JP3025646B2 - Laminated biaxially oriented film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated biaxially oriented film, and more particularly, to a film having uniform projections and irregularities on the film surface, uniform surface roughness, and excellent slip, abrasion and scratch resistance. The present invention relates to a laminated biaxially oriented film which is excellent, particularly useful as a base film of a magnetic recording medium.

[0002]

2. Description of the Related Art A thermoplastic biaxially oriented film represented by a polyethylene terephthalate film has been used as a base film for magnetic recording media such as magnetic tapes and floppy disks because of its excellent physical and chemical properties. .

In such a biaxially oriented film, for example, a polyester film, its slipperiness and abrasion resistance are important factors that determine the workability of the film manufacturing process and the working process in each application, and the quality of the product. It has become. If these are insufficient, for example, a magnetic layer is applied to the polyester film surface, and when used as a magnetic tape, the friction between the coating roll and the film surface at the time of applying the magnetic layer is severe, and the film surface due to this is also severely worn, In extreme cases, wrinkles on the film surface, scratches, etc. occur.

[0004] Even after the film after applying the magnetic layer is slit and processed into an audio, video or computer tape or the like, it can be pulled out from a reel or cassette or the like.
At the time of hoisting and other operations, abrasion occurs remarkably with many guide parts, reproducing heads, etc., causing scratches, distortion,
Further, as a result of precipitation of a white powdery substance due to abrasion of the surface of the polyester film or the like, loss of a magnetic recording signal, that is, dropout is often a major cause.

In general, in order to improve the slipperiness of a film, a method of reducing the contact area between the film and a guide roll or the like by imparting surface irregularities to the film has been adopted. A method in which inert fine particles are precipitated from the catalyst residue during the production process and a method (ii) in which inert fine particles are added are used.
Generally, the larger the size of the fine particles in the raw material polymer, the greater the improvement in the slipperiness.

On the other hand, in the case of a magnetic recording medium, especially a high-density magnetic recording tape or a high-sensitivity floppy disk, the surface of the base film is required to be as flat as possible from the viewpoint of improving the electromagnetic conversion characteristics. However, when the film surface is flat, as described above, the film has poor slipperiness, and causes various troubles.

Therefore, there is a demand for a film for a magnetic recording medium to simultaneously satisfy these contradictory characteristics.

For the purpose of simultaneously satisfying such demands, there has been proposed a method of using a front and back surface different film having different surface roughness such that one surface is flat and the other surface is rough and smooth. Then, a magnetic layer is provided on the flat surface of the film,
When the rough surface is a film running surface, it is possible to have both flatness in terms of improvement of electromagnetic conversion characteristics and slipperiness in terms of film running properties, and to obtain a film in a better direction as a film for a magnetic recording medium. Become like

[0009] However, these means also have problems to be solved, and it is difficult to meet the demands for high-grade, high-density, etc. magnetic recording media as they are.

[0010] The problem of the above-mentioned method of roughening using inert fine particles is considered to be mainly caused by the fact that the individual particles vary in size and have a distribution in particle diameter. If the particle size distribution becomes large (wide), coarse protrusions based on large particles will be present on the film surface, which may cause shaving during processing, and may cause scratches during running as a magnetic tape after processing. , Generation of shavings and the like, dropout increases, and electromagnetic conversion characteristics deteriorate, which is not desirable.

For this reason, it is important that the variation in the particle size is small, that is, the particle size distribution is small (narrow) in order to reduce the coarse projections. However, the smaller the particle size distribution, the smaller the number of large protrusions.
Since runnability tends to be insufficient, it is necessary to increase the amount of addition. However, according to the research results of the present inventors, when the amount of added particles is increased, the particles are overlapped in the film thickness direction, so that the overlapping portion is likely to become a coarse projection even if the particle diameter of the particles is small. These coarse projections cause scraping during processing, as described above, and when magnetic tape is used, shavings and abrasions are generated due to friction with the pins during running, resulting in frequent occurrence of dropouts. Not so desirable. Further, the electromagnetic conversion characteristics are deteriorated due to the large protrusion, which is not desirable.

In recent years, plastic pins such as polyacetal pins have been used in many cases. However, the above-mentioned problems tend to be more remarkable with metal pins than with metal pins, and further improvement is required. I have.

[0013]

As a result of further research, the present inventor has found that in order to satisfy the required characteristics of a base film for a magnetic recording medium, in particular, the particle size distribution of inert particles contained in the film must be reduced. The inventors have found that it is important to prevent the particles from overlapping in the film thickness direction, and have reached the present invention.

Accordingly, it is an object of the present invention to provide a film having a uniform surface roughness, uniform surface protrusions and fine irregularities, and excellent in slipperiness, abrasion resistance, and scratch resistance. There is little rise in the coefficient of friction after repeated running with the pin, and there is also little dropout,
An object of the present invention is to provide a biaxially oriented film having excellent electromagnetic conversion characteristics, particularly a laminated biaxially oriented film useful as a base film for a magnetic recording medium.

[0015]

According to the present invention, there is provided, according to the present invention, (I) at least one surface of a biaxially oriented film comprising a thermoplastic polymer, (II) (A) an average particle size of 0.5 μm. (B) the particle size ratio (major axis / minor axis) of the particles is 1.0 to 1.2, and (c) the relative standard deviation represented by the following formula is 0.5 or less.

[0016]

(Equation 2)

A thermoplastic polymer containing 0.005% by weight or more and less than 0.5% by weight of spherical silica particles;
This is achieved by a laminated biaxially oriented film in which biaxially oriented films having a film thickness of not more than five times the average particle size are laminated.

The film (I) in the present invention is a biaxially oriented film made of a thermoplastic polymer. As the thermoplastic polymer, a thermoplastic aromatic polyester is preferable. Further, as the polyester, a polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component is preferable. Such polyesters are substantially linear and have film forming properties, especially film forming by melt molding. Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, and anthracene dicarboxylic acid. Can be. Examples of the aliphatic glycol include polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, and decamethylene glycol, and 1,4-cyclohexanedimethanol. And alicyclic diols. More specifically, those containing alkylene terephthalate and / or alkylene-2,6-naphthalate as a main component are preferred.

Among such polyesters, not only polyethylene terephthalate and polyethylene-2,6-naphthalate but also, for example, 8% of all dicarboxylic acid components
0 mol% or more is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and is 80% of the total glycol component.
Copolymers in which at least mol% is ethylene glycol are also preferred. At that time, not more than 20 mol% of the total acid component can be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid. ;
It may be an alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid. 20% by mole or less of the total glycol component can be the above-mentioned glycols other than ethylene glycol. For example, aromatic diols such as hydroquinone, resorcinol and 2,2-bis (4-hydroxyphenyl) propane; Aliphatic diols having an aromatic ring such as 1,4-dihydroxymethylbenzene; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol.

In addition, components derived from oxycarboxylic acids such as aromatic oxyacids such as hydroxybenzoic acid; and aliphatic oxyacids such as ω-hydroxycaproic acid may be used as the above-mentioned polyesters. Those which are copolymerized or combined at 20 mol% or less based on the total amount of the components are also included.

Further, the above-mentioned polyester may be used in an amount in a range substantially linear, for example, in an amount of 2 mol% or less based on the total acid components, in a polycarboxylic acid or polyhydroxy compound having three or more functional groups, for example, trimellitic acid. , Pentaerythritol and the like.

Such polyesters are known per se and can be produced by a method known per se.
The polyester has an intrinsic viscosity of about 0.4 measured at 35 ° C. as a solution in o-chlorophenol.
~ 0.9 is preferred.

The film (II) in the present invention is a biaxially oriented film made of a thermoplastic polymer containing spherical silica particles as spherical particles. The thermoplastic polymer may be the same as or different from the polymer forming the film (I), but the same is preferred. The more detailed description of the thermoplastic polymer can be applied to what has been described as the polymer forming the film (I).

The intrinsic viscosity of the film (II) may be the same as or different from that of the film (I). As an example of the embodiment of the laminated biaxially oriented film, in order to efficiently use the recovered material (such as a lug portion at the time of film formation), this is often used by mixing it with the film (I). In this case, the intrinsic viscosity of the film (I) is generally slightly lower than that of the film (II).

The spherical particles dispersed and contained in the film (II) have an average particle diameter of more than 0.5 μm and 2 μm or less and a particle diameter ratio (major axis / minor axis) of 1.0 to 1.2. Silica particles. This average particle size is preferably less than 1.5 μm, more preferably less than 0.8 μm, particularly preferably 0.7 μm or less. If the average particle size is too small, the slip property deteriorates, the running property of the magnetic recording tape becomes poor, and the effect of improving the scratch resistance is insufficient. The particle size ratio of the spherical silica particles is preferably 1.0 to 1.1, more preferably 1.0 to 1.05. If the particle size ratio is too large, the abrasion resistance deteriorates, which is not preferable.

Further, the spherical silica particles need to have a sharp particle size distribution, and the relative standard deviation representing the steepness of the distribution needs to be 0.5 or less. This relative standard deviation is expressed by the following equation.

[0027]

(Equation 3)

When spherical silica particles having a relative standard deviation of 0.5 or less are used, since the particles are spherical and the particle size distribution is extremely steep, the height of the film surface projections becomes extremely uniform, and the number of the same projections is reduced. Even in this case, the sliding property is extremely good as compared with the conventional one. In this sense, the relative standard deviation is preferably equal to or less than 0.4, more preferably equal to or less than 0.3, and particularly preferably equal to or less than 0.2. If the relative standard deviation is too large, the abrasion resistance deteriorates, which is not preferable.

In the present invention, the content of the spherical silica particles is 0.005% by weight or more and less than 0.5% by weight based on the thermoplastic polymer forming the film (II).
Preferably it is 0.01 to less than 0.5% by weight, more preferably 0.02 to less than 0.5% by weight, particularly preferably 0.05 to 0.3% by weight. If this amount is small, the effect of improving the slipperiness and winding property is insufficient, while if it is too large, the surface flatness is deteriorated, the electromagnetic conversion characteristics are reduced, and the particles tend to overlap in the thickness direction. Is not preferred.

The spherical silica particles are not limited at all by the production method and the like.

The spherical silica particles form, for example, hydrous silica [Si (OH) ₄ ] monodisperse spheres from the hydrolysis of ethyl orthosilicate [Si (OC ₂ H ₅ ) ₄ ], and further dehydrate the hydrous silica monodisperse spheres. To form a silica bond [@ Si-
O-Si}] can be manufactured by three-dimensionally growing the same (see Chemical Society of Japan '81, No. 9, P. 150).
3).

[0032]

Embedded image Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH {Si-OH + HO-Si} → {Si-O-Si} + H ₂ O

In the present invention, in addition to the above-mentioned spherical silica particles, other inert particles can be contained within a range that does not impair the characteristics of the spherical silica particles. If the amount of inert particles other than the spherical silica particles increases, the abrasion resistance deteriorates, which is not preferable. In this sense, the amount of the other inert particles is preferably 4.0% by weight or less, more preferably 2.
It is at most 5% by weight, more preferably at most 1.0% by weight, particularly preferably less than 0.5% by weight.

As the inert particles, for example, (1)
Silicon dioxide (including hydrate, diatomaceous earth, silica sand, quartz, etc.); (2) alumina; (3) 30% by weight of SiO ₂
(4) silicates contained above (for example, amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), hot asbestos, zircon, fly ash, etc.);
Oxides of Hg, Zn, Zr, and Ti; (5) sulfates of Ca and Ba; (6) phosphates of Li, Ba, and Ca (including monohydrogen salts and dihydrogen salts); ) Li, Na,
And K benzoate; (8) Ca, Ba, Zn, and M
n terephthalate; (9) Mg, Ca, Ba, Zn,
(10) titanates of Cd, Pb, Sr, Mn, Fe, Co, and Ni; (10) chromates of Ba and Pb;
(12) Glass (eg, glass powder, glass beads, etc.); (13) Ca and Mg carbonates; (14) fluorite; and (15) ZnS. Is done.

The timing of adding the spherical silica particles or other inert particles to the thermoplastic polymer may be any stage before the melt extrusion step. For example, before the polymerization of the polymer, during the polymerization, or during the polymerization. Any of the latter may be used. Also, it may be during the preparation step for melt extrusion. For this example,
There are direct addition and kneading just before melting.

The laminated biaxially oriented film of the present invention has a laminated structure of two or more layers, and at least one of the outermost layers is made of the thermoplastic polymer containing the spherical silica particles. It preferably has a three-layer structure, and both outermost layers are made of the polymer. The other film layers constituting the laminated biaxially oriented film may or may not contain spherical silica particles, other inert particles and the like. However, when inert particles are contained, the spherical silica particles (and other inert particles) contained in the other film layers are replaced with the spherical silica particles (and other inert particles) contained in the film layer forming the surface. It is preferable that the particle size is smaller than or the same as that of the particles. In addition, the content of the spherical silica particles is preferably small or the same. Further, other inert spherical particles may be contained to such an extent that the characteristics of the spherical silica particles are not impaired.

In the laminated biaxially oriented film, a film containing spherical silica particles forming the surface (II)
Needs to have a thickness of 5 times or less the average particle size of the spherical silica particles, preferably 4 times or less, and more preferably 3 times or less. If the film (II) containing the spherical silica particles forming the surface is too thick, the spherical silica particles will overlap in the film thickness direction and coarse projections will be formed, which is not preferable. If it is too thin, the surface will be flat,
It is not preferable because the winding property and the scratch resistance are deteriorated and the fixing force of the spherical silica particles is reduced. Therefore, the thickness of the film (II) layer is preferably at least 1/2 times the average particle size.

In the present invention, as can be seen from the fact that the thickness of the layer of the film (II) containing the spherical silica particles is preferably 5 times or less and 1/2 times or more the average particle size of the spherical silica particles. The average particle size of the spherical silica particles is more than 0.5 μm and close to the range of 2 μm or less, and is characterized in that the thickness of the film (II) layer is thin.

The laminated biaxially oriented film of the present invention can be obtained by a conventionally known method or a method accumulated in the art. For example, it can be obtained by first producing a laminated film and then biaxially orienting the film. This laminated film can be manufactured by a conventionally accumulated method for manufacturing a laminated film. For example,
A method of laminating a film layer forming a surface and a film layer forming a core layer in a molten state or a state of being cooled and solidified can be used. More specifically, it can be manufactured by a method such as co-extrusion or extrusion lamination.

The film laminated by the above-mentioned method can be further made according to the conventional method of manufacturing a biaxially oriented film, thereby obtaining a biaxially oriented film.

For example, an amorphous unstretched film that has been melted and laminated by the above-described method is stretched biaxially, and thermally fixed.
Manufactured by relaxation heat treatment if necessary.
At that time, the film surface characteristics are determined by the particle size of the spherical silica particles,
Since it varies depending on the amount and the like and the stretching conditions, it is appropriately selected from conventional stretching conditions. Further, since the density, the heat shrinkage, and the like also change depending on the temperature, magnification, speed, and the like during stretching and heat treatment, conditions that simultaneously satisfy these properties are determined. For example, in the case of polyethylene terephthalate, the stretching temperature is 1
The stage stretching temperature (for example, the longitudinal stretching temperature: T ₁ ) is (Tg
From the range of (−10) to (Tg + 45) ° C. (where Tg is the glass transition temperature of the polymer), the second-stage stretching temperature (for example, the transverse stretching temperature: T ₂ ) is (T ₁ +5) to (T ₁ +4).
0) It is good to select from the range of ° C. The first stage, 2
After the step stretching, the third step and the fourth step may be performed again in the longitudinal direction and / or the horizontal direction. The stretching ratio may be selected from a range where the stretching ratio in the uniaxial direction is 2.5 times or more, particularly 3 times or more, and the area ratio is 8 times or more, particularly 10 times or more. Furthermore, the heat setting temperature is 180-2.
The temperature is preferably selected from the range of 50 ° C, more preferably from 200 to 230 ° C. The thickness of the film is preferably 1 to 100 μm. More preferably, it is 5 to 80 μm, particularly preferably 7 to 80 μm.
25 μm.

The laminated biaxially oriented film of the present invention has a very good sliding property in spite of the fact that the film surface is flat, has excellent abrasion resistance and excellent scratch resistance, as compared with the conventional one. It has the feature of being. Further, it has a feature that the above characteristics are good not only for metal pins but also for plastic pins.

Although the reason for this is not clear, the shape of each projection on the film surface is sharp because spherical silica particles that are very spherical and nearly monodisperse are used.
In addition, since the film layer containing the spherical silica particles forming the surface is thin, the overlapping of the spherical silica particles in the thickness direction is prevented, and the projection height and shape on the film surface are uniform, and as a result, the film surface Despite good surface flatness, low coefficient of friction, and more uniform contact with other objects, supported by many protrusions, excellent durability, presumed that it is difficult to scrape and scratch Is done.

The laminated biaxially oriented film of the present invention is useful as a base film of a magnetic recording medium, particularly a high-density magnetic recording medium, by taking advantage of such features. In particular, when used as a base film for high-density video tapes such as those for super high grade and 8 mil video, high-density floppy disks, and magnetic tapes for high-density computers, excellent electromagnetic conversion characteristics, slipperiness, running properties, Scratch resistance, scratch resistance, etc. are obtained.

A magnetic recording medium using a laminated biaxially oriented film as a base film can be manufactured by a conventionally known method. For example, the magnetic layer is usually made of a polymer binder containing ferromagnetic powders such as γ-iron oxide, Co-containing iron oxide, chromium oxide, and iron powders such as vinyl chloride-vinyl acetate copolymer and vinyl chloride-vinyl acetate-vinyl alcohol. Vinyl resins such as copolymers, polyvinyl butyral, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butyl acrylate-2-hydroxyethyl methacrylate copolymer, rubber resins such as acrylonitrile-butadiene copolymer, nitrocellulose, It is made of a fibrous resin such as acetylcellulose, a crosslinkable resin such as epoxy, phenoxy, urethane, etc., to which may be added an abrasive, a light-shielding agent, a dispersant, an antistatic agent and the like, if desired. The coating type magnetic layer is formed by applying a magnetic paint. Further, a metal thin film type magnetic layer can be provided.

[0046]

The present invention will be further described below with reference to examples. The various physical properties and characteristics in the present invention were measured as follows.

(1) Particle Size of Spherical Particle The particle diameter is measured in the following states. 1) When the average particle size, the particle size ratio, and the like are determined from the powder. 2) To find the average particle size, particle size ratio, etc. of the particles in the film.

1) From powder: Particle powder is scattered on an electron microscope sample table so that individual particles do not overlap as much as possible, and a gold thin film deposition layer is formed on this surface with a thickness of 200 to 300 mm by a gold sputtering apparatus. After being formed and observed with a scanning electron microscope at a magnification of 10,000 to 30,000, the major axis (Dli), minor axis (Dsi) and area circle equivalent diameter (Di) of at least 100 particles were measured with Luzex 500 manufactured by Nippon Regulator. Ask. Then, the major axis (Dl), minor axis (Ds),

[0049]

[Outside 1]

[0050]

(Equation 4)

[0051]

(Equation 5)

[0052]

(Equation 6)

2) In the case of particles in the film: A small piece of the sample film was fixed on a sample table for a scanning electron microscope, and a JEOL sputtering device (JFC-110) was used.
The film surface is subjected to an ion etching treatment under the following conditions using a zero-type ion sputtering device). The conditions were as follows: the sample was placed in a bell jar, the degree of vacuum was raised to a vacuum of about 10 ^-3 Torr, the voltage was 0.25 KV, and the current was 12.
Perform ion etching at 5 mA for about 10 minutes. Furthermore, the film surface was subjected to gold sputtering with the same apparatus, and observed at a magnification of 10,000 to 30,000 times with a scanning electron microscope.
The major axis (Dli), minor axis (Dsi), and area circle equivalent diameter (Di) of at least 100 particles are determined using Luzex 500 manufactured by Nippon Regulator. Hereinafter, the same operation as in the above 1) is performed.

(2) Relative standard deviation of spherical particles Area circle equivalent diameter (Di) obtained in (1) and its

[0055]

[Outside 2]

Is obtained from the equation described in the text.

(3) Average particle size, particle size ratio, etc. of particles other than spherical particles 1) Average particle size: Centrifugal Particle S, CP-50 type centrifugal particle size analyzer manufactured by Shimadzu Corporation
ize Analyser). The particle size corresponding to 50% by mass was read from the integrated curve of the particles of each particle size and its abundance calculated based on the obtained centrifugal sedimentation curve, and this value was taken as the above average particle size (Book “particle size” Measurement Techniques, published by Nikkan Kogyo Shimbun, 1975, pp. 242-2
47).

2) Particle Size Ratio A small piece of film is fixedly formed with an epoxy resin, and an ultrathin section having a thickness of about 600 angstroms (cut in parallel to the film flow direction) is prepared with a microtome.
This sample was subjected to a transmission electron microscope (H-80 manufactured by Hitachi, Ltd.).
(Type 0), the cross-sectional shape of the lubricant (particles) in the film was observed, and expressed by the ratio of the major axis to the minor axis of the lubricant.

3) Relative standard deviation Calculated from the following equation.

[0060]

(Equation 7)

(4) Surface roughness of film (Ra) This is a value defined by JIS-B0601 as the center line average roughness (Ra). In the present invention, a stylus type surface roughness of Kosaka Laboratory Co., Ltd. Measure using a SURFCORDER SE-30C. The measurement conditions and the like are as follows. (A) Tip radius of the stylus: 2 μm (b) Measurement pressure: 30 mg (c) Cut-off: 0.25 mm (d) Measurement length: 2.5 mm (e) How to summarize the data: Repeated measurement of the same sample 5 times , The largest value is 1
Excluded, the average of the remaining four data is rounded to the fourth decimal place and displayed to the third decimal place.

(5) Film surface roughness PV1 / 1 Using a stylus type surface roughness meter, the reference length direction was enlarged 50 times and the surface roughness direction was enlarged 50,000 times, and a chart was drawn. From among the straight lines parallel to the average line of the part extracted by the reference length of 1.0 mm, the one that passes through the first peak from the highest and the bottom of the first valley from the deep is selected, and the interval between these two straight lines is taken as the vertical magnification. Is expressed in units of microns, and the average of ten PV values is expressed.

(6) Coefficient of friction of film (μk) Measured as follows using the apparatus shown in the figure. In the figure, 1 is an unwinding reel, 2 is a tension controller, 3, 5, 6, 8, 9 and 11 are free rolls,
Is a tension detector (entrance), 7 is stainless steel SUS 30
4 fixed rod (outer diameter 5 mmφ, roughness 0.3 S) or polyacetal plastic fixed rod (outer diameter 5 mm
φ, roughness 0.1 S), 10 is a tension detector (outlet), 12 is a guide roll, and 13 is a take-up reel.

In an environment of a temperature of 20 ° C. and a humidity of 60%, the width 1 /
The magnetic tape cut into 2 inches is moved at a speed of 200 cm / min by contacting a fixed rod (surface roughness: 0.3 μm) of 7 at an angle θ = (152/180) π radian (152 °). ). After the film has traveled 90 m, the exit tension detector detects the exit tension (T ₂ : g) when the tension controller 2 is adjusted so that the entrance tension T ₁ becomes 40 g, and the traveling wear coefficient μk is calculated by the following equation. calculate.

[0065]

(Equation 8) When this is repeatedly run, the running friction coefficient after repetition is set to μk.

(7) Electromagnetic Conversion Characteristics of Magnetic Coating Tape A 50% white level signal (10
The 0% white level signal has a peak-to-peak voltage of 0.2.
714 volts), a signal on which a 100% chroma level signal is superimposed is recorded, and the reproduced signal is measured using a Shivasoku noise meter: type 925R. The definition of chroma S / N is as follows according to the definition of Shibasoku.

[0067]

(Equation 9)

Here, ES (pp) is a peak-to-peak voltage difference (pp) of the reproduced signal of the white level signal.

[0069]

## EQU10 ## ES (pp) = 0.714V (pp) EN (rms) is the square root value of the peak voltage of the reproduced signal of the chroma level signal.

(8) Dropout A commercially available dropout counter (eg, Shibasoku VH)
(01BZ type), the dropout of 4 μsec × 10 dB is counted, and the count number per minute is calculated.

Example 1 Dimethyl terephthalate and ethylene glycol were polymerized by a conventional method using manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, and phosphorous acid as a stabilizer. Chlorophenol, 3
5 ° C.) to obtain a polyethylene terephthalate of 0.62 [hereinafter referred to as polyester I].

On the other hand, polyester I was obtained except that 0.4% by weight of spherical silica particles having an average particle diameter of 0.6 μm, a particle diameter ratio of 1.05 and a relative standard deviation of 0.14 were added as a lubricant and polymerized.
Polyethylene terephthalate having an intrinsic viscosity of 0.61 was obtained in the same manner as described above [hereinafter referred to as polyester II].

The polyester I and the polyester II were dried at 170 ° C. for 3 hours, respectively, and then fed to separate extruders of a co-extrusion film forming machine, where the polyester I formed a film I layer and the polyester II formed a film II. The film was co-extruded from a three-layer die so as to form the following layers and the layer thickness ratio of each layer was adjusted to 1.5: 1: 1: 1.5.

The unstretched film was preheated by a longitudinal stretching preheating roll and an IR heater.
The film is stretched in the machine direction at a stretch ratio of 3.7 times, and then stretched at a stretching temperature of 1
The film was stretched in the transverse direction at a temperature of 05 ° C. and a stretching ratio of 3.9 times.
Heat treatment was performed at 10 ° C. to obtain a three-layered biaxially oriented film having a thickness of 14 μm, in which polyester I was used as a core layer and polyester II was used as both surface layers.

Table 1 shows the characteristics of this film. Further, on this film, 100 parts by weight of iron oxide powder containing the following Co: Essrec A (vinyl chloride-vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.) 10 Nipporan 2304 (polyurethane elastomer manufactured by Nippon Polyurethane) 5) Lecithin 1) Methyl ethyl ketone 75) Methyl isobutyl ketone 75) Toluene 75) Additive (lubricant, silicone resin) 0.15% of magnetic paint is applied by gravure roll, and magnetic knife layer is applied by doctor knife. Is smoothed, magnetically oriented by a conventional method while the magnetic paint is not yet dried, and then guided to an oven, dried and cured, further calendered to make the coating surface uniform, slit, and a thickness of about 4 mm.
A 1/2 inch wide magnetic tape having a μ magnetic layer was prepared. Table 1 shows the characteristics of the film and the magnetic tape.

From the table, it can be seen that the film thus obtained has the same projection height on the surface and has no coarse projections, and thus has good electromagnetic conversion characteristics when formed into a magnetic tape, and has good runnability with metal pins. It can be seen that not only is the runnability good, but also the runnability with the plastic pin is good, and the rise in μk after 200 passes of repeated running is small, and the abrasion resistance is good. Further, it can be seen that the number of dropouts after 200 passes is relatively small and good.

Example 2 and Comparative Example 1 In Example 1, except that the layer thickness ratio of the film I layer made of polyester I and the film II layer made of polyester II was changed as shown in Table 1, A film and a tape were prepared in the same manner as in Example 1.

Table 1 shows the characteristics. From this table, it can be seen from the table that when the layer thickness of the lubricant layer (polyester II layer) is larger than the particle size, the overlap in the thickness direction of the particles increases, and therefore, especially when the friction coefficient μk during repeated running with the plastic pin is increased. It can be seen that the rise is large and the dropout is also large. The tape of Comparative Example 1 cannot be used.

Example 3 The procedure of Example 1 was repeated except that the particle size of the spherical silica particles contained in the polyester II was changed as shown in Table 1, and the amount of addition was changed as shown in Table 1 accordingly. A film and a tape were prepared in the same manner as in Example 1. The characteristics are shown in Table 1.

[0080]

[Table 1]

[0081]

According to the present invention, the roughness of the film surface is uniform, the projections and the fine irregularities on the surface are uniform, and the film has good slipperiness.
A biaxially oriented film, particularly a magnetic recording medium, which has excellent abrasion resistance and scratch resistance, thereby reducing the increase in friction after repeated running with a metal pin or a plastic pin, and has a small dropout, and excellent electromagnetic conversion characteristics. A laminated biaxially oriented film useful as a base film can be provided.

[Brief description of the drawings]

FIG. 1 shows a coefficient of friction (μ) for evaluating film running property.
It is a schematic diagram which measures k).

[Explanation of symbols]

 1: Feeding reel 2: Tension controller 3, 5, 6, 8, 9, 11: Free roll 4: Tension detector (entrance) 7: Fixed pin 10: Tension detector (exit) 12: Guide roll 13: Winding reel

Continuation of the front page (56) References JP-A-2-77431 (JP, A) JP-A-1-176556 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1 / 00-35/00 G11B 5/73-5/733

Claims (3)

(57) [Claims] (I) an average particle diameter of more than 0.5 μm and not more than 2 μm on at least one surface of a biaxially oriented film made of a thermoplastic polymer; (Major axis / minor axis) is 1.0 to 1.2, and (c) the relative standard deviation represented by the following formula is 0.5 or less. Laminated biaxially oriented film comprising a biaxially oriented film made of a thermoplastic polymer containing spherical silica particles in an amount of 0.005% by weight or more and less than 0.5% by weight and having a film thickness of 5 times or less the average particle diameter. Film. 2. The laminated biaxially oriented film according to claim 1, wherein the thermoplastic polymer is a polyester. 3. The laminated biaxially oriented film according to claim 1, wherein the laminated biaxially oriented film is a base film of a magnetic recording medium.