JPH0873624A - Polyester film for magnetic recording media - Google Patents

Abstract

(57) [Summary] (Modified) [Structure] In a polyester film having a laminated structure of at least two layers, one outermost layer A and the other outermost layer B each satisfy the following conditions, and the polyester film Having a total thickness of 5 μm or less and a Young's modulus in the width direction of 1000 kg / mm ² or more, a polyester film for a magnetic recording medium. A: Spherical particles having an average particle diameter of 0.01 to 0.5 μm are contained, and the number of coarse projections of H2 or more is 5/100 cm ² or less, and the three-dimensional surface roughness (SRa) is 7 nm or less. B: Average particle size 0.05 to
Contains spherical particles of 1.0 μm and has three-dimensional surface roughness (SR
a) is 7 to 30 nm, the ratio t _B / d _B between the thickness (t _B ) and the average particle diameter (d _B ) of the particles contained is 0.2 to 10, and the laminated thickness is 1.5 μm or less. [Effect] When a high density magnetic recording medium using a film having a thickness of 5 μm or less as a support is obtained, excellent output characteristics can be obtained, and it can sufficiently endure future long time and high density recording.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium, and more particularly, a polyester film having improved surface properties, mechanical properties and handling properties suitable as a film for a high density magnetic recording medium of a digital recording system. Regarding

[0002]

2. Description of the Related Art As a film for a magnetic recording medium, there is known a film which defines a relationship between a laminated thickness and a contained particle size (for example, JP-A-2-77431).

[0003]

In the conventional film for a magnetic recording medium described above, the height of protrusions on the film surface is made uniform by prescribing the relationship between the laminated thickness and the contained particle diameter, and the electromagnetic conversion characteristics as a magnetic recording medium are obtained. The abrasion resistance of the surface of the base film was improved, but when a thin high-density magnetic recording medium was used, there was a problem that output characteristics were insufficient due to low strength in the width direction.

[0004]

As a result of intensive studies to solve the above problems, the inventors of the present invention found a film capable of satisfying high output characteristics as a thin high-density magnetic recording medium. Arrived

That is, according to the present invention, in a polyester film having a laminated constitution of at least two layers, one outermost layer (A layer) and the other outermost layer (B layer) satisfy the following conditions, and The total thickness of the polyester film is 5 μm or less, and the Young's modulus in the width direction is 1000 kg / m
It is characterized by being m ² or more.

Layer A: Contains spherical particles having an average particle diameter of 0.01 to 0.5 μm, and has 5 coarse projections of H2 or more / 100.
cm ² or less, three-dimensional surface roughness (SRa) is 7 nm or less.

Layer B: contains spherical particles having an average particle diameter of 0.05 to 1.0 μm and has a three-dimensional surface roughness (SRa) of 7 to 3.
0 nm, the ratio t _B / d _B between the thickness (t _B ) and the average particle size (d _B ) of the contained particles is 0.2 to 10, and the layer thickness is 1.5 μm or less.

The present invention will be described in more detail below.

Examples of the polyester constituting the layers A and B of the present invention include aromatic dicarboxylic acids such as naphthalene 2,6-dicarboxylic acid, terephthalic acid and isophthalic acid or esters thereof, ethylene glycol, diethylene glycol and tetramethylene glycol. Polyesters obtained by polycondensing glycols such as A typical example of such polyester is polyethylene-
2,6-naphthalate and the like can be mentioned. The polyester may be a homopolymer or may be a copolymer of a third component. In any case, in the present invention, the ethylene-2,6-naphthalate unit is 80
A polyester having a mol% or more, preferably 90 mol% or more is preferable.

The polyester film of the present invention contains the above-mentioned polymer as a main component, but other polymers may be blended within a range not impairing the object of the present invention, and an antioxidant, a heat stabilizer, Additives such as lubricants and ultraviolet absorbers may be added to the extent that they are usually added. In particular, the layer B constituting the polyester film of the present invention contains 5% by weight of a higher fatty acid and / or its ester, a natural wax, a surfactant-like antistatic agent (specifically, an alkylbenzene sulfonate, etc.). Below (weight of B layer polymer),
It is preferable to add 3% by weight or less, and more preferably 1.5% by weight or less, since handling property, abrasion resistance and running property are improved.

The layer A surface of the film of the present invention is preferably a magnetic surface when used as a magnetic recording medium. Therefore, the particles in the layer A have an average particle diameter of 0.01 to 0.5 μm.
Substantially spherical particles, particularly spherical particles of 0.05 to 0.3 μm are preferably used. Average particle size is 0.5 μm
If it exceeds, it is difficult to obtain high output characteristics when used as a magnetic recording medium. On the other hand, when the average particle diameter is less than 0.01 μm, dispersibility in the polyester becomes difficult, and aggregates may be generated to form coarse protrusions of H2 or more described later.

The spherical particles having an average particle diameter of 0.01 to 0.5 μm include silica and organic particles (polystyrene particles, crosslinked polystyrene particles, crosslinked polyacrylic particles, crosslinked polyester particles, crosslinked polydivinylbenzene particles). Etc.), and crosslinked polydivinylbenzene particles are particularly preferable because they are more excellent in terms of coarse projections and abrasion resistance. In addition, the crystal form is α
Type, γ type, δ type, θ type, η type alumina, zirconia,
Aggregated particles such as silica and titanium may be used together.

These particles may be combined in several sizes and types within a range satisfying the following coarse protrusions and three-dimensional surface roughness.

Further, the layer A has coarse projections of H2 or more of 5 (pieces / 100 cm ² ) or less, preferably 3 (pieces / 100 cm ² ).
² ) or less, more preferably 0 (pieces / 100 cm ² ). 5 or more coarse protrusions of H2 or more
If it exceeds 10 cm ² , the output characteristics of the magnetic recording medium are deteriorated, which is not preferable. The H1 level coarse protrusions are not particularly limited, but are usually 70 (pieces / 100 cm ² ) or less, preferably 60 (pieces / 100 cm ² ) or less, and more preferably 50 (pieces / 100 cm ² ) or less.
The use of non-spherical particles (amorphous particles) is not preferable because the particle size distribution is wide and coarse protrusions increase.

Furthermore, the three-dimensional surface roughness (SRa) of the A layer
Should be 7 nm or less, preferably 6 nm or less, and more preferably 5 nm or less. Three-dimensional surface roughness (SR
When a) exceeds 7 nm, it is difficult to obtain high output characteristics when used as a magnetic recording medium.

The content of particles in the layer A is not particularly limited as long as it satisfies the above SRa, but is usually 0.01 to 2.0.
%, Preferably 0.04 to 1.0% by weight, more preferably 0.07 to 0.7% by weight.

The B layer surface constituting the film of the present invention is preferably a running surface (non-magnetic surface) when used as a magnetic recording medium. Therefore, the particles in layer B have an average particle size of 0.05.
˜1.0 μm, preferably 0.1 to 0.9 μm, more preferably 0.2 to 0.8 μm, substantially spherical particles are used. If the average particle size exceeds 1.0 μm, the total thickness of the film is as thin as 5 μm or less in the manufacturing process of the magnetic recording medium, so that the transfer and / or push-up action in the step may cause a magnetic surface roughness, which is not preferable. . On the other hand, if the average particle size is less than 0.05 μm, the surface formation required for improving running and handling properties is insufficient, which is not preferable.

Examples of the spherical particles having an average particle diameter of 0.05 to 1.0 μm include the same particle types as those used for the layer A. In particular, crosslinked polydivinylbenzene particles are desirable because the effects of the present invention are further improved. These particles may be used in combination of several sizes and types within a range satisfying the following three-dimensional surface roughness and B layer thickness (t _B ) / average particle diameter (d _B ). Especially for small particle / large particle combinations,
It is desirable because the winding property is further improved. In addition, a non-spherical particle, specifically, silica, synthetic calcium carbonate, titanium dioxide, carbon black, a crosslinked organic polymer compound or the like may be supplementarily used in a small amount within the range where the object of the present invention is achieved. Furthermore, the crystal form is α type, γ type, δ type, θ type, η
Agglomerated particles of type alumina, zirconia, silica, titanium, etc. may be used in combination.

Here, in the present invention, the thickness of the B layer (t
_B ) and the average particle diameter (d _B ) of the particles contained, t _B / d _B is 0.2 to 10, preferably 0.25 to 7,
More preferably, it should be 0.3 to 4. t _B /
If d _B exceeds 10, running, handling, and winding characteristics deteriorate, and in extreme cases, particles in the B layer may cause waviness on the surface of the A layer, which may lead to a decrease in output when used as a magnetic recording medium. Not preferable. On the other hand, t _B / d _B
Is less than 0.2, particles are likely to fall off and high output characteristics may not be obtained, which is not preferable.

The layer B has a three-dimensional surface roughness (SR
It is necessary that a) is 7 to 30 nm, preferably 10 to 25 nm, and more preferably 13 to 20 nm. SRa
Is more than 30 nm, the magnetic surface is roughened due to the transfer and / or push-up action in the manufacturing process of the magnetic recording medium, and high output characteristics cannot be obtained, which is not preferable. on the other hand,
When SRa is less than 7 nm, running, handling and winding characteristics are poor, which is not preferable. Further, the layer B has a laminated thickness of 1.5 μm or less, preferably 1.0 μm or less, and more preferably 0.7 μm or less. Layer thickness is 1.5μ
When the thickness exceeds m, the total thickness of the film is 5 μm or less, so that the particles in the layer B cause undulation on the surface of the layer A,
When used as a magnetic recording medium, the output may be reduced, which is not preferable.

The content of particles in the layer B is not particularly limited as long as it can satisfy the above SRa, but is usually 0.1 to 6% by weight, preferably 0.2 to 4% by weight, more preferably 0.
3 to 3% by weight is preferable.

Further, as the polymer constituting the B layer, the intrinsic viscosity IV is 0.7 or more, preferably 0.75 or more, more preferably 0.8, within the range for achieving the object of the present invention.
The above polyethylene terephthalate may be used.

The polyester film of the present invention is a film in which the above composition is biaxially oriented, and a uniaxial or non-oriented film is insufficient in strength in the width direction, which is not preferable. In particular, the film of the present invention, from the viewpoint of output characteristics,
Young's modulus in the width direction is 1000 kg / mm ² or more, preferably 1200 kg / mm ² or more, more preferably 13
It should be 50 kg / mm ² or more.

The Young's modulus in the longitudinal direction of the film of the present invention is not particularly limited, but is usually 500 kg / mm ² or more, preferably 550 kg / mm ² or more.

The total thickness of the polyester film of the present invention must be 5.0 μm or less from the viewpoint of recording / reproducing time or data recording capacity as a high density magnetic recording medium.

In the film of the present invention, the A layer and the B layer may be provided on both outermost layers of the film, and one or more intermediate layers may or may not be present between both layers. Since the total thickness of the film of the present invention is as thin as 5 μm or less, a two-layer structure having no intermediate layer is preferable from the viewpoint of film-forming property, and an intermediate layer containing no particles is provided from the viewpoint of output characteristics. It is preferable that it be present, and it is appropriately selected according to need.

Next, a preferred method for producing the film of the present invention will be described by taking a case of a two-layer structure as an example, but the present invention is not limited to this.

First, as a method of incorporating particles into polyester, a method of dispersing the diol component in the form of a slurry such as ethylene glycol and polymerizing the slurry with a predetermined dicarboxylic acid component, or a form of particles in the form of a water slurry is used. Then, there can be mentioned a method of mixing with polyester which has been preliminarily polymerized and kneading and kneading using a vent type twin-screw extruder. Here, the slurry of particles such as ethylene glycol is heated to 140 to 200 ° C., particularly 180 to 20 ° C.
The method of performing heat treatment at a temperature of 0 ° C. for 30 minutes to 5 hours, particularly 1 to 3 hours, or adding a small amount of a water-soluble polymer dispersant to an aqueous slurry of particles to perform dispersion stabilization treatment has the effects of the present invention. It is very effective in making it even better.

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 polyester which does not substantially contain particles at the time of film formation to control the content of particles. Is effective.

The polyester raw material chips thus prepared are dried if necessary.

Next, the following method is effective for obtaining the film of the present invention.

Polyester raw material chip A forming layer A
The polyester raw material chips B for forming layers B and B are supplied to a known extruder for melt lamination, extruded into a sheet form from a slit die, and cooled and solidified on a casting roll to produce an unstretched film. Here, a method in which polyester raw materials A and B are laminated by using two extruders, a two-layer manifold or a confluent block, a two-layer sheet is extruded from a die, and cooled on a casting roll to prepare an unstretched film Is preferred.

Next, the unstretched film is biaxially stretched and heat set. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, but the sequential biaxial stretching method is preferable. Usually, it is stretched 3.5 times or more in the longitudinal direction at a temperature of 80 to 180 ° C., then stretched 4 times or more at a temperature of 80 to 170 ° C. in the width direction, and then heat treated at a temperature of 170 to 230 ° C. Stretching speed in the longitudinal direction is 5000 to 50000
% / Min is preferable, and the stretching rate in the width direction is 10
It is preferably from 0 to 20000% / min. Of course, after stretching in the longitudinal and width directions, it is re-stretched 1.03 to 1.5 times in the longitudinal direction and / or 13 at a temperature of 110 to 180 ° C.
A method of re-stretching 1.03 to 1.7 times in the width direction at a temperature of 0 to 200 ° C. and then performing heat treatment is also used.

The polyester film of the present invention is preferably used for magnetic recording media. In particular, it is preferably used for a coating type magnetic recording medium of a digital recording type which requires high output.

[0035]

[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) Film Thickness 10 layers of a film having a length of 1 m in the width direction were stacked, and the thickness was measured at 10 places at equal intervals in the width direction, and the average value was divided by 10 to obtain the film. The thickness was used.

(2) Young's modulus According to the method specified in ASTM-D882-67, the film is sampled into a width of 10 mm and a length of 200 mm, and the distance between chucks is 100 mm and the pulling speed is 100 mm.
/ Min using an Instron type tensile tester at 23 ° C. and 65% RH.

(3) Average particle size Polyester is removed from the film by a plasma ashing method to expose the particles. As processing conditions, polyester is incinerated but particles are not damaged. This is observed with a SEM (scanning electron microscope), the image of the particles (light and shade of light generated by the particles) is linked to an image analyzer, and the observation location is changed to 5000 particles.
The following numerical processing is performed on the number of particles or more, and the weight average particle diameter D thus obtained is taken as the average particle diameter.

D = ΣDi / N (where Di is the equivalent circle diameter of the particles and N is the number).

(4) Laminate Thickness The cross section of the film was observed with a TEM (transmission electron microscope),
The interface is recognized from the change state of the particle concentration and the difference in contrast, and the laminated thickness is obtained.

(5) Coarse projections Aluminum was vapor-deposited on the surface of the film and measured using a two-beam interference microscope. The measurement wavelength is 564 nm, and the height of the coarse protrusions is determined from the Newton ring generated by the interference of light, and the coarse protrusion of the single ring is set to H1, and the coarse protrusion of the double ring or more is set to H2 or more, and converted per 100 cm ^2. And showed it. .

(6) Three-dimensional surface roughness manufactured by Kosaka Laboratory Ltd. Surface roughness measuring machine (ET-30H
K), the tip radius of the stylus is 2 μm, sampling pitch is 0.5 μm, cutoff is 0.08 mm, and vertical magnification is 200.
The measurement was performed under the conditions of 00 times, a measurement speed of 100 μm / s, and a recording number of 80.

(A) Three-dimensional center plane average roughness (SRa) The orthogonal coordinate axes X and Y are placed on the center plane of the roughness curved surface, the axis orthogonal to the center plane is taken as the Z axis, and the roughness curved surface is f (X , Y) and the reference plane sizes Lx and Ly, SRa is obtained from the following equation.

[0044]

[Equation 1] (9) Output characteristics A coating composition for the magnetic layer having the following composition, which has been thoroughly mixed and dispersed, is applied to the film A layer side, magnetic field orientation, drying, and calendering are performed, and then a coating composition for the back having the following composition is provided on the film B layer side. Was coated and dried, and further cured at 60 ° C. for 48 hours to obtain a roll-shaped original fabric. Here, the magnetic layer is 2.1μ
The back layer was prepared to have a thickness of 0.4 μm. Finally, the roll-shaped raw fabric was slit into a width of 8 mm and incorporated into a half for 8 mm to obtain a measurement sample.

Coating composition for magnetic layer Ferromagnetic alloy powder 100 parts (coercive force = 1800 Oe, particle size = 0.25 μm, acicular ratio = 10/1) Vinyl chloride / vinyl acetate copolymer 15 parts Polyurethane resin 5 parts Poly Isocyanate 6.5 parts Myristic acid 2 parts Lecithin 1 part Aluminum oxide powder (average particle size: 0.2 μm) 4 parts Carbon black (average particle size: 0.09 μm) 1 part Methyl ethyl ketone 180 parts Toluene 40 parts Cyclohexanone 80 parts Back layer Coating composition for carbon black (average particle size: 0.03 μm) 100 parts Carbon black (average particle size: 0.28 μm) 4 parts Nitrocellulose 100 parts Polyurethane resin 20 parts Polyisocyanate 20 parts Methyl ethyl ketone 480 parts Toluene 20 parts (A) Output characteristics 8mm video cassette recorder Recorded 3 minutes using da,
The RF envelope waveform for reproduction is observed with an oscilloscope, and judgment is made based on the ratio of the peak portion and the valley bottom portion of the envelope waveform (output characteristic-1). At the same time, the relative output to the 8 mm standard tape (for 120 minutes) is measured and judged (output characteristic-2).

Output characteristic-1: ⊚ (80% or more) Output characteristic-1: ○ (less than 80% but no noise is recognized on the reproduced screen) Output characteristic-1: × (less than 80% and on the reproduced screen) Output characteristics-2: ⊚ (+2 dB or more) Output characteristics-2: ○ (0 to +2 dB) Output characteristics-2: × (less than 0 dB) Output characteristics-1 and 2 are both good or good.

[0047]

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.

Example 1 An aqueous slurry of crosslinked polydivinylbenzene particles was directly added to
Mix with 6-polyethylene naphthalate (PEN) chips and knead using a vent type twin-screw kneading extruder to obtain P
An EN particle chip was obtained.

The particle chips and PEN polymer chips containing substantially no particles are mixed in an appropriate amount and dried under reduced pressure at 180 ° C. for 8 hours, and then polymer A (for layer A): crosslinked polydivinylbenzene particles having a diameter of 0.2 μm. Polymer containing 0.07% by weight, polymer B (for layer B): Polymer containing 0.5% by weight of crosslinked polydivinylbenzene particles having a diameter of 0.4 μm was supplied to an extruder 1 and an extruder 2, respectively, and 290 ° C., 295 ° C. Melted at ° C. After high-precision filtration of these polymers, a confluent block was used to make a two-layer stack (A / B).

The polymer was extruded onto a casting drum having a surface temperature of 25 ° C. by an electrostatically applied casting method, and cooled and solidified to obtain an unstretched film having a two-layer structure.

Here, by adjusting the discharge rate of each extruder, the total thickness and the thickness of layer B (ie,
t _B / d _B ) was prepared.

The unstretched film was stretched 4.5 times in the longitudinal direction at a temperature of 135 ° C., and then was stretched to 130 with a tenter.
It was stretched 5.5 times in the width direction at ℃. Further, it was stretched 1.4 times in the width direction at 160 ° C. using a tenter and then heat-treated at 200 ° C. for 5 seconds under a constant length, for a magnetic recording medium having a total thickness of 4.5 μm and a B layer thickness of 0.7 μm. A polyester film was obtained. The characteristics of the film are as shown in Tables 1 and 2, and the output characteristics were good.

Examples 2-5, Comparative Examples 1-8 In the same manner as in Example 1, the kind of particles, particle size, content,
Surface roughness, number of large protrusions, stacking thickness of B layer (that is, t _B /
to obtain a d _B) and polyester film which changed the film width direction strength. As shown in Tables 1 and 2, it can be seen that the films in the scope of the present invention have good output characteristics, but the films not in this range have poor output characteristics.

[0054]

[Table 1]

[Table 2]

[0055]

EFFECT OF THE INVENTION The polyester film of the present invention defines the strength in the width direction, and one surface (A layer surface) is a magnetic surface when used as a magnetic recording medium, and the other surface (B layer surface) is a running surface. Since the surface characteristics of each are specified in, the thickness of 5 μm
When a high density magnetic recording medium using the following films as a support is obtained, excellent output characteristics can be obtained, and it is possible to sufficiently endure future long time high density recording.

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Claims (6)

[Claims] 1. A polyester film having a laminated structure of at least two layers, one outermost layer (A layer)
And the other outermost layer (layer B) satisfies the following conditions, the total thickness of the polyester film is 5 μm or less, and the Young's modulus in the width direction is 1000 kg / mm ² or more. Polyester film for. Layer A: contains spherical particles having an average particle diameter of 0.01 to 0.5 μm and has 5 or more coarse projections of H2 or more / 100 cm ² or less,
Three-dimensional surface roughness (SRa) is 7 nm or less. Layer B: spherical particles having an average particle diameter of 0.05 to 1.0 μm, a three-dimensional surface roughness (SRa) of 7 to 30 nm, and a thickness (t _B ) and the average particle diameter of particles (d _B) ) Ratio t
_B / d _B is from 0.2 to 10, the laminated thickness of 1.5μm or less. 2. The A and / or B layers are 2,6-polyethylene naphthalate.
A polyester film for a magnetic recording medium as described above. 3. The polyester film for a magnetic recording medium according to claim 1, wherein the spherical particles of the A layer are organic particles and the spherical particles of the B layer are organic particles. 4. The polyester film for a magnetic recording medium according to claim 3, wherein the organic particles are crosslinked polydivinylbenzene particles. 5. The polyester film for a magnetic recording medium according to claim 1, which is for a coating type magnetic recording medium. 6. The polyester film for a magnetic recording medium according to claim 5, which is used in a digital recording system.