JP2001031778A - Polyester film for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film for magnetic recording medium which excels in handling properties and in output after storage and repeated running and, simultaneously, can prevent occurrence of damage to tape edge. SOLUTION: The polyester film for magnetic recording medium has a Young' s modulus in the lengthwise and width directions of not higher than 5.0 GPa and not lower than 8.0 GPa, respectively, a surface roughness of the side (A-side) to be provided with a magnetic layer, measured by a non-contact type three- dimensional surface roughness tester at a megnification of 2.5 times and 25 times, of 0.5-3.0 nm and 0.3-1.5 nm, respectively, and at the same time, a surface roughness of the non-magnetic layer side (B-side), measured by the same roughness tester at a magnification of 2.5 times and 25 times, of 2.0-5.0 and 0.6-2.5 nm, respectively, and, in addition, a heat shrinkage both in the lenghtwise and width directions of the film, measured at 105 deg.C for 30 min, of 0.0-1.5% and 0.5-3.5%, respectively, and, at the same time, a heat shrinkage both in the lengthwise and width directions of the film, measured at 150 deg.C for 30 min, of 2.0-5.0% and 6.0-11.0%, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium, and more particularly to a base film of a ferromagnetic metal thin film type magnetic recording medium for recording digital data such as digital video cassette tapes and data storage tapes for a long time and in large quantities. It relates to a suitable polyester film.

[0002]

2. Description of the Related Art A consumer digital video tape (DVC tape) put into practical use in 1995 has a base film of Hi8M in order to have a magnetic force more than that of Hi8ME tape.
A base film that is even smoother than the base film for E tape is used, and a Co metal magnetic thin film is provided on the base film instead of a Co / Ni alloy metal, and diamond is used on the surface to provide good running durability. A carbon film is provided.

The base film comprises, for example, a polyester film, a polymer blend adhered to at least one surface of the film, and a discontinuous film mainly composed of fine particles having a particle size of 50 to 500 Å. The film contains a water-soluble polyester copolymer, and a polyester film in which fine projections are formed on a discontinuous film by fine particles (for example, JP-B-63-57).
No. 238) and the like, and the surface roughness of the metal magnetic film formation surface is further reduced as compared with the base film for Hi8ME tape. Also, the thickness of the base film is 7μ.
A thickness of less than m is required.

[0004] However, such a very thin and smooth base film is difficult to handle in a film forming process and a vapor deposition process, and the produced magnetic tape has an excellent initial output even after being stored for a long period of time. The output and the output after repeated running tend to decrease. Further, when a conventional base film is used as a base for a video tape for long-time recording, the edge of the tape is damaged at the time of recording and reproduction, and the flatness of the tape tends to be poor.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a magnetic recording medium which is excellent in handleability, has excellent output after storage and repeated running when formed into a magnetic tape, and prevents edge damage of the tape. It is intended to provide a polyester film.

[0006]

According to the present invention, there is provided a polyester film having a Young's modulus in the longitudinal direction of 5.0 GPa or less and a Young's modulus in the width direction of 8.0 GPa.
a, the surface roughness WRa (2.5) A of the surface on the side on which the magnetic layer is provided (side A) measured at a magnification of 2.5 using a non-contact type three-dimensional surface roughness meter is 0.5 to 0.5. The surface roughness WRa (25) A measured at 3.0 nm and 25 times magnification is 0.3 to
1.5 nm and the surface (B side) on the non-magnetic layer side,
The surface roughness WRa (2.5) B measured at a magnification of 2.5 using the surface roughness meter is 2.0 to 5.0 nm, and the magnification is 25.
Surface roughness WRa (25) B measured by a factor of 0.6 to 2.5
nm, and the heat shrinkage at 105 ° C. for 30 minutes is 0.0-1.5% in the longitudinal direction of the film and 0.5-1.5 in the width direction.
3.0%, and the heat shrinkage at 150 ° C. for 30 minutes is 2.0 to 5.0% in the longitudinal direction of the film and 6.0 to 6.0 in the width direction.
It is achieved by a polyester film for a magnetic recording medium, which is 11.0%.

The polyester film for a magnetic recording medium preferably has a film thickness of 2 μm or more and less than 7 μm, and / or wherein the polyester is polyethylene terephthalate or polyethylene-2,6-naphthalenedicarboxylate. As

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As the polyester in the present invention, an aromatic polyester which forms a high-strength film by molecular orientation is preferable, and polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are more preferable. The polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are particularly preferably homopoly, but are copolymers in which the third component is copolymerized in an amount of 20% or less, preferably 10% or less of the constituent components. May be. As the third component, for example, diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, 1,4-cyclohexanedimethanol, adipic acid,
Dicarboxylic acid components such as sebacic acid, phthalic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid; polyfunctional carboxylic acid components such as trimellitic acid and pyromellitic acid;
p-oxyethoxybenzoic acid and the like.

Further, the above-mentioned polyesters may contain a film-forming property improver (for example, an alkali metal salt compound, a quaternary phosphonium salt compound of sulfonic acid, etc.), a heat stabilizer (for example, phosphoric acid, phosphorous acid, derivatives thereof, etc.). ), An antioxidant (for example, a hindered phenol compound, etc.) and other additives can be contained as needed within a range not to impair the purpose of the present invention.

The intrinsic viscosity of the polyester (orthochlorophenol, 25 ° C., using an Oswald viscometer) is preferably 0.4 to 0.9.

[0011] The polyester film of the present invention comprises:
The Young's modulus in the longitudinal direction is 5.0 GPa or less, preferably 4.8 GPa or less, and the Young's modulus in the width direction is 8.0 GPa.
As described above, it preferably has a characteristic of 9.0 GPa or more. The Young's modulus in the longitudinal direction is preferably 3 GPa or more, and the Young's modulus in the width direction is 18 GPa.
It is preferable that it is not more than a. If the Young's modulus in the longitudinal direction exceeds 5.0 GPa, when a digital magnetic tape is used, the sound of the rotating head of the digital video recorder striking the tape undesirably resonates. On the other hand, if the Young's modulus in the width direction is less than 8.0 GPa, the width strength of the magnetic tape is insufficient, and the tape is easily broken by guide pins that regulate the tape path when the tape runs, which is not preferable.

The polyester film of the present invention comprises:
Furthermore, the surface roughness WRa (2.5) A of the surface (side A) on which the magnetic layer is provided, measured at a magnification of 2.5 using a non-contact type three-dimensional surface roughness meter, is 0.5 to 3. 0 nm, preferably 0.5 to 2.0 nm, having a property that the surface roughness WRa (25) A measured at a magnification of 25 times is 0.3 to 1.5 nm, preferably 0.4 to 1.5 nm. . This WRa
(2.5) When both A and WRa (25) A are below the lower limit, the running durability of the magnetic tape is insufficient, and when the upper limit is exceeded, the output of the magnetic tape is insufficient, which is not preferable.

The polyester film according to the present invention comprises:
Further, the surface roughness WRa (2.5) B of the surface (side B) of the nonmagnetic layer side (side B) measured at a magnification of 2.5 using a non-contact type three-dimensional surface roughness meter is 2.0 to 2.0. Properties having a surface roughness WRa (25) B of 5.0 nm, preferably 2.5 to 4.0 nm, measured at 25 times magnification of 0.6 to 2.5 nm, preferably 0.8 to 2.0 nm. Having. This WRa
(2.5) When both B and WRa (25) B are below the lower limit, the coefficient of friction increases and the handleability of the film deteriorates. On the other hand, when the upper limit is exceeded, the roughness of the B side when the film is wound up on a roll. However, it is not preferable because set-off or shape transfer is performed on the A side to roughen the A side.

The surface roughness of the polyester film is as follows:
When a coating layer is provided on the film surface before the vapor deposition process, the surface roughness of the coating layer is WRa.
The value of (2.5) is hardly affected by the coating layer in this case as well, and is substantially the same as the surface roughness of the film background.

The polyester forming the surface (side A) of the polyester film on the side on which the magnetic layer is provided in the present invention has substantially no particles, or even if it does, has an average particle size of 30 to 150 nm, preferably 40 to 150 nm. It is desirable that the particles contain fine particles of 100 nm in an amount of 0.1% by weight or less, preferably 0.06% by weight or less. From the viewpoint of the durability of the magnetic layer, it is desirable to include the fine particles.

The surface A of the polyester film has an average particle size of 5 to 30 n for the purpose of improving lubricity.
m, preferably 8 to 30 nm of fine particles of 0.5 to 1
It is desirable that a coating layer composed of an organic compound containing 2.0% by weight, preferably 0.6 to 10.0% by weight is formed. The fine particles include silica, calcium carbonate,
Alumina, polyacrylic particles, and polystyrene particles can be preferably used. As the organic compound, a polar polymer such as a water-soluble (or water-dispersible) polyester, polyurethane, or acrylic resin, or a blend thereof can be preferably used. It is not limited to these. The thickness of this coating layer is preferably 1 to 30 nm.

The surface (B side) of the polyester film in the present invention on the nonmagnetic layer side is WRa (2.5) B
(2.5) It is preferably larger than A. There is no particular limitation on the method of roughening only the B-side in a wide area of 2.5 mm × 1.9 mm of WRa (2.5), but when forming a polyester film, casting the melt-extruded polyester with fine irregularities. It is preferable to use a method in which the solidified surface is cooled and solidified on the drum so that only the surface (surface B) in contact with the casting drum has irregularities. Also, W
An area like Ra (25) (246.6 μm × 187.
The method of roughening only the B side at 5 μm) is not particularly limited, but a method of providing a coating layer forming a rougher surface than the A side on the B side of the polyester film, a polyester film layer containing no fine particles (A side) Layer), a method of laminating a polyester film layer containing fine particles (layer B) on one side of the layer, and laminating two types of polyester film layers having different types, average particle diameters and / or contents of fine particles. A method and the like are exemplified.

The method of providing the coating layer may be performed according to the method of providing the coating layer on the A side. At this time, the average particle size is 1
5 to 40% by weight, more preferably 10 to 30% by weight of fine particles (for example, polyethylene particles, polyacrylic particles, silicone resin particles, calcium carbonate, silica, alumina, etc.) having a size of 0 to 200 nm, more preferably 20 to 100 nm , Or in combination or alone, a part of the binder resin (5 to 50% by weight, more preferably 10 to 4% by weight).
(0% by weight), it is preferable to roughen the surface by using a resin having poor spreadability (stretchability) such as polyvinyl alcohol, gelatin, cellulose, and a styrene copolymer containing a sulfonate group.

As the binder resin, conventionally known binder resins can be used, for example, water-soluble (or water-dispersible) polyester, polyurethane,
Acrylic resin and the like can be mentioned. The thickness of the coating layer is 3 to 50
nm, more preferably 5 to 30 nm.

As a method for laminating the polyester film layer, a co-extrusion method is preferably used. At that time, the thickness of the polyester film layer forming the side B is
Preferably, the thickness is 1/2 to 1/10 of the thickness of the entire film. Examples of the fine particles used in the polyester film layer forming the side B include calcium carbonate, silica, alumina, polystyrene particles, and silicone resin particles. The average particle size is preferably 80 to 8
00 nm, more preferably 100-700 nm,
The amount of addition is preferably 0.05 to 1.0% by weight, more preferably 0.08 to 0.8% by weight.

The polyester film of the present invention comprises:
Further, the heat shrinkage at 150 ° C. for 30 minutes is 2.0 in the longitudinal direction.
To 5.0% and 6.0 to 11.0% in the width direction. If the heat shrinkage is out of this range, a difference occurs in the amount of shrinkage between the magnetic thin film layer and the polyester film that has been heated during the evaporation when the evaporation tape is made, and the tape is curled and the head hits. It becomes bad and is not preferable.

The polyester film further comprises 10
5 ° C., heat contraction rate for 30 minutes is 0.01 to 1.5 in the longitudinal direction.
%, 0.5 to 3.0% in the width direction. If the heat shrinkage is out of this range, the magnetic tape undergoes dimensional change after storage at a high temperature, so-called track deviation occurs, and the output is undesirably reduced.

The thickness of the polyester film in the present invention is preferably 2 μm or more and less than 7 μm.

The polyester film in the present invention comprises:
It can be manufactured according to a conventionally known method or a method accumulated in the art. For example, using a known extruder, polyester is melted (Tm) from a die.
After extruding into a sheet at a temperature of
It is quenched and solidified at 0 to 90 ° C to obtain an unstretched film. Thereafter, the unstretched film is uniaxially (longitudinal or lateral) in a conventional manner at a temperature of (Tg-10) to (Tg + 70) ° C. (where Tg: glass transition temperature of the polyester) by 2.5. -4.5 times magnification, preferably 2.8
Stretching at a magnification of ~ 3.9 times, then applying a coating agent on one or both sides of the film, and drying or drying the coating to provide a predetermined coating layer, and then in a direction perpendicular to the above direction 4.5 times at Tg ~ (Tg + 70) ° C
The film is stretched at a magnification of 8.0 times, preferably at a ratio of 4.5 to 6.0 times, and then, if necessary, again stretched in the machine direction and / or the transverse direction to obtain a biaxially oriented film. That is, two-stage, three-stage, four-stage, or multi-stage stretching may be performed. The total stretching ratio is usually 12 times or more, preferably 12 to 32 times, more preferably 14 to 26 times as the area stretching ratio. Subsequently, the biaxially oriented film is (Tg + 70) ~
Excellent dimensional stability is provided by heat-setting crystallization at a temperature of (Tm-10) ° C, for example, 180 to 250 ° C. The heat fixing time is preferably 1 to 60 seconds. In this heat setting treatment, 3.0% or less in the vertical direction and / or the horizontal direction,
Further, it is preferable to adjust the heat shrinkage by relaxing at a rate of 0.5 to 2.0%.

In the above method, a coating layer is provided on one side or both sides of a single-layer film. However, when a polyester film layer containing fine particles is laminated instead of providing the coating layer on the B side of the film, coextrusion is carried out. The method is preferably used. In this co-extrusion method, the polyester forming the A side and the polyester forming the B side are laminated and co-extruded in a die, then rapidly cooled and solidified at 40 to 90 ° C. to obtain a laminated unstretched film. It is good to carry out similarly to the case of a film.

The polyester film of the present invention comprises:
It is necessary to have the above-mentioned characteristics before the metal deposition process is performed, but a ferromagnetic metal thin film layer formed by vacuum deposition is provided on the surface A (the coating layer if a coating layer is formed). . The metal thin film to be used may be a known thin film, and is not particularly limited, but is preferably made of a ferromagnetic material of iron, cobalt, nickel, or an alloy thereof.
It is desirable to coat a diamond-like carbon film having a thickness of about 10 nm on this metal thin film. The thickness of the metal thin film layer is 100 to 300 nm.

A back coat layer is provided on the B side of the polyester film by applying a solution composed of solid fine particles and a binder, if necessary, to which various additives are added, after the metal vapor deposition treatment. Can be
Known solid particles, binders and additives can be used,
There is no particular limitation. Backcoat layer thickness is 0.3 ~
It is about 1.5 μm.

The polyester film of the present invention is preferably used as a base film of a magnetic recording medium, particularly when used for a digital video tape for long-time recording since excellent results can be obtained. It is also preferable that excellent results can be obtained even when used for data storage tape applications.

The film properties and other properties used herein or in the examples are measured and defined in the following manner.

(1) Intrinsic viscosity of polyester The polyester is dissolved in orthochlorophenol and determined using an Oswald viscometer. Viscosity measurement temperature: 25 ° C.

(2) Film surface roughness WRa (2.5) Non-contact three-dimensional surface roughness meter (NT-20 manufactured by WYKO)
00), measuring magnification 2.5 times, measuring area 2.5 mm
Under the condition of × 1.9 mm (= 4.75 mm ² ), the roughness of the film surface (A surface, B surface) was measured with the number of measurements (n) of 10 or more, and the surface analysis incorporated in the roughness meter was performed. The center plane average roughness (WRa _(2.5) ) is obtained by software.

[0032]

(Equation 1)

Z _jk is the height on the two-dimensional roughness chart at the j-th and k-th positions in each direction when the measuring method (2.5 mm) and the method orthogonal thereto (1.9 mm) are divided into m and n, respectively. That's it.

WRa (25) Non-contact type three-dimensional surface roughness meter (manufactured by WYKO: NT-20)
00), measurement magnification 25 times, measurement area 246.6 μm
Under the condition of mx187.5 μm (= 0.0462 mm ² ), the film surface (A surface, B surface)
Surface), and the average roughness of the center plane (WRa ₍₂₅₎ ) is determined by surface analysis software built into the roughness meter.

[0035]

(Equation 2)

The Z _jk is divided into a measurement method (246.6 μm) and a method orthogonal thereto (187.5 μm) by dividing it into m parts, respectively.
This is the height on the two-dimensional roughness chart at the j-th and k-th positions in each direction when divided into n.

(3) Young's modulus of the film The film was cut into a sample having a width of 10 mm and a length of 15 cm, and the distance between the chucks was set to 100 mm. . The Young's modulus is calculated from the tangent at the rising portion of the obtained load-elongation curve.

(4) 105 ° C. and 150 ° C. of the film
Heat shrinkage rate for 30 minutes A sample having a width of 10 mm and a length of 30 cm is heat-treated for 30 minutes in an oven at each temperature, and the difference in length after heat shrinkage from the original length is divided by the original length, multiplied by 100, Heat shrinkage (%).

(5) Coefficient of friction of the film A fixed glass plate is placed under the two superposed films, and the film on the lower side of the superposed film (the film in contact with the glass) is rolled at a constant speed. (10 cm / min), and a detector is fixed to one end of the upper film (the side opposite to the direction in which the lower film is pulled) to detect the tension (F) between the films. The thread on the upper film used at that time is
The lower area is 50 cm ² (80 mm × 62.5 mm), the surface in contact with the film is 80 ° neoprene rubber, and its weight (W) is 1.2 kg. The coefficient of static friction is calculated by the following equation, and is evaluated based on the following criteria.

[0040]

Μs = F (g) / W (g) Evaluation criteria: ○: less than 0.4 Δ: 0.4 or more and less than 0.6 ×: 0.6 or more

(6) Output Characteristics of Magnetic Tape The output characteristics of a magnetic tape provided with a ferromagnetic thin film on a film are commercially available Hi8
Measurement is made using an 8 mm video tape recorder.
Using a video S / N ratio as an output characteristic, a signal is supplied from a TV test signal generator to an Hi8 system 8 mm video tape recorder, and a video noise meter is used to compare and measure a commercially available standard Hi8ME tape with zero decibel (dB).

The output immediately after the magnetic tape was manufactured was set as the initial output, and the output after storage at 60 ° C. for 10 days was output after storage.
The output after running 100 times repeatedly is defined as the output after running, and evaluated according to the following criteria. ：: +2 dB or more Δ: 0 to less than +2 dB ×: less than 0 dB

In the recording state, it is also observed whether or not the sound of the head hitting the tape resonates. ：: Without resonance ×: With resonance

[0044]

Next, the present invention will be further described with reference to examples.

Example 1 A pellet of polyethylene-2,6-naphthalenedicarboxylate (intrinsic viscosity: 0.6) containing substantially no inert particles was dried at 170 ° C. for 6 hours and then supplied to an extruder. And melted at 305 ° C. This molten polymer is filtered by a usual method, extruded from a die into a sheet, and is contacted with a drum on a casting drum having a surface crack of 60 ° C. with fine cracks formed thereon by using an electrostatic application casting method. The non-magnetic surface is B
It was wound so as to be on the surface side and solidified by cooling to prepare an unstretched film. Subsequently, the unstretched film is heated at 120 ° C.
2. Preheat in the longitudinal direction by heating with a 900 ° C IR heater 15 mm above between low-speed and high-speed rolls.
It is stretched 7 times, and then an aqueous solution (coating agent) having the following composition
Was applied to each film.

Coating agent on side A: Copolymerized polyester (terephthalic acid / isophthalic acid /
5-sodium sulfoisophthalic acid // ethylene glycol / propion oxide 2 mol adduct of bisphenol A = 97/1/2 // 60/40) 80 parts by weight ・ Acrylic resin particles (average particle diameter 20 nm) 5 parts by weight ・ Japan 15 parts by weight of nonionic NS-240 made of oil and fat ・ Solid concentration: 1.0 wt% ・ Thickness of coating layer (after drying): 6 nm

Coating agent on side B: Copolyester (terephthalic acid / isophthalic acid /
5-sodium sulfoisophthalic acid // ethylene glycol / propion oxide 2 mol adduct of bisphenol A = 97/1/2 // 60/40) 60 parts by weight Silica particles (average particle size 60 nm) 10 parts by weight Hydroxypropyl Methylcellulose; 20 parts by weight ・ Nonion NS-208.5 10 parts by weight made by NOF Corporation ・ Sodium concentration: 2.5 wt% ・ Thickness of coating layer (after drying): 15 nm

Subsequently, the mixture was supplied to a stenter, stretched 4.9 times in the transverse direction at 150 ° C., and further heat-treated at 200 ° C. while stretching (toe-out) 1.14 times in the transverse direction. A 1.2% transverse relaxation treatment was performed to obtain a biaxially oriented film having a thickness of 4.7 μm. A cobalt-oxygen thin film having a thickness of 110 nm was formed on the surface (side A) of the polyester film by vacuum. Next, a diamond-like carbon having a thickness of 10 nm was formed on the cobalt-oxygen thin film layer by a sputtering method. Subsequently, a back coat layer made of carbon black, polyurethane, and silicone was provided on surface B to a thickness of 500 nm, slit to a width of 8 mm by a slitter, and wound on a reel to produce a magnetic tape. Table 1 shows the properties of the obtained polyester film and magnetic tape.

Example 2 In the production of the base film of Example 1, polyethylene-2,6-naphthalenedicarboxylate was changed to polyethylene terephthalate (intrinsic viscosity: 0.54), and the drying time of the pellets was 3 hours. The melt extrusion temperature was 295 ° C., the surface temperature of the casting drum was 20 ° C., the longitudinal stretching temperature and the magnification were 110 ° C., 3.0 times, and the film was transversely stretched 3.3 times at 105 ° C. Further heat treatment is performed at 210 ° C. while stretching (toe-out) 1.6 times in the transverse direction, and then at 170 ° C., 1.0%
Was carried out in the same manner as in Example 1 to obtain a 6.4 μm-thick polyester film, and a magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape.
Shown in

Example 3 In the production of the base film of Example 1, raw material A, which is a polyethylene-2,6-naphthalenedicarboxylate containing substantially no inert particles, was mixed with substantially inert particles. The raw material B containing 0.3% by weight of silica having an average particle size of 300 nm in polyethylene-2,6-naphthalenedicarboxylate not containing was changed to co-extrusion at a ratio of 5: 1 in thickness. To obtain a 4.7 μm-thick polyester film. Further, a magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape.

Example 4 In the production of the base film of Example 2, the raw material A, which is a polyethylene terephthalate substantially free of inert particles, and the polyethylene terephthalate substantially free of inert particles, were used. Raw material B containing 0.3% by weight of 200 nm silica
Was changed to co-extrusion at a ratio of 5: 1, and the other steps were carried out in the same manner to obtain a 6.4 μm-thick polyester film. Further, a magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape.

[Comparative Example 1] In the production of the base film of Example 1, the procedure was the same except that a flat casting drum having no cracks on the surface was used.
m, and a magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape.

Comparative Example 2 In the production of the base film of Example 1, the stretching ratio in the machine direction was 4.0 times and the stretching in the transverse direction was first stretched at 150 ° C. to 4.5 times in the transverse direction. Further, a polyester film having a thickness of 4.7 μm was obtained in the same manner except that the film was stretched (toe-out) 1.14 times in the transverse direction at 200 ° C., and a magnetic tape was produced in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape.

Comparative Example 3 In the production of the base film of Example 2, the stretching ratio in the machine direction was 3.5 times, the stretching in the transverse direction was 2.8 times at 105 ° C., and then 1.6 times at 210 ° C. A 6.4 μm-thick polyester film was obtained in the same manner as in Example 1, and a magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape. Looking at the magnetic tape after running, the tape edge was damaged.

[Comparative Example 4] In the production of the base film of Example 2, the same procedure was carried out except that the stretching in the transverse direction was changed to 3.3 times at 105 ° C and subsequently to 1.6 times at 195 ° C. A 6.4 μm-thick polyester film was obtained, and a magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape.

Comparative Example 5 In the production of the base film of Example 3, 0.2% by weight of silica having an average particle diameter of 110 nm was added to polyethylene-2,6-naphthalenedicarboxylate containing no inert particles in the raw material A. A 4.7 μm-thick polyester film was obtained in the same manner except that the raw materials contained were changed, and a magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape.

Comparative Example 6 A 4.7 μm-thick polyester film was obtained in the same manner as in the production of the base film of Example 1, except that the heat treatment temperature after the transverse stretching was changed to 230 ° C. A magnetic tape was prepared in the same manner as in Example 1. Table 1 shows the properties of the obtained polyester film and magnetic tape. Looking at the obtained tape, the curl to the magnetic layer was large in both the longitudinal direction and the lateral direction of the tape.

[0058]

[Table 1]

As is evident from Table 1, the polyester film of the present invention has a low coefficient of friction and excellent handling properties, and when used as a magnetic tape, has excellent output after storage and repeated running, as well as edge damage and curling. No magnetic tape can be manufactured.

[0060]

According to the present invention, a polyester film for a magnetic recording medium which is excellent in handling properties, has excellent output after storage and repeated running when formed into a magnetic tape, and prevents edge damage of the tape. Can be provided.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // B29C 55/14 B29C 55/14 5D006 B29K 67:00 B29L 9:00 F term (reference) 4F071 AA45 AA46 AF61Y AH14 BA01 BB06 BB07 BB08 BC01 BC08 BC16 4F100 AA20D AB01B AK25C AK41A AK41C AK41D AK41K AK42A AL01C AL01D AT00A BA02 BA04 BA07 BA10B CA18C CA18D CA18H CA23C CA23D CA23H DD07A DE01C DE01D EJ38 GB41 JA03A JG06B JK14 JL05 JM02B YY00A 4F210 AA24 AA26 AG03 AH38 QA02 QA03 QC06 QD36 QG01 QG11 QG15 QG18 QL17 QM11 QW12 4J002 CF061 CF081 FD060 FD070 FD200 GS01 4J029 AA03 AB01 AC01 AC02 AE03 BA03 BA08 BA10 BB03A BD07A BF09 BF25 CA02 CA06 CB04A CB05A CB06A CC06A CH02 CB01 FC35 FC02 5

Claims (6)

[Claims] 1. The polyester film has a Young's modulus in the longitudinal direction of 5.0 GPa or less and a Young's modulus in the width direction of 8.0.
GPa or more, and the surface roughness WRa (2.5) A of the surface (side A) on which the magnetic layer is provided, measured at a magnification of 2.5 times using a non-contact type three-dimensional surface roughness meter, is 0.5 to 0.5. 3.0 nm
And the surface roughness WRa (25) A measured at a magnification of 25 times is 0.3 to 1.5 nm, and the surface on the nonmagnetic layer side (B
Surface) has a surface roughness WRa (2.5) B of 2.0 to 5.0 nm measured at a magnification of 2.5 using the surface roughness meter,
The surface roughness WRa (25) B measured at a magnification of 25 was 0.6
The thermal shrinkage at 105 ° C. for 30 minutes is 0.0-1.5% in the longitudinal direction of the film, 0.5-3.0% in the width direction, and 150 ° C., 30%. The polyester film for a magnetic recording medium, wherein the heat shrinkage of the polyester film is 2.0 to 5.0% in the longitudinal direction of the film and 6.0 to 11.0% in the width direction. 2. The polyester film for a magnetic recording medium according to claim 1, wherein the thickness of the film is 2 μm or more and less than 7 μm. 3. The polyester film for a magnetic recording medium according to claim 1, wherein the polyester is polyethylene terephthalate or polyethylene-2,6-naphthalenedicarboxylate. 4. The polyester film for a magnetic recording medium according to claim 1, wherein the magnetic recording medium is a digital recording type magnetic tape. 5. The polyester film for a magnetic recording medium according to claim 1, wherein the magnetic layer comprises a ferromagnetic metal thin film layer. 6. A magnetic recording medium comprising the polyester film according to claim 1 as a support.