JPH07178806A - Polyethylene-2,6-naphthalate film - Google Patents

Abstract

PURPOSE:To obtain a biaxially oriented polyethylene-2,6-naphthalate film having high strength and excellent flatness and especially useful as the base film of a magnetic recording medium capable of long-time recording. CONSTITUTION:A biaxially oriented polyethylene-2,6-naphthalate film is characterized by that Young's modulus (EM) in a longitudinal direction is 800kg/mm<2> or more, Young's modulus (ET) in a lateral direction is 500kg/mm<2> or more, Young's modulus in the longitudinal direction is larger than that in the lateral direction and elongation per load 1kg/mm<2> at 120 deg.C is 0-0.6%.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a biaxially oriented polyethylene-
More specifically, it relates to a 2,6-naphthalate film as a base film for a magnetic recording medium such as a video tape, an audio tape, a data cartridge for a computer, which has a high strength in a longitudinal direction and an excellent flatness and which can record for a long time. It relates to a useful biaxially oriented polyethylene-2,6-naphthalate film.

[0002]

2. Description of the Related Art In recent years, magnetic tapes such as video tapes, audio tapes, and data cartridges for computers have been required to have higher density recording for downsizing and higher image quality. Is required. The base film needs to be thin to meet the demand for long-time recording of the magnetic tape, but the thinness reduces the stiffness of the tape, and the edge of the tape is easily scratched during loading or unloading. Also, when a high tensile force is applied momentarily, the tape may be deformed and the recording may be distorted. Therefore, a high Young's modulus is required for the film that is the base of the long-time recording magnetic tape.

Further, recently, a VTR with a built-in camera has become popular,
Since it is used outdoors or brought into the car, the magnetic tape is often exposed to more severe temperature conditions than before, and the dimensional stability of the tape at high temperatures that does not cause skew distortion, Consequently, the demand for dimensional stability of the base film is increasing.

Conventionally, a biaxially oriented polyethylene terephthalate film has been used as a base film for these magnetic recording tapes, and a so-called super tension film having a high Young's modulus in the longitudinal direction is known for long-time recording. However, with this film, the Young's modulus in the machine direction is at most 850 kg / mm ² , in which case the Young's modulus in the transverse direction is at most 450 kg / mm ² . In addition, if the Young's modulus in the vertical direction is increased, the Young's modulus in the horizontal direction inevitably decreases, and the tape is easily damaged by the edge portion during running. On the other hand, in the manufacture of film,
If you try to increase the direction Young's modulus,
In this case as well, a sufficient Young's modulus in the vertical direction cannot be obtained inevitably, and the touch with the magnetic head becomes poor, resulting in output fluctuation. Further, the base film having a higher Young's modulus which has been subjected to high-strength drawing has a drawback that strain generated during molding remains and dimensional stability is deteriorated. The high-magnification stretching process has another problem that the product yield is reduced.

On the other hand, based on a polyethylene-2,6-naphthalate (hereinafter sometimes referred to as "PEN") film, which is a polyester having better heat-resistant dimensional stability than polyethylene terephthalate (hereinafter sometimes referred to as "PET") Various magnetic tapes have been proposed.

For example, Japanese Unexamined Patent Publication No. 63-60731 discloses a technique for manufacturing a PEN film having a high Young's modulus in the machine direction. However, PE manufactured by such technology
In the N film, the distortion generated during the molding remains, and there is a concern that the film shrinks in the longitudinal direction when the tape is exposed to the severe temperature conditions such as the outdoor use.

Further, for example, in Japanese Patent Laid-Open No. 4-198328, a PEN film is used, and the degree of plane orientation (hereinafter sometimes referred to as "plane orientation coefficient") is specified to be in the range of 0.255 to 0.280 and the slit property of Although technologies such as improvement have been disclosed, there is no specification of the main orientation direction, and improvement in magnetic head touch of the tape and prevention of edge damage by increasing Young's modulus in the longitudinal direction cannot be found. Further, in the publication, the above-mentioned degree of plane orientation is satisfied, and at the same time, the average refractive index is 1.666 to 1.676, preferably 1.668 to.
The range of 1.676 is preferable, and if it is smaller than the range, the heat shrinkage rate becomes large. When the average refractive index is less than 1.666 in the invention film according to the above publication, under the severe temperature condition. It is easily estimated that the dimensional stability of the base film is poor.

[0008] In the same publication, the PEN film is characterized in that aggregate particles having a specific average particle diameter (particles selected from silicon oxide and aluminum oxide) and particles selected from a crosslinked polymer and calcium carbonate are specified. Although it has been disclosed that abrasion resistance and slipperiness are improved by containing the magnetic particles in a ratio, it is difficult to obtain a magnetic tape having a high surface property for high density recording only by such a technique. For example, since silicon oxide or aluminum oxide, which is an agglomerated particle, is used, it is expected that voids will be generated in the film due to the inclusion of the particles, and the occurrence of coarse projections on the film surface or deterioration of abrasion resistance due to it. is expected. Further, in the same publication, although the particle size distribution of the contained particles is not specified, even if the particle size distribution is not the same, the distribution of the projections formed on the surface of the film is not uniform and the projection height is poor unless the particle size distribution is sharp. Uniform and uniform surface protrusions cannot be obtained, and the slipperiness is reduced.

Further, Japanese Patent Laid-Open No. 5-117421 discloses a technique in which the surface roughness of a PEN film is specified within a specific range. In such technique, for example, coating and drying of a magnetic layer in a tape processing step. At this time, the base film is subjected to a high tension load at a high temperature, so that the base film may be stretched at this time, causing waviness and causing coating unevenness of the magnetic layer.

As described above, according to the prior art, there is sufficient demand as a base film for a magnetic recording medium which has a small change in size in the longitudinal direction, high strength, excellent flatness, long-time recording, and high-density recording. We could not find a satisfactory polyester film.

[0011]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above drawbacks and to provide a high density magnetic recording tape with high strength and excellent durability, and excellent thermal dimensional stability and flatness. An object is to provide a biaxially oriented PEN film for a magnetic recording medium.

[0012]

The present invention has the following constitution in order to achieve the above object.

Young's modulus [EM] in the longitudinal direction is 800 kg / mm
² or more, Young's modulus in the lateral direction [ET] is 500 kg / mm ² or more, Young's modulus in the longitudinal direction is larger than Young's modulus in the lateral direction, and elongation in the longitudinal direction per load of 1 kg / mm ^{2 at} 120 ° C. Is in the range of 0 to 0.6%, a biaxially oriented polyethylene-2,6-naphthalate film.

In the present invention, the polyethylene-2,6-naphthalate constituting the film has 2,6-naphthalenedicarboxylic acid as a main acid component, but a small amount of another dicarboxylic acid component may be copolymerized, Although ethylene glycol is the main glycol component, a small amount of another glycol component may be copolymerized. Examples of dicarboxylic acid components other than 2,6-naphthalenedicarboxylic acid include isomers of 2,6-naphthalenedicarboxylic acid such as terephthalic acid, isophthalic acid, diphenylsulfone dicarboxylic acid, benzophenone dicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. Aromatic dicarboxylic acids such as; aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid; hexahydroterephthalic acid, 1,3-
Alicyclic dicarboxylic acids such as adamantane dicarboxylic acid may be mentioned. Examples of glycol components other than ethylene glycol include 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, Diethylene glycol etc. can be mentioned. Further, the polymer may be mixed with additives such as a stabilizer and a colorant.

Such a PEN polymer is usually produced by a known method by a melt polymerization method. At this time, additives such as catalysts can be optionally used as required. P
The intrinsic viscosity of EN is preferably in the range of 0.45 to 0.90.

The PEN film of the present invention has a longitudinal elongation of 0 to 120 ° C. per load of 1 kg / mm ^2.
It is necessary to be in the range of 0.6%, preferably 0.
To 0.5%, more preferably 0 to 0.4%
Is the range. When the elongation percentage exceeds 0.6%, the base film is stretched during application and drying of the magnetic coating material in the tape processing step, causing waviness of the film and uneven coating of the magnetic layer.

In order to obtain a film having an elongation in the machine direction of the present invention, it is necessary to select conditions including means for increasing Young's modulus in the process of producing a biaxially oriented PEN film, and it is necessary to select a harsh temperature. It is also preferable to consider means for reducing the shrinkage in the vertical direction under the conditions. For example, making the stretching ratio in the longitudinal direction larger than that in the lateral direction, selecting heat setting conditions suitable for keeping the elongation low,
Further, if necessary, it is preferable to adjust the thermal relaxation conditions for reducing the thermal contraction. That is, since the elongation percentage in the machine direction of the present invention largely changes depending on the draw ratio and the heat setting temperature, the draw ratio and the heat setting temperature may be changed in advance within an appropriate condition range for obtaining the Young's modulus in the machine direction of the present invention. The elongation in the machine direction of the obtained film is measured at the same time as the Young's modulus in the machine direction, and the optimum stretching ratio and heat setting temperature are selected while comparing the measured values. Furthermore, the PEN film of the present invention can be obtained by selecting the conditions in which the shrinkage rate is set to a preferable range by thermal relaxation and the Young's modulus decrease due to thermal relaxation does not deviate from the longitudinal Young's modulus range of the present invention.

The PEN film of the present invention is required to have a Young's modulus [EM] in the machine direction of 800 kg / mm ² or more, preferably 900 kg / mm ² or more, more preferably 1000 kg / mm ² or more. Is. In the case of a film having a longitudinal Young's modulus of less than 800 kg / mm ² , the Young's modulus as a tape is particularly high in a magnetic tape for long-time recording / reproducing with a base film thickness of 12 μm or less and a tape thickness of 16 μm or less. Is not enough, the tape edge is bent or the tape is extended due to repeated running of the tape, the pressing of the tape against the magnetic head is weakened, the electromagnetic conversion characteristics deteriorate, and the magnetic recording tape is no longer high density and high sensitivity. Cannot be obtained, which is not preferable.

On the other hand, the lateral Young's modulus [ET] is 500.
It is necessary to be kg / mm ² or more, preferably 5
It is 50 kg / mm ² or more, more preferably 600 kg / mm ² or more. This makes it possible to prevent damage to the end surface of the tape when the tape is running. Lateral Young's modulus is 50
If it is less than 0 kg / mm ² , even if a high-strength magnetic binder is used, the tape edge may be deformed into a wakame shape during running of the tape and damage to the tape end face cannot be prevented.

As a means for obtaining such Young's modulus,
It may be stretched simultaneously in the machine and transverse directions using a general roll or a stenter, or may be stretched in the machine direction and in the transverse direction.
Further, the number of stretching in the longitudinal and lateral directions may be once in each of the longitudinal direction and the lateral direction, and may be stretched more times in the longitudinal direction and / or the lateral direction, and is not limited to that number.

For example, when stretching in two stages, PEN is added to Tm.
~ (Tm + 70 ° C) (however, Tm: melting point of PEN) is melt-extruded to obtain an unstretched film having an intrinsic viscosity of 0.45 to 0.9 dl / g, and the unstretched film is uniaxially (longitudinal or transverse). Direction) from (Tg-10) to (Tg + 70) ° C
At the temperature of 2 (Tg: glass transition temperature of PEN).
Stretching at a draw ratio of 5 to 7.0 times, and then Tg (° C.) to (Tg + 70) ° C. in a direction perpendicular to the stretching direction (in the case where the first stage stretching is the longitudinal direction, the second stage stretching is the transverse direction). Stretching at a temperature of 1 to 2.5 to 7.0 times. In this case, the area draw ratio is preferably 15 to 35 times, more preferably 20 to 35 times.

When the film is further stretched in three stages or more, the heat setting temperature of the above-mentioned two-stage stretched film is (Tg + 2).
0) to (Tg + 70) ° C., heat-set, further stretched longitudinally or transversely at a temperature 10 to 40 ° C. higher than the heat-setting temperature, and then further transversely or longitudinally at a temperature 20 to 50 ° C. higher than this temperature. Stretching, the total stretching ratio in the machine direction is 5.0
〜10.0 times, the total stretch ratio in the transverse direction is 4.0 to 8.0.
It is preferably doubled. In this case, the area stretch ratio is 2
It is preferably 0 to 50 times, more preferably 25 to 45 times.

The PEN film of the present invention preferably has a heat shrinkage ratio of 0.1% or less in the longitudinal direction of the base film when it is heat-treated at 70 ° C. for 1 hour under no load.
08% or less is more preferable, and 0.05% or less is particularly preferable. If the heat shrinkage ratio is larger than 0.1%, thermal irreversible change occurs even after being made into a magnetic tape, and if the recording and reproducing temperatures are different in the VTR, skew distortion may occur on the screen, which is not preferable. . Further, when the heat shrinkage rate is large, an offset effect of the base film surface onto the magnetic surface occurs, and the surface roughness of the magnetic surface tends to become rough.

As a means for lowering the heat shrinkage rate, it is common to raise the heat treatment temperature after stretching, but if it is raised too much, the mechanical properties will deteriorate, and scratches during the magnetic tape processing step will result. The amount of dust generated increases and the shavings adhere to the magnetic surface of the magnetic tape, causing dropout. Therefore, the heat shrinkage rate is reduced by heating the film after heat treatment under low tension and relaxing it in the longitudinal direction. As a method of relaxing in the longitudinal direction, for example, a method of relaxing in a non-contact state under heating low tension by a floating treatment method by aerodynamic force, a method of relaxing by giving a speed difference between a heating roll and a cooling roll each having a nip roll. ,
Alternatively, there is a method of loosening in the longitudinal direction by gradually slowing down the moving speed of the clip holding the film in the tenter, but any method can be used as long as it can loosen in the longitudinal direction.

In either method, the biaxially oriented film can be heat-set at a temperature of (Tg + 70) ° C. to Tm (° C.) after the stretching operation. For example, heat setting at 190 to 250 ° C. is preferable, and heat setting time is, for example, 1 to 60.
Seconds. Further, heat relaxation gives a film having the preferred shrinkage ratio of the present invention.

The height and the number of protrusions formed on the surface of the base film for a magnetic tape are within a specific range, and the winding properties of the base film, the running property when used as a magnetic tape, and the electromagnetic conversion properties are excellent. It was revealed. In the present invention, the protrusion height [h (unit: n
m)] is the number of expressions (1) below.

[0027]

[Equation 2]

It is preferably in the range shown by. More preferably, the following formula (1-2)

[0029]

[Equation 3]

Within the range indicated by, and particularly preferably,
Formula (1-3) below

[0031]

[Equation 4]

Those satisfying the above range have good handleability of the base film, and are excellent in runnability and electromagnetic conversion characteristics when used as a magnetic tape. Projection height h of projection (unit n
m), the number of 1 ≦ h <50 is 10000 / mm
^{If it} exceeds ^{2, the} film will be scraped off by the roll during the calendar process when it is used as a magnetic tape. The number of protrusions whose protrusion height is 50 ≦ h <100 is 200 /
If it exceeds mm ² , the electromagnetic conversion characteristics of a magnetic tape will be deteriorated. The number of 100 ≦ h <150 is 1
When the number exceeds 00 pieces / mm ² , the tape running property is good, but the electromagnetic conversion characteristics are deteriorated and dropout occurs. Further, when the protrusions with 150 ≦ h are present, the frequency with which the coarse protrusions are present is increased, so that the electromagnetic conversion characteristics are significantly deteriorated and the dropout frequently occurs. Further, the coarse protrusions of 150 ≦ h cause the protrusions to be scraped when the tape is running, which promotes the occurrence of dropout. The number of 1 ≦ h <50 is 1000 / m
If it is less than m ² , and the number of 50 ≦ h <100 is less than 10 / mm ² and the number of 100 ≦ h <150 is less than 10 / mm ² , the coefficient of friction becomes large and the film is handled. And very difficult to wind up on a roll. Further, the running property of the tape is also poor. Here, the number of protrusions having a protrusion height h <1 is not particularly limited.

In order to obtain a film having the above-mentioned film surface characteristics, for example, several kinds of inert solid fine particles having different particle size distributions are added to PEN. The inert solid fine particles are preferably (1) silicon dioxide (including hydrate, diatomaceous earth, silica sand, quartz, etc.); (2) alumina; (3) silica containing 30% by weight or more of SiO ₂ component. Acid salts (for example, amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrates), hot asbestos, zircon, fly ash, etc.); (4)
Oxides of Mg, Zn, Zr, and Ti; (5) Sulfides of Ca and Ba; (6) Phosphates of Li, Na, and Ca (including monohydrogen salt and dihydrogen salt); (7) Benzoates of Li, Na, and K; (8) Ca, Ba, Zn, and Mn
Terephthalate; (9) Mg, Ca, Ba, Zn, C
Titanates of d, Pb, Sr, Mn, Fe, Co, and Ni; (10) Chromates of Ba and Pb; (11)
Carbon (eg carbon black, graphite, etc.);
(12) glass (for example, glass powder, glass beads, etc.);
(13) Ca and Mg carbonates; (14) Fluorite;
Examples are (15) ZnS and (16) fine particles made of a polymer having high heat resistance such as silicone resin and crosslinked polystyrene. More preferably, silicon dioxide, silicic anhydride, hydrous silicic acid, aluminum oxide, aluminum silicate (including calcined products, hydrates, etc.), 1 lithium phosphate, 3 lithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, Titanium oxide, lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay etc.), talc, diatomaceous earth, calcium carbonate, silicone resin, cross-linked polystyrene, etc. The fine particles of Particularly preferred are silicon dioxide, titanium oxide, calcium carbonate, fine particles of silicone resin, fine particles of crosslinked polystyrene and the like, and these are contained alone or in a combination of a plurality of them in the film.

When the above-mentioned inert solid fine particles are added to PEN, they may be added before the polymerization of PEN, during the polymerization reaction, or when they are pelletized after the completion of the polymerization, they may be kneaded in an extruder. It may be added when melt-extruding into a sheet and dispersed in an extruder and extruded,
From the viewpoint of dispersibility, it is preferable to add it before the polymerization. However, the method for obtaining a film having the film surface characteristics of the present invention is not limited to the method of adding inactive solid fine particles to PEN, but a phosphorus component or other necessary additives are added during polymerization to form a particle source. It is preferable to use a method of allowing it to be present in the film, and a method of blending a polymer obtained by adding a phosphorus component at the time of polymerization and a polymer obtained by adding inert solid fine particles.

As means for adjusting the surface properties of the film of the present invention, a film containing no inert fine particles is
Alternatively, it can be prepared on the film containing the inert fine particles by another surface treatment such as coating treatment.

In the PEN film of the present invention, it is preferable that the plane orientation coefficient [NS] and the average refractive index [nA] satisfy the following equations (2) and (3).

[0037]

[Equation 5]

Here, the surface orientation coefficient [NS] is obtained by the following equation (A), and the average refractive index [nA] is obtained by the following equation (B).

[0039]

[Equation 6]

Nx represents the refractive index in the machine direction of the biaxial film, ny represents the refractive index in the direction orthogonal to the machine direction,
nz represents the refractive index in the film thickness direction.

The expression (2) is more preferably the following (2)
-2) formula

[0042]

[Equation 7]

Within the range indicated by, and particularly preferably,
The following formula (2-3)

[0044]

[Equation 8]

Those satisfying the range of (3) and the range of the formula (3) at the same time have sufficient rigidity of the base film, have a higher degree of orientation in the longitudinal direction than in the lateral direction, and have thickness unevenness. Since a uniform magnetic layer that enables high-density magnetic recording in magnetic processing is obtained, a magnetic recording medium having stable output and good followability with a magnetic head when used as a magnetic tape can be obtained. .

The orientation coefficient [NS] and the average refractive index [nA] do not satisfy the above equation (2), and the following equation (4) is obtained.

[0047]

[Equation 9]

In the case of the range, the Young's modulus becomes low in both the vertical and horizontal directions, the magnetic tape is apt to stretch and edge damage during running of the magnetic tape, and it is difficult to maintain contact with the magnetic head under a certain condition. Playback mistakes are likely to occur. Furthermore, since the flatness such as unevenness in thickness and sagging of the film is poor, unevenness in the magnetic layer or loss of magnetic field is likely to occur, and output fluctuation is likely to occur during reproduction. Also, the heat deterioration resistance is poor.

The upper limit of the orientation coefficient [NS] is within the range in which a PEN film can be produced, but if NS is larger than 0.28, longitudinal tearing may occur in the film, which is not preferable.

When the average refractive index is nA> 1.665,
Since the strength and Young's modulus in the vertical direction tend to be insufficient, when the magnetic tape is used, the head touch between the tape and the magnetic head is poor and a recording error or a reproducing error may occur. When the average refractive index is nA <1.658, the mechanical properties such as the strength and Young's modulus in one or both of the longitudinal direction and the lateral direction may be insufficient, and the tape may not elongate when formed into a magnetic tape. Edge damage is likely to occur and recording / reproducing errors are likely to occur. In particular, a polyethylene terephthalate film falls into this region, resulting in poor balance of longitudinal and transverse mechanical properties and poor heat-resistant dimensional stability.

The PEN film of the present invention is not particularly limited in its thickness, but a thickness of 12 μm or less is preferable, and it is particularly used for 8 mm video tapes or DCC tapes for long-time recording / reproduction of 180 minutes or more. If it is, the thickness is preferably 6 μm or less. The lower limit of the thickness is 3 from the stiffness of the film.
μm is preferred.

[0052]

EXAMPLES The present invention will be further described below with reference to examples. Incidentally, various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Number of surface protrusions Non-contact three-dimensional roughness meter (TOPO-3D) manufactured by WYKO
Measurement magnification of 40 times, measurement area of 242 μm × 239
The measurement was performed under the condition of μm (0.058 mm ² ). A histogram diagram of the height of surface protrusions and the number of protrusions from the average roughness of the film surface was obtained by the protrusion analysis, and the number in each specific protrusion height range was read from the histogram diagram, and the number of protrusions measured 5 times on the same film surface was calculated. Accumulate, unit area (1
It was converted to the number of protrusions per mm ² ).

(2) Young's modulus The film was cut into a sample width of 10 mm and a length of 15 mm, the chuck space was set to 100 mm, the tensile speed was 10 mm / min, and the chart speed was 5
The Young's modulus was calculated from the tangent line of the rising portion of the obtained load-elongation curve by pulling at 00 mm / min with an Instron type universal tensile tester.

(3) Refractive Index The refractive index was measured using an Abbe refractometer with sodium D line (589 nm) as a light source. At the same time Kanzaki Paper Co., Ltd.
The degree of orientation was measured using a molecular orientation meter (MOA-2001A) manufactured by K.K., and a large refractive index that cannot be measured by the Abbe refractometer was determined from the correlation graph of the degree of orientation and the refractive index. .

(4) Film elongation rate Using TMA (TM-3000L) manufactured by Vacuum Riko Co., Ltd., a sample having a film width of 5 mm and a length of 15 mm, load conditions: 0 g (no load), 25 g, 50 g, 75g, 10
20 g at each heating rate of 5 ° C./min under each condition of 0 g
Temperature rises from ℃ to 150 ℃, 120 ℃ for each load
The expansion / contraction ratio in Table 1 was read from the chart, and a correlation graph between the expansion / contraction ratio and the load per film cross-sectional area (kg / mm ² ) was prepared, and the expansion ratio (%) per 1 kg / mm ² was obtained from the graph.

(5) Electromagnetic conversion characteristics Using a noise meter manufactured by Shibasoku Co., Ltd., the S / N ratio of the magnetic tape for video was measured. Further, the difference in S / N ratio with respect to the tape of Comparative Example 3 shown in Table 1 was obtained. The VTR used is EV-S700 manufactured by Sony Corporation.

(6) Running durability of magnetic tape An EV-S700 manufactured by Sony Corporation was run for 100 hours while repeatedly starting and stopping running, and the running state was checked and the output was measured. The running durability of the magnetic tape at this time was determined as follows. <Three-stage judgment> ○ The tape is not stretched, the edge of the tape is broken, or it does not become wakame. There is no output fluctuation. Fairly, the tape was slightly stretched, the edge of the tape was broken, and seaweed was generated, and the output was slightly changed. × Tape stretches, breaks, and wakame are noticeable. In addition, the running of the tape becomes unstable and the output fluctuation is very large.

(7) Heat shrinkage rate A film having a length of about 30 cm and a width of 1 cm measured in advance in an oven set at 70 ° C. was placed without load and heat-treated for 1 hour, and then from the oven. The sample was removed and allowed to come to room temperature before reading its dimensional changes. From the length (L0) before heat treatment and the amount of dimensional change (ΔL) due to heat treatment, the heat shrinkage rate (%) was determined by the following equation (5).

[0060]

[Equation 10]

(8) Skew The skew characteristic is that the video tape recorded at room temperature (20 ° C.) and normal humidity is heat-treated at 70 ° C. for 1 hour and then reproduced again at room temperature and normal humidity to read the shift amount at the head switching point. It was

(9) Average Particle Size of Inert Particles CP-50 type Centrifuge particle size analyzer (Centrifugal Particle S) manufactured by Shimadzu Corporation
ize Analyzer). From the cumulative curve of particles of each particle size calculated based on the obtained centrifugal sedimentation curve and its abundance, the particle size corresponding to 50 mass percent is read, and this value is taken as the above average particle size. did.

[Example 1] 0.25 wt% of spherical silica particles having an average particle size of 0.2 μm and 0.03 wt% of calcium carbonate particles having an average particle size of 0.5 μm were contained, and an intrinsic viscosity of 0.1.
A PEN pellet of 62 dl / g (value measured at 25 ° C. using orthochlorophenol as a solvent) was 170 ° C.
After being melted and extruded at 300 ° C, it is rapidly cooled and solidified on a casting drum kept at 60 ° C to have a thickness of about 17
An unstretched film of 0 μm was obtained.

This unstretched film was sequentially biaxially stretched in the machine direction at 130 ° C. for 5.6 times, then in the transverse direction at 135 ° C. for 3.8 times, and further heat set at 215 ° C. Next, this heat-fixed film was heated to 110 ° C. with a heating roll and then subjected to relaxation treatment by adjusting tension with a cooling roll so that the shrinkage rate in the longitudinal direction was adjusted to 0.05%. The thickness of the obtained biaxially oriented PEN film was 8 μm.

On the other hand, the composition shown below was put in a ball mill, kneaded and dispersed for 16 hours, and then 5 parts by weight of an isocyanate compound (Desmodur L manufactured by Bayer) was added,
High-speed shear dispersion was carried out for 1 hour to obtain a magnetic paint.

Composition of magnetic paint: Needle-like Fe particles 100 parts by weight Vinyl chloride-vinyl acetate copolymer (Eslek 7A manufactured by Sekisui Chemical Co., Ltd.) 15 parts by weight Thermoplastic polyurethane resin 5 parts by weight Chromium oxide 5 parts by weight Carbon black 5 parts by weight Lecithin 2 parts by weight Fatty acid ester 1 part by weight Toluene 50 parts by weight Methyl ethyl ketone 50 parts by weight Cyclohexanone 50 parts by weight This magnetic paint is applied to one side of the above-mentioned biaxially oriented PEN film so that the application thickness is 3 μm, and then 2500
Alignment treatment is performed in a Gaussian DC magnetic field, and after heating and drying at 100 ° C, super calender treatment (linear pressure 200 kg / c
m, temperature 80 degrees) and wound up. The wound roll was left in an oven at 55 ° C for 3 days.

Further, a back coat layer coating material having the following composition was applied to a thickness of 1 μm, dried, and further cut into a width of 8 mm,
I got a magnetic tape.

Composition of coating for back coat layer Carbon black 100 parts by weight Thermoplastic polyurethane resin 60 parts by weight Isocyanate compound (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) 18 parts by weight Silicone oil 0.5 parts by weight Methyl ethyl ketone 250 parts by weight Toluene 50 parts by weight

The characteristics of the obtained film and tape are shown in Table 1.
Shown in. As is clear from this table, the film of the present invention has no problem in processability, is excellent in heat-resistant dimensional stability, has a high Young's modulus in the longitudinal direction, has good electromagnetic conversion characteristics, running durability, and skew, and has a high temperature atmosphere. The use of was also good.

[Example 2] An unstretched film was obtained in the same manner as in Example 1, and the unstretched film was stretched 2.3 times in the machine direction at 130 ° C and then 3.9 times in the transverse direction at 130 ° C. It was stretched and subsequently subjected to intermediate heat treatment at 160 ° C. This film was further stretched 2.6 times in the longitudinal direction at 170 ° C. and 1.3 times in the transverse direction and heat-treated at 215 ° C. Then, in the same manner as in Example 1, the heat shrinkage ratio in the longitudinal direction was adjusted to 0.04%. Thus, a biaxially oriented film having a thickness of 8 μm was obtained. Then, a tape was obtained in the same manner as in Example 1. The results are shown in Table 1. Good results were obtained as in Example 1.

Example 3 An unstretched film was obtained in the same manner as in Example 1, and the unstretched film was stretched 2.5 times in the longitudinal direction at 130 ° C. and then 3.9 times in the transverse direction at 130 ° C. It was stretched and subsequently subjected to intermediate heat treatment at 160 ° C. This film was further stretched 2.8 times in the longitudinal direction at 170 ° C. and 1.2 times in the lateral direction and heat-treated at 215 ° C. Then, in the same manner as in Example 1, the heat shrinkage ratio in the longitudinal direction was adjusted to 0.05%. Thus, a biaxially oriented film having a thickness of 8 μm was obtained, and a tape was obtained in the same manner as in Example 1. The results are shown in Table 1. Good results were obtained as in Example 1.

[Comparative Example 1] An unstretched film was obtained in the same manner as in Example 1, and the unstretched film was stretched 3.5 times at 130 ° C in the longitudinal direction and subsequently 3.5 times at 135 ° C in the transverse direction. Then, biaxial stretching was sequentially performed, and heat setting was further performed at 215 ° C. Then, in the same manner as in Example 1, the heat shrinkage ratio in the longitudinal direction was set to 0.0.
Adjusted to 5%. Thus, a biaxially oriented film having a thickness of 8 μm was obtained, and a tape was obtained in the same manner as in Example 1. The results are shown in Table 1, which was 1 kg / m at 120 ° C.
Since the film elongation rate per m ² is large, the base film is stretched and wavy in the tape processing process,
Coating unevenness of the magnetic layer occurred. Furthermore, the average refractive index is high,
Moreover, since the Young's modulus in the vertical direction is low, the head touch on the magnetic head of the magnetic tape is poor and the electromagnetic conversion characteristics are considerably poor, resulting in recording errors and reproducing errors.

Comparative Example 2 PET containing the same two kinds of particles as in Example 1 and having an intrinsic viscosity of 0.65 dl / g (value measured at 25 ° C. using orthochlorophenol as a solvent)
The pellets were dried at 160 ° C., melt-extruded at 280 ° C., and rapidly solidified on a casting drum kept at 40 ° C. to obtain an unstretched film having a thickness of about 110 μm. This unstretched film was stretched 1.8 times in the machine direction between two rolls having a speed difference, further stretched 3.1 times in the cross direction by a tenter, and subsequently subjected to intermediate heat treatment at 150 ° C. This film was further stretched in the longitudinal direction at 155 ° C by 3.6 times, and heat-set at 230 ° C. Then, this heat-set biaxially oriented PET film was heated with a heating roll to 9
After heating to 0 ° C., the tension between the cooling roll and the cooling roll is adjusted to reduce the heat shrinkage in the longitudinal direction, and the thickness is 8 μm.
A biaxially oriented PET film of m was obtained. Then, Example 1
A tape was obtained in the same manner as. The results are shown in Table 1, but the heat shrinkage rate was high and the skew was remarkably bad because it was a PET material, although the heat shrinkage rate was reduced by the relaxation heat treatment. Further, by increasing the stretching ratio in the machine direction, a film having a high Young's modulus in the machine direction of the present invention was obtained, but the Young's modulus in the machine direction could not be increased in the machine direction and the Young's modulus in the machine direction was considerably low. Edge damage occurs when running the tape, and running durability is poor. Further, since the elongation in the longitudinal direction per load of 1 kg / mm ^{2 at} 120 ° C. is very large, waviness due to the elongation of the film occurred in the tape processing step, and coating unevenness of the magnetic layer occurred. Therefore, the electromagnetic conversion characteristics are also extremely poor. From this, the PET material is inferior in total balance as compared with PEN.

Comparative Example 3 An unstretched film was obtained in the same manner as in Example 1, and the unstretched film was stretched 2.2 times in the machine direction at 130 ° C. and then 3.9 times in the transverse direction at 130 ° C. It was stretched and subsequently subjected to intermediate heat treatment at 160 ° C. This film was further stretched in the machine direction at 170 ° C by 2.2 times and in the transverse direction by 1.8 times, heat-treated at 215 ° C, and then subjected to a relaxation treatment for reducing the heat shrinkage ratio in the machine direction of Example 1. Without carrying out, a 7 μm thick biaxially oriented film and tape were obtained.
The results are shown in Table 1, and the skew was remarkably bad because the heat shrinkage rate was particularly high. Further, since the elongation in the longitudinal direction per load of 1 kg / mm ^{2 at} 120 ° C. was slightly large, there were coating spots on the magnetic layer, and therefore the electromagnetic conversion characteristics were also poor. Further, since the Young's modulus in the longitudinal direction is low and the average refractive index is out of the range of the formula (3) and is high, the head touch is bad and a recording / reproducing error occurs.

[0075]

[Table 1]

[0076]

The magnetic recording tape using the polyethylene-2,6-naphthalate film of the present invention does not cause tape elongation or edge breakage that occurs during running, so that the tape is compatible with the magnetic head (head touch). ) Is good, the electromagnetic conversion characteristics required for high density magnetic recording are obtained, and the heat-resistant dimensional stability is good, so there is little skew distortion, and it is particularly useful as a base film for high-density magnetic recording tapes that can be recorded for a long time.

Claims (3)

[Claims] 1. Young's modulus [EM] in the longitudinal direction is 800 kg /
mm ² or more, lateral Young's modulus [ET] is 500 kg / mm ²
Above, the Young's modulus in the machine direction is larger than the Young's modulus in the machine direction, and the elongation rate in the machine direction per load 1 kg / mm ^{2 at} 120 ° C. is in the range of 0 to 0.6%. -2,6-naphthalate film. 2. The biaxially oriented polyethylene-2,6-naphthalate film according to claim 1, which has a longitudinal thermal shrinkage of 0.1% or less when heat-treated at 70 ° C. for 1 hour without load. 3. The height h of the protrusions formed on the film surface
The biaxially oriented polyethylene- according to claim 1 or 2, wherein the number of (unit: nm) is in the range represented by the following formula (1).
2,6-naphthalate film. [Equation 1]