JPH09278992A - Biaxially oriented polyester film for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject film flat in its surfaces and excellent in scratch resistance, shaving resistance and slitting property by adding specific alumina particles in a specified amount to a polyester. SOLUTION: (A) A polyester [e.g. a (co)polyester having an intrinsic viscosity of 0.4-0.9 determined as a solution in o-chlorophenol and containing terephthalic acid or 2,6-naphthalenedicarboxylic acid in an amount of >=80mol.% based on the whole carboxylic acid component and also ethylene glycol in an amount of >=80mol% based on the whole glycol component] is compounded with (B) 0.01-2.0wt.% of alumina particles having an average primary particle diameter of <=50nm, an average aggregation degree of <=5 and a crystal form of θ and, if necessary, further (C) 0.005-0.3wt.% of particles (e.g. kaolin particles or heat- resistant polymer particles) having an average particles diameter of 0.2-0.8μm and larger than the component B.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film for a magnetic recording medium, and more specifically, it contains θ-alumina particles, has a flat surface, and is excellent in scratch resistance, abrasion resistance and slit resistance. The present invention relates to a biaxially oriented polyester film for magnetic recording media.

[0002]

Biaxially oriented polyester films, typified by polyethylene terephthalate films, are used for magnetic recording media because of their excellent physical and chemical properties.
It is now indispensable as a base film for magnetic tapes and floppy disks.

In recent years, magnetic recording media such as video tapes have been rapidly reduced in size and higher in density.
Since high-density recording is performed at a short wavelength, the magnetic layer is being thinned in order to reduce the output loss of the magnetic layer thickness.
For example, a general-purpose video tape usually has a magnetic layer thickness of 2 to 3 μm, but a metal powder coating tape containing pure iron as a main component, represented by an 8 mm video tape, has a thickness of 1 to 2 μm.
The thickness of the magnetic layer is. With the thinning of the magnetic layer, the influence of the surface property of the base film on the electromagnetic conversion characteristics of the video tape increases, and it is desired that the surface of the base film be as flat as possible.

However, in the conventional technique, the abrasion resistance and scratch resistance of the film are deteriorated as the surface of the film becomes flat, which causes a serious problem. For example, when a magnetic layer is applied to the surface of a biaxially oriented polyester film and used as a magnetic tape, the friction between the coating roll and the film surface is severe, and shavings are generated, or scratches are generated on the film surface. Also, V
Even when used for TR and data cartridges, dust and scratches are generated in the process of winding the cassette at high speed, which causes D / O.

By the way, as a method for improving the slipperiness and abrasion resistance of the biaxially oriented polyester film, for example, a method of adding inorganic fine particles such as silicon dioxide, titanium dioxide, calcium carbonate, talc, clay and calcined kaolin (for example, JP-A-54-57562), a method of precipitating fine particles containing calcium, lithium or phosphorus in a polymerization system for producing polyester (for example, Japanese Patent Publication No.
No. 2-32914), etc. are known, but in a magnetic tape to which these are applied, shavings and scratches are generated in the step of winding the tape in a cassette at a high speed, and the D / O level is increased.

Therefore, in order to solve such a problem, a method of adding fine particles having high Mohs hardness to reduce scratches (for example, JP-A-1-306220 and JP-A-2-18).
No. 5533) has been proposed.

However, in order to obtain sufficiently satisfactory abrasion resistance by this method, it is necessary to sacrifice the flatness of the film, and it is difficult to obtain one that is compatible with the required electromagnetic conversion characteristics. .

[0008]

DISCLOSURE OF THE INVENTION The present inventors have completed the present invention as a result of extensive studies to obtain a film having a flat film surface and excellent scratch resistance, abrasion resistance and slit resistance. Came to do.

[0009]

That is, the present invention contains 0.01 to 2.0% by weight of alumina particles (A) having an average primary particle size of 50 nm or less and a crystal form of θ.
The biaxially oriented polyester film for magnetic recording media is characterized in that the average degree of aggregation of the alumina particles is 5 or less.

The polyester in the present invention 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, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid and anthracenedicarboxylic acid. Can be raised. Examples of the aliphatic glycol include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol,
Examples thereof include polymethylene glycol having 2 to 10 carbon atoms such as decamethylene glycol, and aliphatic diols such as 1,4-cyclohexanedimethanol.

In the present invention, polyesters containing alkylene terephthalate and / or alkylene-2,6-naphthalate as a main constituent are preferably used as the polyester.

Of these polyesters, not only polyethylene terephthalate and polyethylene-2,6-naphthalate, but for example, 80% or more of the total acid component is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid. A copolymer in which 80 mol% or more of the glycol component is ethylene glycol is preferable.

In that case, 20 mol% or less of the total acid component may be the above aromatic dicarboxylic acid other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and, for example, adipic acid, sebacic acid and the like. Alicyclic dicarboxylic acids such as; aliphatic dicarboxylic acids such as cyclohexane-1,4-dicarboxylic acid, and the like. Further, 20 mol% or less of the total glycol component may be the above-mentioned glycol other than ethylene glycol, or, for example, hydroquinone, resorcin, 2,2-bis (4-
Aromatic diol such as hydroxyphenyl) propane; Aliphatic diol having an aromatic ring such as 1,4-dihydroxydimethylbenzene; Polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol ) And so on.

The polyester of the present invention includes
For example, aromatic oxyacids such as hydroxybenzoic acid, ω-
Those in which a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as hydroxycaproic acid is copolymerized or bonded at 20 mol% or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component are also included.

Further, in the polyester of the present invention,
An amount in the range that is substantially linear, for example, 2 for the total acid component
Also included are those obtained by copolymerizing a tri- or higher functional polycarboxylic acid or polyhydroxy compound such as trimellitic acid or pentaerythritol in an amount of not more than mol%.

The above polyester is known per se, and can be produced by a method known per se.
The above polyester preferably has an intrinsic viscosity of about 0.4 to about 0.9 when determined as a solution in o-chlorophenol.

First, the biaxially oriented polyester film of the present invention comprises alumina particles (A) having a θ-type crystal morphology having an average primary particle size of 50 nm or less and an average cohesion degree of 5 or less. There are features.

As is well known, alumina is usually obtained by thermally decomposing alumina hydrates such as dibsite, vialite and boehmite. At this time, the type of raw material, the thermal decomposition conditions, especially the temperature conditions. By α
Alumina having nearly 10 different crystal types including β type, β type, γ type, θ type, κ type, and ηδ type is formed. Alumina can also be obtained by a method in which aluminum chloride is burned and hydrolyzed in an oxyhydrogen flame. In this case, various crystal type aluminas such as α, β, θ, and γ can be obtained depending on the treatment conditions.

Each of these aluminas has a unique property. For example, α type has a small specific surface area and shows almost no catalytic activity, whereas γ type and η type usually have 150 to 3 types.
It has a specific surface area of about 00 m ² / g and has a high catalytic activity. Also, the density can change up to about 2.5 to 4 g / cm ³ depending on the respective crystal type, and the hardness also changes delicately.

As a result of detailed investigations on many aluminas having different properties, the present inventors have found that θ type alumina is particularly suitable for the purpose of the present invention.

That is, the film containing the θ-type alumina particles hardly scratches the film even with a catalyst such as a guide pin or other base material, and hardly produces abrasion powder, which is extremely scratch resistant. Excellent in abrasion resistance and abrasion resistance.

Theta-type alumina particles (A) used in the present invention
Should have an average primary particle size of 50 nm or less, as described above. If the average primary particle diameter exceeds 50 nm, the flatness of the film will be impaired. Also, the degree of aggregation of alumina particles in the film is 5
Must be: When the degree of cohesion exceeds 5, the flatness of the film is impaired, resulting in deterioration of electromagnetic conversion characteristics, which is not preferable. The amount of the alumina particles added was 0.
01-2.0% by weight, preferably 0.2-0.5% by weight
Must be in the range. This addition amount is 0.01% by weight
If it is less than 2.0%, the effect of improving the scratch resistance of the film is not recognized, while if it exceeds 2.0% by weight, the slit property and the flatness of the film are impaired.

As described above, in the present invention, by mixing alumina having a specific crystal type, it is possible to provide the guide post with excellent abrasion resistance, scratch resistance, and good slit property. Is possible.

However, since the alumina particles (A) alone are often inferior in the slipperiness of the film and inferior in handling workability, it is preferable to use other particles (B) together.

As one of the particles (B), so-called additive particles can be preferably mentioned. The added particles refer to particles externally added to the polyester manufacturing process. Specifically, for example, kaolin, talc, carbon, molybdenum sulfide, gypsum, rock salt, calcium carbonate, barium sulfate, lithium fluoride, calcium fluoride. , Zeolite, calcium phosphate, silicon dioxide, titanium dioxide and the like. Further, heat-resistant polymer fine particles such as crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked polystyrene particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, Teflon particles, polyimide particles, polyimide-amide particles, melamine resin particles, etc. You can also list them. In this case, these added particles (B)
Is larger than that of the θ-type alumina particles (A) and is in the range of 0.2 to 0.8 μm, and the compounding amount with respect to the polyester is in the range of 0.005 to 0.3% by weight. preferable.

The biaxially oriented polyester film of the present invention is not restricted by the production method thereof, but for example, the polyester is melt extruded at a temperature of a melting point (Tm: ° C.) to (Tm + 70) ° C. and an intrinsic viscosity of 0. 35-0.
An unstretched film of 9 dl / g was obtained, and the unstretched film was uniaxially (longitudinal or lateral) (Tg-10) to (Tg).
g + 70) ° C. (however, Tg: glass transition temperature of polyester) is stretched at a draw ratio of 2.5 to 5.0, and then in the direction perpendicular to the stretching direction (when the first stage stretching is the longitudinal direction, Tg (° C) ~
It can be preferably produced by stretching at a temperature of (Tg + 70) ° C. at a draw ratio of 2.5 to 7.0. In this case, the area stretch ratio is preferably 9 to 32 times, more preferably 12 to 32 times. The stretching means may be either simultaneous biaxial stretching or sequential biaxial stretching. Furthermore, the biaxially stretched film,
It is preferable to heat-set at a temperature of (Tg + 70) ° C. to Tm (° C.). For example, a polyethylene terephthalate film is preferably heat set at 190 to 230 ° C. The heat fixing time is, for example, 1 to 60 seconds.

[0028]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. The measuring method used in the present invention is as follows.

(1) Average Primary Particle Diameter of θ-Type Alumina Particles A film containing the particles is used as a thin cut side having a thickness of 100 nm in the cross-sectional direction, and a transmission electron microscope (for example, JE manufactured by JEOL Ltd.) is used.
When particles are observed at a magnification of about 100,000 times using EM-1200EX), the smallest particles (primary particles) that cannot be further divided can be observed. Using this photograph, the diameter corresponding to the area circle of each particle is measured for 1000 particles using an image analyzer or the like, and the average particle diameter is taken as the average primary particle diameter (nm) of θ-alumina particles.

(2) Average Coagulation Degree of θ-Alumina Particles About about 1000 particles observed from the photograph obtained by the measurement of the above-mentioned average primary particle size, particularly some of the aggregated particles (secondary particles) The number of primary particles is counted, and the sum of the primary particles is divided by the number of measured particles to obtain the average aggregation degree.

(3) High-speed pin scraping A film cut to a width of 1/2 inch in an environment of a temperature of 20 ° C. and a humidity of 60% was bent into a cylindrical SUS sintered plate, and the surface finish was insufficient (surface. (Roughness Ra = 0.15 nm) An angle θ = (60/180) π radian (60 °) is brought into contact with a fixed guide pin to run (friction) at a speed of 250 m / min and an entrance tension T ₁ = 50 g. After the film has run 200 m, the shavings deposited on the fixed guide pins are evaluated.

<Judgment of shavings> ◎: No shavings are observed ○: Slightly shavings are seen △: Presence of shavings is visible at a glance ×: Shavings are severely adhered

<Scratch Judgment> ⊚: No scratches were found ◯: 1 to 5 scratches were found Δ: 6 to 15 scratches were found ×: 16 or more scratches were found

(4) Blade Scraping A film cut to a width of 1/2 inch in an environment of a temperature of 20 ° C. and a humidity of 60% is formed on the blade edge of a blade (industrial razor tester made by GKI, USA) at an angle θ = ( 6/18)
It is brought into contact with π radians (6 °) and run (rubbed) at a speed of 100 m / min and an entrance tension T ₁ = 50 g. After running the film for 100 m, the amount of shavings adhering to the blade is evaluated.

This evaluation is related to the impact strength of the protrusions formed on the film surface, and corresponds well to the generation of shavings on a calendar or die coater in the magnetic tape manufacturing process. <Judgment> ◎: Less than 0.5 mm of shavings adhering to the blade edge of the blade ◯: 0.5 mm to less than 1.0 mm of shaving powder adhering to the blade edge Δ: 1.0 mm or more of shaving powder adhering to the blade edge 2 Less than 0.0 mm x: Shavings adhering to the blade edge are 2.0 mm or more

(5) Slitting property A film cut to a width of 1/2 inch in an environment of a temperature of 20 ° C. and a humidity of 60% has a blade edge (blade for industrial razor tester manufactured by GKI, USA) with an angle θ = ( 6/18)
It is brought into contact with π radians (6 °) and repeatedly run (rubbed) 10 times at a speed of 100 m / min and an entrance tension T ₁ = 50 g. After running the film, the blade edge of the blade is scanned with a scanning electron microscope (for example, JSM-T3 manufactured by JEOL Ltd.).
00) to observe the wear width of the blade edge.

This evaluation corresponds well to the long and short life of the slitting blade when the film or tape is slit in the polyester film forming step or the tape production step. <Judgment> ◎: The wear width of the blade edge is less than 1.0 μm ◯: The wear width of the blade edge is 1.0 μm or more and 3.0 μm
Less than Δ: Abrasion width of blade edge is 3.0 μm or more and 5.0 μm
Less than ×: The wear width of the blade edge is 5.0 μm or more

(6) Electromagnetic conversion characteristics VHS system VTR (BR640 manufactured by Victor Company of Japan, Ltd.)
0) is modified and a 4 MHz sine wave is input to a recording / reproducing head through an amplifier, recorded on a magnetic tape manufactured by the following method and then reproduced, and the reproduced signal is input to a spectrum analyzer. Carrier signal 4 MHz to 0.1
The noise generated at a distance of MHz is measured, and the carrier-to-noise ratio (C / N) is expressed in dB. The above-mentioned magnetic tape is measured by using this method, and the blank is taken as a reference (± 0 dB), and its relative value is taken as an electromagnetic conversion characteristic.

The electromagnetic tape is manufactured by the following method.
100 parts by weight of γ-Fe ₂ O ₃ (hereinafter, simply referred to as “part”) and the following composition are kneaded and dispersed in a ball mill for 12 hours. Polyester polyurethane resin 12 parts Vinyl chloride-vinyl acetate-malinic anhydride copolymer 10 parts α-alumina 5 parts Carbon black 1 part Butyl acetate 70 parts Methyl ethyl ketone 35 parts Cyclohexanone 100 parts Further after dispersion fatty acid: oleic acid 1 part Fatty acid: palmtimine Acid 1 part Fatty acid: ester (amyl stearate) 1 part Add and knead for 10 to 30 minutes. Then, 7 parts of a 25% ethyl acetate solution of a triisocyanate compound was added, and 1
The magnetic layer coating solution is prepared by dispersing for a long time at high speed. The resulting coating solution was applied onto a polyester film to give a dry film thickness of 2.
Coating is performed so as to be 0 μm.

Then, after orientation treatment in a DC electromagnetic field, 1
Dry at 00 ° C. After drying, it is subjected to a calendering treatment and slit to a width of 1/2 inch to obtain a magnetic tape.

[Examples 1 to 3, Comparative Examples 1 to 3] Dimethyl terephthalate and ethylene glycol, manganese acetate as an ester exchange catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and further as a lubricant. The additive particles shown in Table 1 were added and polymerized by a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity of 0.62 (orthochlorophenol, 35 ° C.).

The polyethylene terephthalate pellets were dried at 170 ° C. for 3 hours, then fed to an extruder popper and melted at a melting temperature of 280 to 300 ° C., and the molten polymer was surface-finished through a 1 mm slit die to a surface finish of 0.
It was extruded onto a rotary cooling drum having a surface temperature of 20 ° C. for about 3 s to obtain a 200 μm unstretched film.

The unstretched film thus obtained is divided into two parts in the longitudinal direction by 2.5 times and 2.3, respectively.
It was stretched twice. This uniaxial film was rapidly cooled, subsequently supplied to a stenter, and stretched in the transverse direction by a factor of 3.6 at 90 ° C. The obtained biaxially stretched film was heat set at a temperature of 205 ° C. for 5 seconds to obtain a heat set biaxially oriented polyester film having a thickness of 8.7 μm.

The characteristics of the film and magnetic tape thus obtained are shown in Table 1.

[0045]

[Table 1]

As is clear from this table, the one according to the present invention has a surface flatness for a magnetic recording medium,
It has excellent scratch resistance, abrasion resistance, and slit resistance, and has extremely excellent properties as a biaxially oriented polyester film for magnetic recording media.

[0047]

INDUSTRIAL APPLICABILITY The biaxially oriented polyester film of the present invention has not only excellent surface properties for magnetic recording media, but also excellent scratch resistance, abrasion resistance and slit properties. It has extremely excellent properties as a base film.

Claims (2)

[Claims] 1. An alumina particle (A) having an average primary particle size of 50 nm or less and a crystal morphology of θ is 0.01 to 2.
0% by weight and the average degree of aggregation of the alumina particles is 5
A biaxially oriented polyester film for a magnetic recording medium, characterized in that: 2. An average particle size of 0.2 to 0.8 μm and θ
0.005 of particles (B) larger than alumina particles (A)
The biaxially oriented polyester film for a magnetic recording medium according to claim 1, wherein the biaxially oriented polyester film contains 0.3 to 0.3% by weight.