JP3024888B2 - High density magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium for a flexible disk, and more particularly, to a flexible, high-yield, high-density recording medium by improving the workability of a base polyester film. The present invention relates to a magnetic recording medium for a disk.

[0002]

2. Description of the Related Art It is common to use a flexible disk drive as an external recording device of a personal computer or a word processor and a flexible disk as a magnetic recording medium thereof. Recently, with the remarkable development and popularization of personal computers and word processors, demands for flexible disks as magnetic recording media have also been demanded for high-density recording, miniaturization, and cost reduction. With these demands,
A biaxially oriented polyester film serving as a base is required to have a surface flatness capable of high-density recording and to be excellent in processability and high in yield.

[0003] In response to this demand for high-density recording, a base film having a flatter surface has been used in order to improve the electromagnetic conversion characteristics. There is a problem. That is, in the case of a base film for a flexible disk, unlike a base film for a magnetic tape, the film is thick and has a strong stiffness. The yield is deteriorated, and the scratches or shaved powder become coating defects (D / O) at the time of manufacturing the flexible disk, which causes the yield of the flexible disk to deteriorate.

(2) When the biaxially oriented film is wound around a roll, the flatness is deteriorated due to the laminated thin band due to the thickness unevenness, and the coating unevenness occurs in the coating process at the time of manufacturing the flexible disk, and the flexible disk becomes flexible. The yield of the disc production is reduced.

On the other hand, two-component lubricant films having high projections dispersed therein have come to be used, but sufficient properties have not always been obtained. In addition, in the coating method using a die coater, in particular, the shaving of the high protrusions by the die coater causes coating streaks, thereby deteriorating the yield as a flexible disk.

[0006] Chips generated during punching of a flexible disk, which has not been a major problem in the past, have also become a problem with high-density recording, and have caused a decrease in yield as a flexible disk. On the other hand, if the punching conditions are changed, the use of carbide blades or a reduction in the speed will eventually result, leading to an increase in cost.

On the other hand, as one problem, track width is becoming narrower with high-density recording, and track misalignment due to temperature and humidity environment is becoming more problematic with miniaturization and outdoorization. On the other hand, it has been conventionally known to provide a mechanism for suppressing a temperature change and a special circuit for track detection (track servo system) to prevent tracking deviation. However, these means make a recording / reproducing apparatus complicated. , Leading to higher prices and not universal. In addition, these methods alone are not always sufficient for the in-plane anisotropy of a flexible disk.

[0008]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies to develop a magnetic recording medium for a flexible disk which has solved the above-mentioned problems, and as a result, have found that a specific lubricant system is contained in a base biaxially oriented polyester film. A magnetic recording medium for a flexible disk having excellent workability, capable of high-density recording, and having a high yield can be obtained by containing it and setting the surface roughness, density, in-plane anisotropy, and the like of the film to a specific range. And arrived at the present invention.

[0009]

That is, the present invention relates to a magnetic recording medium for a flexible disk comprising a biaxially oriented polyester film having a thickness of 25 to 125 .mu.m and a magnetic layer provided thereon. The polyester film contains (A) heat-resistant polymer particles and (B) alumina particles and / or colloidal silica particles,
A magnetic recording medium for a flexible disk, characterized in that the film has a surface roughness, density, in-plane anisotropy and tarmi satisfying the following (1) to (7).

Surface roughness Ra = 6 to 15 nm (1) SRz = 130 to 500 nm (2) Density = 1.385 to 1.400 g / cm ³ (3) Talmi = 15 mm or less (4) In-plane Anisotropy In-plane anisotropy of thermal expansion coefficient = 10 × 10 ⁻⁶ / ° C. or less (5) In-plane anisotropy of humidity expansion coefficient = 5 × 10 ⁻⁶ /% RH or less (6) 60 ° C. , 80% RH, in-plane anisotropy of heat shrinkage after 72 hours = 0.05% or less (7)

In the present invention, the polyester constituting the base biaxially oriented polyester film is a polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyesters are substantially linear and have film-forming properties, especially by melt-forming.

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, anthracene dicarboxylic acid and the like. Can be mentioned.

The aliphatic glycol is, for example, a polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol or the like, or cyclohexanedimethanol. Alicyclic diols and the like can be mentioned.

In the present invention, as the polyester,
For example, those containing alkylene terephthalate and / or alkylene naphthalate as a main component are preferably used.

Of these polyesters, in particular, polyethylene terephthalate, polyethylene-2,6-naphthalate, 80 mol% or more of the total dicarboxylic acid component is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and 80% of the total glycol component. A copolymer in which at least mol% is ethylene glycol is preferred. At that time, 2 of all acid components
0 mol% or less 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; cyclohexane-1,4 An alicyclic dicarboxylic acid such as a dicarboxylic acid; Further, 20 mol% or less of the total glycol component can be the above-mentioned glycol other than ethylene glycol. For example, hydroquinone, resorcin, 2,2-
Aromatic diols such as bis (4-hydroxyphenyl) propane; aliphatic diols having an aromatic ring such as 1,4-dihydroxydimethylbenzene; polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol (poly) Oxyalkylene glycol) and the like.

The polyester in the present invention includes:
For example, aromatic oxyacids such as hydroxybenzoic acid, ω-
It includes those obtained by copolymerizing an oxycarboxylic acid component such as an aliphatic oxyacid such as hydroxycaproic acid in an amount of 20 mol% or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component.

Further, in the polyester of the present invention, a tricarboxylic or polyfunctional polycarboxylic acid component or a polyhydroxy compound component, for example, in an amount in a substantially linear range, for example, 2 mol% or less based on the total acid component, for example, Copolymers of trimellitic acid, pentaerythritol and the like are also included.

The above polyesters are known per se and can be produced by a method known per se.

As the above-mentioned polyester, those having an intrinsic viscosity of about 0.4 to about 0.9 measured at 35 ° C. as a solution in o-chlorophenol are preferred.

In the present invention, the biaxially oriented polyester film has a thickness of 25 to 125 μm from the viewpoint of being used as a base film of a flexible disk. When the thickness is less than 25 μm, the shape retention of the disk is insufficient, while when it exceeds 125 μm, the flexibility as the disk is insufficient.

In the present invention, the particles contained in the biaxially oriented polyester film include (A) heat-resistant polymer particles and (B) alumina particles and / or colloidal silica particles. Particle (A) is larger than particle (B), as shown in the examples. The alumina particles and the colloidal silica particles can be used in combination. A film excellent in abrasion resistance can be obtained by a combination of these particles. Other particles may be added to these particles,
Sufficient abrasion resistance cannot be obtained with a combination between other particles or a combination of the particles (A) or the particles (B) with other particles.

The heat-resistant polymer particles are known and available as non-agglomerated particles.
The heating weight loss temperature is 310 ° C or more, further 330 ° C or more,
Particularly, those having a temperature of 350 ° C. or more are preferable. Examples of such particles include silicone resin particles, crosslinked acrylic resin particles, crosslinked polystyrene particles, crosslinked polyester particles, Teflon particles, polyimide particles and the like. Among them, silicone resin particles are preferred.

The alumina particles are known and available as aggregated particles, but are preferably alumina particles having a Mohs hardness of 8 or less, and more preferably θ-type alumina particles. When α-type alumina particles having a Mohs' hardness of 9 are used, depending on the addition conditions, the added particles are too hard when run for a long time in the manufacturing process of the flexible disk, so that the rolls in the process are damaged. May be undesirable.

The above-mentioned colloidal silica particles are known and available as agglomerated particles.
Preferably, it contains 00 ppm of Na. If the Na content is outside the above range, the effect of improving the scratch resistance is poor, the independent existence ratio of the particles in the film is reduced, and the abrasion resistance is likely to be deteriorated. The method for producing the colloidal silica is a dialysis method using Na silicate as a starting material,
There are a method of producing an active silica sol by an electrolysis method, a salt precipitation method, and an ion exchange resin, followed by polymerization, etc., but the ion exchange resin-polymerization method is most preferable in view of the uniformity of the obtained particles.

In the present invention, the surface roughness of the biaxially oriented polyester film must satisfy the following (1) and (2). Ra = 6 to 15 nm (1) SRz = 130 to 500 nm (2)

Ra is 7 to 13 nm, and further 8 to 11 n
m, and SRz is 140 to 400.
nm, more preferably 150 to 300 nm. If the Ra of the film surface exceeds 15 nm, the surface of the magnetic layer becomes too rough, and a reproduction output (resolution) for high-density recording cannot be obtained. SRz is 500
If it exceeds nm, high protrusions are formed on the magnetic layer, and a reproduction output (resolution) for high-density recording cannot be obtained. In addition, high projections are scraped off in the application step using a die coater, which causes coating streaks. On the other hand, when the biaxially oriented polyester film has a Ra of less than 6 nm or an SRz of less than 130 nm, the film is scratched in the longitudinal stretching step at the time of film production, the film production yield is deteriorated, and the scratch or shaving is caused. The powder becomes a coating defect (D / O) at the time of manufacturing the flexible disk, and the production yield of the flexible disk deteriorates. In addition, the thickness of the laminated thin band resulting from the thickness unevenness becomes stronger, and the flatness is deteriorated. This causes unevenness in the coating process at the time of manufacturing the flexible disk, thereby deteriorating the production yield of the flexible disk.

In the present invention, the density of the biaxially oriented polyester film needs to satisfy the following (3). Density = 1.385 to 1.400 g / cm ³ (3) The density is preferably 1.390 to 1.400 g / cm ³ , and more preferably 1.393 to 1.397 g / cm ³ . When the density of the film is less than 1.385 g / cm ³ , when punched as a flexible disk, burrs are generated on the end face, which becomes cutting powder, which causes D / O and lowers the yield as a flexible disk. I do. If the density is more than 1.400 g / cm ³ , the thickness unevenness of the biaxially oriented polyester film becomes worse, and the flatness due to the thickness unevenness and the laminated thick and thin band caused by the thickness unevenness causes the coating in the coating process during the production of a flexible disk. This may cause spots and deteriorate the production yield of the flexible disk.

In the present invention, the thickness of the biaxially oriented polyester film must satisfy the following formula (4). Talmi = 15 mm or less (4) Talmi is preferably 10 mm or less, more preferably 8 mm or less. When the film thickness exceeds 15 mm,
The flatness of the film deteriorates, which causes coating unevenness in the coating process during the manufacture of the flexible disk, and lowers the production yield of the flexible disk.

In the present invention, the in-plane anisotropy of the biaxially oriented polyester film must satisfy the following (5) to (7). In-plane anisotropy of thermal expansion coefficient = 10 × 10 ⁻⁶ / ° C. or less (5) In-plane anisotropy of humidity expansion coefficient = 5 × 10 ⁻⁶ /% RH or less (6) 60 ° C., 80% RH, in-plane anisotropy of heat shrinkage after 72 hrs = 0.05% or less (7) In-plane anisotropy of thermal expansion coefficient is 8 × 10 ⁻⁶ / ° C. or less, further 6 × 10 ^−6. / ° C or less, and the in-plane anisotropy of humidity expansion coefficient is preferably 4 × 10 ⁻⁶ /% RH or less, more preferably 3 × 10 ⁻⁶ /% RH or less. The in-plane anisotropy of the heat shrinkage after 80% RH and 72 hours is preferably 0.03% or less, more preferably 0.02% or less. Temperature expansion coefficient, humidity expansion coefficient, and 60
When the in-plane anisotropy of the thermal shrinkage after 72 hours at 80 ° C. and 80% RH satisfies this range, tracking mistakes as a flexible disk can be prevented, and it can be used in a wide temperature and humidity range.

In producing the biaxially oriented polyester film of the present invention, heat-resistant polymer particles, alumina particles and / or
Alternatively, in order to mix the colloidal silica particles with the polyester intimately, these fine particles may be melted or extruded in an extruder when pelletizing before or during polymerization of the polyester, in a polymerization vessel after the polymerization, or in a sheet form. What is necessary is just to knead | mix sufficiently with this polyester in an extruder.

The biaxially oriented polyester film of the present invention can be basically produced by a known method from the above polyester. That is, the melted polyester is extruded into a sheet by an extruder, solidified by cooling, then sequentially or simultaneously biaxially stretched, and further heat-treated under tension or limited shrinkage. If necessary, the heat-treated film can be produced by a method of re-heating. In the production of such a film, the density of the film,
In order to set the thickness and the in-plane anisotropy in the above-described ranges, the conditions such as the stretching ratio in the longitudinal and transverse directions, the heat setting temperature, and the amount of heat shrinkage given under restrictions are appropriately selected. Combine. Specifically, the stretching ratio is 3.5 to 4.0 times in the machine direction,
From the range of 3.5 to 4.0 times in the horizontal direction, the heat setting temperature is 18
0 to 240 ° C., and further, the limiting shrinkage (toe-in) in the horizontal direction is set to −3 to 5%, and 80% in the vertical direction.
It is preferable to relax at a temperature of up to 120 ° C. with a tension of 6 to 9 kg / cm ² . It is preferable to avoid applying a strong tension that changes the shrinkage characteristics of the base film in the magnetic layer coating process and the calendering process.

The magnetic recording medium for a flexible disk of the present invention basically comprises a magnetic layer and the above-mentioned biaxially oriented polyester film. The magnetic layer is made of magnetic powder or metal. Examples of the ferromagnetic powder or metal include γ-Fe ₂ O ₃ and Co-containing γ-Fe ₂ O
₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , CrO ₂ , C
o-Ni-P alloy, Co-Ni-Fe alloy, Co-Cr
Examples include ferromagnetic materials such as alloys, Co—Ni alloys, and barium ferrites.

Examples of the binder used together with the magnetic powder in the present invention include known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. Specifically, for example, vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinylidene chloride copolymer, vinyl chloride / acrylonitrile copolymer, acrylate / acrylonitrile copolymer, acrylate / vinylidene chloride copolymer Acrylate / styrene copolymer, methacrylate / acrylonitrile copolymer, methacrylate / vinylidene chloride copolymer, methacrylate / styrene copolymer, urethane elastomer,
Polyvinyl fluoride, vinylidene chloride / acrylonitrile copolymer, butadiene / acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), Butylene / butadiene copolymer, polyester resin, chlorovinyl ether / acrylate copolymer, amino resin, various synthetic rubber-based thermoplastic resins, and mixtures thereof can be used.

The method of applying the magnetic layer on the biaxially oriented polyester film includes, for example, air doctor coat, die coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, Cast coat, spray coat, etc. can be used.

The biaxially oriented polyester film is preferably coated with a magnetic layer to a thickness of 0.1 to 5 μm, more preferably 0.3 to 3 μm.

The method for measuring characteristic values in the present invention is as follows. (1) Average particle size (DP) Shimadzu CP-50 Centrifugal Particle Size Analyzer (Centrifugal Particle S)
ize Analyser). The particle size corresponding to 50% by mass is read from the integrated curve of the particles of each particle size and its abundance calculated on the basis of the obtained centrifugal sedimentation curve, and this value is defined as the above average particle size (Book "particle size measurement Technology, Published by Nikkan Kogyo Shimbun, 1975, pp. 242-2
47).

(2) Surface roughness of film (Ra) Measured according to JIS B0601. Using a probe-type surface roughness meter (SURFOOM 3B) manufactured by Tokyo Seimitsu Co., Ltd.
A chart (film surface roughness curve) was formed under the conditions of a needle radius of 2 μm and a load of 0.07 g. A portion of the measured length L is extracted from the film surface roughness curve in the direction of the center line, the center line of the extracted portion is set as the X axis, the direction of the vertical magnification is set as the Y axis, and the roughness curve is expressed as Y = f (x )), Ra (nm) given by the following equation is defined as the film surface roughness.

[0038]

(Equation 1)

(3) Surface Roughness of Film (SRz) Using a three-dimensional roughness meter (manufactured by Kosaka Laboratories), the needle diameter was 2 μm.
R, stylus pressure 30 mg, measurement length 1 mm, sampling pitch 2 μm, cut-off 0.25 mm, vertical magnification 20,000 times, horizontal magnification 200 times, the number of scanning 100, the biaxially oriented polyester film Three-dimensionally image the profile of the surface projections. Five points are taken from the profile obtained in this order from the highest order of the protrusions and five points from the lowest order of the valleys, and the average value of the heights of both (projections and valleys) is obtained, and the difference is defined as SRz.

(4) Film Density Using a mixed solution of heptane and carbon tetrachloride, the density is measured at 25 ° C. by a density gradient tube method. The unit is [g / cm ³ ].

(5) Thermal Expansion Coefficient A thermomechanical analyzer TM-3000 manufactured by Vacuum Riko Co., Ltd. is placed in a thermo-hygrostat to perform measurement. The original sample dimensions at this time are 15 mm in length and 5 mm in width. The measurement sample is subjected to heat treatment in advance under predetermined conditions (for example, 80 ° C. for 120 minutes), and the sample is attached to a tester, and the temperature is 20 ° C./humidity 60% RH (relative humidity) and the temperature is 40 ° C./humidity 60% RH.
The thermal expansion coefficient is measured by reading the dimensional change at. When determining the difference between the maximum value and the minimum value of the thermal expansion coefficient, a sample is cut out in the plane of the biaxially oriented polyester film, for example, at every 30 degrees, and the respective thermal expansion coefficients are determined, and the maximum value and the minimum value are obtained. And ask. The difference between the maximum value and the minimum value is indicated as in-plane anisotropy of the thermal expansion coefficient.

(6) Humidity expansion coefficient In the same manner as in the case of obtaining the temperature expansion coefficient, a thermomechanical analyzer TM-3000 manufactured by Vacuum Riko Co., Ltd.
A sample pre-processed under the condition of 0% RH (relative humidity) was attached to a tester, and a dimensional change between a temperature of 20 ° C. and a humidity of 30% RH and a temperature of 20 ° C. and a humidity of 70% RH was read to obtain the humidity. Find the expansion coefficient. When determining the difference between the maximum value and the minimum value of the coefficient of humidity expansion, the sample is placed in the plane of the biaxially oriented polyester film, for example, at an angle of
It cuts out every 0 degree, calculates | requires each humidity expansion coefficient, and calculates | requires a maximum value and a minimum value. The difference between the maximum value and the minimum value is displayed as the in-plane anisotropy of the humidity expansion coefficient.

(7) Heat Shrinkage A film having a length of about 30 cm and a width of 1 cm whose exact length was measured in advance was placed in a constant temperature / humidity chamber set at 60 ° C. and 80% RH without load. After a heat treatment for a period of time, the sample is taken out from the thermo-hygrostat, returned to room temperature, and the change in its dimensions is read. From the length before heat treatment (L ₀ ) and the dimensional change due to heat treatment (ΔL), the heat shrinkage is determined by the following equation.

[0044]

(Equation 2)

In order to determine the difference between the maximum value and the minimum value of the heat shrinkage, a sample is cut out in the plane of the biaxially oriented polyester film, for example, at an angle of 30 degrees, and the heat shrinkage of each sample is obtained. The difference between the maximum value and the minimum value is indicated as the in-plane anisotropy of the heat shrinkage.

(8) Tarumi of Film A film wound into a roll with a width of 500 mm was wound at a speed of 3 m / m.
In, a 2 mm tension is applied, and the tape is run on two parallel free rolls installed at an interval of 1000 mm, and the thickness of the end of the film (mm) at the center of the two rolls is read on a scale.

(9) Punching properties After applying a magnetic paint to the biaxially oriented polyester film, the end face of the flexible disk punched out to an outer diameter of 20 cm and an inner diameter of 3.8 cm was observed with a scanning electron microscope.
Evaluate according to the following criteria. A: Good B: Somewhat good C: Somewhat bad X: Bad.

(10) Scratch of Film The biaxially oriented polyester film was light-tick using a flashlight in a dark room, and the degree of occurrence of scratches (scratch-like scratches) entered by a longitudinal stretching roll was determined as follows. Evaluate based on criteria. ：: No scratches are observed at all. ○: Slightly observed, but the frequency is quite low, and the degree of scratch is quite weak. △: The frequency is slightly high, and the degree of scratch is slightly high. Also, the degree of scratch is strong.

(11) Blade Sharpness Measured using the apparatus shown in FIG. 1 as follows. FIG.
Among them, 1 is an unwinding reel, 2 is a tension controller, 3, 5, 6, 8, 9, 11, and 12 are free rollers, 4, 10 is a tension detector, and 7 is a blade (GKI industrial razor testing machine manufactured by US GKI) And take-up reels 13 respectively. A sample film slit to a 1/2 inch width is applied to a blade edge at an angle of 6 degrees at a tension of 50 g and a running speed of 100 m / min.
After traveling for 00 m, the sharpness is evaluated based on the amount of shaving powder adhering to the blade edge. This evaluation relates to the impact strength of the projections formed on the film surface, and corresponds well to the generation of shavings generated by a calender or a die coater in the flexible disk manufacturing process. <Judgment> ：: The width of the shaving powder adhering to the blade tip is 0.5 mm
Less than ○: The width of the shaving powder adhering to the blade edge is 0.5 mm
Above and less than 1.0 mm △: The width of the shaving powder adhering to the blade tip is 1.0 mm
Above and less than 2.0 mm ×: The shaving powder adhesion width adhering to the blade tip is 2.0 mm
that's all

(12) Resolution (resolution) A 3.5-inch flexible disk drive JU-362 (for 1.6 MB) manufactured by Matsushita Communication Industrial Co., Ltd. was used to test a flexible disk manufactured by Tokyo Engineering Co., Ltd. via an interface. Attached to the device SK-403C, the resolution of the innermost track [2F playback output value / 1F
Reproduction output value × 100 (%)]. For the resolution of the standard disc, 0.95 or more
0 or more and less than 0.95 are regarded as Δ, and less than 0.90 as ×.

(13) Unevenness of film thickness Using a continuous film thickness measuring device (electronic micrometer) manufactured by Anritsu Corporation, a film thickness pattern of a film sampled 3.0 mm wide and 2 m long in the longitudinal and transverse directions of the film was recorded. To record. The highest peak (maximum value) and the deepest valley (lowest value) of the obtained 2 m-long thickness pattern
, And the thickness unevenness (%) is calculated by the following equation.

[0052]

(Equation 3)

(14) Planarity of film The biaxially oriented polyester film is spread on a flatness table (a flat table provided with punching holes for air bleeding).
After holding for 1 minute, the flatness of the film is evaluated according to the following criteria. ：: Flute (mountain-like swelling) is scarcely recognized and good. ：: Flute is slightly recognized but weak. Δ: A little strong flute is partially recognized. X: Remarkably strong flute is partially recognized.

(15) Tracking deviation (temperature change) The tracking deviation is measured by the following method. A recording / reproducing apparatus records and reproduces a flexible disk which is coated with a magnetic layer, calendered, and punched into a disk having an outer diameter of 20 cm and an inner diameter of 3.8 cm. The sheet recorder rotates at 360 rpm, and the position of the magnetic head is 8 cm from the center of the disk. Track width is 30
0 μm, and the head material is ferrite. A 1-MHz signal is recorded on the flexible disk in an atmosphere of a temperature of 15 ° C. and a humidity of 60% RH (relative humidity), and the maximum output and the output envelope of the magnetic sheet at that time are measured.
Next, the ambient temperature was maintained at 40 ° C. and the humidity was 60% RH, and the maximum output and the output envelope at that temperature were examined. The output envelope at a temperature of 15 ° C. and a humidity of 60% RH was compared with the temperature of 40 ° C. and the humidity. The output envelope at 60% RH is compared to determine the tracking state.
The smaller the difference, the better the tracking characteristics. If the difference is 3 dB or more, the tracking is poor, and the evaluation is x. If the difference is within 3 dB, the evaluation is ○.

(16) Tracking deviation (humidity change) Temperature 25 ° C./humidity 2
Recording was performed in an atmosphere of 0% RH (relative humidity), and the atmosphere temperature was maintained at 25 ° C. and the humidity was 70% RH.
Output envelope at a humidity of 20% RH and a temperature of 25 ° C,
The output envelope at a humidity of 70% RH is compared. The good tracking is evaluated in the same manner as in the previous section. The evaluation method is the same as the tracking deviation described in the preceding section.

(17) Tracking deviation (60 ° C./80
% RH / 72 hr treatment) In the same manner as the tracking deviation in the above (15), the temperature 25
The recording was performed in an atmosphere at 60 ° C. and a humidity of 60% RH (relative humidity). After measuring the maximum output and the output envelope of the magnetic sheet at that time, the recording was performed in an atmosphere at a temperature of 60 ° C. and a humidity of 80% RH.
hr processing. And again, temperature 25 ° C, humidity 60% R
After returning to the atmosphere of H, the maximum output and the output envelope of the magnetic sheet are examined, and the output envelopes before and after the two processes are compared to evaluate good tracking in the same manner as in the above (15). The evaluation method is the same as the tracking deviation of (15).

[0057]

The present invention will be described below with reference to examples.

Example 1 Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and silicone having an average particle diameter of 0.6 μm as a lubricant. Resin particles 0.
03 wt% and 0.2 wt% of θ-type alumina particles having an average particle diameter of 0.1 μm were added and polymerized by a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62. Was.

The polyethylene terephthalate pellets were dried at 170 ° C. for 3 hours and then supplied to an extruder hopper.
Melt at a melting temperature of 280-300 ° C, pass this molten polymer through a 1 mm slit die for surface finishing 0.3 s
Extruded on a rotating cooling drum with a surface temperature of 20 ° C.
An unstretched film of 050 μm was obtained.

The unstretched film thus obtained is preheated at 75 ° C., and further cooled between low-speed and high-speed rolls.
mm, heat it with a single IR heater with a surface temperature of 900 ° C, stretch it 3.7 times in the vertical direction, cool it, and then supply it to a stenter, and then 3.8 times in the horizontal direction at 105 ° C. Stretched. After heat-setting the obtained biaxially stretched film at a temperature of 220 ° C. for 5 seconds, the limiting shrinkage (toe-in) in the horizontal direction is set to 4%, and the tension is 7 k in the vertical direction at a temperature of 90 ° C.
g / cm ² and relaxed to obtain a 75 μm thick biaxially oriented film.

A magnetic coating solution having the following composition was applied to the obtained biaxially oriented film to a thickness of 1 μm. The above-mentioned paint was sufficiently mixed and stirred to be subjected to a coating treatment.

Next, the coated surface was subjected to a calender roll treatment. Thereafter, a flexible disk having an outer diameter of 20 cm and an inner diameter of 3.8 cm was obtained. Table 1 shows the properties of the obtained film and flexible disk. As is clear from Table 1, good results were obtained.

Comparative Examples 1 to 6 A biaxially oriented film of 75 μm was obtained in the same manner as in Example 1, except that the following particles were added instead of the lubricant particles in Example 1. Then, a magnetic paint was applied thereto and calendered to obtain a flexible disk.

Comparative Example 1: 0.03% by weight of calcium carbonate particles having an average particle size of 0.6 μm and θ having an average particle size of 0.1 μm
0.2% by weight of alumina particles of the type crystal was added.

Comparative Example 2: 0.03% by weight of spherical silica particles having an average particle diameter of 0.6 μm and 0.2% by weight of θ-type alumina particles having an average particle diameter of 0.1 μm were added.

Comparative Example 3: 0.02% by weight of silicone resin particles having an average particle diameter of 0.7 μm and 0.15% by weight of spherical silica particles (non-agglomerated particles) having an average particle diameter of 0.3 μm were added.

Comparative Example 4: 0.03% by weight of silicone resin particles having an average particle size of 1.0 μm and θ having an average particle size of 0.1 μm
0.2% by weight of alumina particles of the type crystal was added.

Comparative Example 5: 0.07% by weight of silicone resin particles having an average particle size of 0.7 μm and θ having an average particle size of 0.1 μm
0.2% by weight of alumina particles of the type crystal was added.

Comparative Example 6: 0.01% by weight of silicone resin particles having an average particle size of 0.4 μm and θ having an average particle size of 0.1 μm
0.2% by weight of alumina particles of the type crystal was added.

Table 1 shows the properties of the obtained film and flexible disk. As is clear from Table 1, characteristics satisfying all are not obtained.

Examples 2-3 and Comparative Examples 7-8 For Comparative Examples 7-8, the same amount of the same lubricant particles as in Example 1 was added, and for Examples 2-3 , the lubricant of Example 1 was added. The following particles were added instead of the particles, and an unstretched film was obtained in the same manner as in Example 1. The unstretched film was prepared in Example 1.
The stretching ratio in the longitudinal direction and the transverse direction is 3.5 to 4.0.
Range, and heat setting temperature in the range of 180 to 240 ° C,
Further, in the range of toe-in (−3) to (+5)%, and after heat setting, the tension is 6 to 9 in the temperature range of 80 to 120 ° C. in the longitudinal direction.
A biaxially oriented film was obtained in the same manner as in Example 1 except that tension was applied to relax in a range of kg / cm ^{2 and} the physical properties shown in Table 1 were adjusted. The biaxially oriented film was further prepared in Example 1.
In the same manner as described above, a magnetic paint was applied and calendered to obtain a flexible disk.

Example 2: 0.04% by weight of silicone resin particles having an average particle size of 0.8 μm and 0.2% by weight of colloidal silica particles having an average particle size of 0.12 μm were added.

[0073] Example 3: Attachment 0.2 wt% alumina particles of θ-type crystal having an average particle size of 0.1μm and 0.015 wt% of silicone resin particles having an average particle diameter of 0.5μm pressure.

Table 1 shows the properties of the obtained film and flexible disk. As is clear from Table 1, good results were obtained for Examples 2 and 3, while Comparative Example 7 and
With regard to No. 8, characteristics satisfying all were not obtained.

[0075]

[Table 1]

COMPARATIVE EXAMPLE 9 The same amount of the same lubricant particles as in Example 1 was added, and the longitudinal stretching ratio was set to 3.9 times, and the transverse stretching ratio was set to 3.8 times. Except that the same is not performed.
Method obtained a biaxially oriented film of 75 μm,
In the same manner as in 1 , the magnetic paint was applied and calendered to obtain a flexible disk. Table 2 shows the characteristics of this film.
Shown in

[0077] In Comparative Example 10 The same lubricant particles as in Example 1 was added the same amount, except that not performed longitudinal relaxation treatment after thermal fixation is the same method as in Example 1 75
A biaxially oriented film having a thickness of μm was obtained, and a magnetic paint was applied and calendered in the same manner as in Example 1 to obtain a flexible disk. Table 2 shows the properties of this film.

Comparative Example 11 The same amount of the same lubricant particles as in Example 1 was added, and the heat setting temperature was set to 1
Except for 75 ° C., the same method as in Example 1
Was obtained, and a magnetic paint was applied and calendered in the same manner as in Example 1 to obtain a flexible disk. Table 2 shows the properties of this film.

Comparative Example 12 The same amount of the same lubricant particles as in Example 1 was added, and the heat setting temperature was adjusted to 2
75 μm in the same manner as in Example 1 except that the temperature is 35 ° C.
Was obtained, and a magnetic paint was applied and calendered in the same manner as in Example 1 to obtain a flexible disk. Table 2 shows the properties of this film.

Comparative Example 13 The same amount of the same lubricant particles as in Example 1 was added, and the toe-in content was 7%.
A 75 μm biaxially oriented film was obtained in the same manner as in Example 1, except that the magnetic paint was applied and calendered in the same manner as in Example 1 to obtain a flexible disk. Table 2 shows the properties of this film .

[0081]

[Table 2]

[0082]

According to the present invention, it is possible to provide a magnetic recording medium for a flexible disk which is excellent in processability of a biaxially oriented polyester film, capable of high-density recording and high in yield.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an apparatus for measuring blade sharpness of a film.

[Explanation of symbols]

 Reference Signs List 1 unwinding reel 2 tension controller 4 tension detector 7 blade 10 tension detector 13 take-up reel

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-288735 (JP, A) JP-A-3-209623 (JP, A) JP-A-3-6239 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G11B 5/733

Claims (3)

(57) [Claims] 1. A magnetic recording medium for a flexible disk comprising a biaxially oriented polyester film having a thickness of 25 to 125 μm as a base and a magnetic layer provided thereon, wherein the biaxially oriented polyester film is (A) a heat-resistant polymer Particles, and (B) alumina particles and / or colloidal silica particles, and the film has a surface roughness, density, in-plane anisotropy and tarmi satisfying the following (1) to (7). Magnetic recording media for flexible disks. Surface roughness Ra = 6 to 15 nm (1) SRz = 130 to 500 nm (2) Density = 1.385 to 1.400 g / cm ³ (3) Talmi = 15 mm or less (4) In-plane anisotropy In-plane anisotropy of thermal expansion coefficient = 10 × 10 ⁻⁶ / ° C. or less (5) In-plane anisotropy of humidity expansion coefficient = 5 × 10 ⁻⁶ /% RH or less (6) 60 ° C., 80% RH, in-plane anisotropy of heat shrinkage after 72 hours = 0.05% or less (7) 2. The magnetic recording medium for a flexible disk according to claim 1, wherein the heat-resistant polymer particles are silicone resin particles. 3. The magnetic recording medium for a flexible disk according to claim 1, wherein the alumina particles are alumina particles of a θ-type crystal.