 1.5×10'Ω-Cm. When the inside of the polyester was observed under a microscope, it was confirmed that the particles were uniformly dispersed.

Next, a biaxially stretched polyester film was produced using the polyester.

That is, the polyester was extruded into a sheet from an extruder at a temperature of 295°C, and was made into a sheet with a thickness of 200°C using an electrostatic cooling method.
An amorphous sheet of μm was obtained.

Next, the amorphous sheet is rotated at 110° in the sheet flow direction.
3.5 times at C, and 11 times in the direction perpendicular to the sheet flow.
The film was stretched 3.5 times at 0°C, heat treated at 220°C for 3 seconds, and then cooled to obtain a biaxially stretched film with a thickness of 15 μm.

Examples 2 to 5 and Comparative Examples 1 to 3 2 were prepared in the same manner as in Example 1, except that the particles contained in the film and the refractive index of the film were changed as shown in Table 1.
An axially stretched film was obtained and finally a magnetic tape was produced.

The particle size distribution values of the heterite carbonate particles used in Example 2.3.4 and Comparative Example 3 are all 1.29, and that of Example 5 is 1.25. All of these are surface-treated with high-molecular polycarboxylic acid.

Further, the calcite type calcium carbonate used in Comparative Example 1 was obtained by a synthetic method, and its particle size distribution value was 1.72. Furthermore, the particle size distribution values of kaolin in Comparative Example 2 and spherical silica in Example 4 are 2.65 and 1.44, respectively.

The aluminum oxide used in Example 3 had a delta crystal type obtained by a thermal decomposition method, and the precipitated particles in Example 5 contained calcium element, lithium element,
and phosphorus element in an amount of 1% by weight or more, respectively.

The results obtained above are summarized in Table 1 below.

All of the films of Examples that meet the requirements of the present invention have good runnability,
It can be seen that the film of Example 3, which has excellent abrasion resistance, particularly in which fine aluminum oxide is used, also has particularly excellent scratch resistance and is suitable as a base film for magnetic recording media. Comparative Examples 1 and 2 are examples in which particles outside the scope of the present invention were used, but the film surface was uneven and the magnetic tape characteristics deteriorated. Furthermore, Comparative Example 3 shows that even if the same vaterite-type calcium carbonate as in the present invention is used, if the film forming conditions are inappropriate, the slipperiness and abrasion resistance deteriorate and the desired electromagnetic properties cannot be obtained. There is.

[Effects of the Invention] The film of the present invention contains specific calcium carbonate particles and has a refractive index in a specific range in the thickness direction of the film, so that it can be used for magnetic recording media with excellent slipperiness and abrasion resistance. It provides films, and its industrial value is high.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a running system of an apparatus for evaluating film running properties. (1) in the figure is 6mmφ, 5US-42(l
J2 fixing pin, ([1) is the inlet ten 7/Yon meter
(III) shows the exit tension meter, and the winding angle (θ) is 135°. FIG. 2 is a schematic diagram of a running system of an apparatus for evaluating the abrasion resistance of a film. In the figure, (
■) is 6n+mφ, 5US-420-J2 fixed bin, (
V) indicates a tension meter, and the winding angle (θ) is 135°. Applicant Diafoil Co., Ltd.

Claims (1)

[Claims] (1) A polyester film containing 0.005 to 2.0% by weight of vaterite-type calcium carbonate particles with an average particle diameter of 0.07 to 1.5 μm and a particle size distribution value of 1.60 or less as defined by the following formula A polyester film for magnetic recording media, characterized in that the refractive index in the thickness direction of the film is 1.492 or more. Particle size distribution value = d_2_5/d_7_5 (In the formula, d_2_5 and d_7_5 are the particle diameters (μm) corresponding to 25% and 75% of the total volume, respectively, measured from the large particle side of the integrated volume of the particle group.)