JPH0441534A - Polyethylene 2,6-naphthalate film - Google Patents

Abstract

PURPOSE:To obtain the title film improved in mechanical properties, traveling performances, abrasion resistance and flatness by forming polyethylene 2,6- naphthalate containing specified vaterite CaCO3 particles into a film and bi- axially orienting the film. CONSTITUTION:Polyethylene 2,6-naphthalate containing 0.005-2.0wt.% vaterite CaCO3 particles having a mean particle diameter of 0.07-1.5mum and a particle diameter distribution defined by the formula [wherein d25 and d75 are diameters (mum) at 25% and 75% cumulative volumes when the particles are weighed from the side of the larger particle] of 1.60 or below is extruded at 280-320 deg.C into a sheet, and this sheet is rapidly cooled to obtain an amorphous sheet. This sheet is oriented biaxially at a draw ratio of 3.5 or above and heat-treated for 0.1-10sec at 180-260 deg.C obtain a biaxially oriented polyethylene 2,6-naphthalate film having a sum of F-5 values in the machine and crosswise directions of 25kg/mm<2> or above, and a resistivity in a molten state of 1X10<7>-5X10<8>OMEGA-cm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a biaxially oriented polyethylene-2,6 naphthalate film having excellent mechanical properties, runnability, abrasion resistance and flatness.

More specifically, it has a uniform surface and excellent tape running properties.
The present invention relates to a biaxially oriented polyethylene-2°6-naphthalate film that generates little abrasion powder and is particularly suitable for high-density magnetic recording applications.

[Prior Art and Problems to be Solved by the Invention] Polyester films are widely used as industrial base materials because of their excellent physical and chemical properties.

Incidentally, in recent years, there has been a strong desire for electrical and electronic equipment to be smaller, lighter, and higher in performance, and as a result, the properties required for the films used have become more stringent. Under these circumstances, among polyester films, polyethylene-2,6-naphthalate film in particular is attracting attention and being put into practical use because of its excellent mechanical strength and heat resistance. A film with a fine surface structure and excellent running properties and abrasion resistance is desired.

Such films are useful as electrical insulating materials and capacitor dielectric materials, and are particularly useful as base films for magnetic recording. For example, as magnetic recording media become smaller and longer, it is desired that the base film be made thinner and stronger.

By the way, the biaxially oriented film of polyethylene-2,6-naphthalate is longitudinally stretched using the difference in circumferential speed between the rolls, similar to that of polyethylene terephthalate.
In this case, the surface of the film is often worn out, and abrasion powder is also generated due to friction and abrasion between the product film and the base material, such as a guide pin.

Conventionally, as a means to improve the runnability and abrasion resistance of polyester films, a method has been known in which inert fine particles are present in the film to appropriately roughen the film surface.
Although improvements have been made to some extent, satisfactory results have not always been obtained.

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.

Also kaolin, silicon oxide, titanium dioxide.

When particles of an inert inorganic compound are added to polyester such as calcium phosphate, the particles are not destroyed or deformed by stretching and runnability is improved because they form relatively steep protrusions; Because the distribution is wide, deterioration of electromagnetic conversion characteristics and frequent dropouts are often observed due to coarse protrusions.

In order to overcome this trade-off, it has recently been proposed to use inorganic or organic particles with a sharp particle size distribution. For example, Japanese Patent Application Laid-Open No. 62207356,
JP-A-59-217755 discloses monodisperse silicon oxide particles 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 has so far been obtained that highly satisfies runnability and abrasion resistance and also has other necessary properties such as flatness and surface uniformity.

In particular, polyethylene 26-naphthalate film, which is often used under severe conditions in terms of film running speed and tension, has insufficient properties, and improvements in these properties are especially desired. Ta.

[Means to solve problems]

In view of the above-mentioned problems, the inventor has conducted extensive studies and has found that:
The present invention was completed based on the finding that a film containing specific calcium carbonate particles and having a specific resistance during melting within a specific range can achieve the above object.

That is, the gist of the present invention is that the average particle size is 0.07 to 1°5μ.
m, 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.
Contains 0% by weight, and the sum of F-5 values in the vertical and horizontal directions is 25
kg/w" or more, specific resistance when melting is 1 x 107 to 5 x 1
08 Ω-cm.

(In the formula, d 2S + d 75 is the cumulative volume of the particle group measured from the large particle side, and is 25% and 75% of the total volume, respectively.
The corresponding particle size (μm) is shown. ) Hereinafter, the present invention will be explained in more detail.

In the present invention, polyethylene-2,6-naphthalate is obtained by performing an esterification reaction or transesterification reaction using naphthalene-2,6-dicarboxylic acid or its alkyl ester as the main acid component and ethylene glycol as the main glycol component. It refers to polyester obtained by performing a polycondensation reaction, but a part of it may be replaced with other components. For example, part of the acid component may be replaced with naphthalene-2,7-dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, adipic acid, sebacic acid, P-hydroxybenzoic acid or a lower alkyl ester thereof, or glycol Some of the ingredients are trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, 1.4-
It may be substituted with cyclohexane dimetatool or the like. In any case, polyethylene-2,6-naphthalate as used in the present invention refers to polyester in which 80 mol% or more, preferably 90 mol% or more, of ethylene-2,6-naphthalate units.

In addition, the polyethylene-2,6-naphthalate film of the present invention refers to a biaxially oriented film using such polyester as a starting material, and in particular, in order to obtain the film of the present invention with high strength in the longitudinal and transverse directions. The following method is preferably adopted.

That is, polyester is usually extruded into a sheet form from an extruder at 280 to 320°C, cooled to below 90°C to form a substantially amorphous sheet, and then biaxially stretched or simultaneously biaxially stretched in length and width. do. In this case, this can be achieved by setting the shrinkage and transverse stretching magnifications to high magnifications, for example, 3.5 times or more each, but after longitudinal and transverse stretching at relatively low magnifications,
Furthermore, stretching may be performed again in each direction at a temperature of 110 to 180°C.

In this case, each stretching may be performed in multiple stages, or heat treatment or the like may be added in between. In any case, in order to keep the heat shrinkage rate low, the film of the present invention has a
It is preferable to perform heat treatment at a temperature range of 0° C. or lower for 0.1 to 10 seconds.

In the present invention, the sum of the F-5 values in the vertical and horizontal directions of the film thus obtained is 25 kg/llll11
It is necessary that the weight is 2 or more, preferably 30 kg/
ff1I112 or more, more preferably 35kg/+aa
+2 or more. If this value is less than 25 kg/mm'', the dimensional stability against external forces will be poor, making it unsuitable for use in magnetic recording media that particularly require precision.

In the present invention, even if the sum of the vertical and horizontal F-5 values is within this range, especially when the vertical F5 value is 13k,
g/capacity 2 or more, and the lateral F-5 value is 12 kg/m2
The above is desirable.

In the present invention, by blending certain specific particles into such a polyester film, a film having excellent running properties and abrasion resistance and particularly suitable for use as a magnetic recording medium is obtained. type calcium carbonate particles should be used.

Calcium carbonate particles can be produced by pulverizing and dispersing natural calcium carbonate, as well as by, for example, Japanese Patent Application Laid-Open No. 59-69.
As disclosed in Japanese Patent Application No. 425, precipitated calcium carbonate is known which is produced by a so-called synthesis method in which a calcium hydroxide solution is reacted with a carbon dioxide-containing gas. In this case, calcite-type calcium carbonate particles with a relatively uniform particle size are obtained, and it is known that these particles are blended into a polyester film as shown in Japanese Patent Publication No. 116856, for example. However, the desired particle size distribution cannot be achieved.

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 AN 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. Examples of surface treatment agents that also serve as dispersants include JP-A-51-6
Surface treating agents such as those described in JP-A-9426 or JP-A-1256558 are preferably used, particularly high-molecular polycarboxylic acids, their sodium salts, ammonium salts, and the like. 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 μm, there is little improvement in runnability or wear resistance, while if it exceeds 1.5 μm, although the roughness is uniform, the absolute value becomes too large and the electromagnetic properties deteriorate.

Further, the content of O, O in the film is selected from the range of 5 to 2.0% by weight, preferably 0.01 to 0.8% by weight. If the blending amount is less than 5% by weight of O or OO, running properties and wear resistance will not improve, and if it exceeds 20% by weight, the electromagnetic properties will deteriorate.

In this way, in the present invention, the properties necessary for a base film for magnetic recording media are improved by using a certain specific calcium carbonate particle. When it is Ω-1, the flatness can be highly improved and is particularly excellent.

That is, according to the findings of the present inventors, the long-term waviness, or flatness, of the conventionally known biaxially oriented polyethylene naphthalate film is not necessarily sufficient (especially for magnetic recording media that require precision). The flatness of the biaxially stretched film largely depends on the uniformity of the amorphous sheet, and the thinner the film is, for example, 30 μm or less, the better the flatness of the biaxially stretched film. Things will happen noticeably.

In order to improve this flatness, when obtaining an amorphous sheet from a molten polymer, it is effective to apply an electrostatic charge to the sheet and electrostatically press the sheet strongly against a rotating cooling drum, that is, the electrostatic application cooling method. When producing a film containing such calcium carbonate particles, the specific resistance when melted is 1 x 107 to 5 x 10''Ω-Ω, preferably 1 x 1
It has been found that a value of 07 to 1×10 8 Ω−0 is good.

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, if necessary, after the transesterification or esterification reaction. Preferably, a method is employed in which a relatively small amount, for example, an equivalent amount or less of a phosphorus compound is added to the added 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, and specifically, for example, a magnesium catalyst, a manganese catalyst, a calcium catalyst, etc. The degree of polymerization of polyester containing core particles is increased in the presence of about twice the equivalent amount of a phosphorus compound.

In this way, the method of the present invention improves mechanical properties, runnability,
Although it is possible to obtain a polyethylene-2,6-naphthalate film with excellent abrasion resistance and flatness, other particles may be added for the purpose of further improving the film properties without departing from the spirit of the present invention. More than one species may be used in combination.

In the case of polyethylene-2,6 naphthalate, so-called precipitated particles are usually difficult to obtain as particles used in combination, so it is desirable to use additive particles. These additive particles refer to particles added externally to the polyester manufacturing process, and specifically include kaolin, tar, carbon, molybdenum sulfide, gypsum, rock salt, aluminum oxide, barium sulfate, lithium fluoride, calcium fluoride, Examples include zeolite, calcium phosphate, silicon dioxide, titanium dioxide, and the like.

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, benzoguanamine resin, or 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 size 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 O, O.
O5 to 0.5 times the weight, more preferably 0.01 to 0.3
It is best to choose from the double weight range. 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 diameters may be used.

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

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.

Among these, delta-type or gamma-type aluminum oxide particles, particularly delta-type aluminum oxide particles having an average particle diameter of 0.5 μm or less, preferably 0.1 μm or less, are preferably used. Examples of methods for producing these particles include a thermal decomposition method, in which anhydrous aluminum chloride is used as a raw material and flame hydrolysis, or an ammonium alum pyrolysis method, in which aluminum hydroxide is used as a starting material and is reacted with sulfuric acid to form aluminum sulfate. Examples include a method of reacting with ammonium sulfate and firing as 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 0.5 μm or less, preferably 0.5 μm or less.
The thickness is preferably 1 μm or less.

As described above, in the present invention, by using vaterite-type calcium carbonate and other particles including fine aluminum oxide particles as necessary, we can produce extremely excellent polyethylene-2,6-naphthalate, which is particularly suitable for magnetic recording media. made it possible to obtain film.

By the way, when producing a polyester 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 becomes large, which is not preferable. In addition, the particle concentration is 50% by weight.
If more slurry is added, the dispersibility of the particles often deteriorates.

In addition, as a polycondensation reaction catalyst for polyester synthesis, s
Commonly used catalysts such as b, G e , T i , Sn, and Si compounds are used.

The film of the present invention, which is particularly 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 0.005 to 0.005 in terms of center line average roughness. 0.1 μm, preferably O
lOO7~0.08 am, more preferably 0. O1~
It is selected from a range of 0.03 μm.

The film of the present invention can be particularly effective when used as a heath film for videotapes, and also when used as an audio film.

Of course, as needed, we will use capacitor dielectrics, packaging, etc.
It can also be used for decoration, plate making, and other uses.

〔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, "parts" and "%" each refer to "parts 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) F-5 Stress at 5% elongation, expressed in kg/all'', measured using an Instron tensile tester.

Length in longitudinal direction of film from biaxially stretched film 150m
m, cut out 5 sample pieces with a transverse length of 6.25 mm, tensile speed 50 mm/m, grip interval and gauge interval 5.
A tensile test was conducted at 0 mm.

The load at 5% elongation was read from the obtained S-3 curve, the F-5 value was calculated according to the following formula, and the average value of the five points was determined.

(3) Specific resistance during melting
Brit, J., Appl, Phya) Volume 17, No. 11
49-1154 (1966).

However, in this case, the melting temperature of the polymer is 295°C, and the value immediately after applying a direct current of 1,000 V is taken as the specific resistance at the time of melting.

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

(5) Film surface roughness center line average roughness (Ra); (1) Determined as follows using a surface roughness measuring machine (SE-3F) manufactured by Koita Research Institute. That is, the reference length is 2°5IIIll in the direction from the film cross-sectional curve to its center line.
Cut out the part, and set the center line of this extracted part to the y-axis,
When expressed by a roughness curve y=f (x) with the direction of vertical magnification as the y axis, the value given by the following equation is expressed in [μm]. The centerline average roughness was determined by determining 10 cross-sectional curves 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 30μ, and the cutoff value is 0.
．． It was set as 08oon.

■Parallel to the average line of the part (hereinafter referred to as the extracted part) extracted by the standard length (2, 5 values) from the cross-sectional curve obtained by the surface roughness measuring machine (SE-3F) made by Koita Research Institute When the cutout part is sandwiched between two straight lines, the distance between the two straight lines is measured in the direction of the longitudinal magnification of the cross-sectional curve, and the value expressed in micrometers (μm) is the maximum height of the cutout 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. still,
The radius of the stylus used at this time was 2.0 μm, the load was 30 mm, and the cutoff value was 0.08 mm. Furthermore, Rt/
The smaller Ra is, the more uniform the surface roughness of the film is.

(6) Evaluation of abrasion resistance Using the tape abrasion evaluation machine shown in Fig. 2, a polyester film with a width of 10 mm was run over a length of 200 m, and a fixing pin (diameter 6 InI 11, material 5 U) indicated by N in the figure was used.
The amount of abrasion powder adhering to S420-J2 (finish 0.23) was visually evaluated and divided into four ranks. The running speed of the film was 11.4 m/min, and the tension was detected with a tension pin knob indicated by (V), and the initial tension was 300 m/min.
g. The angle θ of the winding with the film was 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: Slightly large amount of adhesion (could be a problem 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 slit into 5-inch widths to make video tapes. The following magnetic tape characteristics of this videotape were evaluated using a NV3700 video deck manufactured by Matsushita Electric.

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 back a videotape recording a 4.4 MHz signal, measure the number of dropouts at 15μ5ec-20dB for about 20 minutes using a dropout counter manufactured by Daikin Industries ■, and calculate the number of dropouts per minute. (
pcs/min).

(8) Abrasion resistance A magnetic tape slit to a width of 2 inches is wrapped around a hard chrome-plated metal bottle (diameter drawing, finish 3S) at a tension of 50 g, wrapped at an angle of 135°, and at a running speed of 3 m/sec. Rub once.

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.

(9) Planarity of the film The thickness of the film is measured at 10 points every 1000 m in the longitudinal direction of the film, 10 points every 10 cm in the lateral direction, a total of 100 points.

The film thickness is measured using a micrometer manufactured by Anritsu Electronics Co., Ltd., and the thickness is measured by stacking 10 films around the relevant location and converting it into a value per film.

Among all measured values, the maximum value is X-2 and the minimum value is
m il and the arithmetic average value is represented by X, and the smaller this value is, the more preferable it is.

Example 1 100 parts of dimethyl-2,6-naphthalate, 60 parts of ethylene glycol, and 0.09 parts of maggotium acetate tetrahydrate
The sample was placed in a reactor, heated to raise the temperature, and methanol was distilled off to perform a transesterification reaction.It took 4 hours from the start of the reaction to raise the temperature 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 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 was added as an ethylene glycol slurry, and further 0.03 parts of phosphoric acid and 0.04 parts of antimony trioxide were added to carry out a polycondensation reaction for 4 hours, resulting in an intrinsic viscosity of 0.60.
a Polyethylene 2.6 naphthalate was obtained.

The resulting polymer was then heated to 0.3 mHg235'C
Solid state polymerization was carried out for 7 hours to obtain a polymer with an intrinsic viscosity of 0.68, which was extruded into a sheet form from an extruder at 295° C. using an electrostatic cooling method to obtain an amorphous sheet with a thickness of 110 μm.

Next, it was stretched 3.9 times in the longitudinal direction using the difference in circumferential speed of the rotating rolls, and then 3.7 times in the transverse direction using a tenter, and then stretched at 220°C.
A heat treatment was performed for 5 seconds to obtain a biaxially oriented film with a thickness of 8 μm.

A magnetic layer was then applied to the obtained film to produce a magnetic tape.

Examples 2 and 3 and Comparative Examples 1 to 4 A two-wheel stretched film was obtained in the same manner as in Example 1, except that the particles contained in the film and the film properties were changed as shown in Table 1, and a magnetic tape was also produced.

The film of Comparative Example 4 was not worthy of evaluation because it was weak and easily stuck during winding and unwinding.

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 is excellent in abrasion resistance and in particular uses fine aluminum oxide in combination, is particularly excellent in abrasion resistance and can be used as a base film for magnetic recording media. Comparative Examples 1.2 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.

〔Effect of the invention〕

The film of the present invention is a high-strength film for high-density recording that particularly requires running properties and abrasion resistance, and is highly improved by incorporating specific calcium carbonate particles, and its industrial value is high. is expensive.

[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 6Pengφ, 5US-420-J
2 fixed bins, (It) inlet tension meter, (I
II) indicates the exit tension meter, and the winding is at the corner (
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, (IV
) is 6mmφ, 5US-420-J2 fixing pin, (v)
indicates a tension meter, and the winding angle (θ) is 13
It is 5°.

Claims (1)

[Claims] (1) Contains 0.005 to 2.0% by weight of vaterite-type calcium carbonate particles having an average particle diameter of 0.07 to 1.5 μm and a particle size distribution value defined by the following formula of 1.60 or less,
The sum of the F-5 values in the vertical and horizontal directions is 25 kg/mm^2 or more, and the specific resistance when melting is 1 x 10^7 to 5 x 10^8 Ω-
Biaxially oriented polyethylene-2 characterized by cm
, 6-naphthalate film. Particle size distribution value = d_2_5/d_7_5 (in the formula, d_2_5 and d_7_5 are the cumulative volume of the particle group measured from the large particle side, and are 25% and 75% of the total volume, respectively.
(indicates the particle size (μm) corresponding to