JPH08102041A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE: To provide a polyester film capable of obtaining superior output characteristics based on film working characteristics and adaptable even to reduction in the thickness of a tape in future because of high strength. CONSTITUTION: This polyester film is made of polyethylene-2,6- naphthalenedicarboxylate and has >=700kg/mm<2> Young's modulus in the longitudinal direction, >=50% breaking extension in the longitudinal direction, >=700kg/mm<2> Young's modulus in the transverse direction and <50% breaking extension in the transverse direction. This polyester film has increased strength in the longitudinal and transverse directions and extension anisotropy in the longitudinal and transverse directions.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester film for a magnetic recording medium.

[0002]

2. Description of the Related Art As a polyester film for a magnetic recording medium, a film having a specified strength in the width direction is known (for example, Japanese Patent Laid-Open No. 4-292933).

[0003]

However, the conventional polyester film for magnetic recording medium has been improved by simply increasing the strength in the lateral direction to obtain good electromagnetic conversion characteristics as a magnetic tape. There is a problem that the vertical strength as an absolute value is insufficient. Further, regarding the workability of the film, for example, when slitting to an appropriate width, it is required to give anisotropy to the breaking elongation in the longitudinal direction and the transverse direction while balancing the longitudinal strength and the lateral strength. It has become to. The present invention solves such a problem, the strength in the vertical and horizontal directions is large, and the elongation has anisotropy, as a result,
It is an object of the present invention to provide a polyester film for magnetic recording media, which is particularly excellent in output characteristics.

[0004]

A polyester film for a magnetic recording medium according to the present invention for this purpose is a film made of polyethylene-2,6-naphthalene dicarboxylate and has a Young's modulus in the longitudinal direction of 700 kg / mm. ² or more, the breaking elongation in the longitudinal direction is 50% or more, the Young's modulus in the lateral direction is 700 kg / mm ² or more, and the breaking elongation in the lateral direction is less than 50%.

The polyester film for magnetic recording media of the present invention preferably contains polyethylene-2,6-naphthalenedicarboxylate (hereinafter sometimes referred to as PEN) as a constituent component. Two or more kinds of polymers may be mixed, or a copolymerized polymer may be used, as long as the object of the present invention is not impaired. Further, additives such as antioxidants, heat stabilizers, lubricants, and ultraviolet absorbers may be added to the extent that they are usually added within a range that does not impair the object of the present invention.

The polyester film for magnetic recording media of the present invention is not particularly limited, but from the viewpoint of output characteristics, A layer / B
It preferably comprises at least a two-layer structure of layers. The thickness of the A layer is not particularly limited, but from the viewpoint of output characteristics, it is 0.01 to
The thickness is 3.0 μm, preferably 0.02 to 2.0 μm, and more preferably 0.03 to 1.0 μm. In the case of the laminated structure, the main component of at least one layer may be PEN, and the other layers are not particularly limited, but polyester is preferably exemplified. The polyester is not particularly limited, but a polymer containing polyethylene terephthalate as a main component (hereinafter referred to as PET) or PEN is preferable.

When the polyester film for a magnetic recording medium of the present invention has a laminated structure, the A layer / B layer are PEN /
It may be PET, PEN / PEN or PET / PEN.

The layer A of the polyester film for a magnetic recording medium of the present invention is not particularly limited, but from the viewpoint of output characteristics, it is 0.01 to 1.0 μm, preferably 0.02 to 0.5 μm.
m, more preferably 0.01 to 3.0% by weight, preferably 0.02 to 0.02% by weight of particles having a particle size of 0.03 to 0.3 μm.
It is preferable to contain 2.0% by weight. The particles are not particularly limited, but organic particles, particularly crosslinked organic particles, and particularly polydivinylbenzene particles are preferable from the viewpoint of output characteristics. The polydivinylbenzene particles are mainly composed of divinylbenzene as a crosslinking component. Among them, divinylbenzene is 51% or more of the particle component, preferably 6
It is preferably 0% or more, more preferably 75% or more. Other components are not particularly limited, and examples thereof include non-crosslinking components such as ethylvinylbenzene and diethylbenzene. Further, silicone particles are also preferably exemplified. From that of the silicone particles to the crosslinkable organopolysiloxane (CH ₃ Si O _3/2) a main component. As other particles, the crystal form is α type, γ type, δ type
-Type, θ-type, η-type alumina, zirconia, silica, titanium oxide, and other agglomerated particles, or calcium carbonate, colloidal silica, titanium oxide, and other monodispersed particles can also be used by appropriate particle dispersion in a polymer. Is. A plurality of these particles may be used in combination.

The relation between the thickness A of the layer A and the particle diameter d of the particles contained in the layer A is not particularly limited, but 0.2≤t / d≤10, preferably 0.3≤t / d≤5, and more preferably. 0.3
When ≦ t / d ≦ 3, the output characteristics are particularly good.

Particles may be contained in the polymer constituting the film layers other than the A layer, that is, the B layer and the like. In this case, the particle size is 0.05 to 1.0 μm, preferably 0.1.
It is preferable to contain particles selected from calcium carbonate, alumina, silica, titanium oxide, organic particles, carbon black and the like having a content of 1 to 0.5 μm and a content of 0.05 to 1.0% by weight.

The polyester film for magnetic recording media of the present invention is a film in which the above composition is biaxially oriented. A uniaxial or non-oriented film is not preferable because it lacks strength in the width direction. A part of the film in the thickness direction, for example, the orientation of polymer molecules near the surface layer is non-oriented, or not uniaxially oriented, that is, when the molecular orientation of the entire portion in the thickness direction is biaxially oriented, the output characteristics are better. It will be even better. Abbe refractometer, laser refractometer,
When the molecular orientation measured by the total reflection laser Raman method or the like is biaxial orientation on both the front surface and the back surface, the output characteristics are further improved.

The Young's modulus in the machine direction and the transverse direction of the polyester film for a magnetic recording medium of the present invention is in terms of output characteristics.
700 kg / mm ² or more, preferably 800 kg / mm
² or more, more preferably 1000 kg / mm ² or more.

The breaking elongations in the machine direction and the transverse direction of the polyester film for a magnetic recording medium of the present invention are 50% or more and less than 50%, preferably 6 from the viewpoint of output characteristics.
It is 0% or more and 40% or less.

The film thickness of the polyester film for a magnetic recording medium of the present invention is not particularly limited, but from the viewpoint of output characteristics, it is 7 μm or less, preferably 6 μm or less, and further 5 μm.
m or less is preferable.

In the polyester film for a magnetic recording medium of the present invention, a back coat layer may be provided on the surface opposite to the surface on which the magnetic layer is provided, if necessary.

The polyester film for magnetic recording media of the present invention is preferably used as a polyester film for digital magnetic recording media. Further, it is also preferably used as a polyester film for a magnetic recording medium for HDTV (high definition television, for example, NHK's high vision) in which particularly high output is required.

The polyester film for magnetic recording media of the present invention is also preferably used for data storage such as computers.

Next, a preferable method for producing the polyester film for a magnetic recording medium of the present invention will be shown and described, but the present invention is not limited thereto.

First, as a method of incorporating particles into PEN constituting the film, it is preferable to disperse ethylene glycol as a diol component in the form of a slurry and polymerize the ethylene glycol with a predetermined dicarboxylic acid component. Further, a method of directly mixing an aqueous slurry of particles with a predetermined PEN pellet and kneading the mixture into PEN using a vent type twin-screw kneading extruder is effective for further improving the effect of the present invention.

As a method for controlling the content of particles, a high-concentration master is prepared by the above-mentioned method, and it is diluted with a polymer containing substantially no particles at the time of film formation to control the content of particles. Is effective.

Next, pellets containing a predetermined amount of particles are dried, if necessary, and then fed to a known extruder for melt lamination, extruded in a sheet form from a slit die, and cast on a casting roll. It is cooled and solidified with to make an unstretched film. That is, the polyester in a molten state is laminated using a plurality of extruders, a plurality of manifolds or a merging block. In this case, a method of installing a high-precision filter, a static mixer, and a gear pump in the polymer channel containing particles is effective for further improving the effect of the present invention. Especially high-precision filter 95% filtration is 10μ
m, preferably 5 μm, more preferably 3 μm is particularly effective for the effect of the present invention.

Next, this unstretched film is biaxially stretched and biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, a sequential biaxial stretching method of first stretching in the longitudinal direction and then in the width direction is used, and the longitudinal stretching temperature is 120 to 150 ° C., preferably 12
It is preferable to carry out at 0 to 140 ° C., a total longitudinal stretching ratio of 3.0 to 5.0 times, and a longitudinal stretching speed of 10,000 to 50,000% / min. As a stretching method in the width direction, a method using a tenter is preferable, and a stretching temperature is 140 to 180 ° C., preferably 15
The stretching ratio is set to 0 to 180 ° C., which is higher than the longitudinal stretching temperature, and the transverse stretching ratio is 4.0 to 7.0 times, preferably 5.0 to 6.5 times larger than the longitudinal stretching ratio, and the transverse stretching speed is 1,000. ~
It is preferably performed in the range of 20,000% / min. Further, if necessary, longitudinal re-stretching and lateral re-stretching are performed. In that case, the stretching conditions are preferably 130 to 180 ° C. in the longitudinal direction, 1.1 to 2.0 times the stretching ratio, and a tenter is used as the stretching method in the width direction, and the stretching temperature is 130 to 18
It is preferable to carry out at 0 ° C. and a draw ratio in the width direction of 1.1 to 2.0.

Next, the biaxially oriented film is heat treated.
The heat treatment temperature in this case is 170 to 220 ° C., especially 170
The range of 0.5 to 60 seconds is suitable at ˜210 ° C.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Average Particle Size of Particles The cross section of the film was measured by using a transmission electron microscope (TEM).
Observe at a magnification of 0,000 times or more. Section thickness of TEM is about 1
It is set to 00 nm, and the location is changed to measure 100 fields or more.
The average diameter of the particles is calculated from the weight average diameter (equivalent circle diameter).

(2) Content of particles A solvent in which the polymer is dissolved but not the particles is selected is selected, the particles are centrifuged from the polymer, and the ratio (% by weight) to the total weight of the particles is taken as the particle content. In some cases, the combined use of infrared spectroscopy is also effective.

(3) Film Lamination Thickness Using a secondary ion mass spectrometer (SIMS), the element derived from the highest concentration of particles in the film in the depth range of 3000 nm from the surface layer and the carbon element of polyester The concentration ratio (M ⁺ / C ⁺ ) is defined as the particle concentration, and analysis is performed in the thickness direction from the surface to a depth of 3000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film of the present invention, the particle concentration, which has once reached the maximum value, starts to decrease again. Based on this concentration distribution curve, the depth at which the surface layer particle concentration becomes 1/2 of the maximum value of (the depth is deeper than the maximum value) was determined, and this was taken as the laminated thickness. The conditions are as follows.

(1) Measuring device Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany (2) Measuring conditions Primary ion species: O ₂ ⁺ primary ion accelerating voltage: 12 KV Primary ion current: 200nA Raster area: 400μm □ Analysis area: Gate 30% Measuring vacuum degree: 5.0 × 10 ^-9 Torr E-GUN: 0.5KV-3.0A In addition, most contained in the range of surface depth from 3000nm If the particles to be used are organic polymer particles, it is difficult to measure with SIMS. Therefore, while etching from the surface, measure the same depth profile as above with XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy), etc. The thickness can be obtained, or the layer thickness can be obtained by recognizing the interface from the difference in contrast due to the change state of particle concentration and the difference in polymer by observing the cross section with an electron microscope or the like. Furthermore, after peeling the laminated polymer, the laminated thickness can be obtained using a thin film step measuring machine.

(4) Orientation of film surface It was measured using an Abbe refractometer with sodium D line (589 nm) as a light source. Methylene iodide was used as the mount solution, and measurement was performed at 25 ° C. and 65% RH.

The biaxial orientation of the film is such that when the refractive indices in the longitudinal direction, width direction and thickness direction are N1, N2 and N3,
The absolute value of (N1-N2) is 0.07 or less, and N3 /
One of the criteria is that [(N1 + N2) / 2] is 0.95 or less. Further, the refractive index may be measured using a laser type refractometer. Further, when the measurement is difficult by this method, the total reflection laser Raman method can be used.

(5) Young's modulus According to the method specified in JIS-Z-1702,
Using an Instron type tensile tester,
It was measured at 65% RH.

(6) Elongation at break According to the method specified in JIS K-7127, using an Instron type tensile tester, 25 ° C., 65%
(Extended length / original sample length) when measured by RH
× 100 was defined as the elongation at break (%).

(7) Output characteristics A magnetic paint is applied to the film using a gravure roll. The magnetic paint was prepared as follows.

Fe 100 parts Average particle size Length: 0.3 μm Needle ratio: 10/1 Coercive force: 2000 Oe ・ Polyurethane resin 15 parts ・ Vinyl chloride / vinyl acetate copolymer 5 parts ・ Nitrocellulose resin 5 parts ・Aluminum oxide powder 3 parts (average particle size: 0.3 μm) ・ Carbon black 1 part ・ Lecithin 2 parts ・ Methyl ethyl ketone 100 parts ・ Methyl isobutyl ketone 100 parts ・ Toluene 100 parts ・ Stearic acid 2 parts The above composition was ball milled for 48 hours. After mixing and dispersing, a kneaded product obtained by adding 6 parts of a curing agent is filtered with a filter to prepare a magnetic coating liquid, which is coated on a film, magnetically oriented, dried at 110 ° C., and further a small test calendar. After calendering with a device (steel roll / nylon roll, 5 steps) at a temperature of 70 ° C and a linear pressure of 200 kg / cm,
The coating type magnetic recording medium was obtained by curing at 70 ° C. for 48 hours. This tape roll is incorporated into a VTR cassette
TR tape was used. Commercially available Hi8 VTR on this tape
(EV-BS3000 manufactured by Sony), 7MH
C / N measurement at z ± 1 MHz was performed.

Comparing this C / N with a commercially available Hi8ME video tape, an equivalent one (a difference of +0 dB or less) is output characteristic: defective, and a difference of +3 dB or less is an output characteristic: good, difference is Output characteristics exceeding +3 dB were evaluated as excellent.

[0036]

The present invention will be described in more detail based on the following examples.

Example 1 (Table 1) An aqueous slurry of polydivinylbenzene particles having a particle composition of 81% divinylbenzene was directly kneaded into PEN using a vent type twin-screw kneading extruder to obtain PEN particle pellets. It was

This particle pellet and a PEN polymer pellet containing substantially no particles are mixed in an appropriate amount, dried under reduced pressure (3 Torr) at 180 ° C. for 8 hours, and then polymer A: 0.2 μm.
Polymer containing 1.0% by weight of m-diameter polydivinylbenzene particles and polymer B: a polymer containing no particles were supplied to extruder 1 and extruder 2, respectively, and melted at 290 ° C and 295 ° C. Each of these polymers was filtered through a high-precision filter having 95 μm filtration of 3 μm, and then three layers were laminated at the rectangular confluence (A / B / A).

This was wound around a casting drum having a surface temperature of 25 ° C. by an electrostatically applied cast method and cooled and solidified to prepare an unstretched film. At this time, the ratio of the die slit gap / unstretched film thickness was set to 10. Further, the total thickness and the thickness of the A layer were adjusted by adjusting the discharge amount of each extruder.

This unstretched film was stretched 5.0 times in the longitudinal direction at a temperature of 140 ° C. This stretching is done with two pairs of rolls.
It was carried out in four stages with the peripheral speed difference of Le. This uniaxially stretched film was stretched 4.5 times in the width direction at 140 ° C. using a tenter. Furthermore, it stretched 1.15 times in the width direction at 165 ° C. using a tenter. 2010 this film under fixed length
The film was heat-treated at ℃ for 3 seconds to obtain a biaxially oriented film having a total thickness of 4.5 μm and an A layer thickness of 0.4 μm.

The characteristics of this polyester film for a magnetic recording medium are as shown in Table 1, and the output characteristics were good.

Examples 2 to 4 and Comparative Examples 1 to 4 (Table 1) In the same manner as in Example 1, polyesters for magnetic recording media in which the kind of particles, particle size, content, laminated thickness, draw ratio, etc. were changed. I got a film. As shown in Table 1, the polyester film for a magnetic recording medium within the scope of the present invention has good output characteristics, but those without it have poor output characteristics.

[0043]

[Table 1]

[0044]

The polyester film for a magnetic recording medium of the present invention has high strength in the machine direction and the transverse direction and has anisotropy in the elongation in the machine direction and the transverse direction. It was possible to obtain excellent output characteristics. Further, since it has high strength, it can be applied to future tape thinning.

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Claims (3)

[Claims] 1. A film made of polyethylene-2,6-naphthalenedicarboxylate, having a Young's modulus in the machine direction of 700 kg / mm ² or more and a breaking elongation in the machine direction of 50.
%, The Young's modulus in the lateral direction is 700 kg / mm ² or more, and the breaking elongation in the lateral direction is less than 50%, which is a polyester film for a magnetic recording medium. 2. The film comprises at least two layers A and B.
The polyester film for a magnetic recording medium according to claim 1, which has a layered structure and has an A layer thickness of 0.01 to 3.0 µm. 3. The polyester film for a magnetic recording medium according to claim 2, wherein the A layer and / or the B layer is polyethylene-2,6-naphthalene dicarboxylate.