JPH0890648A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE: To endure sufficiently diversification of hardening method of a mag netic layer for a magnetic recording medium by improving back force properties, by a method wherein light transmittance, the lateral modulas of elasticity and a thickness of a film are specified. CONSTITUTION: In a film comprised of polyethylene 2,6-naphthalene dicarboxylate, light transmittance at a wave length of 550nm and 250nm is taken respectively as at least 70% and not exceeding 10% in terms of film thickness of 10μm. Then the lateral modulus of elasticity and a film thickness are taken respectively as at least 700kg/mm<2> and not exceeding 7μm. Then the film is comprised of at least two layer structure of layers A, B and the thickness of the layer A may be 0.01-3.0μm. Further it is preferable that the layer A and/or the B are the polyethylene 2,6-naphthalene dicarboxylate. It is preferable further that the layer A contains 0.01-3.0wt.% particles having a mean particle diameter of 0.01-1.0μm.

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 film for a magnetic recording medium, a film having a specified strength in the tape width direction is known (for example, Japanese Patent Laid-Open No. 4-292933). Also, as a film for a magnetic recording medium, a film is known in which the relationship between the laminated thickness and the particle diameter of the contained particles is defined (for example, Japanese Patent Laid-Open No. HEI 2
-77431).

However, in the conventional film for a magnetic recording medium described above, the relationship between the laminated thickness and the particle size of the contained particles is specified to make the height of the projections on the film uniform, and the electromagnetic conversion characteristics and the base of the magnetic recording medium are determined. Although the abrasion resistance of the film surface has been improved, higher strength is required for the lateral strength in the case of a further high density magnetic recording medium, and the output characteristics are insufficient in the application. Problems are occurring. It is also important in terms of workability when used as a magnetic recording medium that the base film is not easily deteriorated when the magnetic coating material is cured with, for example, ultraviolet rays. An object of the present invention is to solve the above problems and 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 which meets this object is a film made of polyethylene-2,6-naphthalene dicarboxylate and has a wavelength of 550 in terms of a film thickness of 10 μm.
The light transmittance in nm is 70% or more and the wavelength is 250n.
The polyester film for a magnetic recording medium is characterized in that the light transmittance in m is 10% or less, the Young's modulus in the lateral direction is 700 kg / mm ² or more, and the film thickness is 7 μm or less.

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 in order to keep the light transmittance within the range of the present application. 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 preferably at least 51%, preferably at least 60%, more preferably at least 75% of the particle component. 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. The silicone particles are preferably those containing a two-dimensionally crosslinked organopolysiloxane (CH ₃ Si O _3/2 ) as 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 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 lateral direction of the polyester film for a magnetic recording medium of the present invention is 700 kg / in terms of output characteristics.
mm ² or more, preferably 800 kg / mm ² or more, more preferably 1000 kg / mm ² or more. The difference between the Young's modulus in the longitudinal direction of the film and the Young's modulus in the lateral direction (horizontal-longitudinal) is not particularly limited, but from the viewpoint of output characteristics, 200 to 1500 kg / mm ² ,
Further, 300 to 1300 kg / mm ² is preferable.

Wavelength of 550n in terms of film thickness of 10 μm
It is necessary that the light transmittance at m is 70% or more, preferably 80% or more, and the light transmittance at a wavelength of 250 nm is 10% or less, preferably 5% or less. When the light transmittance is in this range, film deterioration is particularly small,
The durability is increased and the output characteristics are particularly improved for a magnetic recording medium.

The film thickness of the polyester film for a magnetic recording medium of the present invention is 7 μm or less in view of output characteristics,
It is preferably 6 μm or less, more preferably 5 μm or less.

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, the method of installing the static mixer and the gear pump in the polymer channel containing the particles is effective for further improving 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, using a sequential biaxial stretching method in which stretching is first performed in the longitudinal direction and then in the width direction, the stretching in the longitudinal direction is divided into three or more stages, and the longitudinal stretching temperature is 80 to 180 ° C. and the total longitudinal stretching ratio is 3.0. ~ 6.0 times,
It is preferable to carry out at a longitudinal stretching speed of 5,000 to 50,000% / min. As a stretching method in the width direction, a method using a tenter is preferable, the stretching temperature is 80 to 180 ° C., the stretching ratio in the width direction is 4.0 to 7.0 times larger than the longitudinal ratio, and the stretching speed in the width direction is 1,000 to 20,000% /. It is preferable to carry out in the range of minutes. Further, if necessary, longitudinal re-stretching and lateral re-stretching are performed. The stretching conditions in that case are 90 in the longitudinal direction.
˜180 ° C., stretching ratio 1.1 to 2.0 times, a method using a tenter is preferable as a stretching method in the width direction, a stretching temperature of 90 to 180 ° C., and a stretching ratio in the width direction of 1.1 to 2.0. It is preferable to carry out.

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 once reaching 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 used 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) Light transmittance The light transmittance of the film at a wavelength of 220 to 730 nm was measured with a commercially available spectrophotometer. Film thickness is 1
When the thickness is not 0 μm, the transmittance and exp (film thickness) are assumed to be proportional to each other, and the transmittance is converted to the value of 10 μm.

(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

An appropriate amount of PEN polymer pellets containing substantially no particles was mixed with the particle pellets, dried under reduced pressure (3 Torr) at 180 ° C. for 8 hours, and then polymer A: 0.3 μm.
m diameter polydivinylbenzene particles 0.6% by weight, 0.8μ
Polymer containing 0.05% by weight of m-diameter polydivinylbenzene particles, Polymer B: Extruder 1 and extruder 2 containing polymer containing 0.1% by weight of 0.3 μm-diameter polydivinylbenzene particles, respectively.
And melted at 290 ° C and 295 ° C. After high-precision filtration of these polymers, two layers were laminated at the rectangular junction (A / B).

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 4.5 times in the longitudinal direction at a temperature of 145 ° 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 4.0 times in the width direction at 140 ° C. using a tenter. Further, it was stretched 1.55 times in the width direction at 170 ° C. using a tenter. This film under constant length 210 ℃
Heat treatment for 3 seconds at a total thickness of 4.5 μm and an A layer thickness of 0.
A 4 μm biaxially oriented film was obtained.

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, film strength, 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 excellent output characteristics because the lateral strength and the light transmittance at a specific wavelength are defined. Further, it is possible to sufficiently endure the diversification of the magnetic layer curing method for a magnetic recording medium.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area // B29K 67:00 B29L 9:00

Claims (5)

[Claims] 1. A film made of polyethylene-2,6-naphthalene dicarboxylate, which has a light transmittance of 70% or more at a wavelength of 550 nm and a light transmittance of 1 at a wavelength of 250 nm in terms of film thickness of 10 μm.
A polyester film for a magnetic recording medium, which has a lateral Young's modulus of 700 kg / mm ² or more and a film thickness of 7 μm or less. 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. 4. The layer A contains 0.01 to 3.0% by weight of particles having an average particle size of 0.01 to 1.0 μm.
A polyester film for a magnetic recording medium as described above. 5. The average particle diameter d (nm) of the A layer-containing particles and A
The relation with the layer thickness t (nm) of the layer is 0.2 ≦ t / d ≦ 10.
The polyester film for a magnetic recording medium according to claim 4.